GNU Emacs Lisp Reference Manual

GNU Emacs Version 19

for Unix Users

Revision 2.4.2, December 1996

by Bil Lewis, Dan LaLiberte, Richard Stallman and the GNU Manual Group

Copyright \begin{matrix}c \\ ◯ \end{matrix} 1990, 1991, 1992, 1993, 1994, 1995, 1996 Free Software Foundation, Inc.

Edition 2.4.2 Revised for Emacs Version 19.34, July 1996.

ISBN 1-882114-71-X

Published by the Free Software Foundation 59 Temple Place, Suite 330 Boston, MA 02111-1307 USA Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled “GNU General Public License” is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled “GNU General Public License” may be included in a translation approved by the Free Software Foundation instead of in the original English. Cover art by Etienne Suvasa.

GNU GENERAL PUBLIC LICENSE

Version 2, June 1991

Copyright \begin{matrix}c \\ ◯ \end{matrix} 1989, 1991 Free Software Foundation, Inc.

675 Mass Ave, Cambridge, MA 02139, USA

Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

Preamble

The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software—to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation’s software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.

When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.

For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.

We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.

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The precise terms and conditions for copying, distribution and modification follow.

TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

0. This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License. The “Program”, below, refers to any such program or work, and a “work based on the Program” means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term “modification”.) Each licensee is addressed as “you”. Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does.

1. You may copy and distribute verbatim copies of the Program’s source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program. You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.

2. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions: a. You must cause the modified files to carry prominent notices stating that you

changed the files and the date of any change. b. You must cause any work that you distribute or publish, that in whole or in part

contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License.

c. If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.)

These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it. Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program. In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.

3. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following: a. Accompany it with the complete corresponding machine-readable source code,

which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

b. Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

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The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable. If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code.

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NO WARRANTY

11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY AP-PLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IM-PLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE EN-TIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

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END OF TERMS AND CONDITIONS How to Apply These Terms to Your New Programs

If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.

To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.

one line to give the program’s name and an idea of what it does.

Copyright (C) 19yy name of author
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

Also add information on how to contact you by electronic and paper mail. If the program is interactive, make it output a short notice like this when it starts in an

interactive mode:

Gnomovision version 69, Copyright (C) 19yy name of author
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'.  This is free software, and you are welcome
to redistribute it under certain conditions; type `show c'
for details.

The hypothetical commands ‘show w’ and ‘show c’ should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than ‘show w’ and ‘show c’; they could even be mouse-clicks or menu items—whatever suits your program.

You should also get your employer (if you work as a programmer) or your school, if any, to sign a “copyright disclaimer” for the program, if necessary. Here is a sample; alter the names:

Yoyodyne, Inc., hereby disclaims all copyright
interest in the program `Gnomovision'
(which makes passes at compilers) written
by James Hacker.

signature of Ty Coon, 1 April 1989

Ty Coon, President of Vice

This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.

8 GNU Emacs Lisp Reference Manual

1 Introduction

Most of the GNU Emacs text editor is written in the programming language called Emacs Lisp. You can write new code in Emacs Lisp and install it as an extension to the editor. However, Emacs Lisp is more than a mere “extension language”; it is a full computer programming language in its own right. You can use it as you would any other programming language.

Because Emacs Lisp is designed for use in an editor, it has special features for scanning and parsing text as well as features for handling files, buffers, displays, subprocesses, and so on. Emacs Lisp is closely integrated with the editing facilities; thus, editing commands are functions that can also conveniently be called from Lisp programs, and parameters for customization are ordinary Lisp variables.

This manual describes Emacs Lisp, presuming considerable familiarity with the use of Emacs for editing. (See The GNU Emacs Manual for this basic information.) Generally speaking, the earlier chapters describe features of Emacs Lisp that have counterparts in many programming languages, and later chapters describe features that are peculiar to Emacs Lisp or relate specifically to editing.

This is edition 2.4.

1.1 Caveats

This manual has gone through numerous drafts. It is nearly complete but not flawless. There are a few topics that are not covered, either because we consider them secondary (such as most of the individual modes) or because they are yet to be written. Because we are not able to deal with them completely, we have left out several parts intentionally. This includes most information about usage on VMS.

The manual should be fully correct in what it does cover, and it is therefore open to criticism on anything it says—from specific examples and descriptive text, to the ordering of chapters and sections. If something is confusing, or you find that you have to look at the sources or experiment to learn something not covered in the manual, then perhaps the manual should be fixed. Please let us know.

As you use the manual, we ask that you mark pages with corrections so you can later look them up and send them in. If you think of a simple, real-life example for a function or group of functions, please make an effort to write it up and send it in. Please reference any comments to the chapter name, section name, and function name, as appropriate, since page numbers and chapter and section numbers will change and we may have trouble finding the text you are talking about. Also state the number of the edition you are criticizing.

Please mail comments and corrections to

     bug-lisp-manual@prep.ai.mit.edu

We let mail to this list accumulate unread until someone decides to apply the corrections. Months, and sometimes years, go by between updates. So please attach no significance to the lack of a reply—your mail will be acted on in due time. If you want to contact the Emacs maintainers more quickly, send mail to bug-gnu-emacs@prep.ai.mit.edu.

–Bil Lewis, Dan LaLiberte, Richard Stallman

1.2 Lisp History

Lisp (LISt Processing language) was first developed in the late 1950’s at the Massachusetts Institute of Technology for research in artificial intelligence. The great power of the Lisp language makes it superior for other purposes as well, such as writing editing commands.

Dozens of Lisp implementations have been built over the years, each with its own idiosyncrasies. Many of them were inspired by Maclisp, which was written in the 1960’s at MIT’s Project MAC. Eventually the implementors of the descendants of Maclisp came together and developed a standard for Lisp systems, called Common Lisp.

GNU Emacs Lisp is largely inspired by Maclisp, and a little by Common Lisp. If you know Common Lisp, you will notice many similarities. However, many of the features of Common Lisp have been omitted or simplified in order to reduce the memory requirements of GNU Emacs. Sometimes the simplifications are so drastic that a Common Lisp user might be very confused. We will occasionally point out how GNU Emacs Lisp differs from Common Lisp. If you don’t know Common Lisp, don’t worry about it; this manual is self-contained.

1.3 Conventions

This section explains the notational conventions that are used in this manual. You may want to skip this section and refer back to it later.

1.3.1 Some Terms

Throughout this manual, the phrases “the Lisp reader” and “the Lisp printer” are used to refer to those routines in Lisp that convert textual representations of Lisp objects into actual Lisp objects, and vice versa. See Section 2.1 [Printed Representation], page 15, for more details. You, the person reading this manual, are thought of as “the programmer” and are addressed as “you”. “The user” is the person who uses Lisp programs, including those you write.

Examples of Lisp code appear in this font or form: (list 1 2 3). Names that represent arguments or metasyntactic variables appear in this font or form: first-number.

1.3.2 nil and t

In Lisp, the symbol nil has three separate meanings: it is a symbol with the name ‘nil’; it is the logical truth value false; and it is the empty list—the list of zero elements. When used as a variable, nil always has the value nil.

As far as the Lisp reader is concerned, ‘()’ and ‘nil’ are identical: they stand for the same object, the symbol nil. The different ways of writing the symbol are intended entirely for human readers. After the Lisp reader has read either ‘()’ or ‘nil’, there is no way to determine which representation was actually written by the programmer.

In this manual, we use () when we wish to emphasize that it means the empty list, and we use nil when we wish to emphasize that it means the truth value false. That is a good convention to use in Lisp programs also.

(cons 'foo ()) ; Emphasize the empty list (not nil) ; Emphasize the truth value false

In contexts where a truth value is expected, any non-nil value is considered to be true. However, t is the preferred way to represent the truth value true. When you need to choose a value which represents true, and there is no other basis for choosing, use t. The symbol t always has value t.

In Emacs Lisp, nil and t are special symbols that always evaluate to themselves. This is so that you do not need to quote them to use them as constants in a program. An attempt to change their values results in a setting-constant error. See Section 10.7 [Accessing Variables], page 128.

1.3.3 Evaluation Notation

A Lisp expression that you can evaluate is called a form. Evaluating a form always produces a result, which is a Lisp object. In the examples in this manual, this is indicated with ‘⇒’:

     (car '(1 2))
          ⇒ 1

You can read this as “(car '(1 2)) evaluates to 1”.

When a form is a macro call, it expands into a new form for Lisp to evaluate. We show the result of the expansion with ‘↦’. We may or may not show the actual result of the evaluation of the expanded form.

     (third '(a b c))
          ↦ (car (cdr (cdr '(a b c))))
          ⇒ c

Sometimes to help describe one form we show another form that produces identical results. The exact equivalence of two forms is indicated with ‘ ≡ ’.

     (make-sparse-keymap) ≡ (list 'keymap)

1.3.4 Printing Notation

Many of the examples in this manual print text when they are evaluated. If you execute example code in a Lisp Interaction buffer (such as the buffer ‘*scratch*’), the printed text is inserted into the buffer. If you execute the example by other means (such as by evaluating the function eval-region), the printed text is displayed in the echo area. You should be aware that text displayed in the echo area is truncated to a single line.

Examples in this manual indicate printed text with ‘ ⊣ ’, irrespective of where that text goes. The value returned by evaluating the form (here bar) follows on a separate line.

     (progn (print 'foo) (print 'bar))
          ⊣ foo

          ⊣ bar
          ⇒ bar

1.3.5 Error Messages

Some examples signal errors. This normally displays an error message in the echo area. We show the error message on a line starting with ‘ error ’. Note that ‘ error ’ itself does not appear in the echo area.

     (+ 23 'x)
      error Wrong type argument: integer-or-marker-p, x

1.3.6 Buffer Text Notation

Some examples show modifications to text in a buffer, with “before” and “after” versions of the text. These examples show the contents of the buffer in question between two lines of dashes containing the buffer name. In addition, ‘⋆’ indicates the location of point. (The symbol for point, of course, is not part of the text in the buffer; it indicates the place between two characters where point is located.)

     ---------- Buffer: foo ----------
     This is the ⋆contents of foo.
     ---------- Buffer: foo ----------
     (insert "changed ")
          ⇒ nil
     ---------- Buffer: foo ----------
     This is the changed ⋆contents of foo.
     ---------- Buffer: foo ----------

1.3.7 Format of Descriptions

Functions, variables, macros, commands, user options, and special forms are described in this manual in a uniform format. The first line of a description contains the name of the item followed by its arguments, if any. The category—function, variable, or whatever—is printed next to the right margin. The description follows on succeeding lines, sometimes with examples.

1.3.7.1 A Sample Function Description

In a function description, the name of the function being described appears first. It is followed on the same line by a list of parameters. The names used for the parameters are also used in the body of the description.

The appearance of the keyword &optional in the parameter list indicates that the arguments for subsequent parameters may be omitted (omitted parameters default to nil). Do not write &optional when you call the function.

The keyword &rest (which will always be followed by a single parameter) indicates that any number of arguments can follow. The value of the single following parameter will be a list of all these arguments. Do not write &rest when you call the function.

Here is a description of an imaginary function foo:

Function foo integer1 &optional integer2 &rest integers The function foo subtracts integer1 from integer2, then adds all the rest of the arguments to the result. If integer2 is not supplied, then the number 19 is used by default.

          (foo 1 5 3 9)
               ⇒ 16
          (foo 5)
               ⇒ 14

More generally, (foo w x y…)

≡

          (+ (- x w) y. . .)

Any parameter whose name contains the name of a type (e.g., integer, integer1 or buffer) is expected to be of that type. A plural of a type (such as buffers) often means a list of objects of that type. Parameters named object may be of any type. (See Chapter 2 [Lisp Data Types], page 15, for a list of Emacs object types.) Parameters with other sorts of names (e.g., new-file) are discussed specifically in the description of the function. In some sections, features common to parameters of several functions are described at the beginning.

See Section 11.2 [Lambda Expressions], page 140, for a more complete description of optional and rest arguments.

Command, macro, and special form descriptions have the same format, but the word ‘Function’ is replaced by ‘Command’, ‘Macro’, or ‘Special Form’, respectively. Commands are simply functions that may be called interactively; macros process their arguments differently from functions (the arguments are not evaluated), but are presented the same way.

Special form descriptions use a more complex notation to specify optional and repeated parameters because they can break the argument list down into separate arguments in more complicated ways. ‘[optional-arg]’ means that optional-arg is optional and ‘repeatedargs…’ stands for zero or more arguments. Parentheses are used when several arguments are grouped into additional levels of list structure. Here is an example:

Special Form count-loop (var [from to [inc]]) body… This imaginary special form implements a loop that executes the body forms and then increments the variable var on each iteration. On the first iteration, the variable has the value from; on subsequent iterations, it is incremented by 1 (or by inc if that is given). The loop exits before executing body if var equals to. Here is an example:

          (count-loop (i 0 10)
            (prin1 i) (princ " ")
            (prin1 (aref vector i)) (terpri))

If from and to are omitted, then var is bound to nil before the loop begins, and the loop exits if var is non-nil at the beginning of an iteration. Here is an example:

          (count-loop (done)
            (if (pending)
                (fixit)

              (setq done t)))

In this special form, the arguments from and to are optional, but must both be present or both absent. If they are present, inc may optionally be specified as well. These arguments are grouped with the argument var into a list, to distinguish them from body, which includes all remaining elements of the form.

1.3.7.2 A Sample Variable Description

A variable is a name that can hold a value. Although any variable can be set by the user, certain variables that exist specifically so that users can change them are called user options. Ordinary variables and user options are described using a format like that for functions except that there are no arguments.

Here is a description of the imaginary electric-future-map variable.

Variable electric-future-map

The value of this variable is a full keymap used by Electric Command Future mode. The functions in this map allow you to edit commands you have not yet thought about executing.

User option descriptions have the same format, but ‘Variable’ is replaced by ‘User Option’.

1.4 Acknowledgements

This manual was written by Robert Krawitz, Bil Lewis, Dan LaLiberte, Richard M. Stallman and Chris Welty, the volunteers of the GNU manual group, in an effort extending over several years. Robert J. Chassell helped to review and edit the manual, with the support of the Defense Advanced Research Projects Agency, ARPA Order 6082, arranged by Warren A. Hunt, Jr. of Computational Logic, Inc.

Corrections were supplied by Karl Berry, Jim Blandy, Bard Bloom, Stephane Boucher, David Boyes, Alan Carroll, Richard Davis, Lawrence R. Dodd, Peter Doornbosch, David A. Duff, Chris Eich, Beverly Erlebacher, David Eckelkamp, Ralf Fassel, Eirik Fuller, Stephen Gildea, Bob Glickstein, Eric Hanchrow, George Hartzell, Nathan Hess, Masayuki Ida, Dan Jacobson, Jak Kirman, Bob Knighten, Frederick M. Korz, Joe Lammens, Glenn M. Lewis, K. Richard Magill, Brian Marick, Roland McGrath, Skip Montanaro, John Gardiner Myers, Thomas A. Peterson, Francesco Potorti, Friedrich Pukelsheim, Arnold D. Robbins, Raul Rockwell, Per Starback, Shinichirou Sugou, Kimmo Suominen, Edward Tharp, Bill Trost, Rickard Westman, Jean White, Matthew Wilding, Carl Witty, Dale Worley, Rusty Wright, and David D. Zuhn.

2 Lisp Data Types

A Lisp object is a piece of data used and manipulated by Lisp programs. For our purposes, a type or data type is a set of possible objects.

Every object belongs to at least one type. Objects of the same type have similar structures and may usually be used in the same contexts. Types can overlap, and objects can belong to two or more types. Consequently, we can ask whether an object belongs to a particular type, but not for “the” type of an object.

A few fundamental object types are built into Emacs. These, from which all other types are constructed, are called primitive types. Each object belongs to one and only one primitive type. These types include integer, float, cons, symbol, string, vector, subr, bytecode function, and several special types, such as buffer, that are related to editing. (See Section 2.4 [Editing Types], page 26.)

Each primitive type has a corresponding Lisp function that checks whether an object is a member of that type.

Note that Lisp is unlike many other languages in that Lisp objects are self-typing: the primitive type of the object is implicit in the object itself. For example, if an object is a vector, nothing can treat it as a number; Lisp knows it is a vector, not a number.

In most languages, the programmer must declare the data type of each variable, and the type is known by the compiler but not represented in the data. Such type declarations do not exist in Emacs Lisp. A Lisp variable can have any type of value, and it remembers whatever value you store in it, type and all.

This chapter describes the purpose, printed representation, and read syntax of each of the standard types in GNU Emacs Lisp. Details on how to use these types can be found in later chapters.

2.1 Printed Representation and Read Syntax

The printed representation of an object is the format of the output generated by the Lisp printer (the function prin1) for that object. The read syntax of an object is the format of the input accepted by the Lisp reader (the function read) for that object. Most objects have more than one possible read syntax. Some types of object have no read syntax; except for these cases, the printed representation of an object is also a read syntax for it.

In other languages, an expression is text; it has no other form. In Lisp, an expression is primarily a Lisp object and only secondarily the text that is the object’s read syntax. Often there is no need to emphasize this distinction, but you must keep it in the back of your mind, or you will occasionally be very confused.

Every type has a printed representation. Some types have no read syntax, since it may not make sense to enter objects of these types directly in a Lisp program. For example, the buffer type does not have a read syntax. Objects of these types are printed in hash notation: the characters ‘#<’ followed by a descriptive string (typically the type name followed by the name of the object), and closed with a matching ‘>’. Hash notation cannot be read at all, so the Lisp reader signals the error invalid-read-syntax whenever it encounters ‘#<’.

     (current-buffer)
          ⇒ #<buffer objects.texi>

When you evaluate an expression interactively, the Lisp interpreter first reads the textual representation of it, producing a Lisp object, and then evaluates that object (see Chapter 8 [Evaluation], page 95). However, evaluation and reading are separate activities. Reading returns the Lisp object represented by the text that is read; the object may or may not be evaluated later. See Section 16.3 [Input Functions], page 216, for a description of read, the basic function for reading objects.

2.2 Comments

A comment is text that is written in a program only for the sake of humans that read the program, and that has no effect on the meaning of the program. In Lisp, a semicolon (‘;’) starts a comment if it is not within a string or character constant. The comment continues to the end of line. The Lisp reader discards comments; they do not become part of the Lisp objects which represent the program within the Lisp system.

The ‘#@count’ construct, which skips the next count characters, is useful for programgenerated comments containing binary data. The Emacs Lisp byte compiler uses this in its output files (see Chapter 14 [Byte Compilation], page 171). It isn’t meant for source files, however.

See Section A.4 [Comment Tips], page 604, for conventions for formatting comments.

2.3 Programming Types

There are two general categories of types in Emacs Lisp: those having to do with Lisp programming, and those having to do with editing. The former exist in many Lisp implementations, in one form or another. The latter are unique to Emacs Lisp.

2.3.1 Integer Type

The range of values for integers in Emacs Lisp is −134217728 to 134217727 (28 bits; i.e., −2^{27} to 2^{28} − 1) on most machines. (Some machines may provide a wider range.) It is important to note that the Emacs Lisp arithmetic functions do not check for overflow. Thus (1+ 134217727) is −134217728 on most machines.

The read syntax for integers is a sequence of (base ten) digits with an optional sign at the beginning and an optional period at the end. The printed representation produced by the Lisp interpreter never has a leading ‘+’ or a final ‘.’.

-1 ; The integer -1. 1 ; The integer 1.

1. ; Also The integer 1. +1 ; Also the integer 1. 268435457 ; Also the integer 1!

; (on a 28-bit implementation)

See Chapter 3 [Numbers], page 35, for more information.

2.3.2 Floating Point Type

Emacs version 19 supports floating point numbers (though there is a compilation option to disable them). The precise range of floating point numbers is machine-specific.

The printed representation for floating point numbers requires either a decimal point (with at least one digit following), an exponent, or both. For example, ‘1500.0’, ‘15e2’, ‘15.0e2’, ‘1.5e3’, and ‘.15e4’ are five ways of writing a floating point number whose value is 1500. They are all equivalent.

See Chapter 3 [Numbers], page 35, for more information.

2.3.3 Character Type

A character in Emacs Lisp is nothing more than an integer. In other words, characters are represented by their character codes. For example, the character A is represented as the integer 65.

Individual characters are not often used in programs. It is far more common to work with strings, which are sequences composed of characters. See Section 2.3.8 [String Type], page 23.

Characters in strings, buffers, and files are currently limited to the range of 0 to 255— eight bits. If you store a larger integer into a string, buffer or file, it is truncated to that range. Characters that represent keyboard input have a much wider range.

Since characters are really integers, the printed representation of a character is a decimal number. This is also a possible read syntax for a character, but writing characters that way in Lisp programs is a very bad idea. You should always use the special read syntax formats that Emacs Lisp provides for characters. These syntax formats start with a question mark.

The usual read syntax for alphanumeric characters is a question mark followed by the character; thus, ‘?A’ for the character A, ‘?B’ for the character B, and ‘?a’ for the character

a.

For example:

     ?Q ⇒ 81     ?q ⇒ 113

You can use the same syntax for punctuation characters, but it is often a good idea to add a ‘\’ so that the Emacs commands for editing Lisp code don’t get confused. For example, ‘?\ ’ is the way to write the space character. If the character is ‘\’, you must use a second ‘\’ to quote it: ‘?\\’.

You can express the characters Control-g, backspace, tab, newline, vertical tab, formfeed, return, and escape as ‘?\a’, ‘?\b’, ‘?\t’, ‘?\n’, ‘?\v’, ‘?\f’, ‘?\r’, ‘?\e’, respectively. Those values are 7, 8, 9, 10, 11, 12, 13, and 27 in decimal. Thus,

     ?\a ⇒ 7                 ; C-g

?\b ⇒ 8 ; backspace, ^{⟨}\underline{\overline{BS}}^{⟩}, C-h ?\t ⇒ 9 ; tab, ^{⟨}\underline{\overline{TAB}}^{⟩}, C-i ?\n ⇒ 10 ; newline, ^{⟨}\underline{\overline{LFD}}^{⟩}, C-j ?\v ⇒ 11 ; vertical tab, C-k ?\f ⇒ 12 ; formfeed character, C-l ?\r ⇒ 13 ; carriage return, ^{⟨}\underline{\overline{RET}}^{⟩}, C-m ?\e ⇒ 27 ; escape character, ^{⟨}\underline{\overline{ESC}}^{⟩}, C-[

?\\ ⇒ 92 ; backslash character, \ These sequences which start with backslash are also known as escape sequences, because

backslash plays the role of an escape character; this usage has nothing to do with the character ^{⟨}\underline{\overline{ESC}}^{⟩}.

Control characters may be represented using yet another read syntax. This consists of a question mark followed by a backslash, caret, and the corresponding non-control character, in either upper or lower case. For example, both ‘?\^I’ and ‘?\^i’ are valid read syntax for the character C-i, the character whose value is 9.

Instead of the ‘^’, you can use ‘C-’; thus, ‘?\C-i’ is equivalent to ‘?\^I’ and to ‘?\^i’:

     ?\^I ⇒ 9     ?\C-I ⇒ 9

For use in strings and buffers, you are limited to the control characters that exist in ASCII, but for keyboard input purposes, you can turn any character into a control character with ‘C-’. The character codes for these non-ASCII control characters include the $2^26$ bit as well as the code for the corresponding non-control character. Ordinary terminals have no way of generating non-ASCII control characters, but you can generate them straightforwardly using an X terminal.

For historical reasons, Emacs treats the ^{⟨}\underline{\overline{DEL}}^{⟩} character as the control equivalent of ?:

     ?\^? ⇒ 127     ?\C-? ⇒ 127

As a result, it is currently not possible to represent the character Control-?, which is a meaningful input character under X. It is not easy to change this as various Lisp files refer to ^{⟨}\underline{\overline{DEL}}^{⟩} in this way.

For representing control characters to be found in files or strings, we recommend the ‘^’ syntax; for control characters in keyboard input, we prefer the ‘C-’ syntax. This does not affect the meaning of the program, but may guide the understanding of people who read it.

A meta character is a character typed with the ^{⟨}\underline{\overline{META}}^{⟩} modifier key. The integer that represents such a character has the $2^27$ bit set (which on most machines makes it a negative number). We use high bits for this and other modifiers to make possible a wide range of basic character codes.

In a string, the $2^7$ bit indicates a meta character, so the meta characters that can fit in a string have codes in the range from 128 to 255, and are the meta versions of the ordinary ASCII characters. (In Emacs versions 18 and older, this convention was used for characters outside of strings as well.)

The read syntax for meta characters uses ‘\M-’. For example, ‘?\M-A’ stands for M-A. You can use ‘\M-’ together with octal character codes (see below), with ‘\C-’, or with any other syntax for a character. Thus, you can write M-A as ‘?\M-A’, or as ‘?\M-\101’. Likewise, you can write C-M-b as ‘?\M-\C-b’, ‘?\C-\M-b’, or ‘?\M-\002’.

The case of an ordinary letter is indicated by its character code as part of ASCII, but ASCII has no way to represent whether a control character is upper case or lower case. Emacs uses the $2^25$ bit to indicate that the shift key was used for typing a control character. This distinction is possible only when you use X terminals or other special terminals; ordinary terminals do not indicate the distinction to the computer in any way.

The X Window System defines three other modifier bits that can be set in a character: hyper, super and alt. The syntaxes for these bits are ‘\H-’, ‘\s-’ and ‘\A-’. Thus, ‘?\H-\M-\A-x’ represents Alt-Hyper-Meta-x. Numerically, the bit values are $2^22$ for alt, $2^23$ for super and $2^24$ for hyper.

Finally, the most general read syntax consists of a question mark followed by a backslash and the character code in octal (up to three octal digits); thus, ‘?\101’ for the character A, ‘?\001’ for the character C-a, and ?\002 for the character C-b. Although this syntax can represent any ASCII character, it is preferred only when the precise octal value is more important than the ASCII representation.

     ?\012 ⇒ 10         ?\n ⇒ 10         ?\C-j ⇒ 10 ?\101 ⇒ 65         ?A ⇒ 65

A backslash is allowed, and harmless, preceding any character without a special escape meaning; thus, ‘?\+’ is equivalent to ‘?+’. There is no reason to add a backslash before most characters. However, you should add a backslash before any of the characters ‘()\|;'`"#.,’ to avoid confusing the Emacs commands for editing Lisp code. Also add a backslash before whitespace characters such as space, tab, newline and formfeed. However, it is cleaner to use one of the easily readable escape sequences, such as ‘\t’, instead of an actual whitespace character such as a tab.

2.3.4 Symbol Type

A symbol in GNU Emacs Lisp is an object with a name. The symbol name serves as the printed representation of the symbol. In ordinary use, the name is unique—no two symbols have the same name.

A symbol can serve as a variable, as a function name, or to hold a property list. Or it may serve only to be distinct from all other Lisp objects, so that its presence in a data structure may be recognized reliably. In a given context, usually only one of these uses is intended. But you can use one symbol in all of these ways, independently.

A symbol name can contain any characters whatever. Most symbol names are written with letters, digits, and the punctuation characters ‘-+=*/’. Such names require no special punctuation; the characters of the name suffice as long as the name does not look like a number. (If it does, write a ‘\’ at the beginning of the name to force interpretation as a symbol.) The characters ‘_~!@$%^&:<>{}’ are less often used but also require no special punctuation. Any other characters may be included in a symbol’s name by escaping them with a backslash. In contrast to its use in strings, however, a backslash in the name of a symbol simply quotes the single character that follows the backslash. For example, in a string, ‘\t’ represents a tab character; in the name of a symbol, however, ‘\t’ merely quotes the letter t. To have a symbol with a tab character in its name, you must actually use a tab (preceded with a backslash). But it’s rare to do such a thing.

Common Lisp note: In Common Lisp, lower case letters are always “folded” to upper case, unless they are explicitly escaped. In Emacs Lisp, upper case and lower case letters are distinct.

Here are several examples of symbol names. Note that the ‘+’ in the fifth example is escaped to prevent it from being read as a number. This is not necessary in the sixth example because the rest of the name makes it invalid as a number.

foo ; A symbol named ‘foo’.

FOO ; A symbol named ‘FOO’, different from ‘foo’.

     char-to-string      ; A symbol named ‘char-to-string’.

1+ ; A symbol named ‘1+’

; (not ‘+1’, which is an integer).

\+1 ; A symbol named ‘+1’

; (not a very readable name).

\(*\ 1\ 2\) ; A symbol named ‘(* 1 2)’ (a worse name).

     +-*/_~!@$%^&=:<>{}  ; A symbol named ‘+-*/_~!@$%^&=:<>{}’.

; These characters need not be escaped.

2.3.5 Sequence Types

A sequence is a Lisp object that represents an ordered set of elements. There are two kinds of sequence in Emacs Lisp, lists and arrays. Thus, an object of type list or of type array is also considered a sequence.

Arrays are further subdivided into strings and vectors. Vectors can hold elements of any type, but string elements must be characters in the range from 0 to 255. However, the characters in a string can have text properties like characters in a buffer (see Section 29.18 [Text Properties], page 478); vectors do not support text properties even when their elements happen to be characters.

Lists, strings and vectors are different, but they have important similarities. For example, all have a length l, and all have elements which can be indexed from zero to l minus one. Also, several functions, called sequence functions, accept any kind of sequence. For example, the function elt can be used to extract an element of a sequence, given its index. See Chapter 6 [Sequences Arrays Vectors], page 79.

It is impossible to read the same sequence twice, since sequences are always created anew upon reading. If you read the read syntax for a sequence twice, you get two sequences with equal contents. There is one exception: the empty list () always stands for the same object,

nil.

2.3.6 Cons Cell and List Types

A cons cell is an object comprising two pointers named the car and the cdr. Each of them can point to any Lisp object.

A list is a series of cons cells, linked together so that the cdr of each cons cell points either to another cons cell or to the empty list. See Chapter 5 [Lists], page 61, for functions that work on lists. Because most cons cells are used as part of lists, the phrase list structure has come to refer to any structure made out of cons cells.

The names car and cdr have only historical meaning now. The original Lisp implementation ran on an IBM 704 computer which divided words into two parts, called the “address” part and the “decrement”; car was an instruction to extract the contents of the address part of a register, and cdr an instruction to extract the contents of the decrement. By contrast, “cons cells” are named for the function cons that creates them, which in turn is named for its purpose, the construction of cells.

Because cons cells are so central to Lisp, we also have a word for “an object which is not a cons cell”. These objects are called atoms.

The read syntax and printed representation for lists are identical, and consist of a left parenthesis, an arbitrary number of elements, and a right parenthesis.

Upon reading, each object inside the parentheses becomes an element of the list. That is, a cons cell is made for each element. The car of the cons cell points to the element, and its cdr points to the next cons cell of the list, which holds the next element in the list. The cdr of the last cons cell is set to point to nil.

A list can be illustrated by a diagram in which the cons cells are shown as pairs of boxes. (The Lisp reader cannot read such an illustration; unlike the textual notation, which can be understood by both humans and computers, the box illustrations can be understood only by humans.) The following represents the three-element list (rose violet buttercup):

         __________________
        |___|___|--> |___|___|--> |___|___|--> nil
          |            |            |
          |            |            |
           --> rose     --> violet   --> buttercup

In this diagram, each box represents a slot that can refer to any Lisp object. Each pair of boxes represents a cons cell. Each arrow is a reference to a Lisp object, either an atom or another cons cell.

In this example, the first box, the car of the first cons cell, refers to or “contains” rose (a symbol). The second box, the cdr of the first cons cell, refers to the next pair of boxes, the second cons cell. The car of the second cons cell refers to violet and the cdr refers to the third cons cell. The cdr of the third (and last) cons cell refers to nil.

Here is another diagram of the same list, (rose violet buttercup), sketched in a different manner:

      ---------------       ----------------       -------------------
     | car   | cdr   |     | car    | cdr   |     | car       | cdr   |
     | rose  |   o-------->| violet |   o-------->| buttercup |  nil  |
     |       |       |     |        |       |     |           |       |
      ---------------       ----------------       -------------------

A list with no elements in it is the empty list; it is identical to the symbol nil. In other words, nil is both a symbol and a list.

Here are examples of lists written in Lisp syntax:

(A 2 "A") ; A list of three elements.

() ; A list of no elements (the empty list). nil ; A list of no elements (the empty list). ("A ()") ; A list of one element: the string "A ()". (A ()) ; A list of two elements: A and the empty list. (A nil) ; Equivalent to the previous. ((A B C)) ; A list of one element

; (which is a list of three elements).

Here is the list (A ()), or equivalently (A nil), depicted with boxes and arrows:

         ____________
        |___|___|--> |___|___|--> nil
          |            |
          |            |
           --> A        --> nil

2.3.6.1 Dotted Pair Notation

Dotted pair notation is an alternative syntax for cons cells that represents the car and cdr explicitly. In this syntax, (a . b) stands for a cons cell whose car is the object a, and whose cdr is the object b. Dotted pair notation is therefore more general than list syntax. In the dotted pair notation, the list ‘(1 2 3)’ is written as ‘(1 . (2 . (3 . nil)))’. For nil-terminated lists, the two notations produce the same result, but list notation is usually clearer and more convenient when it is applicable. When printing a list, the dotted pair notation is only used if the cdr of a cell is not a list.

Here’s how box notation can illustrate dotted pairs. This example shows the pair (rose

. violet):
         ______
        |___|___|--> violet
          |
          |
           --> rose

Dotted pair notation can be combined with list notation to represent a chain of cons cells with a non-nil final cdr. For example, (rose violet . buttercup) is equivalent to

(rose . (violet . buttercup)). The object looks like this:
         ____________
        |___|___|--> |___|___|--> buttercup
          |            |
          |            |
           --> rose     --> violet

These diagrams make it evident why (rose . violet . buttercup) is invalid syntax; it would require a cons cell that has three parts rather than two.

The list (rose violet) is equivalent to (rose . (violet)) and looks like this:

         ____________
        |___|___|--> |___|___|--> nil
          |            |
          |            |
           --> rose     --> violet

Similarly, the three-element list (rose violet buttercup) is equivalent to (rose .

(violet . (buttercup))).

2.3.6.2 Association List Type

An association list or alist is a specially-constructed list whose elements are cons cells. In each element, the car is considered a key, and the cdr is considered an associated value. (In some cases, the associated value is stored in the car of the cdr.) Association lists are often used as stacks, since it is easy to add or remove associations at the front of the list.

For example,

     (setq alist-of-colors
           '((rose . red) (lily . white)  (buttercup . yellow)))

sets the variable alist-of-colors to an alist of three elements. In the first element, rose is the key and red is the value.

See Section 5.8 [Association Lists], page 74, for a further explanation of alists and for functions that work on alists.

2.3.7 Array Type

An array is composed of an arbitrary number of slots for referring to other Lisp objects, arranged in a contiguous block of memory. Accessing any element of an array takes the same amount of time. In contrast, accessing an element of a list requires time proportional to the position of the element in the list. (Elements at the end of a list take longer to access than elements at the beginning of a list.)

Emacs defines two types of array, strings and vectors. A string is an array of characters and a vector is an array of arbitrary objects. Both are one-dimensional. (Most other programming languages support multidimensional arrays, but they are not essential; you can get the same effect with an array of arrays.) Each type of array has its own read syntax; see Section 2.3.8 [String Type], page 23, and Section 2.3.9 [Vector Type], page 24.

An array may have any length up to the largest integer; but once created, it has a fixed size. The first element of an array has index zero, the second element has index 1, and so on. This is called zero-origin indexing. For example, an array of four elements has indices 0, 1, 2, and 3.

The array type is contained in the sequence type and contains both the string type and the vector type.

2.3.8 String Type

A string is an array of characters. Strings are used for many purposes in Emacs, as can be expected in a text editor; for example, as the names of Lisp symbols, as messages for the user, and to represent text extracted from buffers. Strings in Lisp are constants: evaluation of a string returns the same string.

The read syntax for strings is a double-quote, an arbitrary number of characters, and another double-quote, "like this". The Lisp reader accepts the same formats for reading the characters of a string as it does for reading single characters (without the question mark that begins a character literal). You can enter a nonprinting character such as tab, C-a or M-C-A using the convenient escape sequences, like this: "\t, \C-a, \M-\C-a". You can include a double-quote in a string by preceding it with a backslash; thus, "\"" is a string containing just a single double-quote character. (See Section 2.3.3 [Character Type], page 17, for a description of the read syntax for characters.)

If you use the ‘\M-’ syntax to indicate a meta character in a string constant, this sets the $2^7$ bit of the character in the string. This is not the same representation that the meta modifier has in a character on its own (not inside a string). See Section 2.3.3 [Character Type], page 17.

Strings cannot hold characters that have the hyper, super, or alt modifiers; they can hold ASCII control characters, but no others. They do not distinguish case in ASCII control characters.

The printed representation of a string consists of a double-quote, the characters it contains, and another double-quote. However, you must escape any backslash or double-quote characters in the string with a backslash, like this: "this \" is an embedded quote".

The newline character is not special in the read syntax for strings; if you write a new line between the double-quotes, it becomes a character in the string. But an escaped newline— one that is preceded by ‘\’—does not become part of the string; i.e., the Lisp reader ignores an escaped newline while reading a string.

     "It is useful to include newlines
     in documentation strings,
     but the newline is \
     ignored if escaped."
          ⇒ "It is useful to include newlines
     in documentation strings,
     but the newline is ignored if escaped."

A string can hold properties of the text it contains, in addition to the characters themselves. This enables programs that copy text between strings and buffers to preserve the properties with no special effort. See Section 29.18 [Text Properties], page 478. Strings with text properties have a special read and print syntax:

#("characters" property-data...) where property-data consists of zero or more elements, in groups of three as follows:

beg end plist The elements beg and end are integers, and together specify a range of indices in the string; plist is the property list for that range.

See Chapter 4 [Strings and Characters], page 49, for functions that work on strings.

2.3.9 Vector Type

A vector is a one-dimensional array of elements of any type. It takes a constant amount of time to access any element of a vector. (In a list, the access time of an element is proportional to the distance of the element from the beginning of the list.)

The printed representation of a vector consists of a left square bracket, the elements, and a right square bracket. This is also the read syntax. Like numbers and strings, vectors are considered constants for evaluation.

[1 "two" (three)] ; A vector of three elements.

          ⇒ [1 "two" (three)]

See Section 6.4 [Vectors], page 83, for functions that work with vectors.

2.3.10 Function Type

Just as functions in other programming languages are executable, Lisp function objects are pieces of executable code. However, functions in Lisp are primarily Lisp objects, and only secondarily the text which represents them. These Lisp objects are lambda expressions: lists whose first element is the symbol lambda (see Section 11.2 [Lambda Expressions], page 140).

In most programming languages, it is impossible to have a function without a name. In Lisp, a function has no intrinsic name. A lambda expression is also called an anonymous function (see Section 11.7 [Anonymous Functions], page 148). A named function in Lisp is actually a symbol with a valid function in its function cell (see Section 11.4 [Defining Functions], page 144).

Most of the time, functions are called when their names are written in Lisp expressions in Lisp programs. However, you can construct or obtain a function object at run time and then call it with the primitive functions funcall and apply. See Section 11.5 [Calling Functions], page 145.

2.3.11 Macro Type

A Lisp macro is a user-defined construct that extends the Lisp language. It is represented as an object much like a function, but with different parameter-passing semantics. A Lisp macro has the form of a list whose first element is the symbol macro and whose cdr is a Lisp function object, including the lambda symbol.

Lisp macro objects are usually defined with the built-in defmacro function, but any list that begins with macro is a macro as far as Emacs is concerned. See Chapter 12 [Macros], page 153, for an explanation of how to write a macro.

2.3.12 Primitive Function Type

A primitive function is a function callable from Lisp but written in the C programming language. Primitive functions are also called subrs or built-in functions. (The word “subr” is derived from “subroutine”.) Most primitive functions evaluate all their arguments when they are called. A primitive function that does not evaluate all its arguments is called a special form (see Section 8.2.7 [Special Forms], page 101).

It does not matter to the caller of a function whether the function is primitive. However, this does matter if you try to substitute a function written in Lisp for a primitive of the same name. The reason is that the primitive function may be called directly from C code. Calls to the redefined function from Lisp will use the new definition, but calls from C code may still use the built-in definition.

The term function refers to all Emacs functions, whether written in Lisp or C. See Section 2.3.10 [Function Type], page 24, for information about the functions written in Lisp.

Primitive functions have no read syntax and print in hash notation with the name of the subroutine.

     (symbol-function 'car)          ; Access the function cell

; of the symbol.

          ⇒ #<subr car>
     (subrp (symbol-function 'car))  ; Is this a primitive function?

⇒ t ; Yes.

2.3.13 Byte-Code Function Type

The byte compiler produces byte-code function objects. Internally, a byte-code function object is much like a vector; however, the evaluator handles this data type specially when it appears as a function to be called. See Chapter 14 [Byte Compilation], page 171, for information about the byte compiler.

The printed representation and read syntax for a byte-code function object is like that for a vector, with an additional ‘#’ before the opening ‘[’.

2.3.14 Autoload Type

An autoload object is a list whose first element is the symbol autoload. It is stored as the function definition of a symbol as a placeholder for the real definition; it says that the real definition is found in a file of Lisp code that should be loaded when necessary. The autoload object contains the name of the file, plus some other information about the real definition.

After the file has been loaded, the symbol should have a new function definition that is not an autoload object. The new definition is then called as if it had been there to begin with. From the user’s point of view, the function call works as expected, using the function definition in the loaded file.

An autoload object is usually created with the function autoload, which stores the object in the function cell of a symbol. See Section 13.2 [Autoload], page 164, for more details.

2.4 Editing Types

The types in the previous section are common to many Lisp dialects. Emacs Lisp provides several additional data types for purposes connected with editing.

2.4.1 Buffer Type

A buffer is an object that holds text that can be edited (see Chapter 24 [Buffers], page 369). Most buffers hold the contents of a disk file (see Chapter 22 [Files], page 329) so they can be edited, but some are used for other purposes. Most buffers are also meant to be seen by the user, and therefore displayed, at some time, in a window (see Chapter 25 [Windows], page 383). But a buffer need not be displayed in any window.

The contents of a buffer are much like a string, but buffers are not used like strings in Emacs Lisp, and the available operations are different. For example, insertion of text into a buffer is very efficient, whereas “inserting” text into a string requires concatenating substrings, and the result is an entirely new string object.

Each buffer has a designated position called point (see Chapter 27 [Positions], page 429). At any time, one buffer is the current buffer. Most editing commands act on the contents of the current buffer in the neighborhood of point. Many of the standard Emacs functions manipulate or test the characters in the current buffer; a whole chapter in this manual is devoted to describing these functions (see Chapter 29 [Text], page 449).

Several other data structures are associated with each buffer:

• a local syntax table (see Chapter 31 [Syntax Tables], page 509);

• a local keymap (see Chapter 19 [Keymaps], page 277); and,

• a local variable binding list (see Section 10.10 [Buffer-Local Variables], page 134).

• a list of overlays (see Section 35.9 [Overlays], page 575).

• text properties for the text in the buffer (see Section 29.18 [Text Properties], page 478).

The local keymap and variable list contain entries that individually override global bindings or values. These are used to customize the behavior of programs in different buffers, without actually changing the programs.

A buffer may be indirect, which means it shares the text of another buffer. See Section 24.11 [Indirect Buffers], page 380.

Buffers have no read syntax. They print in hash notation, showing the buffer name.

     (current-buffer)
          ⇒ #<buffer objects.texi>

2.4.2 Marker Type

A marker denotes a position in a specific buffer. Markers therefore have two components: one for the buffer, and one for the position. Changes in the buffer’s text automatically relocate the position value as necessary to ensure that the marker always points between the same two characters in the buffer.

Markers have no read syntax. They print in hash notation, giving the current character position and the name of the buffer.

     (point-marker)
          ⇒ #<marker at 10779 in objects.texi>

See Chapter 28 [Markers], page 441, for information on how to test, create, copy, and move markers.

2.4.3 Window Type

A window describes the portion of the terminal screen that Emacs uses to display a buffer. Every window has one associated buffer, whose contents appear in the window. By contrast, a given buffer may appear in one window, no window, or several windows.

Though many windows may exist simultaneously, at any time one window is designated the selected window. This is the window where the cursor is (usually) displayed when Emacs is ready for a command. The selected window usually displays the current buffer, but this is not necessarily the case.

Windows are grouped on the screen into frames; each window belongs to one and only one frame. See Section 2.4.4 [Frame Type], page 27.

Windows have no read syntax. They print in hash notation, giving the window number and the name of the buffer being displayed. The window numbers exist to identify windows uniquely, since the buffer displayed in any given window can change frequently.

     (selected-window)
          ⇒ #<window 1 on objects.texi>

See Chapter 25 [Windows], page 383, for a description of the functions that work on windows.

2.4.4 Frame Type

A frame is a rectangle on the screen that contains one or more Emacs windows. A frame initially contains a single main window (plus perhaps a minibuffer window) which you can subdivide vertically or horizontally into smaller windows.

Frames have no read syntax. They print in hash notation, giving the frame’s title, plus its address in core (useful to identify the frame uniquely).

     (selected-frame)
          ⇒ #<frame xemacs@mole.gnu.ai.mit.edu 0xdac80>

See Chapter 26 [Frames], page 409, for a description of the functions that work on frames.

2.4.5 Window Configuration Type

A window configuration stores information about the positions, sizes, and contents of the windows in a frame, so you can recreate the same arrangement of windows later.

Window configurations do not have a read syntax; their print syntax looks like ‘#<window-configuration>’. See Section 25.17 [Window Configurations], page 406, for a description of several functions related to window configurations.

2.4.6 Process Type

The word process usually means a running program. Emacs itself runs in a process of this sort. However, in Emacs Lisp, a process is a Lisp object that designates a subprocess created by the Emacs process. Programs such as shells, GDB, ftp, and compilers, running in subprocesses of Emacs, extend the capabilities of Emacs.

An Emacs subprocess takes textual input from Emacs and returns textual output to Emacs for further manipulation. Emacs can also send signals to the subprocess.

Process objects have no read syntax. They print in hash notation, giving the name of the process:

     (process-list)
          ⇒ (#<process shell>)

See Chapter 33 [Processes], page 525, for information about functions that create, delete, return information about, send input or signals to, and receive output from processes.

2.4.7 Stream Type

A stream is an object that can be used as a source or sink for characters—either to supply characters for input or to accept them as output. Many different types can be used this way: markers, buffers, strings, and functions. Most often, input streams (character sources) obtain characters from the keyboard, a buffer, or a file, and output streams (character sinks) send characters to a buffer, such as a ‘*Help*’ buffer, or to the echo area.

The object nil, in addition to its other meanings, may be used as a stream. It stands for the value of the variable standard-input or standard-output. Also, the object t as a stream specifies input using the minibuffer (see Chapter 17 [Minibuffers], page 223) or output in the echo area (see Section 35.4 [The Echo Area], page 569).

Streams have no special printed representation or read syntax, and print as whatever primitive type they are.

See Chapter 16 [Read and Print], page 213, for a description of functions related to streams, including parsing and printing functions.

2.4.8 Keymap Type

A keymap maps keys typed by the user to commands. This mapping controls how the user’s command input is executed. A keymap is actually a list whose car is the symbol

keymap.

See Chapter 19 [Keymaps], page 277, for information about creating keymaps, handling prefix keys, local as well as global keymaps, and changing key bindings.

2.4.9 Syntax Table Type

A syntax table is a vector of 256 integers. Each element of the vector defines how one character is interpreted when it appears in a buffer. For example, in C mode (see Section 20.1 [Major Modes], page 299), the ‘+’ character is punctuation, but in Lisp mode it is a valid character in a symbol. These modes specify different interpretations by changing the syntax table entry for ‘+’, at index 43 in the syntax table.

Syntax tables are used only for scanning text in buffers, not for reading Lisp expressions. The table the Lisp interpreter uses to read expressions is built into the Emacs source code and cannot be changed; thus, to change the list delimiters to be ‘{’ and ‘}’ instead of ‘(’ and ‘)’ would be impossible.

See Chapter 31 [Syntax Tables], page 509, for details about syntax classes and how to make and modify syntax tables.

2.4.10 Display Table Type

A display table specifies how to display each character code. Each buffer and each window can have its own display table. A display table is actually a vector of length 262. See Section 35.14 [Display Tables], page 583.

2.4.11 Overlay Type

An overlay specifies temporary alteration of the display appearance of a part of a buffer. It contains markers delimiting a range of the buffer, plus a property list (a list whose elements are alternating property names and values). Overlays are used to present parts of the buffer temporarily in a different display style. They have no read syntax, and print in hash notation, giving the buffer name and range of positions.

See Section 35.9 [Overlays], page 575, for how to create and use overlays.

2.5 Type Predicates

The Emacs Lisp interpreter itself does not perform type checking on the actual arguments passed to functions when they are called. It could not do so, since function arguments in Lisp do not have declared data types, as they do in other programming languages. It is therefore up to the individual function to test whether each actual argument belongs to a type that the function can use.

All built-in functions do check the types of their actual arguments when appropriate, and signal a wrong-type-argument error if an argument is of the wrong type. For example, here is what happens if you pass an argument to + that it cannot handle:

     (+ 2 'a)
           error Wrong type argument: integer-or-marker-p, a

If you want your program to handle different types differently, you must do explicit type checking. The most common way to check the type of an object is to call a type predicate function. Emacs has a type predicate for each type, as well as some predicates for combinations of types.

A type predicate function takes one argument; it returns t if the argument belongs to the appropriate type, and nil otherwise. Following a general Lisp convention for predicate functions, most type predicates’ names end with ‘p’.

Here is an example which uses the predicates listp to check for a list and symbolp to check for a symbol.

     (defun add-on (x)
       (cond ((symbolp x)
              ;; If X is a symbol, put it on LIST.
              (setq list (cons x list)))
             ((listp x)
              ;; If X is a list, add its elements to LIST.
              (setq list (append x list)))
             (t
              ;; We only handle symbols and lists.
              (error "Invalid argument %s in add-on" x))))

Here is a table of predefined type predicates, in alphabetical order, with references to further information.

atom See Section 5.3 [List-related Predicates], page 62.

arrayp See Section 6.3 [Array Functions], page 82.

bufferp See Section 24.1 [Buffer Basics], page 369.

byte-code-function-p

See Section 2.3.13 [Byte-Code Type], page 25.

case-table-p

See Section 4.8 [Case Table], page 58.

char-or-string-p

See Section 4.2 [Predicates for Strings], page 50.

commandp See Section 18.3 [Interactive Call], page 248.

consp See Section 5.3 [List-related Predicates], page 62.

floatp See Section 3.3 [Predicates on Numbers], page 36.

frame-live-p

See Section 26.5 [Deleting Frames], page 417.

framep See Chapter 26 [Frames], page 409.

integer-or-marker-p

See Section 28.2 [Predicates on Markers], page 442. integerp See Section 3.3 [Predicates on Numbers], page 36. keymapp See Section 19.3 [Creating Keymaps], page 279. listp See Section 5.3 [List-related Predicates], page 62. markerp See Section 28.2 [Predicates on Markers], page 442.

wholenump

See Section 3.3 [Predicates on Numbers], page 36.

nlistp See Section 5.3 [List-related Predicates], page 62. numberp See Section 3.3 [Predicates on Numbers], page 36.

number-or-marker-p

See Section 28.2 [Predicates on Markers], page 442.

overlayp See Section 35.9 [Overlays], page 575. processp See Chapter 33 [Processes], page 525.

sequencep

See Section 6.1 [Sequence Functions], page 79.

stringp See Section 4.2 [Predicates for Strings], page 50. subrp See Section 11.8 [Function Cells], page 149. symbolp See Chapter 7 [Symbols], page 87.

syntax-table-p

See Chapter 31 [Syntax Tables], page 509.

user-variable-p

See Section 10.5 [Defining Variables], page 125.

vectorp See Section 6.4 [Vectors], page 83.

window-configuration-p

See Section 25.17 [Window Configurations], page 406.

window-live-p

See Section 25.3 [Deleting Windows], page 386.

windowp See Section 25.1 [Basic Windows], page 383.

The most general way to check the type of an object is to call the function type-of. Recall that each object belongs to one and only one primitive type; type-of tells you which one (see Chapter 2 [Lisp Data Types], page 15). But type-of knows nothing about nonprimitive types. In most cases, it is more convenient to use type predicates than type-of.

Function type-of object

This function returns a symbol naming the primitive type of object. The value

     is one of the symbols symbol, integer, float, string, cons, vector, marker,
     overlay, window, buffer, subr, compiled-function, process, or window-
     configuration.

(type-of 1)
     ⇒ integer
(type-of 'nil)
     ⇒ symbol
(type-of '())    ; () is nil.
     ⇒ symbol
(type-of '(x))
     ⇒ cons

2.6 Equality Predicates

Here we describe two functions that test for equality between any two objects. Other functions test equality between objects of specific types, e.g., strings. For these predicates, see the appropriate chapter describing the data type.

Function eq object1 object2 This function returns t if object1 and object2 are the same object, nil otherwise. The “same object” means that a change in one will be reflected by the same change in the other.

eq returns t if object1 and object2 are integers with the same value. Also, since symbol names are normally unique, if the arguments are symbols with the same name, they are eq. For other types (e.g., lists, vectors, strings), two arguments with the same contents or elements are not necessarily eq to each other: they are eq only if they are the same object.

(The make-symbol function returns an uninterned symbol that is not interned in the standard obarray. When uninterned symbols are in use, symbol names are no longer unique. Distinct symbols with the same name are not eq. See Section 7.3 [Creating Symbols], page 89.)

(eq 'foo 'foo)
     ⇒ t
(eq 456 456) ⇒ t
(eq "asdf" "asdf")
     ⇒ nil
(eq '(1 (2 (3))) '(1 (2 (3)))) ⇒ nil
(setq foo '(1 (2 (3))))
     ⇒ (1 (2 (3)))
(eq foo foo)
     ⇒ t
(eq foo '(1 (2 (3))))
     ⇒ nil
(eq [(1 2) 3] [(1 2) 3]) ⇒ nil

(eq (point-marker) (point-marker))
     ⇒ nil

Function equal object1 object2 This function returns t if object1 and object2 have equal components, nil otherwise. Whereas eq tests if its arguments are the same object, equal looks inside nonidentical arguments to see if their elements are the same. So, if two objects are eq, they are equal, but the converse is not always true.

(equal 'foo 'foo)
     ⇒ t
(equal 456 456) ⇒ t
(equal "asdf" "asdf")
     ⇒ t
(eq "asdf" "asdf")
     ⇒ nil
(equal '(1 (2 (3))) '(1 (2 (3)))) ⇒ t
(eq '(1 (2 (3))) '(1 (2 (3)))) ⇒ nil
(equal [(1 2) 3] [(1 2) 3]) ⇒ t
(eq [(1 2) 3] [(1 2) 3]) ⇒ nil
(equal (point-marker) (point-marker))
     ⇒ t
(eq (point-marker) (point-marker))
     ⇒ nil

Comparison of strings is case-sensitive and takes account of text properties as well as the characters in the strings. To compare two strings’ characters without comparing their text properties, use string= (see Section 4.4 [Text Comparison], page 52).

(equal "asdf" "ASDF")
     ⇒ nil

Two distinct buffers are never equal, even if their contents are the same.

The test for equality is implemented recursively, and circular lists may therefore cause infinite recursion (leading to an error).

34 GNU Emacs Lisp Reference Manual

3 Numbers

GNU Emacs supports two numeric data types: integers and floating point numbers. Integers are whole numbers such as −3, 0, 7, 13, and 511. Their values are exact. Floating point numbers are numbers with fractional parts, such as −4.5, 0.0, or 2.71828. They can also be expressed in exponential notation: 1.5e2 equals 150; in this example, ‘e2’ stands for ten to the second power, and is multiplied by 1.5. Floating point values are not exact; they have a fixed, limited amount of precision.

Support for floating point numbers is a new feature in Emacs 19, and it is controlled by a separate compilation option, so you may encounter a site where Emacs does not support them.

3.1 Integer Basics

The range of values for an integer depends on the machine. The minimum range is −134217728 to 134217727 (28 bits; i.e., −2^{27} to 2^{27} − 1), but some machines may provide a wider range. Many examples in this chapter assume an integer has 28 bits.

The Lisp reader reads an integer as a sequence of digits with optional initial sign and optional final period.

1 ; The integer 1.

1. ; The integer 1. +1 ; Also the integer 1. -1 ; The integer −1. 268435457 ; Also the integer 1, due to overflow. 0 ; The integer 0. -0 ; The integer 0.

To understand how various functions work on integers, especially the bitwise operators (see Section 3.8 [Bitwise Operations], page 42), it is often helpful to view the numbers in their binary form.

In 28-bit binary, the decimal integer 5 looks like this:

     0000  0000 0000  0000 0000  0000 0101

(We have inserted spaces between groups of 4 bits, and two spaces between groups of 8 bits, to make the binary integer easier to read.)

The integer −1 looks like this:

     1111  1111 1111  1111 1111  1111 1111

−1 is represented as 28 ones. (This is called two’s complement notation.)

The negative integer, −5, is creating by subtracting 4 from −1. In binary, the decimal integer 4 is 100. Consequently, −5 looks like this:

     1111  1111 1111  1111 1111  1111 1011

In this implementation, the largest 28-bit binary integer value is 134,217,727. In binary, it looks like this:

     0111  1111 1111  1111 1111  1111 1111

Since the arithmetic functions do not check whether integers go outside their range, when you add 1 to 134,217,727, the value is the negative integer −134,217,728:

     (+ 1 134217727)
          ⇒ -134217728

          ⇒ 1000  0000 0000  0000 0000  0000 0000

Many of the following functions accept markers for arguments as well as integers. (See Chapter 28 [Markers], page 441.) More precisely, the actual arguments to such functions may be either integers or markers, which is why we often give these arguments the name int-or-marker. When the argument value is a marker, its position value is used and its buffer is ignored.

3.2 Floating Point Basics

Emacs version 19 supports floating point numbers, if compiled with the macro LISP_ FLOAT_TYPE defined. The precise range of floating point numbers is machine-specific; it is the same as the range of the C data type double on the machine in question.

The printed representation for floating point numbers requires either a decimal point (with at least one digit following), an exponent, or both. For example, ‘1500.0’, ‘15e2’, ‘15.0e2’, ‘1.5e3’, and ‘.15e4’ are five ways of writing a floating point number whose value is 1500. They are all equivalent. You can also use a minus sign to write negative floating point numbers, as in ‘-1.0’.

Most modern computers support the IEEE floating point standard, which provides for positive infinity and negative infinity as floating point values. It also provides for a class of values called NaN or “not-a-number”; numerical functions return such values in cases where there is no correct answer. For example, (sqrt -1.0) returns a NaN. For practical purposes, there’s no significant difference between different NaN values in Emacs Lisp, and there’s no rule for precisely which NaN value should be used in a particular case, so this manual doesn’t try to distinguish them. Emacs Lisp has no read syntax for NaNs or infinities; perhaps we should create a syntax in the future.

You can use logb to extract the binary exponent of a floating point number (or estimate the logarithm of an integer):

Function logb number This function returns the binary exponent of number. More precisely, the value is the logarithm of number base 2, rounded down to an integer.

3.3 Type Predicates for Numbers

The functions in this section test whether the argument is a number or whether it is a certain sort of number. The functions integerp and floatp can take any type of Lisp object as argument (the predicates would not be of much use otherwise); but the zerop predicate requires a number as its argument. See also integer-or-marker-p and numberor-marker-p, in Section 28.2 [Predicates on Markers], page 442.

Function floatp object This predicate tests whether its argument is a floating point number and returns t if so, nil otherwise. floatp does not exist in Emacs versions 18 and earlier.

Function integerp object

This predicate tests whether its argument is an integer, and returns t if so, nil otherwise.

Function numberp object

This predicate tests whether its argument is a number (either integer or floating point), and returns t if so, nil otherwise.

Function wholenump object

The wholenump predicate (whose name comes from the phrase “whole-number-p”) tests to see whether its argument is a nonnegative integer, and returns t if so, nil otherwise. 0 is considered non-negative.

natnump is an obsolete synonym for wholenump.

Function zerop number This predicate tests whether its argument is zero, and returns t if so, nil otherwise. The argument must be a number.

These two forms are equivalent: (zerop x) ≡ (= x 0).

3.4 Comparison of Numbers

To test numbers for numerical equality, you should normally use =, not eq. There can be many distinct floating point number objects with the same numeric value. If you use eq to compare them, then you test whether two values are the same object. By contrast, = compares only the numeric values of the objects.

At present, each integer value has a unique Lisp object in Emacs Lisp. Therefore, eq is equivalent = where integers are concerned. It is sometimes convenient to use eq for comparing an unknown value with an integer, because eq does not report an error if the unknown value is not a number—it accepts arguments of any type. By contrast, = signals an error if the arguments are not numbers or markers. However, it is a good idea to use = if you can, even for comparing integers, just in case we change the representation of integers in a future Emacs version.

There is another wrinkle: because floating point arithmetic is not exact, it is often a bad idea to check for equality of two floating point values. Usually it is better to test for approximate equality. Here’s a function to do this:

(defvar fuzz-factor 1.0e-6)
(defun approx-equal (x y)
  (or (and (= x 0) (= y 0))
      (< (/ (abs (- x y))
            (max (abs x) (abs y)))
         fuzz-factor)))

Common Lisp note: Comparing numbers in Common Lisp always requires = because Common Lisp implements multi-word integers, and two distinct integer objects can have the same numeric value. Emacs Lisp can have just one integer object for any given value because it has a limited range of integer values.

Function = number-or-marker1 number-or-marker2 This function tests whether its arguments are numerically equal, and returns t if so, nil otherwise.

Function /= number-or-marker1 number-or-marker2 This function tests whether its arguments are numerically equal, and returns t if they are not, and nil if they are.

Function < number-or-marker1 number-or-marker2 This function tests whether its first argument is strictly less than its second argument. It returns t if so, nil otherwise.

Function <= number-or-marker1 number-or-marker2 This function tests whether its first argument is less than or equal to its second argument. It returns t if so, nil otherwise.

Function > number-or-marker1 number-or-marker2 This function tests whether its first argument is strictly greater than its second argument. It returns t if so, nil otherwise.

Function >= number-or-marker1 number-or-marker2 This function tests whether its first argument is greater than or equal to its second argument. It returns t if so, nil otherwise.

Function max number-or-marker &rest numbers-or-markers

This function returns the largest of its arguments.

     (max 20)
          ⇒ 20
     (max 1 2.5)
          ⇒ 2.5
     (max 1 3 2.5)
          ⇒ 3

Function min number-or-marker &rest numbers-or-markers

This function returns the smallest of its arguments.

     (min -4 1)
          ⇒ -4

3.5 Numeric Conversions

To convert an integer to floating point, use the function float.

Function float number This returns number converted to floating point. If number is already a floating point number, float returns it unchanged.

There are four functions to convert floating point numbers to integers; they differ in how they round. These functions accept integer arguments also, and return such arguments unchanged.

Function truncate number

This returns number, converted to an integer by rounding towards zero.

Function floor number &optional divisor This returns number, converted to an integer by rounding downward (towards negative infinity). If divisor is specified, number is divided by divisor before the floor is taken; this is the division operation that corresponds to mod. An arith-error results if divisor is 0.

Function ceiling number

This returns number, converted to an integer by rounding upward (towards positive infinity).

Function round number This returns number, converted to an integer by rounding towards the nearest integer. Rounding a value equidistant between two integers may choose the integer closer to zero, or it may prefer an even integer, depending on your machine.

3.6 Arithmetic Operations

Emacs Lisp provides the traditional four arithmetic operations: addition, subtraction, multiplication, and division. Remainder and modulus functions supplement the division functions. The functions to add or subtract 1 are provided because they are traditional in Lisp and commonly used.

All of these functions except % return a floating point value if any argument is floating. It is important to note that in GNU Emacs Lisp, arithmetic functions do not check for

overflow. Thus (1+ 134217727) may evaluate to −134217728, depending on your hardware.

Function 1+ number-or-marker

This function returns number-or-marker plus 1. For example,

     (setq foo 4)
          ⇒ 4
     (1+ foo)
          ⇒ 5

This function is not analogous to the C operator ++—it does not increment a variable. It just computes a sum. Thus, if we continue,

     foo

          ⇒ 4

If you want to increment the variable, you must use setq, like this:

     (setq foo (1+ foo))
          ⇒ 5

Function 1- number-or-marker This function returns number-or-marker minus 1.

Function abs number This returns the absolute value of number.

Function + &rest numbers-or-markers This function adds its arguments together. When given no arguments, + returns 0.

     (+)
          ⇒ 0
     (+ 1)
          ⇒ 1
     (+ 1 2 3 4)
          ⇒ 10

Function - &optional number-or-marker &rest other-numbers-or-markers The - function serves two purposes: negation and subtraction. When - has a single argument, the value is the negative of the argument. When there are multiple arguments, - subtracts each of the other-numbers-or-markers from number-or-marker, cumulatively. If there are no arguments, the result is 0.

     (- 10 1 2 3 4)
          ⇒ 0
     (- 10)
          ⇒ -10
     (-)

          ⇒ 0

Function * &rest numbers-or-markers This function multiplies its arguments together, and returns the product. When given no arguments, * returns 1.

     (*)
          ⇒ 1
     (* 1)
          ⇒ 1
     (* 1 2 3 4)
          ⇒ 24

Function / dividend divisor &rest divisors This function divides dividend by divisor and returns the quotient. If there are additional arguments divisors, then it divides dividend by each divisor in turn. Each argument may be a number or a marker. If all the arguments are integers, then the result is an integer too. This means the result has to be rounded. On most machines, the result is rounded towards zero after each division, but some machines may round differently with negative arguments. This is because the Lisp function / is implemented using the C division operator, which also permits machine-dependent rounding. As a practical matter, all known machines round in the standard fashion. If you divide by 0, an arith-error error is signaled. (See Section 9.5.3 [Errors], page 112.)

     (/ 6 2) ⇒ 3
     (/ 5 2)
          ⇒ 2
     (/ 25 3 2)
          ⇒ 4
     (/ -17 6)
          ⇒ -2

The result of (/ -17 6) could in principle be -3 on some machines.

Function % dividend divisor This function returns the integer remainder after division of dividend by divisor. The arguments must be integers or markers. For negative arguments, the remainder is in principle machine-dependent since the quotient is; but in practice, all known machines behave alike. An arith-error results if divisor is 0.

     (% 9 4)
          ⇒ 1
     (% -9 4)
          ⇒ -1
     (% 9 -4)
          ⇒ 1
     (% -9 -4)
          ⇒ -1

For any two integers dividend and divisor,

(+ (% dividend divisor)

(* (/ dividend divisor) divisor))

always equals dividend.

Function mod dividend divisor This function returns the value of dividend modulo divisor; in other words, the remainder after division of dividend by divisor, but with the same sign as divisor. The arguments must be numbers or markers. Unlike %, mod returns a well-defined result for negative arguments. It also permits floating point arguments; it rounds the quotient downward (towards minus infinity) to an integer, and uses that quotient to compute the remainder. An arith-error results if divisor is 0.

     (mod 9 4) ⇒ 1

     (mod -9 4) ⇒ 3
     (mod 9 -4) ⇒ -3
     (mod -9 -4) ⇒ -1

     (mod 5.5 2.5) ⇒ .5

For any two numbers dividend and divisor,

(+ (mod dividend divisor)

(* (floor dividend divisor) divisor))

always equals dividend, subject to rounding error if either argument is floating point. For floor, see Section 3.5 [Numeric Conversions], page 38.

3.7 Rounding Operations

The functions ffloor, fceiling, fround and ftruncate take a floating point argument and return a floating point result whose value is a nearby integer. ffloor returns the nearest integer below; fceiling, the nearest integer above; ftruncate, the nearest integer in the direction towards zero; fround, the nearest integer.

Function ffloor float

This function rounds float to the next lower integral value, and returns that value as a floating point number.

Function fceiling float

This function rounds float to the next higher integral value, and returns that value as a floating point number.

Function ftruncate float

This function rounds float towards zero to an integral value, and returns that value as a floating point number.

Function fround float

This function rounds float to the nearest integral value, and returns that value as a floating point number.

3.8 Bitwise Operations on Integers

In a computer, an integer is represented as a binary number, a sequence of bits (digits which are either zero or one). A bitwise operation acts on the individual bits of such a sequence. For example, shifting moves the whole sequence left or right one or more places, reproducing the same pattern “moved over”.

The bitwise operations in Emacs Lisp apply only to integers.

Function lsh integer1 count lsh, which is an abbreviation for logical shift, shifts the bits in integer1 to the left count places, or to the right if count is negative, bringing zeros into the vacated bits. If count is negative, lsh shifts zeros into the leftmost (mostsignificant) bit, producing a positive result even if integer1 is negative. Contrast this with ash, below. Here are two examples of lsh, shifting a pattern of bits one place to the left. We show only the low-order eight bits of the binary pattern; the rest are all zero.

(lsh 5 1)
     ⇒ 10

;; Decimal 5 becomes decimal 10.

00000101 ⇒ 00001010
(lsh 7 1)
     ⇒ 14

;; Decimal 7 becomes decimal 14.

00000111 ⇒ 00001110

As the examples illustrate, shifting the pattern of bits one place to the left produces a number that is twice the value of the previous number.

Shifting a pattern of bits two places to the left produces results like this (with 8-bit binary numbers):

(lsh 3 2)
     ⇒ 12

;; Decimal 3 becomes decimal 12.

00000011 ⇒ 00001100

On the other hand, shifting one place to the right looks like this:

(lsh 6 -1)
     ⇒ 3

;; Decimal 6 becomes decimal 3.

00000110 ⇒ 00000011
(lsh 5 -1)
     ⇒ 2

;; Decimal 5 becomes decimal 2.

00000101 ⇒ 00000010

As the example illustrates, shifting one place to the right divides the value of a positive integer by two, rounding downward.

The function lsh, like all Emacs Lisp arithmetic functions, does not check for overflow, so shifting left can discard significant bits and change the sign of the number. For example, left shifting 134,217,727 produces −2 on a 28-bit machine:

(lsh 134217727 1)          ; left shift
     ⇒ -2

In binary, in the 28-bit implementation, the argument looks like this:

;; Decimal 134,217,727 0111  1111 1111  1111 1111  1111 1111

which becomes the following when left shifted:

;; Decimal −2 1111  1111 1111  1111 1111  1111 1110

Function ash integer1 count ash (arithmetic shift) shifts the bits in integer1 to the left count places, or to the right if count is negative. ash gives the same results as lsh except when integer1 and count are both negative. In that case, ash puts ones in the empty bit positions on the left, while lsh puts zeros in those bit positions. Thus, with ash, shifting the pattern of bits one place to the right looks like this:

     (ash -6 -1) ⇒ -3

;; Decimal −6 becomes decimal −3.

     1111  1111 1111  1111 1111  1111 1010

⇒

     1111  1111 1111  1111 1111  1111 1101

In contrast, shifting the pattern of bits one place to the right with lsh looks like this:

     (lsh -6 -1) ⇒ 134217725

;; Decimal −6 becomes decimal 134,217,725.

     1111  1111 1111  1111 1111  1111 1010

⇒

     0111  1111 1111  1111 1111  1111 1101

Here are other examples:

; 28-bit binary values

(lsh 5 2) ; 5 = 0000 0000 0000 0000 0000 0000 0101

⇒ 20 ; = 0000 0000 0000 0000 0000 0001 0100

     (ash 5 2)
          ⇒ 20

(lsh -5 2) ; -5 = 1111 1111 1111 1111 1111 1111 1011

⇒ -20 ; = 1111 1111 1111 1111 1111 1110 1100

     (ash -5 2)
          ⇒ -20

(lsh 5 -2) ; 5 = 0000 0000 0000 0000 0000 0000 0101 ⇒ 1 ; = 0000 0000 0000 0000 0000 0000 0001

     (ash 5 -2) ⇒ 1

(lsh -5 -2) ; -5 = 1111 1111 1111 1111 1111 1111 1011 ⇒ 4194302 ; = 0011 1111 1111 1111 1111 1111 1110

(ash -5 -2) ; -5 = 1111 1111 1111 1111 1111 1111 1011 ⇒ -2 ; = 1111 1111 1111 1111 1111 1111 1110

Function logand &rest ints-or-markers This function returns the “logical and” of the arguments: the nth bit is set in the result if, and only if, the nth bit is set in all the arguments. (“Set” means that the value of the bit is 1 rather than 0.) For example, using 4-bit binary numbers, the “logical and” of 13 and 12 is 12: 1101 combined with 1100 produces 1100. In both the binary numbers, the leftmost two bits are set (i.e., they are 1’s), so the leftmost two bits of the returned value are set. However, for the rightmost two bits, each is zero in at least one of the arguments, so the rightmost two bits of the returned value are 0’s.

Therefore,

     (logand 13 12) ⇒ 12

If logand is not passed any argument, it returns a value of −1. This number is an identity element for logand because its binary representation consists entirely of ones. If logand is passed just one argument, it returns that argument.

; 28-bit binary values

(logand 14 13) ; 14 = 0000 0000 0000 0000 0000 0000 1110

; 13 = 0000 0000 0000 0000 0000 0000 1101

⇒ 12 ; 12 = 0000 0000 0000 0000 0000 0000 1100 (logand 14 13 4) ; 14 = 0000 0000 0000 0000 0000 0000 1110

; 13 = 0000 0000 0000 0000 0000 0000 1101 ; 4 = 0000 0000 0000 0000 0000 0000 0100

⇒ 4 ; 4 = 0000 0000 0000 0000 0000 0000 0100 (logand) ⇒ -1 ; -1 = 1111 1111 1111 1111 1111 1111 1111

Function logior &rest ints-or-markers This function returns the “inclusive or” of its arguments: the nth bit is set in the result if, and only if, the nth bit is set in at least one of the arguments. If there are no arguments, the result is zero, which is an identity element for this operation. If logior is passed just one argument, it returns that argument.

; 28-bit binary values

(logior 12 5) ; 12 = 0000 0000 0000 0000 0000 0000 1100

; 5 = 0000 0000 0000 0000 0000 0000 0101

⇒ 13 ; 13 = 0000 0000 0000 0000 0000 0000 1101 (logior 12 5 7) ; 12 = 0000 0000 0000 0000 0000 0000 1100

; 5 = 0000 0000 0000 0000 0000 0000 0101 ; 7 = 0000 0000 0000 0000 0000 0000 0111

⇒ 15 ; 15 = 0000 0000 0000 0000 0000 0000 1111

Function logxor &rest ints-or-markers This function returns the “exclusive or” of its arguments: the nth bit is set in the result if, and only if, the nth bit is set in an odd number of the arguments. If there are no arguments, the result is 0, which is an identity element for this operation. If logxor is passed just one argument, it returns that argument.

; 28-bit binary values

(logxor 12 5) ; 12 = 0000 0000 0000 0000 0000 0000 1100

; 5 = 0000 0000 0000 0000 0000 0000 0101

⇒ 9 ; 9 = 0000 0000 0000 0000 0000 0000 1001 (logxor 12 5 7) ; 12 = 0000 0000 0000 0000 0000 0000 1100

; 5 = 0000 0000 0000 0000 0000 0000 0101 ; 7 = 0000 0000 0000 0000 0000 0000 0111

⇒ 14 ; 14 = 0000 0000 0000 0000 0000 0000 1110 Function lognot integer

This function returns the logical complement of its argument: the nth bit is one in the result if, and only if, the nth bit is zero in integer, and vice-versa.

     (lognot 5)
          ⇒ -6

;; 5 = 0000 0000 0000 0000 0000 0000 0101 ;; becomes ;; -6 = 1111 1111 1111 1111 1111 1111 1010

3.9 Standard Mathematical Functions

These mathematical functions are available if floating point is supported. They allow integers as well as floating point numbers as arguments.

Function sin arg Function cos arg Function tan arg

These are the ordinary trigonometric functions, with argument measured in radians.

Function asin arg

The value of (asin arg) is a number between −pi/2 and pi/2 (inclusive) whose sine is arg; if, however, arg is out of range (outside [-1, 1]), then the result is a NaN.

Function acos arg

The value of (acos arg) is a number between 0 and pi (inclusive) whose cosine is arg; if, however, arg is out of range (outside [-1, 1]), then the result is a NaN.

Function atan arg

The value of (atan arg) is a number between −pi/2 and pi/2 (exclusive) whose tangent is arg.

Function exp arg

This is the exponential function; it returns e to the power arg. e is a fundamental mathematical constant also called the base of natural logarithms.

Function log arg &optional base This function returns the logarithm of arg, with base base. If you don’t specify base, the base e is used. If arg is negative, the result is a NaN.

Function log10 arg

This function returns the logarithm of arg, with base 10. If arg is negative, the result is a NaN. (log10 x) ≡ (log x 10), at least approximately.

Function expt x y

This function returns x raised to power y. If both arguments are integers and y is positive, the result is an integer; in this case, it is truncated to fit the range of possible integer values.

Function sqrt arg

This returns the square root of arg. If arg is negative, the value is a NaN.

3.10 Random Numbers

A deterministic computer program cannot generate true random numbers. For most purposes, pseudo-random numbers suffice. A series of pseudo-random numbers is generated in a deterministic fashion. The numbers are not truly random, but they have certain properties that mimic a random series. For example, all possible values occur equally often in a pseudo-random series.

In Emacs, pseudo-random numbers are generated from a “seed” number. Starting from any given seed, the random function always generates the same sequence of numbers. Emacs always starts with the same seed value, so the sequence of values of random is actually the same in each Emacs run! For example, in one operating system, the first call to (random) after you start Emacs always returns -1457731, and the second one always returns -7692030. This repeatability is helpful for debugging.

If you want truly unpredictable random numbers, execute (random t). This chooses a new seed based on the current time of day and on Emacs’s process id number.

Function random &optional limit This function returns a pseudo-random integer. Repeated calls return a series of pseudo-random integers. If limit is a positive integer, the value is chosen to be nonnegative and less than limit. If limit is t, it means to choose a new seed based on the current time of day and on Emacs’s process id number. On some machines, any integer representable in Lisp may be the result of random. On other machines, the result can never be larger than a certain maximum or less than a certain (negative) minimum.

48 GNU Emacs Lisp Reference Manual

4 Strings and Characters

A string in Emacs Lisp is an array that contains an ordered sequence of characters. Strings are used as names of symbols, buffers, and files, to send messages to users, to hold text being copied between buffers, and for many other purposes. Because strings are so important, Emacs Lisp has many functions expressly for manipulating them. Emacs Lisp programs use strings more often than individual characters.

See Section 18.5.14 [Strings of Events], page 262, for special considerations for strings of keyboard character events.

4.1 String and Character Basics

Strings in Emacs Lisp are arrays that contain an ordered sequence of characters. Characters are represented in Emacs Lisp as integers; whether an integer was intended as a character or not is determined only by how it is used. Thus, strings really contain integers.

The length of a string (like any array) is fixed and independent of the string contents, and cannot be altered. Strings in Lisp are not terminated by a distinguished character code. (By contrast, strings in C are terminated by a character with ASCII code 0.) This means that any character, including the null character (ASCII code 0), is a valid element of a string.

Since strings are considered arrays, you can operate on them with the general array functions. (See Chapter 6 [Sequences Arrays Vectors], page 79.) For example, you can access or change individual characters in a string using the functions aref and aset (see Section 6.3 [Array Functions], page 82).

Each character in a string is stored in a single byte. Therefore, numbers not in the range 0 to 255 are truncated when stored into a string. This means that a string takes up much less memory than a vector of the same length.

Sometimes key sequences are represented as strings. When a string is a key sequence, string elements in the range 128 to 255 represent meta characters (which are extremely large integers) rather than keyboard events in the range 128 to 255.

Strings cannot hold characters that have the hyper, super or alt modifiers; they can hold ASCII control characters, but no other control characters. They do not distinguish case in ASCII control characters. See Section 2.3.3 [Character Type], page 17, for more information about representation of meta and other modifiers for keyboard input characters.

Strings are useful for holding regular expressions. You can also match regular expressions against strings (see Section 30.3 [Regexp Search], page 497). The functions match-string (see Section 30.6.1 [Simple Match Data], page 501) and replace-match (see Section 30.6.2 [Replacing Match], page 503) are useful for decomposing and modifying strings based on regular expression matching.

Like a buffer, a string can contain text properties for the characters in it, as well as the characters themselves. See Section 29.18 [Text Properties], page 478. All the Lisp primitives that copy text from strings to buffers or other strings also copy the properties of the characters being copied.

See Chapter 29 [Text], page 449, for information about functions that display strings or copy them into buffers. See Section 2.3.3 [Character Type], page 17, and Section 2.3.8 [String Type], page 23, for information about the syntax of characters and strings.

4.2 The Predicates for Strings

For more information about general sequence and array predicates, see Chapter 6 [Sequences Arrays Vectors], page 79, and Section 6.2 [Arrays], page 81.

Function stringp object

This function returns t if object is a string, nil otherwise.

Function char-or-string-p object

This function returns t if object is a string or a character (i.e., an integer), nil otherwise.

4.3 Creating Strings

The following functions create strings, either from scratch, or by putting strings together, or by taking them apart.

Function make-string count character This function returns a string made up of count repetitions of character. If count is negative, an error is signaled.

     (make-string 5 ?x)
          ⇒ "xxxxx"
     (make-string 0 ?x)
          ⇒ ""

Other functions to compare with this one include char-to-string (see Section 4.5 [String Conversion], page 53), make-vector (see Section 6.4 [Vectors], page 83), and make-list (see Section 5.5 [Building Lists], page 65).

Function substring string start &optional end This function returns a new string which consists of those characters from string in the range from (and including) the character at the index start up to (but excluding) the character at the index end. The first character is at index zero.

     (substring "abcdefg" 0 3)
          ⇒ "abc"

Here the index for ‘a’ is 0, the index for ‘b’ is 1, and the index for ‘c’ is 2. Thus, three letters, ‘abc’, are copied from the string "abcdefg". The index 3 marks the character position up to which the substring is copied. The character whose index is 3 is actually the fourth character in the string. A negative number counts from the end of the string, so that −1 signifies the index of the last character of the string. For example:

     (substring "abcdefg" -3 -1)
          ⇒ "ef"

In this example, the index for ‘e’ is −3, the index for ‘f’ is −2, and the index for ‘g’ is −1. Therefore, ‘e’ and ‘f’ are included, and ‘g’ is excluded. When nil is used as an index, it stands for the length of the string. Thus,

     (substring "abcdefg" -3 nil)
          ⇒ "efg"

Omitting the argument end is equivalent to specifying nil. It follows that (substring string 0) returns a copy of all of string.

     (substring "abcdefg" 0)
          ⇒ "abcdefg"

But we recommend copy-sequence for this purpose (see Section 6.1 [Sequence Functions], page 79). If the characters copied from string have text properties, the properties are copied into the new string also. See Section 29.18 [Text Properties], page 478. A wrong-type-argument error is signaled if either start or end is not an integer or nil. An args-out-of-range error is signaled if start indicates a character following end, or if either integer is out of range for string. Contrast this function with buffer-substring (see Section 29.2 [Buffer Contents], page 450), which returns a string containing a portion of the text in the current buffer. The beginning of a string is at index 0, but the beginning of a buffer is at index 1.

Function concat &rest sequences This function returns a new string consisting of the characters in the arguments passed to it (along with their text properties, if any). The arguments may be strings, lists of numbers, or vectors of numbers; they are not themselves changed. If concat receives no arguments, it returns an empty string.

     (concat "abc" "-def")
          ⇒ "abc-def"
     (concat "abc" (list 120 (+ 256 121)) [122])
          ⇒ "abcxyz"

;; nil is an empty sequence.

     (concat "abc" nil "-def")
          ⇒ "abc-def"
     (concat "The " "quick brown " "fox.")
          ⇒ "The quick brown fox."
     (concat)
          ⇒ ""

The second example above shows how characters stored in strings are taken modulo 256. In other words, each character in the string is stored in one byte. The concat function always constructs a new string that is not eq to any existing string. When an argument is an integer (not a sequence of integers), it is converted to a string of digits making up the decimal printed representation of the integer. Don’t use this feature; we plan to eliminate it. If you already use this feature, change your programs now! The proper way to convert an integer to a decimal number in this way is with format (see Section 4.6 [Formatting Strings], page 55) or number-to-string (see Section 4.5 [String Conversion], page 53).

     (concat 137)
          ⇒ "137"
     (concat 54 321)
          ⇒ "54321"

For information about other concatenation functions, see the description of mapconcat in Section 11.6 [Mapping Functions], page 147, vconcat in Section 6.4 [Vectors], page 83, and append in Section 5.5 [Building Lists], page 65.

4.4 Comparison of Characters and Strings

Function char-equal character1 character2 This function returns t if the arguments represent the same character, nil otherwise. This function ignores differences in case if case-fold-search is non-nil.

     (char-equal ?x ?x)
          ⇒ t
     (char-to-string (+ 256 ?x))
          ⇒ "x"
     (char-equal ?x  (+ 256 ?x))
          ⇒ t

Function string= string1 string2 This function returns t if the characters of the two strings match exactly; case is significant.

     (string= "abc" "abc")
          ⇒ t
     (string= "abc" "ABC")
          ⇒ nil
     (string= "ab" "ABC")
          ⇒ nil

The function string= ignores the text properties of the two strings. To compare strings in a way that compares their text properties also, use equal (see Section 2.6 [Equality Predicates], page 32).

Function string-equal string1 string2

string-equal is another name for string=.

Function string< string1 string2 This function compares two strings a character at a time. First it scans both the strings at once to find the first pair of corresponding characters that do not match. If the lesser character of those two is the character from string1, then string1 is less, and this function returns t. If the lesser character is the one from string2, then string1 is greater, and this function returns nil. If the two strings match entirely, the value is nil. Pairs of characters are compared by their ASCII codes. Keep in mind that lower case letters have higher numeric values in the ASCII character set than their upper case counterparts; numbers and many punctuation characters have a lower numeric value than upper case letters.

     (string< "abc" "abd")
          ⇒ t
     (string< "abd" "abc")
          ⇒ nil
     (string< "123" "abc")
          ⇒ t

When the strings have different lengths, and they match up to the length of string1, then the result is t. If they match up to the length of string2, the result is nil. A string of no characters is less than any other string.

     (string< "" "abc")
          ⇒ t
     (string< "ab" "abc")
          ⇒ t
     (string< "abc" "")
          ⇒ nil
     (string< "abc" "ab")
          ⇒ nil
     (string< "" "")
          ⇒ nil

Function string-lessp string1 string2

string-lessp is another name for string<.

See also compare-buffer-substrings in Section 29.3 [Comparing Text], page 451, for a way to compare text in buffers. The function string-match, which matches a regular expression against a string, can be used for a kind of string comparison; see Section 30.3 [Regexp Search], page 497.

4.5 Conversion of Characters and Strings

This section describes functions for conversions between characters, strings and integers. format and prin1-to-string (see Section 16.5 [Output Functions], page 218) can also convert Lisp objects into strings. read-from-string (see Section 16.3 [Input Functions], page 216) can “convert” a string representation of a Lisp object into an object.

See Chapter 21 [Documentation], page 319, for functions that produce textual descriptions of text characters and general input events (single-key-description and textchar-description). These functions are used primarily for making help messages.

Function char-to-string character

This function returns a new string with a length of one character. The value of character, modulo 256, is used to initialize the element of the string.

This function is similar to make-string with an integer argument of 1. (See Section 4.3 [Creating Strings], page 50.) This conversion can also be done with format using the ‘%c’ format specification. (See Section 4.6 [Formatting Strings], page 55.)

     (char-to-string ?x)
          ⇒ "x"
     (char-to-string (+ 256 ?x))
          ⇒ "x"
     (make-string 1 ?x)
          ⇒ "x"

Function string-to-char string

This function returns the first character in string. If the string is empty, the function returns 0. The value is also 0 when the first character of string is the null character, ASCII code 0.

     (string-to-char "ABC")
          ⇒ 65
     (string-to-char "xyz")
          ⇒ 120
     (string-to-char "")
          ⇒ 0
     (string-to-char "\000")
          ⇒ 0

This function may be eliminated in the future if it does not seem useful enough to retain.

Function number-to-string number

This function returns a string consisting of the printed representation of number, which may be an integer or a floating point number. The value starts with a sign if the argument is negative.

     (number-to-string 256)
          ⇒ "256"
     (number-to-string -23)
          ⇒ "-23"
     (number-to-string -23.5)
          ⇒ "-23.5"

int-to-string is a semi-obsolete alias for this function.

See also the function format in Section 4.6 [Formatting Strings], page 55.

Function string-to-number string

This function returns the numeric value of the characters in string, read in base ten. It skips spaces and tabs at the beginning of string, then reads as much of string as it can interpret as a number. (On some systems it ignores other whitespace at the beginning, not just spaces and tabs.) If the first character after the ignored whitespace is not a digit or a minus sign, this function returns

          (string-to-number "256")
               ⇒ 256
          (string-to-number "25 is a perfect square.")
               ⇒ 25
          (string-to-number "X256")
               ⇒ 0
          (string-to-number "-4.5")
               ⇒ -4.5

string-to-int is an obsolete alias for this function.

4.6 Formatting Strings

Formatting means constructing a string by substitution of computed values at various places in a constant string. This string controls how the other values are printed as well as where they appear; it is called a format string.

Formatting is often useful for computing messages to be displayed. In fact, the functions message and error provide the same formatting feature described here; they differ from format only in how they use the result of formatting.

Function format string &rest objects This function returns a new string that is made by copying string and then replacing any format specification in the copy with encodings of the corresponding objects. The arguments objects are the computed values to be formatted.

A format specification is a sequence of characters beginning with a ‘%’. Thus, if there is a ‘%d’ in string, the format function replaces it with the printed representation of one of the values to be formatted (one of the arguments objects). For example:

     (format "The value of fill-column is %d." fill-column)
          ⇒ "The value of fill-column is 72."

If string contains more than one format specification, the format specifications correspond with successive values from objects. Thus, the first format specification in string uses the first such value, the second format specification uses the second such value, and so on. Any extra format specifications (those for which there are no corresponding values) cause unpredictable behavior. Any extra values to be formatted are ignored.

Certain format specifications require values of particular types. However, no error is signaled if the value actually supplied fails to have the expected type. Instead, the output is likely to be meaningless.

Here is a table of valid format specifications:

‘%s’ Replace the specification with the printed representation of the object, made without quoting. Thus, strings are represented by their contents alone, with no ‘"’ characters, and symbols appear without ‘\’ characters. If there is no corresponding object, the empty string is used.

‘%S’ Replace the specification with the printed representation of the object, made with quoting. Thus, strings are enclosed in ‘"’ characters, and ‘\’ characters appear where necessary before special characters. If there is no corresponding object, the empty string is used.

‘%o’ Replace the specification with the base-eight representation of an integer.

‘%d’ Replace the specification with the base-ten representation of an integer.

‘%x’ Replace the specification with the base-sixteen representation of an integer.

‘%c’ Replace the specification with the character which is the value given.

‘%e’ Replace the specification with the exponential notation for a floating point number.

‘%f’ Replace the specification with the decimal-point notation for a floating point number.

‘%g’ Replace the specification with notation for a floating point number, using either exponential notation or decimal-point notation whichever is shorter.

‘%%’ A single ‘%’ is placed in the string. This format specification is unusual in that it does not use a value. For example, (format "%% %d" 30) returns "% 30".

Any other format character results in an ‘Invalid format operation’ error.

Here are several examples:

     (format "The name of this buffer is %s." (buffer-name))
          ⇒ "The name of this buffer is strings.texi."
     (format "The buffer object prints as %s." (current-buffer))
          ⇒ "The buffer object prints as strings.texi."
     (format "The octal value of %d is %o,
              and the hex value is %x." 18 18 18)
          ⇒ "The octal value of 18 is 22,
              and the hex value is 12."

All the specification characters allow an optional numeric prefix between the ‘%’ and the character. The optional numeric prefix defines the minimum width for the object. If the printed representation of the object contains fewer characters than this, then it is padded. The padding is on the left if the prefix is positive (or starts with zero) and on the right if the prefix is negative. The padding character is normally a space, but if the numeric prefix starts with a zero, zeros are used for padding.

     (format "%06d is padded on the left with zeros" 123)
          ⇒ "000123 is padded on the left with zeros"
     (format "%-6d is padded on the right" 123)
          ⇒ "123    is padded on the right"

format never truncates an object’s printed representation, no matter what width you specify. Thus, you can use a numeric prefix to specify a minimum spacing between columns with no risk of losing information.

In the following three examples, ‘%7s’ specifies a minimum width of 7. In the first case, the string inserted in place of ‘%7s’ has only 3 letters, so 4 blank spaces are inserted for padding. In the second case, the string "specification" is 13 letters wide but is not truncated. In the third case, the padding is on the right.

(format "The word `%7s' actually has %d letters in it."
        "foo" (length "foo"))
     ⇒ "The word `    foo' actually has 3 letters in it."
(format "The word `%7s' actually has %d letters in it."
        "specification" (length "specification"))
     ⇒ "The word `specification' actually has 13 letters in it."
(format "The word `%-7s' actually has %d letters in it."
        "foo" (length "foo"))
     ⇒ "The word `foo    ' actually has 3 letters in it."

4.7 Character Case

The character case functions change the case of single characters or of the contents of strings. The functions convert only alphabetic characters (the letters ‘A’ through ‘Z’ and ‘a’ through ‘z’); other characters are not altered. The functions do not modify the strings that are passed to them as arguments.

The examples below use the characters ‘X’ and ‘x’ which have ASCII codes 88 and 120 respectively.

Function downcase string-or-char This function converts a character or a string to lower case. When the argument to downcase is a string, the function creates and returns a new string in which each letter in the argument that is upper case is converted to lower case. When the argument to downcase is a character, downcase returns the corresponding lower case character. This value is an integer. If the original character is lower case, or is not a letter, then the value equals the original character.

     (downcase "The cat in the hat")
          ⇒ "the cat in the hat"
     (downcase ?X)
          ⇒ 120

Function upcase string-or-char This function converts a character or a string to upper case. When the argument to upcase is a string, the function creates and returns a new string in which each letter in the argument that is lower case is converted to upper case. When the argument to upcase is a character, upcase returns the corresponding upper case character. This value is an integer. If the original character is upper case, or is not a letter, then the value equals the original character.

     (upcase "The cat in the hat")
          ⇒ "THE CAT IN THE HAT"
     (upcase ?x)
          ⇒ 88

Function capitalize string-or-char This function capitalizes strings or characters. If string-or-char is a string, the function creates and returns a new string, whose contents are a copy of stringor-char in which each word has been capitalized. This means that the first character of each word is converted to upper case, and the rest are converted to lower case. The definition of a word is any sequence of consecutive characters that are assigned to the word constituent syntax class in the current syntax table (See Section 31.2.1 [Syntax Class Table], page 510). When the argument to capitalize is a character, capitalize has the same result as upcase.

          (capitalize "The cat in the hat")
               ⇒ "The Cat In The Hat"
          (capitalize "THE 77TH-HATTED CAT")
               ⇒ "The 77th-Hatted Cat"
          (capitalize ?x)
               ⇒ 88

4.8 The Case Table

You can customize case conversion by installing a special case table. A case table specifies the mapping between upper case and lower case letters. It affects both the string and character case conversion functions (see the previous section) and those that apply to text in the buffer (see Section 29.17 [Case Changes], page 476). You need a case table if you are using a language which has letters other than the standard ASCII letters.

A case table is a list of this form:

(downcase upcase canonicalize equivalences) where each element is either nil or a string of length 256. The element downcase says how to map each character to its lower-case equivalent. The element upcase maps each character to its upper-case equivalent. If lower and upper case characters are in one-to-one correspondence, use nil for upcase; then Emacs deduces the upcase table from downcase.

For some languages, upper and lower case letters are not in one-to-one correspondence. There may be two different lower case letters with the same upper case equivalent. In these cases, you need to specify the maps for both directions.

The element canonicalize maps each character to a canonical equivalent; any two characters that are related by case-conversion have the same canonical equivalent character.

The element equivalences is a map that cyclicly permutes each equivalence class (of characters with the same canonical equivalent). (For ordinary ASCII, this would map ‘a’ into ‘A’ and ‘A’ into ‘a’, and likewise for each set of equivalent characters.)

When you construct a case table, you can provide nil for canonicalize; then Emacs fills in this string from upcase and downcase. You can also provide nil for equivalences; then Emacs fills in this string from canonicalize. In a case table that is actually in use, those components are non-nil. Do not try to specify equivalences without also specifying canonicalize.

Each buffer has a case table. Emacs also has a standard case table which is copied into each buffer when you create the buffer. Changing the standard case table doesn’t affect any existing buffers.

Here are the functions for working with case tables:

Function case-table-p object

This predicate returns non-nil if object is a valid case table.

Function set-standard-case-table table

This function makes table the standard case table, so that it will apply to any buffers created subsequently.

Function standard-case-table

This returns the standard case table.

Function current-case-table

This function returns the current buffer’s case table.

Function set-case-table table

This sets the current buffer’s case table to table.

The following three functions are convenient subroutines for packages that define non-ASCII character sets. They modify a string downcase-table provided as an argument; this should be a string to be used as the downcase part of a case table. They also modify the standard syntax table. See Chapter 31 [Syntax Tables], page 509.

Function set-case-syntax-pair uc lc downcase-table

This function specifies a pair of corresponding letters, one upper case and one lower case.

Function set-case-syntax-delims l r downcase-table

This function makes characters l and r a matching pair of case-invariant delimiters.

Function set-case-syntax char syntax downcase-table This function makes char case-invariant, with syntax syntax.

Command describe-buffer-case-table

This command displays a description of the contents of the current buffer’s case table.

You can load the library ‘iso-syntax’ to set up the standard syntax table and define a case table for the 8-bit ISO Latin 1 character set.

60 GNU Emacs Lisp Reference Manual

5 Lists

A list represents a sequence of zero or more elements (which may be any Lisp objects). The important difference between lists and vectors is that two or more lists can share part of their structure; in addition, you can insert or delete elements in a list without copying the whole list.

5.1 Lists and Cons Cells

Lists in Lisp are not a primitive data type; they are built up from cons cells. A cons cell is a data object that represents an ordered pair. It records two Lisp objects, one labeled as the car, and the other labeled as the cdr. These names are traditional; see Section 2.3.6 [Cons Cell Type], page 20. cdr is pronounced “could-er.”

A list is a series of cons cells chained together, one cons cell per element of the list. By convention, the cars of the cons cells are the elements of the list, and the cdrs are used to chain the list: the cdr of each cons cell is the following cons cell. The cdr of the last cons cell is nil. This asymmetry between the car and the cdr is entirely a matter of convention; at the level of cons cells, the car and cdr slots have the same characteristics.

Because most cons cells are used as part of lists, the phrase list structure has come to mean any structure made out of cons cells.

The symbol nil is considered a list as well as a symbol; it is the list with no elements. For convenience, the symbol nil is considered to have nil as its cdr (and also as its car).

The cdr of any nonempty list l is a list containing all the elements of l except the first.

5.2 Lists as Linked Pairs of Boxes

A cons cell can be illustrated as a pair of boxes. The first box represents the car and the second box represents the cdr. Here is an illustration of the two-element list, (tulip lily), made from two cons cells:

      ---------------         ---------------
     | car   | cdr   |       | car   | cdr   |
     | tulip |   o---------->| lily  |  nil  |
     |       |       |       |       |       |
      ---------------         ---------------

Each pair of boxes represents a cons cell. Each box “refers to”, “points to” or “contains” a Lisp object. (These terms are synonymous.) The first box, which is the car of the first cons cell, contains the symbol tulip. The arrow from the cdr of the first cons cell to the second cons cell indicates that the cdr of the first cons cell points to the second cons cell.

The same list can be illustrated in a different sort of box notation like this:

         ____________
        |___|___|--> |___|___|--> nil
          |            |
          |            |
           --> tulip    --> lily

Here is a more complex illustration, showing the three-element list, ((pine needles) oak maple), the first element of which is a two-element list:

    __________________
   |___|___|--> |___|___|--> |___|___|--> nil
     |            |            |
     |            |            |
     |             --> oak      --> maple
     |
     |     ____________
      --> |___|___|--> |___|___|--> nil
            |            |
            |            |
             --> pine     --> needles

The same list represented in the first box notation looks like this:

 --------------       --------------       --------------
| car   | cdr  |     | car   | cdr  |     | car   | cdr  |
|   o   |   o------->| oak   |   o------->| maple |  nil |
|   |   |      |     |       |      |     |       |      |
 -- | ---------       --------------       --------------
    |
    |
    |        --------------       ----------------
    |       | car   | cdr  |     | car     | cdr  |
     ------>| pine  |   o------->| needles |  nil |
            |       |      |     |         |      |
             --------------       ----------------

See Section 2.3.6 [Cons Cell Type], page 20, for the read and print syntax of cons cells and lists, and for more “box and arrow” illustrations of lists.

5.3 Predicates on Lists

The following predicates test whether a Lisp object is an atom, is a cons cell or is a list, or whether it is the distinguished object nil. (Many of these predicates can be defined in terms of the others, but they are used so often that it is worth having all of them.)

Function consp object This function returns t if object is a cons cell, nil otherwise. nil is not a cons cell, although it is a list.

Function atom object This function returns t if object is an atom, nil otherwise. All objects except cons cells are atoms. The symbol nil is an atom and is also a list; it is the only Lisp object that is both.

     (atom object) ≡ (not (consp object))

Function listp object This function returns t if object is a cons cell or nil. Otherwise, it returns

nil.

     (listp '(1)) ⇒ t
     (listp '()) ⇒ t

Function nlistp object

This function is the opposite of listp: it returns t if object is not a list. Otherwise, it returns nil.

     (listp object) ≡ (not (nlistp object))

Function null object This function returns t if object is nil, and returns nil otherwise. This function is identical to not, but as a matter of clarity we use null when object is considered a list and not when it is considered a truth value (see not in Section 9.3 [Combining Conditions], page 108).

     (null '(1)) ⇒ nil
     (null '()) ⇒ t

5.4 Accessing Elements of Lists

Function car cons-cell This function returns the value pointed to by the first pointer of the cons cell cons-cell. Expressed another way, this function returns the car of cons-cell.

As a special case, if cons-cell is nil, then car is defined to return nil; therefore, any list is a valid argument for car. An error is signaled if the argument is not a cons cell or nil.

     (car '(a b c)) ⇒ a
     (car '()) ⇒ nil

Function cdr cons-cell This function returns the value pointed to by the second pointer of the cons cell cons-cell. Expressed another way, this function returns the cdr of cons-cell.

As a special case, if cons-cell is nil, then cdr is defined to return nil; therefore, any list is a valid argument for cdr. An error is signaled if the argument is not a cons cell or nil.

     (cdr '(a b c))
          ⇒ (b c)
     (cdr '()) ⇒ nil

Function car-safe object

This function lets you take the car of a cons cell while avoiding errors for other data types. It returns the car of object if object is a cons cell, nil otherwise. This is in contrast to car, which signals an error if object is not a list.

     (car-safe object)

≡

     (let ((x object))
       (if (consp x)
           (car x)
         nil))

Function cdr-safe object

This function lets you take the cdr of a cons cell while avoiding errors for other data types. It returns the cdr of object if object is a cons cell, nil otherwise. This is in contrast to cdr, which signals an error if object is not a list.

     (cdr-safe object)

≡

     (let ((x object))
       (if (consp x)
           (cdr x)
         nil))

Function nth n list This function returns the nth element of list. Elements are numbered starting with zero, so the car of list is element number zero. If the length of list is n or less, the value is nil. If n is negative, nth returns the first element of list.

     (nth 2 '(1 2 3 4)) ⇒ 3
     (nth 10 '(1 2 3 4)) ⇒ nil
     (nth -3 '(1 2 3 4))
          ⇒ 1
     (nth n x) ≡ (car (nthcdr n x))

Function nthcdr n list

This function returns the nth cdr of list. In other words, it removes the first n links of list and returns what follows. If n is zero or negative, nthcdr returns all of list. If the length of list is n or less, nthcdr returns nil.

     (nthcdr 1 '(1 2 3 4)) ⇒ (2 3 4)
     (nthcdr 10 '(1 2 3 4))
          ⇒ nil
     (nthcdr -3 '(1 2 3 4)) ⇒ (1 2 3 4)

5.5 Building Cons Cells and Lists

Many functions build lists, as lists reside at the very heart of Lisp. cons is the fundamental list-building function; however, it is interesting to note that list is used more times in the source code for Emacs than cons.

Function cons object1 object2 This function is the fundamental function used to build new list structure. It creates a new cons cell, making object1 the car, and object2 the cdr. It then returns the new cons cell. The arguments object1 and object2 may be any Lisp objects, but most often object2 is a list.

     (cons 1 '(2)) ⇒ (1 2)

     (cons 1 '()) ⇒ (1)
     (cons 1 2) ⇒ (1 . 2)

cons is often used to add a single element to the front of a list. This is called consing the element onto the list. For example:

     (setq list (cons newelt list))

Note that there is no conflict between the variable named list used in this example and the function named list described below; any symbol can serve both purposes.

Function list &rest objects This function creates a list with objects as its elements. The resulting list is always nil-terminated. If no objects are given, the empty list is returned.

     (list 1 2 3 4 5) ⇒ (1 2 3 4 5)
     (list 1 2 '(3 4 5) 'foo)
          ⇒ (1 2 (3 4 5) foo)
     (list) ⇒ nil

Function make-list length object This function creates a list of length length, in which all the elements have the identical value object. Compare make-list with make-string (see Section 4.3 [Creating Strings], page 50).

     (make-list 3 'pigs)
          ⇒ (pigs pigs pigs)
     (make-list 0 'pigs)
          ⇒ nil

Function append &rest sequences This function returns a list containing all the elements of sequences. The sequences may be lists, vectors, or strings, but the last one should be a list. All arguments except the last one are copied, so none of them are altered.

More generally, the final argument to append may be any Lisp object. The final argument is not copied or converted; it becomes the cdr of the last cons cell in the new list. If the final argument is itself a list, then its elements become in effect elements of the result list. If the final element is not a list, the result is a “dotted list” since its final cdr is not nil as required in a true list. See nconc in Section 5.6.3 [Rearrangement], page 70, for a way to join lists with no copying. Here is an example of using append:

     (setq trees '(pine oak))
          ⇒ (pine oak)
     (setq more-trees (append '(maple birch) trees))
          ⇒ (maple birch pine oak)
     trees

          ⇒ (pine oak)

     more-trees
          ⇒ (maple birch pine oak)
     (eq trees (cdr (cdr more-trees)))
          ⇒ t

You can see how append works by looking at a box diagram. The variable trees is set to the list (pine oak) and then the variable more-trees is set to the list (maple birch pine oak). However, the variable trees continues to refer to the original list:

     more-trees                trees
     |                           |
     |     ____________-> ____________
      --> |___|___|--> |___|___|--> |___|___|--> |___|___|--> nil
            |            |            |            |
            |            |            |            |
             --> maple    -->birch     --> pine     --> oak

An empty sequence contributes nothing to the value returned by append. As a consequence of this, a final nil argument forces a copy of the previous argument.

     trees

          ⇒ (pine oak)

     (setq wood (append trees ()))
          ⇒ (pine oak)
     wood

          ⇒ (pine oak)

     (eq wood trees)
          ⇒ nil

This once was the usual way to copy a list, before the function copy-sequence was invented. See Chapter 6 [Sequences Arrays Vectors], page 79. With the help of apply, we can append all the lists in a list of lists:

     (apply 'append '((a b c) nil (x y z) nil))
          ⇒ (a b c x y z)

If no sequences are given, nil is returned:

     (append) ⇒ nil

Here are some examples where the final argument is not a list:

     (append '(x y) 'z)
          ⇒ (x y . z)
     (append '(x y) [z])
          ⇒ (x y . [z])

The second example shows that when the final argument is a sequence but not a list, the sequence’s elements do not become elements of the resulting list. Instead, the sequence becomes the final cdr, like any other non-list final argument. The append function also allows integers as arguments. It converts them to strings of digits, making up the decimal print representation of the integer, and then uses the strings instead of the original integers. Don’t use this feature; we plan to eliminate it. If you already use this feature, change your programs now! The proper way to convert an integer to a decimal number in this way is with format (see Section 4.6 [Formatting Strings], page 55) or number-to-string (see Section 4.5 [String Conversion], page 53).

Function reverse list

This function creates a new list whose elements are the elements of list, but in reverse order. The original argument list is not altered.

     (setq x '(1 2 3 4)) ⇒ (1 2 3 4)
     (reverse x)
          ⇒ (4 3 2 1)
     x

          ⇒ (1 2 3 4)

5.6 Modifying Existing List Structure

You can modify the car and cdr contents of a cons cell with the primitives setcar and

setcdr.

Common Lisp note: Common Lisp uses functions rplaca and rplacd to alter list structure; they change structure the same way as setcar and setcdr, but the Common Lisp functions return the cons cell while setcar and setcdr return the new car or cdr.

5.6.1 Altering List Elements with setcar

Changing the car of a cons cell is done with setcar. When used on a list, setcar replaces one element of a list with a different element.

Function setcar cons object This function stores object as the new car of cons, replacing its previous car. It returns the value object. For example:

     (setq x '(1 2)) ⇒ (1 2)
     (setcar x 4) ⇒ 4
     x  ⇒ (4 2)

When a cons cell is part of the shared structure of several lists, storing a new car into the cons changes one element of each of these lists. Here is an example:

;; Create two lists that are partly shared.

(setq x1 '(a b c))
     ⇒ (a b c)
(setq x2 (cons 'z (cdr x1)))
     ⇒ (z b c)

;; Replace the car of a shared link.

(setcar (cdr x1) 'foo)
     ⇒ foo

x1 ; Both lists are changed.

     ⇒ (a foo c)
x2

     ⇒ (z foo c)

;; Replace the car of a link that is not shared.

(setcar x1 'baz)
     ⇒ baz

x1 ; Only one list is changed.

     ⇒ (baz foo c)
x2

     ⇒ (z foo c)

Here is a graphical depiction of the shared structure of the two lists in the variables x1 and x2, showing why replacing b changes them both:

        __________________
x1---> |___|___|----> |___|___|--> |___|___|--> nil
         |        -->   |            |
         |       |      |            |
          --> a  |       --> b        --> c
                 |
       ______|
x2--> |___|___|--
        |
        |
         --> z

Here is an alternative form of box diagram, showing the same relationship:

x1:
 --------------       --------------       --------------
| car   | cdr  |     | car   | cdr  |     | car   | cdr  |
|   a   |   o------->|   b   |   o------->|   c   |  nil |
|       |      |  -->|       |      |     |       |      |
 --------------  |    --------------       --------------
                 |
x2:              |
 --------------  |
| car   | cdr  | |
|   z   |   o----
|       |      |
 --------------

5.6.2 Altering the CDR of a List

The lowest-level primitive for modifying a cdr is setcdr:

Function setcdr cons object This function stores object as the new cdr of cons, replacing its previous cdr. It returns the value object.

Here is an example of replacing the cdr of a list with a different list. All but the first element of the list are removed in favor of a different sequence of elements. The first element is unchanged, because it resides in the car of the list, and is not reached via the cdr.

(setq x '(1 2 3)) ⇒ (1 2 3)
(setcdr x '(4)) ⇒ (4)
x  ⇒ (1 4)

You can delete elements from the middle of a list by altering the cdrs of the cons cells in the list. For example, here we delete the second element, b, from the list (a b c), by changing the cdr of the first cell:

(setq x1 '(a b c))
     ⇒ (a b c)
(setcdr x1 (cdr (cdr x1)))
     ⇒ (c)
x1

     ⇒ (a c)

Here is the result in box notation:

                   --------------------
                  |                    |
 --------------   |   --------------   |    --------------
| car   | cdr  |  |  | car   | cdr  |   -->| car   | cdr  |
|   a   |   o-----   |   b   |   o-------->|   c   |  nil |
|       |      |     |       |      |      |       |      |
 --------------       --------------        --------------

The second cons cell, which previously held the element b, still exists and its car is still b, but it no longer forms part of this list.

It is equally easy to insert a new element by changing cdrs:

(setq x1 '(a b c))
     ⇒ (a b c)
(setcdr x1 (cons 'd (cdr x1)))
     ⇒ (d b c)
x1

     ⇒ (a d b c)

Here is this result in box notation:

 --------------        -------------       -------------
| car  | cdr   |      | car  | cdr  |     | car  | cdr  |
|   a  |   o   |   -->|   b  |   o------->|   c  |  nil |
|      |   |   |  |   |      |      |     |      |      |
 --------- | --   |    -------------       -------------
           |      |
     -----         --------
    |                      |
    |    ---------------   |
    |   | car   | cdr   |  |
     -->|   d   |   o------
        |       |       |
         ---------------

5.6.3 Functions that Rearrange Lists

Here are some functions that rearrange lists “destructively” by modifying the cdrs of their component cons cells. We call these functions “destructive” because they chew up the original lists passed to them as arguments, to produce a new list that is the returned value.

The function delq in the following section is another example of destructive list manipulation.

Function nconc &rest lists This function returns a list containing all the elements of lists. Unlike append (see Section 5.5 [Building Lists], page 65), the lists are not copied. Instead, the last cdr of each of the lists is changed to refer to the following list. The last of the lists is not altered. For example:

(setq x '(1 2 3)) ⇒ (1 2 3)
(nconc x '(4 5)) ⇒ (1 2 3 4 5)
x  ⇒ (1 2 3 4 5)

Since the last argument of nconc is not itself modified, it is reasonable to use a constant list, such as '(4 5), as in the above example. For the same reason, the last argument need not be a list:

(setq x '(1 2 3)) ⇒ (1 2 3)
(nconc x 'z)
     ⇒ (1 2 3 . z)
x  ⇒ (1 2 3 . z)

A common pitfall is to use a quoted constant list as a non-last argument to nconc. If you do this, your program will change each time you run it! Here is what happens:

(defun add-foo (x) ; We want this function to add

  (nconc '(foo) x))           ;   foo to the front of its arg.
(symbol-function 'add-foo)
     ⇒ (lambda (x) (nconc (quote (foo)) x))
(setq xx (add-foo '(1 2)))    ; It seems to work.
     ⇒ (foo 1 2)
(setq xy (add-foo '(3 4)))    ; What happened?
     ⇒ (foo 1 2 3 4)
(eq xx xy) ⇒ t
(symbol-function 'add-foo)
     ⇒ (lambda (x) (nconc (quote (foo 1 2 3 4) x)))

Function nreverse list

This function reverses the order of the elements of list. Unlike reverse, nreverse alters its argument by reversing the cdrs in the cons cells forming the list. The cons cell that used to be the last one in list becomes the first cell of the value. For example:

(setq x '(1 2 3 4)) ⇒ (1 2 3 4)
x

     ⇒ (1 2 3 4)

(nreverse x)
     ⇒ (4 3 2 1)

;; The cell that was first is now last.

x

     ⇒ (1)

To avoid confusion, we usually store the result of nreverse back in the same variable which held the original list:

     (setq x (nreverse x))

Here is the nreverse of our favorite example, (a b c), presented graphically: Original list head: Reversed list:

      -------------        -------------        ------------
     | car  | cdr  |      | car  | cdr  |      | car | cdr  |
     |   a  |  nil |<--   |   b  |   o  |<--   |   c |   o  |
     |      |      |   |  |      |   |  |   |  |     |   |  |
      -------------    |   --------- | -    |   -------- | -
                       |             |      |            |
                        -------------        ------------

Function sort list predicate This function sorts list stably, though destructively, and returns the sorted list. It compares elements using predicate. A stable sort is one in which elements with equal sort keys maintain their relative order before and after the sort. Stability is important when successive sorts are used to order elements according to different criteria. The argument predicate must be a function that accepts two arguments. It is called with two elements of list. To get an increasing order sort, the predicate should return t if the first element is “less than” the second, or nil if not. The destructive aspect of sort is that it rearranges the cons cells forming list by changing cdrs. A nondestructive sort function would create new cons cells to store the elements in their sorted order. If you wish to make a sorted copy without destroying the original, copy it first with copy-sequence and then sort. Sorting does not change the cars of the cons cells in list; the cons cell that originally contained the element a in list still has a in its car after sorting, but it now appears in a different position in the list due to the change of cdrs. For example:

     (setq nums '(1 3 2 6 5 4 0))
          ⇒ (1 3 2 6 5 4 0)
     (sort nums '<)
          ⇒ (0 1 2 3 4 5 6)
     nums ⇒ (1 2 3 4 5 6)

Note that the list in nums no longer contains 0; this is the same cons cell that it was before, but it is no longer the first one in the list. Don’t assume a variable that formerly held the argument now holds the entire sorted list! Instead, save the result of sort and use that. Most often we store the result back into the variable that held the original list:

     (setq nums (sort nums '<))

See Section 29.14 [Sorting], page 468, for more functions that perform sorting. See documentation in Section 21.2 [Accessing Documentation], page 320, for a useful example of sort.

5.7 Using Lists as Sets

A list can represent an unordered mathematical set—simply consider a value an element of a set if it appears in the list, and ignore the order of the list. To form the union of two sets, use append (as long as you don’t mind having duplicate elements). Other useful functions for sets include memq and delq, and their equal versions, member and delete.

Common Lisp note: Common Lisp has functions union (which avoids duplicate elements) and intersection for set operations, but GNU Emacs Lisp does not have them. You can write them in Lisp if you wish.

Function memq object list This function tests to see whether object is a member of list. If it is, memq returns a list starting with the first occurrence of object. Otherwise, it returns nil. The letter ‘q’ in memq says that it uses eq to compare object against the elements of the list. For example:

     (memq 'b '(a b c b a))
          ⇒ (b c b a)
     (memq '(2) '((1) (2)))    ; (2) and (2) are not eq.
          ⇒ nil

Function delq object list This function destructively removes all elements eq to object from list. The letter ‘q’ in delq says that it uses eq to compare object against the elements of the list, like memq.

When delq deletes elements from the front of the list, it does so simply by advancing down the list and returning a sublist that starts after those elements:

(delq 'a '(a b c)) ≡ (cdr '(a b c))

When an element to be deleted appears in the middle of the list, removing it involves changing the cdrs (see Section 5.6.2 [Setcdr], page 69).

(setq sample-list '(a b c (4)))
     ⇒ (a b c (4))
(delq 'a sample-list)
     ⇒ (b c (4))
sample-list
     ⇒ (a b c (4))
(delq 'c sample-list)
     ⇒ (a b (4))
sample-list
     ⇒ (a b (4))

Note that (delq 'c sample-list) modifies sample-list to splice out the third element, but (delq 'a sample-list) does not splice anything—it just returns a shorter list. Don’t assume that a variable which formerly held the argument list now has fewer elements, or that it still holds the original list! Instead, save the result of delq and use that. Most often we store the result back into the variable that held the original list:

(setq flowers (delq 'rose flowers))

In the following example, the (4) that delq attempts to match and the (4) in the

sample-list are not eq:
(delq '(4) sample-list)
     ⇒ (a c (4))

The following two functions are like memq and delq but use equal rather than eq to compare elements. They are new in Emacs 19.

Function member object list The function member tests to see whether object is a member of list, comparing members with object using equal. If object is a member, member returns a list starting with its first occurrence in list. Otherwise, it returns nil.

Compare this with memq:

     (member '(2) '((1) (2)))  ; (2) and (2) are equal.
          ⇒ ((2))
     (memq '(2) '((1) (2)))    ; (2) and (2) are not eq.
          ⇒ nil

;; Two strings with the same contents are equal.

     (member "foo" '("foo" "bar"))
          ⇒ ("foo" "bar")

Function delete object list This function destructively removes all elements equal to object from list. It is to delq as member is to memq: it uses equal to compare elements with object, like member; when it finds an element that matches, it removes the element just as delq would. For example:

     (delete '(2) '((2) (1) (2))) ⇒ ((1))

Common Lisp note: The functions member and delete in GNU Emacs Lisp are derived from Maclisp, not Common Lisp. The Common Lisp versions do not use equal to compare elements.

See also the function add-to-list, in Section 10.8 [Setting Variables], page 129, for another way to add an element to a list stored in a variable.

5.8 Association Lists

An association list, or alist for short, records a mapping from keys to values. It is a list of cons cells called associations: the car of each cell is the key, and the cdr is the associated value.^{1}

Here is an example of an alist. The key pine is associated with the value cones; the key oak is associated with acorns; and the key maple is associated with seeds.

1 This usage of “key” is not related to the term “key sequence”; it means a value used to look up an item in a table. In this case, the table is the alist, and the alist associations are the items.

     '((pine . cones)
       (oak . acorns)
       (maple . seeds))

The associated values in an alist may be any Lisp objects; so may the keys. For example, in the following alist, the symbol a is associated with the number 1, and the string "b" is associated with the list (2 3), which is the cdr of the alist element:

     ((a . 1) ("b" 2 3))

Sometimes it is better to design an alist to store the associated value in the car of the cdr of the element. Here is an example:

     '((rose red) (lily white) (buttercup yellow))

Here we regard red as the value associated with rose. One advantage of this method is that you can store other related information—even a list of other items—in the cdr of the cdr. One disadvantage is that you cannot use rassq (see below) to find the element containing a given value. When neither of these considerations is important, the choice is a matter of taste, as long as you are consistent about it for any given alist.

Note that the same alist shown above could be regarded as having the associated value in the cdr of the element; the value associated with rose would be the list (red).

Association lists are often used to record information that you might otherwise keep on a stack, since new associations may be added easily to the front of the list. When searching an association list for an association with a given key, the first one found is returned, if there is more than one.

In Emacs Lisp, it is not an error if an element of an association list is not a cons cell. The alist search functions simply ignore such elements. Many other versions of Lisp signal errors in such cases.

Note that property lists are similar to association lists in several respects. A property list behaves like an association list in which each key can occur only once. See Section 7.4 [Property Lists], page 92, for a comparison of property lists and association lists.

Function assoc key alist This function returns the first association for key in alist. It compares key against the alist elements using equal (see Section 2.6 [Equality Predicates], page 32). It returns nil if no association in alist has a car equal to key. For example:

          (setq trees '((pine . cones) (oak . acorns) (maple . seeds)))
               ⇒ ((pine . cones) (oak . acorns) (maple . seeds))
          (assoc 'oak trees)
               ⇒ (oak . acorns)
          (cdr (assoc 'oak trees))
               ⇒ acorns
          (assoc 'birch trees)
               ⇒ nil

Here is another example, in which the keys and values are not symbols:

          (setq needles-per-cluster
                '((2 "Austrian Pine" "Red Pine")
                  (3 "Pitch Pine")

             (5 "White Pine")))
     (cdr (assoc 3 needles-per-cluster))
          ⇒ ("Pitch Pine")
     (cdr (assoc 2 needles-per-cluster))
          ⇒ ("Austrian Pine" "Red Pine")

Function rassoc value alist This function returns the first association with value value in alist. It returns nil if no association in alist has a cdr equal to value. rassoc is like assoc except that it compares the cdr of each alist association instead of the car. You can think of this as “reverse assoc”, finding the key for a given value.

Function assq key alist This function is like assoc in that it returns the first association for key in alist, but it makes the comparison using eq instead of equal. assq returns nil if no association in alist has a car eq to key. This function is used more often than assoc, since eq is faster than equal and most alists use symbols as keys. See Section 2.6 [Equality Predicates], page 32.

     (setq trees '((pine . cones) (oak . acorns) (maple . seeds)))
          ⇒ ((pine . cones) (oak . acorns) (maple . seeds))
     (assq 'pine trees)
          ⇒ (pine . cones)

On the other hand, assq is not usually useful in alists where the keys may not be symbols:

     (setq leaves
           '(("simple leaves" . oak)
             ("compound leaves" . horsechestnut)))
     (assq "simple leaves" leaves)
          ⇒ nil
     (assoc "simple leaves" leaves)
          ⇒ ("simple leaves" . oak)

Function rassq value alist This function returns the first association with value value in alist. It returns nil if no association in alist has a cdr eq to value. rassq is like assq except that it compares the cdr of each alist association instead of the car. You can think of this as “reverse assq”, finding the key for a given value. For example:

     (setq trees '((pine . cones) (oak . acorns) (maple . seeds)))
     (rassq 'acorns trees)
          ⇒ (oak . acorns)
     (rassq 'spores trees)

     ⇒ nil

Note that rassq cannot search for a value stored in the car of the cdr of an element:

(setq colors '((rose red) (lily white) (buttercup yellow)))
(rassq 'white colors)
     ⇒ nil

In this case, the cdr of the association (lily white) is not the symbol white, but rather the list (white). This becomes clearer if the association is written in dotted pair notation:

(lily white) ≡ (lily . (white))

Function copy-alist alist

This function returns a two-level deep copy of alist: it creates a new copy of each association, so that you can alter the associations of the new alist without changing the old one.

(setq needles-per-cluster
      '((2 . ("Austrian Pine" "Red Pine"))
        (3 . ("Pitch Pine"))
        (5 . ("White Pine"))))

⇒

((2 "Austrian Pine" "Red Pine")
 (3 "Pitch Pine")
 (5 "White Pine"))
(setq copy (copy-alist needles-per-cluster))

⇒

((2 "Austrian Pine" "Red Pine")
 (3 "Pitch Pine")
 (5 "White Pine"))
(eq needles-per-cluster copy)
     ⇒ nil
(equal needles-per-cluster copy)
     ⇒ t
(eq (car needles-per-cluster) (car copy))
     ⇒ nil
(cdr (car (cdr needles-per-cluster)))
     ⇒ ("Pitch Pine")
(eq (cdr (car (cdr needles-per-cluster)))
    (cdr (car (cdr copy))))
     ⇒ t

This example shows how copy-alist makes it possible to change the associations of one copy without affecting the other:

(setcdr (assq 3 copy) '("Martian Vacuum Pine"))
(cdr (assq 3 needles-per-cluster))
     ⇒ ("Pitch Pine")

78 GNU Emacs Lisp Reference Manual

6 Sequences, Arrays, and Vectors

Recall that the sequence type is the union of three other Lisp types: lists, vectors, and strings. In other words, any list is a sequence, any vector is a sequence, and any string is a sequence. The common property that all sequences have is that each is an ordered collection of elements.

An array is a single primitive object that has a slot for each elements. All the elements are accessible in constant time, but the length of an existing array cannot be changed. Strings and vectors are the two types of arrays.

A list is a sequence of elements, but it is not a single primitive object; it is made of cons cells, one cell per element. Finding the nth element requires looking through n cons cells, so elements farther from the beginning of the list take longer to access. But it is possible to add elements to the list, or remove elements.

The following diagram shows the relationship between these types:

               ___________________________________
              |                                   |
              |          Sequence                 |
              |  ____________________________|
              | |      | |                      | |
              | | List | |         Array        | |
              | |      | |  _______________| |
              | |______| | |        | |       | | |
              |          | | Vector | | String| | |
              |          | |________| |_______| | |
              |          |______________________| |
              |___________________________________|

The elements of vectors and lists may be any Lisp objects. The elements of strings are all characters.

6.1 Sequences

In Emacs Lisp, a sequence is either a list, a vector or a string. The common property that all sequences have is that each is an ordered collection of elements. This section describes functions that accept any kind of sequence.

Function sequencep object

Returns t if object is a list, vector, or string, nil otherwise.

Function copy-sequence sequence

Returns a copy of sequence. The copy is the same type of object as the original sequence, and it has the same elements in the same order. Storing a new element into the copy does not affect the original sequence, and vice versa. However, the elements of the new sequence are not copies; they are identical (eq) to the elements of the original. Therefore, changes made within these elements, as found via the copied sequence, are also visible in the original sequence.

If the sequence is a string with text properties, the property list in the copy is itself a copy, not shared with the original’s property list. However, the actual values of the properties are shared. See Section 29.18 [Text Properties], page 478. See also append in Section 5.5 [Building Lists], page 65, concat in Section 4.3 [Creating Strings], page 50, and vconcat in Section 6.4 [Vectors], page 83, for others ways to copy sequences.

(setq bar '(1 2)) ⇒ (1 2)
(setq x (vector 'foo bar))
     ⇒ [foo (1 2)]
(setq y (copy-sequence x))
     ⇒ [foo (1 2)]
(eq x y) ⇒ nil
(equal x y) ⇒ t
(eq (elt x 1) (elt y 1))
     ⇒ t

;; Replacing an element of one sequence.

(aset x 0 'quux)
x ⇒ [quux (1 2)]
y ⇒ [foo (1 2)]

;; Modifying the inside of a shared element.

(setcar (aref x 1) 69)
x ⇒ [quux (69 2)]
y ⇒ [foo (69 2)]

Function length sequence Returns the number of elements in sequence. If sequence is a cons cell that is not a list (because the final cdr is not nil), a wrong-type-argument error is signaled.

(length '(1 2 3)) ⇒ 3
(length ()) ⇒ 0
(length "foobar")
    ⇒ 6
(length [1 2 3]) ⇒ 3

Function elt sequence index This function returns the element of sequence indexed by index. Legitimate values of index are integers ranging from 0 up to one less than the length of sequence. If sequence is a list, then out-of-range values of index return nil; otherwise, they trigger an args-out-of-range error.

          (elt [1 2 3 4] 2) ⇒ 3
          (elt '(1 2 3 4) 2) ⇒ 3
          (char-to-string (elt "1234" 2))
               ⇒ "3"
          (elt [1 2 3 4] 4)
                error Args out of range: [1 2 3 4], 4
          (elt [1 2 3 4] -1)
                error Args out of range: [1 2 3 4], -1

This function generalizes aref (see Section 6.3 [Array Functions], page 82) and nth (see Section 5.4 [List Elements], page 63).

6.2 Arrays

An array object has slots that hold a number of other Lisp objects, called the elements of the array. Any element of an array may be accessed in constant time. In contrast, an element of a list requires access time that is proportional to the position of the element in the list.

When you create an array, you must specify how many elements it has. The amount of space allocated depends on the number of elements. Therefore, it is impossible to change the size of an array once it is created; you cannot add or remove elements. However, you can replace an element with a different value.

Emacs defines two types of array, both of which are one-dimensional: strings and vectors. A vector is a general array; its elements can be any Lisp objects. A string is a specialized array; its elements must be characters (i.e., integers between 0 and 255). Each type of array has its own read syntax. See Section 2.3.8 [String Type], page 23, and Section 2.3.9 [Vector Type], page 24.

Both kinds of array share these characteristics:

• The first element of an array has index zero, the second element has index 1, and so on. This is called zero-origin indexing. For example, an array of four elements has indices 0, 1, 2, and 3.

• The elements of an array may be referenced or changed with the functions aref and aset, respectively (see Section 6.3 [Array Functions], page 82).

In principle, if you wish to have an array of text characters, you could use either a string or a vector. In practice, we always choose strings for such applications, for four reasons:

• They occupy one-fourth the space of a vector of the same elements.

• Strings are printed in a way that shows the contents more clearly as characters.

• Strings can hold text properties. See Section 29.18 [Text Properties], page 478.

• Many of the specialized editing and I/O facilities of Emacs accept only strings. For example, you cannot insert a vector of characters into a buffer the way you can insert a string. See Chapter 4 [Strings and Characters], page 49.

By contrast, for an array of keyboard input characters (such as a key sequence), a vector may be necessary, because many keyboard input characters are outside the range that will fit in a string. See Section 18.6.1 [Key Sequence Input], page 263.

6.3 Functions that Operate on Arrays

In this section, we describe the functions that accept both strings and vectors.

Function arrayp object

This function returns t if object is an array (i.e., either a vector or a string).

(arrayp [a])
⇒ t
(arrayp "asdf")
⇒ t

Function aref array index This function returns the indexth element of array. The first element is at index zero.

(setq primes [2 3 5 7 11 13])
     ⇒ [2 3 5 7 11 13]
(aref primes 4)
     ⇒ 11
(elt primes 4)
     ⇒ 11
(aref "abcdefg" 1)

⇒ 98 ; ‘b’ is ASCII code 98.

See also the function elt, in Section 6.1 [Sequence Functions], page 79.

Function aset array index object

This function sets the indexth element of array to be object. It returns object.

(setq w [foo bar baz])
     ⇒ [foo bar baz]
(aset w 0 'fu)
     ⇒ fu
w
     ⇒ [fu bar baz]
(setq x "asdfasfd")
     ⇒ "asdfasfd"
(aset x 3 ?Z)
     ⇒ 90
x
     ⇒ "asdZasfd"

If array is a string and object is not a character, a wrong-type-argument error results.

Function fillarray array object This function fills the array array with object, so that each element of array is object. It returns array.

          (setq a [a b c d e f g])
               ⇒ [a b c d e f g]
          (fillarray a 0)
               ⇒ [0 0 0 0 0 0 0]
          a

               ⇒ [0 0 0 0 0 0 0]

          (setq s "When in the course")
               ⇒ "When in the course"
          (fillarray s ?-)
               ⇒ "------------------"

If array is a string and object is not a character, a wrong-type-argument error results.

The general sequence functions copy-sequence and length are often useful for objects known to be arrays. See Section 6.1 [Sequence Functions], page 79.

6.4 Vectors

Arrays in Lisp, like arrays in most languages, are blocks of memory whose elements can be accessed in constant time. A vector is a general-purpose array; its elements can be any Lisp objects. (The other kind of array in Emacs Lisp is the string, whose elements must be characters.) Vectors in Emacs serve as syntax tables (vectors of integers), as obarrays (vectors of symbols), and in keymaps (vectors of commands). They are also used internally as part of the representation of a byte-compiled function; if you print such a function, you will see a vector in it.

In Emacs Lisp, the indices of the elements of a vector start from zero and count up from there.

Vectors are printed with square brackets surrounding the elements. Thus, a vector whose elements are the symbols a, b and a is printed as [a b a]. You can write vectors in the same way in Lisp input.

A vector, like a string or a number, is considered a constant for evaluation: the result of evaluating it is the same vector. This does not evaluate or even examine the elements of the vector. See Section 8.2.1 [Self-Evaluating Forms], page 98.

Here are examples of these principles:

     (setq avector [1 two '(three) "four" [five]])
          ⇒ [1 two (quote (three)) "four" [five]]
     (eval avector)
          ⇒ [1 two (quote (three)) "four" [five]]
     (eq avector (eval avector))
          ⇒ t

6.5 Functions That Operate on Vectors

Here are some functions that relate to vectors:

Function vectorp object

This function returns t if object is a vector.

     (vectorp [a])
          ⇒ t
     (vectorp "asdf")
          ⇒ nil

Function vector &rest objects This function creates and returns a vector whose elements are the arguments, objects.

     (vector 'foo 23 [bar baz] "rats")
          ⇒ [foo 23 [bar baz] "rats"]
     (vector)
          ⇒ []

Function make-vector length object This function returns a new vector consisting of length elements, each initialized to object.

     (setq sleepy (make-vector 9 'Z))
          ⇒ [Z Z Z Z Z Z Z Z Z]

Function vconcat &rest sequences This function returns a new vector containing all the elements of the sequences. The arguments sequences may be lists, vectors, or strings. If no sequences are given, an empty vector is returned.

The value is a newly constructed vector that is not eq to any existing vector.

     (setq a (vconcat '(A B C) '(D E F)))
          ⇒ [A B C D E F]
     (eq a (vconcat a))
          ⇒ nil
     (vconcat)
          ⇒ []
     (vconcat [A B C] "aa" '(foo (6 7)))
          ⇒ [A B C 97 97 foo (6 7)]

The vconcat function also allows integers as arguments. It converts them to strings of digits, making up the decimal print representation of the integer, and then uses the strings instead of the original integers. Don’t use this feature; we plan to eliminate it. If you already use this feature, change your programs now! The proper way to convert an integer to a decimal number in this way is with format (see Section 4.6 [Formatting Strings], page 55) or number-to-string (see Section 4.5 [String Conversion], page 53).

For other concatenation functions, see mapconcat in Section 11.6 [Mapping Functions], page 147, concat in Section 4.3 [Creating Strings], page 50, and append in Section 5.5 [Building Lists], page 65.

The append function provides a way to convert a vector into a list with the same elements (see Section 5.5 [Building Lists], page 65):

(setq avector [1 two (quote (three)) "four" [five]])
     ⇒ [1 two (quote (three)) "four" [five]]
(append avector nil)
     ⇒ (1 two (quote (three)) "four" [five])

86 GNU Emacs Lisp Reference Manual

7 Symbols

A symbol is an object with a unique name. This chapter describes symbols, their components, their property lists, and how they are created and interned. Separate chapters describe the use of symbols as variables and as function names; see Chapter 10 [Variables], page 121, and Chapter 11 [Functions], page 139. For the precise read syntax for symbols, see Section 2.3.4 [Symbol Type], page 19.

You can test whether an arbitrary Lisp object is a symbol with symbolp:

Function symbolp object

This function returns t if object is a symbol, nil otherwise.

7.1 Symbol Components

Each symbol has four components (or “cells”), each of which references another object:

Print name The print name cell holds a string that names the symbol for reading and printing. See symbol-name in Section 7.3 [Creating Symbols], page 89.

Value The value cell holds the current value of the symbol as a variable. When a symbol is used as a form, the value of the form is the contents of the symbol’s value cell. See symbol-value in Section 10.7 [Accessing Variables], page 128.

Function The function cell holds the function definition of the symbol. When a symbol is used as a function, its function definition is used in its place. This cell is also used to make a symbol stand for a keymap or a keyboard macro, for editor command execution. Because each symbol has separate value and function cells, variables and function names do not conflict. See symbol-function in Section 11.8 [Function Cells], page 149.

Property list The property list cell holds the property list of the symbol. See symbol-plist in Section 7.4 [Property Lists], page 92.

The print name cell always holds a string, and cannot be changed. The other three cells can be set individually to any specified Lisp object.

The print name cell holds the string that is the name of the symbol. Since symbols are represented textually by their names, it is important not to have two symbols with the same name. The Lisp reader ensures this: every time it reads a symbol, it looks for an existing symbol with the specified name before it creates a new one. (In GNU Emacs Lisp, this lookup uses a hashing algorithm and an obarray; see Section 7.3 [Creating Symbols], page 89.)

In normal usage, the function cell usually contains a function or macro, as that is what the Lisp interpreter expects to see there (see Chapter 8 [Evaluation], page 95). Keyboard macros (see Section 18.13 [Keyboard Macros], page 275), keymaps (see Chapter 19 [Keymaps], page 277) and autoload objects (see Section 8.2.8 [Autoloading], page 102) are also sometimes stored in the function cell of symbols. We often refer to “the function foo” when we really mean the function stored in the function cell of the symbol foo. We make the distinction only when necessary.

The property list cell normally should hold a correctly formatted property list (see Section 7.4 [Property Lists], page 92), as a number of functions expect to see a property list there.

The function cell or the value cell may be void, which means that the cell does not reference any object. (This is not the same thing as holding the symbol void, nor the same as holding the symbol nil.) Examining a cell that is void results in an error, such as

‘Symbol's value as variable is void’.
   The four functions symbol-name, symbol-value, symbol-plist, and symbol-function

return the contents of the four cells of a symbol. Here as an example we show the contents of the four cells of the symbol buffer-file-name:

     (symbol-name 'buffer-file-name)
          ⇒ "buffer-file-name"
     (symbol-value 'buffer-file-name)
          ⇒ "/gnu/elisp/symbols.texi"
     (symbol-plist 'buffer-file-name)
          ⇒ (variable-documentation 29529)
     (symbol-function 'buffer-file-name)
          ⇒ #<subr buffer-file-name>

Because this symbol is the variable which holds the name of the file being visited in the current buffer, the value cell contents we see are the name of the source file of this chapter of the Emacs Lisp Manual. The property list cell contains the list (variable-documentation 29529) which tells the documentation functions where to find the documentation string for the variable buffer-file-name in the ‘DOC’ file. (29529 is the offset from the beginning of the ‘DOC’ file to where that documentation string begins.) The function cell contains the function for returning the name of the file. buffer-file-name names a primitive function, which has no read syntax and prints in hash notation (see Section 2.3.12 [Primitive Function Type], page 25). A symbol naming a function written in Lisp would have a lambda expression (or a byte-code object) in this cell.

7.2 Defining Symbols

A definition in Lisp is a special form that announces your intention to use a certain symbol in a particular way. In Emacs Lisp, you can define a symbol as a variable, or define it as a function (or macro), or both independently.

A definition construct typically specifies a value or meaning for the symbol for one kind of use, plus documentation for its meaning when used in this way. Thus, when you define a symbol as a variable, you can supply an initial value for the variable, plus documentation for the variable.

defvar and defconst are special forms that define a symbol as a global variable. They are documented in detail in Section 10.5 [Defining Variables], page 125.

defun defines a symbol as a function, creating a lambda expression and storing it in the function cell of the symbol. This lambda expression thus becomes the function definition of the symbol. (The term “function definition”, meaning the contents of the function cell, is derived from the idea that defun gives the symbol its definition as a function.) defsubst and defalias are two other ways of defining a function. See Chapter 11 [Functions], page 139.

defmacro defines a symbol as a macro. It creates a macro object and stores it in the function cell of the symbol. Note that a given symbol can be a macro or a function, but not both at once, because both macro and function definitions are kept in the function cell, and that cell can hold only one Lisp object at any given time. See Chapter 12 [Macros], page 153.

In Emacs Lisp, a definition is not required in order to use a symbol as a variable or function. Thus, you can make a symbol a global variable with setq, whether you define it first or not. The real purpose of definitions is to guide programmers and programming tools. They inform programmers who read the code that certain symbols are intended to be used as variables, or as functions. In addition, utilities such as ‘etags’ and ‘make-docfile’ recognize definitions, and add appropriate information to tag tables and the ‘emacs/etc/DOC-version’ file. See Section 21.2 [Accessing Documentation], page 320.

7.3 Creating and Interning Symbols

To understand how symbols are created in GNU Emacs Lisp, you must know how Lisp reads them. Lisp must ensure that it finds the same symbol every time it reads the same set of characters. Failure to do so would cause complete confusion.

When the Lisp reader encounters a symbol, it reads all the characters of the name. Then it “hashes” those characters to find an index in a table called an obarray. Hashing is an efficient method of looking something up. For example, instead of searching a telephone book cover to cover when looking up Jan Jones, you start with the J’s and go from there. That is a simple version of hashing. Each element of the obarray is a bucket which holds all the symbols with a given hash code; to look for a given name, it is sufficient to look through all the symbols in the bucket for that name’s hash code.

If a symbol with the desired name is found, the reader uses that symbol. If the obarray does not contain a symbol with that name, the reader makes a new symbol and adds it to the obarray. Finding or adding a symbol with a certain name is called interning it, and the symbol is then called an interned symbol.

Interning ensures that each obarray has just one symbol with any particular name. Other like-named symbols may exist, but not in the same obarray. Thus, the reader gets the same symbols for the same names, as long as you keep reading with the same obarray.

No obarray contains all symbols; in fact, some symbols are not in any obarray. They are called uninterned symbols. An uninterned symbol has the same four cells as other symbols; however, the only way to gain access to it is by finding it in some other object or as the value of a variable.

In Emacs Lisp, an obarray is actually a vector. Each element of the vector is a bucket; its value is either an interned symbol whose name hashes to that bucket, or 0 if the bucket is empty. Each interned symbol has an internal link (invisible to the user) to the next symbol in the bucket. Because these links are invisible, there is no way to find all the symbols in an obarray except using mapatoms (below). The order of symbols in a bucket is not significant.

In an empty obarray, every element is 0, and you can create an obarray with (makevector length 0). This is the only valid way to create an obarray. Prime numbers as lengths tend to result in good hashing; lengths one less than a power of two are also good.

Do not try to put symbols in an obarray yourself. This does not work—only intern can enter a symbol in an obarray properly. Do not try to intern one symbol in two obarrays. This would garble both obarrays, because a symbol has just one slot to hold the following symbol in the obarray bucket. The results would be unpredictable.

It is possible for two different symbols to have the same name in different obarrays; these symbols are not eq or equal. However, this normally happens only as part of the abbrev mechanism (see Chapter 32 [Abbrevs], page 519).

Common Lisp note: In Common Lisp, a single symbol may be interned in several obarrays.

Most of the functions below take a name and sometimes an obarray as arguments. A wrong-type-argument error is signaled if the name is not a string, or if the obarray is not a vector.

Function symbol-name symbol

This function returns the string that is symbol’s name. For example:

     (symbol-name 'foo)
          ⇒ "foo"

Changing the string by substituting characters, etc, does change the name of the symbol, but fails to update the obarray, so don’t do it!

Function make-symbol name

This function returns a newly-allocated, uninterned symbol whose name is name (which must be a string). Its value and function definition are void, and its property list is nil. In the example below, the value of sym is not eq to foo because it is a distinct uninterned symbol whose name is also ‘foo’.

     (setq sym (make-symbol "foo"))
          ⇒ foo
     (eq sym 'foo)
          ⇒ nil

Function intern name &optional obarray This function returns the interned symbol whose name is name. If there is no such symbol in the obarray obarray, intern creates a new one, adds it to the obarray, and returns it. If obarray is omitted, the value of the global variable

obarray is used.
     (setq sym (intern "foo"))
          ⇒ foo
     (eq sym 'foo)
          ⇒ t
     (setq sym1 (intern "foo" other-obarray))
          ⇒ foo
     (eq sym 'foo)
          ⇒ nil

Function intern-soft name &optional obarray This function returns the symbol in obarray whose name is name, or nil if obarray has no symbol with that name. Therefore, you can use intern-soft to test whether a symbol with a given name is already interned. If obarray is omitted, the value of the global variable obarray is used.

     (intern-soft "frazzle")        ; No such symbol exists.
          ⇒ nil
     (make-symbol "frazzle")        ; Create an uninterned one.
          ⇒ frazzle
     (intern-soft "frazzle")        ; That one cannot be found.
          ⇒ nil
     (setq sym (intern "frazzle"))  ; Create an interned one.
          ⇒ frazzle
     (intern-soft "frazzle")        ; That one can be found!
          ⇒ frazzle

(eq sym 'frazzle) ; And it is the same one.

          ⇒ t

Variable obarray

This variable is the standard obarray for use by intern and read.

Function mapatoms function &optional obarray This function calls function for each symbol in the obarray obarray. It returns nil. If obarray is omitted, it defaults to the value of obarray, the standard obarray for ordinary symbols.

     (setq count 0)
          ⇒ 0
     (defun count-syms (s)
       (setq count (1+ count)))
          ⇒ count-syms
     (mapatoms 'count-syms)
          ⇒ nil
     count

          ⇒ 1871

See documentation in Section 21.2 [Accessing Documentation], page 320, for another example using mapatoms.

Function unintern symbol &optional obarray This function deletes symbol from the obarray obarray. If symbol is not actually in the obarray, unintern does nothing. If obarray is nil, the current obarray is used.

If you provide a string instead of a symbol as symbol, it stands for a symbol name. Then unintern deletes the symbol (if any) in the obarray which has that name. If there is no such symbol, unintern does nothing.

If unintern does delete a symbol, it returns t. Otherwise it returns nil.

7.4 Property Lists

A property list (plist for short) is a list of paired elements stored in the property list cell of a symbol. Each of the pairs associates a property name (usually a symbol) with a property or value. Property lists are generally used to record information about a symbol, such as its documentation as a variable, the name of the file where it was defined, or perhaps even the grammatical class of the symbol (representing a word) in a language-understanding system.

Character positions in a string or buffer can also have property lists. See Section 29.18 [Text Properties], page 478.

The property names and values in a property list can be any Lisp objects, but the names are usually symbols. They are compared using eq. Here is an example of a property list, found on the symbol progn when the compiler is loaded:

     (lisp-indent-function 0 byte-compile byte-compile-progn)

Here lisp-indent-function and byte-compile are property names, and the other two elements are the corresponding values.

7.4.1 Property Lists and Association Lists

Association lists (see Section 5.8 [Association Lists], page 74) are very similar to property lists. In contrast to association lists, the order of the pairs in the property list is not significant since the property names must be distinct.

Property lists are better than association lists for attaching information to various Lisp function names or variables. If all the associations are recorded in one association list, the program will need to search that entire list each time a function or variable is to be operated on. By contrast, if the information is recorded in the property lists of the function names or variables themselves, each search will scan only the length of one property list, which is usually short. This is why the documentation for a variable is recorded in a property named variable-documentation. The byte compiler likewise uses properties to record those functions needing special treatment.

However, association lists have their own advantages. Depending on your application, it may be faster to add an association to the front of an association list than to update a property. All properties for a symbol are stored in the same property list, so there is a possibility of a conflict between different uses of a property name. (For this reason, it is a good idea to choose property names that are probably unique, such as by including the name of the library in the property name.) An association list may be used like a stack where associations are pushed on the front of the list and later discarded; this is not possible with a property list.

7.4.2 Property List Functions for Symbols

Function symbol-plist symbol

This function returns the property list of symbol.

Function setplist symbol plist This function sets symbol’s property list to plist. Normally, plist should be a well-formed property list, but this is not enforced.

     (setplist 'foo '(a 1 b (2 3) c nil))
          ⇒ (a 1 b (2 3) c nil)
     (symbol-plist 'foo)
          ⇒ (a 1 b (2 3) c nil)

For symbols in special obarrays, which are not used for ordinary purposes, it may make sense to use the property list cell in a nonstandard fashion; in fact, the abbrev mechanism does so (see Chapter 32 [Abbrevs], page 519).

Function get symbol property This function finds the value of the property named property in symbol’s property list. If there is no such property, nil is returned. Thus, there is no distinction between a value of nil and the absence of the property. The name property is compared with the existing property names using eq, so any object is a legitimate property. See put for an example.

Function put symbol property value This function puts value onto symbol’s property list under the property name property, replacing any previous property value. The put function returns value.

     (put 'fly 'verb 'transitive)
          ⇒'transitive
     (put 'fly 'noun '(a buzzing little bug))
          ⇒ (a buzzing little bug)
     (get 'fly 'verb)
          ⇒ transitive
     (symbol-plist 'fly)
          ⇒ (verb transitive noun (a buzzing little bug))

7.4.3 Property Lists Outside Symbols

These two functions are useful for manipulating property lists that are stored in places other than symbols:

Function plist-get plist property This returns the value of the property property stored in the property list plist. For example,

     (plist-get '(foo 4) 'foo)
          ⇒ 4

Function plist-put plist property value This stores value as the value of the property property in the property list plist. It may modify plist destructively, or it may construct a new list structure without altering the old. The function returns the modified property list, so you can store that back in the place where you got plist. For example, 94 GNU Emacs Lisp Reference Manual

(setq my-plist '(bar t foo 4))
     ⇒ (bar t foo 4)
(setq my-plist (plist-put my-plist 'foo 69))
     ⇒ (bar t foo 69)
(setq my-plist (plist-put my-plist 'quux '(a)))
     ⇒ (quux (a) bar t foo 5)

8 Evaluation

The evaluation of expressions in Emacs Lisp is performed by the Lisp interpreter—a program that receives a Lisp object as input and computes its value as an expression. How it does this depends on the data type of the object, according to rules described in this chapter. The interpreter runs automatically to evaluate portions of your program, but can also be called explicitly via the Lisp primitive function eval.

A Lisp object that is intended for evaluation is called an expression or a form. The fact that expressions are data objects and not merely text is one of the fundamental differences between Lisp-like languages and typical programming languages. Any object can be evaluated, but in practice only numbers, symbols, lists and strings are evaluated very often.

It is very common to read a Lisp expression and then evaluate the expression, but reading and evaluation are separate activities, and either can be performed alone. Reading per se does not evaluate anything; it converts the printed representation of a Lisp object to the object itself. It is up to the caller of read whether this object is a form to be evaluated, or serves some entirely different purpose. See Section 16.3 [Input Functions], page 216.

Do not confuse evaluation with command key interpretation. The editor command loop translates keyboard input into a command (an interactively callable function) using the active keymaps, and then uses call-interactively to invoke the command. The execution of the command itself involves evaluation if the command is written in Lisp, but that is not a part of command key interpretation itself. See Chapter 18 [Command Loop], page 243.

Evaluation is a recursive process. That is, evaluation of a form may call eval to evaluate parts of the form. For example, evaluation of a function call first evaluates each argument of the function call, and then evaluates each form in the function body. Consider evaluation of the form (car x): the subform x must first be evaluated recursively, so that its value can be passed as an argument to the function car.

Evaluation of a function call ultimately calls the function specified in it. See Chapter 11 [Functions], page 139. The execution of the function may itself work by evaluating the function definition; or the function may be a Lisp primitive implemented in C, or it may be a byte-compiled function (see Chapter 14 [Byte Compilation], page 171).

The evaluation of forms takes place in a context called the environment, which consists of the current values and bindings of all Lisp variables.^{1} Whenever the form refers to a variable without creating a new binding for it, the value of the binding in the current environment is used. See Chapter 10 [Variables], page 121.

Evaluation of a form may create new environments for recursive evaluation by binding variables (see Section 10.3 [Local Variables], page 122). These environments are temporary and vanish by the time evaluation of the form is complete. The form may also make changes that persist; these changes are called side effects. An example of a form that produces side

effects is (setq foo 1).

The details of what evaluation means for each kind of form are described below (see Section 8.2 [Forms], page 97).

1 This definition of “environment” is specifically not intended to include all the data that can affect the result of a program.

8.1 Eval

Most often, forms are evaluated automatically, by virtue of their occurrence in a program being run. On rare occasions, you may need to write code that evaluates a form that is computed at run time, such as after reading a form from text being edited or getting one from a property list. On these occasions, use the eval function.

Note: it is generally cleaner and more flexible to call functions that are stored in data structures, rather than to evaluate expressions stored in data structures. Using functions provides the ability to pass information to them as arguments.

The functions and variables described in this section evaluate forms, specify limits to the evaluation process, or record recently returned values. Loading a file also does evaluation (see Chapter 13 [Loading], page 161).

Function eval form

This is the basic function for performing evaluation. It evaluates form in the current environment and returns the result. How the evaluation proceeds depends on the type of the object (see Section 8.2 [Forms], page 97). Since eval is a function, the argument expression that appears in a call to eval is evaluated twice: once as preparation before eval is called, and again by the eval function itself. Here is an example:

     (setq foo 'bar)
          ⇒ bar
     (setq bar 'baz)
          ⇒ baz

;; eval receives argument bar, which is the value of foo

     (eval foo)
          ⇒ baz
     (eval 'foo)
          ⇒ bar

The number of currently active calls to eval is limited to max-lisp-eval-depth (see below).

Command eval-region start end &optional stream This function evaluates the forms in the current buffer in the region defined by the positions start and end. It reads forms from the region and calls eval on them until the end of the region is reached, or until an error is signaled and not handled. If stream is supplied, standard-output is bound to it during the evaluation. You can use the variable load-read-function to specify a function for evalregion to use instead of read for reading expressions. See Section 13.1 [How Programs Do Loading], page 161.

eval-region always returns nil.

Command eval-current-buffer &optional stream

This is like eval-region except that it operates on the whole buffer.

Variable max-lisp-eval-depth

This variable defines the maximum depth allowed in calls to eval, apply, and funcall before an error is signaled (with error message "Lisp nesting exceeds max-lisp-eval-depth"). This counts internal uses of those functions, such as for calling the functions mentioned in Lisp expressions, and recursive evaluation of function call arguments and function body forms.

This limit, with the associated error when it is exceeded, is one way that Lisp avoids infinite recursion on an ill-defined function.

The default value of this variable is 200. If you set it to a value less than 100, Lisp will reset it to 100 if the given value is reached.

max-specpdl-size provides another limit on nesting. See Section 10.3 [Local Variables], page 122.

Variable values

The value of this variable is a list of the values returned by all the expressions that were read from buffers (including the minibuffer), evaluated, and printed. The elements are ordered most recent first.

     (setq x 1) ⇒ 1
     (list 'A (1+ 2) auto-save-default)
          ⇒ (A 3 t)
     values

          ⇒ ((A 3 t) 1 . . .)

This variable is useful for referring back to values of forms recently evaluated. It is generally a bad idea to print the value of values itself, since this may be very long. Instead, examine particular elements, like this:

;; Refer to the most recent evaluation result.

     (nth 0 values)
          ⇒ (A 3 t)

;; That put a new element on, ;; so all elements move back one.

     (nth 1 values)
          ⇒ (A 3 t)

;; This gets the element that was next-to-most-recent ;; before this example.

     (nth 3 values)
          ⇒ 1

8.2 Kinds of Forms

A Lisp object that is intended to be evaluated is called a form. How Emacs evaluates a form depends on its data type. Emacs has three different kinds of form that are evaluated differently: symbols, lists, and “all other types”. This section describes all three kinds, starting with “all other types” which are self-evaluating forms.

8.2.1 Self-Evaluating Forms

A self-evaluating form is any form that is not a list or symbol. Self-evaluating forms evaluate to themselves: the result of evaluation is the same object that was evaluated. Thus, the number 25 evaluates to 25, and the string "foo" evaluates to the string "foo". Likewise, evaluation of a vector does not cause evaluation of the elements of the vector—it returns the same vector with its contents unchanged.

'123 ; An object, shown without evaluation.

          ⇒ 123

123 ; Evaluated as usual—result is the same.

          ⇒ 123

(eval '123) ; Evaluated “by hand”—result is the same.

          ⇒ 123

(eval (eval '123)) ; Evaluating twice changes nothing.

          ⇒ 123

It is common to write numbers, characters, strings, and even vectors in Lisp code, taking advantage of the fact that they self-evaluate. However, it is quite unusual to do this for types that lack a read syntax, because there’s no way to write them textually. It is possible to construct Lisp expressions containing these types by means of a Lisp program. Here is an example:

;; Build an expression containing a buffer object.

     (setq buffer (list 'print (current-buffer)))
          ⇒ (print #<buffer eval.texi>)

;; Evaluate it.

     (eval buffer)
          ⊣ #<buffer eval.texi>
          ⇒ #<buffer eval.texi>

8.2.2 Symbol Forms

When a symbol is evaluated, it is treated as a variable. The result is the variable’s value, if it has one. If it has none (if its value cell is void), an error is signaled. For more information on the use of variables, see Chapter 10 [Variables], page 121.

In the following example, we set the value of a symbol with setq. Then we evaluate the symbol, and get back the value that setq stored.

     (setq a 123) ⇒ 123
     (eval 'a) ⇒ 123
     a  ⇒ 123

The symbols nil and t are treated specially, so that the value of nil is always nil, and the value of t is always t; you cannot set or bind them to any other values. Thus, these two symbols act like self-evaluating forms, even though eval treats them like any other symbol.

8.2.3 Classification of List Forms

A form that is a nonempty list is either a function call, a macro call, or a special form, according to its first element. These three kinds of forms are evaluated in different ways, described below. The remaining list elements constitute the arguments for the function, macro, or special form.

The first step in evaluating a nonempty list is to examine its first element. This element alone determines what kind of form the list is and how the rest of the list is to be processed. The first element is not evaluated, as it would be in some Lisp dialects such as Scheme.

8.2.4 Symbol Function Indirection

If the first element of the list is a symbol then evaluation examines the symbol’s function cell, and uses its contents instead of the original symbol. If the contents are another symbol, this process, called symbol function indirection, is repeated until it obtains a non-symbol. See Section 11.3 [Function Names], page 143, for more information about using a symbol as a name for a function stored in the function cell of the symbol.

One possible consequence of this process is an infinite loop, in the event that a symbol’s function cell refers to the same symbol. Or a symbol may have a void function cell, in which case the subroutine symbol-function signals a void-function error. But if neither of these things happens, we eventually obtain a non-symbol, which ought to be a function or other suitable object.

More precisely, we should now have a Lisp function (a lambda expression), a byte-code function, a primitive function, a Lisp macro, a special form, or an autoload object. Each of these types is a case described in one of the following sections. If the object is not one of these types, the error invalid-function is signaled.

The following example illustrates the symbol indirection process. We use fset to set the function cell of a symbol and symbol-function to get the function cell contents (see Section 11.8 [Function Cells], page 149). Specifically, we store the symbol car into the function cell of first, and the symbol first into the function cell of erste.

;; Build this function cell linkage:

     ;;   -------------       -----        -------        -------
     ;;  | #<subr car> | <-- | car |  <-- | first |  <-- | erste |
     ;;   -------------       -----        -------        -------
     (symbol-function 'car)
          ⇒ #<subr car>
     (fset 'first 'car)
          ⇒ car
     (fset 'erste 'first)
          ⇒ first

(erste '(1 2 3)) ; Call the function referenced by erste.

          ⇒ 1

By contrast, the following example calls a function without any symbol function indirection, because the first element is an anonymous Lisp function, not a symbol.

     ((lambda (arg) (erste arg))
      '(1 2 3))
          ⇒ 1

Executing the function itself evaluates its body; this does involve symbol function indirection when calling erste.

The built-in function indirect-function provides an easy way to perform symbol function indirection explicitly.

Function indirect-function function

This function returns the meaning of function as a function. If function is a symbol, then it finds function’s function definition and starts over with that value. If function is not a symbol, then it returns function itself. Here is how you could define indirect-function in Lisp:

          (defun indirect-function (function)
            (if (symbolp function)
                (indirect-function (symbol-function function))
              function))

8.2.5 Evaluation of Function Forms

If the first element of a list being evaluated is a Lisp function object, byte-code object or primitive function object, then that list is a function call. For example, here is a call to the function +:

     (+ 1 x)

The first step in evaluating a function call is to evaluate the remaining elements of the list from left to right. The results are the actual argument values, one value for each list element. The next step is to call the function with this list of arguments, effectively using the function apply (see Section 11.5 [Calling Functions], page 145). If the function is written in Lisp, the arguments are used to bind the argument variables of the function (see Section 11.2 [Lambda Expressions], page 140); then the forms in the function body are evaluated in order, and the value of the last body form becomes the value of the function call.

8.2.6 Lisp Macro Evaluation

If the first element of a list being evaluated is a macro object, then the list is a macro call. When a macro call is evaluated, the elements of the rest of the list are not initially evaluated. Instead, these elements themselves are used as the arguments of the macro. The macro definition computes a replacement form, called the expansion of the macro, to be evaluated in place of the original form. The expansion may be any sort of form: a selfevaluating constant, a symbol, or a list. If the expansion is itself a macro call, this process of expansion repeats until some other sort of form results.

Ordinary evaluation of a macro call finishes by evaluating the expansion. However, the macro expansion is not necessarily evaluated right away, or at all, because other programs also expand macro calls, and they may or may not evaluate the expansions.

Normally, the argument expressions are not evaluated as part of computing the macro expansion, but instead appear as part of the expansion, so they are computed when the expansion is computed.

For example, given a macro defined as follows:

     (defmacro cadr (x)
       (list 'car (list 'cdr x)))

an expression such as (cadr (assq 'handler list)) is a macro call, and its expansion is:

     (car (cdr (assq 'handler list)))

Note that the argument (assq 'handler list) appears in the expansion.

See Chapter 12 [Macros], page 153, for a complete description of Emacs Lisp macros.

8.2.7 Special Forms

A special form is a primitive function specially marked so that its arguments are not all evaluated. Most special forms define control structures or perform variable bindings—things which functions cannot do.

Each special form has its own rules for which arguments are evaluated and which are used without evaluation. Whether a particular argument is evaluated may depend on the results of evaluating other arguments.

Here is a list, in alphabetical order, of all of the special forms in Emacs Lisp with a reference to where each is described. and see Section 9.3 [Combining Conditions], page 108 catch see Section 9.5.1 [Catch and Throw], page 110 cond see Section 9.2 [Conditionals], page 106

condition-case

see Section 9.5.3.3 [Handling Errors], page 114

defconst see Section 10.5 [Defining Variables], page 125 defmacro see Section 12.4 [Defining Macros], page 155 defun see Section 11.4 [Defining Functions], page 144 defvar see Section 10.5 [Defining Variables], page 125 function see Section 11.7 [Anonymous Functions], page 148 if see Section 9.2 [Conditionals], page 106

interactive

see Section 18.3 [Interactive Call], page 248

let

let* see Section 10.3 [Local Variables], page 122 or see Section 9.3 [Combining Conditions], page 108

prog1
prog2

progn see Section 9.1 [Sequencing], page 105 quote see Section 8.3 [Quoting], page 102

save-excursion

see Section 27.3 [Excursions], page 437

save-restriction

see Section 27.4 [Narrowing], page 438

save-window-excursion

see Section 25.17 [Window Configurations], page 406

setq see Section 10.8 [Setting Variables], page 129

setq-default

see Section 10.10.2 [Creating Buffer-Local], page 135

track-mouse

see Section 26.13 [Mouse Tracking], page 422

unwind-protect

see Section 9.5 [Nonlocal Exits], page 110

while see Section 9.4 [Iteration], page 109

with-output-to-temp-buffer

see Section 35.8 [Temporary Displays], page 573

Common Lisp note: Here are some comparisons of special forms in GNU Emacs Lisp and Common Lisp. setq, if, and catch are special forms in both Emacs Lisp and Common Lisp. defun is a special form in Emacs Lisp, but a macro in Common Lisp. save-excursion is a special form in Emacs Lisp, but doesn’t exist in Common Lisp. throw is a special form in Common Lisp (because it must be able to throw multiple values), but it is a function in Emacs Lisp (which doesn’t have multiple values).

8.2.8 Autoloading

The autoload feature allows you to call a function or macro whose function definition has not yet been loaded into Emacs. It specifies which file contains the definition. When an autoload object appears as a symbol’s function definition, calling that symbol as a function automatically loads the specified file; then it calls the real definition loaded from that file. See Section 13.2 [Autoload], page 164.

8.3 Quoting

The special form quote returns its single argument, as written, without evaluating it. This provides a way to include constant symbols and lists, which are not self-evaluating objects, in a program. (It is not necessary to quote self-evaluating objects such as numbers, strings, and vectors.)

Special Form quote object This special form returns object, without evaluating it.

Because quote is used so often in programs, Lisp provides a convenient read syntax for it. An apostrophe character (‘'’) followed by a Lisp object (in read syntax) expands to a list whose first element is quote, and whose second element is the object. Thus, the read syntax 'x is an abbreviation for (quote x).

Here are some examples of expressions that use quote:

     (quote (+ 1 2)) ⇒ (+ 1 2)
     (quote foo) ⇒ foo
     'foo ⇒ foo
     ''foo
          ⇒ (quote foo)
     '(quote foo)
          ⇒ (quote foo)
     ['foo]
          ⇒ [(quote foo)]

Other quoting constructs include function (see Section 11.7 [Anonymous Functions], page 148), which causes an anonymous lambda expression written in Lisp to be compiled, and ‘`’ (see Section 12.5 [Backquote], page 155), which is used to quote only part of a list, while computing and substituting other parts.

104 GNU Emacs Lisp Reference Manual

9 Control Structures

A Lisp program consists of expressions or forms (see Section 8.2 [Forms], page 97). We control the order of execution of the forms by enclosing them in control structures. Control structures are special forms which control when, whether, or how many times to execute the forms they contain.

The simplest order of execution is sequential execution: first form a, then form b, and so on. This is what happens when you write several forms in succession in the body of a function, or at top level in a file of Lisp code—the forms are executed in the order written. We call this textual order. For example, if a function body consists of two forms a and b, evaluation of the function evaluates first a and then b, and the function’s value is the value of b.

Explicit control structures make possible an order of execution other than sequential.

Emacs Lisp provides several kinds of control structure, including other varieties of sequencing, conditionals, iteration, and (controlled) jumps—all discussed below. The built-in control structures are special forms since their subforms are not necessarily evaluated or not evaluated sequentially. You can use macros to define your own control structure constructs (see Chapter 12 [Macros], page 153).

9.1 Sequencing

Evaluating forms in the order they appear is the most common way control passes from one form to another. In some contexts, such as in a function body, this happens automatically. Elsewhere you must use a control structure construct to do this: progn, the simplest control construct of Lisp.

A progn special form looks like this:

     (progn a b c . . .)

and it says to execute the forms a, b, c and so on, in that order. These forms are called the body of the progn form. The value of the last form in the body becomes the value of the entire progn.

In the early days of Lisp, progn was the only way to execute two or more forms in succession and use the value of the last of them. But programmers found they often needed to use a progn in the body of a function, where (at that time) only one form was allowed. So the body of a function was made into an “implicit progn”: several forms are allowed just as in the body of an actual progn. Many other control structures likewise contain an implicit progn. As a result, progn is not used as often as it used to be. It is needed now most often inside an unwind-protect, and, or, or in the then-part of an if.

Special Form progn forms…

This special form evaluates all of the forms, in textual order, returning the result of the final form.

     (progn (print "The first form")
            (print "The second form")
            (print "The third form"))
          ⊣ "The first form"
          ⊣ "The second form"
          ⊣ "The third form"
     ⇒ "The third form"

Two other control constructs likewise evaluate a series of forms but return a different value:

Special Form prog1 form1 forms… This special form evaluates form1 and all of the forms, in textual order, returning the result of form1.

     (prog1 (print "The first form")
            (print "The second form")
            (print "The third form"))
          ⊣ "The first form"
          ⊣ "The second form"
          ⊣ "The third form"
     ⇒ "The first form"

Here is a way to remove the first element from a list in the variable x, then return the value of that former element:

     (prog1 (car x) (setq x (cdr x)))

Special Form prog2 form1 form2 forms… This special form evaluates form1, form2, and all of the following forms, in textual order, returning the result of form2.

     (prog2 (print "The first form")
            (print "The second form")
            (print "The third form"))
          ⊣ "The first form"
          ⊣ "The second form"
          ⊣ "The third form"
     ⇒ "The second form"

9.2 Conditionals

Conditional control structures choose among alternatives. Emacs Lisp has two conditional forms: if, which is much the same as in other languages, and cond, which is a generalized case statement.

Special Form if condition then-form else-forms… if chooses between the then-form and the else-forms based on the value of condition. If the evaluated condition is non-nil, then-form is evaluated and the result returned. Otherwise, the else-forms are evaluated in textual order, and the value of the last one is returned. (The else part of if is an example of an implicit progn. See Section 9.1 [Sequencing], page 105.)

If condition has the value nil, and no else-forms are given, if returns nil. if is a special form because the branch that is not selected is never evaluated— it is ignored. Thus, in the example below, true is not printed because print is never called.

     (if nil
         (print 'true)
       'very-false)
     ⇒ very-false

Special Form cond clause… cond chooses among an arbitrary number of alternatives. Each clause in the cond must be a list. The car of this list is the condition; the remaining elements, if any, the body-forms. Thus, a clause looks like this:

(condition body-forms…) cond tries the clauses in textual order, by evaluating the condition of each clause. If the value of condition is non-nil, the clause “succeeds”; then cond evaluates its body-forms, and the value of the last of body-forms becomes the value of the cond. The remaining clauses are ignored. If the value of condition is nil, the clause “fails”, so the cond moves on to the following clause, trying its condition. If every condition evaluates to nil, so that every clause fails, cond returns nil. A clause may also look like this:

(condition) Then, if condition is non-nil when tested, the value of condition becomes the value of the cond form. The following example has four clauses, which test for the cases where the value of x is a number, string, buffer and symbol, respectively:

     (cond ((numberp x) x)
           ((stringp x) x)
           ((bufferp x)
            (setq temporary-hack x) ; multiple body-forms
            (buffer-name x))        ; in one clause
           ((symbolp x) (symbol-value x)))

Often we want to execute the last clause whenever none of the previous clauses was successful. To do this, we use t as the condition of the last clause, like this: (t body-forms). The form t evaluates to t, which is never nil, so this clause never fails, provided the cond gets to it at all. For example,

     (cond ((eq a 'hack) 'foo)
           (t "default"))
     ⇒ "default"

This expression is a cond which returns foo if the value of a is 1, and returns the string "default" otherwise.

Any conditional construct can be expressed with cond or with if. Therefore, the choice between them is a matter of style. For example:

(if a b c)

≡

(cond (a b) (t c))

9.3 Constructs for Combining Conditions

This section describes three constructs that are often used together with if and cond to express complicated conditions. The constructs and and or can also be used individually as kinds of multiple conditional constructs.

Function not condition This function tests for the falsehood of condition. It returns t if condition is nil, and nil otherwise. The function not is identical to null, and we recommend using the name null if you are testing for an empty list.

Special Form and conditions… The and special form tests whether all the conditions are true. It works by evaluating the conditions one by one in the order written.

If any of the conditions evaluates to nil, then the result of the and must be nil regardless of the remaining conditions; so and returns right away, ignoring the remaining conditions.

If all the conditions turn out non-nil, then the value of the last of them becomes the value of the and form.

Here is an example. The first condition returns the integer 1, which is not nil. Similarly, the second condition returns the integer 2, which is not nil. The third condition is nil, so the remaining condition is never evaluated.

     (and (print 1) (print 2) nil (print 3))
          ⊣ 1

          ⊣ 2

     ⇒ nil

Here is a more realistic example of using and:

     (if (and (consp foo) (eq (car foo) 'x))
         (message "foo is a list starting with x"))

Note that (car foo) is not executed if (consp foo) returns nil, thus avoiding an error.

and can be expressed in terms of either if or cond. For example:

(and arg1 arg2 arg3)

≡ (if arg1 (if arg2 arg3)) ≡

     (cond (arg1 (cond (arg2 arg3))))

Special Form or conditions… The or special form tests whether at least one of the conditions is true. It works by evaluating all the conditions one by one in the order written. If any of the conditions evaluates to a non-nil value, then the result of the or must be non-nil; so or returns right away, ignoring the remaining conditions. The value it returns is the non-nil value of the condition just evaluated. If all the conditions turn out nil, then the or expression returns nil. For example, this expression tests whether x is either 0 or nil:

     (or (eq x nil) (eq x 0))

Like the and construct, or can be written in terms of cond. For example: (or arg1 arg2 arg3) ≡

     (cond (arg1)

(arg2) (arg3))

You could almost write or in terms of if, but not quite:

(if arg1 arg1 (if arg2 arg2 arg3))

This is not completely equivalent because it can evaluate arg1 or arg2 twice. By contrast, (or arg1 arg2 arg3) never evaluates any argument more than once.

9.4 Iteration

Iteration means executing part of a program repetitively. For example, you might want to repeat some computation once for each element of a list, or once for each integer from 0 to n. You can do this in Emacs Lisp with the special form while:

Special Form while condition forms… while first evaluates condition. If the result is non-nil, it evaluates forms in textual order. Then it reevaluates condition, and if the result is non-nil, it evaluates forms again. This process repeats until condition evaluates to nil. There is no limit on the number of iterations that may occur. The loop will continue until either condition evaluates to nil or until an error or throw jumps out of it (see Section 9.5 [Nonlocal Exits], page 110). The value of a while form is always nil.

     (setq num 0) ⇒ 0
     (while (< num 4)
       (princ (format "Iteration %d." num))
       (setq num (1+ num)))
          ⊣ Iteration 0.
          ⊣ Iteration 1.
          ⊣ Iteration 2.
          ⊣ Iteration 3.
          ⇒ nil

If you would like to execute something on each iteration before the end-test, put it together with the end-test in a progn as the first argument of while, as shown here:

          (while (progn
                   (forward-line 1)
                   (not (looking-at "^$"))))

This moves forward one line and continues moving by lines until it reaches an empty. It is unusual in that the while has no body, just the end test (which also does the real work of moving point).

9.5 Nonlocal Exits

A nonlocal exit is a transfer of control from one point in a program to another remote point. Nonlocal exits can occur in Emacs Lisp as a result of errors; you can also use them under explicit control. Nonlocal exits unbind all variable bindings made by the constructs being exited.

9.5.1 Explicit Nonlocal Exits: catch and throw

Most control constructs affect only the flow of control within the construct itself. The function throw is the exception to this rule of normal program execution: it performs a nonlocal exit on request. (There are other exceptions, but they are for error handling only.) throw is used inside a catch, and jumps back to that catch. For example:

     (catch 'foo
       (progn

…

         (throw 'foo t)

…))

The throw transfers control straight back to the corresponding catch, which returns immediately. The code following the throw is not executed. The second argument of throw is used as the return value of the catch.

The throw and the catch are matched through the first argument: throw searches for a catch whose first argument is eq to the one specified. Thus, in the above example, the throw specifies foo, and the catch specifies the same symbol, so that catch is applicable. If there is more than one applicable catch, the innermost one takes precedence.

Executing throw exits all Lisp constructs up to the matching catch, including function calls. When binding constructs such as let or function calls are exited in this way, the bindings are unbound, just as they are when these constructs exit normally (see Section 10.3 [Local Variables], page 122). Likewise, throw restores the buffer and position saved by save-excursion (see Section 27.3 [Excursions], page 437), and the narrowing status saved

by save-restriction and the window selection saved by save-window-excursion (see

Section 25.17 [Window Configurations], page 406). It also runs any cleanups established with the unwind-protect special form when it exits that form (see Section 9.5.4 [Cleanups], page 118).

The throw need not appear lexically within the catch that it jumps to. It can equally well be called from another function called within the catch. As long as the throw takes place chronologically after entry to the catch, and chronologically before exit from it, it has access to that catch. This is why throw can be used in commands such as exitrecursive-edit that throw back to the editor command loop (see Section 18.10 [Recursive Editing], page 271).

Common Lisp note: Most other versions of Lisp, including Common Lisp, have several ways of transferring control nonsequentially: return, return-from, and go, for example. Emacs Lisp has only throw.

Special Form catch tag body… catch establishes a return point for the throw function. The return point is distinguished from other such return points by tag, which may be any Lisp object. The argument tag is evaluated normally before the return point is established. With the return point in effect, catch evaluates the forms of the body in textual order. If the forms execute normally, without error or nonlocal exit, the value of the last body form is returned from the catch. If a throw is done within body specifying the same value tag, the catch exits immediately; the value it returns is whatever was specified as the second argument of throw.

Function throw tag value The purpose of throw is to return from a return point previously established with catch. The argument tag is used to choose among the various existing return points; it must be eq to the value specified in the catch. If multiple return points match tag, the innermost one is used. The argument value is used as the value to return from that catch. If no return point is in effect with tag tag, then a no-catch error is signaled with data (tag value).

9.5.2 Examples of catch and throw

One way to use catch and throw is to exit from a doubly nested loop. (In most languages, this would be done with a “go to”.) Here we compute (foo i j) for i and j varying from 0 to 9:

(defun search-foo ()
  (catch 'loop
    (let ((i 0))
      (while (< i 10)
        (let ((j 0))
          (while (< j 10)
            (if (foo i j)
                (throw 'loop (list i j)))
            (setq j (1+ j))))
        (setq i (1+ i))))))

If foo ever returns non-nil, we stop immediately and return a list of i and j. If foo always returns nil, the catch returns normally, and the value is nil, since that is the result of the

while.

Here are two tricky examples, slightly different, showing two return points at once. First, two return points with the same tag, hack:

     (defun catch2 (tag)
       (catch tag
         (throw 'hack 'yes)))
     ⇒ catch2
     (catch 'hack
       (print (catch2 'hack))
       'no)
     ⊣ yes
     ⇒ no

Since both return points have tags that match the throw, it goes to the inner one, the one established in catch2. Therefore, catch2 returns normally with value yes, and this value is printed. Finally the second body form in the outer catch, which is 'no, is evaluated and returned from the outer catch.

Now let’s change the argument given to catch2:

     (defun catch2 (tag)
       (catch tag
         (throw 'hack 'yes)))
     ⇒ catch2
     (catch 'hack
       (print (catch2 'quux))
       'no)
     ⇒ yes

We still have two return points, but this time only the outer one has the tag hack; the inner one has the tag quux instead. Therefore, throw makes the outer catch return the value yes. The function print is never called, and the body-form 'no is never evaluated.

9.5.3 Errors

When Emacs Lisp attempts to evaluate a form that, for some reason, cannot be evaluated, it signals an error.

When an error is signaled, Emacs’s default reaction is to print an error message and terminate execution of the current command. This is the right thing to do in most cases, such as if you type C-f at the end of the buffer.

In complicated programs, simple termination may not be what you want. For example, the program may have made temporary changes in data structures, or created temporary buffers that should be deleted before the program is finished. In such cases, you would use unwind-protect to establish cleanup expressions to be evaluated in case of error. (See Section 9.5.4 [Cleanups], page 118.) Occasionally, you may wish the program to continue execution despite an error in a subroutine. In these cases, you would use condition-case to establish error handlers to recover control in case of error.

Resist the temptation to use error handling to transfer control from one part of the program to another; use catch and throw instead. See Section 9.5.1 [Catch and Throw], page 110.

9.5.3.1 How to Signal an Error

Most errors are signaled “automatically” within Lisp primitives which you call for other purposes, such as if you try to take the car of an integer or move forward a character at the end of the buffer; you can also signal errors explicitly with the functions error and

signal.

Quitting, which happens when the user types C-g, is not considered an error, but it is handled almost like an error. See Section 18.8 [Quitting], page 268.

Function error format-string &rest args This function signals an error with an error message constructed by applying format (see Section 4.5 [String Conversion], page 53) to format-string and args. These examples show typical uses of error:

     (error "You have committed an error.
             Try something else.")
           error You have committed an error.
             Try something else.
     (error "You have committed %d errors." 10)
           error You have committed 10 errors.

error works by calling signal with two arguments: the error symbol error, and a list containing the string returned by format. If you want to use your own string as an error message verbatim, don’t just write (error string). If string contains ‘%’, it will be interpreted as a format specifier, with undesirable results. Instead, use (error "%s" string).

Function signal error-symbol data This function signals an error named by error-symbol. The argument data is a list of additional Lisp objects relevant to the circumstances of the error. The argument error-symbol must be an error symbol—a symbol bearing a property error-conditions whose value is a list of condition names. This is how Emacs Lisp classifies different sorts of errors. The number and significance of the objects in data depends on error-symbol. For example, with a wrong-type-arg error, there are two objects in the list: a predicate that describes the type that was expected, and the object that failed to fit that type. See Section 9.5.3.4 [Error Symbols], page 117, for a description of error symbols. Both error-symbol and data are available to any error handlers that handle the error: condition-case binds a local variable to a list of the form (errorsymbol . data) (see Section 9.5.3.3 [Handling Errors], page 114). If the error is not handled, these two values are used in printing the error message. The function signal never returns (though in older Emacs versions it could sometimes return).

     (signal 'wrong-number-of-arguments '(x y))
           error Wrong number of arguments: x, y
     (signal 'no-such-error '("My unknown error condition."))
           error peculiar error: "My unknown error condition."

Common Lisp note: Emacs Lisp has nothing like the Common Lisp concept of continuable errors.

9.5.3.2 How Emacs Processes Errors

When an error is signaled, signal searches for an active handler for the error. A handler is a sequence of Lisp expressions designated to be executed if an error happens in part of the Lisp program. If the error has an applicable handler, the handler is executed, and control resumes following the handler. The handler executes in the environment of the condition-case that established it; all functions called within that condition-case have already been exited, and the handler cannot return to them.

If there is no applicable handler for the error, the current command is terminated and control returns to the editor command loop, because the command loop has an implicit handler for all kinds of errors. The command loop’s handler uses the error symbol and associated data to print an error message.

An error that has no explicit handler may call the Lisp debugger. The debugger is enabled if the variable debug-on-error (see Section 15.1.1 [Error Debugging], page 181) is non-nil. Unlike error handlers, the debugger runs in the environment of the error, so that you can examine values of variables precisely as they were at the time of the error.

9.5.3.3 Writing Code to Handle Errors

The usual effect of signaling an error is to terminate the command that is running and return immediately to the Emacs editor command loop. You can arrange to trap errors occurring in a part of your program by establishing an error handler, with the special form condition-case. A simple example looks like this:

     (condition-case nil
         (delete-file filename)
       (error nil))

This deletes the file named filename, catching any error and returning nil if an error occurs.

The second argument of condition-case is called the protected form. (In the example above, the protected form is a call to delete-file.) The error handlers go into effect when this form begins execution and are deactivated when this form returns. They remain in effect for all the intervening time. In particular, they are in effect during the execution of functions called by this form, in their subroutines, and so on. This is a good thing, since, strictly speaking, errors can be signaled only by Lisp primitives (including signal and error) called by the protected form, not by the protected form itself.

The arguments after the protected form are handlers. Each handler lists one or more condition names (which are symbols) to specify which errors it will handle. The error symbol specified when an error is signaled also defines a list of condition names. A handler applies to an error if they have any condition names in common. In the example above, there is one handler, and it specifies one condition name, error, which covers all errors.

The search for an applicable handler checks all the established handlers starting with the most recently established one. Thus, if two nested condition-case forms offer to handle the same error, the inner of the two will actually handle it.

When an error is handled, control returns to the handler. Before this happens, Emacs unbinds all variable bindings made by binding constructs that are being exited and executes the cleanups of all unwind-protect forms that are exited. Once control arrives at the handler, the body of the handler is executed.

After execution of the handler body, execution returns from the condition-case form. Because the protected form is exited completely before execution of the handler, the handler cannot resume execution at the point of the error, nor can it examine variable bindings that were made within the protected form. All it can do is clean up and proceed.

condition-case is often used to trap errors that are predictable, such as failure to open a file in a call to insert-file-contents. It is also used to trap errors that are totally unpredictable, such as when the program evaluates an expression read from the user.

Error signaling and handling have some resemblance to throw and catch, but they are entirely separate facilities. An error cannot be caught by a catch, and a throw cannot be handled by an error handler (though using throw when there is no suitable catch signals an error that can be handled).

Special Form condition-case var protected-form handlers… This special form establishes the error handlers handlers around the execution of protected-form. If protected-form executes without error, the value it returns becomes the value of the condition-case form; in this case, the conditioncase has no effect. The condition-case form makes a difference when an error occurs during protected-form. Each of the handlers is a list of the form (conditions body…). Here conditions is an error condition name to be handled, or a list of condition names; body is one or more Lisp expressions to be executed when this handler handles an error. Here are examples of handlers:

     (error nil)
     (arith-error (message "Division by zero"))
     ((arith-error file-error)
      (message
       "Either division by zero or failure to open a file"))

Each error that occurs has an error symbol that describes what kind of error it is. The error-conditions property of this symbol is a list of condition names (see Section 9.5.3.4 [Error Symbols], page 117). Emacs searches all the active condition-case forms for a handler that specifies one or more of these condition names; the innermost matching condition-case handles the error. Within this condition-case, the first applicable handler handles the error. After executing the body of the handler, the condition-case returns normally, using the value of the last form in the handler body as the overall value. The argument var is a variable. condition-case does not bind this variable when executing the protected-form, only when it handles an error. At that time, it binds var locally to an error description, which is a list giving the particulars of the error. The error description has the form (error-symbol . data). The handler can refer to this list to decide what to do. For example, if the error is for failure opening a file, the file name is the second element of data—the third element of the error description. If var is nil, that means no variable is bound. Then the error symbol and associated data are not available to the handler.

Function error-message-string error-description

This function returns the error message string for a given error descriptor. It is useful if you want to handle an error by printing the usual error message for that error.

Here is an example of using condition-case to handle the error that results from dividing by zero. The handler displays the error message (but without a beep), then returns a very large number.

(defun safe-divide (dividend divisor)
  (condition-case err

;; Protected form.

      (/ dividend divisor)

;; The handler.

    (arith-error                        ; Condition.

;; Display the usual message for this error.

     (message "%s" (error-message-string err))
     1000000)))
⇒ safe-divide
(safe-divide 5 0)
     ⊣ Arithmetic error: (arith-error)
⇒ 1000000

The handler specifies condition name arith-error so that it will handle only division-by-zero errors. Other kinds of errors will not be handled, at least not by this condition-case. Thus,

(safe-divide nil 3)
      error Wrong type argument: integer-or-marker-p, nil

Here is a condition-case that catches all kinds of errors, including those signaled with

error:
(setq baz 34) ⇒ 34
(condition-case err
    (if (eq baz 35)
        t

;; This is a call to the function error.

      (error "Rats!  The variable %s was %s, not 35" 'baz baz))

;; This is the handler; it is not a form.

  (error (princ (format "The error was: %s" err))
         2))
⊣ The error was: (error "Rats!  The variable baz was 34, not 35")
⇒ 2

9.5.3.4 Error Symbols and Condition Names

When you signal an error, you specify an error symbol to specify the kind of error you have in mind. Each error has one and only one error symbol to categorize it. This is the finest classification of errors defined by the Emacs Lisp language.

These narrow classifications are grouped into a hierarchy of wider classes called error conditions, identified by condition names. The narrowest such classes belong to the error symbols themselves: each error symbol is also a condition name. There are also condition names for more extensive classes, up to the condition name error which takes in all kinds of errors. Thus, each error has one or more condition names: error, the error symbol if that is distinct from error, and perhaps some intermediate classifications.

In order for a symbol to be an error symbol, it must have an error-conditions property which gives a list of condition names. This list defines the conditions that this kind of error belongs to. (The error symbol itself, and the symbol error, should always be members of this list.) Thus, the hierarchy of condition names is defined by the error-conditions properties of the error symbols.

In addition to the error-conditions list, the error symbol should have an errormessage property whose value is a string to be printed when that error is signaled but not handled. If the error-message property exists, but is not a string, the error message

‘peculiar error’ is used.

Here is how we define a new error symbol, new-error:

     (put 'new-error
          'error-conditions
          '(error my-own-errors new-error))
     ⇒ (error my-own-errors new-error)
     (put 'new-error 'error-message "A new error")
     ⇒ "A new error"

This error has three condition names: new-error, the narrowest classification; my-own-errors, which we imagine is a wider classification; and error, which is the widest of all.

The error string should start with a capital letter but it should not end with a period. This is for consistency with the rest of Emacs.

Naturally, Emacs will never signal new-error on its own; only an explicit call to signal (see Section 9.5.3.1 [Signaling Errors], page 113) in your code can do this:

     (signal 'new-error '(x y))
           error A new error: x, y

This error can be handled through any of the three condition names. This example handles new-error and any other errors in the class my-own-errors:

     (condition-case foo
         (bar nil t)
       (my-own-errors nil))

The significant way that errors are classified is by their condition names—the names used to match errors with handlers. An error symbol serves only as a convenient way to specify the intended error message and list of condition names. It would be cumbersome to give signal a list of condition names rather than one error symbol.

By contrast, using only error symbols without condition names would seriously decrease the power of condition-case. Condition names make it possible to categorize errors at various levels of generality when you write an error handler. Using error symbols alone would eliminate all but the narrowest level of classification.

See Appendix C [Standard Errors], page 623, for a list of all the standard error symbols and their conditions.

9.5.4 Cleaning Up from Nonlocal Exits

The unwind-protect construct is essential whenever you temporarily put a data structure in an inconsistent state; it permits you to ensure the data are consistent in the event of an error or throw.

Special Form unwind-protect body cleanup-forms… unwind-protect executes the body with a guarantee that the cleanup-forms will be evaluated if control leaves body, no matter how that happens. The body may complete normally, or execute a throw out of the unwind-protect, or cause an error; in all cases, the cleanup-forms will be evaluated. If the body forms finish normally, unwind-protect returns the value of the last body form, after it evaluates the cleanup-forms. If the body forms do not finish, unwind-protect does not return any value in the normal sense. Only the body is actually protected by the unwind-protect. If any of the cleanup-forms themselves exits nonlocally (e.g., via a throw or an error), unwind-protect is not guaranteed to evaluate the rest of them. If the failure of one of the cleanup-forms has the potential to cause trouble, then protect it with another unwind-protect around that form. The number of currently active unwind-protect forms counts, together with the number of local variable bindings, against the limit max-specpdl-size (see Section 10.3 [Local Variables], page 122).

For example, here we make an invisible buffer for temporary use, and make sure to kill it before finishing:

(save-excursion
  (let ((buffer (get-buffer-create " *temp*")))
    (set-buffer buffer)
    (unwind-protect

body

      (kill-buffer buffer))))

You might think that we could just as well write (kill-buffer (current-buffer)) and dispense with the variable buffer. However, the way shown above is safer, if body happens to get an error after switching to a different buffer! (Alternatively, you could write another save-excursion around the body, to ensure that the temporary buffer becomes current in time to kill it.)

Here is an actual example taken from the file ‘ftp.el’. It creates a process (see Chapter 33 [Processes], page 525) to try to establish a connection to a remote machine. As the function ftp-login is highly susceptible to numerous problems that the writer of the function cannot anticipate, it is protected with a form that guarantees deletion of the process in the event of failure. Otherwise, Emacs might fill up with useless subprocesses.

     (let ((win nil))
       (unwind-protect
           (progn
             (setq process (ftp-setup-buffer host file))
             (if (setq win (ftp-login process host user password))
                 (message "Logged in")
               (error "Ftp login failed")))
         (or win (and process (delete-process process)))))

This example actually has a small bug: if the user types C-g to quit, and the quit happens immediately after the function ftp-setup-buffer returns but before the variable process is set, the process will not be killed. There is no easy way to fix this bug, but at least it is very unlikely.

Here is another example which uses unwind-protect to make sure to kill a temporary buffer. In this example, the value returned by unwind-protect is used.

     (defun shell-command-string (cmd)
       "Return the output of the shell command CMD, as a string."
       (save-excursion
         (set-buffer (generate-new-buffer " OS*cmd"))
         (shell-command cmd t)
         (unwind-protect
             (buffer-string)
           (kill-buffer (current-buffer)))))

120 GNU Emacs Lisp Reference Manual

10 Variables

A variable is a name used in a program to stand for a value. Nearly all programming languages have variables of some sort. In the text of a Lisp program, variables are written using the syntax for symbols.

In Lisp, unlike most programming languages, programs are represented primarily as Lisp objects and only secondarily as text. The Lisp objects used for variables are symbols: the symbol name is the variable name, and the variable’s value is stored in the value cell of the symbol. The use of a symbol as a variable is independent of its use as a function name. See Section 7.1 [Symbol Components], page 87.

The Lisp objects that constitute a Lisp program determine the textual form of the program—it is simply the read syntax for those Lisp objects. This is why, for example, a variable in a textual Lisp program is written using the read syntax for the symbol that represents the variable.

10.1 Global Variables

The simplest way to use a variable is globally. This means that the variable has just one value at a time, and this value is in effect (at least for the moment) throughout the Lisp system. The value remains in effect until you specify a new one. When a new value replaces the old one, no trace of the old value remains in the variable.

You specify a value for a symbol with setq. For example,

     (setq x '(a b))

gives the variable x the value (a b). Note that setq does not evaluate its first argument, the name of the variable, but it does evaluate the second argument, the new value.

Once the variable has a value, you can refer to it by using the symbol by itself as an expression. Thus,

     x ⇒ (a b)

assuming the setq form shown above has already been executed.

If you do another setq, the new value replaces the old one:

     x  ⇒ (a b)
     (setq x 4) ⇒ 4
     x  ⇒ 4

10.2 Variables That Never Change

Emacs Lisp has two special symbols, nil and t, that always evaluate to themselves. These symbols cannot be rebound, nor can their value cells be changed. An attempt to change the value of nil or t signals a setting-constant error.

     nil ≡ 'nil ⇒ nil
     (setq nil 500)
      error Attempt to set constant symbol: nil

10.3 Local Variables

Global variables have values that last until explicitly superseded with new values. Sometimes it is useful to create variable values that exist temporarily—only while within a certain part of the program. These values are called local, and the variables so used are called local variables.

For example, when a function is called, its argument variables receive new local values that last until the function exits. The let special form explicitly establishes new local values for specified variables; these last until exit from the let form.

Establishing a local value saves away the previous value (or lack of one) of the variable. When the life span of the local value is over, the previous value is restored. In the mean time, we say that the previous value is shadowed and not visible. Both global and local values may be shadowed (see Section 10.9.1 [Scope], page 131).

If you set a variable (such as with setq) while it is local, this replaces the local value; it does not alter the global value, or previous local values that are shadowed. To model this behavior, we speak of a local binding of the variable as well as a local value.

The local binding is a conceptual place that holds a local value. Entry to a function, or a special form such as let, creates the local binding; exit from the function or from the let removes the local binding. As long as the local binding lasts, the variable’s value is stored within it. Use of setq or set while there is a local binding stores a different value into the local binding; it does not create a new binding.

We also speak of the global binding, which is where (conceptually) the global value is kept.

A variable can have more than one local binding at a time (for example, if there are nested let forms that bind it). In such a case, the most recently created local binding that still exists is the current binding of the variable. (This is called dynamic scoping; see Section 10.9 [Variable Scoping], page 131.) If there are no local bindings, the variable’s global binding is its current binding. We also call the current binding the most-local existing binding, for emphasis. Ordinary evaluation of a symbol always returns the value of its current binding.

The special forms let and let* exist to create local bindings.

Special Form let (bindings…) forms… This special form binds variables according to bindings and then evaluates all of the forms in textual order. The let-form returns the value of the last form in forms. Each of the bindings is either (i) a symbol, in which case that symbol is bound to nil; or (ii) a list of the form (symbol value-form), in which case symbol is bound to the result of evaluating value-form. If value-form is omitted, nil is used.

All of the value-forms in bindings are evaluated in the order they appear and before any of the symbols are bound. Here is an example of this: Z is bound to the old value of Y, which is 2, not the new value, 1.

     (setq Y 2) ⇒ 2
     (let ((Y 1) (Z Y)) (list Y Z)) ⇒ (1 2)

Special Form let* (bindings…) forms… This special form is like let, but it binds each variable right after computing its local value, before computing the local value for the next variable. Therefore, an expression in bindings can reasonably refer to the preceding symbols bound in this let* form. Compare the following example with the example above for

let.
     (setq Y 2) ⇒ 2
     (let* ((Y 1)

(Z Y)) ; Use the just-established value of Y.

       (list Y Z))
          ⇒ (1 1)

Here is a complete list of the other facilities that create local bindings:

• Function calls (see Chapter 11 [Functions], page 139).

• Macro calls (see Chapter 12 [Macros], page 153).

• condition-case (see Section 9.5.3 [Errors], page 112).

Variables can also have buffer-local bindings (see Section 10.10 [Buffer-Local Variables], page 134); a few variables have terminal-local bindings (see Section 26.2 [Multiple Displays], page 409). These kinds of bindings work somewhat like ordinary local bindings, but they are localized depending on “where” you are in Emacs, rather than localized in time.

Variable max-specpdl-size

This variable defines the limit on the total number of local variable bindings and unwind-protect cleanups (see Section 9.5 [Nonlocal Exits], page 110) that are allowed before signaling an error (with data "Variable binding depth

exceeds max-specpdl-size").

This limit, with the associated error when it is exceeded, is one way that Lisp avoids infinite recursion on an ill-defined function.

The default value is 600.

max-lisp-eval-depth provides another limit on depth of nesting. See Section 8.1 [Eval], page 96.

10.4 When a Variable is “Void”

If you have never given a symbol any value as a global variable, we say that that symbol’s global value is void. In other words, the symbol’s value cell does not have any Lisp object in it. If you try to evaluate the symbol, you get a void-variable error rather than a value.

Note that a value of nil is not the same as void. The symbol nil is a Lisp object and can be the value of a variable just as any other object can be; but it is a value. A void variable does not have any value.

After you have given a variable a value, you can make it void once more using

makunbound.

Function makunbound symbol

This function makes the current binding of symbol void. Subsequent attempts to use this symbol’s value as a variable will signal the error void-variable, unless or until you set it again. makunbound returns symbol.

(makunbound 'x) ; Make the global value

; of x void.

          ⇒ x
     x
      error Symbol's value as variable is void: x

If symbol is locally bound, makunbound affects the most local existing binding. This is the only way a symbol can have a void local binding, since all the constructs that create local bindings create them with values. In this case, the voidness lasts at most as long as the binding does; when the binding is removed due to exit from the construct that made it, the previous or global binding is reexposed as usual, and the variable is no longer void unless the newly reexposed binding was void all along.

(setq x 1) ; Put a value in the global binding.

          ⇒ 1

(let ((x 2)) ; Locally bind it.

(makunbound 'x) ; Void the local binding.

       x)
      error Symbol's value as variable is void: x

x ; The global binding is unchanged.

          ⇒ 1

(let ((x 2)) ; Locally bind it.

       (let ((x 3))           ; And again.

(makunbound 'x) ; Void the innermost-local binding. x)) ; And refer: it’s void.

      error Symbol's value as variable is void: x
     (let ((x 2))
       (let ((x 3))

(makunbound 'x)) ; Void inner binding, then remove it.

x) ; Now outer let binding is visible.

          ⇒ 2

A variable that has been made void with makunbound is indistinguishable from one that has never received a value and has always been void.

You can use the function boundp to test whether a variable is currently void.

Function boundp variable boundp returns t if variable (a symbol) is not void; more precisely, if its current binding is not void. It returns nil otherwise.

          (boundp 'abracadabra)          ; Starts out void.
               ⇒ nil
          (let ((abracadabra 5))         ; Locally bind it.
            (boundp 'abracadabra))
               ⇒ t
          (boundp 'abracadabra)          ; Still globally void.
               ⇒ nil

(setq abracadabra 5) ; Make it globally nonvoid.

               ⇒ 5
          (boundp 'abracadabra)
               ⇒ t

10.5 Defining Global Variables

You may announce your intention to use a symbol as a global variable with a variable definition: a special form, either defconst or defvar.

In Emacs Lisp, definitions serve three purposes. First, they inform people who read the code that certain symbols are intended to be used a certain way (as variables). Second, they inform the Lisp system of these things, supplying a value and documentation. Third, they provide information to utilities such as etags and make-docfile, which create data bases of the functions and variables in a program.

The difference between defconst and defvar is primarily a matter of intent, serving to inform human readers of whether programs will change the variable. Emacs Lisp does not restrict the ways in which a variable can be used based on defconst or defvar declarations. However, it does make a difference for initialization: defconst unconditionally initializes the variable, while defvar initializes it only if it is void.

One would expect user option variables to be defined with defconst, since programs do not change them. Unfortunately, this has bad results if the definition is in a library that is not preloaded: defconst would override any prior value when the library is loaded. Users would like to be able to set user options in their init files, and override the default values given in the definitions. For this reason, user options must be defined with defvar.

Special Form defvar symbol [value [doc-string]] This special form defines symbol as a value and initializes it. The definition informs a person reading your code that symbol is used as a variable that programs are likely to set or change. It is also used for all user option variables except in the preloaded parts of Emacs. Note that symbol is not evaluated; the symbol to be defined must appear explicitly in the defvar.

If symbol already has a value (i.e., it is not void), value is not even evaluated, and symbol’s value remains unchanged. If symbol is void and value is specified, defvar evaluates it and sets symbol to the result. (If value is omitted, the value of symbol is not changed in any case.) When you evaluate a top-level defvar form with C-M-x in Emacs Lisp mode (eval-defun), a special feature of eval-defun evaluates it as a defconst. The purpose of this is to make sure the variable’s value is reinitialized, when you ask for it specifically. If symbol has a buffer-local binding in the current buffer, defvar sets the default value, not the local value. See Section 10.10 [Buffer-Local Variables], page 134. If the doc-string argument appears, it specifies the documentation for the variable. (This opportunity to specify documentation is one of the main benefits of defining the variable.) The documentation is stored in the symbol’s variabledocumentation property. The Emacs help functions (see Chapter 21 [Documentation], page 319) look for this property. If the first character of doc-string is ‘*’, it means that this variable is considered a user option. This lets users set the variable conventiently using the commands

set-variable and edit-options.

For example, this form defines foo but does not set its value:

     (defvar foo)
          ⇒ foo

The following example sets the value of bar to 23, and gives it a documentation string:

     (defvar bar 23
       "The normal weight of a bar.")
          ⇒ bar

The following form changes the documentation string for bar, making it a user option, but does not change the value, since bar already has a value. (The addition (1+ 23) is not even performed.)

     (defvar bar (1+ 23)
       "*The normal weight of a bar.")
          ⇒ bar
     bar ⇒ 23

Here is an equivalent expression for the defvar special form:

(defvar symbol value doc-string) ≡

     (progn
       (if (not (boundp 'symbol))

(setq symbol value)) (if 'doc-string

         (put 'symbol 'variable-documentation 'doc-string))

'symbol) The defvar form returns symbol, but it is normally used at top level in a file where its value does not matter.

Special Form defconst symbol [value [doc-string]] This special form defines symbol as a value and initializes it. It informs a person reading your code that symbol has a global value, established here, that will not normally be changed or locally bound by the execution of the program. The user, however, may be welcome to change it. Note that symbol is not evaluated; the symbol to be defined must appear explicitly in the defconst. defconst always evaluates value and sets the global value of symbol to the result, provided value is given. If symbol has a buffer-local binding in the current buffer, defconst sets the default value, not the local value. Please note: Don’t use defconst for user option variables in libraries that are not standardly preloaded. The user should be able to specify a value for such a variable in the ‘.emacs’ file, so that it will be in effect if and when the library is loaded later. Here, pi is a constant that presumably ought not to be changed by anyone (attempts by the Indiana State Legislature notwithstanding). As the second form illustrates, however, this is only advisory.

     (defconst pi 3.1415 "Pi to five places.")
          ⇒ pi
     (setq pi 3) ⇒ pi
     pi ⇒ 3

Function user-variable-p variable

This function returns t if variable is a user option—a variable intended to be set by the user for customization—and nil otherwise. (Variables other than user options exist for the internal purposes of Lisp programs, and users need not know about them.) User option variables are distinguished from other variables by the first character of the variable-documentation property. If the property exists and is a string, and its first character is ‘*’, then the variable is a user option.

If a user option variable has a variable-interactive property, the set-variable command uses that value to control reading the new value for the variable. The property’s value is used as if it were to interactive (see Section 18.2.1 [Using Interactive], page 244).

Warning: If the defconst and defvar special forms are used while the variable has a local binding, they set the local binding’s value; the global binding is not changed. This is not what we really want. To prevent it, use these special forms at top level in a file, where normally no local binding is in effect, and make sure to load the file before making a local binding for the variable.

10.6 Tips for Defining Variables Robustly

When defining and initializing a variable that holds a complicated value (such as a keymap with bindings in it), it’s best to put the entire computation of the value into the defvar, like this:

     (defvar my-mode-map
       (let ((map (make-sparse-keymap)))
         (define-key my-mode-map "\C-c\C-a" 'my-command)

…

         map)

docstring)

This method has several benefits. First, if the user quits while loading the file, the variable is either still uninitialized or initialized properly, never in-between. If it is uninitialized, reloading the file will initialize it properly. Second, reloading the file once the variable is initialized will not alter it; that is important if the user has run hooks to alter part of the contents (such as, to rebind keys). Third, evaluating the defvar form with C-M-x will reinitialize the map completely.

Putting so much code in the defvar form has one disadvantage: it puts the documentation string far away from the line which names the variable. Here’s a safe way to avoid that:

     (defvar my-mode-map nil

docstring)

     (if my-mode-map
         nil
       (let ((map (make-sparse-keymap)))
         (define-key my-mode-map "\C-c\C-a" 'my-command)

…

         (setq my-mode-map map)))

This has all the same advantages as putting the initialization inside the defvar, except that you must type C-M-x twice, once on each form, if you do want to reinitialize the variable.

But be careful not to write the code like this:

     (defvar my-mode-map nil

docstring)

     (if my-mode-map
         nil
       (setq my-mode-map (make-sparse-keymap))
       (define-key my-mode-map "\C-c\C-a" 'my-command)

…)

This code sets the variable, then alters it, but only if the variable had been ni. If the user quits just after the setq, that leaves the variable neither correctly initialized nor void nor nil. Once that happens, reloading the file will not initialize the variable; it will remain incomplete.

10.7 Accessing Variable Values

The usual way to reference a variable is to write the symbol which names it (see Section 8.2.2 [Symbol Forms], page 98). This requires you to specify the variable name when you write the program. Usually that is exactly what you want to do. Occasionally you need to choose at run time which variable to reference; then you can use symbol-value.

Function symbol-value symbol

This function returns the value of symbol. This is the value in the innermost local binding of the symbol, or its global value if it has no local bindings.

(setq abracadabra 5)
     ⇒ 5
(setq foo 9) ⇒ 9
;; Here the symbol abracadabra

;; is the symbol whose value is examined.

(let ((abracadabra 'foo))
  (symbol-value 'abracadabra))
     ⇒ foo

;; Here the value of abracadabra, ;; which is foo, ;; is the symbol whose value is examined.

(let ((abracadabra 'foo))
  (symbol-value abracadabra))
     ⇒ 9
(symbol-value 'abracadabra)
     ⇒ 5

A void-variable error is signaled if symbol has neither a local binding nor a global value.

10.8 How to Alter a Variable Value

The usual way to change the value of a variable is with the special form setq. When you need to compute the choice of variable at run time, use the function set.

Special Form setq [symbol form]… This special form is the most common method of changing a variable’s value. Each symbol is given a new value, which is the result of evaluating the corresponding form. The most-local existing binding of the symbol is changed.

setq does not evaluate symbol; it sets the symbol that you write. We say that this argument is automatically quoted. The ‘q’ in setq stands for “quoted.”

The value of the setq form is the value of the last form.

(setq x (1+ 2)) ⇒ 3

x ; x now has a global value.

     ⇒ 3
(let ((x 5))

(setq x 6) ; The local binding of x is set.

  x)
     ⇒ 6

x ; The global value is unchanged.

     ⇒ 3

Note that the first form is evaluated, then the first symbol is set, then the second form is evaluated, then the second symbol is set, and so on:

(setq x 10 ; Notice that x is set before y (1+ x)) ; the value of y is computed.

          ⇒ 11

Function set symbol value This function sets symbol’s value to value, then returns value. Since set is a function, the expression written for symbol is evaluated to obtain the symbol to set. The most-local existing binding of the variable is the binding that is set; shadowed bindings are not affected.

     (set one 1)
      error Symbol's value as variable is void: one
     (set 'one 1) ⇒ 1
     (set 'two 'one)
          ⇒ one

(set two 2) ; two evaluates to symbol one.

          ⇒ 2

one ; So it is one that was set.

          ⇒ 2

(let ((one 1)) ; This binding of one is set, (set 'one 3) ; not the global value.

       one)
          ⇒ 3
     one ⇒ 2

If symbol is not actually a symbol, a wrong-type-argument error is signaled.

     (set '(x y) 'z)
      error Wrong type argument: symbolp, (x y)

Logically speaking, set is a more fundamental primitive than setq. Any use of setq can be trivially rewritten to use set; setq could even be defined as a macro, given the availability of set. However, set itself is rarely used; beginners hardly need to know about it. It is useful only for choosing at run time which variable to set. For example, the command set-variable, which reads a variable name from the user and then sets the variable, needs to use set.

Common Lisp note: In Common Lisp, set always changes the symbol’s special value, ignoring any lexical bindings. In Emacs Lisp, all variables and all bindings are (in effect) special, so set always affects the most local existing binding.

One other function for setting a variable is designed to add an element to a list if it is not already present in the list.

Function add-to-list symbol element This function sets the variable symbol by consing element onto the old value, if element is not already a member of that value. It returns the resulting list, whether updated or not. The value of symbol had better be a list already before the call. The argument symbol is not implicitly quoted; add-to-list is an ordinary function, like set and unlike setq. Quote the argument yourself if that is what you want. Here’s a scenario showing how to use add-to-list:

          (setq foo '(a b))
               ⇒ (a b)
          (add-to-list 'foo 'c)     ;; Add c.
               ⇒ (c a b)
          (add-to-list 'foo 'b)     ;; No effect.
               ⇒ (c a b)

foo ;; foo was changed.

               ⇒ (c a b)

An equivalent expression for (add-to-list 'var value) is this:

     (or (member value var)
         (setq var (cons value var)))

10.9 Scoping Rules for Variable Bindings

A given symbol foo may have several local variable bindings, established at different places in the Lisp program, as well as a global binding. The most recently established binding takes precedence over the others.

Local bindings in Emacs Lisp have indefinite scope and dynamic extent. Scope refers to where textually in the source code the binding can be accessed. Indefinite scope means that any part of the program can potentially access the variable binding. Extent refers to when, as the program is executing, the binding exists. Dynamic extent means that the binding lasts as long as the activation of the construct that established it.

The combination of dynamic extent and indefinite scope is called dynamic scoping. By contrast, most programming languages use lexical scoping, in which references to a local variable must be located textually within the function or block that binds the variable.

Common Lisp note: Variables declared “special” in Common Lisp are dynamically scoped, like variables in Emacs Lisp.

10.9.1 Scope

Emacs Lisp uses indefinite scope for local variable bindings. This means that any function anywhere in the program text might access a given binding of a variable. Consider the following function definitions:

     (defun binder (x)   ; x is bound in binder.

(foo 5)) ; foo is some other function.

     (defun user ()      ; x is used in user.
       (list x))

In a lexically scoped language, the binding of x in binder would never be accessible in user, because user is not textually contained within the function binder. However, in dynamically scoped Emacs Lisp, user may or may not refer to the binding of x established in binder, depending on circumstances:

• If we call user directly without calling binder at all, then whatever binding of x is found, it cannot come from binder.

• If we define foo as follows and call binder, then the binding made in binder will be

seen in user:

         (defun foo (lose)
           (user))

• If we define foo as follows and call binder, then the binding made in binder will not

be seen in user:

         (defun foo (x)
           (user))

Here, when foo is called by binder, it binds x. (The binding in foo is said to shadow the one made in binder.) Therefore, user will access the x bound by foo instead of the one bound by binder.

10.9.2 Extent

Extent refers to the time during program execution that a variable name is valid. In Emacs Lisp, a variable is valid only while the form that bound it is executing. This is called dynamic extent. “Local” or “automatic” variables in most languages, including C and Pascal, have dynamic extent.

One alternative to dynamic extent is indefinite extent. This means that a variable binding can live on past the exit from the form that made the binding. Common Lisp and Scheme, for example, support this, but Emacs Lisp does not.

To illustrate this, the function below, make-add, returns a function that purports to add n to its own argument m. This would work in Common Lisp, but it does not work as intended in Emacs Lisp, because after the call to make-add exits, the variable n is no longer bound to the actual argument 2.

     (defun make-add (n)
         (function (lambda (m) (+ n m))))  ; Return a function.
          ⇒ make-add
     (fset 'add2 (make-add 2))  ; Define function add2
                                ; with (make-add 2).
          ⇒ (lambda (m) (+ n m))

(add2 4) ; Try to add 2 to 4.

      error Symbol's value as variable is void: n

Some Lisp dialects have “closures”, objects that are like functions but record additional variable bindings. Emacs Lisp does not have closures.

10.9.3 Implementation of Dynamic Scoping

A simple sample implementation (which is not how Emacs Lisp actually works) may help you understand dynamic binding. This technique is called deep binding and was used in early Lisp systems.

Suppose there is a stack of bindings: variable-value pairs. At entry to a function or to a let form, we can push bindings on the stack for the arguments or local variables created there. We can pop those bindings from the stack at exit from the binding construct.

We can find the value of a variable by searching the stack from top to bottom for a binding for that variable; the value from that binding is the value of the variable. To set the variable, we search for the current binding, then store the new value into that binding.

As you can see, a function’s bindings remain in effect as long as it continues execution, even during its calls to other functions. That is why we say the extent of the binding is dynamic. And any other function can refer to the bindings, if it uses the same variables while the bindings are in effect. That is why we say the scope is indefinite.

The actual implementation of variable scoping in GNU Emacs Lisp uses a technique called shallow binding. Each variable has a standard place in which its current value is always found—the value cell of the symbol.

In shallow binding, setting the variable works by storing a value in the value cell. Creating a new binding works by pushing the old value (belonging to a previous binding) on a stack, and storing the local value in the value cell. Eliminating a binding works by popping the old value off the stack, into the value cell.

We use shallow binding because it has the same results as deep binding, but runs faster, since there is never a need to search for a binding.

10.9.4 Proper Use of Dynamic Scoping

Binding a variable in one function and using it in another is a powerful technique, but if used without restraint, it can make programs hard to understand. There are two clean ways to use this technique:

• Use or bind the variable only in a few related functions, written close together in one file. Such a variable is used for communication within one program. You should write comments to inform other programmers that they can see all uses of the variable before them, and to advise them not to add uses elsewhere.

• Give the variable a well-defined, documented meaning, and make all appropriate functions refer to it (but not bind it or set it) wherever that meaning is relevant. For example, the variable case-fold-search is defined as “non-nil means ignore case when searching”; various search and replace functions refer to it directly or through their subroutines, but do not bind or set it. Then you can bind the variable in other programs, knowing reliably what the effect will be.

In either case, you should define the variable with defvar. This helps other people understand your program by telling them to look for inter-function usage. It also avoids a warning from the byte compiler. Choose the variable’s name to avoid name conflicts—don’t use short names like x.

10.10 Buffer-Local Variables

Global and local variable bindings are found in most programming languages in one form or another. Emacs also supports another, unusual kind of variable binding: bufferlocal bindings, which apply only to one buffer. Emacs Lisp is meant for programming editing commands, and having different values for a variable in different buffers is an important customization method. (A few variables have bindings that are local to a given X terminal; see Section 26.2 [Multiple Displays], page 409.)

10.10.1 Introduction to Buffer-Local Variables

A buffer-local variable has a buffer-local binding associated with a particular buffer. The binding is in effect when that buffer is current; otherwise, it is not in effect. If you set the variable while a buffer-local binding is in effect, the new value goes in that binding, so the global binding is unchanged; this means that the change is visible in that buffer alone.

A variable may have buffer-local bindings in some buffers but not in others. The global binding is shared by all the buffers that don’t have their own bindings. Thus, if you set the variable in a buffer that does not have a buffer-local binding for it, the new value is visible in all buffers except those with buffer-local bindings. (Here we are assuming that there are no let-style local bindings to complicate the issue.)

The most common use of buffer-local bindings is for major modes to change variables that control the behavior of commands. For example, C mode and Lisp mode both set the variable paragraph-start to specify that only blank lines separate paragraphs. They do this by making the variable buffer-local in the buffer that is being put into C mode or Lisp mode, and then setting it to the new value for that mode.

The usual way to make a buffer-local binding is with make-local-variable, which is what major mode commands use. This affects just the current buffer; all other buffers (including those yet to be created) continue to share the global value.

A more powerful operation is to mark the variable as automatically buffer-local by calling make-variable-buffer-local. You can think of this as making the variable local in all buffers, even those yet to be created. More precisely, the effect is that setting the variable automatically makes the variable local to the current buffer if it is not already so. All buffers start out by sharing the global value of the variable as usual, but any setq creates a buffer-local binding for the current buffer. The new value is stored in the buffer-local binding, leaving the (default) global binding untouched. The global value can no longer be changed with setq; you need to use setq-default to do that.

Warning: When a variable has local values in one or more buffers, you can get Emacs very confused by binding the variable with let, changing to a different current buffer in which a different binding is in effect, and then exiting the let. This can scramble the values of the global and local bindings.

To preserve your sanity, avoid that series of actions. If you use save-excursion around each piece of code that changes to a different current buffer, you will not have this problem. Here is an example of what to avoid:

     (setq foo 'b)
     (set-buffer "a")
     (make-local-variable 'foo)

(setq foo 'a)
(let ((foo 'temp))
  (set-buffer "b")

body…) foo ⇒ 'a ; The old buffer-local value from buffer ‘a’

; is now the default value.

(set-buffer "a")

foo ⇒ 'temp ; The local value that should be gone ; is now the buffer-local value in buffer ‘a’.

But save-excursion as shown here avoids the problem:

(let ((foo 'temp))
  (save-excursion
    (set-buffer "b")

body…))

Note that references to foo in body access the buffer-local binding of buffer ‘b’.

When a file specifies local variable values, these become buffer-local values when you visit the file. See Section 20.1.3 [Auto Major Mode], page 305.

10.10.2 Creating and Deleting Buffer-Local Bindings

Command make-local-variable variable

This function creates a buffer-local binding in the current buffer for variable (a symbol). Other buffers are not affected. The value returned is variable.

The buffer-local value of variable starts out as the same value variable previously had. If variable was void, it remains void.

;; In buffer ‘b1’:

(setq foo 5) ; Affects all buffers.

          ⇒ 5
     (make-local-variable 'foo)  ; Now it is local in ‘b1’.
          ⇒ foo

foo ; That did not change ⇒ 5 ; the value. (setq foo 6) ; Change the value ⇒ 6 ; in ‘b1’.

     foo ⇒ 6

;; In buffer ‘b2’, the value hasn’t changed.

     (save-excursion
       (set-buffer "b2")
       foo)
          ⇒ 5

Making a variable buffer-local within a let-binding for that variable does not work. This is because let does not distinguish between different kinds of bindings; it knows only which variable the binding was made for.

If the variable is terminal-local, this function signals an error. Such variables cannot have buffer-local bindings as well. See Section 26.2 [Multiple Displays], page 409. Note: do not use make-local-variable for a hook variable. Instead, use make-local-hook. See Section 20.4 [Hooks], page 316.

Command make-variable-buffer-local variable

This function marks variable (a symbol) automatically buffer-local, so that any subsequent attempt to set it will make it local to the current buffer at the time. The value returned is variable. Note: It is a mistake to use make-variable-buffer-local for user-option variables, simply because users might want to customize them differently in different buffers. Users can make any variable local, when they wish to. The main use of make-variable-buffer-local is when a variable is used for internal purposes, and the Lisp program depends on having separate values in separate buffers.

Function local-variable-p variable &optional buffer This returns t if variable is buffer-local in buffer buffer (which defaults to the current buffer); otherwise, nil.

Function buffer-local-variables &optional buffer

This function returns a list describing the buffer-local variables in buffer buffer. It returns an association list (see Section 5.8 [Association Lists], page 74) in which each association contains one buffer-local variable and its value. When a buffer-local variable is void in buffer, then it appears directly in the resulting list. If buffer is omitted, the current buffer is used.

     (make-local-variable 'foobar)
     (makunbound 'foobar)
     (make-local-variable 'bind-me)
     (setq bind-me 69)
     (setq lcl (buffer-local-variables))

;; First, built-in variables local in all buffers:

     ⇒ ((mark-active . nil)
         (buffer-undo-list nil)
         (mode-name . "Fundamental")

…

;; Next, non-built-in local variables.

;; This one is local and void:

         foobar

;; This one is local and nonvoid:

         (bind-me . 69))

Note that storing new values into the cdrs of cons cells in this list does not change the local values of the variables.

Command kill-local-variable variable

This function deletes the buffer-local binding (if any) for variable (a symbol) in the current buffer. As a result, the global (default) binding of variable becomes visible in this buffer. Usually this results in a change in the value of variable, since the global value is usually different from the buffer-local value just eliminated. If you kill the local binding of a variable that automatically becomes local when set, this makes the global value visible in the current buffer. However, if you set the variable again, that will once again create a local binding for it.

kill-local-variable returns variable.

This function is a command because it is sometimes useful to kill one bufferlocal variable interactively, just as it is useful to create buffer-local variables interactively.

Function kill-all-local-variables

This function eliminates all the buffer-local variable bindings of the current buffer except for variables marked as “permanent”. As a result, the buffer will see the default values of most variables. This function also resets certain other information pertaining to the buffer: it sets the local keymap to nil, the syntax table to the value of standard-syntax-

table, and the abbrev table to the value of fundamental-mode-abbrev-table.

Every major mode command begins by calling this function, which has the effect of switching to Fundamental mode and erasing most of the effects of the previous major mode. To ensure that this does its job, the variables that major modes set should not be marked permanent.

kill-all-local-variables returns nil.

A local variable is permanent if the variable name (a symbol) has a permanent-local property that is non-nil. Permanent locals are appropriate for data pertaining to where the file came from or how to save it, rather than with how to edit the contents.

10.10.3 The Default Value of a Buffer-Local Variable

The global value of a variable with buffer-local bindings is also called the default value, because it is the value that is in effect except when specifically overridden.

The functions default-value and setq-default access and change a variable’s default value regardless of whether the current buffer has a buffer-local binding. For example, you could use setq-default to change the default setting of paragraph-start for most buffers; and this would work even when you are in a C or Lisp mode buffer that has a buffer-local value for this variable.

The special forms defvar and defconst also set the default value (if they set the variable at all), rather than any local value.

Function default-value symbol

This function returns symbol’s default value. This is the value that is seen in buffers that do not have their own values for this variable. If symbol is not buffer-local, this is equivalent to symbol-value (see Section 10.7 [Accessing Variables], page 128).

Function default-boundp symbol

The function default-boundp tells you whether symbol’s default value is non-

void. If (default-boundp 'foo) returns nil, then (default-value 'foo)

would get an error.

default-boundp is to default-value as boundp is to symbol-value.

Special Form setq-default symbol value

This sets the default value of symbol to value. It does not evaluate symbol, but does evaluate value. The value of the setq-default form is value. If a symbol is not buffer-local for the current buffer, and is not marked automatically buffer-local, setq-default has the same effect as setq. If symbol is buffer-local for the current buffer, then this changes the value that other buffers will see (as long as they don’t have a buffer-local value), but not the value that the current buffer sees.

;; In buffer ‘foo’:

(make-local-variable 'local)
     ⇒ local
(setq local 'value-in-foo)
     ⇒ value-in-foo
(setq-default local 'new-default)
     ⇒ new-default
local
     ⇒ value-in-foo
(default-value 'local)
     ⇒ new-default

;; In (the new) buffer ‘bar’:

local
     ⇒ new-default
(default-value 'local)
     ⇒ new-default
(setq local 'another-default)
     ⇒ another-default
(default-value 'local)
     ⇒ another-default

;; Back in buffer ‘foo’:

local
     ⇒ value-in-foo
(default-value 'local)
     ⇒ another-default

Function set-default symbol value

This function is like setq-default, except that symbol is evaluated.

(set-default (car '(a b c)) 23)
     ⇒ 23
(default-value 'a)
     ⇒ 23

11 Functions

A Lisp program is composed mainly of Lisp functions. This chapter explains what functions are, how they accept arguments, and how to define them.

11.1 What Is a Function?

In a general sense, a function is a rule for carrying on a computation given several values called arguments. The result of the computation is called the value of the function. The computation can also have side effects: lasting changes in the values of variables or the contents of data structures.

Here are important terms for functions in Emacs Lisp and for other function-like objects.

function In Emacs Lisp, a function is anything that can be applied to arguments in a Lisp program. In some cases, we use it more specifically to mean a function written in Lisp. Special forms and macros are not functions.

primitive A primitive is a function callable from Lisp that is written in C, such as car or append. These functions are also called built-in functions or subrs. (Special forms are also considered primitives.) Usually the reason that a function is a primitives is because it is fundamental, because it provides a low-level interface to operating system services, or because it needs to run fast. Primitives can be modified or added only by changing the C sources and recompiling the editor. See Section B.4 [Writing Emacs Primitives], page 614.

lambda expression A lambda expression is a function written in Lisp. These are described in the following section.

special form A special form is a primitive that is like a function but does not evaluate all of its arguments in the usual way. It may evaluate only some of the arguments, or may evaluate them in an unusual order, or several times. Many special forms are described in Chapter 9 [Control Structures], page 105.

macro A macro is a construct defined in Lisp by the programmer. It differs from a function in that it translates a Lisp expression that you write into an equivalent expression to be evaluated instead of the original expression. Macros enable Lisp programmers to do the sorts of things that special forms can do. See Chapter 12 [Macros], page 153, for how to define and use macros.

command A command is an object that command-execute can invoke; it is a possible definition for a key sequence. Some functions are commands; a function written in Lisp is a command if it contains an interactive declaration (see Section 18.2 [Defining Commands], page 244). Such a function can be called from Lisp expressions like other functions; in this case, the fact that the function is a command makes no difference.

Keyboard macros (strings and vectors) are commands also, even though they are not functions. A symbol is a command if its function definition is a command; such symbols can be invoked with M-x. The symbol is a function as well if the definition is a function. See Section 18.1 [Command Overview], page 243.

keystroke command A keystroke command is a command that is bound to a key sequence (typically one to three keystrokes). The distinction is made here merely to avoid confusion with the meaning of “command” in non-Emacs editors; for Lisp programs, the distinction is normally unimportant.

byte-code function A byte-code function is a function that has been compiled by the byte compiler. See Section 2.3.13 [Byte-Code Type], page 25.

Function subrp object

This function returns t if object is a built-in function (i.e., a Lisp primitive).

          (subrp 'message)            ; message is a symbol,

⇒ nil ; not a subr object.

          (subrp (symbol-function 'message))
               ⇒ t

Function byte-code-function-p object

This function returns t if object is a byte-code function. For example:

          (byte-code-function-p (symbol-function 'next-line))
               ⇒ t

11.2 Lambda Expressions

A function written in Lisp is a list that looks like this:

(lambda (arg-variables…) [documentation-string] [interactive-declaration] body-forms…)

Such a list is called a lambda expression. In Emacs Lisp, it actually is valid as an expression—it evaluates to itself. In some other Lisp dialects, a lambda expression is not a valid expression at all. In either case, its main use is not to be evaluated as an expression, but to be called as a function.

11.2.1 Components of a Lambda Expression

The first element of a lambda expression is always the symbol lambda. This indicates that the list represents a function. The reason functions are defined to start with lambda is so that other lists, intended for other uses, will not accidentally be valid as functions.

The second element is a list of symbols–the argument variable names. This is called the lambda list. When a Lisp function is called, the argument values are matched up against the variables in the lambda list, which are given local bindings with the values provided. See Section 10.3 [Local Variables], page 122.

The documentation string is a Lisp string object placed within the function definition to describe the function for the Emacs help facilities. See Section 11.2.4 [Function Documentation], page 143.

The interactive declaration is a list of the form (interactive code-string). This declares how to provide arguments if the function is used interactively. Functions with this declaration are called commands; they can be called using M-x or bound to a key. Functions not intended to be called in this way should not have interactive declarations. See Section 18.2 [Defining Commands], page 244, for how to write an interactive declaration.

The rest of the elements are the body of the function: the Lisp code to do the work of the function (or, as a Lisp programmer would say, “a list of Lisp forms to evaluate”). The value returned by the function is the value returned by the last element of the body.

11.2.2 A Simple Lambda-Expression Example

Consider for example the following function:

     (lambda (a b c) (+ a b c))

We can call this function by writing it as the car of an expression, like this:

     ((lambda (a b c) (+ a b c))
      1 2 3)

This call evaluates the body of the lambda expression with the variable a bound to 1, b bound to 2, and c bound to 3. Evaluation of the body adds these three numbers, producing the result 6; therefore, this call to the function returns the value 6.

Note that the arguments can be the results of other function calls, as in this example:

     ((lambda (a b c) (+ a b c))
      1 (* 2 3) (- 5 4))

This evaluates the arguments 1, (* 2 3), and (- 5 4) from left to right. Then it applies the lambda expression to the argument values 1, 6 and 1 to produce the value 8.

It is not often useful to write a lambda expression as the car of a form in this way. You can get the same result, of making local variables and giving them values, using the special form let (see Section 10.3 [Local Variables], page 122). And let is clearer and easier to use. In practice, lambda expressions are either stored as the function definitions of symbols, to produce named functions, or passed as arguments to other functions (see Section 11.7 [Anonymous Functions], page 148).

However, calls to explicit lambda expressions were very useful in the old days of Lisp, before the special form let was invented. At that time, they were the only way to bind and initialize local variables.

11.2.3 Advanced Features of Argument Lists

Our simple sample function, (lambda (a b c) (+ a b c)), specifies three argument variables, so it must be called with three arguments: if you try to call it with only two arguments or four arguments, you get a wrong-number-of-arguments error.

It is often convenient to write a function that allows certain arguments to be omitted. For example, the function substring accepts three arguments—a string, the start index and the end index—but the third argument defaults to the length of the string if you omit it. It is also convenient for certain functions to accept an indefinite number of arguments, as the functions list and + do.

To specify optional arguments that may be omitted when a function is called, simply include the keyword &optional before the optional arguments. To specify a list of zero or more extra arguments, include the keyword &rest before one final argument.

Thus, the complete syntax for an argument list is as follows:

(required-vars…

[&optional optional-vars…]

[&rest rest-var]) The square brackets indicate that the &optional and &rest clauses, and the variables that follow them, are optional.

A call to the function requires one actual argument for each of the required-vars. There may be actual arguments for zero or more of the optional-vars, and there cannot be any actual arguments beyond that unless the lambda list uses &rest. In that case, there may be any number of extra actual arguments.

If actual arguments for the optional and rest variables are omitted, then they always default to nil. There is no way for the function to distinguish between an explicit argument of nil and an omitted argument. However, the body of the function is free to consider nil an abbreviation for some other meaningful value. This is what substring does; nil as the third argument to substring means to use the length of the string supplied.

Common Lisp note: Common Lisp allows the function to specify what default value to use when an optional argument is omitted; Emacs Lisp always uses

     nil.

For example, an argument list that looks like this:

     (a b &optional c d &rest e)

binds a and b to the first two actual arguments, which are required. If one or two more arguments are provided, c and d are bound to them respectively; any arguments after the first four are collected into a list and e is bound to that list. If there are only two arguments, c is nil; if two or three arguments, d is nil; if four arguments or fewer, e is nil.

There is no way to have required arguments following optional ones—it would not make sense. To see why this must be so, suppose that c in the example were optional and d were required. Suppose three actual arguments are given; which variable would the third argument be for? Similarly, it makes no sense to have any more arguments (either required or optional) after a &rest argument.

Here are some examples of argument lists and proper calls:

     ((lambda (n) (1+ n))                ; One required:

1) ; requires exactly one argument.

          ⇒ 2

((lambda (n &optional n1) ; One required and one optional:

              (if n1 (+ n n1) (1+ n)))   ; 1 or 2 arguments.
      1 2)

          ⇒ 3

((lambda (n &rest ns) ; One required and one rest:

              (+ n (apply '+ ns)))       ; 1 or more arguments.
      1 2 3 4 5)
          ⇒ 15

11.2.4 Documentation Strings of Functions

A lambda expression may optionally have a documentation string just after the lambda list. This string does not affect execution of the function; it is a kind of comment, but a systematized comment which actually appears inside the Lisp world and can be used by the Emacs help facilities. See Chapter 21 [Documentation], page 319, for how the documentation-string is accessed.

It is a good idea to provide documentation strings for all the functions in your program, even those that are only called from within your program. Documentation strings are like comments, except that they are easier to access.

The first line of the documentation string should stand on its own, because apropos displays just this first line. It should consist of one or two complete sentences that summarize the function’s purpose.

The start of the documentation string is usually indented in the source file, but since these spaces come before the starting double-quote, they are not part of the string. Some people make a practice of indenting any additional lines of the string so that the text lines up in the program source. This is a mistake. The indentation of the following lines is inside the string; what looks nice in the source code will look ugly when displayed by the help commands.

You may wonder how the documentation string could be optional, since there are required components of the function that follow it (the body). Since evaluation of a string returns that string, without any side effects, it has no effect if it is not the last form in the body. Thus, in practice, there is no confusion between the first form of the body and the documentation string; if the only body form is a string then it serves both as the return value and as the documentation.

11.3 Naming a Function

In most computer languages, every function has a name; the idea of a function without a name is nonsensical. In Lisp, a function in the strictest sense has no name. It is simply a list whose first element is lambda, or a primitive subr-object.

However, a symbol can serve as the name of a function. This happens when you put the function in the symbol’s function cell (see Section 7.1 [Symbol Components], page 87). Then the symbol itself becomes a valid, callable function, equivalent to the list or subrobject that its function cell refers to. The contents of the function cell are also called the symbol’s function definition. The procedure of using a symbol’s function definition in place of the symbol is called symbol function indirection; see Section 8.2.4 [Function Indirection], page 99.

In practice, nearly all functions are given names in this way and referred to through their names. For example, the symbol car works as a function and does what it does because the primitive subr-object #<subr car> is stored in its function cell.

We give functions names because it is convenient to refer to them by their names in Lisp expressions. For primitive subr-objects such as #<subr car>, names are the only way you can refer to them: there is no read syntax for such objects. For functions written in Lisp, the name is more convenient to use in a call than an explicit lambda expression. Also, a function with a name can refer to itself—it can be recursive. Writing the function’s name in its own definition is much more convenient than making the function definition point to itself (something that is not impossible but that has various disadvantages in practice).

We often identify functions with the symbols used to name them. For example, we often speak of “the function car”, not distinguishing between the symbol car and the primitive subr-object that is its function definition. For most purposes, there is no need to distinguish.

Even so, keep in mind that a function need not have a unique name. While a given function object usually appears in the function cell of only one symbol, this is just a matter of convenience. It is easy to store it in several symbols using fset; then each of the symbols is equally well a name for the same function.

A symbol used as a function name may also be used as a variable; these two uses of a symbol are independent and do not conflict.

11.4 Defining Functions

We usually give a name to a function when it is first created. This is called defining a function, and it is done with the defun special form.

Special Form defun name argument-list body-forms defun is the usual way to define new Lisp functions. It defines the symbol name as a function that looks like this:

(lambda argument-list . body-forms) defun stores this lambda expression in the function cell of name. It returns the value name, but usually we ignore this value. As described previously (see Section 11.2 [Lambda Expressions], page 140), argument-list is a list of argument names and may include the keywords &optional and &rest. Also, the first two forms in body-forms may be a documentation string and an interactive declaration. There is no conflict if the same symbol name is also used as a variable, since the symbol’s value cell is independent of the function cell. See Section 7.1 [Symbol Components], page 87. Here are some examples:

          (defun foo () 5)
               ⇒ foo
          (foo)⇒ 5
          (defun bar (a &optional b &rest c)
              (list a b c))
               ⇒ bar
          (bar 1 2 3 4 5) ⇒ (1 2 (3 4 5))

     (bar 1)
          ⇒ (1 nil nil)
     (bar)
      error Wrong number of arguments.
     (defun capitalize-backwards ()
       "Upcase the last letter of a word."
       (interactive)
       (backward-word 1)
       (forward-word 1)
       (backward-char 1)
       (capitalize-word 1))
          ⇒ capitalize-backwards

Be careful not to redefine existing functions unintentionally. defun redefines even primitive functions such as car without any hesitation or notification. Redefining a function already defined is often done deliberately, and there is no way to distinguish deliberate redefinition from unintentional redefinition.

Function defalias name definition This special form defines the symbol name as a function, with definition definition (which can be any valid Lisp function).

The proper place to use defalias is where a specific function name is being defined—especially where that name appears explicitly in the source file being loaded. This is because defalias records which file defined the function, just like defun (see Section 13.5 [Unloading], page 168).

By contrast, in programs that manipulate function definitions for other purposes, it is better to use fset, which does not keep such records.

See also defsubst, which defines a function like defun and tells the Lisp compiler to open-code it. See Section 11.9 [Inline Functions], page 151.

11.5 Calling Functions

Defining functions is only half the battle. Functions don’t do anything until you call them, i.e., tell them to run. Calling a function is also known as invocation.

The most common way of invoking a function is by evaluating a list. For example, evaluating the list (concat "a" "b") calls the function concat with arguments "a" and "b". See Chapter 8 [Evaluation], page 95, for a description of evaluation.

When you write a list as an expression in your program, the function name is part of the program. This means that you choose which function to call, and how many arguments to give it, when you write the program. Usually that’s just what you want. Occasionally you need to decide at run time which function to call. To do that, use the functions funcall

and apply.

Function funcall function &rest arguments funcall calls function with arguments, and returns whatever function returns.

Since funcall is a function, all of its arguments, including function, are evaluated before funcall is called. This means that you can use any expression to obtain the function to be called. It also means that funcall does not see the expressions you write for the arguments, only their values. These values are not evaluated a second time in the act of calling function; funcall enters the normal procedure for calling a function at the place where the arguments have already been evaluated.

The argument function must be either a Lisp function or a primitive function. Special forms and macros are not allowed, because they make sense only when given the “unevaluated” argument expressions. funcall cannot provide these because, as we saw above, it never knows them in the first place.

     (setq f 'list)
          ⇒ list
     (funcall f 'x 'y 'z)
          ⇒ (x y z)
     (funcall f 'x 'y '(z))
          ⇒ (x y (z))
     (funcall 'and t nil)
      error Invalid function: #<subr and>

Compare these example with the examples of apply.

Function apply function &rest arguments apply calls function with arguments, just like funcall but with one difference: the last of arguments is a list of arguments to give to function, rather than a single argument. We also say that apply spreads this list so that each individual element becomes an argument.

apply returns the result of calling function. As with funcall, function must either be a Lisp function or a primitive function; special forms and macros do not make sense in apply.

     (setq f 'list)
          ⇒ list
     (apply f 'x 'y 'z)
      error Wrong type argument: listp, z
     (apply '+ 1 2 '(3 4)) ⇒ 10
     (apply '+ '(1 2 3 4)) ⇒ 10
     (apply 'append '((a b c) nil (x y z) nil))
          ⇒ (a b c x y z)

For an interesting example of using apply, see the description of mapcar, in Section 11.6 [Mapping Functions], page 147.

It is common for Lisp functions to accept functions as arguments or find them in data structures (especially in hook variables and property lists) and call them using funcall or apply. Functions that accept function arguments are often called functionals.

Sometimes, when you call a functional, it is useful to supply a no-op function as the argument. Here are two different kinds of no-op function:

Function identity arg

This function returns arg and has no side effects.

Function ignore &rest args This function ignores any arguments and returns nil.

11.6 Mapping Functions

A mapping function applies a given function to each element of a list or other collection. Emacs Lisp has three such functions; mapcar and mapconcat, which scan a list, are described here. For the third mapping function, mapatoms, see Section 7.3 [Creating Symbols], page 89.

Function mapcar function sequence mapcar applies function to each element of sequence in turn, and returns a list of the results. The argument sequence may be a list, a vector, or a string. The result is always a list. The length of the result is the same as the length of sequence. For example:

     (mapcar 'car '((a b) (c d) (e f)))
          ⇒ (a c e)
     (mapcar '1+ [1 2 3])
          ⇒ (2 3 4)
     (mapcar 'char-to-string "abc")
          ⇒ ("a" "b" "c")

;; Call each function in my-hooks.

     (mapcar 'funcall my-hooks)
     (defun mapcar* (f &rest args)
       "Apply FUNCTION to successive cars of all ARGS.
     Return the list of results."

;; If no list is exhausted,

       (if (not (memq 'nil args))

;; apply function to CARs.

           (cons (apply f (mapcar 'car args))
                 (apply 'mapcar* f

;; Recurse for rest of elements.

                        (mapcar 'cdr args)))))
     (mapcar* 'cons '(a b c) '(1 2 3 4))
          ⇒ ((a . 1) (b . 2) (c . 3))

Function mapconcat function sequence separator mapconcat applies function to each element of sequence: the results, which must be strings, are concatenated. Between each pair of result strings, mapconcat inserts the string separator. Usually separator contains a space or comma or other suitable punctuation. The argument function must be a function that can take one argument and return a string.

          (mapconcat 'symbol-name
                     '(The cat in the hat)
                     " ")
               ⇒ "The cat in the hat"
          (mapconcat (function (lambda (x) (format "%c" (1+ x))))
                     "HAL-8000"
                     "")
               ⇒ "IBM.9111"

11.7 Anonymous Functions

In Lisp, a function is a list that starts with lambda, a byte-code function compiled from such a list, or alternatively a primitive subr-object; names are “extra”. Although usually functions are defined with defun and given names at the same time, it is occasionally more concise to use an explicit lambda expression—an anonymous function. Such a list is valid wherever a function name is.

Any method of creating such a list makes a valid function. Even this:

     (setq silly (append '(lambda (x)) (list (list '+ (* 3 4) 'x))))
     ⇒ (lambda (x) (+ 12 x))

This computes a list that looks like (lambda (x) (+ 12 x)) and makes it the value (not the function definition!) of silly.

Here is how we might call this function:

     (funcall silly 1)
     ⇒ 13

(It does not work to write (silly 1), because this function is not the function definition of silly. We have not given silly any function definition, just a value as a variable.)

Most of the time, anonymous functions are constants that appear in your program. For example, you might want to pass one as an argument to the function mapcar, which applies any given function to each element of a list. Here we pass an anonymous function that multiplies a number by two:

     (defun double-each (list)
       (mapcar '(lambda (x) (* 2 x)) list))
     ⇒ double-each
     (double-each '(2 11))
     ⇒ (4 22)

In such cases, we usually use the special form function instead of simple quotation to quote the anonymous function.

Special Form function function-object This special form returns function-object without evaluating it. In this, it is equivalent to quote. However, it serves as a note to the Emacs Lisp compiler that function-object is intended to be used only as a function, and therefore can safely be compiled. Contrast this with quote, in Section 8.3 [Quoting], page 102.

Using function instead of quote makes a difference inside a function or macro that you are going to compile. For example:

     (defun double-each (list)
       (mapcar (function (lambda (x) (* 2 x))) list))
     ⇒ double-each
     (double-each '(2 11))
     ⇒ (4 22)

If this definition of double-each is compiled, the anonymous function is compiled as well. By contrast, in the previous definition where ordinary quote is used, the argument passed to mapcar is the precise list shown:

     (lambda (x) (* x 2))

The Lisp compiler cannot assume this list is a function, even though it looks like one, since it does not know what mapcar does with the list. Perhaps mapcar will check that the car of the third element is the symbol *! The advantage of function is that it tells the compiler to go ahead and compile the constant function.

We sometimes write function instead of quote when quoting the name of a function, but this usage is just a sort of comment.

(function symbol) ≡ (quote symbol) ≡ 'symbol See documentation in Section 21.2 [Accessing Documentation], page 320, for a realistic

example using function and an anonymous function.

11.8 Accessing Function Cell Contents

The function definition of a symbol is the object stored in the function cell of the symbol. The functions described here access, test, and set the function cell of symbols.

See also the function indirect-function in Section 8.2.4 [Function Indirection], page 99.

Function symbol-function symbol

This returns the object in the function cell of symbol. If the symbol’s function cell is void, a void-function error is signaled. This function does not check that the returned object is a legitimate function.

          (defun bar (n) (+ n 2))
               ⇒ bar
          (symbol-function 'bar)
               ⇒ (lambda (n) (+ n 2))
          (fset 'baz 'bar)
               ⇒ bar
          (symbol-function 'baz)
               ⇒ bar

If you have never given a symbol any function definition, we say that that symbol’s function cell is void. In other words, the function cell does not have any Lisp object in it. If you try to call such a symbol as a function, it signals a void-function error.

Note that void is not the same as nil or the symbol void. The symbols nil and void are Lisp objects, and can be stored into a function cell just as any other object can be (and they can be valid functions if you define them in turn with defun). A void function cell contains no object whatsoever.

You can test the voidness of a symbol’s function definition with fboundp. After you have given a symbol a function definition, you can make it void once more using fmakunbound.

Function fboundp symbol

This function returns t if the symbol has an object in its function cell, nil otherwise. It does not check that the object is a legitimate function.

Function fmakunbound symbol

This function makes symbol’s function cell void, so that a subsequent attempt to access this cell will cause a void-function error. (See also makunbound, in Section 10.3 [Local Variables], page 122.)

     (defun foo (x) x)
          ⇒ x
     (foo 1) ⇒1
     (fmakunbound 'foo)
          ⇒ x
     (foo 1)
      error Symbol's function definition is void: foo

Function fset symbol object This function stores object in the function cell of symbol. The result is object. Normally object should be a function or the name of a function, but this is not checked. There are three normal uses of this function:

• Copying one symbol’s function definition to another. (In other words, making an alternate name for a function.)

• Giving a symbol a function definition that is not a list and therefore cannot be made with defun. For example, you can use fset to give a symbol s1 a function definition which is another symbol s2; then s1 serves as an alias for whatever definition s2 presently has.

• In constructs for defining or altering functions. If defun were not a primitive, it could be written in Lisp (as a macro) using fset.

Here are examples of the first two uses:

;; Give first the same definition car has.

     (fset 'first (symbol-function 'car))
          ⇒ #<subr car>
     (first '(1 2 3)) ⇒ 1

;; Make the symbol car the function definition of xfirst.

          (fset 'xfirst 'car)
               ⇒ car
          (xfirst '(1 2 3)) ⇒ 1
          (symbol-function 'xfirst)
               ⇒ car
          (symbol-function (symbol-function 'xfirst))
               ⇒ #<subr car>

;; Define a named keyboard macro.

          (fset 'kill-two-lines "\^u2\^k")
               ⇒ "\^u2\^k"

See also the related function defalias, in Section 11.4 [Defining Functions], page 144.

When writing a function that extends a previously defined function, the following idiom is sometimes used:

     (fset 'old-foo (symbol-function 'foo))
     (defun foo ()
       "Just like old-foo, except more so."
       (old-foo) (more-so))

This does not work properly if foo has been defined to autoload. In such a case, when foo calls old-foo, Lisp attempts to define old-foo by loading a file. Since this presumably defines foo rather than old-foo, it does not produce the proper results. The only way to avoid this problem is to make sure the file is loaded before moving aside the old definition

of foo.

But it is unmodular and unclean, in any case, for a Lisp file to redefine a function defined elsewhere.

11.9 Inline Functions

You can define an inline function by using defsubst instead of defun. An inline function works just like an ordinary function except for one thing: when you compile a call to the function, the function’s definition is open-coded into the caller.

Making a function inline makes explicit calls run faster. But it also has disadvantages. For one thing, it reduces flexibility; if you change the definition of the function, calls already inlined still use the old definition until you recompile them. Since the flexibility of redefining functions is an important feature of Emacs, you should not make a function inline unless its speed is really crucial.

Another disadvantage is that making a large function inline can increase the size of compiled code both in files and in memory. Since the speed advantage of inline functions is greatest for small functions, you generally should not make large functions inline.

It’s possible to define a macro to expand into the same code that an inline function would execute. But the macro would have a limitation: you can use it only explicitly—a macro cannot be called with apply, mapcar and so on. Also, it takes some work to convert an ordinary function into a macro. (See Chapter 12 [Macros], page 153.) To convert it into an inline function is very easy; simply replace defun with defsubst. Since each argument of an inline function is evaluated exactly once, you needn’t worry about how many times the body uses the arguments, as you do for macros. (See Section 12.6.1 [Argument Evaluation], page 156.)

Inline functions can be used and open-coded later on in the same file, following the definition, just like macros.

11.10 Other Topics Related to Functions

Here is a table of several functions that do things related to function calling and function definitions. They are documented elsewhere, but we provide cross references here. apply See Section 11.5 [Calling Functions], page 145. autoload See Section 13.2 [Autoload], page 164.

call-interactively

See Section 18.3 [Interactive Call], page 248.

commandp See Section 18.3 [Interactive Call], page 248.

documentation

See Section 21.2 [Accessing Documentation], page 320.

eval See Section 8.1 [Eval], page 96. funcall See Section 11.5 [Calling Functions], page 145. ignore See Section 11.5 [Calling Functions], page 145.

indirect-function

See Section 8.2.4 [Function Indirection], page 99.

interactive

See Section 18.2.1 [Using Interactive], page 244.

interactive-p

See Section 18.3 [Interactive Call], page 248.

mapatoms See Section 7.3 [Creating Symbols], page 89. mapcar See Section 11.6 [Mapping Functions], page 147.

mapconcat

See Section 11.6 [Mapping Functions], page 147.

undefined

See Section 19.7 [Key Lookup], page 284.

12 Macros

Macros enable you to define new control constructs and other language features. A macro is defined much like a function, but instead of telling how to compute a value, it tells how to compute another Lisp expression which will in turn compute the value. We call this expression the expansion of the macro.

Macros can do this because they operate on the unevaluated expressions for the arguments, not on the argument values as functions do. They can therefore construct an expansion containing these argument expressions or parts of them.

If you are using a macro to do something an ordinary function could do, just for the sake of speed, consider using an inline function instead. See Section 11.9 [Inline Functions], page 151.

12.1 A Simple Example of a Macro

Suppose we would like to define a Lisp construct to increment a variable value, much like the ++ operator in C. We would like to write (inc x) and have the effect of (setq x (1+ x)). Here’s a macro definition that does the job:

     (defmacro inc (var)
        (list 'setq var (list '1+ var)))

When this is called with (inc x), the argument var has the value x—not the value of x. The body of the macro uses this to construct the expansion, which is (setq x (1+ x)). Once the macro definition returns this expansion, Lisp proceeds to evaluate it, thus incrementing x.

12.2 Expansion of a Macro Call

A macro call looks just like a function call in that it is a list which starts with the name of the macro. The rest of the elements of the list are the arguments of the macro.

Evaluation of the macro call begins like evaluation of a function call except for one crucial difference: the macro arguments are the actual expressions appearing in the macro call. They are not evaluated before they are given to the macro definition. By contrast, the arguments of a function are results of evaluating the elements of the function call list.

Having obtained the arguments, Lisp invokes the macro definition just as a function is invoked. The argument variables of the macro are bound to the argument values from the macro call, or to a list of them in the case of a &rest argument. And the macro body executes and returns its value just as a function body does.

The second crucial difference between macros and functions is that the value returned by the macro body is not the value of the macro call. Instead, it is an alternate expression for computing that value, also known as the expansion of the macro. The Lisp interpreter proceeds to evaluate the expansion as soon as it comes back from the macro.

Since the expansion is evaluated in the normal manner, it may contain calls to other macros. It may even be a call to the same macro, though this is unusual.

You can see the expansion of a given macro call by calling macroexpand.

Function macroexpand form &optional environment This function expands form, if it is a macro call. If the result is another macro call, it is expanded in turn, until something which is not a macro call results. That is the value returned by macroexpand. If form is not a macro call to begin with, it is returned as given. Note that macroexpand does not look at the subexpressions of form (although some macro definitions may do so). Even if they are macro calls themselves, macroexpand does not expand them. The function macroexpand does not expand calls to inline functions. Normally there is no need for that, since a call to an inline function is no harder to understand than a call to an ordinary function. If environment is provided, it specifies an alist of macro definitions that shadow the currently defined macros. Byte compilation uses this feature.

          (defmacro inc (var)
              (list 'setq var (list '1+ var)))
               ⇒ inc
          (macroexpand '(inc r))
               ⇒ (setq r (1+ r))
          (defmacro inc2 (var1 var2)
              (list 'progn (list 'inc var1) (list 'inc var2)))
               ⇒ inc2
          (macroexpand '(inc2 r s))
               ⇒ (progn (inc r) (inc s))  ; inc not expanded here.

12.3 Macros and Byte Compilation

You might ask why we take the trouble to compute an expansion for a macro and then evaluate the expansion. Why not have the macro body produce the desired results directly? The reason has to do with compilation.

When a macro call appears in a Lisp program being compiled, the Lisp compiler calls the macro definition just as the interpreter would, and receives an expansion. But instead of evaluating this expansion, it compiles the expansion as if it had appeared directly in the program. As a result, the compiled code produces the value and side effects intended for the macro, but executes at full compiled speed. This would not work if the macro body computed the value and side effects itself—they would be computed at compile time, which is not useful.

In order for compilation of macro calls to work, the macros must be defined in Lisp when the calls to them are compiled. The compiler has a special feature to help you do this: if a file being compiled contains a defmacro form, the macro is defined temporarily for the rest of the compilation of that file. To use this feature, you must define the macro in the same file where it is used and before its first use.

Byte-compiling a file executes any require calls at top-level in the file. This is in case the file needs the required packages for proper compilation. One way to ensure that necessary macro definitions are available during compilation is to require the files that define them (see Section 13.4 [Named Features], page 166). To avoid loading the macro definition files when someone runs the compiled program, write eval-when-compile around the require calls (see Section 14.5 [Eval During Compile], page 175).

12.4 Defining Macros

A Lisp macro is a list whose car is macro. Its cdr should be a function; expansion of the macro works by applying the function (with apply) to the list of unevaluated argumentexpressions from the macro call.

It is possible to use an anonymous Lisp macro just like an anonymous function, but this is never done, because it does not make sense to pass an anonymous macro to functionals such as mapcar. In practice, all Lisp macros have names, and they are usually defined with the special form defmacro.

Special Form defmacro name argument-list body-forms…

defmacro defines the symbol name as a macro that looks like this:

(macro lambda argument-list . body-forms) This macro object is stored in the function cell of name. The value returned by evaluating the defmacro form is name, but usually we ignore this value. The shape and meaning of argument-list is the same as in a function, and the keywords &rest and &optional may be used (see Section 11.2.3 [Argument List], page 141). Macros may have a documentation string, but any interactive declaration is ignored since macros cannot be called interactively.

12.5 Backquote

Macros often need to construct large list structures from a mixture of constants and nonconstant parts. To make this easier, use the macro ‘`’ (often called backquote).

Backquote allows you to quote a list, but selectively evaluate elements of that list. In the simplest case, it is identical to the special form quote (see Section 8.3 [Quoting], page 102). For example, these two forms yield identical results:

     `(a list of (+ 2 3) elements)
          ⇒ (a list of (+ 2 3) elements)
     '(a list of (+ 2 3) elements)
          ⇒ (a list of (+ 2 3) elements)

The special marker ‘,’ inside of the argument to backquote indicates a value that isn’t constant. Backquote evaluates the argument of ‘,’ and puts the value in the list structure:

     (list 'a 'list 'of (+ 2 3) 'elements)
          ⇒ (a list of 5 elements)
     `(a list of ,(+ 2 3) elements)
          ⇒ (a list of 5 elements)

You can also splice an evaluated value into the resulting list, using the special marker ‘,@’. The elements of the spliced list become elements at the same level as the other elements of the resulting list. The equivalent code without using ‘`’ is often unreadable. Here are some examples:

(setq some-list '(2 3))
     ⇒ (2 3)
(cons 1 (append some-list '(4) some-list))
     ⇒ (1 2 3 4 2 3)
`(1 ,@some-list 4 ,@some-list)
     ⇒ (1 2 3 4 2 3)
(setq list '(hack foo bar))
     ⇒ (hack foo bar)
(cons 'use
  (cons 'the
    (cons 'words (append (cdr list) '(as elements)))))
     ⇒ (use the words foo bar as elements)
`(use the words ,@(cdr list) as elements)
     ⇒ (use the words foo bar as elements)

Before Emacs version 19.29, ‘`’ used a different syntax which required an extra level of parentheses around the entire backquote construct. Likewise, each ‘,’ or ‘,@’ substition required an extra level of parentheses surrounding both the ‘,’ or ‘,@’ and the following expression. The old syntax required whitespace between the ‘`’, ‘,’ or ‘,@’ and the following expression. This syntax is still accepted, but no longer recommended except for compatibility with old Emacs versions.

12.6 Common Problems Using Macros

The basic facts of macro expansion have counterintuitive consequences. This section describes some important consequences that can lead to trouble, and rules to follow to avoid trouble.

12.6.1 Evaluating Macro Arguments Repeatedly

When defining a macro you must pay attention to the number of times the arguments will be evaluated when the expansion is executed. The following macro (used to facilitate iteration) illustrates the problem. This macro allows us to write a simple “for” loop such as one might find in Pascal.

(defmacro for (var from init to final do &rest body)
  "Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."
  (list 'let (list (list var init))
        (cons 'while (cons (list '<= var final)
                           (append body (list (list 'inc var)))))))
⇒ for
(for i from 1 to 3 do
   (setq square (* i i))
   (princ (format "\n%d %d" i square)))

↦

     (let ((i 1))
       (while (<= i 3)
         (setq square (* i i))
         (princ (format "%d      %d" i square))
         (inc i)))
     ⊣ 1       1 ⊣ 2       4 ⊣ 3       9 ⇒ nil

(The arguments from, to, and do in this macro are “syntactic sugar”; they are entirely ignored. The idea is that you will write noise words (such as from, to, and do) in those positions in the macro call.)

Here’s an equivalent definition simplified through use of backquote:

     (defmacro for (var from init to final do &rest body)
       "Execute a simple \"for\" loop.
     For example, (for i from 1 to 10 do (print i))."
       `(let ((,var ,init))
          (while (<= ,var ,final)
            ,@body
            (inc ,var))))

Both forms of this definition (with backquote and without) suffer from the defect that final is evaluated on every iteration. If final is a constant, this is not a problem. If it is a more complex form, say (long-complex-calculation x), this can slow down the execution significantly. If final has side effects, executing it more than once is probably incorrect.

A well-designed macro definition takes steps to avoid this problem by producing an expansion that evaluates the argument expressions exactly once unless repeated evaluation is part of the intended purpose of the macro. Here is a correct expansion for the for macro:

     (let ((i 1)
           (max 3))
       (while (<= i max)
         (setq square (* i i))
         (princ (format "%d      %d" i square))
         (inc i)))

Here is a macro definition that creates this expansion:

     (defmacro for (var from init to final do &rest body)
       "Execute a simple for loop: (for i from 1 to 10 do (print i))."
       `(let ((,var ,init)
              (max ,final))
          (while (<= ,var max)
            ,@body
            (inc ,var))))

Unfortunately, this introduces another problem.

12.6.2 Local Variables in Macro Expansions

The new definition of for has a new problem: it introduces a local variable named max which the user does not expect. This causes trouble in examples such as the following:

     (let ((max 0))
       (for x from 0 to 10 do
         (let ((this (frob x)))
           (if (< max this)
               (setq max this)))))

The references to max inside the body of the for, which are supposed to refer to the user’s binding of max, really access the binding made by for.

The way to correct this is to use an uninterned symbol instead of max (see Section 7.3 [Creating Symbols], page 89). The uninterned symbol can be bound and referred to just like any other symbol, but since it is created by for, we know that it cannot already appear in the user’s program. Since it is not interned, there is no way the user can put it into the program later. It will never appear anywhere except where put by for. Here is a definition of for that works this way:

     (defmacro for (var from init to final do &rest body)
       "Execute a simple for loop: (for i from 1 to 10 do (print i))."
       (let ((tempvar (make-symbol "max")))
         `(let ((,var ,init)
                (,tempvar ,final))
            (while (<= ,var ,tempvar)
              ,@body
              (inc ,var)))))

This creates an uninterned symbol named max and puts it in the expansion instead of the usual interned symbol max that appears in expressions ordinarily.

12.6.3 Evaluating Macro Arguments in Expansion

Another problem can happen if you evaluate any of the macro argument expressions during the computation of the expansion, such as by calling eval (see Section 8.1 [Eval], page 96). If the argument is supposed to refer to the user’s variables, you may have trouble if the user happens to use a variable with the same name as one of the macro arguments. Inside the macro body, the macro argument binding is the most local binding of this variable, so any references inside the form being evaluated do refer to it. Here is an example:

     (defmacro foo (a)
       (list 'setq (eval a) t))
          ⇒ foo
     (setq x 'b)
     (foo x) ↦ (setq b t)

⇒ t ; and b has been set. ;; but

     (setq a 'c)
     (foo a) ↦ (setq a t)

⇒ t ; but this set a, not c.

It makes a difference whether the user’s variable is named a or x, because a conflicts with the macro argument variable a.

Another reason not to call eval in a macro definition is that it probably won’t do what you intend in a compiled program. The byte-compiler runs macro definitions while compiling the program, when the program’s own computations (which you might have wished to access with eval) don’t occur and its local variable bindings don’t exist.

The safe way to work with the run-time value of an expression is to put the expression into the macro expansion, so that its value is computed as part of executing the expansion.

12.6.4 How Many Times is the Macro Expanded?

Occasionally problems result from the fact that a macro call is expanded each time it is evaluated in an interpreted function, but is expanded only once (during compilation) for a compiled function. If the macro definition has side effects, they will work differently depending on how many times the macro is expanded.

In particular, constructing objects is a kind of side effect. If the macro is called once, then the objects are constructed only once. In other words, the same structure of objects is used each time the macro call is executed. In interpreted operation, the macro is reexpanded each time, producing a fresh collection of objects each time. Usually this does not matter— the objects have the same contents whether they are shared or not. But if the surrounding program does side effects on the objects, it makes a difference whether they are shared. Here is an example:

     (defmacro empty-object ()
       (list 'quote (cons nil nil)))
     (defun initialize (condition)
       (let ((object (empty-object)))
         (if condition
             (setcar object condition))
         object))

If initialize is interpreted, a new list (nil) is constructed each time initialize is called. Thus, no side effect survives between calls. If initialize is compiled, then the macro empty-object is expanded during compilation, producing a single “constant” (nil) that is reused and altered each time initialize is called.

One way to avoid pathological cases like this is to think of empty-object as a funny kind of constant, not as a memory allocation construct. You wouldn’t use setcar on a constant such as '(nil), so naturally you won’t use it on (empty-object) either.

160 GNU Emacs Lisp Reference Manual

13 Loading

Loading a file of Lisp code means bringing its contents into the Lisp environment in the form of Lisp objects. Emacs finds and opens the file, reads the text, evaluates each form, and then closes the file.

The load functions evaluate all the expressions in a file just as the eval-current-buffer function evaluates all the expressions in a buffer. The difference is that the load functions read and evaluate the text in the file as found on disk, not the text in an Emacs buffer.

The loaded file must contain Lisp expressions, either as source code or as byte-compiled code. Each form in the file is called a top-level form. There is no special format for the forms in a loadable file; any form in a file may equally well be typed directly into a buffer and evaluated there. (Indeed, most code is tested this way.) Most often, the forms are function definitions and variable definitions.

A file containing Lisp code is often called a library. Thus, the “Rmail library” is a file containing code for Rmail mode. Similarly, a “Lisp library directory” is a directory of files containing Lisp code.

13.1 How Programs Do Loading

Emacs Lisp has several interfaces for loading. For example, autoload creates a placeholder object for a function in a file; trying to call the autoloading function loads the file to get the function’s real definition (see Section 13.2 [Autoload], page 164). require loads a file if it isn’t already loaded (see Section 13.4 [Named Features], page 166). Ultimately, all these facilities call the load function to do the work.

Function load filename &optional missing-ok nomessage nosuffix This function finds and opens a file of Lisp code, evaluates all the forms in it, and closes the file. To find the file, load first looks for a file named ‘filename.elc’, that is, for a file whose name is filename with ‘.elc’ appended. If such a file exists, it is loaded. If there is no file by that name, then load looks for a file named ‘filename.el’. If that file exists, it is loaded. Finally, if neither of those names is found, load looks for a file named filename with nothing appended, and loads it if it exists. (The load function is not clever about looking at filename. In the perverse case of a file named ‘foo.el.el’, evaluation of (load "foo.el") will indeed find it.) If the optional argument nosuffix is non-nil, then the suffixes ‘.elc’ and ‘.el’ are not tried. In this case, you must specify the precise file name you want. If filename is a relative file name, such as ‘foo’ or ‘baz/foo.bar’, load searches for the file using the variable load-path. It appends filename to each of the directories listed in load-path, and loads the first file it finds whose name matches. The current default directory is tried only if it is specified in loadpath, where nil stands for the default directory. load tries all three possible suffixes in the first directory in load-path, then all three suffixes in the second directory, and so on.

If you get a warning that ‘foo.elc’ is older than ‘foo.el’, it means you should consider recompiling ‘foo.el’. See Chapter 14 [Byte Compilation], page 171.

Messages like ‘Loading foo...’ and ‘Loading foo...done’ appear in the echo area during loading unless nomessage is non-nil.

Any unhandled errors while loading a file terminate loading. If the load was done for the sake of autoload, any function definitions made during the loading are undone.

If load can’t find the file to load, then normally it signals the error file-error (with ‘Cannot open load file filename’). But if missing-ok is non-nil, then load just returns nil.

You can use the variable load-read-function to specify a function for load to use instead of read for reading expressions. See below.

load returns t if the file loads successfully.

User Option load-path

The value of this variable is a list of directories to search when loading files with load. Each element is a string (which must be a directory name) or nil (which stands for the current working directory). The value of loadpath is initialized from the environment variable EMACSLOADPATH, if that exists; otherwise its default value is specified in ‘emacs/src/paths.h’ when Emacs is built.

The syntax of EMACSLOADPATH is the same as used for PATH; ‘:’ (or ‘;’, according to the operating system) separates directory names, and ‘.’ is used for the current default directory. Here is an example of how to set your EMACSLOADPATH variable from a csh ‘.login’ file:

     setenv EMACSLOADPATH .:/user/bil/emacs:/usr/lib/emacs/lisp

Here is how to set it using sh:

     export EMACSLOADPATH
     EMACSLOADPATH=.:/user/bil/emacs:/usr/local/lib/emacs/lisp

Here is an example of code you can place in a ‘.emacs’ file to add several directories to the front of your default load-path:

     (setq load-path
           (append (list nil "/user/bil/emacs"
                         "/usr/local/lisplib"
                         "~/emacs")
                   load-path))

In this example, the path searches the current working directory first, followed then by the ‘/user/bil/emacs’ directory, the ‘/usr/local/lisplib’ directory, and the ‘~/emacs’ directory, which are then followed by the standard directories for Lisp code.

The command line options ‘-l’ or ‘-load’ specify a Lisp library to load as part of Emacs startup. Since this file might be in the current directory, Emacs 18 temporarily adds the current directory to the front of load-path so the file can be found there. Newer Emacs versions also find such files in the current directory, but without altering load-path.

Dumping Emacs uses a special value of load-path. If the value of load-path at the end of dumping is unchanged (that is, still the same special value), the dumped Emacs switches to the ordinary load-path value when it starts up, as described above. But if load-path has any other value at the end of dumping, that value is used for execution of the dumped Emacs also.

Therefore, if you want to change load-path temporarily for loading a few li-

braries in ‘site-init.el’ or ‘site-load.el’, you should bind load-path lo-

cally with let around the calls to load.

The default value of load-path, when running an Emacs which has been installed on the system, looks like this:

("/usr/local/share/emacs/version/site-lisp"
 "/usr/local/share/emacs/site-lisp"
 "/usr/local/share/emacs/version/lisp")

The last of these three directories is where the Lisp files of Emacs itself are installed; the first two are for additional Lisp packages installed at your site. The first directory is for locally installed packages that belong with a particular Emacs version; the second is for locally installed packages that can be used with any installed Emacs version.

There are several reasons why a Lisp package that works well in one Emacs version can cause trouble in another. Sometimes packages need updating for incompatible changes in Emacs; sometimes they depend on undocumented internal Emacs data that can change without notice; sometimes a newer Emacs version incorporates a version of the package, and should be used only with that version.

If you run Emacs from the directory where it was built—that is, an executable that has not been formally installed—then load-path normally contains two additional directories. These are the lisp and site-lisp subdirectories of the main build directory. (Both are represented as absolute file names.)

Variable load-in-progress

This variable is non-nil if Emacs is in the process of loading a file, and it is nil otherwise.

Variable load-read-function

This variable specifies an alternate expression-reading function for load and eval-region to use instead of read. The function should accept one argument, just as read does.

Normally, the variable’s value is nil, which means those functions should use

read.

To learn how load is used to build Emacs, see Section B.1 [Building Emacs], page 609.

13.2 Autoload

The autoload facility allows you to make a function or macro known in Lisp, but put off loading the file that defines it. The first call to the function automatically reads the proper file to install the real definition and other associated code, then runs the real definition as if it had been loaded all along.

There are two ways to set up an autoloaded function: by calling autoload, and by writing a special “magic” comment in the source before the real definition. autoload is the low-level primitive for autoloading; any Lisp program can call autoload at any time. Magic comments do nothing on their own; they serve as a guide for the command updatefile-autoloads, which constructs calls to autoload and arranges to execute them when Emacs is built. Magic comments are the most convenient way to make a function autoload, but only for packages installed along with Emacs.

Function autoload function filename &optional docstring interactive type This function defines the function (or macro) named function so as to load automatically from filename. The string filename specifies the file to load to get the real definition of function.

The argument docstring is the documentation string for the function. Normally, this is the identical to the documentation string in the function definition itself. Specifying the documentation string in the call to autoload makes it possible to look at the documentation without loading the function’s real definition.

If interactive is non-nil, then the function can be called interactively. This lets completion in M-x work without loading the function’s real definition. The complete interactive specification need not be given here; it’s not needed unless the user actually calls function, and when that happens, it’s time to load the real definition.

You can autoload macros and keymaps as well as ordinary functions. Specify type as macro if function is really a macro. Specify type as keymap if function is really a keymap. Various parts of Emacs need to know this information without loading the real definition.

An autoloaded keymap loads automatically during key lookup when a prefix key’s binding is the symbol function. Autoloading does not occur for other kinds of access to the keymap. In particular, it does not happen when a Lisp program gets the keymap from the value of a variable and calls define-key; not even if the variable name is the same symbol function.

If function already has a non-void function definition that is not an autoload object, autoload does nothing and returns nil. If the function cell of function is void, or is already an autoload object, then it is defined as an autoload object like this:

(autoload filename docstring interactive type)

For example,

     (symbol-function 'run-prolog)
          ⇒ (autoload "prolog" 169681 t nil)

In this case, "prolog" is the name of the file to load, 169681 refers to the documentation string in the ‘emacs/etc/DOC’ file (see Section 21.1 [Documentation Basics], page 319), t means the function is interactive, and nil that it is not a macro or a keymap.

The autoloaded file usually contains other definitions and may require or provide one or more features. If the file is not completely loaded (due to an error in the evaluation of its contents), any function definitions or provide calls that occurred during the load are undone. This is to ensure that the next attempt to call any function autoloading from this file will try again to load the file. If not for this, then some of the functions in the file might appear defined, but they might fail to work properly for the lack of certain subroutines defined later in the file and not loaded successfully.

If the autoloaded file fails to define the desired Lisp function or macro, then an error is

signaled with data "Autoloading failed to define function function-name".

A magic autoload comment looks like ‘;;;###autoload’, on a line by itself, just before the real definition of the function in its autoloadable source file. The command M-x updatefile-autoloads writes a corresponding autoload call into ‘loaddefs.el’. Building Emacs

loads ‘loaddefs.el’ and thus calls autoload. M-x update-directory-autoloads is even

more powerful; it updates autoloads for all files in the current directory.

The same magic comment can copy any kind of form into ‘loaddefs.el’. If the form following the magic comment is not a function definition, it is copied verbatim. You can also use a magic comment to execute a form at build time without executing it when the file itself is loaded. To do this, write the form on the same line as the magic comment. Since it is in a comment, it does nothing when you load the source file; but update-file-autoloads copies it to ‘loaddefs.el’, where it is executed while building Emacs.

The following example shows how doctor is prepared for autoloading with a magic comment:

     ;;;###autoload
     (defun doctor ()
       "Switch to *doctor* buffer and start giving psychotherapy."
       (interactive)
       (switch-to-buffer "*doctor*")
       (doctor-mode))

Here’s what that produces in ‘loaddefs.el’:

     (autoload 'doctor "doctor"
       "\
     Switch to *doctor* buffer and start giving psychotherapy."
       t)

The backslash and newline immediately following the double-quote are a convention used only in the preloaded Lisp files such as ‘loaddefs.el’; they tell make-docfile to put the documentation string in the ‘etc/DOC’ file. See Section B.1 [Building Emacs], page 609.

13.3 Repeated Loading

You may load one file more than once in an Emacs session. For example, after you have rewritten and reinstalled a function definition by editing it in a buffer, you may wish to return to the original version; you can do this by reloading the file it came from.

When you load or reload files, bear in mind that the load and load-library functions automatically load a byte-compiled file rather than a non-compiled file of similar name. If you rewrite a file that you intend to save and reinstall, remember to byte-compile it if necessary; otherwise you may find yourself inadvertently reloading the older, byte-compiled file instead of your newer, non-compiled file!

When writing the forms in a Lisp library file, keep in mind that the file might be loaded more than once. For example, the choice of defvar vs. defconst for defining a variable depends on whether it is desirable to reinitialize the variable if the library is reloaded: defconst does so, and defvar does not. (See Section 10.5 [Defining Variables], page 125.)

The simplest way to add an element to an alist is like this:

     (setq minor-mode-alist
           (cons '(leif-mode " Leif") minor-mode-alist))

But this would add multiple elements if the library is reloaded. To avoid the problem, write this:

     (or (assq 'leif-mode minor-mode-alist)
         (setq minor-mode-alist
               (cons '(leif-mode " Leif") minor-mode-alist)))

To add an element to a list just once, use add-to-list (see Section 10.8 [Setting Variables], page 129).

Occasionally you will want to test explicitly whether a library has already been loaded. Here’s one way to test, in a library, whether it has been loaded before:

     (defvar foo-was-loaded)
     (if (not (boundp 'foo-was-loaded))

execute-first-time-only)

     (setq foo-was-loaded t)

If the library uses provide to provide a named feature, you can use featurep to test whether the library has been loaded.

13.4 Features

provide and require are an alternative to autoload for loading files automatically. They work in terms of named features. Autoloading is triggered by calling a specific function, but a feature is loaded the first time another program asks for it by name.

A feature name is a symbol that stands for a collection of functions, variables, etc. The file that defines them should provide the feature. Another program that uses them may ensure they are defined by requiring the feature. This loads the file of definitions if it hasn’t been loaded already.

To require the presence of a feature, call require with the feature name as argument. require looks in the global variable features to see whether the desired feature has been provided already. If not, it loads the feature from the appropriate file. This file should call provide at the top level to add the feature to features; if it fails to do so, require signals an error.

Features are normally named after the files that provide them, so that require need not be given the file name.

For example, in ‘emacs/lisp/prolog.el’, the definition for run-prolog includes the following code:

     (defun run-prolog ()
       "Run an inferior Prolog process, with I/O via buffer *prolog*."
       (interactive)
       (require 'comint)
       (switch-to-buffer (make-comint "prolog" prolog-program-name))
       (inferior-prolog-mode))

The expression (require 'comint) loads the file ‘comint.el’ if it has not yet been loaded. This ensures that make-comint is defined.

The ‘comint.el’ file contains the following top-level expression:

     (provide 'comint)

This adds comint to the global features list, so that (require 'comint) will henceforth know that nothing needs to be done.

When require is used at top level in a file, it takes effect when you byte-compile that file (see Chapter 14 [Byte Compilation], page 171) as well as when you load it. This is in case the required package contains macros that the byte compiler must know about.

Although top-level calls to require are evaluated during byte compilation, provide calls are not. Therefore, you can ensure that a file of definitions is loaded before it is bytecompiled by including a provide followed by a require for the same feature, as in the following example.

(provide 'my-feature) ; Ignored by byte compiler,

; evaluated by load.

(require 'my-feature) ; Evaluated by byte compiler. The compiler ignores the provide, then processes the require by loading the file in question. Loading the file does execute the provide call, so the subsequent require call does nothing while loading.

Function provide feature

This function announces that feature is now loaded, or being loaded, into the current Emacs session. This means that the facilities associated with feature are or will be available for other Lisp programs. The direct effect of calling provide is to add feature to the front of the list features if it is not already in the list. The argument feature must be a symbol. provide returns feature.

          features
               ⇒ (bar bish)

     (provide 'foo)
          ⇒ foo
     features
          ⇒ (foo bar bish)

When a file is loaded to satisfy an autoload, and it stops due to an error in the evaluating its contents, any function definitions or provide calls that occurred during the load are undone. See Section 13.2 [Autoload], page 164.

Function require feature &optional filename This function checks whether feature is present in the current Emacs session (using (featurep feature); see below). If it is not, then require loads filename with load. If filename is not supplied, then the name of the symbol feature is used as the file name to load. If loading the file fails to provide feature, require signals an error, ‘Required

feature feature was not provided’.

Function featurep feature

This function returns t if feature has been provided in the current Emacs session (i.e., feature is a member of features.)

Variable features

The value of this variable is a list of symbols that are the features loaded in the current Emacs session. Each symbol was put in this list with a call to provide. The order of the elements in the features list is not significant.

13.5 Unloading

You can discard the functions and variables loaded by a library to reclaim memory for other Lisp objects. To do this, use the function unload-feature:

Command unload-feature feature &optional force This command unloads the library that provided feature feature. It undefines all functions, macros, and variables defined in that library with defconst, defvar, defun, defmacro, defsubst and defalias. It then restores any autoloads formerly associated with those symbols. (Loading saves these in the autoload property of the symbol.) Ordinarily, unload-feature refuses to unload a library on which other loaded libraries depend. (A library a depends on library b if a contains a require for b.) If the optional argument force is non-nil, dependencies are ignored and you can unload any library.

The unload-feature function is written in Lisp; its actions are based on the variable

load-history.

Variable load-history

This variable’s value is an alist connecting library names with the names of functions and variables they define, the features they provide, and the features they require.

Each element is a list and describes one library. The car of the list is the name of the library, as a string. The rest of the list is composed of these kinds of objects:

• Symbols that were defined by this library.

• Lists of the form (require . feature) indicating features that were required.

• Lists of the form (provide . feature) indicating features that were provided.

The value of load-history may have one element whose car is nil. This element describes definitions made with eval-buffer on a buffer that is not visiting a file.

The command eval-region updates load-history, but does so by adding the symbols defined to the element for the file being visited, rather than replacing that element.

13.6 Hooks for Loading

You can ask for code to be executed if and when a particular library is loaded, by calling

eval-after-load.

Function eval-after-load library form

This function arranges to evaluate form at the end of loading the library library, if and when library is loaded. If library is already loaded, it evaluates form right away. The library name library must exactly match the argument of load. To get the proper results when an installed library is found by searching load-path, you should not include any directory names in library. An error in form does not undo the load, but does prevent execution of the rest of form.

In general, well-designed Lisp programs should not use this feature. The clean and modular ways to interact with a Lisp library are (1) examine and set the library’s variables (those which are meant for outside use), and (2) call the library’s functions. If you wish to do (1), you can do it immediately—there is no need to wait for when the library is loaded. To do (2), you must load the library (preferably with require).

But it is ok to use eval-after-load in your personal customizations if you don’t feel they must meet the design standards of programs to be released.

Variable after-load-alist

An alist of expressions to evaluate if and when particular libraries are loaded. Each element looks like this:

(filename forms…) The function load checks after-load-alist in order to implement eval-

after-load.

170 GNU Emacs Lisp Reference Manual

14 Byte Compilation

GNU Emacs Lisp has a compiler that translates functions written in Lisp into a special representation called byte-code that can be executed more efficiently. The compiler replaces Lisp function definitions with byte-code. When a byte-code function is called, its definition is evaluated by the byte-code interpreter.

Because the byte-compiled code is evaluated by the byte-code interpreter, instead of being executed directly by the machine’s hardware (as true compiled code is), byte-code is completely transportable from machine to machine without recompilation. It is not, however, as fast as true compiled code.

In general, any version of Emacs can run byte-compiled code produced by recent earlier versions of Emacs, but the reverse is not true. In particular, if you compile a program with Emacs 19.29, the compiled code does not run in earlier versions. See Section 14.3 [Docs and Compilation], page 174. Files compiled in versions before 19.29 may not work in 19.29 if they contain character constants with modifier bits, because the bits were renumbered in Emacs 19.29.

See Section 15.3 [Compilation Errors], page 190, for how to investigate errors occurring in byte compilation.

14.1 Performance of Byte-Compiled Code

A byte-compiled function is not as efficient as a primitive function written in C, but runs much faster than the version written in Lisp. Here is an example:

     (defun silly-loop (n)
       "Return time before and after N iterations of a loop."
       (let ((t1 (current-time-string)))
         (while (> (setq n (1- n))
                   0))
         (list t1 (current-time-string))))
     ⇒ silly-loop
     (silly-loop 100000)
     ⇒ ("Fri Mar 18 17:25:57 1994"
         "Fri Mar 18 17:26:28 1994")  ; 31 seconds
     (byte-compile 'silly-loop)

⇒ [Compiled code not shown]

     (silly-loop 100000)
     ⇒ ("Fri Mar 18 17:26:52 1994"
         "Fri Mar 18 17:26:58 1994")  ; 6 seconds

In this example, the interpreted code required 31 seconds to run, whereas the bytecompiled code required 6 seconds. These results are representative, but actual results will vary greatly.

14.2 The Compilation Functions

You can byte-compile an individual function or macro definition with the byte-compile function. You can compile a whole file with byte-compile-file, or several files with

byte-recompile-directory or batch-byte-compile.

The byte compiler produces error messages and warnings about each file in a buffer called ‘*Compile-Log*’. These report things in your program that suggest a problem but are not necessarily erroneous.

Be careful when byte-compiling code that uses macros. Macro calls are expanded when they are compiled, so the macros must already be defined for proper compilation. For more details, see Section 12.3 [Compiling Macros], page 154.

Normally, compiling a file does not evaluate the file’s contents or load the file. But it does execute any require calls at top level in the file. One way to ensure that necessary macro definitions are available during compilation is to require the file that defines them (see Section 13.4 [Named Features], page 166). To avoid loading the macro definition files when someone runs the compiled program, write eval-when-compile around the require calls (see Section 14.5 [Eval During Compile], page 175).

Function byte-compile symbol

This function byte-compiles the function definition of symbol, replacing the previous definition with the compiled one. The function definition of symbol must be the actual code for the function; i.e., the compiler does not follow indirection to another symbol. byte-compile returns the new, compiled definition of symbol.

If symbol’s definition is a byte-code function object, byte-compile does nothing and returns nil. Lisp records only one function definition for any symbol, and if that is already compiled, non-compiled code is not available anywhere. So there is no way to “compile the same definition again.”

     (defun factorial (integer)
       "Compute factorial of INTEGER."
       (if (= 1 integer) 1
         (* integer (factorial (1- integer)))))
     ⇒ factorial
     (byte-compile 'factorial)

⇒

     #[(integer)
       "^H\301U\203^H^@\301\207\302^H\303^HS!\"\207"
       [integer 1 * factorial]
       4 "Compute factorial of INTEGER."]

The result is a byte-code function object. The string it contains is the actual byte-code; each character in it is an instruction or an operand of an instruction. The vector contains all the constants, variable names and function names used by the function, except for certain primitives that are coded as special instructions.

Command compile-defun

This command reads the defun containing point, compiles it, and evaluates the result. If you use this on a defun that is actually a function definition, the effect is to install a compiled version of that function.

Command byte-compile-file filename

This function compiles a file of Lisp code named filename into a file of byte-code. The output file’s name is made by appending ‘c’ to the end of filename. Compilation works by reading the input file one form at a time. If it is a definition of a function or macro, the compiled function or macro definition is written out. Other forms are batched together, then each batch is compiled, and written so that its compiled code will be executed when the file is read. All comments are discarded when the input file is read. This command returns t. When called interactively, it prompts for the file name.

     % ls -l push*
     -rw-r--r--  1 lewis     791 Oct  5 20:31 push.el
     (byte-compile-file "~/emacs/push.el")
          ⇒ t
     % ls -l push*
     -rw-r--r--  1 lewis     791 Oct  5 20:31 push.el
     -rw-rw-rw-  1 lewis     638 Oct  8 20:25 push.elc

Command byte-recompile-directory directory flag

This function recompiles every ‘.el’ file in directory that needs recompilation. A file needs recompilation if a ‘.elc’ file exists but is older than the ‘.el’ file. When a ‘.el’ file has no corresponding ‘.elc’ file, then flag says what to do. If it is nil, these files are ignored. If it is non-nil, the user is asked whether to compile each such file. The returned value of this command is unpredictable.

Function batch-byte-compile

This function runs byte-compile-file on files specified on the command line. This function must be used only in a batch execution of Emacs, as it kills Emacs on completion. An error in one file does not prevent processing of subsequent files. (The file that gets the error will not, of course, produce any compiled code.)

     % emacs -batch -f batch-byte-compile *.el

Function byte-code code-string data-vector max-stack This function actually interprets byte-code. A byte-compiled function is actually defined with a body that calls byte-code. Don’t call this function yourself. Only the byte compiler knows how to generate valid calls to this function. In newer Emacs versions (19 and up), byte-code is usually executed as part of a byte-code function object, and only rarely due to an explicit call to byte-code.

14.3 Documentation Strings and Compilation

Functions and variables loaded from a byte-compiled file access their documentation strings dynamically from the file whenever needed. This saves space within Emacs, and makes loading faster because the documentation strings themselves need not be processed while loading the file. Actual access to the documentation strings becomes slower as a result, but this normally is not enough to bother users.

Dynamic access to documentation strings does have drawbacks:

• If you delete or move the compiled file after loading it, Emacs can no longer access the documentation strings for the functions and variables in the file.

• If you alter the compiled file (such as by compiling a new version), then further access to documentation strings in this file will give nonsense results.

If your site installs Emacs following the usual procedures, these problems will never normally occur. Installing a new version uses a new directory with a different name; as long as the old version remains installed, its files will remain unmodified in the places where they are expected to be.

However, if you have built Emacs yourself and use it from the directory where you built it, you will experience this problem occasionally if you edit and recompile Lisp files. When it happens, you can cure the problem by reloading the file after recompiling it.

Byte-compiled files made with Emacs 19.29 will not load into older versions because the older versions don’t support this feature. You can turn off this feature by setting bytecompile-dynamic-docstrings to nil. Once this is done, you can compile files that will load into older Emacs versions. You can do this globally, or for one source file by specifying a file-local binding for the variable. Here’s one way to do that:

     -*-byte-compile-dynamic-docstrings: nil;-*-

Variable byte-compile-dynamic-docstrings

If this is non-nil, the byte compiler generates compiled files that are set up for dynamic loading of documentation strings.

The dynamic documentation string feature writes compiled files that use a special Lisp reader construct, ‘#@count’. This construct skips the next count characters. It also uses the ‘#$’ construct, which stands for “the name of this file, as a string.” It is best not to use these constructs in Lisp source files.

14.4 Dynamic Loading of Individual Functions

When you compile a file, you can optionally enable the dynamic function loading feature (also known as lazy loading). With dynamic function loading, loading the file doesn’t fully read the function definitions in the file. Instead, each function definition contains a placeholder which refers to the file. The first time each function is called, it reads the full definition from the file, to replace the place-holder.

The advantage of dynamic function loading is that loading the file becomes much faster. This is a good thing for a file which contains many separate commands, provided that using one of them does not imply you will soon (or ever) use the rest. A specialized mode which provides many keyboard commands often has that usage pattern: a user may invoke the mode, but use only a few of the commands it provides.

The dynamic loading feature has certain disadvantages:

• If you delete or move the compiled file after loading it, Emacs can no longer load the remaining function definitions not already loaded.

• If you alter the compiled file (such as by compiling a new version), then trying to load any function not already loaded will get nonsense results.

If you compile a new version of the file, the best thing to do is immediately load the new compiled file. That will prevent any future problems.

The byte compiler uses the dynamic function loading feature if the variable bytecompile-dynamic is non-nil at compilation time. Do not set this variable globally, since dynamic loading is desirable only for certain files. Instead, enable the feature for specific source files with file-local variable bindings, like this:

-*-byte-compile-dynamic: t;-*-

Variable byte-compile-dynamic

If this is non-nil, the byte compiler generates compiled files that are set up for dynamic function loading.

Function fetch-bytecode function

This immediately finishes loading the definition of function from its bytecompiled file, if it is not fully loaded already. The argument function may be a byte-code function object or a function name.

14.5 Evaluation During Compilation

These features permit you to write code to be evaluated during compilation of a program.

Special Form eval-and-compile body

This form marks body to be evaluated both when you compile the containing code and when you run it (whether compiled or not).

You can get a similar result by putting body in a separate file and referring to that file with require. Using require is preferable if there is a substantial amount of code to be executed in this way.

Special Form eval-when-compile body

This form marks body to be evaluated at compile time and not when the compiled program is loaded. The result of evaluation by the compiler becomes a constant which appears in the compiled program. When the program is interpreted, not compiled at all, body is evaluated normally.

At top level, this is analogous to the Common Lisp idiom (eval-when (compile eval) …). Elsewhere, the Common Lisp ‘#.’ reader macro (but not when interpreting) is closer to what eval-when-compile does.

14.6 Byte-Code Function Objects

Byte-compiled functions have a special data type: they are byte-code function objects. Internally, a byte-code function object is much like a vector; however, the evaluator

handles this data type specially when it appears as a function to be called. The printed representation for a byte-code function object is like that for a vector, with an additional ‘#’ before the opening ‘[’.

In Emacs version 18, there was no byte-code function object data type; compiled functions used the function byte-code to run the byte code.

A byte-code function object must have at least four elements; there is no maximum number, but only the first six elements are actually used. They are:

arglist The list of argument symbols.

byte-code The string containing the byte-code instructions.

constants The vector of Lisp objects referenced by the byte code. These include symbols used as function names and variable names.

stacksize The maximum stack size this function needs.

docstring The documentation string (if any); otherwise, nil. The value may be a number or a list, in case the documentation string is stored in a file. Use the function documentation to get the real documentation string (see Section 21.2 [Accessing Documentation], page 320).

interactive The interactive spec (if any). This can be a string or a Lisp expression. It is nil for a function that isn’t interactive.

Here’s an example of a byte-code function object, in printed representation. It is the definition of the command backward-sexp.

     #[(&optional arg)
       "^H\204^F^@\301^P\302^H[!\207"
       [arg 1 forward-sexp]
       2
       254435
       "p"]

The primitive way to create a byte-code object is with make-byte-code:

Function make-byte-code &rest elements

This function constructs and returns a byte-code function object with elements as its elements.

You should not try to come up with the elements for a byte-code function yourself, because if they are inconsistent, Emacs may crash when you call the function. Always leave it to the byte compiler to create these objects; it makes the elements consistent (we hope).

You can access the elements of a byte-code object using aref; you can also use vconcat to create a vector with the same elements.

14.7 Disassembled Byte-Code

People do not write byte-code; that job is left to the byte compiler. But we provide a disassembler to satisfy a cat-like curiosity. The disassembler converts the byte-compiled code into humanly readable form.

The byte-code interpreter is implemented as a simple stack machine. It pushes values onto a stack of its own, then pops them off to use them in calculations whose results are themselves pushed back on the stack. When a byte-code function returns, it pops a value off the stack and returns it as the value of the function.

In addition to the stack, byte-code functions can use, bind, and set ordinary Lisp variables, by transferring values between variables and the stack.

Command disassemble object &optional stream This function prints the disassembled code for object. If stream is supplied, then output goes there. Otherwise, the disassembled code is printed to the stream standard-output. The argument object can be a function name or a lambda expression. As a special exception, if this function is used interactively, it outputs to a

     buffer named ‘*Disassemble*’.

Here are two examples of using the disassemble function. We have added explanatory comments to help you relate the byte-code to the Lisp source; these do not appear in the output of disassemble. These examples show unoptimized byte-code. Nowadays byte-code is usually optimized, but we did not want to rewrite these examples, since they still serve their purpose.

     (defun factorial (integer)
       "Compute factorial of an integer."
       (if (= 1 integer) 1
         (* integer (factorial (1- integer)))))
          ⇒ factorial
     (factorial 4)
          ⇒ 24
     (disassemble 'factorial)
          ⊣ byte-code for factorial:
      doc: Compute factorial of an integer.
      args: (integer)

0 constant 1 ; Push 1 onto stack.

     1   varref   integer        ; Get value of integer

; from the environment ; and push the value ; onto the stack.

2 eqlsign ; Pop top two values off stack, ; compare them, ; and push result onto stack.

3 goto-if-nil 10 ; Pop and test top of stack; ; if nil, go to 10, ; else continue.

6 constant 1 ; Push 1 onto top of stack.

7 goto 17 ; Go to 17 (in this case, 1 will be ; returned by the function).

10 constant * ; Push symbol * onto stack.

11  varref   integer        ; Push value of integer onto stack.
12  constant factorial      ; Push factorial onto stack.
13  varref   integer        ; Push value of integer onto stack.

14 sub1 ; Pop integer, decrement value, ; push new value onto stack.

; Stack now contains: ; − decremented value of integer

; − factorial
; − value of integer
; − *
15  call     1              ; Call function factorial using

; the first (i.e., the top) element ; of the stack as the argument; ; push returned value onto stack.

; Stack now contains: ; − result of recursive

;  call to factorial
; − value of integer
; − *

16 call 2 ; Using the first two ; (i.e., the top two) ; elements of the stack ; as arguments, ; call the function *, ; pushing the result onto the stack.

17 return ; Return the top element

; of the stack.

⇒ nil

The silly-loop function is somewhat more complex:

(defun silly-loop (n)
"Return time before and after N iterations of a loop."
(let ((t1 (current-time-string)))
(while (> (setq n (1- n))
0))
(list t1 (current-time-string))))
⇒ silly-loop
(disassemble 'silly-loop)
⊣ byte-code for silly-loop:
doc: Return time before and after N iterations of a loop.
args: (n)
0   constant current-time-string  ; Push
      ;   current-time-string

; onto top of stack.

1   call     0              ; Call current-time-string

; with no argument, ; pushing result onto stack.

2 varbind t1 ; Pop stack and bind t1 ; to popped value.

3 varref n ; Get value of n from ; the environment and push ; the value onto the stack.

4 sub1 ; Subtract 1 from top of stack.

5 dup ; Duplicate the top of the stack; ; i.e., copy the top of ; the stack and push the ; copy onto the stack.

6 varset n ; Pop the top of the stack, ; and bind n to the value.

; In effect, the sequence dup varset ; copies the top of the stack ; into the value of n ; without popping it.

7 constant 0 ; Push 0 onto stack.

8 gtr ; Pop top two values off stack, ; test if n is greater than 0 ; and push result onto stack.

9   goto-if-nil-else-pop 17 ; Goto 17 if n <= 0

; (this exits the while loop). ; else pop top of stack ; and continue

12  constant nil            ; Push nil onto stack

; (this is the body of the loop).

13 discard ; Discard result of the body ; of the loop (a while loop ; is always evaluated for ; its side effects).

14 goto 3 ; Jump back to beginning ; of while loop.

17 discard ; Discard result of while loop ; by popping top of stack. ; This result is the value nil that ; was not popped by the goto at 9.

18 varref t1 ; Push value of t1 onto stack.

19  constant current-time-string  ; Push
                                  ;   current-time-string

; onto top of stack.

20  call     0              ; Call current-time-string again.

21 list2 ; Pop top two elements off stack, ; create a list of them, ; and push list onto stack.

22 unbind 1 ; Unbind t1 in local environment.

23 return ; Return value of the top of stack.

     ⇒ nil

15 Debugging Lisp Programs

There are three ways to investigate a problem in an Emacs Lisp program, depending on what you are doing with the program when the problem appears.

• If the problem occurs when you run the program, you can use a Lisp debugger (either the default debugger or Edebug) to investigate what is happening during execution.

• If the problem is syntactic, so that Lisp cannot even read the program, you can use the Emacs facilities for editing Lisp to localize it.

• If the problem occurs when trying to compile the program with the byte compiler, you need to know how to examine the compiler’s input buffer.

Another useful debugging tool is the dribble file. When a dribble file is open, Emacs copies all keyboard input characters to that file. Afterward, you can examine the file to find out what input was used. See Section 34.8 [Terminal Input], page 558.

For debugging problems in terminal descriptions, the open-termscript function can be useful. See Section 34.9 [Terminal Output], page 562.

15.1 The Lisp Debugger

The Lisp debugger provides the ability to suspend evaluation of a form. While evaluation is suspended (a state that is commonly known as a break), you may examine the run time stack, examine the values of local or global variables, or change those values. Since a break is a recursive edit, all the usual editing facilities of Emacs are available; you can even run programs that will enter the debugger recursively. See Section 18.10 [Recursive Editing], page 271.

15.1.1 Entering the Debugger on an Error

The most important time to enter the debugger is when a Lisp error happens. This allows you to investigate the immediate causes of the error.

However, entry to the debugger is not a normal consequence of an error. Many commands frequently get Lisp errors when invoked in inappropriate contexts (such as C-f at the end of the buffer) and during ordinary editing it would be very unpleasant to enter the debugger each time this happens. If you want errors to enter the debugger, set the variable debug-

on-error to non-nil.

User Option debug-on-error

This variable determines whether the debugger is called when an error is signaled and not handled. If debug-on-error is t, all errors call the debugger. If it is nil, none call the debugger. The value can also be a list of error conditions that should call the debugger. For example, if you set it to the list (void-variable), then only errors about a variable that has no value invoke the debugger. When this variable is non-nil, Emacs does not catch errors that happen in process filter functions and sentinels. Therefore, these errors also can invoke the debugger. See Chapter 33 [Processes], page 525.

User Option debug-ignored-errors

This variable specifies certain kinds of errors that should not enter the debugger. Its value is a list of error condition symbols and/or regular expressions. If the error has any of those condition symbols, or if the error message matches any of the regular expressions, then that error does not enter the debugger, regardless

     of the value of debug-on-error.

The normal value of this variable lists several errors that happen often during editing but rarely result from bugs in Lisp programs.

To debug an error that happens during loading of the ‘.emacs’ file, use the option ‘-debug-init’, which binds debug-on-error to t while ‘.emacs’ is loaded and inhibits use of condition-case to catch init file errors.

If your ‘.emacs’ file sets debug-on-error, the effect may not last past the end of loading ‘.emacs’. (This is an undesirable byproduct of the code that implements the ‘-debug-init’ command line option.) The best way to make ‘.emacs’ set debug-on-error permanently is with after-init-hook, like this:

     (add-hook 'after-init-hook
               '(lambda () (setq debug-on-error t)))

15.1.2 Debugging Infinite Loops

When a program loops infinitely and fails to return, your first problem is to stop the loop. On most operating systems, you can do this with C-g, which causes quit.

Ordinary quitting gives no information about why the program was looping. To get more information, you can set the variable debug-on-quit to non-nil. Quitting with C-g is not considered an error, and debug-on-error has no effect on the handling of C-g. Likewise, debug-on-quit has no effect on errors.

Once you have the debugger running in the middle of the infinite loop, you can proceed from the debugger using the stepping commands. If you step through the entire loop, you will probably get enough information to solve the problem.

User Option debug-on-quit

This variable determines whether the debugger is called when quit is signaled and not handled. If debug-on-quit is non-nil, then the debugger is called whenever you quit (that is, type C-g). If debug-on-quit is nil, then the debugger is not called when you quit. See Section 18.8 [Quitting], page 268.

15.1.3 Entering the Debugger on a Function Call

To investigate a problem that happens in the middle of a program, one useful technique is to enter the debugger whenever a certain function is called. You can do this to the function in which the problem occurs, and then step through the function, or you can do this to a function called shortly before the problem, step quickly over the call to that function, and then step through its caller.

Command debug-on-entry function-name

This function requests function-name to invoke the debugger each time it is called. It works by inserting the form (debug 'debug) into the function definition as the first form. Any function defined as Lisp code may be set to break on entry, regardless of whether it is interpreted code or compiled code. If the function is a command, it will enter the debugger when called from Lisp and when called interactively (after the reading of the arguments). You can’t debug primitive functions (i.e., those written in C) this way. When debug-on-entry is called interactively, it prompts for function-name in the minibuffer. If the function is already set up to invoke the debugger on entry, debug-on-entry does nothing. Note: if you redefine a function after using debug-on-entry on it, the code to enter the debugger is lost. debug-on-entry returns function-name.

     (defun fact (n)
       (if (zerop n) 1
           (* n (fact (1- n)))))
          ⇒ fact
     (debug-on-entry 'fact)
          ⇒ fact
     (fact 3)
     ------ Buffer: *Backtrace* ------
     Entering:
     * fact(3)
       eval-region(4870 4878 t)
       byte-code("...")
       eval-last-sexp(nil)
       (let ...)
       eval-insert-last-sexp(nil)
     * call-interactively(eval-insert-last-sexp)
     ------ Buffer: *Backtrace* ------
     (symbol-function 'fact)
          ⇒ (lambda (n)
               (debug (quote debug))
               (if (zerop n) 1 (* n (fact (1- n)))))

Command cancel-debug-on-entry function-name

This function undoes the effect of debug-on-entry on function-name. When called interactively, it prompts for function-name in the minibuffer. If functionname is nil or the empty string, it cancels debugging for all functions. If cancel-debug-on-entry is called more than once on the same function, the second call does nothing. cancel-debug-on-entry returns function-name.

15.1.4 Explicit Entry to the Debugger

You can cause the debugger to be called at a certain point in your program by writing the expression (debug) at that point. To do this, visit the source file, insert the text ‘(debug)’ at the proper place, and type C-M-x. Be sure to undo this insertion before you save the file!

The place where you insert ‘(debug)’ must be a place where an additional form can be evaluated and its value ignored. (If the value of (debug) isn’t ignored, it will alter the execution of the program!) The most common suitable places are inside a progn or an implicit progn (see Section 9.1 [Sequencing], page 105).

15.1.5 Using the Debugger

When the debugger is entered, it displays the previously selected buffer in one window and a buffer named ‘*Backtrace*’ in another window. The backtrace buffer contains one line for each level of Lisp function execution currently going on. At the beginning of this buffer is a message describing the reason that the debugger was invoked (such as the error message and associated data, if it was invoked due to an error).

The backtrace buffer is read-only and uses a special major mode, Debugger mode, in which letters are defined as debugger commands. The usual Emacs editing commands are available; thus, you can switch windows to examine the buffer that was being edited at the time of the error, switch buffers, visit files, or do any other sort of editing. However, the debugger is a recursive editing level (see Section 18.10 [Recursive Editing], page 271) and it is wise to go back to the backtrace buffer and exit the debugger (with the q command) when you are finished with it. Exiting the debugger gets out of the recursive edit and kills the backtrace buffer.

The backtrace buffer shows you the functions that are executing and their argument values. It also allows you to specify a stack frame by moving point to the line describing that frame. (A stack frame is the place where the Lisp interpreter records information about a particular invocation of a function.) The frame whose line point is on is considered the current frame. Some of the debugger commands operate on the current frame.

The debugger itself must be run byte-compiled, since it makes assumptions about how many stack frames are used for the debugger itself. These assumptions are false if the debugger is running interpreted.

15.1.6 Debugger Commands

Inside the debugger (in Debugger mode), these special commands are available in addition to the usual cursor motion commands. (Keep in mind that all the usual facilities of Emacs, such as switching windows or buffers, are still available.)

The most important use of debugger commands is for stepping through code, so that you can see how control flows. The debugger can step through the control structures of an interpreted function, but cannot do so in a byte-compiled function. If you would like to step through a byte-compiled function, replace it with an interpreted definition of the same function. (To do this, visit the source file for the function and type C-M-x on its definition.)

Here is a list of Debugger mode commands:

c Exit the debugger and continue execution. When continuing is possible, it resumes execution of the program as if the debugger had never been entered (aside from the effect of any variables or data structures you may have changed while inside the debugger). Continuing is possible after entry to the debugger due to function entry or exit, explicit invocation, or quitting. You cannot continue if the debugger was entered because of an error.

d Continue execution, but enter the debugger the next time any Lisp function is called. This allows you to step through the subexpressions of an expression, seeing what values the subexpressions compute, and what else they do. The stack frame made for the function call which enters the debugger in this way will be flagged automatically so that the debugger will be called again when the frame is exited. You can use the u command to cancel this flag.

b Flag the current frame so that the debugger will be entered when the frame is exited. Frames flagged in this way are marked with stars in the backtrace buffer.

u Don’t enter the debugger when the current frame is exited. This cancels a b command on that frame.

e Read a Lisp expression in the minibuffer, evaluate it, and print the value in the echo area. The debugger alters certain important variables, and the current buffer, as part of its operation; e temporarily restores their outside-the-debugger values so you can examine them. This makes the debugger more transparent. By contrast, M-: does nothing special in the debugger; it shows you the variable values within the debugger.

q Terminate the program being debugged; return to top-level Emacs command execution. If the debugger was entered due to a C-g but you really want to quit, and not debug, use the q command.

r Return a value from the debugger. The value is computed by reading an expression with the minibuffer and evaluating it.

The r command is useful when the debugger was invoked due to exit from a Lisp call frame (as requested with b); then the value specified in the r command is used as the value of that frame. It is also useful if you call debug and use its return value. Otherwise, r has the same effect as c, and the specified return value does not matter. You can’t use r when the debugger was entered due to an error.

15.1.7 Invoking the Debugger

Here we describe fully the function used to invoke the debugger.

Function debug &rest debugger-args This function enters the debugger. It switches buffers to a buffer named ‘*Backtrace*’ (or ‘*Backtrace*<2>’ if it is the second recursive entry to the debugger, etc.), and fills it with information about the stack of Lisp function calls. It then enters a recursive edit, showing the backtrace buffer in Debugger mode. The Debugger mode c and r commands exit the recursive edit; then debug switches back to the previous buffer and returns to whatever called debug. This is the only way the function debug can return to its caller. If the first of the debugger-args passed to debug is nil (or if it is not one of the special values in the table below), then debug displays the rest of its arguments at the top of the ‘*Backtrace*’ buffer. This mechanism is used to display a message to the user. However, if the first argument passed to debug is one of the following special values, then it has special significance. Normally, these values are passed to debug only by the internals of Emacs and the debugger, and not by programmers calling debug. The special values are:

lambda A first argument of lambda means debug was called because of entry to a function when debug-on-next-call was non-nil. The debugger displays ‘Entering:’ as a line of text at the top of the buffer.

debug debug as first argument indicates a call to debug because of entry to a function that was set to debug on entry. The debugger displays ‘Entering:’, just as in the lambda case. It also marks the stack frame for that function so that it will invoke the debugger when exited.

t When the first argument is t, this indicates a call to debug due to evaluation of a list form when debug-on-next-call is non-nil. The debugger displays the following as the top line in the buffer:

               Beginning evaluation of function call form:

exit When the first argument is exit, it indicates the exit of a stack frame previously marked to invoke the debugger on exit. The second argument given to debug in this case is the value being returned from the frame. The debugger displays ‘Return value:’ on the top line of the buffer, followed by the value being returned.

error When the first argument is error, the debugger indicates that it is being entered because an error or quit was signaled and not handled, by displaying ‘Signaling:’ followed by the error signaled and any arguments to signal. For example,

               (let ((debug-on-error t))
                 (/ 1 0))
               ------ Buffer: *Backtrace* ------
               Signaling: (arith-error)
                 /(1 0)
               ...
               ------ Buffer: *Backtrace* ------

If an error was signaled, presumably the variable debug-on-error is non-nil. If quit was signaled, then presumably the variable

          debug-on-quit is non-nil.

nil Use nil as the first of the debugger-args when you want to enter the debugger explicitly. The rest of the debugger-args are printed on the top line of the buffer. You can use this feature to display messages—for example, to remind yourself of the conditions under which debug is called.

15.1.8 Internals of the Debugger

This section describes functions and variables used internally by the debugger.

Variable debugger

The value of this variable is the function to call to invoke the debugger. Its value must be a function of any number of arguments (or, more typically, the name of a function). Presumably this function will enter some kind of debugger. The default value of the variable is debug. The first argument that Lisp hands to the function indicates why it was called. The convention for arguments is detailed in the description of debug.

Command backtrace

This function prints a trace of Lisp function calls currently active. This is the function used by debug to fill up the ‘*Backtrace*’ buffer. It is written in C, since it must have access to the stack to determine which function calls are active. The return value is always nil. In the following example, a Lisp expression calls backtrace explicitly. This prints the backtrace to the stream standard-output: in this case, to the buffer ‘backtrace-output’. Each line of the backtrace represents one function call. The line shows the values of the function’s arguments if they are all known. If they are still being computed, the line says so. The arguments of special forms are elided.

     (with-output-to-temp-buffer "backtrace-output"
       (let ((var 1))
         (save-excursion
           (setq var (eval '(progn
                              (1+ var)
                              (list 'testing (backtrace))))))))

          ⇒ nil

     ----------- Buffer: backtrace-output ------------
       backtrace()
       (list ...computing arguments...)
       (progn ...)
       eval((progn (1+ var) (list (quote testing) (backtrace))))
       (setq ...)
       (save-excursion ...)
       (let ...)
       (with-output-to-temp-buffer ...)
       eval-region(1973 2142 #<buffer *scratch*>)
       byte-code("...  for eval-print-last-sexp ...")
       eval-print-last-sexp(nil)
     * call-interactively(eval-print-last-sexp)
     ----------- Buffer: backtrace-output ------------

The character ‘*’ indicates a frame whose debug-on-exit flag is set.

Variable debug-on-next-call

If this variable is non-nil, it says to call the debugger before the next eval,

apply or funcall. Entering the debugger sets debug-on-next-call to nil.

The d command in the debugger works by setting this variable.

Function backtrace-debug level flag

This function sets the debug-on-exit flag of the stack frame level levels down the stack, giving it the value flag. If flag is non-nil, this will cause the debugger to be entered when that frame later exits. Even a nonlocal exit through that frame will enter the debugger.

This function is used only by the debugger.

Variable command-debug-status

This variable records the debugging status of the current interactive command. Each time a command is called interactively, this variable is bound to nil. The debugger can set this variable to leave information for future debugger invocations during the same command.

The advantage, for the debugger, of using this variable rather than another global variable is that the data will never carry over to a subsequent command invocation.

Function backtrace-frame frame-number

The function backtrace-frame is intended for use in Lisp debuggers. It returns information about what computation is happening in the stack frame framenumber levels down. If that frame has not evaluated the arguments yet (or is a special form), the value is (nil function arg-forms…). If that frame has evaluated its arguments and called its function already, the value is (t function arg-values…). In the return value, function is whatever was supplied as the car of the evaluated list, or a lambda expression in the case of a macro call. If the function has a &rest argument, that is represented as the tail of the list arg-values. If frame-number is out of range, backtrace-frame returns nil.

15.2 Debugging Invalid Lisp Syntax

The Lisp reader reports invalid syntax, but cannot say where the real problem is. For example, the error “End of file during parsing” in evaluating an expression indicates an excess of open parentheses (or square brackets). The reader detects this imbalance at the end of the file, but it cannot figure out where the close parenthesis should have been. Likewise, “Invalid read syntax: ")"” indicates an excess close parenthesis or missing open parenthesis, but does not say where the missing parenthesis belongs. How, then, to find what to change?

If the problem is not simply an imbalance of parentheses, a useful technique is to try C-M-e at the beginning of each defun, and see if it goes to the place where that defun appears to end. If it does not, there is a problem in that defun.

However, unmatched parentheses are the most common syntax errors in Lisp, and we can give further advice for those cases.

15.2.1 Excess Open Parentheses

The first step is to find the defun that is unbalanced. If there is an excess open parenthesis, the way to do this is to insert a close parenthesis at the end of the file and type C-M-b (backward-sexp). This will move you to the beginning of the defun that is unbalanced. (Then type C-^{⟨}\underline{\overline{SPC}}^{⟩} C-_C-u C-^{⟨}\underline{\overline{SPC}}^{⟩} to set the mark there, undo the insertion of the close parenthesis, and finally return to the mark.)

The next step is to determine precisely what is wrong. There is no way to be sure of this except to study the program, but often the existing indentation is a clue to where the parentheses should have been. The easiest way to use this clue is to reindent with C-M-q and see what moves.

Before you do this, make sure the defun has enough close parentheses. Otherwise, C-M-q will get an error, or will reindent all the rest of the file until the end. So move to the end of the defun and insert a close parenthesis there. Don’t use C-M-e to move there, since that too will fail to work until the defun is balanced.

Now you can go to the beginning of the defun and type C-M-q. Usually all the lines from a certain point to the end of the function will shift to the right. There is probably a missing close parenthesis, or a superfluous open parenthesis, near that point. (However, don’t assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the C-M-q with C-_, since the old indentation is probably appropriate to the intended parentheses.

After you think you have fixed the problem, use C-M-q again. If the old indentation actually fit the intended nesting of parentheses, and you have put back those parentheses, C-M-q should not change anything.

15.2.2 Excess Close Parentheses

To deal with an excess close parenthesis, first insert an open parenthesis at the beginning of the file, back up over it, and type C-M-f to find the end of the unbalanced defun. (Then type C-^{⟨}\underline{\overline{SPC}}^{⟩} C-_C-u C-^{⟨}\underline{\overline{SPC}}^{⟩} to set the mark there, undo the insertion of the open parenthesis, and finally return to the mark.)

Then find the actual matching close parenthesis by typing C-M-f at the beginning of the defun. This will leave you somewhere short of the place where the defun ought to end. It is possible that you will find a spurious close parenthesis in that vicinity.

If you don’t see a problem at that point, the next thing to do is to type C-M-q at the beginning of the defun. A range of lines will probably shift left; if so, the missing open parenthesis or spurious close parenthesis is probably near the first of those lines. (However, don’t assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the C-M-q with C-_, since the old indentation is probably appropriate to the intended parentheses.

After you think you have fixed the problem, use C-M-q again. If the old indentation actually fit the intended nesting of parentheses, and you have put back those parentheses, C-M-q should not change anything.

15.3 Debugging Problems in Compilation

When an error happens during byte compilation, it is normally due to invalid syntax in the program you are compiling. The compiler prints a suitable error message in the ‘*Compile-Log*’ buffer, and then stops. The message may state a function name in which the error was found, or it may not. Either way, here is how to find out where in the file the error occurred.

What you should do is switch to the buffer ‘ *Compiler Input*’. (Note that the buffer name starts with a space, so it does not show up in M-x list-buffers.) This buffer contains the program being compiled, and point shows how far the byte compiler was able to read.

If the error was due to invalid Lisp syntax, point shows exactly where the invalid syntax was detected. The cause of the error is not necessarily near by! Use the techniques in the previous section to find the error.

If the error was detected while compiling a form that had been read successfully, then point is located at the end of the form. In this case, this technique can’t localize the error precisely, but can still show you which function to check.

15.4 Edebug

Edebug is a source-level debugger for Emacs Lisp programs with which you can:

• Step through evaluation, stopping before and after each expression.

• Set conditional or unconditional breakpoints.

• Stop when a specified condition is true (the global break event).

• Trace slow or fast, stopping briefly at each stop point, or at each breakpoint.

• Display expression results and evaluate expressions as if outside of Edebug.

• Automatically reevaluate a list of expressions and display their results each time Edebug updates the display.

• Output trace info on function enter and exit.

• Stop when an error occurs.

• Display a backtrace, omitting Edebug’s own frames.

• Specify argument evaluation for macros and defining forms.

• Obtain rudimentary coverage testing and frequency counts.

The first three sections below should tell you enough about Edebug to enable you to use it.

15.4.1 Using Edebug

To debug a Lisp program with Edebug, you must first instrument the Lisp code that you want to debug. A simple way to do this is to first move point into the definition of a function or macro and then do C-u C-M-x (eval-defun with a prefix argument). See Section 15.4.2 [Instrumenting], page 192, for alternative ways to instrument code.

Once a function is instrumented, any call to the function activates Edebug. Activating Edebug may stop execution and let you step through the function, or it may update the display and continue execution while checking for debugging commands, depending on which Edebug execution mode you have selected. The default execution mode is step, which does stop execution. See Section 15.4.3 [Edebug Execution Modes], page 193.

Within Edebug, you normally view an Emacs buffer showing the source of the Lisp code you are debugging. This is referred to as the source code buffer. This buffer is temporarily read-only.

An arrow at the left margin indicates the line where the function is executing. Point initially shows where within the line the function is executing, but this ceases to be true if you move point yourself.

If you instrument the definition of fac (shown below) and then execute (fac 3), here is what you normally see. Point is at the open-parenthesis before if.

     (defun fac (n)
     =>⋆(if (< 0 n)
           (* n (fac (1- n)))
         1))

The places within a function where Edebug can stop execution are called stop points. These occur both before and after each subexpression that is a list, and also after each variable reference. Here we show with periods the stop points found in the function fac:

     (defun fac (n)
       .(if .(< 0 n.).
           .(* n. .(fac (1- n.).).).
         1).)

The special commands of Edebug are available in the source code buffer in addition to the commands of Emacs Lisp mode. For example, you can type the Edebug command ^{⟨}\underline{\overline{SPC}}^{⟩} to execute until the next stop point. If you type ^{⟨}\underline{\overline{SPC}}^{⟩} once after entry to fac, here is the display you will see:

     (defun fac (n)
     =>(if ⋆(< 0 n)
           (* n (fac (1- n)))
         1))

When Edebug stops execution after an expression, it displays the expression’s value in the echo area.

Other frequently used commands are b to set a breakpoint at a stop point, g to execute until a breakpoint is reached, and q to exit Edebug and return to the top-level command loop. Type ? to display a list of all Edebug commands.

15.4.2 Instrumenting for Edebug

In order to use Edebug to debug Lisp code, you must first instrument the code. Instrumenting code inserts additional code into it, to invoke Edebug at the proper places.

Once you have loaded Edebug, the command C-M-x (eval-defun) is redefined so that when invoked with a prefix argument on a definition, it instruments the definition before evaluating it. (The source code itself is not modified.) If the variable edebug-all-defs is non-nil, that inverts the meaning of the prefix argument: then C-M-x instruments the definition unless it has a prefix argument. The default value of edebug-all-defs is nil. The command M-x edebug-all-defs toggles the value of the variable edebug-all-defs.

   If edebug-all-defs is non-nil, then the commands eval-region, eval-current-

buffer, and eval-buffer also instrument any definitions they evaluate. Similarly, edebugall-forms controls whether eval-region should instrument any form, even non-defining forms. This doesn’t apply to loading or evaluations in the minibuffer. The command M-x edebug-all-forms toggles this option.

Another command, M-x edebug-eval-top-level-form, is available to instrument any top-level form regardless of the value of edebug-all-defs or edebug-all-forms.

When Edebug is about to instrument code for the first time in a session, it runs the hook edebug-setup-hook, then sets it to nil. You can use this to load up Edebug specifications associated with a package you are using, but only when you also use Edebug.

While Edebug is active, the command I (edebug-instrument-callee) instruments the definition of the function or macro called by the list form after point, if is not already instrumented. This is possible only if Edebug knows where to find the source for that function; after loading Edebug, eval-region records the position of every definition it evaluates, even if not instrumenting it. See also the i command (see Section 15.4.4 [Jumping], page 194), which steps into the call after instrumenting the function.

Edebug knows how to instrument all the standard special forms, an interactive form with an expression argument, anonymous lambda expressions, and other defining forms. Edebug cannot know what a user-defined macro will do with the arguments of a macro call, so you must tell it; See Section 15.4.15 [Instrumenting Macro Calls], page 204, for details.

To remove instrumentation from a definition, simply reevaluate its definition in a way that does not instrument. There are two ways of evaluating forms that never instrument them: from a file with load, and from the minibuffer with eval-expression (M-:).

If Edebug detects a syntax error while instrumenting, it leaves point at the erroneous code and signals an invalid-read-syntax error.

See Section 15.4.9 [Edebug Eval], page 198, for other evaluation functions available inside of Edebug.

15.4.3 Edebug Execution Modes

Edebug supports several execution modes for running the program you are debugging. We call these alternatives Edebug execution modes; do not confuse them with major or minor modes. The current Edebug execution mode determines how far Edebug continues execution before stopping—whether it stops at each stop point, or continues to the next breakpoint, for example—and how much Edebug displays the progress of the evaluation before it stops.

Normally, you specify the Edebug execution mode by typing a command to continue the program in a certain mode. Here is a table of these commands. All except for S resume execution of the program, at least for a certain distance.

S Stop: don’t execute any more of the program for now, just wait for more Edebug

          commands (edebug-stop).

⟨\underline{\overline{SPC}}^{⟩} Step: stop at the next stop point encountered (edebug-step-mode).

n Next: stop at the next stop point encountered after an expression (edebugnext-mode). Also see edebug-forward-sexp in Section 15.4.5 [Edebug Misc], page 195.

t Trace: pause one second at each Edebug stop point (edebug-trace-mode).

T Rapid trace: update the display at each stop point, but don’t actually pause

          (edebug-Trace-fast-mode).

g Go: run until the next breakpoint (edebug-go-mode). See Section 15.4.6 [Breakpoints], page 195.

c Continue: pause one second at each breakpoint, and then continue (edebug-

          continue-mode).

C Rapid continue: move point to each breakpoint, but don’t pause (edebug-

          Continue-fast-mode).

G Go non-stop: ignore breakpoints (edebug-Go-nonstop-mode). You can still stop the program by typing S, or any editing command.

In general, the execution modes earlier in the above list run the program more slowly or stop sooner than the modes later in the list.

While executing or tracing, you can interrupt the execution by typing any Edebug command. Edebug stops the program at the next stop point and then executes the command you typed. For example, typing t during execution switches to trace mode at the next stop point. You can use S to stop execution without doing anything else.

If your function happens to read input, a character you type intending to interrupt execution may be read by the function instead. You can avoid such unintended results by paying attention to when your program wants input.

Keyboard macros containing the commands in this section do not completely work: exiting from Edebug, to resume the program, loses track of the keyboard macro. This is not easy to fix. Also, defining or executing a keyboard macro outside of Edebug does not affect commands inside Edebug. This is usually an advantage. But see the edebugcontinue-kbd-macro option (see Section 15.4.16 [Edebug Options], page 209).

When you enter a new Edebug level, the initial execution mode comes from the value of the variable edebug-initial-mode. By default, this specifies step mode. Note that you may reenter the same Edebug level several times if, for example, an instrumented function is called several times from one command.

15.4.4 Jumping

The commands described in this section execute until they reach a specified location. All except i make a temporary breakpoint to establish the place to stop, then switch to go mode. Any other breakpoint reached before the intended stop point will also stop execution. See Section 15.4.6 [Breakpoints], page 195, for the details on breakpoints.

These commands may fail to work as expected in case of nonlocal exit, because a nonlocal exit can bypass the temporary breakpoint where you expected the program to stop.

h Proceed to the stop point near where point is (edebug-goto-here).

f Run the program forward over one expression (edebug-forward-sexp).

o Run the program until the end of the containing sexp.

i Step into the function or macro called by the form after point.

The h command proceeds to the stop point near the current location if point, using a temporary breakpoint. See Section 15.4.6 [Breakpoints], page 195, for more about breakpoints.

The f command runs the program forward over one expression. More precisely, it sets a temporary breakpoint at the position that C-M-f would reach, then executes in go mode so that the program will stop at breakpoints.

With a prefix argument n, the temporary breakpoint is placed n sexps beyond point. If the containing list ends before n more elements, then the place to stop is after the containing expression.

Be careful that the position C-M-f finds is a place that the program will really get to; this may not be true in a cond, for example.

The f command does forward-sexp starting at point, rather than at the stop point, for flexibility. If you want to execute one expression from the current stop point, type w first, to move point there, and then type f.

The o command continues “out of” an expression. It places a temporary breakpoint at the end of the sexp containing point. If the containing sexp is a function definition itself, o continues until just before the last sexp in the definition. If that is where you are now, it returns from the function and then stops. In other words, this command does not exit the currently executing function unless you are positioned after the last sexp.

The i command steps into the function or macro called by the list form after point, and stops at its first stop point. Note that the form need not be the one about to be evaluated. But if the form is a function call about to be evaluated, remember to use this command before any of the arguments are evaluated, since otherwise it will be too late.

The i command instruments the function or macro it’s supposed to step into, if it isn’t instrumented already. This is convenient, but keep in mind that the function or macro remains instrumented unless you explicitly arrange to deinstrument it.

15.4.5 Miscellaneous Edebug Commands

Some miscellaneous Edebug commands are described here.

? Display the help message for Edebug (edebug-help).

C-] Abort one level back to the previous command level (abort-recursive-edit).

q Return to the top level editor command loop (top-level). This exits all recursive editing levels, including all levels of Edebug activity. However, instrumented code protected with unwind-protect or condition-case forms may resume debugging.

Q Like q but don’t stop even for protected code (top-level-nonstop).

r Redisplay the most recently known expression result in the echo area (edebug-

          previous-result).

d Display a backtrace, excluding Edebug’s own functions for clarity (edebug-

          backtrace).

You cannot use debugger commands in the backtrace buffer in Edebug as you would in the standard debugger. The backtrace buffer is killed automatically when you continue execution.

From the Edebug recursive edit, you may invoke commands that activate Edebug again recursively. Any time Edebug is active, you can quit to the top level with q or abort one recursive edit level with C-]. You can display a backtrace of all the pending evaluations with d.

15.4.6 Breakpoints

Edebug’s step mode stops execution at the next stop point reached. There are three other ways to stop Edebug execution once it has started: breakpoints, the global break condition, and source breakpoints.

While using Edebug, you can specify breakpoints in the program you are testing: points where execution should stop. You can set a breakpoint at any stop point, as defined in Section 15.4.1 [Using Edebug], page 191. For setting and unsetting breakpoints, the stop point that is affected is the first one at or after point in the source code buffer. Here are the Edebug commands for breakpoints:

b Set a breakpoint at the stop point at or after point (edebug-set-breakpoint). If you use a prefix argument, the breakpoint is temporary (it turns off the first time it stops the program).

u Unset the breakpoint (if any) at the stop point at or after point (edebug-unset-

          breakpoint).

x condition ^{⟨}\underline{\overline{RET}}^{⟩} Set a conditional breakpoint which stops the program only if condition evaluates

          to a non-nil value (edebug-set-conditional-breakpoint). With a prefix

argument, the breakpoint is temporary.

B Move point to the next breakpoint in the current definition (edebug-next-

          breakpoint).

While in Edebug, you can set a breakpoint with b and unset one with u. First move point to the Edebug stop point of your choice, then type b or u to set or unset a breakpoint there. Unsetting a breakpoint where none has been set has no effect.

Reevaluating or reinstrumenting a definition forgets all its breakpoints.

A conditional breakpoint tests a condition each time the program gets there. Any errors that occur as a result of evaluating the condition are ignored, as if the result were nil. To set a conditional breakpoint, use x, and specify the condition expression in the minibuffer. Setting a conditional breakpoint at a stop point that has a previously established conditional breakpoint puts the previous condition expression in the minibuffer so you can edit it.

You can make a conditional or unconditional breakpoint temporary by using a prefix arg with the command to set the breakpoint. When a temporary breakpoint stops the program, it is automatically unset.

Edebug always stops or pauses at a breakpoint except when the Edebug mode is Gononstop. In that mode, it ignores breakpoints entirely.

To find out where your breakpoints are, use the B command, which moves point to the next breakpoint following point, within the same function, or to the first breakpoint if there are no following breakpoints. This command does not continue execution—it just moves point in the buffer.

15.4.6.1 Global Break Condition

A global break condition stops execution when a specified condition is satisfied, no matter where that may occur. Edebug evaluates the global break condition at every stop point. If it evaluates to a non-nil value, then execution stops or pauses depending on the execution mode, as if a breakpoint had been hit. If evaluating the condition gets an error, execution does not stop.

The condition expression is stored in edebug-global-break-condition. You can specify a new expression using the X command (edebug-set-global-break-condition).

The global break condition is the simplest way to find where in your code some event occurs, but it makes code run much more slowly. So you should reset the condition to nil when not using it.

15.4.6.2 Source Breakpoints

All breakpoints in a definition are forgotten each time you reinstrument it. To make a breakpoint that won’t be forgotten, you can write a source breakpoint, which is simply a call to the function edebug in your source code. You can, of course, make such a call conditional. For example, in the fac function, insert the first line as shown below to stop when the argument reaches zero:

     (defun fac (n)
       (if (= n 0) (edebug))
       (if (< 0 n)
           (* n (fac (1- n)))
         1))

When the fac definition is instrumented and the function is called, the call to edebug acts as a breakpoint. Depending on the execution mode, Edebug stops or pauses there.

If no instrumented code is being executed when edebug is called, that function calls

debug.

15.4.7 Trapping Errors

Emacs normally displays an error message when an error is signaled and not handled with condition-case. While Edebug is active, it normally responds to all unhandled errors. You can customize this with the options edebug-on-error and edebug-on-quit; see Section 15.4.16 [Edebug Options], page 209.

When Edebug responds to an error, it shows the last stop point encountered before the error. This may be the location of a call to a function which was not instrumented, within which the error actually occurred. For an unbound variable error, the last known stop point might be quite distant from the offending variable reference. In that case you might want to display a full backtrace (see Section 15.4.5 [Edebug Misc], page 195).

If you change debug-on-error or debug-on-quit while Edebug is active, these changes will be forgotten when Edebug becomes inactive. Furthermore, during Edebug’s recursive edit, these variables are bound to the values they had outside of Edebug.

15.4.8 Edebug Views

These Edebug commands let you view aspects of the buffer and window status that obtained before entry to Edebug. The outside window configuration is the collection of windows and contents that were in effect outside of Edebug.

v Temporarily view the outside window configuration (edebug-view-outside). p Temporarily display the outside current buffer with point at its outside posi-

tion (edebug-bounce-point). With a prefix argument n, pause for n seconds instead.

w Move point back to the current stop point (edebug-where) in the source code buffer. Also, if you use this command in a different window displaying the same buffer, that window will be used instead to display the current definition in the future.

W Toggle whether Edebug saves and restores the outside window configuration

          (edebug-toggle-save-windows).

With a prefix argument, W only toggles saving and restoring of the selected window. To specify a window that is not displaying the source code buffer, you must use C-x X W from the global keymap.

You can view the outside window configuration with v or just bounce to the point in the current buffer with p, even if it is not normally displayed. After moving point, you may wish to jump back to the stop point with w from a source code buffer.

Each time you use W to turn saving off, Edebug forgets the saved outside window configuration—so that even if you turn saving back on, the current window configuration remains unchanged when you next exit Edebug (by continuing the program). However, the automatic redisplay of ‘*edebug*’ and ‘*edebug-trace*’ may conflict with the buffers you wish to see unless you have enough windows open.

15.4.9 Evaluation

While within Edebug, you can evaluate expressions “as if” Edebug were not running. Edebug tries to be invisible to the expression’s evaluation and printing. Evaluation of expressions that cause side effects will work as expected except for things that Edebug explicitly saves and restores. See Section 15.4.14 [The Outside Context], page 202, for details on this process.

e exp ^{⟨}\underline{\overline{RET}}^{⟩} Evaluate expression exp in the context outside of Edebug (edebug-eval-expression). That is, Edebug tries to minimize its interference with the evaluation.

M-: exp ^{⟨}\underline{\overline{RET}}^{⟩} Evaluate expression exp in the context of Edebug itself.

C-x C-e Evaluate the expression before point, in the context outside of Edebug (edebug-

          eval-last-sexp).

Edebug supports evaluation of expressions containing references to lexically bound symbols created by the following constructs in ‘cl.el’ (version 2.03 or later): lexical-let,

macrolet, and symbol-macrolet.

15.4.10 Evaluation List Buffer

You can use the evaluation list buffer, called ‘*edebug*’, to evaluate expressions interactively. You can also set up the evaluation list of expressions to be evaluated automatically each time Edebug updates the display.

E Switch to the evaluation list buffer ‘*edebug*’ (edebug-visit-eval-list).

In the ‘*edebug*’ buffer you can use the commands of Lisp Interaction mode (see section “Lisp Interaction” in The GNU Emacs Manual) as well as these special commands:

LFD Evaluate the expression before point, in the outside context, and insert the

          value in the buffer (edebug-eval-print-last-sexp).

C-x C-e Evaluate the expression before point, in the context outside of Edebug (edebug-

          eval-last-sexp).

C-c C-u Build a new evaluation list from the contents of the buffer (edebug-update-

          eval-list).

C-c C-d Delete the evaluation list group that point is in (edebug-delete-eval-item).

C-c C-w Switch back to the source code buffer at the current stop point (edebug-where).

You can evaluate expressions in the evaluation list window with LFD or C-x C-e, just as you would in ‘*scratch*’; but they are evaluated in the context outside of Edebug.

The expressions you enter interactively (and their results) are lost when you continue execution; but you can set up an evaluation list consisting of expressions to be evaluated each time execution stops.

To do this, write one or more evaluation list groups in the evaluation list buffer. An evaluation list group consists of one or more Lisp expressions. Groups are separated by comment lines.

The command C-c C-u (edebug-update-eval-list) rebuilds the evaluation list, scanning the buffer and using the first expression of each group. (The idea is that the second expression of the group is the value previously computed and displayed.)

Be careful not to add expressions that execute instrumented code since that would cause an infinite loop.

Each entry to Edebug redisplays the evaluation list by inserting each expression in the buffer, followed by its current value. It also inserts comment lines so that each expression becomes its own group. Thus, if you type C-c C-u again without changing the buffer text, the evaluation list is effectively unchanged.

If an error occurs during an evaluation from the evaluation list, the error message is displayed in a string as if it were the result. Therefore, expressions that use variables not currently valid do not interrupt your debugging.

Here is an example of what the evaluation list window looks like after several expressions have been added to it:

     (current-buffer)
     #<buffer *scratch*>
     ;---------------------------------------------------------------

(selected-window)
#<window 16 on *scratch*>
;---------------------------------------------------------------
(point)
196
;---------------------------------------------------------------
bad-var
"Symbol's value as variable is void: bad-var"
;---------------------------------------------------------------
(recursion-depth)
0
;---------------------------------------------------------------
this-command
eval-last-sexp
;---------------------------------------------------------------

To delete a group, move point into it and type C-c C-d, or simply delete the text for the group and update the evaluation list with C-c C-u. To add a new expression to the evaluation list, insert the expression at a suitable place, and insert a new comment line. (You need not insert dashes in the comment line—its contents don’t matter.) Then type

C-c C-u.

After selecting ‘*edebug*’, you can return to the source code buffer with C-c C-w. The ‘*edebug*’ buffer is killed when you continue execution, and recreated next time it is needed.

15.4.11 Printing in Edebug

If an expression in your program produces a value containing circular list structure, you may get an error when Edebug attempts to print it.

One way to cope with circular structure is to set print-length or print-level to truncate the printing. Edebug does this for you; it binds print-length and print-level to 50

if they were nil. (Actually, the variables edebug-print-length and edebug-print-level

specify the values to use within Edebug.) See Section 16.6 [Output Variables], page 220.

You can also print circular structures and structures that share elements more informatively by using the ‘cust-print’ package.

To load ‘cust-print’ and activate custom printing only for Edebug, simply use the command M-x edebug-install-custom-print. To restore the standard print functions,

use M-x edebug-uninstall-custom-print.

Here is an example of code that creates a circular structure:

(setq a '(x y))
(setcar a a))

Custom printing prints this as ‘Result: #1=(#1# y)’. The ‘#1=’ notation labels the structure that follows it with the label ‘1’, and the ‘#1#’ notation references the previously labelled structure. This notation is used for any shared elements of lists or vectors.

Other programs can also use custom printing; see ‘cust-print.el’ for details.

15.4.12 Trace Buffer

Edebug can record an execution trace, storing it in a buffer named ‘*edebug-trace*’. This is a log of function calls and returns, showing the function names and their arguments and values. To enable trace recording, set edebug-trace to a non-nil value.

Making a trace buffer is not the same thing as using trace execution mode (see Section 15.4.3 [Edebug Execution Modes], page 193).

When trace recording is enabled, each function entry and exit adds lines to the trace buffer. A function entry record looks like ‘::::{’ followed by the function name and argument values. A function exit record looks like ‘::::}’ followed by the function name and result of the function.

The number of ‘:’s in an entry shows its recursion depth. You can use the braces in the trace buffer to find the matching beginning or end of function calls.

You can customize trace recording for function entry and exit by redefining the functions

edebug-print-trace-before and edebug-print-trace-after.

Macro edebug-tracing string body…

This macro requests additional trace information around the execution of the body forms. The argument string specifies text to put in the trace buffer. All the arguments are evaluated. edebug-tracing returns the value of the last form in body.

Function edebug-trace format-string &rest format-args This function inserts text in the trace buffer. It computes the text with (apply 'format format-string format-args). It also appends a newline to separate entries.

edebug-tracing and edebug-trace insert lines in the trace buffer even if Edebug is not active.

Adding text to the trace buffer also scrolls its window to show the last lines inserted.

15.4.13 Coverage Testing

Edebug provides rudimentary coverage testing and display of execution frequency. All execution of an instrumented function accumulates frequency counts, both before and after evaluation of each instrumented expression, even if the execution mode is Go-nonstop. Coverage testing is more expensive, so it is only done if edebug-test-coverage is non-nil. The command M-x edebug-display-freq-count displays both the frequency data and the coverage data (if recorded).

Command edebug-display-freq-count

This command displays the frequency count data for each line of the current definition. The frequency counts appear as comment lines after each line of code, and you can undo all insertions with one undo command. The counts appear under the ( before an expression or the ) after an expression, or on the last character of a symbol. Values do not appear if they are equal to the previous count on the same line. The character ‘=’ following the count for an expression says that the expression has returned the same value each time it was evaluated This is the only coverage information that Edebug records. To clear the frequency count and coverage data for a definition, reinstrument it.

For example, after evaluating (fac 5) with a source breakpoint, and setting edebugtest-coverage to t, when the breakpoint is reached, the frequency data looks like this:

     (defun fac (n)
       (if (= n 0) (edebug))
     ;#6           1      0 =5
       (if (< 0 n)
     ;#5         =
           (* n (fac (1- n)))
     ;#    5               0
         1))
     ;#   0

The comment lines show that fac was called 6 times. The first if statement returned 5 times with the same result each time; the same is true of the condition on the second if. The recursive call of fac did not return at all.

15.4.14 The Outside Context

Edebug tries to be transparent to the program you are debugging, but it does not succeed completely. Edebug also tries to be transparent when you evaluate expressions with e or with the evaluation list buffer, by temporarily restoring the outside context. This section explains precisely what context Edebug restores, and how Edebug fails to be completely transparent.

15.4.14.1 Checking Whether to Stop

Whenever Edebug is entered, it needs to save and restore certain data before even deciding whether to make trace information or stop the program.

  • max-lisp-eval-depth and max-specpdl-size are both incremented one time to re-

duce Edebug’s impact on the stack. You could, however, still run out of stack space when using Edebug.

• The state of keyboard macro execution is saved and restored. While Edebug is active,

    executing-macro is bound to edebug-continue-kbd-macro.

15.4.14.2 Edebug Display Update

When Edebug needs to display something (e.g., in trace mode), it saves the current window configuration from “outside” Edebug (see Section 25.17 [Window Configurations], page 406). When you exit Edebug (by continuing the program), it restores the previous window configuration.

Emacs redisplays only when it pauses. Usually, when you continue execution, the program comes back into Edebug at a breakpoint or after stepping without pausing or reading input in between. In such cases, Emacs never gets a chance to redisplay the “outside” configuration. What you see is the same window configuration as the last time Edebug was active, with no interruption.

Entry to Edebug for displaying something also saves and restores the following data, but some of these are deliberately not restored if an error or quit signal occurs.

• Which buffer is current, and the positions of point and the mark in the current buffer, are saved and restored.

• The outside window configuration is saved and restored if edebug-save-windows is non-nil (see Section 15.4.14.2 [Edebug Display Update], page 202). The window configuration is not restored on error or quit, but the outside selected window is reselected even on error or quit in case a save-excursion is active. If the value of edebug-save-windows is a list, only the listed windows are saved and restored. The window start and horizontal scrolling of the source code buffer are not restored, however, so that the display remains coherent within Edebug.

• The value of point in each displayed buffer is saved and restored if edebug-save-

displayed-buffer-points is non-nil.
• The variables overlay-arrow-position and overlay-arrow-string are saved and

restored. So you can safely invoke Edebug from the recursive edit elsewhere in the same buffer.

• cursor-in-echo-area is locally bound to nil so that the cursor shows up in the window.

15.4.14.3 Edebug Recursive Edit

When Edebug is entered and actually reads commands from the user, it saves (and later restores) these additional data:

• The current match data. See Section 30.6 [Match Data], page 501.

• last-command, this-command, last-command-char, last-input-char, last-input-
event, last-command-event, last-event-frame, last-nonmenu-event, and track-

mouse. Commands used within Edebug do not affect these variables outside of Edebug. The key sequence returned by this-command-keys is changed by executing commands within Edebug and there is no way to reset the key sequence from Lisp. Edebug cannot save and restore the value of unread-command-events. Entering Edebug while this variable has a nontrivial value can interfere with execution of the program you are debugging.

• Complex commands executed while in Edebug are added to the variable commandhistory. In rare cases this can alter execution.

• Within Edebug, the recursion depth appears one deeper than the recursion depth outside Edebug. This is not true of the automatically updated evaluation list window.

• standard-output and standard-input are bound to nil by the recursive-edit, but

Edebug temporarily restores them during evaluations.

• The state of keyboard macro definition is saved and restored. While Edebug is active,

    defining-kbd-macro is bound to edebug-continue-kbd-macro.

15.4.15 Instrumenting Macro Calls

When Edebug instruments an expression that calls a Lisp macro, it needs additional advice to do the job properly. This is because there is no way to tell which subexpressions of the macro call are forms to be evaluated. (Evaluation may occur explicitly in the macro body, or when the resulting expansion is evaluated, or any time later.) You must explain the format of calls to each macro to enable Edebug to handle it. To do this, use defedebug-spec to define the format of calls to a given macro.

Macro def-edebug-spec macro specification Specify which expressions of a call to macro macro are forms to be evaluated. For simple macros, the specification often looks very similar to the formal argument list of the macro definition, but specifications are much more general than macro arguments. The macro argument may actually be any symbol, not just a macro name.

Here is a simple example that defines the specification for the for macro described in the Emacs Lisp Reference Manual, followed by an alternative, equivalent specification.

     (def-edebug-spec for
       (symbolp "from" form "to" form "do" &rest form))
     (def-edebug-spec for
       (symbolp ['from form] ['to form] ['do body]))

Here is a table of the possibilities for specification and how each directs processing of arguments.

t All arguments are instrumented for evaluation.

0 None of the arguments is instrumented.

a symbol The symbol must have an Edebug specification which is used instead. This indirection is repeated until another kind of specification is found. This allows you to inherit the specification for another macro.

a list The elements of the list describe the types of the arguments of a calling form. The possible elements of a specification list are described in the following sections.

15.4.15.1 Specification List

A specification list is required for an Edebug specification if some arguments of a macro call are evaluated while others are not. Some elements in a specification list match one or more arguments, but others modify the processing of all following elements. The latter, called specification keywords, are symbols beginning with ‘&’ (such as &optional).

A specification list may contain sublists which match arguments that are themselves lists, or it may contain vectors used for grouping. Sublists and groups thus subdivide the specification list into a hierarchy of levels. Specification keywords only apply to the remainder of the sublist or group they are contained in.

When a specification list involves alternatives or repetition, matching it against an actual macro call may require backtracking. See Section 15.4.15.2 [Backtracking], page 207, for more details.

Edebug specifications provide the power of regular expression matching, plus some context-free grammar constructs: the matching of sublists with balanced parentheses, recursive processing of forms, and recursion via indirect specifications.

Here’s a table of the possible elements of a specification list, with their meanings:

sexp A single Lisp object, not unevaluated.

form A single evaluated expression, which is instrumented.

place A place to store a value, as in the Common Lisp setf construct.

body  Short for &rest form. See &rest below.
function-form

A function form: either a quoted function symbol, a quoted lambda expression, or a form (that should evaluate to a function symbol or lambda expression). This is useful when an argument that’s a lambda expression might be quoted with quote rather than function, since it instruments the body of the lambda expression either way.

lambda-expr

A lambda expression with no quoting.

&optional

All following elements in the specification list are optional; as soon as one does not match, Edebug stops matching at this level. To make just a few elements optional followed by non-optional elements, use [&optional specs…]. To specify that several elements must all match or none, use &optional [specs…]. See the defun example below.

&rest All following elements in the specification list are repeated zero or more times. All the elements need not match in the last repetition, however. To repeat only a few elements, use [&rest specs…]. To specify several elements that must all match on every repetition, use &rest [specs…].

&or Each of the following elements in the specification list is an alternative. One of the alternatives must match, or the &or specification fails. Each list element following &or is a single alternative. To group two or more list elements as a single alternative, enclose them in […].

&not Each of the following elements is matched as alternatives as if by using &or, but if any of them match, the specification fails. If none of them match, nothing is matched, but the &not specification succeeds.

&define Indicates that the specification is for a defining form. The defining form itself is not instrumented (i.e. Edebug does not stop before and after the defining form), but forms inside it typically will be instrumented. The &define keyword should be the first element in a list specification.

nil This is successful when there are no more arguments to match at the current argument list level; otherwise it fails. See sublist specifications and the backquote example below.

gate No argument is matched but backtracking through the gate is disabled while matching the remainder of the specifications at this level. This is primarily used to generate more specific syntax error messages. See Section 15.4.15.2 [Backtracking], page 207, for more details. Also see the let example below.

other-symbol Any other symbol in a specification list may be a predicate or an indirect specification. If the symbol has an Edebug specification, this indirect specification should be either a list specification that is used in place of the symbol, or a function that is called to process the arguments. The specification may be defined with def-edebug-spec just as for macros. See the defun example below. Otherwise, the symbol should be a predicate. The predicate is called with the argument and the specification fails if the predicate returns nil. In either case, that argument is not instrumented. Some suitable predicates include symbolp, integerp, stringp, vectorp, and

atom.

[elements…] A vector of elements groups the elements into a single group specification. Its meaning has nothing to do with vectors.

"string" The argument should be a symbol named string. This specification is equivalent to the quoted symbol, 'symbol, where the name of symbol is the string, but the string form is preferred.

(vector elements…)

The argument should be a vector whose elements must match the elements in the specification. See the backquote example below.

(elements…)

Any other list is a sublist specification and the argument must be a list whose elements match the specification elements. A sublist specification may be a dotted list and the corresponding list argument may then be a dotted list. Alternatively, the last cdr of a dotted list specification may be another sublist specification (via a grouping or an indirect specification, e.g. (spec . [(more specs…)])) whose elements match the non-dotted list arguments. This is useful in recursive specifications such as in the backquote example below. Also see the description of a nil specification above for terminating such recursion. Note that a sublist specification written as (specs . nil) is equivalent to

(specs), and (specs . (sublist-elements. . .)) is equivalent to (specs
sublist-elements. . .).

Here is a list of additional specifications that may only appear after &define. See the defun example below.

name The argument, a symbol, is the name of the defining form.

A defining form is not required to have a name field; and it may have multiple name fields.

:name This construct does not actually match an argument. The element following :name should be a symbol; it is used as an additional name component for the definition. You can use this to add a unique, static component to the name of the definition. It may be used more than once.

arg The argument, a symbol, is the name of an argument of the defining form. However, lambda list keywords (symbols starting with ‘&’) are not allowed.

lambda-list

This matches a lambda list—the argument list of a lambda expression.

def-body The argument is the body of code in a definition. This is like body, described above, but a definition body must be instrumented with a different Edebug call that looks up information associated with the definition. Use def-body for the highest level list of forms within the definition.

def-form The argument is a single, highest-level form in a definition. This is like defbody, except use this to match a single form rather than a list of forms. As a special case, def-form also means that tracing information is not output when the form is executed. See the interactive example below.

15.4.15.2 Backtracking

If a specification fails to match at some point, this does not necessarily mean a syntax error will be signaled; instead, backtracking will take place until all alternatives have been exhausted. Eventually every element of the argument list must be matched by some element in the specification, and every required element in the specification must match some argument.

Backtracking is disabled for the remainder of a sublist or group when certain conditions occur, described below. Backtracking is reenabled when a new alternative is established by &optional, &rest, or &or. It is also reenabled initially when processing a sublist or group specification or an indirect specification.

You might want to disable backtracking to commit to some alternative so that Edebug can provide a more specific syntax error message. Normally, if no alternative matches, Edebug reports that none matched, but if one alternative is committed to, Edebug can report how it failed to match.

First, backtracking is disabled while matching any of the form specifications (i.e. form, body, def-form, and def-body). These specifications will match any form so any error must be in the form itself rather than at a higher level.

Second, backtracking is disabled after successfully matching a quoted symbol or string specification, since this usually indicates a recognized construct. If you have a set of alternative constructs that all begin with the same symbol, you can usually work around this constraint by factoring the symbol out of the alternatives, e.g., ["foo" &or [first case]

[second case] ...].

Third, backtracking may be explicitly disabled by using the gate specification. This is useful when you know that no higher alternatives may apply.

15.4.15.3 Specification Examples

It may be easier to understand Edebug specifications by studying the examples provided here.

A let special form has a sequence of bindings and a body. Each of the bindings is either a symbol or a sublist with a symbol and optional value. In the specification below, notice the gate inside of the sublist to prevent backtracking once a sublist is found.

     (def-edebug-spec let
       ((&rest
         &or symbolp (gate symbolp &optional form))
        body))

Edebug uses the following specifications for defun and defmacro and the associated argument list and interactive specifications. It is necessary to handle interactive forms specially since an expression argument it is actually evaluated outside of the function body.

     (def-edebug-spec defmacro defun) ; Indirect ref to defun spec.
     (def-edebug-spec defun
       (&define name lambda-list

[&optional stringp] ; Match the doc string, if present.

                [&optional ("interactive" interactive)]
                def-body))
     (def-edebug-spec lambda-list
       (([&rest arg]
         [&optional ["&optional" arg &rest arg]]
         &optional ["&rest" arg]
         )))
     (def-edebug-spec interactive
       (&optional &or stringp def-form))    ; Notice: def-form

The specification for backquote below illustrates how to match dotted lists and use nil to terminate recursion. It also illustrates how components of a vector may be matched. (The actual specification defined by Edebug does not support dotted lists because doing so causes very deep recursion that could fail.)

     (def-edebug-spec ` (backquote-form))   ; Alias just for clarity.
     (def-edebug-spec backquote-form
       (&or ([&or "," ",@"] &or ("quote" backquote-form) form)
            (backquote-form . [&or nil backquote-form])
            (vector &rest backquote-form)
            sexp))

15.4.16 Edebug Options

These options affect the behavior of Edebug:

User Option edebug-setup-hook

Functions to call before Edebug is used. Each time it is set to a new value, Edebug will call those functions once and then edebug-setup-hook is reset to nil. You could use this to load up Edebug specifications associated with a package you are using but only when you also use Edebug. See Section 15.4.2 [Instrumenting], page 192.

User Option edebug-all-defs

If this is non-nil, normal evaluation of defining forms such as defun and defmacro instruments them for Edebug. This applies to eval-defun, eval-

region, eval-buffer, and eval-current-buffer.

Use the command M-x edebug-all-defs to toggle the value of this option. See Section 15.4.2 [Instrumenting], page 192.

User Option edebug-all-forms

If this is non-nil, the commands eval-defun, eval-region, eval-buffer,

and eval-current-buffer instrument all forms, even those that don’t define anything. This doesn’t apply to loading or evaluations in the minibuffer. Use the command M-x edebug-all-forms to toggle the value of this option. See Section 15.4.2 [Instrumenting], page 192.

User Option edebug-save-windows

If this is non-nil, Edebug saves and restores the window configuration. That takes some time, so if your program does not care what happens to the window configurations, it is better to set this variable to nil. If the value is a list, only the listed windows are saved and restored. You can use the W command in Edebug to change this variable interactively. See Section 15.4.14.2 [Edebug Display Update], page 202.

User Option edebug-save-displayed-buffer-points

If this is non-nil, Edebug saves and restores point in all displayed buffers. Saving and restoring point in other buffers is necessary if you are debugging code that changes the point of a buffer which is displayed in a non-selected window. If Edebug or the user then selects the window, point in that buffer will move to the window’s value of point. Saving and restoring point in all buffers is expensive, since it requires selecting each window twice, so enable this only if you need it. See Section 15.4.14.2 [Edebug Display Update], page 202.

User Option edebug-initial-mode

If this variable is non-nil, it specifies the initial execution mode for Edebug when it is first activated. Possible values are step, next, go, Go-nonstop,

trace, Trace-fast, continue, and Continue-fast.

The default value is step. See Section 15.4.3 [Edebug Execution Modes], page 193.

User Option edebug-trace

Non-nil means display a trace of function entry and exit. Tracing output is displayed in a buffer named ‘*edebug-trace*’, one function entry or exit per line, indented by the recursion level. The default value is nil. Also see edebug-tracing, in See Section 15.4.12 [Trace Buffer], page 201.

User Option edebug-test-coverage

If non-nil, Edebug tests coverage of all expressions debugged. This is done by comparing the result of each expression with the previous result. Coverage is considered OK if two different results are found. So to sufficiently test the coverage of your code, try to execute it under conditions that evaluate all expressions more than once, and produce different results for each expression. Use M-x edebug-display-freq-count to display the frequency count and coverage information for a definition. See Section 15.4.13 [Coverage Testing], page 201.

User Option edebug-continue-kbd-macro

If non-nil, continue defining or executing any keyboard macro that is executing outside of Edebug. Use this with caution since it is not debugged. See Section 15.4.3 [Edebug Execution Modes], page 193.

User Option edebug-print-length

If non-nil, bind print-length to this while printing results in Edebug. The default value is 50. See Section 15.4.11 [Printing in Edebug], page 200.

User Option edebug-print-level

If non-nil, bind print-level to this while printing results in Edebug. The default value is 50.

User Option edebug-print-circle

If non-nil, bind print-circle to this while printing results in Edebug. The default value is nil.

User Option edebug-on-error

Edebug binds debug-on-error to this value, if debug-on-error was previously nil. See Section 15.4.7 [Trapping Errors], page 197.

User Option edebug-on-quit

Edebug binds debug-on-quit to this value, if debug-on-quit was previously nil. See Section 15.4.7 [Trapping Errors], page 197.

If you change the values of edebug-on-error or edebug-on-quit while Edebug is active, their values won’t be used until the next time Edebug is invoked via a new command.

User Option edebug-global-break-condition

If non-nil, an expression to test for at every stop point. If the result is non-nil, then break. Errors are ignored. See Section 15.4.6.1 [Global Break Condition], page 196.

212 GNU Emacs Lisp Reference Manual

16 Reading and Printing Lisp Objects

Printing and reading are the operations of converting Lisp objects to textual form and vice versa. They use the printed representations and read syntax described in Chapter 2 [Lisp Data Types], page 15.

This chapter describes the Lisp functions for reading and printing. It also describes streams, which specify where to get the text (if reading) or where to put it (if printing).

16.1 Introduction to Reading and Printing

Reading a Lisp object means parsing a Lisp expression in textual form and producing a corresponding Lisp object. This is how Lisp programs get into Lisp from files of Lisp code. We call the text the read syntax of the object. For example, the text ‘(a . 5)’ is the read syntax for a cons cell whose car is a and whose cdr is the number 5.

Printing a Lisp object means producing text that represents that object—converting the object to its printed representation. Printing the cons cell described above produces the text ‘(a . 5)’.

Reading and printing are more or less inverse operations: printing the object that results from reading a given piece of text often produces the same text, and reading the text that results from printing an object usually produces a similar-looking object. For example, printing the symbol foo produces the text ‘foo’, and reading that text returns the symbol foo. Printing a list whose elements are a and b produces the text ‘(a b)’, and reading that text produces a list (but not the same list) with elements a and b.

However, these two operations are not precisely inverses. There are three kinds of exceptions:

• Printing can produce text that cannot be read. For example, buffers, windows, frames, subprocesses and markers print into text that starts with ‘#’; if you try to read this text, you get an error. There is no way to read those data types.

• One object can have multiple textual representations. For example, ‘1’ and ‘01’ represent the same integer, and ‘(a b)’ and ‘(a . (b))’ represent the same list. Reading will accept any of the alternatives, but printing must choose one of them.

• Comments can appear at certain points in the middle of an object’s read sequence without affecting the result of reading it.

16.2 Input Streams

Most of the Lisp functions for reading text take an input stream as an argument. The input stream specifies where or how to get the characters of the text to be read. Here are the possible types of input stream:

buffer The input characters are read from buffer, starting with the character directly after point. Point advances as characters are read.

marker The input characters are read from the buffer that marker is in, starting with the character directly after the marker. The marker position advances as characters are read. The value of point in the buffer has no effect when the stream is a marker.

string The input characters are taken from string, starting at the first character in the string and using as many characters as required.

function The input characters are generated by function, one character per call. Normally function is called with no arguments, and should return a character. Occasionally function is called with one argument (always a character). When that happens, function should save the argument and arrange to return it on the next call. This is called unreading the character; it happens when the Lisp reader reads one character too many and wants to “put it back where it came from”.

t t used as a stream means that the input is read from the minibuffer. In fact, the minibuffer is invoked once and the text given by the user is made into a string that is then used as the input stream.

nil nil supplied as an input stream means to use the value of standard-input instead; that value is the default input stream, and must be a non-nil input stream.

symbol A symbol as input stream is equivalent to the symbol’s function definition (if any).

Here is an example of reading from a stream that is a buffer, showing where point is located before and after:

---------- Buffer: foo ----------
This⋆ is the contents of foo.
---------- Buffer: foo ----------
(read (get-buffer "foo"))
⇒ is
(read (get-buffer "foo"))
⇒ the
---------- Buffer: foo ----------
This is the⋆ contents of foo.
---------- Buffer: foo ----------

Note that the first read skips a space. Reading skips any amount of whitespace preceding the significant text.

In Emacs 18, reading a symbol discarded the delimiter terminating the symbol. Thus, point would end up at the beginning of ‘contents’ rather than after ‘the’. The Emacs 19 behavior is superior because it correctly handles input such as ‘bar(foo)’, where the open-parenthesis that ends one object is needed as the beginning of another object.

Here is an example of reading from a stream that is a marker, initially positioned at the beginning of the buffer shown. The value read is the symbol This.

---------- Buffer: foo ----------
This is the contents of foo.
---------- Buffer: foo ----------

(setq m (set-marker (make-marker) 1 (get-buffer "foo")))
     ⇒ #<marker at 1 in foo>
(read m) ⇒ This
m

⇒ #<marker at 5 in foo> ;; Before the first space.

Here we read from the contents of a string:

(read "(When in) the course")
     ⇒ (When in)

The following example reads from the minibuffer. The prompt is: ‘Lisp expression: ’. (That is always the prompt used when you read from the stream t.) The user’s input is shown following the prompt.

(read t)
     ⇒ 23
---------- Buffer: Minibuffer ----------
Lisp expression: 23 ^{⟨}\underline{\overline{RET}}^{⟩}
---------- Buffer: Minibuffer ----------

Finally, here is an example of a stream that is a function, named useless-stream. Before we use the stream, we initialize the variable useless-list to a list of characters. Then each call to the function useless-stream obtains the next character in the list or unreads a character by adding it to the front of the list.

(setq useless-list (append "XY()" nil))
     ⇒ (88 89 40 41)
(defun useless-stream (&optional unread)
  (if unread
      (setq useless-list (cons unread useless-list))
    (prog1 (car useless-list)
           (setq useless-list (cdr useless-list)))))
     ⇒ useless-stream

Now we read using the stream thus constructed:

(read 'useless-stream)
     ⇒ XY
useless-list
     ⇒ (40 41)

Note that the open and close parentheses remains in the list. The Lisp reader encountered the open parenthesis, decided that it ended the input, and unread it. Another attempt to read from the stream at this point would read ‘()’ and return nil.

Function get-file-char

This function is used internally as an input stream to read from the input file opened by the function load. Don’t use this function yourself.

16.3 Input Functions

This section describes the Lisp functions and variables that pertain to reading. In the functions below, stream stands for an input stream (see the previous section). If

stream is nil or omitted, it defaults to the value of standard-input.

An end-of-file error is signaled if reading encounters an unterminated list, vector, or string.

Function read &optional stream This function reads one textual Lisp expression from stream, returning it as a Lisp object. This is the basic Lisp input function.

Function read-from-string string &optional start end This function reads the first textual Lisp expression from the text in string. It returns a cons cell whose car is that expression, and whose cdr is an integer giving the position of the next remaining character in the string (i.e., the first one not read). If start is supplied, then reading begins at index start in the string (where the first character is at index 0). If end is also supplied, then reading stops just before that index, as if the rest of the string were not there. For example:

     (read-from-string "(setq x 55) (setq y 5)")
          ⇒ ((setq x 55) . 11)
     (read-from-string "\"A short string\"")
          ⇒ ("A short string" . 16)

;; Read starting at the first character.

     (read-from-string "(list 112)" 0)
          ⇒ ((list 112) . 10)

;; Read starting at the second character.

     (read-from-string "(list 112)" 1)
          ⇒ (list . 5)

;; Read starting at the seventh character,

;; and stopping at the ninth.

     (read-from-string "(list 112)" 6 8)
          ⇒ (11 . 8)

Variable standard-input

This variable holds the default input stream—the stream that read uses when the stream argument is nil.

16.4 Output Streams

An output stream specifies what to do with the characters produced by printing. Most print functions accept an output stream as an optional argument. Here are the possible types of output stream:

buffer The output characters are inserted into buffer at point. Point advances as characters are inserted. marker The output characters are inserted into the buffer that marker points into, at

the marker position. The marker position advances as characters are inserted. The value of point in the buffer has no effect on printing when the stream is a marker.

function The output characters are passed to function, which is responsible for storing them away. It is called with a single character as argument, as many times as there are characters to be output, and is free to do anything at all with the characters it receives.

t The output characters are displayed in the echo area.

nil nil specified as an output stream means to the value of standard-output instead; that value is the default output stream, and must be a non-nil output stream.

symbol A symbol as output stream is equivalent to the symbol’s function definition (if any).

Many of the valid output streams are also valid as input streams. The difference between input and output streams is therefore mostly one of how you use a Lisp object, not a distinction of types of object.

Here is an example of a buffer used as an output stream. Point is initially located as shown immediately before the ‘h’ in ‘the’. At the end, point is located directly before that same ‘h’.

(setq m (set-marker (make-marker) 10 (get-buffer "foo")))
     ⇒ #<marker at 10 in foo>
---------- Buffer: foo ----------
This is t⋆he contents of foo.
---------- Buffer: foo ----------
(print "This is the output" (get-buffer "foo"))
     ⇒ "This is the output"
m
     ⇒ #<marker at 32 in foo>
---------- Buffer: foo ----------
This is t
"This is the output"
⋆he contents of foo.
---------- Buffer: foo ----------

Now we show a use of a marker as an output stream. Initially, the marker is in buffer foo, between the ‘t’ and the ‘h’ in the word ‘the’. At the end, the marker has advanced over the inserted text so that it remains positioned before the same ‘h’. Note that the location of point, shown in the usual fashion, has no effect.

---------- Buffer: foo ----------
"This is the ⋆output"
---------- Buffer: foo ----------
m
     ⇒ #<marker at 11 in foo>

(print "More output for foo." m)
     ⇒ "More output for foo."
---------- Buffer: foo ----------
"This is t
"More output for foo."
he ⋆output"
---------- Buffer: foo ----------
m
     ⇒ #<marker at 35 in foo>

The following example shows output to the echo area:

(print "Echo Area output" t)
     ⇒ "Echo Area output"
---------- Echo Area ----------
"Echo Area output"
---------- Echo Area ----------

Finally, we show the use of a function as an output stream. The function eat-output takes each character that it is given and conses it onto the front of the list last-output (see Section 5.5 [Building Lists], page 65). At the end, the list contains all the characters output, but in reverse order.

(setq last-output nil)
     ⇒ nil
(defun eat-output (c)
  (setq last-output (cons c last-output)))
     ⇒ eat-output
(print "This is the output" 'eat-output)
     ⇒ "This is the output"
last-output
     ⇒ (10 34 116 117 112 116 117 111 32 101 104
    116 32 115 105 32 115 105 104 84 34 10)

Now we can put the output in the proper order by reversing the list:

(concat (nreverse last-output))
     ⇒ "
\"This is the output\"
"

Calling concat converts the list to a string so you can see its contents more clearly.

16.5 Output Functions

This section describes the Lisp functions for printing Lisp objects. Some of the Emacs printing functions add quoting characters to the output when nec-

essary so that it can be read properly. The quoting characters used are ‘"’ and ‘\’; they distinguish strings from symbols, and prevent punctuation characters in strings and symbols from being taken as delimiters when reading. See Section 2.1 [Printed Representation], page 15, for full details. You specify quoting or no quoting by the choice of printing function.

If the text is to be read back into Lisp, then it is best to print with quoting characters to avoid ambiguity. Likewise, if the purpose is to describe a Lisp object clearly for a Lisp programmer. However, if the purpose of the output is to look nice for humans, then it is better to print without quoting.

Printing a self-referent Lisp object requires an infinite amount of text. In certain cases, trying to produce this text leads to a stack overflow. Emacs detects such recursion and prints ‘#level’ instead of recursively printing an object already being printed. For example, here ‘#0’ indicates a recursive reference to the object at level 0 of the current print operation:

     (setq foo (list nil))
          ⇒ (nil)
     (setcar foo foo)
          ⇒ (#0)

In the functions below, stream stands for an output stream. (See the previous section for a description of output streams.) If stream is nil or omitted, it defaults to the value of

standard-output.

Function print object &optional stream The print function is a convenient way of printing. It outputs the printed representation of object to stream, printing in addition one newline before object and another after it. Quoting characters are used. print returns object. For example:

          (progn (print 'The\ cat\ in)
                 (print "the hat")
                 (print " came back"))

⊣

               ⊣ The\ cat\ in

⊣

               ⊣ "the hat"

⊣

               ⊣ " came back"

⊣

               ⇒ " came back"

Function prin1 object &optional stream This function outputs the printed representation of object to stream. It does not print newlines to separate output as print does, but it does use quoting characters just like print. It returns object.

          (progn (prin1 'The\ cat\ in)
                 (prin1 "the hat")
                 (prin1 " came back"))
               ⊣ The\ cat\ in"the hat"" came back"
               ⇒ " came back"

Function princ object &optional stream This function outputs the printed representation of object to stream. It returns object.

This function is intended to produce output that is readable by people, not by read, so it doesn’t insert quoting characters and doesn’t put double-quotes around the contents of strings. It does not add any spacing between calls.

     (progn
       (princ 'The\ cat)
       (princ " in the \"hat\""))
          ⊣ The cat in the "hat"
          ⇒ " in the \"hat\""

Function terpri &optional stream This function outputs a newline to stream. The name stands for “terminate print”.

Function write-char character &optional stream This function outputs character to stream. It returns character.

Function prin1-to-string object &optional noescape This function returns a string containing the text that prin1 would have printed for the same argument.

     (prin1-to-string 'foo)
          ⇒ "foo"
     (prin1-to-string (mark-marker))
          ⇒ "#<marker at 2773 in strings.texi>"

If noescape is non-nil, that inhibits use of quoting characters in the output. (This argument is supported in Emacs versions 19 and later.)

     (prin1-to-string "foo")
          ⇒ "\"foo\""
     (prin1-to-string "foo" t)
          ⇒ "foo"

See format, in Section 4.5 [String Conversion], page 53, for other ways to obtain the printed representation of a Lisp object as a string.

16.6 Variables Affecting Output

Variable standard-output

The value of this variable is the default output stream—the stream that print functions use when the stream argument is nil.

Variable print-escape-newlines

If this variable is non-nil, then newline characters in strings are printed as ‘\n’ and formfeeds are printed as ‘\f’. Normally these characters are printed as actual newlines and formfeeds.

This variable affects the print functions prin1 and print, as well as everything that uses them. It does not affect princ. Here is an example using prin1:

     (prin1 "a\nb")
          ⊣ "a

          ⊣ b"
          ⇒ "a

     b"
     (let ((print-escape-newlines t))
       (prin1 "a\nb"))
          ⊣ "a\nb"
          ⇒ "a
     b"

In the second expression, the local binding of print-escape-newlines is in effect during the call to prin1, but not during the printing of the result.

Variable print-length

The value of this variable is the maximum number of elements of a list, vector or bitvector that will be printed. If an object being printed has more than this many elements, it is abbreviated with an ellipsis. If the value is nil (the default), then there is no limit.

     (setq print-length 2)
          ⇒ 2
     (print '(1 2 3 4 5))
          ⊣ (1 2 ...)

          ⇒ (1 2 ...)

Variable print-level

The value of this variable is the maximum depth of nesting of parentheses and brackets when printed. Any list or vector at a depth exceeding this limit is abbreviated with an ellipsis. A value of nil (which is the default) means no limit. This variable exists in version 19 and later versions.

222 GNU Emacs Lisp Reference Manual

17 Minibuffers

A minibuffer is a special buffer that Emacs commands use to read arguments more complicated than the single numeric prefix argument. These arguments include file names, buffer names, and command names (as in M-x). The minibuffer is displayed on the bottom line of the screen, in the same place as the echo area, but only while it is in use for reading an argument.

17.1 Introduction to Minibuffers

In most ways, a minibuffer is a normal Emacs buffer. Most operations within a buffer, such as editing commands, work normally in a minibuffer. However, many operations for managing buffers do not apply to minibuffers. The name of a minibuffer always has the form ‘ *Minibuf-number’, and it cannot be changed. Minibuffers are displayed only in special windows used only for minibuffers; these windows always appear at the bottom of a frame. (Sometime frames have no minibuffer window, and sometimes a special kind of frame contains nothing but a minibuffer window; see Section 26.8 [Minibuffers and Frames], page 418.)

The minibuffer’s window is normally a single line. You can resize it temporarily with the window sizing commands; it reverts to its normal size when the minibuffer is exited. You can resize it permanently by using the window sizing commands in the frame’s other window, when the minibuffer is not active. If the frame contains just a minibuffer, you can change the minibuffer’s size by changing the frame’s size.

If a command uses a minibuffer while there is an active minibuffer, this is called a recursive minibuffer. The first minibuffer is named ‘ *Minibuf-0*’. Recursive minibuffers are named by incrementing the number at the end of the name. (The names begin with a space so that they won’t show up in normal buffer lists.) Of several recursive minibuffers, the innermost (or most recently entered) is the active minibuffer. We usually call this “the” minibuffer. You can permit or forbid recursive minibuffers by setting the variable enablerecursive-minibuffers or by putting properties of that name on command symbols (see Section 17.8 [Minibuffer Misc], page 240).

Like other buffers, a minibuffer may use any of several local keymaps (see Chapter 19 [Keymaps], page 277); these contain various exit commands and in some cases completion commands (see Section 17.5 [Completion], page 228).

• minibuffer-local-map is for ordinary input (no completion).

• minibuffer-local-ns-map is similar, except that ^{⟨}\underline{\overline{SPC}}^{⟩} exits just like ^{⟨}\underline{\overline{RET}}^{⟩}. This is used mainly for Mocklisp compatibility.

  • minibuffer-local-completion-map is for permissive completion.

• minibuffer-local-must-match-map is for strict completion and for cautious completion.

17.2 Reading Text Strings with the Minibuffer

Most often, the minibuffer is used to read text as a string. It can also be used to read a Lisp object in textual form. The most basic primitive for minibuffer input is read-from-minibuffer; it can do either one.

In most cases, you should not call minibuffer input functions in the middle of a Lisp function. Instead, do all minibuffer input as part of reading the arguments for a command, in the interactive spec. See Section 18.2 [Defining Commands], page 244.

Function read-from-minibuffer prompt-string &optional initial-contents

keymap read hist This function is the most general way to get input through the minibuffer. By default, it accepts arbitrary text and returns it as a string; however, if read is non-nil, then it uses read to convert the text into a Lisp object (see Section 16.3 [Input Functions], page 216).

The first thing this function does is to activate a minibuffer and display it with prompt-string as the prompt. This value must be a string.

Then, if initial-contents is a string, read-from-minibuffer inserts it into the minibuffer, leaving point at the end. The minibuffer appears with this text as its contents.

The value of initial-contents may also be a cons cell of the form (string . position). This means to insert string in the minibuffer but put point position characters from the beginning, rather than at the end.

If keymap is non-nil, that keymap is the local keymap to use in the minibuffer. If keymap is omitted or nil, the value of minibuffer-local-map is used as the keymap. Specifying a keymap is the most important way to customize the minibuffer for various applications such as completion.

The argument hist specifies which history list variable to use for saving the input and for history commands used in the minibuffer. It defaults to minibufferhistory. See Section 17.4 [Minibuffer History], page 227.

When the user types a command to exit the minibuffer, read-from-minibuffer uses the text in the minibuffer to produce its return value. Normally it simply makes a string containing that text. However, if read is non-nil, read-from-minibuffer reads the text and returns the resulting Lisp object, unevaluated. (See Section 16.3 [Input Functions], page 216, for information about reading.)

Function read-string prompt &optional initial This function reads a string from the minibuffer and returns it. The arguments prompt and initial are used as in read-from-minibuffer. The keymap used

is minibuffer-local-map.

This is a simplified interface to the read-from-minibuffer function:

     (read-string prompt initial)

≡

     (read-from-minibuffer prompt initial nil nil nil)

Variable minibuffer-local-map

This is the default local keymap for reading from the minibuffer. By default, it makes the following bindings:

⟨\underline{\overline{LFD}}^{⟩}  exit-minibuffer
⟨\underline{\overline{RET}}^{⟩}  exit-minibuffer
C-g       abort-recursive-edit
M-n       next-history-element
M-p       previous-history-element
M-r       next-matching-history-element
M-s       previous-matching-history-element

Function read-no-blanks-input prompt &optional initial This function reads a string from the minibuffer, but does not allow whitespace characters as part of the input: instead, those characters terminate the input. The arguments prompt and initial are used as in read-from-minibuffer.

This is a simplified interface to the read-from-minibuffer function, and passes the value of the minibuffer-local-ns-map keymap as the keymap argument for that function. Since the keymap minibuffer-local-ns-map does not rebind C-q, it is possible to put a space into the string, by quoting it.

     (read-no-blanks-input prompt initial)

≡

     (read-from-minibuffer prompt initial minibuffer-local-ns-map)

Variable minibuffer-local-ns-map

This built-in variable is the keymap used as the minibuffer local keymap in the function read-no-blanks-input. By default, it makes the following bindings,

in addition to those of minibuffer-local-map:
⟨\underline{\overline{SPC}}^{⟩}  exit-minibuffer
⟨\underline{\overline{TAB}}^{⟩}  exit-minibuffer
?         self-insert-and-exit

17.3 Reading Lisp Objects with the Minibuffer

This section describes functions for reading Lisp objects with the minibuffer.

Function read-minibuffer prompt &optional initial This function reads a Lisp object in the minibuffer and returns it, without evaluating it. The arguments prompt and initial are used as in read-from-

minibuffer.

This is a simplified interface to the read-from-minibuffer function:

     (read-minibuffer prompt initial)

≡

     (read-from-minibuffer prompt initial nil t)

Here is an example in which we supply the string "(testing)" as initial input:

     (read-minibuffer
      "Enter an expression: " (format "%s" '(testing)))

;; Here is how the minibuffer is displayed:

     ---------- Buffer: Minibuffer ----------
     Enter an expression: (testing)⋆
     ---------- Buffer: Minibuffer ----------

The user can type ^{⟨}\underline{\overline{RET}}^{⟩} immediately to use the initial input as a default, or can edit the input.

Function eval-minibuffer prompt &optional initial This function reads a Lisp expression in the minibuffer, evaluates it, then returns the result. The arguments prompt and initial are used as in read-from-

minibuffer.

This function simply evaluates the result of a call to read-minibuffer:

     (eval-minibuffer prompt initial)

≡

     (eval (read-minibuffer prompt initial))

Function edit-and-eval-command prompt form

This function reads a Lisp expression in the minibuffer, and then evaluates it. The difference between this command and eval-minibuffer is that here the initial form is not optional and it is treated as a Lisp object to be converted to printed representation rather than as a string of text. It is printed with prin1, so if it is a string, double-quote characters (‘"’) appear in the initial text. See Section 16.5 [Output Functions], page 218.

The first thing edit-and-eval-command does is to activate the minibuffer with prompt as the prompt. Then it inserts the printed representation of form in the minibuffer, and lets the user edit. When the user exits the minibuffer, the edited text is read with read and then evaluated. The resulting value becomes

the value of edit-and-eval-command.

In the following example, we offer the user an expression with initial text which is a valid form already:

     (edit-and-eval-command "Please edit: " '(forward-word 1))

;; After evaluation of the preceding expression, ;; the following appears in the minibuffer:

     ---------- Buffer: Minibuffer ----------
     Please edit: (forward-word 1)⋆
     ---------- Buffer: Minibuffer ----------

Typing ^{⟨}\underline{\overline{RET}}^{⟩} right away would exit the minibuffer and evaluate the expression, thus moving point forward one word. edit-and-eval-command returns nil in this example.

17.4 Minibuffer History

A minibuffer history list records previous minibuffer inputs so the user can reuse them conveniently. A history list is actually a symbol, not a list; it is a variable whose value is a list of strings (previous inputs), most recent first.

There are many separate history lists, used for different kinds of inputs. It’s the Lisp programmer’s job to specify the right history list for each use of the minibuffer.

   The basic minibuffer input functions read-from-minibuffer and completing-read

both accept an optional argument named hist which is how you specify the history list. Here are the possible values:

variable Use variable (a symbol) as the history list.

(variable . startpos)

Use variable (a symbol) as the history list, and assume that the initial history position is startpos (an integer, counting from zero which specifies the most recent element of the history). If you specify startpos, then you should also specify that element of the history as the initial minibuffer contents, for consistency.

If you don’t specify hist, then the default history list minibuffer-history is used. For other standard history lists, see below. You can also create your own history list variable; just initialize it to nil before the first use.

   Both read-from-minibuffer and completing-read add new elements to the history

list automatically, and provide commands to allow the user to reuse items on the list. The only thing your program needs to do to use a history list is to initialize it and to pass its name to the input functions when you wish. But it is safe to modify the list by hand when the minibuffer input functions are not using it.

Variable minibuffer-history

The default history list for minibuffer history input.

Variable query-replace-history

A history list for arguments to query-replace (and similar arguments to other commands).

Variable file-name-history

A history list for file name arguments.

Variable regexp-history

A history list for regular expression arguments.

Variable extended-command-history

A history list for arguments that are names of extended commands.

Variable shell-command-history

A history list for arguments that are shell commands.

Variable read-expression-history

A history list for arguments that are Lisp expressions to evaluate.

17.5 Completion

Completion is a feature that fills in the rest of a name starting from an abbreviation for it. Completion works by comparing the user’s input against a list of valid names and determining how much of the name is determined uniquely by what the user has typed. For example, when you type C-x b (switch-to-buffer) and then type the first few letters of the name of the buffer to which you wish to switch, and then type ^{⟨}\underline{\overline{TAB}}^{⟩} (minibuffercomplete), Emacs extends the name as far as it can.

Standard Emacs commands offer completion for names of symbols, files, buffers, and processes; with the functions in this section, you can implement completion for other kinds of names.

The try-completion function is the basic primitive for completion: it returns the longest determined completion of a given initial string, with a given set of strings to match against.

The function completing-read provides a higher-level interface for completion. A call to completing-read specifies how to determine the list of valid names. The function then activates the minibuffer with a local keymap that binds a few keys to commands useful for completion. Other functions provide convenient simple interfaces for reading certain kinds of names with completion.

17.5.1 Basic Completion Functions

The two functions try-completion and all-completions have nothing in themselves to do with minibuffers. We describe them in this chapter so as to keep them near the higher-level completion features that do use the minibuffer.

Function try-completion string collection &optional predicate This function returns the longest common substring of all possible completions of string in collection. The value of collection must be an alist, an obarray, or a function that implements a virtual set of strings (see below). Completion compares string against each of the permissible completions specified by collection; if the beginning of the permissible completion equals string, it matches. If no permissible completions match, try-completion returns nil. If only one permissible completion matches, and the match is exact, then trycompletion returns t. Otherwise, the value is the longest initial sequence common to all the permissible completions that match. If collection is an alist (see Section 5.8 [Association Lists], page 74), the cars of the alist elements form the set of permissible completions. If collection is an obarray (see Section 7.3 [Creating Symbols], page 89), the names of all symbols in the obarray form the set of permissible completions. The global variable obarray holds an obarray containing the names of all interned Lisp symbols. Note that the only valid way to make a new obarray is to create it empty and then add symbols to it one by one using intern. Also, you cannot intern a given symbol in more than one obarray. If the argument predicate is non-nil, then it must be a function of one argument. It is used to test each possible match, and the match is accepted only if predicate returns non-nil. The argument given to predicate is either a cons cell from the alist (the car of which is a string) or else it is a symbol (not a symbol name) from the obarray. You can also use a symbol that is a function as collection. Then the function is solely responsible for performing completion; try-completion returns whatever this function returns. The function is called with three arguments: string, predicate and nil. (The reason for the third argument is so that the same function can be used in all-completions and do the appropriate thing in either case.) See Section 17.5.6 [Programmed Completion], page 236. In the first of the following examples, the string ‘foo’ is matched by three of the alist cars. All of the matches begin with the characters ‘fooba’, so that is the result. In the second example, there is only one possible match, and it is exact, so the value is t.

     (try-completion
      "foo"
      '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)))
          ⇒ "fooba"
     (try-completion "foo" '(("barfoo" 2) ("foo" 3)))
          ⇒ t

In the following example, numerous symbols begin with the characters ‘forw’, and all of them begin with the word ‘forward’. In most of the symbols, this is followed with a ‘-’, but not in all, so no more than ‘forward’ can be completed.

     (try-completion "forw" obarray)
          ⇒ "forward"

Finally, in the following example, only two of the three possible matches pass the predicate test (the string ‘foobaz’ is too short). Both of those begin with the string ‘foobar’.

     (defun test (s)
       (> (length (car s)) 6))
          ⇒ test
     (try-completion
      "foo"
      '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
      'test)
          ⇒ "foobar"

Function all-completions string collection &optional predicate nospace This function returns a list of all possible completions of string. The parameters to this function are the same as to try-completion.

If collection is a function, it is called with three arguments: string, predicate and t; then all-completions returns whatever the function returns. See Section 17.5.6 [Programmed Completion], page 236. If nospace is non-nil, completions that start with a space are ignored unless string also starts with a space. Here is an example, using the function test shown in the example for try-

completion:
     (defun test (s)
       (> (length (car s)) 6))
          ⇒ test
     (all-completions
      "foo"
      '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
      'test)
          ⇒ ("foobar1" "foobar2")

Variable completion-ignore-case

If the value of this variable is non-nil, Emacs does not consider case significant in completion.

17.5.2 Completion and the Minibuffer

This section describes the basic interface for reading from the minibuffer with completion.

Function completing-read prompt collection &optional predicate

require-match initial hist This function reads a string in the minibuffer, assisting the user by providing completion. It activates the minibuffer with prompt prompt, which must be a string. If initial is non-nil, completing-read inserts it into the minibuffer as part of the input. Then it allows the user to edit the input, providing several commands to attempt completion. The actual completion is done by passing collection and predicate to the function try-completion. This happens in certain commands bound in the local keymaps used for completion. If require-match is t, the usual minibuffer exit commands won’t exit unless the input completes to an element of collection. If require-match is neither nil nor t, then the exit commands won’t exit unless the input typed is itself an element of collection. If require-match is nil, the exit commands work regardless of the input in the minibuffer. The user can exit with null input by typing ^{⟨}\underline{\overline{RET}}^{⟩} with an empty minibuffer. Then completing-read returns "". This is how the user requests whatever default the command uses for the value being read. The user can return using ⟨\underline{\overline{RET}}^{⟩} in this way regardless of the value of require-match, and regardless of whether the empty string is included in collection. The function completing-read works by calling read-minibuffer. It uses

minibuffer-local-completion-map as the keymap if require-match is nil,

and uses minibuffer-local-must-match-map if require-match is non-nil. See

Section 17.5.3 [Completion Commands], page 231. The argument hist specifies which history list variable to use for saving the input and for minibuffer history commands. It defaults to minibuffer-history. See Section 17.4 [Minibuffer History], page 227. Completion ignores case when comparing the input against the possible matches, if the built-in variable completion-ignore-case is non-nil. See Section 17.5.1 [Basic Completion], page 228. Here’s an example of using completing-read:

     (completing-read
      "Complete a foo: "
      '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
      nil t "fo")

;; After evaluation of the preceding expression, ;; the following appears in the minibuffer:

     ---------- Buffer: Minibuffer ----------
     Complete a foo: fo⋆
     ---------- Buffer: Minibuffer ----------

If the user then types ^{⟨}\underline{\overline{DEL}}^{⟩} ^{⟨}\underline{\overline{DEL}}^{⟩} b ^{⟨}\underline{\overline{RET}}^{⟩}, completing-read returns barfoo. The completing-read function binds three variables to pass information to the commands that actually do completion. These variables are minibuffer-

completion-table, minibuffer-completion-predicate and minibuffer-

completion-confirm. For more information about them, see Section 17.5.3 [Completion Commands], page 231.

17.5.3 Minibuffer Commands That Do Completion

This section describes the keymaps, commands and user options used in the minibuffer to do completion.

Variable minibuffer-local-completion-map

completing-read uses this value as the local keymap when an exact match of one of the completions is not required. By default, this keymap makes the following bindings:

?         minibuffer-completion-help
⟨\underline{\overline{SPC}}^{⟩}  minibuffer-complete-word
⟨\underline{\overline{TAB}}^{⟩}  minibuffer-complete

with other characters bound as in minibuffer-local-map (see Section 17.2 [Text from Minibuffer], page 224).

Variable minibuffer-local-must-match-map

completing-read uses this value as the local keymap when an exact match of one of the completions is required. Therefore, no keys are bound to exitminibuffer, the command that exits the minibuffer unconditionally. By default, this keymap makes the following bindings:

?         minibuffer-completion-help
⟨\underline{\overline{SPC}}^{⟩}  minibuffer-complete-word
⟨\underline{\overline{TAB}}^{⟩}  minibuffer-complete
⟨\underline{\overline{LFD}}^{⟩}  minibuffer-complete-and-exit
⟨\underline{\overline{RET}}^{⟩}  minibuffer-complete-and-exit

with other characters bound as in minibuffer-local-map.

Variable minibuffer-completion-table

The value of this variable is the alist or obarray used for completion in the minibuffer. This is the global variable that contains what completing-read passes to try-completion. It is used by minibuffer completion commands

such as minibuffer-complete-word.

Variable minibuffer-completion-predicate

This variable’s value is the predicate that completing-read passes to trycompletion. The variable is also used by the other minibuffer completion functions.

Command minibuffer-complete-word

This function completes the minibuffer contents by at most a single word. Even if the minibuffer contents have only one completion, minibuffer-complete-word does not add any characters beyond the first character that is not a word constituent. See Chapter 31 [Syntax Tables], page 509.

Command minibuffer-complete

This function completes the minibuffer contents as far as possible.

Command minibuffer-complete-and-exit

This function completes the minibuffer contents, and exits if confirmation is not required, i.e., if minibuffer-completion-confirm is nil. If confirmation is required, it is given by repeating this command immediately—the command is programmed to work without confirmation when run twice in succession.

Variable minibuffer-completion-confirm

When the value of this variable is non-nil, Emacs asks for confirmation of a completion before exiting the minibuffer. The function minibuffer-complete-and-exit checks the value of this variable before it exits.

Command minibuffer-completion-help

This function creates a list of the possible completions of the current minibuffer contents. It works by calling all-completions using the value of the variable minibuffer-completion-table as the collection argument, and the value of minibuffer-completion-predicate as the predicate argument. The list of completions is displayed as text in a buffer named ‘*Completions*’.

Function display-completion-list completions

This function displays completions to the stream in standard-output, usually a buffer. (See Chapter 16 [Read and Print], page 213, for more information about streams.) The argument completions is normally a list of completions just returned by all-completions, but it does not have to be. Each element may be a symbol or a string, either of which is simply printed, or a list of two strings, which is printed as if the strings were concatenated. This function is called by minibuffer-completion-help. The most common way to use it is together with with-output-to-temp-buffer, like this:

     (with-output-to-temp-buffer "*Completions*"
       (display-completion-list
         (all-completions (buffer-string) my-alist)))

User Option completion-auto-help

If this variable is non-nil, the completion commands automatically display a list of possible completions whenever nothing can be completed because the next character is not uniquely determined.

17.5.4 High-Level Completion Functions

This section describes the higher-level convenient functions for reading certain sorts of names with completion.

In most cases, you should not call these functions in the middle of a Lisp function. When possible, do all minibuffer input as part of reading the arguments for a command, in the interactive spec. See Section 18.2 [Defining Commands], page 244.

Function read-buffer prompt &optional default existing This function reads the name of a buffer and returns it as a string. The argument default is the default name to use, the value to return if the user exits with an empty minibuffer. If non-nil, it should be a string or a buffer. It is mentioned in the prompt, but is not inserted in the minibuffer as initial input. If existing is non-nil, then the name specified must be that of an existing buffer. The usual commands to exit the minibuffer do not exit if the text is not valid, and ^{⟨}\underline{\overline{RET}}^{⟩} does completion to attempt to find a valid name. (However, default is not checked for validity; it is returned, whatever it is, if the user exits with the minibuffer empty.) In the following example, the user enters ‘minibuffer.t’, and then types ^{⟨}\underline{\overline{RET}}^{⟩}. The argument existing is t, and the only buffer name starting with the given input is ‘minibuffer.texi’, so that name is the value.

     (read-buffer "Buffer name? " "foo" t)

;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer:

     ---------- Buffer: Minibuffer ----------
     Buffer name? (default foo) ⋆
     ---------- Buffer: Minibuffer ----------

;; The user types minibuffer.t ^{⟨}\underline{\overline{RET}}^{⟩}.

     ⇒ "minibuffer.texi"

Function read-command prompt

This function reads the name of a command and returns it as a Lisp symbol. The argument prompt is used as in read-from-minibuffer. Recall that a command is anything for which commandp returns t, and a command name is a symbol for which commandp returns t. See Section 18.3 [Interactive Call], page 248.

(read-command "Command name? ")

;; After evaluation of the preceding expression, ;; the following prompt appears with an empty minibuffer:

---------- Buffer: Minibuffer ----------
Command name?
---------- Buffer: Minibuffer ----------

If the user types forward-c ^{⟨}\underline{\overline{RET}}^{⟩}, then this function returns forward-char.

The read-command function is a simplified interface to completing-read. It uses the variable obarray so as to complete in the set of extant Lisp symbols, and it uses the commandp predicate so as to accept only command names:

(read-command prompt)

≡

(intern (completing-read prompt obarray
                         'commandp t nil))

Function read-variable prompt

This function reads the name of a user variable and returns it as a symbol.

(read-variable "Variable name? ")

;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer:

---------- Buffer: Minibuffer ----------
Variable name? ⋆
---------- Buffer: Minibuffer ----------

If the user then types fill-p ^{⟨}\underline{\overline{RET}}^{⟩}, read-variable returns fill-prefix.

This function is similar to read-command, but uses the predicate user-

variable-p instead of commandp:
(read-variable prompt)

≡

(intern
 (completing-read prompt obarray
                  'user-variable-p t nil))

17.5.5 Reading File Names

Here is another high-level completion function, designed for reading a file name. It provides special features including automatic insertion of the default directory.

Function read-file-name prompt &optional directory default existing initial This function reads a file name in the minibuffer, prompting with prompt and providing completion. If default is non-nil, then the function returns default if the user just types ^{⟨}\underline{\overline{RET}}^{⟩}. default is not checked for validity; it is returned, whatever it is, if the user exits with the minibuffer empty. If existing is non-nil, then the user must specify the name of an existing file; ⟨\underline{\overline{RET}}^{⟩} performs completion to make the name valid if possible, and then refuses to exit if it is not valid. If the value of existing is neither nil nor t, then ^{⟨}\underline{\overline{RET}}^{⟩} also requires confirmation after completion. If existing is nil, then the name of a nonexistent file is acceptable. The argument directory specifies the directory to use for completion of relative file names. If insert-default-directory is non-nil, directory is also inserted in the minibuffer as initial input. It defaults to the current buffer’s value of

default-directory.

If you specify initial, that is an initial file name to insert in the buffer (after with directory, if that is inserted). In this case, point goes at the beginning of initial. The default for initial is nil—don’t insert any file name. To see what initial does, try the command C-x C-v. Here is an example:

     (read-file-name "The file is ")

;; After evaluation of the preceding expression, ;; the following appears in the minibuffer:

     ---------- Buffer: Minibuffer ----------
     The file is /gp/gnu/elisp/⋆
     ---------- Buffer: Minibuffer ----------

Typing manual ^{⟨}\underline{\overline{TAB}}^{⟩} results in the following:

     ---------- Buffer: Minibuffer ----------
     The file is /gp/gnu/elisp/manual.texi⋆
     ---------- Buffer: Minibuffer ----------

If the user types ^{⟨}\underline{\overline{RET}}^{⟩}, read-file-name returns the file name as the string

"/gp/gnu/elisp/manual.texi".

User Option insert-default-directory

This variable is used by read-file-name. Its value controls whether readfile-name starts by placing the name of the default directory in the minibuffer, plus the initial file name if any. If the value of this variable is nil, then readfile-name does not place any initial input in the minibuffer (unless you specify initial input with the initial argument). In that case, the default directory is still used for completion of relative file names, but is not displayed. For example:

;; Here the minibuffer starts out with the default directory.

(let ((insert-default-directory t))
  (read-file-name "The file is "))
---------- Buffer: Minibuffer ----------
The file is ~lewis/manual/⋆
---------- Buffer: Minibuffer ----------

;; Here the minibuffer is empty and only the prompt ;; appears on its line.

(let ((insert-default-directory nil))
  (read-file-name "The file is "))
---------- Buffer: Minibuffer ----------
The file is ⋆
---------- Buffer: Minibuffer ----------

17.5.6 Programmed Completion

Sometimes it is not possible to create an alist or an obarray containing all the intended possible completions. In such a case, you can supply your own function to compute the completion of a given string. This is called programmed completion.

To use this feature, pass a symbol with a function definition as the collection argument to completing-read. The function completing-read arranges to pass your completion function along to try-completion and all-completions, which will then let your function do all the work.

The completion function should accept three arguments:

• The string to be completed.

• The predicate function to filter possible matches, or nil if none. Your function should call the predicate for each possible match, and ignore the possible match if the predicate returns nil.

• A flag specifying the type of operation.

There are three flag values for three operations:

• nil specifies try-completion. The completion function should return the completion of the specified string, or t if the string is a unique and exact match already, or nil if the string matches no possibility. If the string is an exact match for one possibility, but also matches other longer possibilities, the function shuold return the string, not t.

• t specifies all-completions. The completion function should return a list of all possible completions of the specified string.

• lambda specifies a test for an exact match. The completion function should return t if the specified string is an exact match for some possibility; nil otherwise.

It would be consistent and clean for completion functions to allow lambda expressions (lists that are functions) as well as function symbols as collection, but this is impossible. Lists as completion tables are already assigned another meaning—as alists. It would be unreliable to fail to handle an alist normally because it is also a possible function. So you must arrange for any function you wish to use for completion to be encapsulated in a symbol.

Emacs uses programmed completion when completing file names. See Section 22.8.6 [File Name Completion], page 349.

17.6 Yes-or-No Queries

This section describes functions used to ask the user a yes-or-no question. The function y-or-n-p can be answered with a single character; it is useful for questions where an inadvertent wrong answer will not have serious consequences. yes-or-no-p is suitable for more momentous questions, since it requires three or four characters to answer.

If either of these functions is called in a command that was invoked using the mouse— more precisely, if last-nonmenu-event (see Section 18.4 [Command Loop Info], page 250) is either nil or a list—then it uses a dialog box or pop-up menu to ask the question. Otherwise, it uses keyboard input. You can force use of the mouse or use of keyboard input by binding last-nonmenu-event to a suitable value around the call.

Strictly speaking, yes-or-no-p uses the minibuffer and y-or-n-p does not; but it seems best to describe them together.

Function y-or-n-p prompt

This function asks the user a question, expecting input in the echo area. It returns t if the user types y, nil if the user types n. This function also accepts ⟨\underline{\overline{SPC}}^{⟩} to mean yes and ^{⟨}\underline{\overline{DEL}}^{⟩} to mean no. It accepts C-] to mean “quit”, like C-g, because the question might look like a minibuffer and for that reason the user might try to use C-] to get out. The answer is a single character, with no ⟨\underline{\overline{RET}}^{⟩} needed to terminate it. Upper and lower case are equivalent.

“Asking the question” means printing prompt in the echo area, followed by the string ‘(y or n) ’. If the input is not one of the expected answers (y, n, ⟨\underline{\overline{SPC}}^{⟩}, ^{⟨}\underline{\overline{DEL}}^{⟩}, or something that quits), the function responds ‘Please answer y or n.’, and repeats the request.

This function does not actually use the minibuffer, since it does not allow editing of the answer. It actually uses the echo area (see Section 35.4 [The Echo Area], page 569), which uses the same screen space as the minibuffer. The cursor moves to the echo area while the question is being asked.

The answers and their meanings, even ‘y’ and ‘n’, are not hardwired. The keymap query-replace-map specifies them. See Section 30.5 [Search and Replace], page 500.

In the following example, the user first types q, which is invalid. At the next prompt the user types y.

     (y-or-n-p "Do you need a lift? ")

;; After evaluation of the preceding expression, ;; the following prompt appears in the echo area:

---------- Echo area ----------
Do you need a lift? (y or n)
---------- Echo area ----------

;; If the user then types q, the following appears:

---------- Echo area ----------
Please answer y or n.  Do you need a lift? (y or n)
---------- Echo area ----------

;; When the user types a valid answer, ;; it is displayed after the question:

---------- Echo area ----------
Do you need a lift? (y or n) y
---------- Echo area ----------

We show successive lines of echo area messages, but only one actually appears on the screen at a time.

Function y-or-n-p-with-timeout prompt seconds default-value Like y-or-n-p, except that if the user fails to answer within seconds seconds, this function stops waiting and returns default-value. It works by setting up a timer; see Section 34.7 [Timers], page 556. The argument seconds may be an integer or a floating point number.

Function yes-or-no-p prompt

This function asks the user a question, expecting input in the minibuffer. It returns t if the user enters ‘yes’, nil if the user types ‘no’. The user must type ⟨\underline{\overline{RET}}^{⟩} to finalize the response. Upper and lower case are equivalent.

yes-or-no-p starts by displaying prompt in the echo area, followed by ‘(yes or no) ’. The user must type one of the expected responses; otherwise, the function responds ‘Please answer yes or no.’, waits about two seconds and repeats the request.

yes-or-no-p requires more work from the user than y-or-n-p and is appropriate for more crucial decisions.

Here is an example:

(yes-or-no-p "Do you really want to remove everything? ")

;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer:

---------- Buffer: minibuffer ----------
Do you really want to remove everything? (yes or no)
---------- Buffer: minibuffer ----------

If the user first types y ^{⟨}\underline{\overline{RET}}^{⟩}, which is invalid because this function demands the entire word ‘yes’, it responds by displaying these prompts, with a brief pause between them:

     ---------- Buffer: minibuffer ----------
     Please answer yes or no.
     Do you really want to remove everything? (yes or no)
     ---------- Buffer: minibuffer ----------

17.7 Asking Multiple Y-or-N Questions

When you have a series of similar questions to ask, such as “Do you want to save this buffer” for each buffer in turn, you should use map-y-or-n-p to ask the collection of questions, rather than asking each question individually. This gives the user certain convenient facilities such as the ability to answer the whole series at once.

Function map-y-or-n-p prompter actor list &optional help action-alist This function, new in Emacs 19, asks the user a series of questions, reading a single-character answer in the echo area for each one. The value of list specifies the objects to ask questions about. It should be either a list of objects or a generator function. If it is a function, it should expect no arguments, and should return either the next object to ask about, or nil meaning stop asking questions. The argument prompter specifies how to ask each question. If prompter is a string, the question text is computed like this:

(format prompter object) where object is the next object to ask about (as obtained from list). If not a string, prompter should be a function of one argument (the next object to ask about) and should return the question text. If the value is a string, that is the question to ask the user. The function can also return t meaning do act on this object (and don’t ask the user), or nil meaning ignore this object (and don’t ask the user). The argument actor says how to act on the answers that the user gives. It should be a function of one argument, and it is called with each object that the user says yes for. Its argument is always an object obtained from list. If the argument help is given, it should be a list of this form:

(singular plural action) where singular is a string containing a singular noun that describes the objects conceptually being acted on, plural is the corresponding plural noun, and action is a transitive verb describing what actor does. If you don’t specify help, the default is ("object" "objects" "act on"). Each time a question is asked, the user may enter y, Y, or ^{⟨}\underline{\overline{SPC}}^{⟩} to act on that object; n, N, or^{⟨}\underline{\overline{DEL}}^{⟩} to skip that object; ! to act on all following objects; ^{⟨}\underline{\overline{ESC}}^{⟩} or q to exit (skip all following objects); . (period) to act on the current object and then exit; or C-h to get help. These are the same answers that query-replace accepts. The keymap query-replace-map defines their meaning for map-y-or-n-p as well as for query-replace; see Section 30.5 [Search and Replace], page 500.

You can use action-alist to specify additional possible answers and what they mean. It is an alist of elements of the form (char function help), each of which defines one additional answer. In this element, char is a character (the answer); function is a function of one argument (an object from list); help is a string. When the user responds with char, map-y-or-n-p calls function. If it returns non-nil, the object is considered “acted upon”, and map-y-or-n-p advances to the next object in list. If it returns nil, the prompt is repeated for the same object. If map-y-or-n-p is called in a command that was invoked using the mouse— more precisely, if last-nonmenu-event (see Section 18.4 [Command Loop Info], page 250) is either nil or a list—then it uses a dialog box or pop-up menu to ask the question. In this case, it does not use keyboard input or the echo area. You can force use of the mouse or use of keyboard input by binding last-nonmenu-event to a suitable value around the call. The return value of map-y-or-n-p is the number of objects acted on.

17.8 Minibuffer Miscellany

This section describes some basic functions and variables related to minibuffers.

Command exit-minibuffer

This command exits the active minibuffer. It is normally bound to keys in minibuffer local keymaps.

Command self-insert-and-exit

This command exits the active minibuffer after inserting the last character typed on the keyboard (found in last-command-char; see Section 18.4 [Command Loop Info], page 250).

Command previous-history-element n

This command replaces the minibuffer contents with the value of the nth previous (older) history element.

Command next-history-element n

This command replaces the minibuffer contents with the value of the nth more recent history element.

Command previous-matching-history-element pattern

This command replaces the minibuffer contents with the value of the previous (older) history element that matches pattern (a regular expression).

Command next-matching-history-element pattern

This command replaces the minibuffer contents with the value of the next (newer) history element that matches pattern (a regular expression).

Function minibuffer-prompt

This function returns the prompt string of the currently active minibuffer. If no minibuffer is active, it returns nil.

Function minibuffer-prompt-width

This function returns the display width of the prompt string of the currently active minibuffer. If no minibuffer is active, it returns 0.

Variable minibuffer-setup-hook

This is a normal hook that is run whenever the minibuffer is entered. See Section 20.4 [Hooks], page 316.

Variable minibuffer-exit-hook

This is a normal hook that is run whenever the minibuffer is exited. See Section 20.4 [Hooks], page 316.

Variable minibuffer-help-form

The current value of this variable is used to rebind help-form locally inside the minibuffer (see Section 21.5 [Help Functions], page 324).

Function active-minibuffer-window

This function returns the currently active minibuffer window, or nil if none is currently active.

Function minibuffer-window &optional frame

This function returns the minibuffer window used for frame frame. If frame is nil, that stands for the current frame. Note that the minibuffer window used by a frame need not be part of that frame—a frame that has no minibuffer of its own necessarily uses some other frame’s minibuffer window.

Function window-minibuffer-p window

This function returns non-nil if window is a minibuffer window.

It is not correct to determine whether a given window is a minibuffer by comparing it with the result of (minibuffer-window), because there can be more than one minibuffer window if there is more than one frame.

Function minibuffer-window-active-p window

This function returns non-nil if window, assumed to be a minibuffer window, is currently active.

Variable minibuffer-scroll-window

If the value of this variable is non-nil, it should be a window object. When the function scroll-other-window is called in the minibuffer, it scrolls this window.

Finally, some functions and variables deal with recursive minibuffers (see Section 18.10 [Recursive Editing], page 271):

Function minibuffer-depth

This function returns the current depth of activations of the minibuffer, a nonnegative integer. If no minibuffers are active, it returns zero.

User Option enable-recursive-minibuffers

If this variable is non-nil, you can invoke commands (such as find-file) that use minibuffers even while in the minibuffer window. Such invocation produces a recursive editing level for a new minibuffer. The outer-level minibuffer is invisible while you are editing the inner one. This variable only affects invoking the minibuffer while the minibuffer window is selected. If you switch windows while in the minibuffer, you can always invoke minibuffer commands while some other window is selected.

If a command name has a property enable-recursive-minibuffers that is non-nil, then the command can use the minibuffer to read arguments even if it is invoked from the minibuffer. The minibuffer command next-matching-history-element (normally M-s in the minibuffer) uses this feature.

18 Command Loop

When you run Emacs, it enters the editor command loop almost immediately. This loop reads key sequences, executes their definitions, and displays the results. In this chapter, we describe how these things are done, and the subroutines that allow Lisp programs to do them.

18.1 Command Loop Overview

The first thing the command loop must do is read a key sequence, which is a sequence of events that translates into a command. It does this by calling the function read-key-sequence. Your Lisp code can also call this function (see Section 18.6.1 [Key Sequence Input], page 263). Lisp programs can also do input at a lower level with read-event (see Section 18.6.2 [Reading One Event], page 264) or discard pending input with discardinput (see Section 18.6.4 [Event Input Misc], page 266).

The key sequence is translated into a command through the currently active keymaps. See Section 19.7 [Key Lookup], page 284, for information on how this is done. The result should be a keyboard macro or an interactively callable function. If the key is M-x, then it reads the name of another command, which it then calls. This is done by the command execute-extended-command (see Section 18.3 [Interactive Call], page 248).

To execute a command requires first reading the arguments for it. This is done by calling command-execute (see Section 18.3 [Interactive Call], page 248). For commands written in Lisp, the interactive specification says how to read the arguments. This may use the prefix argument (see Section 18.9 [Prefix Command Arguments], page 270) or may read with prompting in the minibuffer (see Chapter 17 [Minibuffers], page 223). For example, the command find-file has an interactive specification which says to read a file name using the minibuffer. The command’s function body does not use the minibuffer; if you call this command from Lisp code as a function, you must supply the file name string as an ordinary Lisp function argument.

If the command is a string or vector (i.e., a keyboard macro) then execute-kbd-macro is used to execute it. You can call this function yourself (see Section 18.13 [Keyboard Macros], page 275).

To terminate the execution of a running command, type C-g. This character causes quitting (see Section 18.8 [Quitting], page 268).

Variable pre-command-hook

The editor command loop runs this normal hook before each command. At that time, this-command contains the command that is about to run, and lastcommand describes the previous command. See Section 20.4 [Hooks], page 316.

Variable post-command-hook

The editor command loop runs this normal hook after each command (including commands terminated prematurely by quitting or by errors), and also when the command loop is first entered. At that time, this-command describes the command that just ran, and last-command describes the command before that. See Section 20.4 [Hooks], page 316.

Quitting is suppressed while running pre-command-hook and post-command-hook. If an error happens while executing one of these hooks, it terminates execution of the hook, but that is all it does.

18.2 Defining Commands

A Lisp function becomes a command when its body contains, at top level, a form that calls the special form interactive. This form does nothing when actually executed, but its presence serves as a flag to indicate that interactive calling is permitted. Its argument controls the reading of arguments for an interactive call.

18.2.1 Using interactive

This section describes how to write the interactive form that makes a Lisp function an interactively-callable command.

Special Form interactive arg-descriptor This special form declares that the function in which it appears is a command, and that it may therefore be called interactively (via M-x or by entering a key sequence bound to it). The argument arg-descriptor declares how to compute the arguments to the command when the command is called interactively. A command may be called from Lisp programs like any other function, but then the caller supplies the arguments and arg-descriptor has no effect. The interactive form has its effect because the command loop (actually, its subroutine call-interactively) scans through the function definition looking for it, before calling the function. Once the function is called, all its body forms including the interactive form are executed, but at this time interactive simply returns nil without even evaluating its argument.

There are three possibilities for the argument arg-descriptor:

• It may be omitted or nil; then the command is called with no arguments. This leads quickly to an error if the command requires one or more arguments.

• It may be a Lisp expression that is not a string; then it should be a form that is evaluated to get a list of arguments to pass to the command. If this expression reads keyboard input (this includes using the minibuffer), keep in mind that the integer value of point or the mark before reading input may be incorrect after reading input. This is because the current buffer may be receiving subprocess output; if subprocess output arrives while the command is waiting for input, it could relocate point and the mark. Here’s an example of what not to do:

    (interactive
     (list (region-beginning) (region-end)
           (read-string "Foo: " nil 'my-history)))

Here’s how to avoid the problem, by examining point and the mark only after reading the keyboard input:

     (interactive
      (let ((string (read-string "Foo: " nil 'my-history)))
        (list (region-beginning) (region-end) string)))

• It may be a string; then its contents should consist of a code character followed by a prompt (which some code characters use and some ignore). The prompt ends either with the end of the string or with a newline. Here is a simple example:

     (interactive "bFrobnicate buffer: ")

The code letter ‘b’ says to read the name of an existing buffer, with completion. The buffer name is the sole argument passed to the command. The rest of the string is a prompt. If there is a newline character in the string, it terminates the prompt. If the string does not end there, then the rest of the string should contain another code character and prompt, specifying another argument. You can specify any number of arguments in this way. The prompt string can use ‘%’ to include previous argument values (starting with the first argument) in the prompt. This is done using format (see Section 4.6 [Formatting Strings], page 55). For example, here is how you could read the name of an existing buffer followed by a new name to give to that buffer:

     (interactive "bBuffer to rename: \nsRename buffer %s to: ")

If the first character in the string is ‘*’, then an error is signaled if the buffer is read-only. If the first character in the string is ‘@’, and if the key sequence used to invoke the command includes any mouse events, then the window associated with the first of those events is selected before the command is run. You can use ‘*’ and ‘@’ together; the order does not matter. Actual reading of arguments is controlled by the rest of the prompt string (starting with the first character that is not ‘*’ or ‘@’).

18.2.2 Code Characters for interactive

The code character descriptions below contain a number of key words, defined here as follows:

Completion Provide completion. ^{⟨}\underline{\overline{TAB}}^{⟩}, ^{⟨}\underline{\overline{SPC}}^{⟩}, and ^{⟨}\underline{\overline{RET}}^{⟩} perform name completion because the argument is read using completing-read (see Section 17.5 [Completion], page 228). ? displays a list of possible completions.

Existing Require the name of an existing object. An invalid name is not accepted; the commands to exit the minibuffer do not exit if the current input is not valid.

Default A default value of some sort is used if the user enters no text in the minibuffer. The default depends on the code character.

No I/O This code letter computes an argument without reading any input. Therefore, it does not use a prompt string, and any prompt string you supply is ignored. Even though the code letter doesn’t use a prompt string, you must follow it with a newline if it is not the last code character in the string.

Prompt A prompt immediately follows the code character. The prompt ends either with the end of the string or with a newline.

Special This code character is meaningful only at the beginning of the interactive string, and it does not look for a prompt or a newline. It is a single, isolated character.

Here are the code character descriptions for use with interactive:

‘*’ Signal an error if the current buffer is read-only. Special.

‘@’ Select the window mentioned in the first mouse event in the key sequence that invoked this command. Special.

‘a’ A function name (i.e., a symbol satisfying fboundp). Existing, Completion, Prompt.

‘b’ The name of an existing buffer. By default, uses the name of the current buffer (see Chapter 24 [Buffers], page 369). Existing, Completion, Default, Prompt.

‘B’ A buffer name. The buffer need not exist. By default, uses the name of a recently used buffer other than the current buffer. Completion, Default, Prompt.

‘c’ A character. The cursor does not move into the echo area. Prompt.

‘C’ A command name (i.e., a symbol satisfying commandp). Existing, Completion, Prompt.

‘d’ The position of point, as an integer (see Section 27.1 [Point], page 429). No I/O.

‘D’ A directory name. The default is the current default directory of the current buffer, default-directory (see Section 34.3 [System Environment], page 549). Existing, Completion, Default, Prompt.

‘e’ The first or next mouse event in the key sequence that invoked the command. More precisely, ‘e’ gets events that are lists, so you can look at the data in the lists. See Section 18.5 [Input Events], page 252. No I/O. You can use ‘e’ more than once in a single command’s interactive specification. If the key sequence that invoked the command has n events that are lists, the nth ‘e’ provides the nth such event. Events that are not lists, such as function keys and ASCII characters, do not count where ‘e’ is concerned.

‘f’ A file name of an existing file (see Section 22.8 [File Names], page 344). The default directory is default-directory. Existing, Completion, Default, Prompt.

‘F’ A file name. The file need not exist. Completion, Default, Prompt.

‘k’ A key sequence (see Section 19.1 [Keymap Terminology], page 277). This keeps reading events until a command (or undefined command) is found in the current key maps. The key sequence argument is represented as a string or vector. The cursor does not move into the echo area. Prompt. This kind of input is used by commands such as describe-key and global-

set-key.

‘K’ A key sequence, whose definition you intend to change. This works like ‘k’, except that it suppresses, for the last input event in the key sequence, the conversions that are normally used (when necessary) to convert an undefined key into a defined one.

‘m’ The position of the mark, as an integer. No I/O.

‘n’ A number read with the minibuffer. If the input is not a number, the user is asked to try again. The prefix argument, if any, is not used. Prompt.

‘N’ The numeric prefix argument; but if there is no prefix argument, read a number as with n. Requires a number. See Section 18.9 [Prefix Command Arguments], page 270. Prompt.

‘p’ The numeric prefix argument. (Note that this ‘p’ is lower case.) No I/O.

‘P’ The raw prefix argument. (Note that this ‘P’ is upper case.) No I/O.

‘r’ Point and the mark, as two numeric arguments, smallest first. This is the only code letter that specifies two successive arguments rather than one. No I/O.

‘s’ Arbitrary text, read in the minibuffer and returned as a string (see Section 17.2 [Text from Minibuffer], page 224). Terminate the input with either ^{⟨}\underline{\overline{LFD}}^{⟩} or ⟨\underline{\overline{RET}}^{⟩}. (C-q may be used to include either of these characters in the input.) Prompt.

‘S’ An interned symbol whose name is read in the minibuffer. Any whitespace character terminates the input. (Use C-q to include whitespace in the string.) Other characters that normally terminate a symbol (e.g., parentheses and brackets) do not do so here. Prompt.

‘v’ A variable declared to be a user option (i.e., satisfying the predicate uservariable-p). See Section 17.5.4 [High-Level Completion], page 233. Existing, Completion, Prompt.

‘x’ A Lisp object, specified with its read syntax, terminated with a ^{⟨}\underline{\overline{LFD}}^{⟩} or ⟨\underline{\overline{RET}}^{⟩}. The object is not evaluated. See Section 17.3 [Object from Minibuffer], page 225. Prompt.

‘X’ A Lisp form is read as with x, but then evaluated so that its value becomes the argument for the command. Prompt.

18.2.3 Examples of Using interactive

Here are some examples of interactive:

(defun foo1 ()              ; foo1 takes no arguments,

(interactive) ; just moves forward two words.

(forward-word 2))
⇒ foo1
(defun foo2 (n)             ; foo2 takes one argument,

(interactive "p") ; which is the numeric prefix.

(forward-word (* 2 n)))
⇒ foo2

(defun foo3 (n)             ; foo3 takes one argument,

(interactive "nCount:") ; which is read with the Minibuffer.

    (forward-word (* 2 n)))
     ⇒ foo3
(defun three-b (b1 b2 b3)
  "Select three existing buffers.
Put them into three windows, selecting the last one."
    (interactive "bBuffer1:\nbBuffer2:\nbBuffer3:")
    (delete-other-windows)
    (split-window (selected-window) 8)
    (switch-to-buffer b1)
    (other-window 1)
    (split-window (selected-window) 8)
    (switch-to-buffer b2)
    (other-window 1)
    (switch-to-buffer b3))
     ⇒ three-b
(three-b "*scratch*" "declarations.texi" "*mail*")
     ⇒ nil

18.3 Interactive Call

After the command loop has translated a key sequence into a definition, it invokes that definition using the function command-execute. If the definition is a function that is a command, command-execute calls call-interactively, which reads the arguments and calls the command. You can also call these functions yourself.

Function commandp object

Returns t if object is suitable for calling interactively; that is, if object is a command. Otherwise, returns nil. The interactively callable objects include strings and vectors (treated as keyboard macros), lambda expressions that contain a top-level call to interactive, byte-code function objects made from such lambda expressions, autoload objects that are declared as interactive (non-nil fourth argument to autoload), and some of the primitive functions. A symbol is commandp if its function definition is commandp. Keys and keymaps are not commands. Rather, they are used to look up commands (see Chapter 19 [Keymaps], page 277). See documentation in Section 21.2 [Accessing Documentation], page 320, for a realistic example of using commandp.

Function call-interactively command &optional record-flag This function calls the interactively callable function command, reading arguments according to its interactive calling specifications. An error is signaled if command is not a function or if it cannot be called interactively (i.e., is not a command). Note that keyboard macros (strings and vectors) are not accepted, even though they are considered commands, because they are not functions.

If record-flag is non-nil, then this command and its arguments are unconditionally added to the list command-history. Otherwise, the command is added only if it uses the minibuffer to read an argument. See Section 18.12 [Command History], page 274.

Function command-execute command &optional record-flag This function executes command as an editing command. The argument command must satisfy the commandp predicate; i.e., it must be an interactively callable function or a keyboard macro.

A string or vector as command is executed with execute-kbd-macro. A function is passed to call-interactively, along with the optional record-flag.

A symbol is handled by using its function definition in its place. A symbol with an autoload definition counts as a command if it was declared to stand for an interactively callable function. Such a definition is handled by loading the specified library and then rechecking the definition of the symbol.

Command execute-extended-command prefix-argument

This function reads a command name from the minibuffer using completingread (see Section 17.5 [Completion], page 228). Then it uses command-execute to call the specified command. Whatever that command returns becomes the

value of execute-extended-command.

If the command asks for a prefix argument, it receives the value prefix-argument. If execute-extended-command is called interactively, the current raw prefix argument is used for prefix-argument, and thus passed on to whatever command is run.

execute-extended-command is the normal definition of M-x, so it uses the string ‘M-x ’ as a prompt. (It would be better to take the prompt from the events used to invoke execute-extended-command, but that is painful to implement.) A description of the value of the prefix argument, if any, also becomes part of the prompt.

     (execute-extended-command 1)
     ---------- Buffer: Minibuffer ----------
     1 M-x forward-word RET
     ---------- Buffer: Minibuffer ----------
          ⇒ t

Function interactive-p

This function returns t if the containing function (the one whose code includes the call to interactive-p) was called interactively, with the function call-

interactively. (It makes no difference whether call-interactively was

called from Lisp or directly from the editor command loop.) If the containing function was called by Lisp evaluation (or with apply or funcall), then it was not called interactively.

The most common use of interactive-p is for deciding whether to print an informative message. As a special exception, interactive-p returns nil whenever a keyboard macro is being run. This is to suppress the informative messages and speed execution of the macro. For example:

     (defun foo ()
       (interactive)
       (and (interactive-p)
            (message "foo")))
          ⇒ foo
     (defun bar ()
       (interactive)
       (setq foobar (list (foo) (interactive-p))))
          ⇒ bar
     ;; Type M-x foo.
          ⊣ foo
     ;; Type M-x bar.

;; This does not print anything.

     foobar ⇒ (nil t)

18.4 Information from the Command Loop

The editor command loop sets several Lisp variables to keep status records for itself and for commands that are run.

Variable last-command

This variable records the name of the previous command executed by the command loop (the one before the current command). Normally the value is a symbol with a function definition, but this is not guaranteed. The value is copied from this-command when a command returns to the command loop, except when the command specifies a prefix argument for the following command. This variable is always local to the current terminal and cannot be buffer-local. See Section 26.2 [Multiple Displays], page 409.

Variable this-command

This variable records the name of the command now being executed by the editor command loop. Like last-command, it is normally a symbol with a function definition. The command loop sets this variable just before running a command, and copies its value into last-command when the command finishes (unless the command specifies a prefix argument for the following command). Some commands set this variable during their execution, as a flag for whatever command runs next. In particular, the functions for killing text set thiscommand to kill-region so that any kill commands immediately following will know to append the killed text to the previous kill.

If you do not want a particular command to be recognized as the previous command in the case where it got an error, you must code that command to prevent this. One way is to set this-command to t at the beginning of the command, and set this-command back to its proper value at the end, like this:

(defun foo (args. . .)
  (interactive . . .)
  (let ((old-this-command this-command))
    (setq this-command t)

…do the work…

    (setq this-command old-this-command)))

Function this-command-keys

This function returns a string or vector containing the key sequence that invoked the present command, plus any previous commands that generated the prefix argument for this command. The value is a string if all those events were characters. See Section 18.5 [Input Events], page 252.

     (this-command-keys)

;; Now use C-u C-x C-e to evaluate that.

          ⇒ "^U^X^E"

Variable last-nonmenu-event

This variable holds the last input event read as part of a key sequence, not counting events resulting from mouse menus.

One use of this variable is to figure out a good default location to pop up another menu.

Variable last-command-event Variable last-command-char

This variable is set to the last input event that was read by the command loop as part of a command. The principal use of this variable is in self-insert-command, which uses it to decide which character to insert.

     last-command-event

;; Now use C-u C-x C-e to evaluate that.

          ⇒ 5

The value is 5 because that is the ASCII code for C-e.

The alias last-command-char exists for compatibility with Emacs version 18.

Variable last-event-frame

This variable records which frame the last input event was directed to. Usually this is the frame that was selected when the event was generated, but if that frame has redirected input focus to another frame, the value is the frame to which the event was redirected. See Section 26.9 [Input Focus], page 419.

18.5 Input Events

The Emacs command loop reads a sequence of input events that represent keyboard or mouse activity. The events for keyboard activity are characters or symbols; mouse events are always lists. This section describes the representation and meaning of input events in detail.

Function eventp object

This function returns non-nil if object is an input event.

18.5.1 Keyboard Events

There are two kinds of input you can get from the keyboard: ordinary keys, and function keys. Ordinary keys correspond to characters; the events they generate are represented in Lisp as characters. In Emacs versions 18 and earlier, characters were the only events. The event type of a character event is the character itself (an integer); see Section 18.5.12 [Classifying Events], page 259.

An input character event consists of a basic code between 0 and 255, plus any or all of these modifier bits:

meta The $2^27$ bit in the character code indicates a character typed with the meta key held down.

control The $2^26$ bit in the character code indicates a non-ASCII control character. ASCII control characters such as C-a have special basic codes of their own, so Emacs needs no special bit to indicate them. Thus, the code for C-a is just 1. But if you type a control combination not in ASCII, such as % with the control key, the numeric value you get is the code for % plus $2^26$ (assuming the terminal supports non-ASCII control characters).

shift The $2^25$ bit in the character code indicates an ASCII control character typed with the shift key held down. For letters, the basic code indicates upper versus lower case; for digits and punctuation, the shift key selects an entirely different character with a different basic code. In order to keep within the ASCII character set whenever possible, Emacs avoids using the $2^25$ bit for those characters. However, ASCII provides no way to distinguish C-A from C-a, so Emacs uses the $2^25$ bit in C-A and not in C-a.

hyper The $2^24$ bit in the character code indicates a character typed with the hyper key held down.

super The $2^23$ bit in the character code indicates a character typed with the super key held down.

alt The $2^22$ bit in the character code indicates a character typed with the alt key held down. (On some terminals, the key labeled ^{⟨}\underline{\overline{ALT}}^{⟩} is actually the meta key.)

It is best to avoid mentioning specific bit numbers in your program. To test the modifier bits of a character, use the function event-modifiers (see Section 18.5.12 [Classifying Events], page 259). When making key bindings, you can use the read syntax for characters with modifier bits (‘\C-’, ‘\M-’, and so on). For making key bindings with define-key, you can use lists such as (control hyper ?x) to specify the characters (see Section 19.9 [Changing Key Bindings], page 288). The function event-convert-list converts such a list into an event type (see Section 18.5.12 [Classifying Events], page 259).

18.5.2 Function Keys

Most keyboards also have function keys—keys that have names or symbols that are not characters. Function keys are represented in Lisp as symbols; the symbol’s name is the function key’s label, in lower case. For example, pressing a key labeled ^{⟨}\underline{\overline{F1}}^{⟩} places the symbol f1 in the input stream.

The event type of a function key event is the event symbol itself. See Section 18.5.12 [Classifying Events], page 259.

Here are a few special cases in the symbol-naming convention for function keys:

backspace, tab, newline, return, delete

These keys correspond to common ASCII control characters that have special keys on most keyboards. In ASCII, C-i and ^{⟨}\underline{\overline{TAB}}^{⟩} are the same character. If the terminal can distinguish between them, Emacs conveys the distinction to Lisp programs by representing the former as the integer 9, and the latter as the symbol tab. Most of the time, it’s not useful to distinguish the two. So normally functionkey-map (see Section 34.8.2 [Translating Input], page 559) is set up to map tab into 9. Thus, a key binding for character code 9 (the character C-i) also applies to tab. Likewise for the other symbols in this group. The function read-char likewise converts these events into characters. In ASCII, ^{⟨}\underline{\overline{BS}}^{⟩} is really C-h. But backspace converts into the character code 127 (^{⟨}\underline{\overline{DEL}}^{⟩}), not into code 8 (^{⟨}\underline{\overline{BS}}^{⟩}). This is what most users prefer.

left, up, right, down

Cursor arrow keys

kp-add, kp-decimal, kp-divide, . . .

Keypad keys (to the right of the regular keyboard).

kp-0, kp-1, . . .

Keypad keys with digits.

kp-f1, kp-f2, kp-f3, kp-f4

Keypad PF keys.

kp-home, kp-left, kp-up, kp-right, kp-down

Keypad arrow keys. Emacs normally translates these into the non-keypad keys

home, left, . . .

kp-prior, kp-next, kp-end, kp-begin, kp-insert, kp-delete

Additional keypad duplicates of keys ordinarily found elsewhere. Emacs normally translates these into the like-named non-keypad keys.

You can use the modifier keys ^{⟨}\underline{\overline{ALT}}^{⟩}, ^{⟨}\underline{\overline{CTRL}}^{⟩}, ^{⟨}\underline{\overline{HYPER}}^{⟩}, ^{⟨}\underline{\overline{META}}^{⟩}, ^{⟨}\underline{\overline{SHIFT}}^{⟩}, and ^{⟨}\underline{\overline{SUPER}}^{⟩} with function keys. The way to represent them is with prefixes in the symbol name:

‘A-’ The alt modifier.

‘C-’ The control modifier.

‘H-’ The hyper modifier.

‘M-’ The meta modifier.

‘S-’ The shift modifier.

‘s-’ The super modifier.

Thus, the symbol for the key ^{⟨}\underline{\overline{F3}}^{⟩} with ^{⟨}\underline{\overline{META}}^{⟩} held down is M-f3. When you use more than one prefix, we recommend you write them in alphabetical order; but the order does not matter in arguments to the key-binding lookup and modification functions.

18.5.3 Mouse Events

Emacs supports four kinds of mouse events: click events, drag events, button-down events, and motion events. All mouse events are represented as lists. The car of the list is the event type; this says which mouse button was involved, and which modifier keys were used with it. The event type can also distinguish double or triple button presses (see Section 18.5.7 [Repeat Events], page 256). The rest of the list elements give position and time information.

For key lookup, only the event type matters: two events of the same type necessarily run the same command. The command can access the full values of these events using the ‘e’ interactive code. See Section 18.2.2 [Interactive Codes], page 245.

A key sequence that starts with a mouse event is read using the keymaps of the buffer in the window that the mouse was in, not the current buffer. This does not imply that clicking in a window selects that window or its buffer—that is entirely under the control of the command binding of the key sequence.

18.5.4 Click Events

When the user presses a mouse button and releases it at the same location, that generates a click event. Mouse click events have this form:

(event-type (window buffer-pos (x . y) timestamp) click-count)

Here is what the elements normally mean:

event-type This is a symbol that indicates which mouse button was used. It is one of the symbols mouse-1, mouse-2, …, where the buttons are numbered left to right.

You can also use prefixes ‘A-’, ‘C-’, ‘H-’, ‘M-’, ‘S-’ and ‘s-’ for modifiers alt, control, hyper, meta, shift and super, just as you would with function keys. This symbol also serves as the event type of the event. Key bindings describe events by their types; thus, if there is a key binding for mouse-1, that binding would apply to all events whose event-type is mouse-1.

window This is the window in which the click occurred.

x, y These are the pixel-denominated coordinates of the click, relative to the top left corner of window, which is (0 . 0).

buffer-pos This is the buffer position of the character clicked on.

timestamp This is the time at which the event occurred, in milliseconds. (Since this value wraps around the entire range of Emacs Lisp integers in about five hours, it is useful only for relating the times of nearby events.)

click-count This is the number of rapid repeated presses so far of the same mouse button. See Section 18.5.7 [Repeat Events], page 256.

The meanings of buffer-pos, x and y are somewhat different when the event location is in a special part of the screen, such as the mode line or a scroll bar.

If the location is in a scroll bar, then buffer-pos is the symbol vertical-scroll-bar or horizontal-scroll-bar, and the pair (x . y) is replaced with a pair (portion . whole), where portion is the distance of the click from the top or left end of the scroll bar, and whole is the length of the entire scroll bar.

If the position is on a mode line or the vertical line separating window from its neighbor to the right, then buffer-pos is the symbol mode-line or vertical-line. For the mode line, y does not have meaningful data. For the vertical line, x does not have meaningful data.

In one special case, buffer-pos is a list containing a symbol (one of the symbols listed above) instead of just the symbol. This happens after the imaginary prefix keys for the event are inserted into the input stream. See Section 18.6.1 [Key Sequence Input], page 263.

18.5.5 Drag Events

With Emacs, you can have a drag event without even changing your clothes. A drag event happens every time the user presses a mouse button and then moves the mouse to a different character position before releasing the button. Like all mouse events, drag events are represented in Lisp as lists. The lists record both the starting mouse position and the final position, like this:

(event-type (window1 buffer-pos1 (x1 . y1) timestamp1) (window2 buffer-pos2 (x2 . y2) timestamp2) click-count)

For a drag event, the name of the symbol event-type contains the prefix ‘drag-’. The second and third elements of the event give the starting and ending position of the drag.

Aside from that, the data have the same meanings as in a click event (see Section 18.5.4 [Click Events], page 254). You can access the second element of any mouse event in the same way, with no need to distinguish drag events from others.

The ‘drag-’ prefix follows the modifier key prefixes such as ‘C-’ and ‘M-’.

If read-key-sequence receives a drag event that has no key binding, and the corresponding click event does have a binding, it changes the drag event into a click event at the drag’s starting position. This means that you don’t have to distinguish between click and drag events unless you want to.

18.5.6 Button-Down Events

Click and drag events happen when the user releases a mouse button. They cannot happen earlier, because there is no way to distinguish a click from a drag until the button is released.

If you want to take action as soon as a button is pressed, you need to handle button-down events.^{1} These occur as soon as a button is pressed. They are represented by lists that look exactly like click events (see Section 18.5.4 [Click Events], page 254), except that the event-type symbol name contains the prefix ‘down-’. The ‘down-’ prefix follows modifier key prefixes such as ‘C-’ and ‘M-’.

The function read-key-sequence, and therefore the Emacs command loop as well, ignore any button-down events that don’t have command bindings. This means that you need not worry about defining button-down events unless you want them to do something. The usual reason to define a button-down event is so that you can track mouse motion (by reading motion events) until the button is released. See Section 18.5.8 [Motion Events], page 257.

18.5.7 Repeat Events

If you press the same mouse button more than once in quick succession without moving the mouse, Emacs generates special repeat mouse events for the second and subsequent presses.

The most common repeat events are double-click events. Emacs generates a double-click event when you click a button twice; the event happens when you release the button (as is normal for all click events).

The event type of a double-click event contains the prefix ‘double-’. Thus, a double click on the second mouse button with ^{⟨}\underline{\overline{meta}}^{⟩} held down comes to the Lisp program as Mdouble-mouse-2. If a double-click event has no binding, the binding of the corresponding ordinary click event is used to execute it. Thus, you need not pay attention to the double click feature unless you really want to.

When the user performs a double click, Emacs generates first an ordinary click event, and then a double-click event. Therefore, you must design the command binding of the double click event to assume that the single-click command has already run. It must produce the desired results of a double click, starting from the results of a single click.

1 Button-down is the conservative antithesis of drag.

This is convenient, if the meaning of a double click somehow “builds on” the meaning of a single click—which is recommended user interface design practice for double clicks.

If you click a button, then press it down again and start moving the mouse with the button held down, then you get a double-drag event when you ultimately release the button. Its event type contains ‘double-drag’ instead of just ‘drag’. If a double-drag event has no binding, Emacs looks for an alternate binding as if the event were an ordinary drag.

Before the double-click or double-drag event, Emacs generates a double-down event when the user presses the button down for the second time. Its event type contains ‘double-down’ instead of just ‘down’. If a double-down event has no binding, Emacs looks for an alternate binding as if the event were an ordinary button-down event. If it finds no binding that way either, the double-down event is ignored.

To summarize, when you click a button and then press it again right away, Emacs generates a down event and a click event for the first click, a double-down event when you press the button again, and finally either a double-click or a double-drag event.

If you click a button twice and then press it again, all in quick succession, Emacs generates a triple-down event, followed by either a triple-click or a triple-drag. The event types of these events contain ‘triple’ instead of ‘double’. If any triple event has no binding, Emacs uses the binding that it would use for the corresponding double event.

If you click a button three or more times and then press it again, the events for the presses beyond the third are all triple events. Emacs does not have separate event types for quadruple, quintuple, etc. events. However, you can look at the event list to find out precisely how many times the button was pressed.

Function event-click-count event

This function returns the number of consecutive button presses that led up to event. If event is a double-down, double-click or double-drag event, the value is 2. If event is a triple event, the value is 3 or greater. If event is an ordinary mouse event (not a repeat event), the value is 1.

Variable double-click-time

To generate repeat events, successive mouse button presses must be at the same screen position, and the number of milliseconds between successive button presses must be less than the value of double-click-time. Setting doubleclick-time to nil disables multi-click detection entirely. Setting it to t removes the time limit; Emacs then detects multi-clicks by position only.

18.5.8 Motion Events

Emacs sometimes generates mouse motion events to describe motion of the mouse without any button activity. Mouse motion events are represented by lists that look like this:

     (mouse-movement

(window buffer-pos (x . y) timestamp))

The second element of the list describes the current position of the mouse, just as in a click event (see Section 18.5.4 [Click Events], page 254).

The special form track-mouse enables generation of motion events within its body. Outside of track-mouse forms, Emacs does not generate events for mere motion of the mouse, and these events do not appear.

Special Form track-mouse body…

This special form executes body, with generation of mouse motion events enabled. Typically body would use read-event to read the motion events and modify the display accordingly. When the user releases the button, that generates a click event. Typically, body should return when it sees the click event, and discard that event.

18.5.9 Focus Events

Window systems provide general ways for the user to control which window gets keyboard input. This choice of window is called the focus. When the user does something to switch between Emacs frames, that generates a focus event. The normal definition of a focus event, in the global keymap, is to select a new frame within Emacs, as the user would expect. See Section 26.9 [Input Focus], page 419.

Focus events are represented in Lisp as lists that look like this:

     (switch-frame new-frame)

where new-frame is the frame switched to.

Most X window managers are set up so that just moving the mouse into a window is enough to set the focus there. Emacs appears to do this, because it changes the cursor to solid in the new frame. However, there is no need for the Lisp program to know about the focus change until some other kind of input arrives. So Emacs generates a focus event only when the user actually types a keyboard key or presses a mouse button in the new frame; just moving the mouse between frames does not generate a focus event.

A focus event in the middle of a key sequence would garble the sequence. So Emacs never generates a focus event in the middle of a key sequence. If the user changes focus in the middle of a key sequence—that is, after a prefix key—then Emacs reorders the events so that the focus event comes either before or after the multi-event key sequence, and not within it.

18.5.10 Miscellaneous Window System Events

A few other event types represent occurrences within the window system.

(delete-frame (frame))

This kind of event indicates that the user gave the window manager a command to delete a particular window, which happens to be an Emacs frame. The standard definition of the delete-frame event is to delete frame.

(iconify-frame (frame))

This kind of event indicates that the user iconified frame using the window manager. Its standard definition is ignore; since the frame has already been iconified, Emacs has no work to do. The purpose of this event type is so that you can keep track of such events if you want to.

(make-frame-visible (frame))

This kind of event indicates that the user deiconified frame using the window manager. Its standard definition is ignore; since the frame has already been made visible, Emacs has no work to do.

If one of these events arrives in the middle of a key sequence—that is, after a prefix key—then Emacs reorders the events so that this event comes either before or after the multi-event key sequence, not within it.

18.5.11 Event Examples

If the user presses and releases the left mouse button over the same location, that generates a sequence of events like this:

     (down-mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864320))
     (mouse-1      (#<window 18 on NEWS> 2613 (0 . 38) -864180))

While holding the control key down, the user might hold down the second mouse button, and drag the mouse from one line to the next. That produces two events, as shown here:

     (C-down-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219))
     (C-drag-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219)
                     (#<window 18 on NEWS> 3510 (0 . 28) -729648))

While holding down the meta and shift keys, the user might press the second mouse button on the window’s mode line, and then drag the mouse into another window. That produces a pair of events like these:

     (M-S-down-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844))
     (M-S-drag-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844)
                       (#<window 20 on carlton-sanskrit.tex> 161 (33 . 3)
                        -453816))

18.5.12 Classifying Events

Every event has an event type, which classifies the event for key binding purposes. For a keyboard event, the event type equals the event value; thus, the event type for a character is the character, and the event type for a function key symbol is the symbol itself. For events that are lists, the event type is the symbol in the car of the list. Thus, the event type is always a symbol or a character.

Two events of the same type are equivalent where key bindings are concerned; thus, they always run the same command. That does not necessarily mean they do the same things, however, as some commands look at the whole event to decide what to do. For example, some commands use the location of a mouse event to decide where in the buffer to act.

Sometimes broader classifications of events are useful. For example, you might want to ask whether an event involved the ^{⟨}\underline{\overline{META}}^{⟩} key, regardless of which other key or mouse button was used.

The functions event-modifiers and event-basic-type are provided to get such information conveniently.

Function event-modifiers event

This function returns a list of the modifiers that event has. The modifiers are symbols; they include shift, control, meta, alt, hyper and super. In addition, the modifiers list of a mouse event symbol always contains one of

click, drag, and down.

The argument event may be an entire event object, or just an event type. Here are some examples:

(event-modifiers ?a)
     ⇒ nil
(event-modifiers ?\C-a)
     ⇒ (control)
(event-modifiers ?\C-%)
     ⇒ (control)
(event-modifiers ?\C-\S-a)
     ⇒ (control shift)
(event-modifiers 'f5)
     ⇒ nil
(event-modifiers 's-f5)
     ⇒ (super)
(event-modifiers 'M-S-f5)
     ⇒ (meta shift)
(event-modifiers 'mouse-1)
     ⇒ (click)
(event-modifiers 'down-mouse-1)
     ⇒ (down)

The modifiers list for a click event explicitly contains click, but the event symbol name itself does not contain ‘click’.

Function event-basic-type event

This function returns the key or mouse button that event describes, with all modifiers removed. For example:

(event-basic-type ?a)
     ⇒ 97
(event-basic-type ?A)
     ⇒ 97
(event-basic-type ?\C-a)
     ⇒ 97
(event-basic-type ?\C-\S-a)
     ⇒ 97
(event-basic-type 'f5)
     ⇒ f5
(event-basic-type 's-f5)
     ⇒ f5
(event-basic-type 'M-S-f5)
     ⇒ f5
(event-basic-type 'down-mouse-1)
     ⇒ mouse-1

Function mouse-movement-p object

This function returns non-nil if object is a mouse movement event.

Function event-convert-list list

This function converts a list of modifier names and a basic event type to an event type which specifies all of them. For example,

     (event-convert-list '(control ?a))
          ⇒ 1
     (event-convert-list '(control meta ?a))
          ⇒ -134217727
     (event-convert-list '(control super f1))
          ⇒ C-s-f1

18.5.13 Accessing Events

This section describes convenient functions for accessing the data in a mouse button or motion event.

These two functions return the starting or ending position of a mouse-button event. The position is a list of this form:

(window buffer-position (x . y) timestamp)

Function event-start event

This returns the starting position of event. If event is a click or button-down event, this returns the location of the event. If event is a drag event, this returns the drag’s starting position.

Function event-end event

This returns the ending position of event. If event is a drag event, this returns the position where the user released the mouse button. If event is a click or button-down event, the value is actually the starting position, which is the only position such events have.

These five functions take a position as described above, and return various parts of it.

Function posn-window position

Return the window that position is in.

Function posn-point position

Return the buffer position in position. This is an integer.

Function posn-x-y position

Return the pixel-based x and y coordinates in position, as a cons cell (x . y).

Function posn-col-row position

Return the row and column (in units of characters) of position, as a cons cell (col . row). These are computed from the x and y values actually found in position.

Function posn-timestamp position

Return the timestamp in position.

Function scroll-bar-event-ratio event

This function returns the fractional vertical position of a scroll bar event within the scroll bar. The value is a cons cell (portion . whole) containing two integers whose ratio is the fractional position.

Function scroll-bar-scale ratio total

This function multiplies (in effect) ratio by total, rounding the result to an integer. The argument ratio is not a number, but rather a pair (num . denom)—typically a value returned by scroll-bar-event-ratio.

This function is handy for scaling a position on a scroll bar into a buffer position.

Here’s how to do that:

          (+ (point-min)
             (scroll-bar-scale
                (posn-x-y (event-start event))
                (- (point-max) (point-min))))

Recall that scroll bar events have two integers forming ratio in place of a pair of x and y coordinates.

18.5.14 Putting Keyboard Events in Strings

In most of the places where strings are used, we conceptualize the string as containing text characters—the same kind of characters found in buffers or files. Occasionally Lisp programs use strings that conceptually contain keyboard characters; for example, they may be key sequences or keyboard macro definitions. There are special rules for how to put keyboard characters into a string, because they are not limited to the range of 0 to 255 as text characters are.

A keyboard character typed using the^{⟨}\underline{\overline{META}}^{⟩} key is called a meta character. The numeric code for such an event includes the $2^27$ bit; it does not even come close to fitting in a string. However, earlier Emacs versions used a different representation for these characters, which gave them codes in the range of 128 to 255. That did fit in a string, and many Lisp programs contain string constants that use ‘\M-’ to express meta characters, especially as the argument to define-key and similar functions.

We provide backward compatibility to run those programs using special rules for how to put a keyboard character event in a string. Here are the rules:

• If the keyboard character value is in the range of 0 to 127, it can go in the string unchanged.

• The meta variants of those characters, with codes in the range of $2^27$ to $2^27 + 127$, can also go in the string, but you must change their numeric values. You must set the $2^7$ bit instead of the $2^27$ bit, resulting in a value between 128 and 255.

• Other keyboard character events cannot fit in a string. This includes keyboard events in the range of 128 to 255.

Functions such as read-key-sequence that can construct strings of keyboard input characters follow these rules. They construct vectors instead of strings, when the events won’t fit in a string.

When you use the read syntax ‘\M-’ in a string, it produces a code in the range of 128 to 255—the same code that you get if you modify the corresponding keyboard event to put it in the string. Thus, meta events in strings work consistently regardless of how they get into the strings.

The reason we changed the representation of meta characters as keyboard events is to make room for basic character codes beyond 127, and support meta variants of such larger character codes.

New programs can avoid dealing with these special compatibility rules by using vectors instead of strings for key sequences when there is any possibility that they might contain meta characters, and by using listify-key-sequence to access a string of events.

Function listify-key-sequence key

This function converts the string or vector key to a list of events, which you can put in unread-command-events. Converting a vector is simple, but converting a string is tricky because of the special representation used for meta characters in a string.

18.6 Reading Input

The editor command loop reads keyboard input using the function read-key-sequence, which uses read-event. These and other functions for keyboard input are also available for use in Lisp programs. See also momentary-string-display in Section 35.8 [Temporary Displays], page 573, and sit-for in Section 18.7 [Waiting], page 267. See Section 34.8 [Terminal Input], page 558, for functions and variables for controlling terminal input modes and debugging terminal input. See Section 34.8.2 [Translating Input], page 559, for features you can use for translating or modifying input events while reading them.

For higher-level input facilities, see Chapter 17 [Minibuffers], page 223.

18.6.1 Key Sequence Input

The command loop reads input a key sequence at a time, by calling read-key-sequence. Lisp programs can also call this function; for example, describe-key uses it to read the key to describe.

Function read-key-sequence prompt

This function reads a key sequence and returns it as a string or vector. It keeps reading events until it has accumulated a full key sequence; that is, enough to specify a non-prefix command using the currently active keymaps. If the events are all characters and all can fit in a string, then read-key-sequence returns a string (see Section 18.5.14 [Strings of Events], page 262). Otherwise, it returns a vector, since a vector can hold all kinds of events— characters, symbols, and lists. The elements of the string or vector are the events in the key sequence.

The function read-key-sequence suppresses quitting: C-g typed while reading with this function works like any other character, and does not set quit-flag. See Section 18.8 [Quitting], page 268. The argument prompt is either a string to be displayed in the echo area as a prompt, or nil, meaning not to display a prompt. In the example below, the prompt ‘?’ is displayed in the echo area, and the user

     types C-x C-f.
          (read-key-sequence "?")
          ---------- Echo Area ----------
          ?C-x C-f
          ---------- Echo Area ----------

               ⇒ "^X^F"

Variable num-input-keys

This variable’s value is the number of key sequences processed so far in this Emacs session. This includes key sequences read from the terminal and key sequences read from keyboard macros being executed.

If an input character is an upper-case letter and has no key binding, but its lower-case equivalent has one, then read-key-sequence converts the character to lower case. Note that lookup-key does not perform case conversion in this way.

The function read-key-sequence also transforms some mouse events. It converts unbound drag events into click events, and discards unbound button-down events entirely. It also reshuffles focus events and miscellaneous window events so that they never appear in a key sequence with any other events.

When mouse events occur in special parts of a window, such as a mode line or a scroll bar, the event type shows nothing special—it is the same symbol that would normally represent that combination of mouse button and modifier keys. The information about the window part is kept elsewhere in the event—in the coordinates. But read-key-sequence translates this information into imaginary prefix keys, all of which are symbols: mode-line,

vertical-line, horizontal-scroll-bar and vertical-scroll-bar.

You can define meanings for mouse clicks in special window parts by defining key sequences using these imaginary prefix keys.

For example, if you call read-key-sequence and then click the mouse on the window’s mode line, you get two events, like this:

     (read-key-sequence "Click on the mode line: ")
          ⇒ [mode-line
              (mouse-1
               (#<window 6 on NEWS> mode-line
                (40 . 63) 5959987))]

18.6.2 Reading One Event

The lowest level functions for command input are those that read a single event.

Function read-event

This function reads and returns the next event of command input, waiting if necessary until an event is available. Events can come directly from the user or from a keyboard macro.

The function read-event does not display any message to indicate it is waiting for input; use message first, if you wish to display one. If you have not displayed a message, read-event prompts by echoing: it displays descriptions of the events that led to or were read by the current command. See Section 35.4 [The Echo Area], page 569.

If cursor-in-echo-area is non-nil, then read-event moves the cursor tem-

porarily to the echo area, to the end of any message displayed there. Otherwise read-event does not move the cursor.

Here is what happens if you call read-event and then press the right-arrow function key:

     (read-event)
          ⇒ right

Function read-char

This function reads and returns a character of command input. It discards any events that are not characters, until it gets a character.

In the first example, the user types the character 1 (ASCII code 49). The second example shows a keyboard macro definition that calls read-char from the minibuffer using eval-expression. read-char reads the keyboard macro’s very next character, which is 1. Then eval-expression displays its return value in the echo area.

     (read-char) ⇒ 49

;; We assume here you use M-: to evaluate this.

     (symbol-function 'foo)
          ⇒ "^[:(read-char)^M1"
     (execute-kbd-macro 'foo)
          ⊣ 49

          ⇒ nil

18.6.3 Quoted Character Input

You can use the function read-quoted-char to ask the user to specify a character, and allow the user to specify a control or meta character conveniently, either literally or as an octal character code. The command quoted-insert uses this function.

Function read-quoted-char &optional prompt

This function is like read-char, except that if the first character read is an octal digit (0-7), it reads up to two more octal digits (but stopping if a nonoctal digit is found) and returns the character represented by those digits in octal.

Quitting is suppressed when the first character is read, so that the user can enter a C-g. See Section 18.8 [Quitting], page 268. If prompt is supplied, it specifies a string for prompting the user. The prompt string is always displayed in the echo area, followed by a single ‘-’. In the following example, the user types in the octal number 177 (which is 127 in decimal).

     (read-quoted-char "What character")
     ---------- Echo Area ----------
     What character-177
     ---------- Echo Area ----------

          ⇒ 127

18.6.4 Miscellaneous Event Input Features

This section describes how to “peek ahead” at events without using them up, how to check for pending input, and how to discard pending input.

Variable unread-command-events

This variable holds a list of events waiting to be read as command input. The events are used in the order they appear in the list, and removed one by one as they are used. The variable is needed because in some cases a function reads a event and then decides not to use it. Storing the event in this variable causes it to be processed normally, by the command loop or by the functions to read command input. For example, the function that implements numeric prefix arguments reads any number of digits. When it finds a non-digit event, it must unread the event so that it can be read normally by the command loop. Likewise, incremental search uses this feature to unread events with no special meaning in a search, because these events should exit the search and then execute normally. The reliable and easy way to extract events from a key sequence so as to put

them in unread-command-events is to use listify-key-sequence (see Sec-

tion 18.5.14 [Strings of Events], page 262).

Variable unread-command-char

This variable holds a character to be read as command input. A value of -1 means “empty”. This variable is mostly obsolete now that you can use unread-command-events instead; it exists only to support programs written for Emacs versions 18 and earlier.

Function input-pending-p

This function determines whether any command input is currently available to be read. It returns immediately, with value t if there is available input, nil otherwise. On rare occasions it may return t when no input is available.

Variable last-input-event

This variable records the last terminal input event read, whether as part of a command or explicitly by a Lisp program. In the example below, the Lisp program reads the character 1, ASCII code

49. It becomes the value of last-input-event, while C-e (we assume C-x C-e command is used to evaluate this expression) remains the value of last-

command-event.
     (progn (print (read-char))
            (print last-command-event)
            last-input-event)
          ⊣ 49
          ⊣ 5
          ⇒ 49

The alias last-input-char exists for compatibility with Emacs version 18.

Function discard-input

This function discards the contents of the terminal input buffer and cancels any keyboard macro that might be in the process of definition. It returns nil. In the following example, the user may type a number of characters right after starting the evaluation of the form. After the sleep-for finishes sleeping, discard-input discards any characters typed during the sleep.

     (progn (sleep-for 2)
            (discard-input))
          ⇒ nil

18.7 Waiting for Elapsed Time or Input

The wait functions are designed to wait for a certain amount of time to pass or until there is input. For example, you may wish to pause in the middle of a computation to allow the user time to view the display. sit-for pauses and updates the screen, and returns immediately if input comes in, while sleep-for pauses without updating the screen.

Function sit-for seconds &optional millisec nodisp This function performs redisplay (provided there is no pending input from the user), then waits seconds seconds, or until input is available. The value is t if sit-for waited the full time with no input arriving (see input-pending-p in Section 18.6.4 [Event Input Misc], page 266). Otherwise, the value is nil. The argument seconds need not be an integer. If it is a floating point number, sit-for waits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down. The optional argument millisec specifies an additional waiting period measured in milliseconds. This adds to the period specified by seconds. If the system doesn’t support waiting fractions of a second, you get an error if you specify nonzero millisec. Redisplay is always preempted if input arrives, and does not happen at all if input is available before it starts. Thus, there is no way to force screen updating if there is pending input; however, if there is no input pending, you can force an update with no delay by using (sit-for 0). If nodisp is non-nil, then sit-for does not redisplay, but it still returns as soon as input is available (or when the timeout elapses). Iconifying or deiconifying a frame makes sit-for return, because that generates an event. See Section 18.5.10 [Misc Events], page 258. The usual purpose of sit-for is to give the user time to read text that you display.

Function sleep-for seconds &optional millisec This function simply pauses for seconds seconds without updating the display. It pays no attention to available input. It returns nil. The argument seconds need not be an integer. If it is a floating point number, sleep-for waits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down. The optional argument millisec specifies an additional waiting period measured in milliseconds. This adds to the period specified by seconds. If the system doesn’t support waiting fractions of a second, you get an error if you specify nonzero millisec. Use sleep-for when you wish to guarantee a delay.

See Section 34.5 [Time of Day], page 553, for functions to get the current time.

18.8 Quitting

Typing C-g while a Lisp function is running causes Emacs to quit whatever it is doing. This means that control returns to the innermost active command loop.

Typing C-g while the command loop is waiting for keyboard input does not cause a quit; it acts as an ordinary input character. In the simplest case, you cannot tell the difference, because C-g normally runs the command keyboard-quit, whose effect is to quit. However, when C-g follows a prefix key, the result is an undefined key. The effect is to cancel the prefix key as well as any prefix argument.

In the minibuffer, C-g has a different definition: it aborts out of the minibuffer. This means, in effect, that it exits the minibuffer and then quits. (Simply quitting would return to the command loop within the minibuffer.) The reason why C-g does not quit directly when the command reader is reading input is so that its meaning can be redefined in the minibuffer in this way. C-g following a prefix key is not redefined in the minibuffer, and it has its normal effect of canceling the prefix key and prefix argument. This too would not be possible if C-g always quit directly.

When C-g does directly quit, it does so by setting the variable quit-flag to t. Emacs checks this variable at appropriate times and quits if it is not nil. Setting quit-flag non-nil in any way thus causes a quit.

At the level of C code, quitting cannot happen just anywhere; only at the special places that check quit-flag. The reason for this is that quitting at other places might leave an inconsistency in Emacs’s internal state. Because quitting is delayed until a safe place, quitting cannot make Emacs crash.

Certain functions such as read-key-sequence or read-quoted-char prevent quitting entirely even though they wait for input. Instead of quitting, C-g serves as the requested input. In the case of read-key-sequence, this serves to bring about the special behavior of C-g in the command loop. In the case of read-quoted-char, this is so that C-q can be used to quote a C-g.

You can prevent quitting for a portion of a Lisp function by binding the variable inhibit-quit to a non-nil value. Then, although C-g still sets quit-flag to t as usual, the usual result of this—a quit—is prevented. Eventually, inhibit-quit will become nil again, such as when its binding is unwound at the end of a let form. At that time, if quit-flag is still non-nil, the requested quit happens immediately. This behavior is ideal when you wish to make sure that quitting does not happen within a “critical section” of the program.

In some functions (such as read-quoted-char), C-g is handled in a special way that does not involve quitting. This is done by reading the input with inhibit-quit bound to t, and setting quit-flag to nil before inhibit-quit becomes nil again. This excerpt from the definition of read-quoted-char shows how this is done; it also shows that normal quitting is permitted after the first character of input.

     (defun read-quoted-char (&optional prompt)

"…documentation…"

       (let ((count 0) (code 0) char)
         (while (< count 3)
           (let ((inhibit-quit (zerop count))
                 (help-form nil))
             (and prompt (message "%s-" prompt))
             (setq char (read-char))
             (if inhibit-quit (setq quit-flag nil)))

…)

         (logand 255 code)))

Variable quit-flag

If this variable is non-nil, then Emacs quits immediately, unless inhibitquit is non-nil. Typing C-g ordinarily sets quit-flag non-nil, regardless of

     inhibit-quit.

Variable inhibit-quit

This variable determines whether Emacs should quit when quit-flag is set to a value other than nil. If inhibit-quit is non-nil, then quit-flag has no special effect.

Command keyboard-quit

This function signals the quit condition with (signal 'quit nil). This is the same thing that quitting does. (See signal in Section 9.5.3 [Errors], page 112.)

You can specify a character other than C-g to use for quitting. See the function setinput-mode in Section 34.8 [Terminal Input], page 558.

18.9 Prefix Command Arguments

Most Emacs commands can use a prefix argument, a number specified before the command itself. (Don’t confuse prefix arguments with prefix keys.) The prefix argument is at all times represented by a value, which may be nil, meaning there is currently no prefix argument. Each command may use the prefix argument or ignore it.

There are two representations of the prefix argument: raw and numeric. The editor command loop uses the raw representation internally, and so do the Lisp variables that store the information, but commands can request either representation.

Here are the possible values of a raw prefix argument:

• nil, meaning there is no prefix argument. Its numeric value is 1, but numerous commands make a distinction between nil and the integer 1.

• An integer, which stands for itself.

• A list of one element, which is an integer. This form of prefix argument results from one or a succession of C-u’s with no digits. The numeric value is the integer in the list, but some commands make a distinction between such a list and an integer alone.

• The symbol -. This indicates that M-- or C-u - was typed, without following digits. The equivalent numeric value is −1, but some commands make a distinction between the integer −1 and the symbol -.

We illustrate these possibilities by calling the following function with various prefixes:

     (defun display-prefix (arg)
       "Display the value of the raw prefix arg."
       (interactive "P")
       (message "%s" arg))

Here are the results of calling display-prefix with various raw prefix arguments:

             M-x display-prefix ⊣ nil
     C-u     M-x display-prefix ⊣ (4)
     C-u C-u M-x display-prefix ⊣ (16)
     C-u 3   M-x display-prefix ⊣ 3
     M-3     M-x display-prefix ⊣ 3      ; (Same as C-u 3.)
     C-u -   M-x display-prefix ⊣ -
     M--     M-x display-prefix ⊣ -      ; (Same as C-u -.)
     C-u - 7 M-x display-prefix ⊣ -7
     M-- 7   M-x display-prefix ⊣ -7     ; (Same as C-u -7.)

Emacs uses two variables to store the prefix argument: prefix-arg and currentprefix-arg. Commands such as universal-argument that set up prefix arguments for other commands store them in prefix-arg. In contrast, current-prefix-arg conveys the prefix argument to the current command, so setting it has no effect on the prefix arguments for future commands.

Normally, commands specify which representation to use for the prefix argument, either numeric or raw, in the interactive declaration. (See Section 18.2.1 [Using Interactive], page 244.) Alternatively, functions may look at the value of the prefix argument directly in the variable current-prefix-arg, but this is less clean.

Function prefix-numeric-value arg

This function returns the numeric meaning of a valid raw prefix argument value, arg. The argument may be a symbol, a number, or a list. If it is nil, the value 1 is returned; if it is -, the value −1 is returned; if it is a number, that number is returned; if it is a list, the car of that list (which should be a number) is returned.

Variable current-prefix-arg

This variable holds the raw prefix argument for the current command. Commands may examine it directly, but the usual method for accessing it is with

(interactive "P").

Variable prefix-arg

The value of this variable is the raw prefix argument for the next editing command. Commands that specify prefix arguments for the following command work by setting this variable.

Do not call universal-argument, digit-argument, or negative-argument unless you

intend to let the user enter the prefix argument for the next command.

Command universal-argument

This command reads input and specifies a prefix argument for the following command. Don’t call this command yourself unless you know what you are doing.

Command digit-argument arg

This command adds to the prefix argument for the following command. The argument arg is the raw prefix argument as it was before this command; it is used to compute the updated prefix argument. Don’t call this command yourself unless you know what you are doing.

Command negative-argument arg

This command adds to the numeric argument for the next command. The argument arg is the raw prefix argument as it was before this command; its value is negated to form the new prefix argument. Don’t call this command yourself unless you know what you are doing.

18.10 Recursive Editing

The Emacs command loop is entered automatically when Emacs starts up. This top-level invocation of the command loop never exits; it keeps running as long as Emacs does. Lisp programs can also invoke the command loop. Since this makes more than one activation of the command loop, we call it recursive editing. A recursive editing level has the effect of suspending whatever command invoked it and permitting the user to do arbitrary editing before resuming that command.

The commands available during recursive editing are the same ones available in the top-level editing loop and defined in the keymaps. Only a few special commands exit the recursive editing level; the others return to the recursive editing level when they finish. (The special commands for exiting are always available, but they do nothing when recursive editing is not in progress.)

All command loops, including recursive ones, set up all-purpose error handlers so that an error in a command run from the command loop will not exit the loop.

Minibuffer input is a special kind of recursive editing. It has a few special wrinkles, such as enabling display of the minibuffer and the minibuffer window, but fewer than you might suppose. Certain keys behave differently in the minibuffer, but that is only because of the minibuffer’s local map; if you switch windows, you get the usual Emacs commands.

To invoke a recursive editing level, call the function recursive-edit. This function contains the command loop; it also contains a call to catch with tag exit, which makes it possible to exit the recursive editing level by throwing to exit (see Section 9.5.1 [Catch and Throw], page 110). If you throw a value other than t, then recursive-edit returns normally to the function that called it. The command C-M-c (exit-recursive-edit) does this. Throwing a t value causes recursive-edit to quit, so that control returns to the command loop one level up. This is called aborting, and is done by C-] (abort-recursive-

edit).

Most applications should not use recursive editing, except as part of using the minibuffer. Usually it is more convenient for the user if you change the major mode of the current buffer temporarily to a special major mode, which should have a command to go back to the previous mode. (The e command in Rmail uses this technique.) Or, if you wish to give the user different text to edit “recursively”, create and select a new buffer in a special mode. In this mode, define a command to complete the processing and go back to the previous buffer. (The m command in Rmail does this.)

Recursive edits are useful in debugging. You can insert a call to debug into a function definition as a sort of breakpoint, so that you can look around when the function gets there. debug invokes a recursive edit but also provides the other features of the debugger.

Recursive editing levels are also used when you type C-r in query-replace or use C-x

q (kbd-macro-query).

Function recursive-edit

This function invokes the editor command loop. It is called automatically by the initialization of Emacs, to let the user begin editing. When called from a Lisp program, it enters a recursive editing level.

In the following example, the function simple-rec first advances point one word, then enters a recursive edit, printing out a message in the echo area. The user can then do any editing desired, and then type C-M-c to exit and continue

     executing simple-rec.

     (defun simple-rec ()
       (forward-word 1)
       (message "Recursive edit in progress")
       (recursive-edit)
       (forward-word 1))
          ⇒ simple-rec
     (simple-rec)
          ⇒ nil

Command exit-recursive-edit

This function exits from the innermost recursive edit (including minibuffer input). Its definition is effectively (throw 'exit nil).

Command abort-recursive-edit

This function aborts the command that requested the innermost recursive edit (including minibuffer input), by signaling quit after exiting the recursive edit. Its definition is effectively (throw 'exit t). See Section 18.8 [Quitting], page 268.

Command top-level

This function exits all recursive editing levels; it does not return a value, as it jumps completely out of any computation directly back to the main command loop.

Function recursion-depth

This function returns the current depth of recursive edits. When no recursive edit is active, it returns 0.

18.11 Disabling Commands

Disabling a command marks the command as requiring user confirmation before it can be executed. Disabling is used for commands which might be confusing to beginning users, to prevent them from using the commands by accident.

The low-level mechanism for disabling a command is to put a non-nildisabled property on the Lisp symbol for the command. These properties are normally set up by the user’s ‘.emacs’ file with Lisp expressions such as this:

(put 'upcase-region 'disabled t)

For a few commands, these properties are present by default and may be removed by the

‘.emacs’ file.

If the value of the disabled property is a string, the message saying the command is disabled includes that string. For example:

(put 'delete-region 'disabled
     "Text deleted this way cannot be yanked back!\n")

See section “Disabling” in The GNU Emacs Manual, for the details on what happens when a disabled command is invoked interactively. Disabling a command has no effect on calling it as a function from Lisp programs.

Command enable-command command

Allow command to be executed without special confirmation from now on, and (if the user confirms) alter the user’s ‘.emacs’ file so that this will apply to future sessions.

Command disable-command command

Require special confirmation to execute command from now on, and (if the user confirms) alter the user’s ‘.emacs’ file so that this will apply to future sessions.

Variable disabled-command-hook

This normal hook is run instead of a disabled command, when the user invokes the disabled command interactively. The hook functions can use thiscommand-keys to determine what the user typed to run the command, and thus find the command itself. See Section 20.4 [Hooks], page 316.

By default, disabled-command-hook contains a function that asks the user whether to proceed.

18.12 Command History

The command loop keeps a history of the complex commands that have been executed, to make it convenient to repeat these commands. A complex command is one for which the interactive argument reading uses the minibuffer. This includes any M-x command, any M-: command, and any command whose interactive specification reads an argument from the minibuffer. Explicit use of the minibuffer during the execution of the command itself does not cause the command to be considered complex.

Variable command-history

This variable’s value is a list of recent complex commands, each represented as a form to evaluate. It continues to accumulate all complex commands for the duration of the editing session, but all but the first (most recent) thirty elements are deleted when a garbage collection takes place (see Section B.3 [Garbage Collection], page 611).

     command-history
     ⇒ ((switch-to-buffer "chistory.texi")
         (describe-key "^X^[")
         (visit-tags-table "~/emacs/src/")
         (find-tag "repeat-complex-command"))

This history list is actually a special case of minibuffer history (see Section 17.4 [Minibuffer History], page 227), with one special twist: the elements are expressions rather than strings.

There are a number of commands devoted to the editing and recall of previous com-

mands. The commands repeat-complex-command, and list-command-history are de-

scribed in the user manual (see section “Repetition” in The GNU Emacs Manual). Within the minibuffer, the history commands used are the same ones available in any minibuffer.

18.13 Keyboard Macros

A keyboard macro is a canned sequence of input events that can be considered a command and made the definition of a key. The Lisp representation of a keyboard macro is a string or vector containing the events. Don’t confuse keyboard macros with Lisp macros (see Chapter 12 [Macros], page 153).

Function execute-kbd-macro macro &optional count This function executes macro as a sequence of events. If macro is a string or vector, then the events in it are executed exactly as if they had been input by the user. The sequence is not expected to be a single key sequence; normally a keyboard macro definition consists of several key sequences concatenated. If macro is a symbol, then its function definition is used in place of macro. If that is another symbol, this process repeats. Eventually the result should be a string or vector. If the result is not a symbol, string, or vector, an error is signaled. The argument count is a repeat count; macro is executed that many times. If count is omitted or nil, macro is executed once. If it is 0, macro is executed over and over until it encounters an error or a failing search.

Variable executing-macro

This variable contains the string or vector that defines the keyboard macro that is currently executing. It is nil if no macro is currently executing. A command can test this variable to behave differently when run from an executing macro. Do not set this variable yourself.

Variable defining-kbd-macro

This variable indicates whether a keyboard macro is being defined. A command can test this variable to behave differently while a macro is being defined. The commands start-kbd-macro and end-kbd-macro set this variable—do not set it yourself. The variable is always local to the current terminal and cannot be buffer-local. See Section 26.2 [Multiple Displays], page 409.

Variable last-kbd-macro

This variable is the definition of the most recently defined keyboard macro. Its value is a string or vector, or nil. The variable is always local to the current terminal and cannot be buffer-local. See Section 26.2 [Multiple Displays], page 409.

276 GNU Emacs Lisp Reference Manual

19 Keymaps

The bindings between input events and commands are recorded in data structures called keymaps. Each binding in a keymap associates (or binds) an individual event type either with another keymap or with a command. When an event is bound to a keymap, that keymap is used to look up the next input event; this continues until a command is found. The whole process is called key lookup.

19.1 Keymap Terminology

A keymap is a table mapping event types to definitions (which can be any Lisp objects, though only certain types are meaningful for execution by the command loop). Given an event (or an event type) and a keymap, Emacs can get the event’s definition. Events include ordinary ASCII characters, function keys, and mouse actions (see Section 18.5 [Input Events], page 252).

A sequence of input events that form a unit is called a key sequence, or key for short. A sequence of one event is always a key sequence, and so are some multi-event sequences.

A keymap determines a binding or definition for any key sequence. If the key sequence is a single event, its binding is the definition of the event in the keymap. The binding of a key sequence of more than one event is found by an iterative process: the binding of the first event is found, and must be a keymap; then the second event’s binding is found in that keymap, and so on until all the events in the key sequence are used up.

If the binding of a key sequence is a keymap, we call the key sequence a prefix key. Otherwise, we call it a complete key (because no more events can be added to it). If the binding is nil, we call the key undefined. Examples of prefix keys are C-c, C-x, and C-x 4. Examples of defined complete keys are X, ^{⟨}\underline{\overline{RET}}^{⟩}, and C-x 4 C-f. Examples of undefined complete keys are C-x C-g, and C-c 3. See Section 19.5 [Prefix Keys], page 280, for more details.

The rule for finding the binding of a key sequence assumes that the intermediate bindings (found for the events before the last) are all keymaps; if this is not so, the sequence of events does not form a unit—it is not really a key sequence. In other words, removing one or more events from the end of any valid key must always yield a prefix key. For example, C-f C-n is not a key; C-f is not a prefix key, so a longer sequence starting with C-f cannot be a key.

Note that the set of possible multi-event key sequences depends on the bindings for prefix keys; therefore, it can be different for different keymaps, and can change when bindings are changed. However, a one-event sequence is always a key sequence, because it does not depend on any prefix keys for its well-formedness.

At any time, several primary keymaps are active—that is, in use for finding key bindings. These are the global map, which is shared by all buffers; the local keymap, which is usually associated with a specific major mode; and zero or more minor mode keymaps, which belong to currently enabled minor modes. (Not all minor modes have keymaps.) The local keymap bindings shadow (i.e., take precedence over) the corresponding global bindings. The minor mode keymaps shadow both local and global keymaps. See Section 19.6 [Active Keymaps], page 281, for details.

19.2 Format of Keymaps

A keymap is a list whose car is the symbol keymap. The remaining elements of the list define the key bindings of the keymap. Use the function keymapp (see below) to test whether an object is a keymap.

Each ordinary binding applies to events of a particular event type, which is always a character or a symbol. See Section 18.5.12 [Classifying Events], page 259.

An ordinary element of a keymap is a cons cell of the form (type . binding). This specifies one binding, for events of type type.

A cons cell whose car is t is a default key binding; any event not bound by other elements of the keymap is given binding as its binding. Default bindings allow a keymap to bind all possible event types without having to enumerate all of them. A keymap that has a default binding completely masks any lower-precedence keymap.

If an element of a keymap is a vector, the vector counts as bindings for all the ASCII characters; vector element n is the binding for the character with code n. This is a compact way to record lots of bindings. A keymap with such a vector is called a full keymap. Other keymaps are called sparse keymaps.

When a keymap contains a vector, it always defines a binding for every ASCII character even if the vector element is nil. Such a binding of nil overrides any default binding in the keymap. However, default bindings are still meaningful for events that are not ASCII characters. A binding of nil does not override lower-precedence keymaps; thus, if the local map gives a binding of nil, Emacs uses the binding from the global map.

Aside from bindings, a keymap can also have a string as an element. This is called the overall prompt string and makes it possible to use the keymap as a menu. See Section 19.12 [Menu Keymaps], page 294.

Keymaps do not directly record bindings for the meta characters, whose codes are from 128 to 255. Instead, meta characters are regarded for purposes of key lookup as sequences of two characters, the first of which is ^{⟨}\underline{\overline{ESC}}^{⟩} (or whatever is currently the value of metaprefix-char). Thus, the key M-a is really represented as ^{⟨}\underline{\overline{ESC}}^{⟩} a, and its global binding is found at the slot for a in esc-map (see Section 19.5 [Prefix Keys], page 280).

Here as an example is the local keymap for Lisp mode, a sparse keymap. It defines bindings for ^{⟨}\underline{\overline{DEL}}^{⟩} and ^{⟨}\underline{\overline{TAB}}^{⟩}, plus C-c C-l, M-C-q, and M-C-x.

     lisp-mode-map

⇒

     (keymap

;; ^{⟨}\underline{\overline{TAB}}^{⟩}

      (9 . lisp-indent-line)

;; ^{⟨}\underline{\overline{DEL}}^{⟩}

      (127 . backward-delete-char-untabify)
      (3 keymap
         ;; C-c C-l
         (12 . run-lisp))

 (27 keymap

;; M-C-q, treated as ^{⟨}\underline{\overline{ESC}}^{⟩} C-q

     (17 . indent-sexp)

;; M-C-x, treated as ^{⟨}\underline{\overline{ESC}}^{⟩} C-x

     (24 . lisp-send-defun)))

Function keymapp object

This function returns t if object is a keymap, nil otherwise. More precisely, this function tests for a list whose car is keymap.

     (keymapp '(keymap))
         ⇒ t
     (keymapp (current-global-map))
         ⇒ t

19.3 Creating Keymaps

Here we describe the functions for creating keymaps.

Function make-keymap &optional prompt This function creates and returns a new full keymap (i.e., one containing a vector of length 128 for defining all the ASCII characters). The new keymap initially binds all ASCII characters to nil, and does not bind any other kind of event.

     (make-keymap)
         ⇒ (keymap [nil nil nil . . . nil nil])

If you specify prompt, that becomes the overall prompt string for the keymap. The prompt string is useful for menu keymaps (see Section 19.12 [Menu Keymaps], page 294).

Function make-sparse-keymap &optional prompt

This function creates and returns a new sparse keymap with no entries. The new keymap does not bind any events. The argument prompt specifies a prompt string, as in make-keymap.

     (make-sparse-keymap)
         ⇒ (keymap)

Function copy-keymap keymap

This function returns a copy of keymap. Any keymaps that appear directly as bindings in keymap are also copied recursively, and so on to any number of levels. However, recursive copying does not take place when the definition of a character is a symbol whose function definition is a keymap; the same symbol appears in the new copy.

     (setq map (copy-keymap (current-local-map)))
     ⇒ (keymap

;; (This implements meta characters.)

          (27 keymap
              (83 . center-paragraph)
              (115 . center-line))
          (9 . tab-to-tab-stop))

          (eq map (current-local-map))
              ⇒ nil
          (equal map (current-local-map))
              ⇒ t

19.4 Inheritance and Keymaps

A keymap can inherit the bindings of another keymap, which we call the parent keymap. Such a keymap looks like this:

(keymap bindings. … parent-keymap) The effect is that this keymap inherits all the bindings of parent-keymap, whatever they may be at the time a key is looked up, but can add to them or override them with bindings.

If you change the bindings in parent-keymap using define-key or other key-binding functions, these changes are visible in the inheriting keymap unless shadowed by bindings. The converse is not true: if you use define-key to change the inheriting keymap, that affects bindings, but has no effect on parent-keymap.

The proper way to construct a keymap with a parent is to use set-keymap-parent; if you have code that directly constructs a keymap with a parent, please convert the program

to use set-keymap-parent instead.

Function keymap-parent keymap

This returns the parent keymap of keymap. If keymap has no parent, keymap-

     parent returns nil.

Function set-keymap-parent keymap parent

This sets the parent keymap of keymap to parent, and returns parent. If parent is nil, this function gives keymap no parent at all. If keymap has submaps (bindings for prefix keys), they too receive new parent keymaps that reflect what parent specifies for those prefix keys.

Here is an example showing how to make a keymap that inherits from text-mode-map:

     (let ((map (make-sparse-keymap)))
       (set-keymap-parent map text-mode-map)
       map)

19.5 Prefix Keys

A prefix key has an associated keymap that defines what to do with key sequences that start with the prefix key. For example, C-x is a prefix key, and it uses a keymap that is also stored in the variable ctl-x-map. Here is a list of the standard prefix keys of Emacs and their keymaps:

• esc-map is used for events that follow ^{⟨}\underline{\overline{ESC}}^{⟩}. Thus, the global definitions of all meta characters are actually found here. This map is also the function definition of ESC-

    prefix.

• help-map is used for events that follow C-h.

• mode-specific-map is for events that follow C-c. This map is not actually mode specific; its name was chosen to be informative for the user in C-h b (display-bindings), where it describes the main use of the C-c prefix key.

• ctl-x-map is the map used for events that follow C-x. This map is also the function

    definition of Control-X-prefix.

• ctl-x-4-map is used for events that follow C-x 4.

• ctl-x-5-map is used for events that follow C-x 5.

• The prefix keys C-x n, C-x r and C-x a use keymaps that have no special name.

The binding of a prefix key is the keymap to use for looking up the events that follow the prefix key. (It may instead be a symbol whose function definition is a keymap. The effect is the same, but the symbol serves as a name for the prefix key.) Thus, the binding of C-x is the symbol Control-X-prefix, whose function definition is the keymap for C-x commands. (The same keymap is also the value of ctl-x-map.)

Prefix key definitions can appear in any active keymap. The definitions of C-c, C-x, C-h and ^{⟨}\underline{\overline{ESC}}^{⟩} as prefix keys appear in the global map, so these prefix keys are always available. Major and minor modes can redefine a key as a prefix by putting a prefix key definition for it in the local map or the minor mode’s map. See Section 19.6 [Active Keymaps], page 281.

If a key is defined as a prefix in more than one active map, then its various definitions are in effect merged: the commands defined in the minor mode keymaps come first, followed by those in the local map’s prefix definition, and then by those from the global map.

In the following example, we make C-p a prefix key in the local keymap, in such a way that C-p is identical to C-x. Then the binding for C-p C-f is the function find-file, just like C-x C-f. The key sequence C-p 6 is not found in any active keymap.

     (use-local-map (make-sparse-keymap))
         ⇒ nil
     (local-set-key "\C-p" ctl-x-map)
         ⇒ nil
     (key-binding "\C-p\C-f")
         ⇒ find-file
     (key-binding "\C-p6")
         ⇒ nil

Function define-prefix-command symbol

This function defines symbol as a prefix command: it creates a full keymap and stores it as symbol’s function definition. Storing the symbol as the binding of a key makes the key a prefix key that has a name. The function also sets symbol as a variable, to have the keymap as its value. It returns symbol. In Emacs version 18, only the function definition of symbol was set, not the value as a variable.

19.6 Active Keymaps

Emacs normally contains many keymaps; at any given time, just a few of them are active in that they participate in the interpretation of user input. These are the global keymap, the current buffer’s local keymap, and the keymaps of any enabled minor modes.

The global keymap holds the bindings of keys that are defined regardless of the current buffer, such as C-f. The variable global-map holds this keymap, which is always active.

Each buffer may have another keymap, its local keymap, which may contain new or overriding definitions for keys. The current buffer’s local keymap is always active except when overriding-local-map overrides it. Text properties can specify an alternative local map for certain parts of the buffer; see Section 29.18.4 [Special Properties], page 482.

Each minor mode may have a keymap; if it does, the keymap is active when the minor mode is enabled.

The variable overriding-local-map, if non-nil, specifies another local keymap that overrides the buffer’s local map and all the minor mode keymaps.

All the active keymaps are used together to determine what command to execute when a key is entered. Emacs searches these maps one by one, in order of decreasing precedence, until it finds a binding in one of the maps.

Normally, Emacs first searches for the key in the minor mode maps (one map at a time); if they do not supply a binding for the key, Emacs searches the local map; if that too has no binding, Emacs then searches the global map. However, if overriding-local-map is non-nil, Emacs searches that map first, followed by the global map.

The procedure for searching a single keymap is called key lookup; see Section 19.7 [Key Lookup], page 284.

Since every buffer that uses the same major mode normally uses the same local keymap, you can think of the keymap as local to the mode. A change to the local keymap of a buffer (using local-set-key, for example) is seen also in the other buffers that share that keymap.

The local keymaps that are used for Lisp mode, C mode, and several other major modes exist even if they have not yet been used. These local maps are the values of the variables lisp-mode-map, c-mode-map, and so on. For most other modes, which are less frequently used, the local keymap is constructed only when the mode is used for the first time in a session.

The minibuffer has local keymaps, too; they contain various completion and exit commands. See Section 17.1 [Intro to Minibuffers], page 223.

See Appendix E [Standard Keymaps], page 631, for a list of standard keymaps.

Variable global-map

This variable contains the default global keymap that maps Emacs keyboard input to commands. The global keymap is normally this keymap. The default global keymap is a full keymap that binds self-insert-command to all of the printing characters.

It is normal practice to change the bindings in the global map, but you should not assign this variable any value other than the keymap it starts out with.

Function current-global-map

This function returns the current global keymap. This is the same as the value of global-map unless you change one or the other.

     (current-global-map)
     ⇒ (keymap [set-mark-command beginning-of-line . . .
                 delete-backward-char])

Function current-local-map

This function returns the current buffer’s local keymap, or nil if it has none. In the following example, the keymap for the ‘*scratch*’ buffer (using Lisp Interaction mode) is a sparse keymap in which the entry for ^{⟨}\underline{\overline{ESC}}^{⟩}, ASCII code 27, is another sparse keymap.

     (current-local-map)
     ⇒ (keymap
         (10 . eval-print-last-sexp)
         (9 . lisp-indent-line)
         (127 . backward-delete-char-untabify)
         (27 keymap
             (24 . eval-defun)
             (17 . indent-sexp)))

Function current-minor-mode-maps

This function returns a list of the keymaps of currently enabled minor modes.

Function use-global-map keymap

This function makes keymap the new current global keymap. It returns nil. It is very unusual to change the global keymap.

Function use-local-map keymap

This function makes keymap the new local keymap of the current buffer. If keymap is nil, then the buffer has no local keymap. use-local-map returns nil. Most major mode commands use this function.

Variable minor-mode-map-alist

This variable is an alist describing keymaps that may or may not be active according to the values of certain variables. Its elements look like this:

(variable . keymap) The keymap keymap is active whenever variable has a non-nil value. Typically variable is the variable that enables or disables a minor mode. See Section 20.2.2 [Keymaps and Minor Modes], page 310. Note that elements of minor-mode-map-alist do not have the same structure as elements of minor-mode-alist. The map must be the cdr of the element; a list with the map as the second element will not do. What’s more, the keymap itself must appear in the cdr. It does not work to store a variable in the cdr and make the map the value of that variable. When more than one minor mode keymap is active, their order of priority is the order of minor-mode-map-alist. But you should design minor modes so that they don’t interfere with each other. If you do this properly, the order will not matter. See also minor-mode-key-binding, above. See Section 20.2.2 [Keymaps and Minor Modes], page 310, for more information about minor modes.

Variable overriding-local-map

If non-nil, this variable holds a keymap to use instead of the buffer’s local keymap and instead of all the minor mode keymaps. This keymap, if any, overrides all other maps that would have been active, except for the current global map.

Variable overriding-terminal-local-map

If non-nil, this variable holds a keymap to use instead of overriding-local-map, the buffer’s local keymap and all the minor mode keymaps. This variable is always local to the current terminal and cannot be bufferlocal. See Section 26.2 [Multiple Displays], page 409. It is used to implement incremental search mode.

Variable overriding-local-map-menu-flag

If this variable is non-nil, the value of overriding-local-map or overriding-

terminal-local-map can affect the display of the menu bar. The default value is nil, so those map variables have no effect on the menu bar. Note that these two map variables do affect the execution of key sequences entered using the menu bar, even if they do not affect the menu bar display. So if a menu bar key sequence comes in, you should clear the variables before looking up and executing that key sequence. Modes that use the variables would typically do this anyway; normally they respond to events that they do not handle by “unreading” them and exiting.

19.7 Key Lookup

Key lookup is the process of finding the binding of a key sequence from a given keymap. Actual execution of the binding is not part of key lookup.

Key lookup uses just the event type of each event in the key sequence; the rest of the event is ignored. In fact, a key sequence used for key lookup may designate mouse events with just their types (symbols) instead of with entire mouse events (lists). See Section 18.5 [Input Events], page 252. Such a pseudo-key-sequence is insufficient for command-execute, but it is sufficient for looking up or rebinding a key.

When the key sequence consists of multiple events, key lookup processes the events sequentially: the binding of the first event is found, and must be a keymap; then the second event’s binding is found in that keymap, and so on until all the events in the key sequence are used up. (The binding thus found for the last event may or may not be a keymap.) Thus, the process of key lookup is defined in terms of a simpler process for looking up a single event in a keymap. How that is done depends on the type of object associated with the event in that keymap.

Let’s use the term keymap entry to describe the value found by looking up an event type in a keymap. (This doesn’t include the item string and other extra elements in menu key bindings because lookup-key and other key lookup functions don’t include them in the returned value.) While any Lisp object may be stored in a keymap as a keymap entry, not all make sense for key lookup. Here is a list of the meaningful kinds of keymap entries: nil nil means that the events used so far in the lookup form an undefined key.

When a keymap fails to mention an event type at all, and has no default binding, that is equivalent to a binding of nil for that event type.

keymap The events used so far in the lookup form a prefix key. The next event of the key sequence is looked up in keymap.

command The events used so far in the lookup form a complete key, and command is its binding. See Section 11.1 [What Is a Function], page 139.

array The array (either a string or a vector) is a keyboard macro. The events used so far in the lookup form a complete key, and the array is its binding. See Section 18.13 [Keyboard Macros], page 275, for more information.

list The meaning of a list depends on the types of the elements of the list.

• If the car of list is the symbol keymap, then the list is a keymap, and is treated as a keymap (see above).

• If the car of list is lambda, then the list is a lambda expression. This is presumed to be a command, and is treated as such (see above).

• If the car of list is a keymap and the cdr is an event type, then this is an

indirect entry:

(othermap . othertype) When key lookup encounters an indirect entry, it looks up instead the binding of othertype in othermap and uses that. This feature permits you to define one key as an alias for another key. For example, an entry whose car is the keymap called esc-map and whose cdr is 32 (the code for^{⟨}\underline{\overline{SPC}}^{⟩}) means, “Use the global binding of Meta-^{⟨}\underline{\overline{SPC}}^{⟩}, whatever that may be.”

symbol The function definition of symbol is used in place of symbol. If that too is a symbol, then this process is repeated, any number of times. Ultimately this should lead to an object that is a keymap, a command or a keyboard macro. A list is allowed if it is a keymap or a command, but indirect entries are not understood when found via symbols. Note that keymaps and keyboard macros (strings and vectors) are not valid functions, so a symbol with a keymap, string, or vector as its function definition is invalid as a function. It is, however, valid as a key binding. If the definition is a keyboard macro, then the symbol is also valid as an argument to commandexecute (see Section 18.3 [Interactive Call], page 248). The symbol undefined is worth special mention: it means to treat the key as undefined. Strictly speaking, the key is defined, and its binding is the command undefined; but that command does the same thing that is done automatically for an undefined key: it rings the bell (by calling ding) but does not signal an error. undefined is used in local keymaps to override a global key binding and make the key “undefined” locally. A local binding of nil would fail to do this because it would not override the global binding. anything else

If any other type of object is found, the events used so far in the lookup form a complete key, and the object is its binding, but the binding is not executable as a command.

In short, a keymap entry may be a keymap, a command, a keyboard macro, a symbol that leads to one of them, or an indirection or nil. Here is an example of a sparse keymap with two characters bound to commands and one bound to another keymap. This map is the normal value of emacs-lisp-mode-map. Note that 9 is the code for ^{⟨}\underline{\overline{TAB}}^{⟩}, 127 for ^{⟨}\underline{\overline{DEL}}^{⟩}, 27 for ^{⟨}\underline{\overline{ESC}}^{⟩}, 17 for C-q and 24 for C-x.

(keymap (9 . lisp-indent-line)
        (127 . backward-delete-char-untabify)
        (27 keymap (17 . indent-sexp) (24 . eval-defun)))

19.8 Functions for Key Lookup

Here are the functions and variables pertaining to key lookup.

Function lookup-key keymap key &optional accept-defaults This function returns the definition of key in keymap. If the string or vector key is not a valid key sequence according to the prefix keys specified in keymap (which means it is “too long” and has extra events at the end), then the value is a number, the number of events at the front of key that compose a complete key. If accept-defaults is non-nil, then lookup-key considers default bindings as well as bindings for the specific events in key. Otherwise, lookup-key reports only bindings for the specific sequence key, ignoring default bindings except when you explicitly ask about them. (To do this, supply t as an element of key; see Section 19.2 [Format of Keymaps], page 278.) All the other functions described in this chapter that look up keys use lookup-

key.
     (lookup-key (current-global-map) "\C-x\C-f")
         ⇒ find-file
     (lookup-key (current-global-map) "\C-x\C-f12345")
         ⇒ 2

If key contains a meta character, that character is implicitly replaced by a two-character sequence: the value of meta-prefix-char, followed by the corresponding non-meta character. Thus, the first example below is handled by conversion into the second example.

     (lookup-key (current-global-map) "\M-f")
         ⇒ forward-word
     (lookup-key (current-global-map) "\ef")
         ⇒ forward-word

Unlike read-key-sequence, this function does not modify the specified events in ways that discard information (see Section 18.6.1 [Key Sequence Input], page 263). In particular, it does not convert letters to lower case and it does not change drag events to clicks.

Command undefined

Used in keymaps to undefine keys. It calls ding, but does not cause an error.

Function key-binding key &optional accept-defaults This function returns the binding for key in the current keymaps, trying all the active keymaps. The result is nil if key is undefined in the keymaps. The argument accept-defaults controls checking for default bindings, as in

lookup-key (above).

An error is signaled if key is not a string or a vector.

     (key-binding "\C-x\C-f")
         ⇒ find-file

Function local-key-binding key &optional accept-defaults This function returns the binding for key in the current local keymap, or nil if it is undefined there. The argument accept-defaults controls checking for default bindings, as in

lookup-key (above).

Function global-key-binding key &optional accept-defaults This function returns the binding for command key in the current global keymap, or nil if it is undefined there. The argument accept-defaults controls checking for default bindings, as in

lookup-key (above).

Function minor-mode-key-binding key &optional accept-defaults This function returns a list of all the active minor mode bindings of key. More precisely, it returns an alist of pairs (modename . binding), where modename is the variable that enables the minor mode, and binding is key’s binding in that mode. If key has no minor-mode bindings, the value is nil. If the first binding is not a prefix command, all subsequent bindings from other minor modes are omitted, since they would be completely shadowed. Similarly, the list omits non-prefix bindings that follow prefix bindings. The argument accept-defaults controls checking for default bindings, as in

lookup-key (above).

Variable meta-prefix-char

This variable is the meta-prefix character code. It is used when translating a meta character to a two-character sequence so it can be looked up in a keymap. For useful results, the value should be a prefix event (see Section 19.5 [Prefix Keys], page 280). The default value is 27, which is the ASCII code for ^{⟨}\underline{\overline{ESC}}^{⟩}. As long as the value of meta-prefix-char remains 27, key lookup translates M-b into ^{⟨}\underline{\overline{ESC}}^{⟩} b, which is normally defined as the backward-word command. However, if you set meta-prefix-char to 24, the code for C-x, then Emacs will translate M-b into C-x b, whose standard binding is the switch-to-buffer command.

          meta-prefix-char                    ; The default value.
               ⇒ 27
          (key-binding "\M-b")
               ⇒ backward-word

?\C-x ; The print representation ⇒ 24 ; of a character.

          (setq meta-prefix-char 24)
               ⇒ 24
          (key-binding "\M-b")
               ⇒ switch-to-buffer            ; Now, typing M-b is

; like typing C-x b.

          (setq meta-prefix-char 27)          ; Avoid confusion!

⇒ 27 ; Restore the default value!

19.9 Changing Key Bindings

The way to rebind a key is to change its entry in a keymap. If you change a binding in the global keymap, the change is effective in all buffers (though it has no direct effect in buffers that shadow the global binding with a local one). If you change the current buffer’s local map, that usually affects all buffers using the same major mode. The globalset-key and local-set-key functions are convenient interfaces for these operations (see Section 19.10 [Key Binding Commands], page 291). You can also use define-key, a more general function; then you must specify explicitly the map to change.

In writing the key sequence to rebind, it is good to use the special escape sequences for control and meta characters (see Section 2.3.8 [String Type], page 23). The syntax ‘\C-’ means that the following character is a control character and ‘\M-’ means that the following character is a meta character. Thus, the string "\M-x" is read as containing a single M-x, "\C-f" is read as containing a single C-f, and "\M-\C-x" and "\C-\M-x" are both read as containing a single C-M-x. You can also use this escape syntax in vectors, as well as others that aren’t allowed in strings; one example is ‘[?\C-\H-x home]’. See Section 2.3.3 [Character Type], page 17.

The key definition and lookup functions accept an alternate syntax for event types in a key sequence that is a vector: you can use a list containing modifier names plus one base event (a character or function key name). For example, (control ?a) is equivalent to

?\C-a and (hyper control left) is equivalent to C-H-left.

One advantage of using a list to represent the event type is that the precise numeric codes for the modifier bits don’t appear in compiled files.

For the functions below, an error is signaled if keymap is not a keymap or if key is not a string or vector representing a key sequence. You can use event types (symbols) as shorthand for events that are lists.

Function define-key keymap key binding This function sets the binding for key in keymap. (If key is more than one event long, the change is actually made in another keymap reached from keymap.)

The argument binding can be any Lisp object, but only certain types are meaningful. (For a list of meaningful types, see Section 19.7 [Key Lookup], page 284.) The value returned by define-key is binding.

Every prefix of key must be a prefix key (i.e., bound to a keymap) or undefined; otherwise an error is signaled.

If some prefix of key is undefined, then define-key defines it as a prefix key so that the rest of key may be defined as specified.

Here is an example that creates a sparse keymap and makes a number of bindings in it:

(setq map (make-sparse-keymap))
    ⇒ (keymap)
(define-key map "\C-f" 'forward-char)
    ⇒ forward-char
map
    ⇒ (keymap (6 . forward-char))

;; Build sparse submap for C-x and bind f in that.

(define-key map "\C-xf" 'forward-word)
    ⇒ forward-word
map
⇒ (keymap
    (24 keymap                ; C-x
        (102 . forward-word)) ;      f
    (6 . forward-char))       ; C-f
;; Bind C-p to the ctl-x-map.
(define-key map "\C-p" ctl-x-map)
;; ctl-x-map
⇒ [nil . . . find-file . . . backward-kill-sentence]
;; Bind C-f to foo in the ctl-x-map.
(define-key map "\C-p\C-f" 'foo)
⇒ 'foo
map
⇒ (keymap     ; Note foo in ctl-x-map.
    (16 keymap [nil . . . foo . . . backward-kill-sentence])
    (24 keymap
        (102 . forward-word))
    (6 . forward-char))

Note that storing a new binding for C-p C-f actually works by changing an entry in ctlx-map, and this has the effect of changing the bindings of both C-p C-f and C-x C-f in the default global map.

Function substitute-key-definition olddef newdef keymap &optional

oldmap This function replaces olddef with newdef for any keys in keymap that were bound to olddef. In other words, olddef is replaced with newdef wherever it appears. The function returns nil.

For example, this redefines C-x C-f, if you do it in an Emacs with standard bindings:

     (substitute-key-definition
      'find-file 'find-file-read-only (current-global-map))

If oldmap is non-nil, then its bindings determine which keys to rebind. The rebindings still happen in keymap, not in oldmap. Thus, you can change one map under the control of the bindings in another. For example,

     (substitute-key-definition
       'delete-backward-char 'my-funny-delete
       my-map global-map)

puts the special deletion command in my-map for whichever keys are globally bound to the standard deletion command.

Here is an example showing a keymap before and after substitution:

     (setq map '(keymap
                 (?1 . olddef-1)
                 (?2 . olddef-2)
                 (?3 . olddef-1)))
     ⇒ (keymap (49 . olddef-1) (50 . olddef-2) (51 . olddef-1))
     (substitute-key-definition 'olddef-1 'newdef map)
     ⇒ nil
     map
     ⇒ (keymap (49 . newdef) (50 . olddef-2) (51 . newdef))

Function suppress-keymap keymap &optional nodigits This function changes the contents of the full keymap keymap by making all the printing characters undefined. More precisely, it binds them to the command undefined. This makes ordinary insertion of text impossible. suppress-

keymap returns nil.

If nodigits is nil, then suppress-keymap defines digits to run digit-argument, and - to run negative-argument. Otherwise it makes them undefined like the rest of the printing characters.

The suppress-keymap function does not make it impossible to modify a buffer, as it does not suppress commands such as yank and quoted-insert. To prevent any modification of a buffer, make it read-only (see Section 24.7 [Read Only Buffers], page 376).

Since this function modifies keymap, you would normally use it on a newly created keymap. Operating on an existing keymap that is used for some other purpose is likely to cause trouble; for example, suppressing global-map would make it impossible to use most of Emacs.

Most often, suppress-keymap is used to initialize local keymaps of modes such as Rmail and Dired where insertion of text is not desirable and the buffer is read-only. Here is an example taken from the file ‘emacs/lisp/dired.el’, showing how the local keymap for Dired mode is set up:

…

(setq dired-mode-map (make-keymap))
(suppress-keymap dired-mode-map)
(define-key dired-mode-map "r" 'dired-rename-file)
(define-key dired-mode-map "\C-d" 'dired-flag-file-deleted)
(define-key dired-mode-map "d" 'dired-flag-file-deleted)
(define-key dired-mode-map "v" 'dired-view-file)
(define-key dired-mode-map "e" 'dired-find-file)
(define-key dired-mode-map "f" 'dired-find-file)

…

19.10 Commands for Binding Keys

This section describes some convenient interactive interfaces for changing key bindings. They work by calling define-key.

People often use global-set-key in their ‘.emacs’ file for simple customization. For example,

(global-set-key "\C-x\C-\\" 'next-line)

or

(global-set-key [?\C-x ?\C-\\] 'next-line)

or

(global-set-key [(control ?x) (control ?\\)] 'next-line)

redefines C-x C-\ to move down a line.

(global-set-key [M-mouse-1] 'mouse-set-point)

redefines the first (leftmost) mouse button, typed with the Meta key, to set point where you click.

Command global-set-key key definition

This function sets the binding of key in the current global map to definition.

(global-set-key key definition)

≡

(define-key (current-global-map) key definition)

Command global-unset-key key

This function removes the binding of key from the current global map. One use of this function is in preparation for defining a longer key that uses key as a prefix—which would not be allowed if key has a non-prefix binding. For example:

(global-unset-key "\C-l")
  ⇒ nil
(global-set-key "\C-l\C-l" 'redraw-display)
  ⇒ nil

This function is implemented simply using define-key:

(global-unset-key key)

≡

(define-key (current-global-map) key nil)

Command local-set-key key definition

This function sets the binding of key in the current local keymap to definition.

     (local-set-key key definition)

≡

     (define-key (current-local-map) key definition)

Command local-unset-key key

This function removes the binding of key from the current local map.

     (local-unset-key key)

≡

     (define-key (current-local-map) key nil)

19.11 Scanning Keymaps

This section describes functions used to scan all the current keymaps for the sake of printing help information.

Function accessible-keymaps keymap &optional prefix This function returns a list of all the keymaps that can be accessed (via prefix keys) from keymap. The value is an association list with elements of the form (key . map), where key is a prefix key whose definition in keymap is map. The elements of the alist are ordered so that the key increases in length. The first element is always ("" . keymap), because the specified keymap is accessible from itself with a prefix of no events. If prefix is given, it should be a prefix key sequence; then accessible-keymaps includes only the submaps whose prefixes start with prefix. These elements look just as they do in the value of (accessible-keymaps); the only difference is that some elements are omitted. In the example below, the returned alist indicates that the key ^{⟨}\underline{\overline{ESC}}^{⟩}, which is displayed as ‘^[’, is a prefix key whose definition is the sparse keymap (keymap

(83 . center-paragraph) (115 . foo)).
     (accessible-keymaps (current-local-map))
     ⇒(("" keymap

(27 keymap ; Note this keymap for ^{⟨}\underline{\overline{ESC}}^{⟩} is repeated below.

               (83 . center-paragraph)
               (115 . center-line))
           (9 . tab-to-tab-stop))
        ("^[" keymap
         (83 . center-paragraph)
         (115 . foo)))

In the following example, C-h is a prefix key that uses a sparse keymap starting

with (keymap (118 . describe-variable). . .). Another prefix, C-x 4, uses a

keymap which is also the value of the variable ctl-x-4-map. The event modeline is one of several dummy events used as prefixes for mouse actions in special parts of a window.

     (accessible-keymaps (current-global-map))
     ⇒ (("" keymap [set-mark-command beginning-of-line . . .
                        delete-backward-char])
         ("^H" keymap (118 . describe-variable) . . .
          (8 . help-for-help))
         ("^X" keymap [x-flush-mouse-queue . . .
          backward-kill-sentence])
         ("^[" keymap [mark-sexp backward-sexp . . .
          backward-kill-word])
         ("^X4" keymap (15 . display-buffer) . . .)
         ([mode-line] keymap
          (S-mouse-2 . mouse-split-window-horizontally) . . .))

These are not all the keymaps you would see in an actual case.

Function where-is-internal command &optional keymap firstonly

noindirect This function returns a list of key sequences (of any length) that are bound to command in a set of keymaps. The argument command can be any object; it is compared with all keymap entries using eq. If keymap is nil, then the maps used are the current active keymaps, disregarding overriding-local-map (that is, pretending its value is nil). If keymap is non-nil, then the maps searched are keymap and the global keymap. Usually it’s best to use overriding-local-map as the expression for keymap. Then where-is-internal searches precisely the keymaps that are active. To search only the global map, pass (keymap) (an empty keymap) as keymap. If firstonly is non-ascii, then the value is a single string representing the first key sequence found, rather than a list of all possible key sequences. If firstonly is t, then the value is the first key sequence, except that key sequences consisting entirely of ASCII characters (or meta variants of ASCII characters) are preferred to all other key sequences. If noindirect is non-nil, where-is-internal doesn’t follow indirect keymap bindings. This makes it possible to search for an indirect definition itself. This function is used by where-is (see section “Help” in The GNU Emacs Manual).

     (where-is-internal 'describe-function)
         ⇒ ("\^hf" "\^hd")

Command describe-bindings prefix

This function creates a listing of all defined keys and their definitions. It writes the listing in a buffer named ‘*Help*’ and displays it in a window. If prefix is non-nil, it should be a prefix key; then the listing includes only keys that start with prefix. The listing describes meta characters as ^{⟨}\underline{\overline{ESC}}^{⟩} followed by the corresponding non-meta character.

When several characters with consecutive ASCII codes have the same definition, they are shown together, as ‘firstchar..lastchar’. In this instance, you need to know the ASCII codes to understand which characters this means. For example, in the default global map, the characters ‘^{⟨}\underline{\overline{SPC}}^{⟩} .. ~’ are described by a single line. ^{⟨}\underline{\overline{SPC}}^{⟩} is ASCII 32, ~ is ASCII 126, and the characters between them include all the normal printing characters, (e.g., letters, digits, punctuation, etc.); all these characters are bound to self-insert-command.

19.12 Menu Keymaps

A keymap can define a menu as well as bindings for keyboard keys and mouse button. Menus are usually actuated with the mouse, but they can work with the keyboard also.

19.12.1 Defining Menus

A keymap is suitable for menu use if it has an overall prompt string, which is a string that appears as an element of the keymap. (See Section 19.2 [Format of Keymaps], page 278.) The string should describe the purpose of the menu. The easiest way to construct a keymap with a prompt string is to specify the string as an argument when you call make-keymap or make-sparse-keymap (see Section 19.3 [Creating Keymaps], page 279).

The order of items in the menu is the same as the order of bindings in the keymap. Since define-key puts new bindings at the front, you should define the menu items starting at the bottom of the menu and moving to the top, if you care about the order. When you add an item to an existing menu, you can specify its position in the menu using define-key-after (see Section 19.12.6 [Modifying Menus], page 298).

The individual bindings in the menu keymap should have item strings; these strings become the items displayed in the menu. A binding with an item string looks like this:

(string . real-binding) The item string for a binding should be short—one or two words. It should describe the

action of the command it corresponds to.

You can also supply a second string, called the help string, as follows:

(string help-string . real-binding) Currently Emacs does not actually use help-string; it knows only how to ignore help-

string in order to extract real-binding. In the future we may use help-string as extended documentation for the menu item, available on request.

As far as define-key is concerned, string and help-string are part of the event’s binding. However, lookup-key returns just real-binding, and only real-binding is used for executing the key.

If real-binding is nil, then string appears in the menu but cannot be selected.

If real-binding is a symbol and has a non-nil menu-enable property, that property is an expression that controls whether the menu item is enabled. Every time the keymap is used to display a menu, Emacs evaluates the expression, and it enables the menu item only if the expression’s value is non-nil. When a menu item is disabled, it is displayed in a “fuzzy” fashion, and cannot be selected with the mouse.

The menu bar does not recalculate which items are enabled every time you look at a menu. This is because the X toolkit requires the whole tree of menus in advance. To force recalculation of the menu bar, call force-mode-line-update (see Section 20.3 [Mode Line Format], page 310).

You’ve probably noticed that menu items show the equivalent keyboard key sequence (if any) to invoke the same command. To save time on recalculation, menu display caches this information in a sublist in the binding, like this:

(string [help-string] (key-binding-data) . real-binding) Don’t put these sublists in the menu item yourself; menu display calculates them auto-

matically. Don’t add keyboard equivalents to the item strings in a mouse menu, since that is redundant.

Sometimes it is useful to make menu items that use the “same” command but with different enable conditions. You can do this by defining alias commands. Here’s an example that makes two aliases for toggle-read-only and gives them different enable conditions:

     (defalias 'make-read-only 'toggle-read-only)
     (put 'make-read-only 'menu-enable '(not buffer-read-only))
     (defalias 'make-writable 'toggle-read-only)
     (put 'make-writable 'menu-enable 'buffer-read-only)

When using aliases in menus, often it is useful to display the equivalent key bindings for the “real” command name, not the aliases (which typically don’t have any key bindings except for the menu itself). To request this, give the alias symbol a non-nil menu-alias property. Thus,

     (put 'make-read-only 'menu-alias t)
     (put 'make-writable 'menu-alias t)

causes menu items for make-read-only and make-writable to show the keyboard bindings

for toggle-read-only.

19.12.2 Menus and the Mouse

The way to make a menu keymap produce a menu is to make it the definition of a prefix key.

If the prefix key ends with a mouse event, Emacs handles the menu keymap by popping up a visible menu, so that the user can select a choice with the mouse. When the user clicks on a menu item, the event generated is whatever character or symbol has the binding that brought about that menu item. (A menu item may generate a series of events if the menu has multiple levels or comes from the menu bar.)

It’s often best to use a button-down event to trigger the menu. Then the user can select a menu item by releasing the button.

A single keymap can appear as multiple menu panes, if you explicitly arrange for this. The way to do this is to make a keymap for each pane, then create a binding for each of those maps in the main keymap of the menu. Give each of these bindings an item string that starts with ‘@’. The rest of the item string becomes the name of the pane. See the file ‘lisp/mouse.el’ for an example of this. Any ordinary bindings with ‘@’-less item strings are grouped into one pane, which appears along with the other panes explicitly created for the submaps.

X toolkit menus don’t have panes; instead, they can have submenus. Every nested keymap becomes a submenu, whether the item string starts with ‘@’ or not. In a toolkit version of Emacs, the only thing special about ‘@’ at the beginning of an item string is that the ‘@’ doesn’t appear in the menu item.

You can also get multiple panes from separate keymaps. The full definition of a prefix key always comes from merging the definitions supplied by the various active keymaps (minor mode, local, and global). When more than one of these keymaps is a menu, each of them makes a separate pane or panes. See Section 19.6 [Active Keymaps], page 281.

In toolkit versions of Emacs, menus don’t have panes, so submenus are used to represent the separate keymaps. Each keymap’s contribution becomes one submenu.

A Lisp program can explicitly pop up a menu and receive the user’s choice. You can use keymaps for this also. See Section 26.15 [Pop-Up Menus], page 423.

19.12.3 Menus and the Keyboard

When a prefix key ending with a keyboard event (a character or function key) has a definition that is a menu keymap, the user can use the keyboard to choose a menu item.

Emacs displays the menu alternatives (the item strings of the bindings) in the echo area. If they don’t all fit at once, the user can type ^{⟨}\underline{\overline{SPC}}^{⟩} to see the next line of alternatives. Successive uses of ^{⟨}\underline{\overline{SPC}}^{⟩} eventually get to the end of the menu and then cycle around to the beginning. (The variable menu-prompt-more-char specifies which character is used for this; ^{⟨}\underline{\overline{SPC}}^{⟩} is the default.)

When the user has found the desired alternative from the menu, he or she should type the corresponding character—the one whose binding is that alternative.

This way of using menus in an Emacs-like editor was inspired by the Hierarkey system.

Variable menu-prompt-more-char

This variable specifies the character to use to ask to see the next line of a menu.

Its initial value is 32, the code for ^{⟨}\underline{\overline{SPC}}^{⟩}.

19.12.4 Menu Example

Here is a simple example of how to set up a menu for mouse use.

     (defvar my-menu-map
       (make-sparse-keymap "Key Commands <==> Functions"))
     (fset 'help-for-keys my-menu-map)
     (define-key my-menu-map [bindings]
       '("List all keystroke commands" . describe-bindings))
     (define-key my-menu-map [key]
       '("Describe key briefly" . describe-key-briefly))
     (define-key my-menu-map [key-verbose]
       '("Describe key verbose" . describe-key))
     (define-key my-menu-map [function]
       '("Describe Lisp function" . describe-function))
     (define-key my-menu-map [where-is]

       '("Where is this command" . where-is))
     (define-key global-map [C-S-down-mouse-1] 'help-for-keys)

The symbols used in the key sequences bound in the menu are fictitious “function keys”; they don’t appear on the keyboard, but that doesn’t stop you from using them in the menu. Their names were chosen to be mnemonic, because they show up in the output of where-is and apropos to identify the corresponding menu items.

However, if you want the menu to be usable from the keyboard as well, you must bind real ASCII characters as well as fictitious function keys.

19.12.5 The Menu Bar

Most window systems allow each frame to have a menu bar—a permanently displayed menu stretching horizontally across the top of the frame. The items of the menu bar are the subcommands of the fake “function key” menu-bar, as defined by all the active keymaps.

To add an item to the menu bar, invent a fake “function key” of your own (let’s call it key), and make a binding for the key sequence [menu-bar key]. Most often, the binding is a menu keymap, so that pressing a button on the menu bar item leads to another menu.

When more than one active keymap defines the same fake function key for the menu bar, the item appears just once. If the user clicks on that menu bar item, it brings up a single, combined submenu containing all the subcommands of that item—the global subcommands, the local subcommands, and the minor mode subcommands, all together.

The variable overriding-local-map is normally ignored when determining the menu bar contents. That is, the menu bar is computed from the keymaps that would be active if overriding-local-map were nil. See Section 19.6 [Active Keymaps], page 281.

In order for a frame to display a menu bar, its menu-bar-lines parameter must be greater than zero. Emacs uses just one line for the menu bar itself; if you specify more than one line, the other lines serve to separate the menu bar from the windows in the frame. We recommend 1 or 2 as the value of menu-bar-lines. See Section 26.3.3 [X Frame Parameters], page 412.

Here’s an example of setting up a menu bar item:

     (modify-frame-parameters (selected-frame)
                              '((menu-bar-lines . 2)))

;; Make a menu keymap (with a prompt string) ;; and make it the menu bar item’s definition.

     (define-key global-map [menu-bar words]
       (cons "Words" (make-sparse-keymap "Words")))

;; Define specific subcommands in the item’s menu.

     (define-key global-map
       [menu-bar words forward]
       '("Forward word" . forward-word))
     (define-key global-map
       [menu-bar words backward]
       '("Backward word" . backward-word))

A local keymap can cancel a menu bar item made by the global keymap by rebinding the same fake function key with undefined as the binding. For example, this is how Dired suppresses the ‘Edit’ menu bar item:

(define-key dired-mode-map [menu-bar edit] 'undefined)

edit is the fake function key used by the global map for the ‘Edit’ menu bar item. The main reason to suppress a global menu bar item is to regain space for mode-specific items.

Variable menu-bar-final-items

Normally the menu bar shows global items followed by items defined by the local maps. This variable holds a list of fake function keys for items to display at the end of the menu bar rather than in normal sequence. The default value is (help); thus, the ‘Help’ menu item normally appears at the end of the menu bar, following local menu items.

Variable menu-bar-update-hook

This normal hook is run whenever the user clicks on the menu bar, before displaying a submenu. You can use it to update submenus whose contents should vary.

19.12.6 Modifying Menus

When you insert a new item in an existing menu, you probably want to put it in a particular place among the menu’s existing items. If you use define-key to add the item, it normally goes at the front of the menu. To put it elsewhere, use define-key-after:

Function define-key-after map key binding after Define a binding in map for key, with value binding, just like define-key, but position the binding in map after the binding for the event after. The argument key should be of length one—a vector or string with just one element. For example,

     (define-key-after my-menu [drink]
                       '("Drink" . drink-command) 'eat)

makes a binding for the fake function key ^{⟨}\underline{\overline{drink}}^{⟩} and puts it right after the binding for ^{⟨}\underline{\overline{eat}}^{⟩}. Here is how to insert an item called ‘Work’ in the ‘Signals’ menu of Shell mode, after the item break:

     (define-key-after
       (lookup-key shell-mode-map [menu-bar signals])
       [work] '("Work" . work-command) 'break)

Note that key is a sequence containing just one event type, but after is just an event type (not a sequence).

20 Major and Minor Modes

A mode is a set of definitions that customize Emacs and can be turned on and off while you edit. There are two varieties of modes: major modes, which are mutually exclusive and used for editing particular kinds of text, and minor modes, which provide features that users can enable individually.

This chapter describes how to write both major and minor modes, how to indicate them in the mode line, and how they run hooks supplied by the user. For related topics such as keymaps and syntax tables, see Chapter 19 [Keymaps], page 277, and Chapter 31 [Syntax Tables], page 509.

20.1 Major Modes

Major modes specialize Emacs for editing particular kinds of text. Each buffer has only one major mode at a time.

The least specialized major mode is called Fundamental mode. This mode has no modespecific definitions or variable settings, so each Emacs command behaves in its default manner, and each option is in its default state. All other major modes redefine various keys and options. For example, Lisp Interaction mode provides special key bindings for ^{⟨}\underline{\overline{LFD}}^{⟩}

(eval-print-last-sexp), ^{⟨}\underline{\overline{TAB}}^{⟩} (lisp-indent-line), and other keys.

When you need to write several editing commands to help you perform a specialized editing task, creating a new major mode is usually a good idea. In practice, writing a major mode is easy (in contrast to writing a minor mode, which is often difficult).

If the new mode is similar to an old one, it is often unwise to modify the old one to serve two purposes, since it may become harder to use and maintain. Instead, copy and rename an existing major mode definition and alter the copy—or define a derived mode (see Section 20.1.5 [Derived Modes], page 308). For example, Rmail Edit mode, which is in ‘emacs/lisp/rmailedit.el’, is a major mode that is very similar to Text mode except that it provides three additional commands. Its definition is distinct from that of Text mode, but was derived from it.

Rmail Edit mode is an example of a case where one piece of text is put temporarily into a different major mode so it can be edited in a different way (with ordinary Emacs commands rather than Rmail). In such cases, the temporary major mode usually has a command to switch back to the buffer’s usual mode (Rmail mode, in this case). You might be tempted to present the temporary redefinitions inside a recursive edit and restore the usual ones when the user exits; but this is a bad idea because it constrains the user’s options when it is done in more than one buffer: recursive edits must be exited most-recently-entered first. Using alternative major modes avoids this limitation. See Section 18.10 [Recursive Editing], page 271.

The standard GNU Emacs Lisp library directory contains the code for several major

modes, in files including ‘text-mode.el’, ‘texinfo.el’, ‘lisp-mode.el’, ‘c-mode.el’, and

‘rmail.el’. You can look at these libraries to see how modes are written. Text mode is perhaps the simplest major mode aside from Fundamental mode. Rmail mode is a complicated and specialized mode.

20.1.1 Major Mode Conventions

The code for existing major modes follows various coding conventions, including conventions for local keymap and syntax table initialization, global names, and hooks. Please follow these conventions when you define a new major mode:

• Define a command whose name ends in ‘-mode’, with no arguments, that switches to the new mode in the current buffer. This command should set up the keymap, syntax table, and local variables in an existing buffer without changing the buffer’s text.

• Write a documentation string for this command that describes the special commands available in this mode. C-h m (describe-mode) in your mode will display this string. The documentation string may include the special documentation substrings, ‘\[command]’, ‘\{keymap}’, and ‘\<keymap>’, that enable the documentation to adapt automatically to the user’s own key bindings. See Section 21.3 [Keys in Documentation], page 322.

• The major mode command should start by calling kill-all-local-variables. This is what gets rid of the local variables of the major mode previously in effect.

• The major mode command should set the variable major-mode to the major mode command symbol. This is how describe-mode discovers which documentation to print.

• The major mode command should set the variable mode-name to the “pretty” name of the mode, as a string. This appears in the mode line.

• Since all global names are in the same name space, all the global variables, constants, and functions that are part of the mode should have names that start with the major mode name (or with an abbreviation of it if the name is long). See Section A.1 [Style Tips], page 599.

• The major mode should usually have its own keymap, which is used as the local keymap in all buffers in that mode. The major mode function should call use-local-map to install this local map. See Section 19.6 [Active Keymaps], page 281, for more information. This keymap should be kept in a global variable named modename-mode-map. Normally the library that defines the mode sets this variable. See Section 10.6 [Tips for Defining], page 127, for advice about how to write the code to set up the mode’s keymap variable.

• The mode may have its own syntax table or may share one with other related modes. If it has its own syntax table, it should store this in a variable named modename-mode-syntax-table. See Chapter 31 [Syntax Tables], page 509.

• If the mode handles a language that has a syntax for comments, it should set the variables that define the comment syntax. See section “Options Controlling Comments” in The GNU Emacs Manual.

• The mode may have its own abbrev table or may share one with other related modes. If it has its own abbrev table, it should store this in a variable named modenamemode-abbrev-table. See Section 32.2 [Abbrev Tables], page 519.

• The mode should specify how to do highlighting for Font Lock mode, by setting up a buffer-local value for the variable font-lock-defaults.

• The mode should specify how Imenu should find the definitions or sections of a buffer, by setting up a buffer-local value for the variable imenu-generic-expression or imenu-

create-index-function.

• Use defvar to set mode-related variables, so that they are not reinitialized if they already have a value. (Such reinitialization could discard customizations made by the user.)

• To make a buffer-local binding for an Emacs customization variable, use make-local-variable in the major mode command, not make-variable-buffer-local. The latter function would make the variable local to every buffer in which it is subsequently set, which would affect buffers that do not use this mode. It is undesirable for a mode to have such global effects. See Section 10.10 [Buffer-Local Variables], page 134. It’s ok to use make-variable-buffer-local, if you wish, for a variable used only within a single Lisp package.

• Each major mode should have a mode hook named modename-mode-hook. The major mode command should run that hook, with run-hooks, as the very last thing it does. See Section 20.4 [Hooks], page 316.

• The major mode command may also run the hooks of some more basic modes. For

example, indented-text-mode runs text-mode-hook as well as indented-text-mode-

hook. It may run these other hooks immediately before the mode’s own hook (that is, after everything else), or it may run them earlier.

• If something special should be done if the user switches a buffer from this mode to any other major mode, the mode can set a local value for change-major-mode-hook.

• If this mode is appropriate only for specially-prepared text, then the major mode command symbol should have a property named mode-class with value special, put on as follows:

     (put 'funny-mode 'mode-class 'special)

This tells Emacs that new buffers created while the current buffer has Funny mode should not inherit Funny mode. Modes such as Dired, Rmail, and Buffer List use this feature.

• If you want to make the new mode the default for files with certain recognizable names, add an element to auto-mode-alist to select the mode for those file names. If you define the mode command to autoload, you should add this element in the same file that calls autoload. Otherwise, it is sufficient to add the element in the file that contains the mode definition. See Section 20.1.3 [Auto Major Mode], page 305.

• In the documentation, you should provide a sample autoload form and an example of how to add to auto-mode-alist, that users can include in their ‘.emacs’ files.

• The top-level forms in the file defining the mode should be written so that they may be evaluated more than once without adverse consequences. Even if you never load the file more than once, someone else will.

Variable change-major-mode-hook

This normal hook is run by kill-all-local-variables before it does anything else. This gives major modes a way to arrange for something special to be done if the user switches to a different major mode. For best results, make this variable buffer-local, so that it will disappear after doing its job and will not interfere with the subsequent major mode. See Section 20.4 [Hooks], page 316.

20.1.2 Major Mode Examples

Text mode is perhaps the simplest mode besides Fundamental mode. Here are excerpts from ‘text-mode.el’ that illustrate many of the conventions listed above:

;; Create mode-specific tables.

(defvar text-mode-syntax-table nil
"Syntax table used while in text mode.")
(if text-mode-syntax-table

() ; Do not change the table if it is already set up.

(setq text-mode-syntax-table (make-syntax-table))
(modify-syntax-entry ?\" ".   " text-mode-syntax-table)
(modify-syntax-entry ?\\ ".   " text-mode-syntax-table)
(modify-syntax-entry ?' "w   " text-mode-syntax-table))
(defvar text-mode-abbrev-table nil
"Abbrev table used while in text mode.")
(define-abbrev-table 'text-mode-abbrev-table ())

(defvar text-mode-map nil) ; Create a mode-specific keymap.

(if text-mode-map

() ; Do not change the keymap if it is already set up.

(setq text-mode-map (make-sparse-keymap))
(define-key text-mode-map "\t" 'tab-to-tab-stop)
(define-key text-mode-map "\es" 'center-line)
(define-key text-mode-map "\eS" 'center-paragraph))

Here is the complete major mode function definition for Text mode:

(defun text-mode ()
"Major mode for editing text intended for humans to read.
Special commands: \\{text-mode-map}
Turning on text-mode runs the hook `text-mode-hook'."
(interactive)
(kill-all-local-variables)
(use-local-map text-mode-map)     ; This provides the local keymap.

(setq mode-name "Text") ; This name goes into the mode line.

(setq major-mode 'text-mode)      ; This is how describe-mode

; finds the doc string to print.

(setq local-abbrev-table text-mode-abbrev-table)
(set-syntax-table text-mode-syntax-table)
(run-hooks 'text-mode-hook))      ; Finally, this permits the user to

; customize the mode with a hook.

The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction mode) have more features than Text mode and the code is correspondingly more complicated. Here are excerpts from ‘lisp-mode.el’ that illustrate how these modes are written.

;; Create mode-specific table variables.

(defvar lisp-mode-syntax-table nil "")
(defvar emacs-lisp-mode-syntax-table nil "")
(defvar lisp-mode-abbrev-table nil "")
(if (not emacs-lisp-mode-syntax-table) ; Do not change the table

; if it is already set.

(let ((i 0))
(setq emacs-lisp-mode-syntax-table (make-syntax-table))

;; Set syntax of chars up to 0 to class of chars that are ;; part of symbol names but not words. ;; (The number 0 is 48 in the ASCII character set.)

(while (< i ?0)
  (modify-syntax-entry i "_" emacs-lisp-mode-syntax-table)
  (setq i (1+ i)))

… ;; Set the syntax for other characters.

(modify-syntax-entry ?  "    " emacs-lisp-mode-syntax-table)
(modify-syntax-entry ?\t "    " emacs-lisp-mode-syntax-table)

…

(modify-syntax-entry ?\( "()  " emacs-lisp-mode-syntax-table)
(modify-syntax-entry ?\) ")(  " emacs-lisp-mode-syntax-table)

…)) ;; Create an abbrev table for lisp-mode.

(define-abbrev-table 'lisp-mode-abbrev-table ())

Much code is shared among the three Lisp modes. The following function sets various variables; it is called by each of the major Lisp mode functions:

(defun lisp-mode-variables (lisp-syntax)

;; The lisp-syntax argument is nil in Emacs Lisp mode, ;; and t in the other two Lisp modes.

(cond (lisp-syntax
   (if (not lisp-mode-syntax-table)

;; The Emacs Lisp mode syntax table always exists, but ;; the Lisp Mode syntax table is created the first time a ;; mode that needs it is called. This is to save space.

       (progn (setq lisp-mode-syntax-table
                 (copy-syntax-table emacs-lisp-mode-syntax-table))

;; Change some entries for Lisp mode.

              (modify-syntax-entry ?\| "\"   "
                                   lisp-mode-syntax-table)
              (modify-syntax-entry ?\[ "_"
                                   lisp-mode-syntax-table)
              (modify-syntax-entry ?\] "_"
                                   lisp-mode-syntax-table)))
    (set-syntax-table lisp-mode-syntax-table)))
(setq local-abbrev-table lisp-mode-abbrev-table)

…)

Functions such as forward-paragraph use the value of the paragraph-start variable. Since Lisp code is different from ordinary text, the paragraph-start variable needs to be set specially to handle Lisp. Also, comments are indented in a special fashion in Lisp and the Lisp modes need their own mode-specific comment-indent-function. The code to set these variables is the rest of lisp-mode-variables.

(make-local-variable 'paragraph-start)

;; Having ‘^’ is not clean, but page-delimiter ;; has them too, and removing those is a pain.

(setq paragraph-start (concat "^$\\|" page-delimiter))

…

(make-local-variable 'comment-indent-function)
(setq comment-indent-function 'lisp-comment-indent))

Each of the different Lisp modes has a slightly different keymap. For example, Lisp mode binds C-c C-l to run-lisp, but the other Lisp modes do not. However, all Lisp modes have some commands in common. The following function adds these common commands to a given keymap.

(defun lisp-mode-commands (map)
(define-key map "\e\C-q" 'indent-sexp)
(define-key map "\177" 'backward-delete-char-untabify)
(define-key map "\t" 'lisp-indent-line))

Here is an example of using lisp-mode-commands to initialize a keymap, as part of the code for Emacs Lisp mode. First we declare a variable with defvar to hold the modespecific keymap. When this defvar executes, it sets the variable to nil if it was void. Then we set up the keymap if the variable is nil.

This code avoids changing the keymap or the variable if it is already set up. This lets the user customize the keymap.

(defvar emacs-lisp-mode-map () "")
(if emacs-lisp-mode-map
  ()
(setq emacs-lisp-mode-map (make-sparse-keymap))
(define-key emacs-lisp-mode-map "\e\C-x" 'eval-defun)
(lisp-mode-commands emacs-lisp-mode-map))

Finally, here is the complete major mode function definition for Emacs Lisp mode.

(defun emacs-lisp-mode ()
"Major mode for editing Lisp code to run in Emacs.
Commands:
Delete converts tabs to spaces as it moves back.
Blank lines separate paragraphs.  Semicolons start comments.
\\{emacs-lisp-mode-map}
Entry to this mode runs the hook `emacs-lisp-mode-hook'."
(interactive)
(kill-all-local-variables)
(use-local-map emacs-lisp-mode-map)    ; This provides the local keymap.
(set-syntax-table emacs-lisp-mode-syntax-table)

  (setq major-mode 'emacs-lisp-mode)     ; This is how describe-mode

; finds out what to describe.

  (setq mode-name "Emacs-Lisp")          ; This goes into the mode line.

(lisp-mode-variables nil) ; This defines various variables.

  (run-hooks 'emacs-lisp-mode-hook))     ; This permits the user to use a

; hook to customize the mode.

20.1.3 How Emacs Chooses a Major Mode

Based on information in the file name or in the file itself, Emacs automatically selects a major mode for the new buffer when a file is visited.

Command fundamental-mode

Fundamental mode is a major mode that is not specialized for anything in particular. Other major modes are defined in effect by comparison with this one—their definitions say what to change, starting from Fundamental mode. The fundamental-mode function does not run any hooks; you’re not supposed to customize it. (If you want Emacs to behave differently in Fundamental mode, change the global state of Emacs.)

Command normal-mode &optional find-file This function establishes the proper major mode and local variable bindings for the current buffer. First it calls set-auto-mode, then it runs hack-local-variables to parse, and bind or evaluate as appropriate, any local variables. If the find-file argument to normal-mode is non-nil, normal-mode assumes that the find-file function is calling it. In this case, it may process a local variables list at the end of the file and in the ‘-*-’ line. The variable enablelocal-variables controls whether to do so. If you run normal-mode interactively, the argument find-file is normally nil. In this case, normal-mode unconditionally processes any local variables list. See section “Local Variables in Files” in The GNU Emacs Manual, for the syntax of the local variables section of a file. normal-mode uses condition-case around the call to the major mode function, so errors are caught and reported as a ‘File mode specification error’, followed by the original error message.

User Option enable-local-variables

This variable controls processing of local variables lists in files being visited. A value of t means process the local variables lists unconditionally; nil means ignore them; anything else means ask the user what to do for each file. The default value is t.

Variable ignored-local-variables

This variable holds a list of variables that should not be set by a local variables list. Any value specified for one of these variables is ignored.

In addition to this list, any variable whose name has a non-nil risky-local-variable property is also ignored.

User Option enable-local-eval

This variable controls processing of ‘Eval:’ in local variables lists in files being visited. A value of t means process them unconditionally; nil means ignore them; anything else means ask the user what to do for each file. The default value is maybe.

Function set-auto-mode

This function selects the major mode that is appropriate for the current buffer. It may base its decision on the value of the ‘-*-’ line, on the visited file name

(using auto-mode-alist), on the ‘#!’ line (using interpreter-mode-alist),

or on the value of a local variable. However, this function does not look for the ‘mode:’ local variable near the end of a file; the hack-local-variables function does that. See section “How Major Modes are Chosen” in The GNU Emacs Manual.

User Option default-major-mode

This variable holds the default major mode for new buffers. The standard value

is fundamental-mode.

If the value of default-major-mode is nil, Emacs uses the (previously) current buffer’s major mode for the major mode of a new buffer. However, if the major mode symbol has a mode-class property with value special, then it is not used for new buffers; Fundamental mode is used instead. The modes that have this property are those such as Dired and Rmail that are useful only with text that has been specially prepared.

Function set-buffer-major-mode buffer

This function sets the major mode of buffer to the value of default-major-mode. If that variable is nil, it uses the current buffer’s major mode (if that is suitable). The low-level primitives for creating buffers do not use this function, but

medium-level commands such as switch-to-buffer and find-file-noselect

use it whenever they create buffers.

Variable initial-major-mode

The value of this variable determines the major mode of the initial ‘*scratch*’ buffer. The value should be a symbol that is a major mode command name.

The default value is lisp-interaction-mode.

Variable auto-mode-alist

This variable contains an association list of file name patterns (regular expressions; see Section 30.2 [Regular Expressions], page 492) and corresponding major mode functions. Usually, the file name patterns test for suffixes, such as ‘.el’ and ‘.c’, but this need not be the case. An ordinary element of the alist looks like (regexp . mode-function). For example,

     (("^/tmp/fol/" . text-mode)
      ("\\.texinfo\\'" . texinfo-mode)
      ("\\.texi\\'" . texinfo-mode)

      ("\\.el\\'" . emacs-lisp-mode)
      ("\\.c\\'" . c-mode)
      ("\\.h\\'" . c-mode)

…) When you visit a file whose expanded file name (see Section 22.8.4 [File Name Expansion], page 347) matches a regexp, set-auto-mode calls the corresponding mode-function. This feature enables Emacs to select the proper major mode for most files. If an element of auto-mode-alist has the form (regexp function t), then after calling function, Emacs searches auto-mode-alist again for a match against the portion of the file name that did not match before. This match-again feature is useful for uncompression packages: an entry of the form ("\\.gz\\'" . function) can uncompress the file and then put the uncompressed file in the proper mode according to the name sans ‘.gz’. Here is an example of how to prepend several pattern pairs to auto-mode-alist. (You might use this sort of expression in your ‘.emacs’ file.)

     (setq auto-mode-alist
       (append

;; File name starts with a dot.

        '(("/\\.[^/]*\\'" . fundamental-mode)

;; File name has no dot.

          ("[^\\./]*\\'" . fundamental-mode)

;; File name ends in ‘.C’.

          ("\\.C\\'" . c++-mode))
        auto-mode-alist))

Variable interpreter-mode-alist

This variable specifes major modes to use for scripts that specify a command interpreter in an ‘#!’ line. Its value is a list of elements of the form (interpreter . mode); for example, ("perl" . perl-mode) is one element present by default. The element says to use mode mode if the file specifies interpreter. This variable is applicable only when the auto-mode-alist does not indicate which major mode to use.

Function hack-local-variables &optional force

This function parses, and binds or evaluates as appropriate, any local variables for the current buffer.

The handling of enable-local-variables documented for normal-mode ac-

tually takes place here. The argument force usually comes from the argument find-file given to normal-mode.

20.1.4 Getting Help about a Major Mode

The describe-mode function is used to provide information about major modes. It is normally called with C-h m. The describe-mode function uses the value of major-mode, which is why every major mode function needs to set the major-mode variable.

Command describe-mode

This function displays the documentation of the current major mode. The describe-mode function calls the documentation function using the value of major-mode as an argument. Thus, it displays the documentation string of the major mode function. (See Section 21.2 [Accessing Documentation], page 320.)

Variable major-mode

This variable holds the symbol for the current buffer’s major mode. This symbol should have a function definition that is the command to switch to that major mode. The describe-mode function uses the documentation string of the function as the documentation of the major mode.

20.1.5 Defining Derived Modes

It’s often useful to define a new major mode in terms of an existing one. An easy way

to do this is to use define-derived-mode.

Macro define-derived-mode variant parent name docstring body… This construct defines variant as a major mode command, using name as the string form of the mode name. The new command variant is defined to call the function parent, then override certain aspects of that parent mode:

• The new mode has its own keymap, named variant-map. define-derived-mode initializes this map to inherit from parent-map, if it is not already set.

• The new mode has its own syntax table, kept in the variable variantsyntax-table. define-derived-mode initializes this variable by copying parent-syntax-table, if it is not already set.

• The new mode has its own abbrev table, kept in the variable variantabbrev-table. define-derived-mode initializes this variable by copying parent-abbrev-table, if it is not already set.

• The new mode has its own mode hook, variant-hook, which it runs in standard fashion as the very last thing that it does. (The new mode also runs the mode hook of parent as part of calling parent.)

In addition, you can specify how to override other aspects of parent with body. The command variant evaluates the forms in body after setting up all its usual overrides, just before running variant-hook. The argument docstring specifies the documentation string for the new mode. If you omit docstring, define-derived-mode generates a documentation string. Here is a hypothetical example:

     (define-derived-mode hypertext-mode
       text-mode "Hypertext"
       "Major mode for hypertext.
     \\{hypertext-mode-map}"
       (setq case-fold-search nil))

          (define-key hypertext-mode-map
            [down-mouse-3] 'do-hyper-link)

20.2 Minor Modes

A minor mode provides features that users may enable or disable independently of the choice of major mode. Minor modes can be enabled individually or in combination. Minor modes would be better named “Generally available, optional feature modes” except that such a name is unwieldy.

A minor mode is not usually a modification of single major mode. For example, Auto Fill mode may be used in any major mode that permits text insertion. To be general, a minor mode must be effectively independent of the things major modes do.

A minor mode is often much more difficult to implement than a major mode. One reason is that you should be able to activate and deactivate minor modes in any order. A minor mode should be able to have its desired effect regardless of the major mode and regardless of the other minor modes in effect.

Often the biggest problem in implementing a minor mode is finding a way to insert the necessary hook into the rest of Emacs. Minor mode keymaps make this easier than it used to be.

20.2.1 Conventions for Writing Minor Modes

There are conventions for writing minor modes just as there are for major modes. Several of the major mode conventions apply to minor modes as well: those regarding the name of the mode initialization function, the names of global symbols, and the use of keymaps and other tables.

In addition, there are several conventions that are specific to minor modes.

• Make a variable whose name ends in ‘-mode’ to represent the minor mode. Its value should enable or disable the mode (nil to disable; anything else to enable.) We call this the mode variable. This variable is used in conjunction with the minor-mode-alist to display the minor mode name in the mode line. It can also enable or disable a minor mode keymap. Individual commands or hooks can also check the variable’s value. If you want the minor mode to be enabled separately in each buffer, make the variable buffer-local.

• Define a command whose name is the same as the mode variable. Its job is to enable and disable the mode by setting the variable. The command should accept one optional argument. If the argument is nil, it should toggle the mode (turn it on if it is off, and off if it is on). Otherwise, it should turn the mode on if the argument is a positive integer, a symbol other than nil or -, or a list whose car is such an integer or symbol; it should turn the mode off otherwise. Here is an example taken from the definition of transient-mark-mode. It shows the use of transient-mark-mode as a variable that enables or disables the mode’s behavior, and also shows the proper way to toggle, enable or disable the minor mode based on the raw prefix argument value.

         (setq transient-mark-mode
               (if (null arg) (not transient-mark-mode)
                 (> (prefix-numeric-value arg) 0)))

• Add an element to minor-mode-alist for each minor mode (see Section 20.3.2 [Mode

Line Variables], page 312). This element should be a list of the following form:

(mode-variable string) Here mode-variable is the variable that controls enabling of the minor mode, and string is a short string, starting with a space, to represent the mode in the mode line. These strings must be short so that there is room for several of them at once. When you add an element to minor-mode-alist, use assq to check for an existing element, to avoid duplication. For example:

         (or (assq 'leif-mode minor-mode-alist)
             (setq minor-mode-alist
                   (cons '(leif-mode " Leif") minor-mode-alist)))

20.2.2 Keymaps and Minor Modes

Each minor mode can have its own keymap, which is active when the mode is enabled. To set up a keymap for a minor mode, add an element to the alist minor-mode-map-alist. See Section 19.6 [Active Keymaps], page 281.

One use of minor mode keymaps is to modify the behavior of certain self-inserting characters so that they do something else as well as self-insert. In general, this is the only way to do that, since the facilities for customizing self-insert-command are limited to special cases (designed for abbrevs and Auto Fill mode). (Do not try substituting your own definition of self-insert-command for the standard one. The editor command loop handles this function specially.)

20.3 Mode Line Format

Each Emacs window (aside from minibuffer windows) includes a mode line, which displays status information about the buffer displayed in the window. The mode line contains information about the buffer, such as its name, associated file, depth of recursive editing, and the major and minor modes.

This section describes how the contents of the mode line are controlled. It is in the chapter on modes because much of the information displayed in the mode line relates to the enabled major and minor modes.

mode-line-format is a buffer-local variable that holds a template used to display the mode line of the current buffer. All windows for the same buffer use the same mode-line-format and their mode lines appear the same (except for scrolling percentages and line numbers).

The mode line of a window is normally updated whenever a different buffer is shown in the window, or when the buffer’s modified-status changes from nil to t or vice-versa. If you modify any of the variables referenced by mode-line-format (see Section 20.3.2 [Mode Line Variables], page 312), you may want to force an update of the mode line so as to display the new information.

Function force-mode-line-update

Force redisplay of the current buffer’s mode line.

The mode line is usually displayed in inverse video; see mode-line-inverse-video in Section 35.12 [Inverse Video], page 582.

20.3.1 The Data Structure of the Mode Line

The mode line contents are controlled by a data structure of lists, strings, symbols, and numbers kept in the buffer-local variable mode-line-format. The data structure is called a mode line construct, and it is built in recursive fashion out of simpler mode line constructs. The same data structure is used for constructing frame titles (see Section 26.4 [Frame Titles], page 416).

Variable mode-line-format

The value of this variable is a mode line construct with overall responsibility for the mode line format. The value of this variable controls which other variables are used to form the mode line text, and where they appear.

A mode line construct may be as simple as a fixed string of text, but it usually specifies how to use other variables to construct the text. Many of these variables are themselves defined to have mode line constructs as their values.

The default value of mode-line-format incorporates the values of variables such as mode-name and minor-mode-alist. Because of this, very few modes need to alter modeline-format. For most purposes, it is sufficient to alter the variables referenced by mode-

line-format.

A mode line construct may be a list, a symbol, or a string. If the value is a list, each element may be a list, a symbol, or a string.

string A string as a mode line construct is displayed verbatim in the mode line except for %-constructs. Decimal digits after the ‘%’ specify the field width for space filling on the right (i.e., the data is left justified). See Section 20.3.3 [%-Constructs], page 314.

symbol A symbol as a mode line construct stands for its value. The value of symbol is used as a mode line construct, in place of symbol. However, the symbols t and nil are ignored; so is any symbol whose value is void. There is one exception: if the value of symbol is a string, it is displayed verbatim: the %-constructs are not recognized.

(string rest…) or (list rest…)

A list whose first element is a string or list means to process all the elements recursively and concatenate the results. This is the most common form of mode line construct.

(symbol then else)

A list whose first element is a symbol is a conditional. Its meaning depends on the value of symbol. If the value is non-nil, the second element, then, is processed recursively as a mode line element. But if the value of symbol is nil, the third element, else, is processed recursively. You may omit else; then the mode line element displays nothing if the value of symbol is nil.

(width rest…)

A list whose first element is an integer specifies truncation or padding of the results of rest. The remaining elements rest are processed recursively as mode line constructs and concatenated together. Then the result is space filled (if width is positive) or truncated (to −width columns, if width is negative) on the right. For example, the usual way to show what percentage of a buffer is above the top of the window is to use a list like this: (-3 "%p").

If you do alter mode-line-format itself, the new value should use the same variables that appear in the default value (see Section 20.3.2 [Mode Line Variables], page 312), rather than duplicating their contents or displaying the information in another fashion. This way, customizations made by the user or by Lisp programs (such as display-time and major modes) via changes to those variables remain effective.

Here is an example of a mode-line-format that might be useful for shell-mode, since it contains the hostname and default directory.

(setq mode-line-format
(list ""
'mode-line-modified
"%b--"

(getenv "HOST") ; One element is not constant.

":"
'default-directory
"   "
'global-mode-string
"   %[("
'mode-name
'mode-line-process
'minor-mode-alist
"%n"
")%]----"
'(line-number-mode "L%l--")
'(-3 . "%p")
"-%-"))

20.3.2 Variables Used in the Mode Line

This section describes variables incorporated by the standard value of mode-line-format into the text of the mode line. There is nothing inherently special about these variables; any other variables could have the same effects on the mode line if mode-line-format were changed to use them.

Variable mode-line-modified

This variable holds the value of the mode-line construct that displays whether the current buffer is modified.

The default value of mode-line-modified is ("--%1*%1+-"). This means that the mode line displays ‘--**-’ if the buffer is modified, ‘-----’ if the buffer is not modified, ‘--%%-’ if the buffer is read only, and ‘--%*--’ if the buffer is read only and modified.

Changing this variable does not force an update of the mode line.

Variable mode-line-buffer-identification

This variable identifies the buffer being displayed in the window. Its default value is ("%F: %17b"), which means that it usually displays ‘Emacs:’ followed by seventeen characters of the buffer name. (In a terminal frame, it displays the frame name instead of ‘Emacs’; this has the effect of showing the frame number.) You may want to change this in modes such as Rmail that do not behave like a “normal” Emacs.

Variable global-mode-string

This variable holds a mode line spec that appears in the mode line by default, just after the buffer name. The command display-time sets global-mode-string to refer to the variable display-time-string, which holds a string containing the time and load information.

The ‘%M’ construct substitutes the value of global-mode-string, but this is obsolete, since the variable is included directly in the mode line.

Variable mode-name

This buffer-local variable holds the “pretty” name of the current buffer’s major mode. Each major mode should set this variable so that the mode name will appear in the mode line.

Variable minor-mode-alist

This variable holds an association list whose elements specify how the mode line should indicate that a minor mode is active. Each element of the minormode-alist should be a two-element list:

(minor-mode-variable mode-line-string)

More generally, mode-line-string can be any mode line spec. It appears in the mode line when the value of minor-mode-variable is non-nil, and not otherwise. These strings should begin with spaces so that they don’t run together. Conventionally, the minor-mode-variable for a specific mode is set to a non-nil value when that minor mode is activated.

The default value of minor-mode-alist is:

     minor-mode-alist
     ⇒ ((vc-mode vc-mode)
         (abbrev-mode " Abbrev")
         (overwrite-mode overwrite-mode)
         (auto-fill-function " Fill")
         (defining-kbd-macro " Def")
         (isearch-mode isearch-mode))

minor-mode-alist is not buffer-local. The variables mentioned in the alist should be buffer-local if the minor mode can be enabled separately in each buffer.

Variable mode-line-process

This buffer-local variable contains the mode line information on process status in modes used for communicating with subprocesses. It is displayed immediately following the major mode name, with no intervening space. For example, its value in the ‘*shell*’ buffer is (": %s"), which allows the shell to display its status along with the major mode as: ‘(Shell: run)’. Normally this variable

is nil.

Variable default-mode-line-format

This variable holds the default mode-line-format for buffers that do not over-

ride it. This is the same as (default-value 'mode-line-format).
The default value of default-mode-line-format is:
     (""
      mode-line-modified
      mode-line-buffer-identification
      "   "
      global-mode-string
      "   %[("
      mode-name
      mode-line-process
      minor-mode-alist
      "%n"
      ")%]----"
      (line-number-mode "L%l--")
      (-3 . "%p")
      "-%-")

Variable vc-mode

The variable vc-mode, local in each buffer, records whether the buffer’s visited file is maintained with version control, and, if so, which kind. Its value is nil for no version control, or a string that appears in the mode line.

20.3.3 %-Constructs in the Mode Line

The following table lists the recognized %-constructs and what they mean. In any construct except ‘%%’, you can add a decimal integer after the ‘%’ to specify how many characters to display.

%b The current buffer name, obtained with the buffer-name function. See Sec-

tion 24.3 [Buffer Names], page 371.

%f The visited file name, obtained with the buffer-file-name function. See Sec-

tion 24.4 [Buffer File Name], page 372.

%F The name of the selected frame. %c The current column number of point. %l The current line number of point. %* ‘%’ if the buffer is read only (see buffer-read-only);

‘*’ if the buffer is modified (see buffer-modified-p);

‘-’ otherwise. See Section 24.5 [Buffer Modification], page 374.

%+ ‘*’ if the buffer is modified (see buffer-modified-p); ‘%’ if the buffer is read only (see buffer-read-only); ‘-’ otherwise. This differs from ‘%*’ only for a modified read-only buffer. See Section 24.5 [Buffer Modification], page 374.

%& ‘*’ if the buffer is modified, and ‘-’ otherwise. %s The status of the subprocess belonging to the current buffer, obtained with

process-status. See Section 33.6 [Process Information], page 531.

%t Whether the visited file is a text file or a binary file. (This is a meaningful

distinction only on certain operating systems.)

%p The percentage of the buffer text above the top of window, or ‘Top’, ‘Bottom’

or ‘All’.

%P The percentage of the buffer text that is above the bottom of the window (which includes the text visible in the window, as well as the text above the top), plus ‘Top’ if the top of the buffer is visible on screen; or ‘Bottom’ or ‘All’.

%n ‘Narrow’ when narrowing is in effect; nothing otherwise (see narrow-to-region

in Section 27.4 [Narrowing], page 438).

%[ An indication of the depth of recursive editing levels (not counting minibuffer levels): one ‘[’ for each editing level. See Section 18.10 [Recursive Editing], page 271.

%] One ‘]’ for each recursive editing level (not counting minibuffer levels). %% The character ‘%’—this is how to include a literal ‘%’ in a string in which %-

constructs are allowed.

%- Dashes sufficient to fill the remainder of the mode line.

The following two %-constructs are still supported, but they are obsolete, since you can get the same results with the variables mode-name and global-mode-string.

%m  The value of mode-name.

%M The value of global-mode-string. Currently, only display-time modifies the

          value of global-mode-string.

20.4 Hooks

A hook is a variable where you can store a function or functions to be called on a particular occasion by an existing program. Emacs provides hooks for the sake of customization. Most often, hooks are set up in the ‘.emacs’ file, but Lisp programs can set them also. See Appendix F [Standard Hooks], page 635, for a list of standard hook variables.

Most of the hooks in Emacs are normal hooks. These variables contain lists of functions to be called with no arguments. When the hook name ends in ‘-hook’, that tells you it is normal. We try to make all hooks normal, as much as possible, so that you can use them in a uniform way.

Every major mode function is supposed to run a normal hook called the mode hook as the last step of initialization. This makes it easy for a user to customize the behavior of the mode, by overriding the local variable assignments already made by the mode. But hooks are used in other contexts too. For example, the hook suspend-hook runs just before Emacs suspends itself (see Section 34.2.2 [Suspending Emacs], page 548).

The recommended way to add a hook function to a normal hook is by calling add-hook (see below). The hook functions may be any of the valid kinds of functions that funcall accepts (see Section 11.1 [What Is a Function], page 139). Most normal hook variables are initially void; add-hook knows how to deal with this.

If the hook variable’s name does not end with ‘-hook’, that indicates it is probably an abnormal hook; you should look at its documentation to see how to use the hook properly.

If the variable’s name ends in ‘-functions’ or ‘-hooks’, then the value is a list of functions, but it is abnormal in that either these functions are called with arguments or their values are used in some way. You can use add-hook to add a function to the list, but you must take care in writing the function. (A few of these variables are actually normal hooks which were named before we established the convention of using ‘-hook’ for them.)

If the variable’s name ends in ‘-function’, then its value is just a single function, not a list of functions.

Here’s an expression that uses a mode hook to turn on Auto Fill mode when in Lisp Interaction mode:

     (add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill)

The next example shows how to use a hook to customize the way Emacs formats C code. (People often have strong personal preferences for one format or another.) Here the hook function is an anonymous lambda expression.

     (add-hook 'c-mode-hook
       (function (lambda ()
                   (setq c-indent-level 4
                         c-argdecl-indent 0
                         c-label-offset -4
                         c-continued-statement-indent 0
                         c-brace-offset 0
                         comment-column 40))))
     (setq c++-mode-hook c-mode-hook)

At the appropriate time, Emacs uses the run-hooks function to run particular hooks. This function calls the hook functions that have been added with add-hook.

Function run-hooks &rest hookvar This function takes one or more hook variable names as arguments, and runs each hook in turn. Each hookvar argument should be a symbol that is a hook variable. These arguments are processed in the order specified. If a hook variable has a non-nil value, that value may be a function or a list of functions. If the value is a function (either a lambda expression or a symbol with a function definition), it is called. If it is a list, the elements are called, in order. The hook functions are called with no arguments. For example, here’s how emacs-lisp-mode runs its mode hook:

     (run-hooks 'emacs-lisp-mode-hook)

Function add-hook hook function &optional append local This function is the handy way to add function function to hook variable hook. The argument function may be any valid Lisp function with the proper number of arguments. For example,

     (add-hook 'text-mode-hook 'my-text-hook-function)
adds my-text-hook-function to the hook called text-mode-hook.

You can use add-hook for abnormal hooks as well as for normal hooks. It is best to design your hook functions so that the order in which they are executed does not matter. Any dependence on the order is “asking for trouble.” However, the order is predictable: normally, function goes at the front of the hook list, so it will be executed first (barring another add-hook call). If the optional argument append is non-nil, the new hook function goes at the end of the hook list and will be executed last. If local is non-nil, that says to make the new hook function local to the current buffer. Before you can do this, you must make the hook itself buffer-local by

calling make-local-hook (not make-local-variable). If the hook itself is not

buffer-local, then the value of local makes no difference—the hook function is always global.

Function remove-hook hook function &optional local This function removes function from the hook variable hook. If local is non-nil, that says to remove function from the local hook list instead of from the global hook list. If the hook itself is not buffer-local, then the value of local makes no difference.

Function make-local-hook hook

This function makes the hook variable hook local to the current buffer. When a hook variable is local, it can have local and global hook functions, and runhooks runs all of them. This function works by making t an element of the buffer-local value. That serves as a flag to use the hook functions in the default value of the hook variable as well as those in the local value. Since run-hooks understands this flag, make-local-hook works with all normal hooks. It works for only some non-normal hooks—those whose callers have been updated to understand this meaning of t. Do not use make-local-variable directly for hook variables; it is not sufficient.

21 Documentation

GNU Emacs Lisp has convenient on-line help facilities, most of which derive their information from the documentation strings associated with functions and variables. This chapter describes how to write good documentation strings for your Lisp programs, as well as how to write programs to access documentation.

Note that the documentation strings for Emacs are not the same thing as the Emacs manual. Manuals have their own source files, written in the Texinfo language; documentation strings are specified in the definitions of the functions and variables they apply to. A collection of documentation strings is not sufficient as a manual because a good manual is not organized in that fashion; it is organized in terms of topics of discussion.

21.1 Documentation Basics

A documentation string is written using the Lisp syntax for strings, with double-quote characters surrounding the text of the string. This is because it really is a Lisp string object. The string serves as documentation when it is written in the proper place in the definition of a function or variable. In a function definition, the documentation string follows the argument list. In a variable definition, the documentation string follows the initial value of the variable.

When you write a documentation string, make the first line a complete sentence (or two complete sentences) since some commands, such as apropos, show only the first line of a multi-line documentation string. Also, you should not indent the second line of a documentation string, if you have one, because that looks odd when you use C-h f

(describe-function) or C-h v (describe-variable). See Section A.3 [Documentation

Tips], page 603.

Documentation strings may contain several special substrings, which stand for key bindings to be looked up in the current keymaps when the documentation is displayed. This allows documentation strings to refer to the keys for related commands and be accurate even when a user rearranges the key bindings. (See Section 21.2 [Accessing Documentation], page 320.)

Within the Lisp world, a documentation string accessible through the function or variable that it describes:

• The documentation for a function is stored in the function definition itself (see Section 11.2 [Lambda Expressions], page 140). The function documentation knows how to extract it.

• The documentation for a variable is stored in the variable’s property list under the

    property name variable-documentation. The function documentation-property

knows how to extract it.

To save space, the documentation for preloaded functions and variables (including primitive functions and autoloaded functions) is stored in the file ‘emacs/etc/DOC-version’. The documentation for functions and variables loaded during the Emacs session from bytecompiled files is stored in those files (see Section 14.3 [Docs and Compilation], page 174).

The data structure inside Emacs has an integer offset into the file, or a list containing a string and an integer, in place of the documentation string. The functions documentation and documentation-property use that information to read the documentation from the appropriate file; this is transparent to the user.

For information on the uses of documentation strings, see section “Help” in The GNU Emacs Manual.

The ‘emacs/lib-src’ directory contains two utilities that you can use to print nicelooking hardcopy for the file ‘emacs/etc/DOC-version’. These are ‘sorted-doc.c’ and

‘digest-doc.c’.

21.2 Access to Documentation Strings

Function documentation-property symbol property &optional verbatim This function returns the documentation string that is recorded symbol’s property list under property property. It retrieves the text from a file if necessary, and runs substitute-command-keys to substitute actual key bindings. (This substitution is not done if verbatim is non-nil; the verbatim argument exists only as of Emacs 19.)

     (documentation-property 'command-line-processed
        'variable-documentation)
          ⇒ "t once command line has been processed"
     (symbol-plist 'command-line-processed)
          ⇒ (variable-documentation 188902)

Function documentation function &optional verbatim This function returns the documentation string of function. It reads the text from a file if necessary. Then (unless verbatim is non-nil) it calls substitutecommand-keys, to return a value containing the actual (current) key bindings.

The function documentation signals a void-function error if function has no function definition. However, it is ok if the function definition has no documentation string. In that case, documentation returns nil.

Here is an example of using the two functions, documentation and documentationproperty, to display the documentation strings for several symbols in a ‘*Help*’ buffer.

(defun describe-symbols (pattern)
  "Describe the Emacs Lisp symbols matching PATTERN.
All symbols that have PATTERN in their name are described
in the `*Help*' buffer."
  (interactive "sDescribe symbols matching: ")
  (let ((describe-func
         (function
          (lambda (s)

;; Print description of symbol.

            (if (fboundp s)             ; It is a function.
                (princ
                 (format "%s\t%s\n%s\n\n" s
                   (if (commandp s)
                       (let ((keys (where-is-internal s)))
                         (if keys
                             (concat
                              "Keys: "
                              (mapconcat 'key-description
                                         keys " "))
                           "Keys: none"))
                     "Function")
                   (or (documentation s)
                       "not documented"))))

(if (boundp s) ; It is a variable.

                (princ
                 (format "%s\t%s\n%s\n\n" s
                   (if (user-variable-p s)
                       "Option " "Variable")
                   (or (documentation-property
                         s 'variable-documentation)
                       "not documented")))))))
        sym-list)

;; Build a list of symbols that match pattern.

    (mapatoms (function
               (lambda (sym)
                 (if (string-match pattern (symbol-name sym))
                     (setq sym-list (cons sym sym-list))))))

;; Display the data.

    (with-output-to-temp-buffer "*Help*"
      (mapcar describe-func (sort sym-list 'string<))
      (print-help-return-message))))

The describe-symbols function works like apropos, but provides more information.

(describe-symbols "goal")
---------- Buffer: *Help* ----------
goal-column     Option
*Semipermanent goal column for vertical motion, as set by . . .
set-goal-column Command: C-x C-n
Set the current horizontal position as a goal for C-n and C-p.
Those commands will move to this position in the line moved to
rather than trying to keep the same horizontal position.
With a non-nil argument, clears out the goal column
so that C-n and C-p resume vertical motion.
The goal column is stored in the variable `goal-column'.

temporary-goal-column   Variable
Current goal column for vertical motion.
It is the column where point was
at the start of current run of vertical motion commands.
When the `track-eol' feature is doing its job, the value is 9999.
---------- Buffer: *Help* ----------

Function Snarf-documentation filename

This function is used only during Emacs initialization, just before the runnable Emacs is dumped. It finds the file offsets of the documentation strings stored in the file filename, and records them in the in-core function definitions and variable property lists in place of the actual strings. See Section B.1 [Building Emacs], page 609. Emacs finds the file filename in the ‘emacs/etc’ directory. When the dumped Emacs is later executed, the same file is found in the directory doc-directory. Usually filename is "DOC-version".

Variable doc-directory

This variable holds the name of the directory which should contion the file "DOC-version" that contains documentation strings for built-in and preloaded functions and variables. In most cases, this is the same as data-directory. They may be different when you run Emacs from the directory where you built it, without actually installing it. See data-directory in Section 21.5 [Help Functions], page 324. In older Emacs versions, exec-directory was used for this.

21.3 Substituting Key Bindings in Documentation

When documentation strings refer to key sequences, they should use the current, actual key bindings. They can do so using certain special text sequences described below. Accessing documentation strings in the usual way substitutes current key binding information for these special sequences. This works by calling substitute-command-keys. You can also call that function yourself.

Here is a list of the special sequences and what they mean:

\[command] stands for a key sequence that will invoke command, or ‘M-x command’ if command has no key bindings.

\{mapvar} stands for a summary of the value of mapvar, which should be a keymap. The

     summary is made by describe-bindings.

\<mapvar> stands for no text itself. It is used for a side effect: it specifies mapvar as the keymap for any following ‘\[command]’ sequences in this documentation string.

\= quotes the following character and is discarded; thus, ‘\=\[’ puts ‘\[’ into the output, and ‘\=\=’ puts ‘\=’ into the output.

Please note: Each ‘\’ must be doubled when written in a string in Emacs Lisp.

Function substitute-command-keys string

This function scans string for the above special sequences and replaces them by what they stand for, returning the result as a string. This permits display of documentation that refers accurately to the user’s own customized key bindings.

Here are examples of the special sequences:

(substitute-command-keys
   "To abort recursive edit, type: \\[abort-recursive-edit]")
⇒ "To abort recursive edit, type: C-]"
(substitute-command-keys
   "The keys that are defined for the minibuffer here are:
  \\{minibuffer-local-must-match-map}")
⇒ "The keys that are defined for the minibuffer here are:
?               minibuffer-completion-help
SPC             minibuffer-complete-word
TAB             minibuffer-complete
LFD             minibuffer-complete-and-exit
RET             minibuffer-complete-and-exit
C-g             abort-recursive-edit
"
(substitute-command-keys
   "To abort a recursive edit from the minibuffer, type\
\\<minibuffer-local-must-match-map>\\[abort-recursive-edit].")
⇒ "To abort a recursive edit from the minibuffer, type C-g."

21.4 Describing Characters for Help Messages

These functions convert events, key sequences or characters to textual descriptions. These descriptions are useful for including arbitrary text characters or key sequences in messages, because they convert non-printing and whitespace characters to sequences of printing characters. The description of a non-whitespace printing character is the character itself.

Function key-description sequence

This function returns a string containing the Emacs standard notation for the input events in sequence. The argument sequence may be a string, vector or list. See Section 18.5 [Input Events], page 252, for more information about valid events. See also the examples for single-key-description, below.

Function single-key-description event

This function returns a string describing event in the standard Emacs notation for keyboard input. A normal printing character appears as itself, but a control character turns into a string starting with ‘C-’, a meta character turns into a string starting with ‘M-’, and space, linefeed, etc. appear as ‘SPC’, ‘LFD’, etc. A function key symbol appears as itself. An event that is a list appears as the name of the symbol in the car of the list.

     (single-key-description ?\C-x)
          ⇒ "C-x"
     (key-description "\C-x \M-y \n \t \r \f123")
          ⇒ "C-x SPC M-y SPC LFD SPC TAB SPC RET SPC C-l 1 2 3"
     (single-key-description 'C-mouse-1)
          ⇒ "C-mouse-1"

Function text-char-description character

This function returns a string describing character in the standard Emacs notation for characters that appear in text—like single-key-description, except that control characters are represented with a leading caret (which is how control characters in Emacs buffers are usually displayed).

     (text-char-description ?\C-c)
          ⇒ "^C"
     (text-char-description ?\M-m)
          ⇒ "M-m"
     (text-char-description ?\C-\M-m)
          ⇒ "M-^M"

21.5 Help Functions

Emacs provides a variety of on-line help functions, all accessible to the user as subcommands of the prefix C-h. For more information about them, see section “Help” in The GNU Emacs Manual. Here we describe some program-level interfaces to the same information.

Command apropos regexp &optional do-all predicate This function finds all symbols whose names contain a match for the regular expression regexp, and returns a list of them (see Section 30.2 [Regular Expressions], page 492). It also displays the symbols in a buffer named ‘*Help*’, each with a one-line description. If do-all is non-nil, then apropos also shows key bindings for the functions that are found. If predicate is non-nil, it should be a function to be called on each symbol that has matched regexp. Only symbols for which predicate returns a non-nil value are listed or displayed. In the first of the following examples, apropos finds all the symbols with names containing ‘exec’. In the second example, it finds and returns only those symbols that are also commands. (We don’t show the output that results in the ‘*Help*’ buffer.)

     (apropos "exec")
          ⇒ (Buffer-menu-execute command-execute exec-directory
         exec-path execute-extended-command execute-kbd-macro
         executing-kbd-macro executing-macro)

     (apropos "exec" nil 'commandp)
          ⇒ (Buffer-menu-execute execute-extended-command)

The command C-h a (command-apropos) calls apropos, but specifies a predicate to restrict the output to symbols that are commands. The call to apropos looks like this:

     (apropos string t 'commandp)

Command super-apropos regexp &optional do-all This function differs from apropos in that it searches documentation strings as well as symbol names for matches for regexp. By default, it searches the documentation strings only for preloaded functions and variables. If do-all is non-nil, it scans the names and documentation strings of all functions and variables.

Variable help-map

The value of this variable is a local keymap for characters following the Help key, C-h.

Prefix Command help-command

This symbol is not a function; its function definition is actually the keymap known as help-map. It is defined in ‘help.el’ as follows:

     (define-key global-map "\C-h" 'help-command)
     (fset 'help-command help-map)

Function print-help-return-message &optional function

This function builds a string that explains how to restore the previous state of the windows after a help command. After building the message, it applies function to it if function is non-nil. Otherwise it calls message to display it in the echo area. This function expects to be called inside a with-output-to-temp-buffer special form, and expects standard-output to have the value bound by that special form. For an example of its use, see the long example in Section 21.2 [Accessing Documentation], page 320.

Variable help-char

The value of this variable is the help character—the character that Emacs recognizes as meaning Help. By default, it is 8, which is C-h. When Emacs reads this character, if help-form is non-nil Lisp expression, it evaluates that expression, and displays the result in a window if it is a string. Usually the value of help-form’s value is nil. Then the help character has no special meaning at the level of command input, and it becomes part of a key sequence in the normal way. The standard key binding of C-h is a prefix key for several general-purpose help features. The help character is special after prefix keys, too. If it has no binding as a subcommand of the prefix key, it runs describe-prefix-bindings, which displays a list of all the subcommands of the prefix key.

Variable help-form

If this variable is non-nil, its value is a form to evaluate whenever the character help-char is read. If evaluating the form produces a string, that string is displayed. A command that calls read-event or read-char probably should bind helpform to a non-nil expression while it does input. (The exception is when C-h is meaningful input.) Evaluating this expression should result in a string that explains what the input is for and how to enter it properly. Entry to the minibuffer binds this variable to the value of minibuffer-help-form (see Section 17.8 [Minibuffer Misc], page 240).

Variable prefix-help-command

This variable holds a function to print help for a prefix character. The function is called when the user types a prefix key followed by the help character, and the help character has no binding after that prefix. The variable’s default value

is describe-prefix-bindings.

Function describe-prefix-bindings

This function calls describe-bindings to display a list of all the subcommands of the prefix key of the most recent key sequence. The prefix described consists of all but the last event of that key sequence. (The last event is, presumably, the help character.)

The following two functions are found in the library ‘helper’. They are for modes that want to provide help without relinquishing control, such as the “electric” modes. You must load that library with (require 'helper) in order to use them. Their names begin with ‘Helper’ to distinguish them from the ordinary help functions.

Command Helper-describe-bindings

This command pops up a window displaying a help buffer containing a listing of all of the key bindings from both the local and global keymaps. It works by

calling describe-bindings.

Command Helper-help

This command provides help for the current mode. It prompts the user in the minibuffer with the message ‘Help (Type ? for further options)’, and then provides assistance in finding out what the key bindings are, and what the mode is intended for. It returns nil. This can be customized by changing the map Helper-help-map.

Variable data-directory

This variable holds the name of the directory in which Emacs finds certain documentation and text files that come with Emacs. In older Emacs versions, exec-directory was used for this.

Macro make-help-screen fname help-line help-text help-map This macro defines a help command named fname that acts like a prefix key that shows a list of the subcommands it offers.

When invoked, fname displays help-text in a window, then reads and executes a key sequence according to help-map. The string help-text should describe the bindings available in help-map. The command fname is defined to handle a few events itself, by scrolling the display of help-text. When fname reads one of those special events, it does the scrolling and then reads another event. When it reads an event that is not one of those few, and which has a binding in help-map, it executes that key’s binding and then returns. The argument help-line should be a single-line summary of the alternatives in help-map. In the current version of Emacs, this argument is used only if you

set the option three-step-help to t.

User Option three-step-help

If this variable is non-nil, commands defined with make-help-screen display their help-line strings in the echo area at first, and display the longer help-text strings only if the user types the help character again.

328 GNU Emacs Lisp Reference Manual

22 Files

In Emacs, you can find, create, view, save, and otherwise work with files and file directories. This chapter describes most of the file-related functions of Emacs Lisp, but a few others are described in Chapter 24 [Buffers], page 369, and those related to backups and auto-saving are described in Chapter 23 [Backups and Auto-Saving], page 359.

Many of the file functions take one or more arguments that are file names. A file name is actually a string. Most of these functions expand file name arguments using expandfile-name, so that ‘~’ is handled correctly, as are relative file names (including ‘../’). These functions don’t recognize environment variable substitutions such as ‘$HOME’. See Section 22.8.4 [File Name Expansion], page 347.

22.1 Visiting Files

Visiting a file means reading a file into a buffer. Once this is done, we say that the buffer is visiting that file, and call the file “the visited file” of the buffer.

A file and a buffer are two different things. A file is information recorded permanently in the computer (unless you delete it). A buffer, on the other hand, is information inside of Emacs that will vanish at the end of the editing session (or when you kill the buffer). Usually, a buffer contains information that you have copied from a file; then we say the buffer is visiting that file. The copy in the buffer is what you modify with editing commands. Such changes to the buffer do not change the file; therefore, to make the changes permanent, you must save the buffer, which means copying the altered buffer contents back into the file.

In spite of the distinction between files and buffers, people often refer to a file when they mean a buffer and vice-versa. Indeed, we say, “I am editing a file,” rather than, “I am editing a buffer that I will soon save as a file of the same name.” Humans do not usually need to make the distinction explicit. When dealing with a computer program, however, it is good to keep the distinction in mind.

22.1.1 Functions for Visiting Files

This section describes the functions normally used to visit files. For historical reasons, these functions have names starting with ‘find-’ rather than ‘visit-’. See Section 24.4 [Buffer File Name], page 372, for functions and variables that access the visited file name of a buffer or that find an existing buffer by its visited file name.

In a Lisp program, if you want to look at the contents of a file but not alter it, the fastest way is to use insert-file-contents in a temporary buffer. Visiting the file is not necessary and takes longer. See Section 22.3 [Reading from Files], page 334.

Command find-file filename

This command selects a buffer visiting the file filename, using an existing buffer if there is one, and otherwise creating a new buffer and reading the file into it. It also returns that buffer.

The body of the find-file function is very simple and looks like this:

     (switch-to-buffer (find-file-noselect filename))

(See switch-to-buffer in Section 25.7 [Displaying Buffers], page 391.) When find-file is called interactively, it prompts for filename in the minibuffer.

Function find-file-noselect filename

This function is the guts of all the file-visiting functions. It finds or creates a buffer visiting the file filename, and returns it. It uses an existing buffer if there is one, and otherwise creates a new buffer and reads the file into it. You may make the buffer current or display it in a window if you wish, but this function does not do so. When find-file-noselect uses an existing buffer, it first verifies that the file has not changed since it was last visited or saved in that buffer. If the file has changed, then this function asks the user whether to reread the changed file. If the user says ‘yes’, any changes previously made in the buffer are lost. If find-file-noselect needs to create a buffer, and there is no file named filename, it displays the message ‘New file’ in the echo area, and leaves the buffer empty.

The find-file-noselect function calls after-find-file after reading the

file (see Section 22.1.2 [Subroutines of Visiting], page 331). That function sets the buffer major mode, parses local variables, warns the user if there exists an auto-save file more recent than the file just visited, and finishes by running the

functions in find-file-hooks.

The find-file-noselect function returns the buffer that is visiting the file filename.

     (find-file-noselect "/etc/fstab")
          ⇒ #<buffer fstab>

Command find-file-other-window filename

This command selects a buffer visiting the file filename, but does so in a window other than the selected window. It may use another existing window or split a window; see Section 25.7 [Displaying Buffers], page 391. When this command is called interactively, it prompts for filename.

Command find-file-read-only filename

This command selects a buffer visiting the file filename, like find-file, but it marks the buffer as read-only. See Section 24.7 [Read Only Buffers], page 376, for related functions and variables. When this command is called interactively, it prompts for filename.

Command view-file filename

This command visits filename in View mode, and displays it in a recursive edit, returning to the previous buffer when done. View mode is a mode that allows you to skim rapidly through the file but does not let you modify it. Entering View mode runs the normal hook view-mode-hook. See Section 20.4 [Hooks], page 316. When view-file is called interactively, it prompts for filename.

Variable find-file-hooks

The value of this variable is a list of functions to be called after a file is visited. The file’s local-variables specification (if any) will have been processed before the hooks are run. The buffer visiting the file is current when the hook functions are run. This variable works just like a normal hook, but we think that renaming it would not be advisable.

Variable find-file-not-found-hooks

The value of this variable is a list of functions to be called when find-file or

find-file-noselect is passed a nonexistent file name. find-file-noselect

calls these functions as soon as it detects a nonexistent file. It calls them in the order of the list, until one of them returns non-nil. buffer-file-name is already set up. This is not a normal hook because the values of the functions are used and they may not all be called.

22.1.2 Subroutines of Visiting

The find-file-noselect function uses the create-file-buffer and after-find-

file functions as subroutines. Sometimes it is useful to call them directly.

Function create-file-buffer filename

This function creates a suitably named buffer for visiting filename, and returns it. It uses filename (sans directory) as the name if that name is free; otherwise, it appends a string such as ‘<2>’ to get an unused name. See also Section 24.9 [Creating Buffers], page 378. Please note: create-file-buffer does not associate the new buffer with a file and does not select the buffer. It also does not use the default major mode.

     (create-file-buffer "foo")
          ⇒ #<buffer foo>
     (create-file-buffer "foo")
          ⇒ #<buffer foo<2>>
     (create-file-buffer "foo")
          ⇒ #<buffer foo<3>>
This function is used by find-file-noselect. It uses generate-new-buffer

(see Section 24.9 [Creating Buffers], page 378).

Function after-find-file &optional error warn This function sets the buffer major mode, and parses local variables (see Section 20.1.3 [Auto Major Mode], page 305). It is called by find-file-noselect and by the default revert function (see Section 23.3 [Reverting], page 366). If reading the file got an error because the file does not exist, but its directory does exist, the caller should pass a non-nil value for error. In that case, afterfind-file issues a warning: ‘(New File)’. For more serious errors, the caller should usually not call after-find-file.

If warn is non-nil, then this function issues a warning if an auto-save file exists and is more recent than the visited file. The last thing after-find-file does is call all the functions in find-file-

hooks.

22.2 Saving Buffers

When you edit a file in Emacs, you are actually working on a buffer that is visiting that file—that is, the contents of the file are copied into the buffer and the copy is what you edit. Changes to the buffer do not change the file until you save the buffer, which means copying the contents of the buffer into the file.

Command save-buffer &optional backup-option This function saves the contents of the current buffer in its visited file if the buffer has been modified since it was last visited or saved. Otherwise it does nothing. save-buffer is responsible for making backup files. Normally, backup-option is nil, and save-buffer makes a backup file only if this is the first save since visiting the file. Other values for backup-option request the making of backup files in other circumstances:

• With an argument of 4 or 64, reflecting 1 or 3 C-u’s, the save-buffer function marks this version of the file to be backed up when the buffer is next saved.

• With an argument of 16 or 64, reflecting 2 or 3 C-u’s, the save-buffer function unconditionally backs up the previous version of the file before saving it.

Command save-some-buffers &optional save-silently-p exiting This command saves some modified file-visiting buffers. Normally it asks the user about each buffer. But if save-silently-p is non-nil, it saves all the filevisiting buffers without querying the user. The optional exiting argument, if non-nil, requests this function to offer also to save certain other buffers that are not visiting files. These are buffers that have a non-nil local value of buffer-offer-save. (A user who says yes to saving one of these is asked to specify a file name to use.) The save-buffers-kill-emacs function passes a non-nil value for this argument.

Variable buffer-offer-save

When this variable is non-nil in a buffer, Emacs offers to save the buffer on exit even if the buffer is not visiting a file. The variable is automatically local in all buffers. Normally, Mail mode (used for editing outgoing mail) sets this to t.

Command write-file filename

This function writes the current buffer into file filename, makes the buffer visit that file, and marks it not modified. Then it renames the buffer based on filename, appending a string like ‘<2>’ if necessary to make a unique buffer name. It does most of this work by calling set-visited-file-name and save-

buffer.

Saving a buffer runs several hooks. It also performs format conversion (see Section 22.12 [Format Conversion], page 354), and may save text properties in “annotations” (see Section 29.18.7 [Saving Properties], page 485).

Variable write-file-hooks

The value of this variable is a list of functions to be called before writing out a buffer to its visited file. If one of them returns non-nil, the file is considered already written and the rest of the functions are not called, nor is the usual code for writing the file executed. If a function in write-file-hooks returns non-nil, it is responsible for making a backup file (if that is appropriate). To do so, execute the following code:

     (or buffer-backed-up (backup-buffer))

You might wish to save the file modes value returned by backup-buffer and use that to set the mode bits of the file that you write. This is what save-buffer normally does. Even though this is not a normal hook, you can use add-hook and remove-hook to manipulate the list. See Section 20.4 [Hooks], page 316.

Variable local-write-file-hooks

This works just like write-file-hooks, but it is intended to be made local to particular buffers. It’s not a good idea to make write-file-hooks local to a buffer—use this variable instead. The variable is marked as a permanent local, so that changing the major mode does not alter a buffer-local value. This is convenient for packages that read “file” contents in special ways, and set up hooks to save the data in a corresponding way.

Variable write-contents-hooks

This works just like write-file-hooks, but it is intended for hooks that pertain to the contents of the file, as opposed to hooks that pertain to where the file came from. Such hooks are usually set up by major modes, as buffer-local bindings for this variable. This variable automatically becomes buffer-local whenever it is set; switching to a new major mode always resets this variable. When you use add-hooks to add an element to this hook, you should not specify a non-nil local argument, since this variable is used only locally.

Variable after-save-hook

This normal hook runs after a buffer has been saved in its visited file.

Variable file-precious-flag

If this variable is non-nil, then save-buffer protects against I/O errors while saving by writing the new file to a temporary name instead of the name it is supposed to have, and then renaming it to the intended name after it is clear there are no errors. This procedure prevents problems such as a lack of disk space from resulting in an invalid file. As a side effect, backups are necessarily made by copying. See Section 23.1.2 [Rename or Copy], page 360. Yet, at the same time, saving a precious file always breaks all hard links between the file you save and other file names. Some modes set this variable non-nil locally in particular buffers.

User Option require-final-newline

This variable determines whether files may be written out that do not end with a newline. If the value of the variable is t, then save-buffer silently adds a newline at the end of the file whenever the buffer being saved does not already end in one. If the value of the variable is non-nil, but not t, then save-buffer asks the user whether to add a newline each time the case arises. If the value of the variable is nil, then save-buffer doesn’t add newlines at all. nil is the default value, but a few major modes set it to t in particular buffers.

Command set-visited-file-name filename &optional no-query This function changes the visited file name of the current buffer to filename. It also renames the buffer based on filename, appending a string like ‘<2>’ if necessary to make a unique buffer name. It marks the buffer as modified,a since the contents do not (as far as Emacs knows) match the actual file’s contents. If the specified file already exists, set-visited-file-name asks for confirmation unless no-query is non-nil.

22.3 Reading from Files

You can copy a file from the disk and insert it into a buffer using the insert-file-contents function. Don’t use the user-level command insert-file in a Lisp program, as that sets the mark.

Function insert-file-contents filename &optional visit beg end replace This function inserts the contents of file filename into the current buffer after point. It returns a list of the absolute file name and the length of the data inserted. An error is signaled if filename is not the name of a file that can be read. The function insert-file-contents checks the file contents against the defined file formats, and converts the file contents if appropriate. See Section 22.12 [Format Conversion], page 354. It also calls the functions in the list afterinsert-file-functions; see Section 29.18.7 [Saving Properties], page 485. If visit is non-nil, this function additionally marks the buffer as unmodified and sets up various fields in the buffer so that it is visiting the file filename: these include the buffer’s visited file name and its last save file modtime. This feature is used by find-file-noselect and you probably should not use it yourself.

If beg and end are non-nil, they should be integers specifying the portion of the file to insert. In this case, visit must be nil. For example,

     (insert-file-contents filename nil 0 500)

inserts the first 500 characters of a file. If the argument replace is non-nil, it means to replace the contents of the buffer (actually, just the accessible portion) with the contents of the file. This is better than simply deleting the buffer contents and inserting the whole file, because (1) it preserves some marker positions and (2) it puts less data in the undo list.

If you want to pass a file name to another process so that another program can read the file, use the function file-local-copy; see Section 22.11 [Magic File Names], page 352.

22.4 Writing to Files

You can write the contents of a buffer, or part of a buffer, directly to a file on disk using the append-to-file and write-region functions. Don’t use these functions to write to files that are being visited; that could cause confusion in the mechanisms for visiting.

Command append-to-file start end filename This function appends the contents of the region delimited by start and end in the current buffer to the end of file filename. If that file does not exist, it is created. This function returns nil. An error is signaled if filename specifies a nonwritable file, or a nonexistent file in a directory where files cannot be created.

Command write-region start end filename &optional append visit This function writes the region delimited by start and end in the current buffer into the file specified by filename. If start is a string, then write-region writes or appends that string, rather than text from the buffer. If append is non-nil, then the specified text is appended to the existing file contents (if any). If visit is t, then Emacs establishes an association between the buffer and the file: the buffer is then visiting that file. It also sets the last file modification time for the current buffer to filename’s modtime, and marks the buffer as not modified. This feature is used by save-buffer, but you probably should not use it yourself. If visit is a string, it specifies the file name to visit. This way, you can write the data to one file (filename) while recording the buffer as visiting another file (visit). The argument visit is used in the echo area message and also for file locking; visit is stored in buffer-file-name. This feature is used to implement file-precious-flag; don’t use it yourself unless you really know what you’re doing. The function write-region converts the data which it writes to the appropriate file formats specified by buffer-file-format. See Section 22.12 [Format Conversion], page 354. It also calls the functions in the list write-region-annotate-functions; see Section 29.18.7 [Saving Properties], page 485.

Normally, write-region displays a message ‘Wrote file filename’ in the echo area. If visit is neither t nor nil nor a string, then this message is inhibited. This feature is useful for programs that use files for internal purposes, files that the user does not need to know about.

22.5 File Locks

When two users edit the same file at the same time, they are likely to interfere with each other. Emacs tries to prevent this situation from arising by recording a file lock when a file is being modified. Emacs can then detect the first attempt to modify a buffer visiting a file that is locked by another Emacs job, and ask the user what to do.

File locks do not work properly when multiple machines can share file systems, such as with NFS. Perhaps a better file locking system will be implemented in the future. When file locks do not work, it is possible for two users to make changes simultaneously, but Emacs can still warn the user who saves second. Also, the detection of modification of a buffer visiting a file changed on disk catches some cases of simultaneous editing; see Section 24.6 [Modification Time], page 375.

Function file-locked-p filename

This function returns nil if the file filename is not locked by this Emacs process. It returns t if it is locked by this Emacs, and it returns the name of the user who has locked it if it is locked by someone else.

     (file-locked-p "foo")
          ⇒ nil

Function lock-buffer &optional filename This function locks the file filename, if the current buffer is modified. The argument filename defaults to the current buffer’s visited file. Nothing is done if the current buffer is not visiting a file, or is not modified.

Function unlock-buffer

This function unlocks the file being visited in the current buffer, if the buffer is modified. If the buffer is not modified, then the file should not be locked, so this function does nothing. It also does nothing if the current buffer is not visiting a file.

Function ask-user-about-lock file other-user

This function is called when the user tries to modify file, but it is locked by another user named other-user. The value it returns determines what happens next:

• A value of t says to grab the lock on the file. Then this user may edit the file and other-user loses the lock.

• A value of nil says to ignore the lock and let this user edit the file anyway.

• This function may instead signal a file-locked error, in which case the change that the user was about to make does not take place. The error message for this error looks like this:

error File is locked: file other-user where file is the name of the file and other-user is the name of the user who has locked the file.

The default definition of this function asks the user to choose what to do. If you wish, you can replace the ask-user-about-lock function with your own version that decides in another way. The code for its usual definition is in

‘userlock.el’.

22.6 Information about Files

The functions described in this section all operate on strings that designate file names. All the functions have names that begin with the word ‘file’. These functions all return information about actual files or directories, so their arguments must all exist as actual files or directories unless otherwise noted.

22.6.1 Testing Accessibility

These functions test for permission to access a file in specific ways.

Function file-exists-p filename

This function returns t if a file named filename appears to exist. This does not mean you can necessarily read the file, only that you can find out its attributes. (On Unix, this is true if the file exists and you have execute permission on the containing directories, regardless of the protection of the file itself.) If the file does not exist, or if fascist access control policies prevent you from finding the attributes of the file, this function returns nil.

Function file-readable-p filename

This function returns t if a file named filename exists and you can read it. It returns nil otherwise.

     (file-readable-p "files.texi")
          ⇒ t
     (file-exists-p "/usr/spool/mqueue")
          ⇒ t
     (file-readable-p "/usr/spool/mqueue")
          ⇒ nil

Function file-executable-p filename

This function returns t if a file named filename exists and you can execute it. It returns nil otherwise. If the file is a directory, execute permission means you can check the existence and attributes of files inside the directory, and open those files if their modes permit.

Function file-writable-p filename

This function returns t if the file filename can be written or created by you, and nil otherwise. A file is writable if the file exists and you can write it. It is creatable if it does not exist, but the specified directory does exist and you can write in that directory.

In the third example below, ‘foo’ is not writable because the parent directory does not exist, even though the user could create such a directory.

     (file-writable-p "~/foo")
          ⇒ t
     (file-writable-p "/foo")
          ⇒ nil
     (file-writable-p "~/no-such-dir/foo")
          ⇒ nil

Function file-accessible-directory-p dirname

This function returns t if you have permission to open existing files in the directory whose name as a file is dirname; otherwise (or if there is no such directory), it returns nil. The value of dirname may be either a directory name or the file name of a directory.

Example: after the following,

     (file-accessible-directory-p "/foo")
          ⇒ nil

we can deduce that any attempt to read a file in ‘/foo/’ will give an error.

Function file-ownership-preserved-p filename

This function returns t if deleting the file filename and then creating it anew would keep the file’s owner unchanged.

Function file-newer-than-file-p filename1 filename2

This function returns t if the file filename1 is newer than file filename2. If filename1 does not exist, it returns nil. If filename2 does not exist, it returns

t.

In the following example, assume that the file ‘aug-19’ was written on the 19th, ‘aug-20’ was written on the 20th, and the file ‘no-file’ doesn’t exist at all.

     (file-newer-than-file-p "aug-19" "aug-20")
          ⇒ nil
     (file-newer-than-file-p "aug-20" "aug-19")
          ⇒ t
     (file-newer-than-file-p "aug-19" "no-file")
          ⇒ t
     (file-newer-than-file-p "no-file" "aug-19")
          ⇒ nil

You can use file-attributes to get a file’s last modification time as a list of two numbers. See Section 22.6.4 [File Attributes], page 340.

22.6.2 Distinguishing Kinds of Files

This section describes how to distinguish various kinds of files, such as directories, symbolic links, and ordinary files.

Function file-symlink-p filename

If the file filename is a symbolic link, the file-symlink-p function returns the file name to which it is linked. This may be the name of a text file, a directory, or even another symbolic link, or it may be a nonexistent file name.

If the file filename is not a symbolic link (or there is no such file), file-

symlink-p returns nil.
     (file-symlink-p "foo")
          ⇒ nil
     (file-symlink-p "sym-link")
          ⇒ "foo"
     (file-symlink-p "sym-link2")
          ⇒ "sym-link"
     (file-symlink-p "/bin")
          ⇒ "/pub/bin"

Function file-directory-p filename

This function returns t if filename is the name of an existing directory, nil otherwise.

     (file-directory-p "~rms")
          ⇒ t
     (file-directory-p "~rms/lewis/files.texi")
          ⇒ nil
     (file-directory-p "~rms/lewis/no-such-file")
          ⇒ nil
     (file-directory-p "$HOME")
          ⇒ nil
     (file-directory-p
      (substitute-in-file-name "$HOME"))
          ⇒ t

Function file-regular-p filename

This function returns t if the file filename exists and is a regular file (not a directory, symbolic link, named pipe, terminal, or other I/O device).

22.6.3 Truenames

The truename of a file is the name that you get by following symbolic links until none remain, then expanding to get rid of ‘.’ and ‘..’ as components. Strictly speaking, a file need not have a unique truename; the number of distinct truenames a file has is equal to the number of hard links to the file. However, truenames are useful because they eliminate symbolic links as a cause of name variation.

Function file-truename filename

The function file-truename returns the true name of the file filename. This is the name that you get by following symbolic links until none remain. The argument must be an absolute file name.

See Section 24.4 [Buffer File Name], page 372, for related information.

22.6.4 Other Information about Files

This section describes the functions for getting detailed information about a file, other than its contents. This information includes the mode bits that control access permission, the owner and group numbers, the number of names, the inode number, the size, and the times of access and modification.

Function file-modes filename

This function returns the mode bits of filename, as an integer. The mode bits are also called the file permissions, and they specify access control in the usual Unix fashion. If the low-order bit is 1, then the file is executable by all users, if the second-lowest-order bit is 1, then the file is writable by all users, etc.

The highest value returnable is 4095 (7777 octal), meaning that everyone has read, write, and execute permission, that the suid bit is set for both others and group, and that the sticky bit is set.

     (file-modes "~/junk/diffs")

⇒ 492 ; Decimal integer.

     (format "%o" 492)

⇒ "754" ; Convert to octal.

     (set-file-modes "~/junk/diffs" 438)
          ⇒ nil
     (format "%o" 438)

⇒ "666" ; Convert to octal.

     % ls -l diffs
       -rw-rw-rw-  1 lewis 0 3063 Oct 30 16:00 diffs

Function file-nlinks filename

This functions returns the number of names (i.e., hard links) that file filename has. If the file does not exist, then this function returns nil. Note that symbolic links have no effect on this function, because they are not considered to be names of the files they link to.

     % ls -l foo*
     -rw-rw-rw-  2 rms       4 Aug 19 01:27 foo
     -rw-rw-rw-  2 rms       4 Aug 19 01:27 foo1
     (file-nlinks "foo")
          ⇒ 2
     (file-nlinks "doesnt-exist")
          ⇒ nil

Function file-attributes filename

This function returns a list of attributes of file filename. If the specified file cannot be opened, it returns nil. The elements of the list, in order, are:

0. t for a directory, a string for a symbolic link (the name linked to), or nil for a text file.

1. The number of names the file has. Alternate names, also known as hard links, can be created by using the add-name-to-file function (see Section 22.7 [Changing File Attributes], page 342).

2. The file’s uid.

3. The file’s gid.

4. The time of last access, as a list of two integers. The first integer has the high-order 16 bits of time, the second has the low 16 bits. (This is similar to the value of current-time; see Section 34.5 [Time of Day], page 553.)

5. The time of last modification as a list of two integers (as above).

6. The time of last status change as a list of two integers (as above).

7. The size of the file in bytes.

8. The file’s modes, as a string of ten letters or dashes, as in ‘ls -l’.

9. t if the file’s gid would change if file were deleted and recreated; nil otherwise.

10. The file’s inode number.

11. The file system number of the file system that the file is in. This element and the file’s inode number together give enough information to distinguish any two files on the system—no two files can have the same values for both of these numbers.

For example, here are the file attributes for ‘files.texi’:

(file-attributes "files.texi")
⇒ (nil
1
2235
75
(8489 20284)
(8489 20284)
(8489 20285)
14906
"-rw-rw-rw-"
nil
129500
-32252)

and here is how the result is interpreted: nil is neither a directory nor a symbolic link. 1 has only one name (the name ‘files.texi’ in the current default

directory).

2235 is owned by the user with uid 2235.

75 is in the group with gid 75.

(8489 20284)

was last accessed on Aug 19 00:09.

(8489 20284)

was last modified on Aug 19 00:09.

(8489 20285)

last had its inode changed on Aug 19 00:09.

14906 is 14906 characters long.

"-rw-rw-rw-"

has a mode of read and write access for the owner, group, and world.

nil would retain the same gid if it were recreated.

129500 has an inode number of 129500.

-32252 is on file system number -32252.

22.7 Changing File Names and Attributes

The functions in this section rename, copy, delete, link, and set the modes of files. In the functions that have an argument newname, if a file by the name of newname

already exists, the actions taken depend on the value of the argument ok-if-already-exists: • Signal a file-already-exists error if ok-if-already-exists is nil.

• Request confirmation if ok-if-already-exists is a number.

• Replace the old file without confirmation if ok-if-already-exists is any other value.

Function add-name-to-file oldname newname &optional

ok-if-already-exists This function gives the file named oldname the additional name newname. This means that newname becomes a new “hard link” to oldname. In the first part of the following example, we list two files, ‘foo’ and ‘foo3’.

     % ls -l fo*
     -rw-rw-rw-  1 rms       29 Aug 18 20:32 foo
     -rw-rw-rw-  1 rms       24 Aug 18 20:31 foo3

Now we create a hard link, by calling add-name-to-file, then list the files again. This shows two names for one file, ‘foo’ and ‘foo2’.

     (add-name-to-file "~/lewis/foo1" "~/lewis/foo2")
          ⇒ nil
     % ls -l fo*
     -rw-rw-rw-  2 rms       29 Aug 18 20:32 foo
     -rw-rw-rw-  2 rms       29 Aug 18 20:32 foo2
     -rw-rw-rw-  1 rms       24 Aug 18 20:31 foo3

Finally, we evaluate the following:

     (add-name-to-file "~/lewis/foo" "~/lewis/foo3" t)

and list the files again. Now there are three names for one file: ‘foo’, ‘foo2’, and ‘foo3’. The old contents of ‘foo3’ are lost.

     (add-name-to-file "~/lewis/foo1" "~/lewis/foo3")
          ⇒ nil
     % ls -l fo*
     -rw-rw-rw-  3 rms       29 Aug 18 20:32 foo
     -rw-rw-rw-  3 rms       29 Aug 18 20:32 foo2
     -rw-rw-rw-  3 rms       29 Aug 18 20:32 foo3

This function is meaningless on VMS, where multiple names for one file are not allowed. See also file-nlinks in Section 22.6.4 [File Attributes], page 340.

Command rename-file filename newname &optional ok-if-already-exists This command renames the file filename as newname. If filename has additional names aside from filename, it continues to have those names. In fact, adding the name newname with add-name-to-file and then deleting filename has the same effect as renaming, aside from momentary intermediate states. In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.

Command copy-file oldname newname &optional ok-if-exists time This command copies the file oldname to newname. An error is signaled if oldname does not exist. If time is non-nil, then this functions gives the new file the same last-modified time that the old one has. (This works on only some operating systems.) In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.

Command delete-file filename

This command deletes the file filename, like the shell command ‘rm filename’. If the file has multiple names, it continues to exist under the other names. A suitable kind of file-error error is signaled if the file does not exist, or is not deletable. (On Unix, a file is deletable if its directory is writable.) See also delete-directory in Section 22.10 [Create/Delete Dirs], page 352.

Command make-symbolic-link filename newname &optional ok-if-exists This command makes a symbolic link to filename, named newname. This is like the shell command ‘ln -s filename newname’. In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.

Function define-logical-name varname string

This function defines the logical name name to have the value string. It is available only on VMS.

Function set-file-modes filename mode

This function sets mode bits of filename to mode (which must be an integer).

Only the low 12 bits of mode are used.

Function set-default-file-modes mode

This function sets the default file protection for new files created by Emacs and its subprocesses. Every file created with Emacs initially has this protection. On Unix, the default protection is the bitwise complement of the “umask” value. The argument mode must be an integer. Only the low 9 bits of mode are used. Saving a modified version of an existing file does not count as creating the file; it does not change the file’s mode, and does not use the default file protection.

Function default-file-modes

This function returns the current default protection value.

On MS-DOS, there is no such thing as an “executable” file mode bit. So Emacs considers a file executable if its name ends in ‘.com’, ‘.bat’ or ‘.exe’. This is reflected in the values

returned by file-modes and file-attributes.

22.8 File Names

Files are generally referred to by their names, in Emacs as elsewhere. File names in Emacs are represented as strings. The functions that operate on a file all expect a file name argument.

In addition to operating on files themselves, Emacs Lisp programs often need to operate on the names; i.e., to take them apart and to use part of a name to construct related file names. This section describes how to manipulate file names.

The functions in this section do not actually access files, so they can operate on file names that do not refer to an existing file or directory.

On VMS, all these functions understand both VMS file-name syntax and Unix syntax. This is so that all the standard Lisp libraries can specify file names in Unix syntax and work properly on VMS without change. On MS-DOS, these functions understand MS-DOS file-name syntax as well as Unix syntax.

22.8.1 File Name Components

The operating system groups files into directories. To specify a file, you must specify the directory and the file’s name within that directory. Therefore, Emacs considers a file name as having two main parts: the directory name part, and the nondirectory part (or file name within the directory). Either part may be empty. Concatenating these two parts reproduces the original file name.

On Unix, the directory part is everything up to and including the last slash; the nondirectory part is the rest. The rules in VMS syntax are complicated.

For some purposes, the nondirectory part is further subdivided into the name proper and the version number. On Unix, only backup files have version numbers in their names; on VMS, every file has a version number, but most of the time the file name actually used in Emacs omits the version number. Version numbers are found mostly in directory lists.

Function file-name-directory filename

This function returns the directory part of filename (or nil if filename does not include a directory part). On Unix, the function returns a string ending in a slash. On VMS, it returns a string ending in one of the three characters ‘:’, ‘]’, or ‘>’.

(file-name-directory "lewis/foo")  ; Unix example
     ⇒ "lewis/"
(file-name-directory "foo")        ; Unix example
     ⇒ nil
(file-name-directory "[X]FOO.TMP") ; VMS example
     ⇒ "[X]"

Function file-name-nondirectory filename

This function returns the nondirectory part of filename.

(file-name-nondirectory "lewis/foo")
     ⇒ "foo"
(file-name-nondirectory "foo")
     ⇒ "foo"

;; The following example is accurate only on VMS.

(file-name-nondirectory "[X]FOO.TMP")
     ⇒ "FOO.TMP"

Function file-name-sans-versions filename

This function returns filename without any file version numbers, backup version numbers, or trailing tildes.

(file-name-sans-versions "~rms/foo.~1~")
     ⇒ "~rms/foo"
(file-name-sans-versions "~rms/foo~")
     ⇒ "~rms/foo"
(file-name-sans-versions "~rms/foo")
     ⇒ "~rms/foo"

;; The following example applies to VMS only.

(file-name-sans-versions "foo;23")
     ⇒ "foo"

Function file-name-sans-extension filename

This function returns filename minus its “extension,” if any. The extension, in a file name, is the part that starts with the last ‘.’ in the last name component. For example,

(file-name-sans-extension "foo.lose.c")
     ⇒ "foo.lose"
(file-name-sans-extension "big.hack/foo")
     ⇒ "big.hack/foo"

22.8.2 Directory Names

A directory name is the name of a directory. A directory is a kind of file, and it has a file name, which is related to the directory name but not identical to it. (This is not quite the same as the usual Unix terminology.) These two different names for the same entity are related by a syntactic transformation. On Unix, this is simple: a directory name ends in a slash, whereas the directory’s name as a file lacks that slash. On VMS, the relationship is more complicated.

The difference between a directory name and its name as a file is subtle but crucial. When an Emacs variable or function argument is described as being a directory name, a file name of a directory is not acceptable.

The following two functions convert between directory names and file names. They do nothing special with environment variable substitutions such as ‘$HOME’, and the constructs ‘~’, and ‘..’.

Function file-name-as-directory filename

This function returns a string representing filename in a form that the operating system will interpret as the name of a directory. In Unix, this means appending a slash to the string. On VMS, the function converts a string of the form

‘[X]Y.DIR.1’ to the form ‘[X.Y]’.
     (file-name-as-directory "~rms/lewis")
          ⇒ "~rms/lewis/"

Function directory-file-name dirname

This function returns a string representing dirname in a form that the operating system will interpret as the name of a file. On Unix, this means removing a final slash from the string. On VMS, the function converts a string of the form

‘[X.Y]’ to ‘[X]Y.DIR.1’.
     (directory-file-name "~lewis/")
          ⇒ "~lewis"

Directory name abbreviations are useful for directories that are normally accessed through symbolic links. Sometimes the users recognize primarily the link’s name as “the name” of the directory, and find it annoying to see the directory’s “real” name. If you define the link name as an abbreviation for the “real” name, Emacs shows users the abbreviation instead.

Variable directory-abbrev-alist

The variable directory-abbrev-alist contains an alist of abbreviations to use for file directories. Each element has the form (from . to), and says to replace from with to when it appears in a directory name. The from string is actually a regular expression; it should always start with ‘^’. The function abbreviate-file-name performs these substitutions. You can set this variable in ‘site-init.el’ to describe the abbreviations appropriate for your site. Here’s an example, from a system on which file system ‘/home/fsf’ and so on are normally accessed through symbolic links named ‘/fsf’ and so on.

     (("^/home/fsf" . "/fsf")
      ("^/home/gp" . "/gp")
      ("^/home/gd" . "/gd"))

To convert a directory name to its abbreviation, use this function:

Function abbreviate-file-name dirname

This function applies abbreviations from directory-abbrev-alist to its argument, and substitutes ‘~’ for the user’s home directory.

22.8.3 Absolute and Relative File Names

All the directories in the file system form a tree starting at the root directory. A file name can specify all the directory names starting from the root of the tree; then it is called an absolute file name. Or it can specify the position of the file in the tree relative to a default directory; then it is called a relative file name. On Unix, an absolute file name starts with a slash or a tilde (‘~’), and a relative one does not. The rules on VMS are complicated.

Function file-name-absolute-p filename

This function returns t if file filename is an absolute file name, nil otherwise.

On VMS, this function understands both Unix syntax and VMS syntax.

          (file-name-absolute-p "~rms/foo")
               ⇒ t
          (file-name-absolute-p "rms/foo")
               ⇒ nil
          (file-name-absolute-p "/user/rms/foo")
               ⇒ t

22.8.4 Functions that Expand Filenames

Expansion of a file name means converting a relative file name to an absolute one. Since this is done relative to a default directory, you must specify the default directory name as well as the file name to be expanded. Expansion also simplifies file names by eliminating redundancies such as ‘./’ and ‘name/../’.

Function expand-file-name filename &optional directory This function converts filename to an absolute file name. If directory is supplied, it is the directory to start with if filename is relative. (The value of directory should itself be an absolute directory name; it may start with ‘~’.) Otherwise, the current buffer’s value of default-directory is used. For example:

          (expand-file-name "foo")
               ⇒ "/xcssun/users/rms/lewis/foo"
          (expand-file-name "../foo")
               ⇒ "/xcssun/users/rms/foo"
          (expand-file-name "foo" "/usr/spool/")
               ⇒ "/usr/spool/foo"
          (expand-file-name "$HOME/foo")
               ⇒ "/xcssun/users/rms/lewis/$HOME/foo"

Filenames containing ‘.’ or ‘..’ are simplified to their canonical form:

     (expand-file-name "bar/../foo")
          ⇒ "/xcssun/users/rms/lewis/foo"

‘~/’ is expanded into the user’s home directory. A ‘/’ or ‘~’ following a ‘/’ is taken to be the start of an absolute file name that overrides what precedes it, so everything before that ‘/’ or ‘~’ is deleted. For example:

     (expand-file-name
      "/a1/gnu//usr/local/lib/emacs/etc/MACHINES")
          ⇒ "/usr/local/lib/emacs/etc/MACHINES"
     (expand-file-name "/a1/gnu/~/foo")
          ⇒ "/xcssun/users/rms/foo"

In both cases, ‘/a1/gnu/’ is discarded because an absolute file name follows it. Note that expand-file-name does not expand environment variables; only

substitute-in-file-name does that.

Function file-relative-name filename directory

This function does the inverse of expansion—it tries to return a relative name that is equivalent to filename when interpreted relative to directory. (If such a relative name would be longer than the absolute name, it returns the absolute name instead.)

     (file-relative-name "/foo/bar" "/foo/")
          ⇒ "bar")
     (file-relative-name "/foo/bar" "/hack/")
          ⇒ "/foo/bar")

Variable default-directory

The value of this buffer-local variable is the default directory for the current buffer. It should be an absolute directory name; it may start with ‘~’. This variable is local in every buffer. expand-file-name uses the default directory when its second argument is nil. On Unix systems, the value is always a string ending with a slash.

     default-directory
          ⇒ "/user/lewis/manual/"

Function substitute-in-file-name filename

This function replaces environment variables references in filename with the environment variable values. Following standard Unix shell syntax, ‘$’ is the prefix to substitute an environment variable value. The environment variable name is the series of alphanumeric characters (including underscores) that follow the ‘$’. If the character following the ‘$’ is a ‘{’, then the variable name is everything up to the matching ‘}’. Here we assume that the environment variable HOME, which holds the user’s home directory name, has value ‘/xcssun/users/rms’.

     (substitute-in-file-name "$HOME/foo")
          ⇒ "/xcssun/users/rms/foo"

If a ‘~’ or a ‘/’ appears following a ‘/’, after substitution, everything before the following ‘/’ is discarded:

     (substitute-in-file-name "bar/~/foo")
          ⇒ "~/foo"
     (substitute-in-file-name "/usr/local/$HOME/foo")
          ⇒ "/xcssun/users/rms/foo"

On VMS, ‘$’ substitution is not done, so this function does nothing on VMS except discard superfluous initial components as shown above.

22.8.5 Generating Unique File Names

Some programs need to write temporary files. Here is the usual way to construct a name for such a file:

(make-temp-name (concat "/tmp/" name-of-application))

Here we use the directory ‘/tmp/’ because that is the standard place on Unix for temporary files. The job of make-temp-name is to prevent two different users or two different jobs from trying to use the same name.

Function make-temp-name string

This function generates string that can be used as a unique name. The name starts with string, and ends with a number that is different in each Emacs job.

     (make-temp-name "/tmp/foo")
          ⇒ "/tmp/foo021304"

To prevent conflicts among different libraries running in the same Emacs, each Lisp program that uses make-temp-name should have its own string. The number added to the end of the name distinguishes between the same application running in different Emacs jobs.

22.8.6 File Name Completion

This section describes low-level subroutines for completing a file name. For other completion functions, see Section 17.5 [Completion], page 228.

Function file-name-all-completions partial-filename directory

This function returns a list of all possible completions for a file whose name starts with partial-filename in directory directory. The order of the completions is the order of the files in the directory, which is unpredictable and conveys no useful information. The argument partial-filename must be a file name containing no directory part and no slash. The current buffer’s default directory is prepended to directory, if directory is not absolute. In the following example, suppose that ‘~rms/lewis’ is the current default directory, and has five files whose names begin with ‘f’: ‘foo’, ‘file~’, ‘file.c’,

‘file.c.~1~’, and ‘file.c.~2~’.
     (file-name-all-completions "f" "")
          ⇒ ("foo" "file~" "file.c.~2~"
                     "file.c.~1~" "file.c")
     (file-name-all-completions "fo" "")
          ⇒ ("foo")

Function file-name-completion filename directory

This function completes the file name filename in directory directory. It returns the longest prefix common to all file names in directory directory that start with filename. If only one match exists and filename matches it exactly, the function returns t. The function returns nil if directory directory contains no name starting with filename. In the following example, suppose that the current default directory has five files whose names begin with ‘f’: ‘foo’, ‘file~’, ‘file.c’, ‘file.c.~1~’, and

‘file.c.~2~’.
     (file-name-completion "fi" "")
          ⇒ "file"
     (file-name-completion "file.c.~1" "")
          ⇒ "file.c.~1~"
     (file-name-completion "file.c.~1~" "")
          ⇒ t
     (file-name-completion "file.c.~3" "")
          ⇒ nil

User Option completion-ignored-extensions

file-name-completion usually ignores file names that end in any string in this list. It does not ignore them when all the possible completions end in one of these suffixes or when a buffer showing all possible completions is displayed. A typical value might look like this:

     completion-ignored-extensions
          ⇒ (".o" ".elc" "~" ".dvi")

22.8.7 Standard File Names

Most of the file names used in Lisp programs are entered by the user. But occasionally a Lisp program needs to specify a standard file name for a particular use—typically, to hold customization information about each user. For example, abbrev definitions are stored (by default) in the file ‘~/.abbrev_defs’; the completion package stores completions in the file ‘~/.completions’. These are two of the many standard file names used by parts of Emacs for certain purposes.

Various operating systems have their own conventions for valid file names and for which file names to use for user profile data. A Lisp program which reads a file using a standard file name ought to use, on each type of system, a file name suitable for that system. The function convert-standard-filename makes this easy to do.

Function convert-standard-filename filename

This function alters the file name filename to fit the conventions of the operating system in use, and returns the result as a new string.

The recommended way to specify a standard file name in a Lisp program is to choose a name which fits the conventions of GNU and Unix systems, usually with a nondirectory part that starts with a period, and pass it to convert-standard-filename instead of using it directly. Here is an example from the completion package:

(defvar save-completions-file-name
        (convert-standard-filename "~/.completions")
  "*The file name to save completions to.")

On GNU and Unix systems, and on some other systems as well, convert-standard-filename returns its argument unchanged. On some other systems, it alters the name to fit the systems’s conventions.

For example, on MS-DOS the alterations made by this function include converting a leading ‘.’ to ‘_’, converting a ‘_’ in the middle of the name to ‘.’ if there is no other ‘.’, inserting a ‘.’ after eight characters if there is none, and truncating to three characters after the ‘.’. (It makes other changes as well.) Thus, ‘.abbrev_defs’ becomes ‘_abbrev.def’,

and ‘.completions’ becomes ‘_complet.ion’.

22.9 Contents of Directories

A directory is a kind of file that contains other files entered under various names. Directories are a feature of the file system.

Emacs can list the names of the files in a directory as a Lisp list, or display the names in a buffer using the ls shell command. In the latter case, it can optionally display information about each file, depending on the options passed to the ls command.

Function directory-files directory &optional full-name match-regexp nosort This function returns a list of the names of the files in the directory directory. By default, the list is in alphabetical order.

If full-name is non-nil, the function returns the files’ absolute file names. Otherwise, it returns the names relative to the specified directory.

If match-regexp is non-nil, this function returns only those file names that contain a match for that regular expression—the other file names are excluded from the list.

If nosort is non-nil, directory-files does not sort the list, so you get the file names in no particular order. Use this if you want the utmost possible speed and don’t care what order the files are processed in. If the order of processing is visible to the user, then the user will probably be happier if you do sort the names.

     (directory-files "~lewis")
          ⇒ ("#foo#" "#foo.el#" "." ".."
              "dired-mods.el" "files.texi"
              "files.texi.~1~")

An error is signaled if directory is not the name of a directory that can be read.

Function file-name-all-versions file dirname

This function returns a list of all versions of the file named file in directory dirname.

Function insert-directory file switches &optional wildcard full-directory-p This function inserts (in the current buffer) a directory listing for directory file, formatted with ls according to switches. It leaves point after the inserted text. The argument file may be either a directory name or a file specification including wildcard characters. If wildcard is non-nil, that means treat file as a file specification with wildcards. If full-directory-p is non-nil, that means file is a directory and switches do not contain ‘-d’, so that the listing should show the full contents of the directory. (The ‘-d’ option to ls says to describe a directory itself rather than its contents.) This function works by running a directory listing program whose name is in the variable insert-directory-program. If wildcard is non-nil, it also runs the shell specified by shell-file-name, to expand the wildcards.

Variable insert-directory-program

This variable’s value is the program to run to generate a directory listing for

the function insert-directory.

22.10 Creating and Deleting Directories

Most Emacs Lisp file-manipulation functions get errors when used on files that are directories. For example, you cannot delete a directory with delete-file. These special functions exist to create and delete directories.

Function make-directory dirname

This function creates a directory named dirname.

Function delete-directory dirname

This function deletes the directory named dirname. The function delete-file does not work for files that are directories; you must use delete-directory for them. If the directory contains any files, delete-directory signals an error.

22.11 Making Certain File Names “Magic”

You can implement special handling for certain file names. This is called making those names magic. You must supply a regular expression to define the class of names (all those that match the regular expression), plus a handler that implements all the primitive Emacs file operations for file names that do match.

The variable file-name-handler-alist holds a list of handlers, together with regular expressions that determine when to apply each handler. Each element has this form:

(regexp . handler) All the Emacs primitives for file access and file name transformation check the given file name against file-name-handler-alist. If the file name matches regexp, the primitives handle that file by calling handler.

The first argument given to handler is the name of the primitive; the remaining arguments are the arguments that were passed to that operation. (The first of these arguments is typically the file name itself.) For example, if you do this:

     (file-exists-p filename)

and filename has handler handler, then handler is called like this:

     (funcall handler 'file-exists-p filename)

Here are the operations that a magic file name handler gets to handle:

add-name-to-file, copy-file, delete-directory, delete-file,
diff-latest-backup-file, directory-file-name, directory-files,
dired-call-process, dired-compress-file, dired-uncache, expand-file-name,
file-accessible-directory-p, file-attributes, file-directory-p,
file-executable-p, file-exists-p, file-local-copy, file-modes, file-name-all-
completions, file-name-as-directory, file-name-completion,
file-name-directory, file-name-nondirectory, file-name-sans-versions, file-
newer-than-file-p, file-ownership-preserved-p, file-readable-p, file-regular-
p, file-symlink-p, file-truename, file-writable-p, find-backup-file-name, get-
file-buffer, insert-directory,
insert-file-contents, load, make-directory, make-symbolic-link, rename-file,
set-file-modes, set-visited-file-modtime, shell-command. unhandled-file-name-
directory,
vc-registered, verify-visited-file-modtime, write-region.

Handlers for insert-file-contents typically need to clear the buffer’s modified flag, with (set-buffer-modified-p nil), if the visit argument is non-nil. This also has the effect of unlocking the buffer if it is locked.

The handler function must handle all of the above operations, and possibly others to be added in the future. It need not implement all these operations itself—when it has nothing special to do for a certain operation, it can reinvoke the primitive, to handle the operation “in the usual way”. It should always reinvoke the primitive for an operation it does not recognize. Here’s one way to do this:

     (defun my-file-handler (operation &rest args)

;; First check for the specific operations ;; that we have special handling for.

       (cond ((eq operation 'insert-file-contents) . . .)
             ((eq operation 'write-region) . . .)

…

;; Handle any operation we don’t know about.

             (t (let ((inhibit-file-name-handlers
                      (cons 'my-file-handler
                            (and (eq inhibit-file-name-operation operation)
                                 inhibit-file-name-handlers)))
                     (inhibit-file-name-operation operation))
                  (apply operation args)))))

When a handler function decides to call the ordinary Emacs primitive for the operation at hand, it needs to prevent the primitive from calling the same handler once again, thus leading to an infinite recursion. The example above shows how to do this, with the vari-

ables inhibit-file-name-handlers and inhibit-file-name-operation. Be careful to

use them exactly as shown above; the details are crucial for proper behavior in the case of multiple handlers, and for operations that have two file names that may each have handlers.

Variable inhibit-file-name-handlers

This variable holds a list of handlers whose use is presently inhibited for a certain operation.

Variable inhibit-file-name-operation

The operation for which certain handlers are presently inhibited.

Function find-file-name-handler file operation

This function returns the handler function for file name file, or nil if there is none. The argument operation should be the operation to be performed on the file—the value you will pass to the handler as its first argument when you call it. The operation is needed for comparison with inhibit-file-name-operation.

Function file-local-copy filename

This function copies file filename to an ordinary non-magic file, if it isn’t one already. If filename specifies a “magic” file name, which programs outside Emacs cannot directly read or write, this copies the contents to an ordinary file and returns that file’s name. If filename is an ordinary file name, not magic, then this function does nothing and returns nil.

Function unhandled-file-name-directory filename

This function returns the name of a directory that is not magic. It uses the directory part of filename if that is not magic. Otherwise, it asks the handler what to do. This is useful for running a subprocess; every subprocess must have a non-magic directory to serve as its current directory, and this function is a good way to come up with one.

22.12 File Format Conversion

The variable format-alist defines a list of file formats, which describe textual representations used in files for the data (text, text-properties, and possibly other information) in an Emacs buffer. Emacs performs format conversion if appropriate when reading and writing files.

Variable format-alist

This list contains one format definition for each defined file format.

Each format definition is a list of this form:

(name doc-string regexp from-fn to-fn modify mode-fn) Here is what the elements in a format definition mean:

name The name of this format.

doc-string A documentation string for the format.

regexp A regular expression which is used to recognize files represented in this format. from-fn A function to call to decode data in this format (to convert file data into the

usual Emacs data representation).

The from-fn is called with two args, begin and end, which specify the part of the buffer it should convert. It should convert the text by editing it in place. Since this can change the length of the text, from-fn should return the modified end position. One responsibility of from-fn is to make sure that the beginning of the file no longer matches regexp. Otherwise it is likely to get called again.

to-fn A function to call to encode data in this format (to convert the usual Emacs data representation into this format). The to-fn is called with two args, begin and end, which specify the part of the buffer it should convert. There are two ways it can do the conversion:

• By editing the buffer in place. In this case, to-fn should return the endposition of the range of text, as modified.

• By returning a list of annotations. This is a list of elements of the form (position . string), where position is an integer specifying the relative position in the text to be written, and string is the annotation to add there. The list must be sorted in order of position when to-fn returns it. When write-region actually writes the text from the buffer to the file, it intermixes the specified annotations at the corresponding positions. All this takes place without modifying the buffer.

modify A flag, t if the encoding function modifies the buffer, and nil if it works by returning a list of annotations.

mode A mode function to call after visiting a file converted from this format.

The function insert-file-contents automatically recognizes file formats when it reads the specified file. It checks the text of the beginning of the file against the regular expressions of the format definitions, and if it finds a match, it calls the decoding function for that format. Then it checks all the known formats over again. It keeps checking them until none of them is applicable.

Visiting a file, with find-file-noselect or the commands that use it, performs conversion likewise (because it calls insert-file-contents); it also calls the mode function for each format that it decodes. It stores a list of the format names in the buffer-local variable

buffer-file-format.

Variable buffer-file-format

This variable states the format of the visited file. More precisely, this is a list of the file format names that were decoded in the course of visiting the current buffer’s file. It is always local in all buffers.

When write-region writes data into a file, it first calls the encoding functions for the formats listed in buffer-file-format, in the order of appearance in the list.

Function format-write-file file format

This command writes the current buffer contents into the file file in format format, and makes that format the default for future saves of the buffer. The argument format is a list of format names.

Function format-find-file file format

This command finds the file file, converting it according to format format. It also makes format the default if the buffer is saved later. The argument format is a list of format names. If format is nil, no conversion takes place. Interactively, typing just ^{⟨}\underline{\overline{RET}}^{⟩} for format specifies nil.

Function format-insert-file file format %optional beg end This command inserts the contents of file file, converting it according to format format. If beg and end are non-nil, they specify which part of the file to read, as in insert-file-contents (see Section 22.3 [Reading from Files], page 334). The return value is like what insert-file-contents returns: a list of the absolute file name and the length of the data inserted (after conversion). The argument format is a list of format names. If format is nil, no conversion takes place. Interactively, typing just ^{⟨}\underline{\overline{RET}}^{⟩} for format specifies nil.

Variable auto-save-file-format

This variable specifies the format to use for auto-saving. Its value is a list of format names, just like the value of buffer-file-format; but it is used instead of buffer-file-format for writing auto-save files. This variable is always local in all buffers.

22.13 Files and MS-DOS

Emacs on MS-DOS and on Windows NT or 95 makes a distinction between text files and binary files. This is necessary because ordinary text files on MS-DOS use a two character sequence between lines: carriage-return and linefeed (crlf). Emacs expects just a newline character (a linefeed) between lines. When Emacs reads or writes a text file on MS-DOS, it needs to convert the line separators. This means it needs to know which files are text files and which are binary. It makes this decision when visiting a file, and records the decision in the variable buffer-file-type for use when the file is saved.

See Section 33.3 [MS-DOS Subprocesses], page 529, for a related feature for subprocesses.

Variable buffer-file-type

This variable, automatically local in each buffer, records the file type of the buffer’s visited file. The value is nil for text, t for binary.

Function find-buffer-file-type filename

This function determines whether file filename is a text file or a binary file. It returns nil for text, t for binary.

User Option file-name-buffer-file-type-alist

This variable holds an alist for distinguishing text files from binary files. Each element has the form (regexp . type), where regexp is matched against the file name, and type may be is nil for text, t for binary, or a function to call to compute which. If it is a function, then it is called with a single argument (the file name) and should return t or nil.

User Option default-buffer-file-type

This variable specifies the default file type for files whose names don’t indicate anything in particular. Its value should be nil for text, or t for binary.

Command find-file-text filename

Like find-file, but treat the file as text regardless of its name.

Command find-file-binary filename

Like find-file, but treat the file as binary regardless of its name.

358 GNU Emacs Lisp Reference Manual

23 Backups and Auto-Saving

Backup files and auto-save files are two methods by which Emacs tries to protect the user from the consequences of crashes or of the user’s own errors. Auto-saving preserves the text from earlier in the current editing session; backup files preserve file contents prior to the current session.

23.1 Backup Files

A backup file is a copy of the old contents of a file you are editing. Emacs makes a backup file the first time you save a buffer into its visited file. Normally, this means that the backup file contains the contents of the file as it was before the current editing session. The contents of the backup file normally remain unchanged once it exists.

Backups are usually made by renaming the visited file to a new name. Optionally, you can specify that backup files should be made by copying the visited file. This choice makes a difference for files with multiple names; it also can affect whether the edited file remains owned by the original owner or becomes owned by the user editing it.

By default, Emacs makes a single backup file for each file edited. You can alternatively request numbered backups; then each new backup file gets a new name. You can delete old numbered backups when you don’t want them any more, or Emacs can delete them automatically.

23.1.1 Making Backup Files

Function backup-buffer

This function makes a backup of the file visited by the current buffer, if appropriate. It is called by save-buffer before saving the buffer the first time.

Variable buffer-backed-up

This buffer-local variable indicates whether this buffer’s file has been backed up on account of this buffer. If it is non-nil, then the backup file has been written. Otherwise, the file should be backed up when it is next saved (if backups are enabled). This is a permanent local; kill-local-variables does not alter it.

User Option make-backup-files

This variable determines whether or not to make backup files. If it is nonnil, then Emacs creates a backup of each file when it is saved for the first time—provided that backup-inhibited is nil (see below). The following example shows how to change the make-backup-files variable only in the ‘RMAIL’ buffer and not elsewhere. Setting it nil stops Emacs from making backups of the ‘RMAIL’ file, which may save disk space. (You would put this code in your ‘.emacs’ file.)

          (add-hook 'rmail-mode-hook
                    (function (lambda ()
                                (make-local-variable
                                 'make-backup-files)
                                (setq make-backup-files nil))))

Variable backup-enable-predicate

This variable’s value is a function to be called on certain occasions to decide whether a file should have backup files. The function receives one argument, a file name to consider. If the function returns nil, backups are disabled for that file. Otherwise, the other variables in this section say whether and how to make backups. The default value is this:

     (lambda (name)
       (or (< (length name) 5)
           (not (string-equal "/tmp/"
                              (substring name 0 5)))))

Variable backup-inhibited

If this variable is non-nil, backups are inhibited. It records the result of testing backup-enable-predicate on the visited file name. It can also coherently be used by other mechanisms that inhibit backups based on which file is visited. For example, VC sets this variable non-nil to prevent making backups for files managed with a version control system. This is a permanent local, so that changing the major mode does not lose its value. Major modes should not set this variable—they should set make-backup-files instead.

23.1.2 Backup by Renaming or by Copying?

There are two ways that Emacs can make a backup file:

• Emacs can rename the original file so that it becomes a backup file, and then write the buffer being saved into a new file. After this procedure, any other names (i.e., hard links) of the original file now refer to the backup file. The new file is owned by the user doing the editing, and its group is the default for new files written by the user in that directory.

• Emacs can copy the original file into a backup file, and then overwrite the original file with new contents. After this procedure, any other names (i.e., hard links) of the original file still refer to the current version of the file. The file’s owner and group will be unchanged.

The first method, renaming, is the default. The variable backup-by-copying, if non-nil, says to use the second method, which is

to copy the original file and overwrite it with the new buffer contents. The variable fileprecious-flag, if non-nil, also has this effect (as a sideline of its main significance). See Section 22.2 [Saving Buffers], page 332.

Variable backup-by-copying

If this variable is non-nil, Emacs always makes backup files by copying.

The following two variables, when non-nil, cause the second method to be used in certain special cases. They have no effect on the treatment of files that don’t fall into the special cases.

Variable backup-by-copying-when-linked

If this variable is non-nil, Emacs makes backups by copying for files with multiple names (hard links). This variable is significant only if backup-by-copying is nil, since copying is always used when that variable is non-nil.

Variable backup-by-copying-when-mismatch

If this variable is non-nil, Emacs makes backups by copying in cases where renaming would change either the owner or the group of the file. The value has no effect when renaming would not alter the owner or group of the file; that is, for files which are owned by the user and whose group matches the default for a new file created there by the user. This variable is significant only if backup-by-copying is nil, since copying is always used when that variable is non-nil.

23.1.3 Making and Deleting Numbered Backup Files

If a file’s name is ‘foo’, the names of its numbered backup versions are ‘foo.~v~’, for various integers v, like this: ‘foo.~1~’, ‘foo.~2~’, ‘foo.~3~’, …, ‘foo.~259~’, and so on.

User Option version-control

This variable controls whether to make a single non-numbered backup file or multiple numbered backups.

nil Make numbered backups if the visited file already has numbered backups; otherwise, do not.

never Do not make numbered backups.

anything else Make numbered backups.

The use of numbered backups ultimately leads to a large number of backup versions, which must then be deleted. Emacs can do this automatically or it can ask the user whether to delete them.

User Option kept-new-versions

The value of this variable is the number of newest versions to keep when a new numbered backup is made. The newly made backup is included in the count. The default value is 2.

User Option kept-old-versions

The value of this variable is the number of oldest versions to keep when a new numbered backup is made. The default value is 2.

If there are backups numbered 1, 2, 3, 5, and 7, and both of these variables have the value 2, then the backups numbered 1 and 2 are kept as old versions and those numbered 5 and 7 are kept as new versions; backup version 3 is excess. The function find-backup-file-name (see Section 23.1.4 [Backup Names], page 362) is responsible for determining which backup versions to delete, but does not delete them itself.

User Option trim-versions-without-asking

If this variable is non-nil, then saving a file deletes excess backup versions silently. Otherwise, it asks the user whether to delete them.

User Option dired-kept-versions

This variable specifies how many of the newest backup versions to keep in the Dired command . (dired-clean-directory). That’s the same thing keptnew-versions specifies when you make a new backup file. The default value is 2.

23.1.4 Naming Backup Files

The functions in this section are documented mainly because you can customize the naming conventions for backup files by redefining them. If you change one, you probably need to change the rest.

Function backup-file-name-p filename

This function returns a non-nil value if filename is a possible name for a backup file. A file with the name filename need not exist; the function just checks the name.

     (backup-file-name-p "foo")
          ⇒ nil
     (backup-file-name-p "foo~")
          ⇒ 3

The standard definition of this function is as follows:

     (defun backup-file-name-p (file)
       "Return non-nil if FILE is a backup file \
     name (numeric or not)..."
       (string-match "~$" file))

Thus, the function returns a non-nil value if the file name ends with a ‘~’. (We use a backslash to split the documentation string’s first line into two lines in the text, but produce just one line in the string itself.) This simple expression is placed in a separate function to make it easy to redefine for customization.

Function make-backup-file-name filename

This function returns a string that is the name to use for a non-numbered backup file for file filename. On Unix, this is just filename with a tilde appended. The standard definition of this function is as follows:

     (defun make-backup-file-name (file)
       "Create the non-numeric backup file name for FILE.

…"

       (concat file "~"))

You can change the backup-file naming convention by redefining this function. The following example redefines make-backup-file-name to prepend a ‘.’ in addition to appending a tilde:

     (defun make-backup-file-name (filename)
       (concat "." filename "~"))
     (make-backup-file-name "backups.texi")
          ⇒ ".backups.texi~"

Function find-backup-file-name filename

This function computes the file name for a new backup file for filename. It may also propose certain existing backup files for deletion. find-backup-file-name returns a list whose car is the name for the new backup file and whose cdr is a list of backup files whose deletion is proposed.

Two variables, kept-old-versions and kept-new-versions, determine which

backup versions should be kept. This function keeps those versions by excluding them from the cdr of the value. See Section 23.1.3 [Numbered Backups], page 361. In this example, the value says that ‘~rms/foo.~5~’ is the name to use for the new backup file, and ‘~rms/foo.~3~’ is an “excess” version that the caller should consider deleting now.

     (find-backup-file-name "~rms/foo")
          ⇒ ("~rms/foo.~5~" "~rms/foo.~3~")

Function file-newest-backup filename

This function returns the name of the most recent backup file for filename, or nil if that file has no backup files. Some file comparison commands use this function so that they can automatically compare a file with its most recent backup.

23.2 Auto-Saving

Emacs periodically saves all files that you are visiting; this is called auto-saving. Autosaving prevents you from losing more than a limited amount of work if the system crashes. By default, auto-saves happen every 300 keystrokes, or after around 30 seconds of idle time. See section “Auto-Saving: Protection Against Disasters” in The GNU Emacs Manual, for information on auto-save for users. Here we describe the functions used to implement auto-saving and the variables that control them.

Variable buffer-auto-save-file-name

This buffer-local variable is the name of the file used for auto-saving the current buffer. It is nil if the buffer should not be auto-saved.

     buffer-auto-save-file-name
     => "/xcssun/users/rms/lewis/#files.texi#"

Command auto-save-mode arg

When used interactively without an argument, this command is a toggle switch: it turns on auto-saving of the current buffer if it is off, and vice-versa. With an argument arg, the command turns auto-saving on if the value of arg is t, a nonempty list, or a positive integer. Otherwise, it turns auto-saving off.

Function auto-save-file-name-p filename

This function returns a non-nil value if filename is a string that could be the name of an auto-save file. It works based on knowledge of the naming convention for auto-save files: a name that begins and ends with hash marks (‘#’) is a possible auto-save file name. The argument filename should not contain a directory part.

     (make-auto-save-file-name)
          ⇒ "/xcssun/users/rms/lewis/#files.texi#"
     (auto-save-file-name-p "#files.texi#")
          ⇒ 0
     (auto-save-file-name-p "files.texi")
          ⇒ nil

The standard definition of this function is as follows:

     (defun auto-save-file-name-p (filename)
       "Return non-nil if FILENAME can be yielded by..."
       (string-match "^#.*#$" filename))

This function exists so that you can customize it if you wish to change the naming convention for auto-save files. If you redefine it, be sure to redefine the

function make-auto-save-file-name correspondingly.

Function make-auto-save-file-name

This function returns the file name to use for auto-saving the current buffer. This is just the file name with hash marks (‘#’) appended and prepended to it. This function does not look at the variable auto-save-visited-file-name (described below); you should check that before calling this function.

     (make-auto-save-file-name)
          ⇒ "/xcssun/users/rms/lewis/#backup.texi#"

The standard definition of this function is as follows:

     (defun make-auto-save-file-name ()
       "Return file name to use for auto-saves \
     of current buffer.

…"

       (if buffer-file-name
           (concat
            (file-name-directory buffer-file-name)
            "#"
            (file-name-nondirectory buffer-file-name)
            "#")
         (expand-file-name
          (concat "#%" (buffer-name) "#"))))

This exists as a separate function so that you can redefine it to customize the naming convention for auto-save files. Be sure to change auto-save-file-name-p in a corresponding way.

Variable auto-save-visited-file-name

If this variable is non-nil, Emacs auto-saves buffers in the files they are visiting. That is, the auto-save is done in the same file that you are editing. Normally, this variable is nil, so auto-save files have distinct names that are created by

make-auto-save-file-name.

When you change the value of this variable, the value does not take effect until the next time auto-save mode is reenabled in any given buffer. If auto-save mode is already enabled, auto-saves continue to go in the same file name until

auto-save-mode is called again.

Function recent-auto-save-p

This function returns t if the current buffer has been auto-saved since the last time it was read in or saved.

Function set-buffer-auto-saved

This function marks the current buffer as auto-saved. The buffer will not be auto-saved again until the buffer text is changed again. The function returns

nil.

User Option auto-save-interval

The value of this variable is the number of characters that Emacs reads from the keyboard between auto-saves. Each time this many more characters are read, auto-saving is done for all buffers in which it is enabled.

User Option auto-save-timeout

The value of this variable is the number of seconds of idle time that should cause auto-saving. Each time the user pauses for this long, Emacs auto-saves any buffers that need it. (Actually, the specified timeout is multiplied by a factor depending on the size of the current buffer.)

Variable auto-save-hook

This normal hook is run whenever an auto-save is about to happen.

User Option auto-save-default

If this variable is non-nil, buffers that are visiting files have auto-saving enabled by default. Otherwise, they do not.

Command do-auto-save &optional no-message current-only This function auto-saves all buffers that need to be auto-saved. It saves all buffers for which auto-saving is enabled and that have been changed since the previous auto-save.

Normally, if any buffers are auto-saved, a message that says ‘Auto-saving...’ is displayed in the echo area while auto-saving is going on. However, if nomessage is non-nil, the message is inhibited.

If current-only is non-nil, only the current buffer is auto-saved.

Function delete-auto-save-file-if-necessary

This function deletes the current buffer’s auto-save file if delete-auto-save-files is non-nil. It is called every time a buffer is saved.

Variable delete-auto-save-files

This variable is used by the function delete-auto-save-file-if-necessary.

If it is non-nil, Emacs deletes auto-save files when a true save is done (in the visited file). This saves disk space and unclutters your directory.

Function rename-auto-save-file

This function adjusts the current buffer’s auto-save file name if the visited file name has changed. It also renames an existing auto-save file. If the visited file name has not changed, this function does nothing.

Variable buffer-saved-size

The value of this buffer-local variable is the length of the current buffer as of the last time it was read in, saved, or auto-saved. This is used to detect a substantial decrease in size, and turn off auto-saving in response. If it is -1, that means auto-saving is temporarily shut off in this buffer due to a substantial deletion. Explicitly saving the buffer stores a positive value in this variable, thus reenabling auto-saving. Turning auto-save mode off or on also alters this variable.

Variable auto-save-list-file-name

This variable (if non-nil) specifies a file for recording the names of all the autosave files. Each time Emacs does auto-saving, it writes two lines into this file for each buffer that has auto-saving enabled. The first line gives the name of the visited file (it’s empty if the buffer has none), and the second gives the name of the auto-save file. If Emacs exits normally, it deletes this file. If Emacs crashes, you can look in the file to find all the auto-save files that might contain work that was otherwise lost. The recover-session command uses these files. The default name for this file is in your home directory and starts with ‘.saves-’. It also contains the Emacs process id and the host name.

23.3 Reverting

If you have made extensive changes to a file and then change your mind about them, you can get rid of them by reading in the previous version of the file with the revert-buffer command. See section “Reverting a Buffer” in The GNU Emacs Manual.

Command revert-buffer &optional check-auto-save noconfirm This command replaces the buffer text with the text of the visited file on disk. This action undoes all changes since the file was visited or saved. If the argument check-auto-save is non-nil, and the latest auto-save file is more recent than the visited file, revert-buffer asks the user whether to use that instead. Otherwise, it always uses the text of the visited file itself. Interactively, check-auto-save is set if there is a numeric prefix argument. Normally, revert-buffer asks for confirmation before it changes the buffer; but if the argument noconfirm is non-nil, revert-buffer does not ask for confirmation.

Reverting tries to preserve marker positions in the buffer by using the replacement feature of insert-file-contents. If the buffer contents and the file contents are identical before the revert operation, reverting preserves all the markers. If they are not identical, reverting does change the buffer; then it preserves the markers in the unchanged text (if any) at the beginning and end of the buffer. Preserving any additional markers would be problematical.

You can customize how revert-buffer does its work by setting these variables— typically, as buffer-local variables.

Variable revert-buffer-function

The value of this variable is the function to use to revert this buffer. If non-nil, it is called as a function with no arguments to do the work of reverting. If the value is nil, reverting works the usual way. Modes such as Dired mode, in which the text being edited does not consist of a file’s contents but can be regenerated in some other fashion, give this variable a buffer-local value that is a function to regenerate the contents.

Variable revert-buffer-insert-file-contents-function

The value of this variable, if non-nil, is the function to use to insert the updated contents when reverting this buffer. The function receives two arguments: first the file name to use; second, t if the user has asked to read the auto-save file.

Variable before-revert-hook

This normal hook is run by revert-buffer before actually inserting the mod-

ified contents—but only if revert-buffer-function is nil.

Font Lock mode uses this hook to record that the buffer contents are no longer fontified.

Variable after-revert-hook

This normal hook is run by revert-buffer after actually inserting the modified

contents—but only if revert-buffer-function is nil.

Font Lock mode uses this hook to recompute the fonts for the updated buffer contents.

368 GNU Emacs Lisp Reference Manual

24 Buffers

A buffer is a Lisp object containing text to be edited. Buffers are used to hold the contents of files that are being visited; there may also be buffers that are not visiting files. While several buffers may exist at one time, exactly one buffer is designated the current buffer at any time. Most editing commands act on the contents of the current buffer. Each buffer, including the current buffer, may or may not be displayed in any windows.

24.1 Buffer Basics

Buffers in Emacs editing are objects that have distinct names and hold text that can be edited. Buffers appear to Lisp programs as a special data type. You can think of the contents of a buffer as an extendable string; insertions and deletions may occur in any part of the buffer. See Chapter 29 [Text], page 449.

A Lisp buffer object contains numerous pieces of information. Some of this information is directly accessible to the programmer through variables, while other information is accessible only through special-purpose functions. For example, the visited file name is directly accessible through a variable, while the value of point is accessible only through a primitive function.

Buffer-specific information that is directly accessible is stored in buffer-local variable bindings, which are variable values that are effective only in a particular buffer. This feature allows each buffer to override the values of certain variables. Most major modes override variables such as fill-column or comment-column in this way. For more information about buffer-local variables and functions related to them, see Section 10.10 [Buffer-Local Variables], page 134.

For functions and variables related to visiting files in buffers, see Section 22.1 [Visiting Files], page 329 and Section 22.2 [Saving Buffers], page 332. For functions and variables related to the display of buffers in windows, see Section 25.6 [Buffers and Windows], page 390.

Function bufferp object

This function returns t if object is a buffer, nil otherwise.

24.2 The Current Buffer

There are, in general, many buffers in an Emacs session. At any time, one of them is designated as the current buffer. This is the buffer in which most editing takes place, because most of the primitives for examining or changing text in a buffer operate implicitly on the current buffer (see Chapter 29 [Text], page 449). Normally the buffer that is displayed on the screen in the selected window is the current buffer, but this is not always so: a Lisp program can designate any buffer as current temporarily in order to operate on its contents, without changing what is displayed on the screen.

The way to designate a current buffer in a Lisp program is by calling set-buffer. The specified buffer remains current until a new one is designated.

When an editing command returns to the editor command loop, the command loop designates the buffer displayed in the selected window as current, to prevent confusion: the buffer that the cursor is in when Emacs reads a command is the buffer that the command will apply to. (See Chapter 18 [Command Loop], page 243.) Therefore, set-buffer is not the way to switch visibly to a different buffer so that the user can edit it. For this, you must use the functions described in Section 25.7 [Displaying Buffers], page 391.

However, Lisp functions that change to a different current buffer should not depend on the command loop to set it back afterwards. Editing commands written in Emacs Lisp can be called from other programs as well as from the command loop. It is convenient for the caller if the subroutine does not change which buffer is current (unless, of course, that is the subroutine’s purpose). Therefore, you should normally use set-buffer within a saveexcursion that will restore the current buffer when your function is done (see Section 27.3 [Excursions], page 437). Here is an example, the code for the command append-to-buffer (with the documentation string abridged):

     (defun append-to-buffer (buffer start end)
       "Append to specified buffer the text of the region.

…"

       (interactive "BAppend to buffer: \nr")
       (let ((oldbuf (current-buffer)))
         (save-excursion
           (set-buffer (get-buffer-create buffer))
           (insert-buffer-substring oldbuf start end))))

This function binds a local variable to the current buffer, and then save-excursion records the values of point, the mark, and the original buffer. Next, set-buffer makes another buffer current. Finally, insert-buffer-substring copies the string from the original current buffer to the new current buffer.

If the buffer appended to happens to be displayed in some window, the next redisplay will show how its text has changed. Otherwise, you will not see the change immediately on the screen. The buffer becomes current temporarily during the execution of the command, but this does not cause it to be displayed.

If you make local bindings (with let or function arguments) for a variable that may also have buffer-local bindings, make sure that the same buffer is current at the beginning and at the end of the local binding’s scope. Otherwise you might bind it in one buffer and unbind it in another! There are two ways to do this. In simple cases, you may see that nothing ever changes the current buffer within the scope of the binding. Otherwise, use save-excursion to make sure that the buffer current at the beginning is current again whenever the variable is unbound.

It is not reliable to change the current buffer back with set-buffer, because that won’t do the job if a quit happens while the wrong buffer is current. Here is what not to do:

     (let (buffer-read-only
           (obuf (current-buffer)))
       (set-buffer . . .)

…

       (set-buffer obuf))

Using save-excursion, as shown below, handles quitting, errors, and throw, as well as ordinary evaluation.

(let (buffer-read-only)
  (save-excursion
    (set-buffer . . .)

…))

Function current-buffer

This function returns the current buffer.

     (current-buffer)
          ⇒ #<buffer buffers.texi>

Function set-buffer buffer-or-name This function makes buffer-or-name the current buffer. It does not display the buffer in the currently selected window or in any other window, so the user cannot necessarily see the buffer. But Lisp programs can in any case work on it.

This function returns the buffer identified by buffer-or-name. An error is signaled if buffer-or-name does not identify an existing buffer.

24.3 Buffer Names

Each buffer has a unique name, which is a string. Many of the functions that work on buffers accept either a buffer or a buffer name as an argument. Any argument called buffer-or-name is of this sort, and an error is signaled if it is neither a string nor a buffer. Any argument called buffer must be an actual buffer object, not a name.

Buffers that are ephemeral and generally uninteresting to the user have names starting with a space, so that the list-buffers and buffer-menu commands don’t mention them. A name starting with space also initially disables recording undo information; see Section 29.9 [Undo], page 461.

Function buffer-name &optional buffer This function returns the name of buffer as a string. If buffer is not supplied, it defaults to the current buffer.

If buffer-name returns nil, it means that buffer has been killed. See Section 24.10 [Killing Buffers], page 379.

     (buffer-name)
          ⇒ "buffers.texi"
     (setq foo (get-buffer "temp"))
          ⇒ #<buffer temp>
     (kill-buffer foo)
          ⇒ nil
     (buffer-name foo)
          ⇒ nil
     foo
          ⇒ #<killed buffer>

Command rename-buffer newname &optional unique This function renames the current buffer to newname. An error is signaled if newname is not a string, or if there is already a buffer with that name. The function returns newname. Ordinarily, rename-buffer signals an error if newname is already in use. However, if unique is non-nil, it modifies newname to make a name that is not in use. Interactively, you can make unique non-nil with a numeric prefix argument. One application of this command is to rename the ‘*shell*’ buffer to some other name, thus making it possible to create a second shell buffer under the

name ‘*shell*’.

Function get-buffer buffer-or-name This function returns the buffer specified by buffer-or-name. If buffer-or-name is a string and there is no buffer with that name, the value is nil. If bufferor-name is a buffer, it is returned as given. (That is not very useful, so the argument is usually a name.) For example:

     (setq b (get-buffer "lewis"))
          ⇒ #<buffer lewis>
     (get-buffer b)
          ⇒ #<buffer lewis>
     (get-buffer "Frazzle-nots")
          ⇒ nil

See also the function get-buffer-create in Section 24.9 [Creating Buffers], page 378.

Function generate-new-buffer-name starting-name

This function returns a name that would be unique for a new buffer—but does not create the buffer. It starts with starting-name, and produces a name not currently in use for any buffer by appending a number inside of ‘<…>’. See the related function generate-new-buffer in Section 24.9 [Creating Buffers], page 378.

24.4 Buffer File Name

The buffer file name is the name of the file that is visited in that buffer. When a buffer is not visiting a file, its buffer file name is nil. Most of the time, the buffer name is the same as the nondirectory part of the buffer file name, but the buffer file name and the buffer name are distinct and can be set independently. See Section 22.1 [Visiting Files], page 329.

Function buffer-file-name &optional buffer

This function returns the absolute file name of the file that buffer is visiting. If buffer is not visiting any file, buffer-file-name returns nil. If buffer is not supplied, it defaults to the current buffer.

     (buffer-file-name (other-buffer))
          ⇒ "/usr/user/lewis/manual/files.texi"

Variable buffer-file-name

This buffer-local variable contains the name of the file being visited in the current buffer, or nil if it is not visiting a file. It is a permanent local, unaffected

by kill-local-variables.
     buffer-file-name
          ⇒ "/usr/user/lewis/manual/buffers.texi"

It is risky to change this variable’s value without doing various other things. See the definition of set-visited-file-name in ‘files.el’; some of the things done there, such as changing the buffer name, are not strictly necessary, but others are essential to avoid confusing Emacs.

Variable buffer-file-truename

This buffer-local variable holds the truename of the file visited in the current buffer, or nil if no file is visited. It is a permanent local, unaffected by killlocal-variables. See Section 22.6.3 [Truenames], page 339.

Variable buffer-file-number

This buffer-local variable holds the file number and directory device number of the file visited in the current buffer, or nil if no file or a nonexistent file is visited. It is a permanent local, unaffected by kill-local-variables. See Section 22.6.3 [Truenames], page 339. The value is normally a list of the form (filenum devnum). This pair of numbers uniquely identifies the file among all files accessible on the system. See the function file-attributes, in Section 22.6.4 [File Attributes], page 340, for more information about them.

Function get-file-buffer filename

This function returns the buffer visiting file filename. If there is no such buffer, it returns nil. The argument filename, which must be a string, is expanded (see Section 22.8.4 [File Name Expansion], page 347), then compared against the visited file names of all live buffers.

     (get-file-buffer "buffers.texi")
         ⇒ #<buffer buffers.texi>

In unusual circumstances, there can be more than one buffer visiting the same file name. In such cases, this function returns the first such buffer in the buffer list.

Command set-visited-file-name filename

If filename is a non-empty string, this function changes the name of the file visited in current buffer to filename. (If the buffer had no visited file, this gives it one.) The next time the buffer is saved it will go in the newly-specified file. This command marks the buffer as modified, since it does not (as far as Emacs knows) match the contents of filename, even if it matched the former visited file. If filename is nil or the empty string, that stands for “no visited file”. In this case, set-visited-file-name marks the buffer as having no visited file.

When the function set-visited-file-name is called interactively, it prompts for filename in the minibuffer.

See also clear-visited-file-modtime and verify-visited-file-modtime

in Section 24.5 [Buffer Modification], page 374.

Variable list-buffers-directory

This buffer-local variable records a string to display in a buffer listing in place of the visited file name, for buffers that don’t have a visited file name. Dired buffers use this variable.

24.5 Buffer Modification

Emacs keeps a flag called the modified flag for each buffer, to record whether you have changed the text of the buffer. This flag is set to t whenever you alter the contents of the buffer, and cleared to nil when you save it. Thus, the flag shows whether there are unsaved changes. The flag value is normally shown in the mode line (see Section 20.3.2 [Mode Line Variables], page 312), and controls saving (see Section 22.2 [Saving Buffers], page 332) and auto-saving (see Section 23.2 [Auto-Saving], page 363).

Some Lisp programs set the flag explicitly. For example, the function set-visited-file-name sets the flag to t, because the text does not match the newly-visited file, even if it is unchanged from the file formerly visited.

The functions that modify the contents of buffers are described in Chapter 29 [Text], page 449.

Function buffer-modified-p &optional buffer

This function returns t if the buffer buffer has been modified since it was last read in from a file or saved, or nil otherwise. If buffer is not supplied, the current buffer is tested.

Function set-buffer-modified-p flag

This function marks the current buffer as modified if flag is non-nil, or as unmodified if the flag is nil. Another effect of calling this function is to cause unconditional redisplay of the mode line for the current buffer. In fact, the function force-mode-line-update works by doing this:

     (set-buffer-modified-p (buffer-modified-p))

Command not-modified

This command marks the current buffer as unmodified, and not needing to be saved. With prefix arg, it marks the buffer as modified, so that it will be saved at the next suitable occasion. Don’t use this function in programs, since it prints a message in the echo area;

use set-buffer-modified-p (above) instead.

Function buffer-modified-tick &optional buffer

This function returns buffer’s modification-count. This is a counter that increments every time the buffer is modified. If buffer is nil (or omitted), the current buffer is used.

24.6 Comparison of Modification Time

Suppose that you visit a file and make changes in its buffer, and meanwhile the file itself is changed on disk. At this point, saving the buffer would overwrite the changes in the file. Occasionally this may be what you want, but usually it would lose valuable information. Emacs therefore checks the file’s modification time using the functions described below before saving the file.

Function verify-visited-file-modtime buffer

This function compares what buffer has recorded for the modification time of its visited file against the actual modification time of the file as recorded by the operating system. The two should be the same unless some other process has written the file since Emacs visited or saved it. The function returns t if the last actual modification time and Emacs’s recorded modification time are the same, nil otherwise.

Function clear-visited-file-modtime

This function clears out the record of the last modification time of the file being visited by the current buffer. As a result, the next attempt to save this buffer will not complain of a discrepancy in file modification times. This function is called in set-visited-file-name and other exceptional places where the usual test to avoid overwriting a changed file should not be done.

Function visited-file-modtime

This function returns the buffer’s recorded last file modification time, as a list of the form (high . low). (This is the same format that file-attributes uses to return time values; see Section 22.6.4 [File Attributes], page 340.)

Function set-visited-file-modtime &optional time

This function updates the buffer’s record of the last modification time of the visited file, to the value specified by time if time is not nil, and otherwise to the last modification time of the visited file. If time is not nil, it should have the form (high . low) or (high low), in either case containing two integers, each of which holds 16 bits of the time. This function is useful if the buffer was not read from the file normally, or if the file itself has been changed for some known benign reason.

Function ask-user-about-supersession-threat filename

This function is used to ask a user how to proceed after an attempt to modify an obsolete buffer visiting file filename. An obsolete buffer is an unmodified buffer for which the associated file on disk is newer than the last save-time of the buffer. This means some other program has probably altered the file. Depending on the user’s answer, the function may return normally, in which case the modification of the buffer proceeds, or it may signal a file-supersession error with data (filename), in which case the proposed buffer modification is not allowed.

This function is called automatically by Emacs on the proper occasions. It exists so you can customize Emacs by redefining it. See the file ‘userlock.el’ for the standard definition.

See also the file locking mechanism in Section 22.5 [File Locks], page 336.

24.7 Read-Only Buffers

If a buffer is read-only, then you cannot change its contents, although you may change your view of the contents by scrolling and narrowing.

Read-only buffers are used in two kinds of situations:

• A buffer visiting a write-protected file is normally read-only.

Here, the purpose is to show the user that editing the buffer with the aim of saving it in the file may be futile or undesirable. The user who wants to change the buffer text despite this can do so after clearing the read-only flag with C-x C-q.

• Modes such as Dired and Rmail make buffers read-only when altering the contents with the usual editing commands is probably a mistake. The special commands of these modes bind buffer-read-only to nil (with let) or bind inhibit-read-only to t around the places where they change the text.

Variable buffer-read-only

This buffer-local variable specifies whether the buffer is read-only. The buffer is read-only if this variable is non-nil.

Variable inhibit-read-only

If this variable is non-nil, then read-only buffers and read-only characters may be modified. Read-only characters in a buffer are those that have non-nil read-only properties (either text properties or overlay properties). See Section 29.18.4 [Special Properties], page 482, for more information about text properties. See Section 35.9 [Overlays], page 575, for more information about overlays and their properties.

If inhibit-read-only is t, all read-only character properties have no effect. If inhibit-read-only is a list, then read-only character properties have no effect if they are members of the list (comparison is done with eq).

Command toggle-read-only

This command changes whether the current buffer is read-only. It is intended for interactive use; don’t use it in programs. At any given point in a program, you should know whether you want the read-only flag on or off; so you can set buffer-read-only explicitly to the proper value, t or nil.

Function barf-if-buffer-read-only

This function signals a buffer-read-only error if the current buffer is readonly. See Section 18.3 [Interactive Call], page 248, for another way to signal an error if the current buffer is read-only.

24.8 The Buffer List

The buffer list is a list of all live buffers. Creating a buffer adds it to this list, and killing a buffer deletes it. The order of the buffers in the list is based primarily on how recently each buffer has been displayed in the selected window. Buffers move to the front of the list when they are selected and to the end when they are buried. Several functions, notably other-buffer, use this ordering. A buffer list displayed for the user also follows this order.

Function buffer-list

This function returns a list of all buffers, including those whose names begin with a space. The elements are actual buffers, not their names.

     (buffer-list)
          ⇒ (#<buffer buffers.texi>
              #<buffer  *Minibuf-1*> #<buffer buffer.c>
              #<buffer *Help*> #<buffer TAGS>)

;; Note that the name of the minibuffer

;; begins with a space!

     (mapcar (function buffer-name) (buffer-list))
         ⇒ ("buffers.texi" " *Minibuf-1*"
             "buffer.c" "*Help*" "TAGS")

The list that buffer-list returns is constructed specifically by buffer-list; it is not an internal Emacs data structure, and modifying it has no effect on the order of buffers. If you want to change the order of buffers in the list, here is an easy way:

(defun reorder-buffer-list (new-list)
  (while new-list
    (bury-buffer (car new-list))
    (setq new-list (cdr new-list))))

With this method, you can specify any order for the list, but there is no danger of losing a buffer or adding something that is not a valid live buffer.

Function other-buffer &optional buffer visible-ok This function returns the first buffer in the buffer list other than buffer. Usually this is the buffer most recently shown in the selected window, aside from buffer. Buffers whose names start with a space are not considered. If buffer is not supplied (or if it is not a buffer), then other-buffer returns the first buffer on the buffer list that is not visible in any window in a visible frame. If the selected frame has a non-nilbuffer-predicate parameter, then otherbuffer uses that predicate to decide which buffers to consider. It calls the predicate once for each buffer, and if the value is nil, that buffer is ignored. See Section 26.3.3 [X Frame Parameters], page 412. If visible-ok is nil, other-buffer avoids returning a buffer visible in any window on any visible frame, except as a last resort. If visible-ok is non-nil, then it does not matter whether a buffer is displayed somewhere or not. If no suitable buffer exists, the buffer ‘*scratch*’ is returned (and created, if necessary).

Command bury-buffer &optional buffer-or-name This function puts buffer-or-name at the end of the buffer list without changing the order of any of the other buffers on the list. This buffer therefore becomes the least desirable candidate for other-buffer to return. If buffer-or-name is nil or omitted, this means to bury the current buffer. In addition, if the buffer is displayed in the selected window, this switches to some other buffer (obtained using other-buffer) in the selected window. But if the buffer is displayed in some other window, it remains displayed there. If you wish to replace a buffer in all the windows that display it, use replacebuffer-in-windows. See Section 25.6 [Buffers and Windows], page 390.

24.9 Creating Buffers

This section describes the two primitives for creating buffers. get-buffer-create creates a buffer if it finds no existing buffer with the specified name; generate-new-buffer always creates a new buffer and gives it a unique name.

Other functions you can use to create buffers include with-output-to-temp-buffer (see Section 35.8 [Temporary Displays], page 573) and create-file-buffer (see Section 22.1 [Visiting Files], page 329). Starting a subprocess can also create a buffer (see Chapter 33 [Processes], page 525).

Function get-buffer-create name

This function returns a buffer named name. It returns an existing buffer with that name, if one exists; otherwise, it creates a new buffer. The buffer does not become the current buffer—this function does not change which buffer is current. An error is signaled if name is not a string.

     (get-buffer-create "foo")
          ⇒ #<buffer foo>

The major mode for the new buffer is set to Fundamental mode. The variable default-major-mode is handled at a higher level. See Section 20.1.3 [Auto Major Mode], page 305.

Function generate-new-buffer name

This function returns a newly created, empty buffer, but does not make it current. If there is no buffer named name, then that is the name of the new buffer. If that name is in use, this function adds suffixes of the form ‘<n>’ to name, where n is an integer. It tries successive integers starting with 2 until it finds an available name. An error is signaled if name is not a string.

     (generate-new-buffer "bar")
          ⇒ #<buffer bar>
     (generate-new-buffer "bar")
          ⇒ #<buffer bar<2>>
     (generate-new-buffer "bar")
          ⇒ #<buffer bar<3>>

The major mode for the new buffer is set to Fundamental mode. The variable default-major-mode is handled at a higher level. See Section 20.1.3 [Auto Major Mode], page 305. See the related function generate-new-buffer-name in Section 24.3 [Buffer Names], page 371.

24.10 Killing Buffers

Killing a buffer makes its name unknown to Emacs and makes its text space available for other use.

The buffer object for the buffer that has been killed remains in existence as long as anything refers to it, but it is specially marked so that you cannot make it current or display it. Killed buffers retain their identity, however; two distinct buffers, when killed, remain distinct according to eq.

If you kill a buffer that is current or displayed in a window, Emacs automatically selects or displays some other buffer instead. This means that killing a buffer can in general change the current buffer. Therefore, when you kill a buffer, you should also take the precautions associated with changing the current buffer (unless you happen to know that the buffer being killed isn’t current). See Section 24.2 [Current Buffer], page 369.

If you kill a buffer that is the base buffer of one or more indirect buffers, the indirect buffers are automatically killed as well.

The buffer-name of a killed buffer is nil. You can use this feature to test whether a buffer has been killed:

(defun buffer-killed-p (buffer)
  "Return t if BUFFER is killed."
  (not (buffer-name buffer)))

Command kill-buffer buffer-or-name This function kills the buffer buffer-or-name, freeing all its memory for other uses or to be returned to the operating system. It returns nil. Any processes that have this buffer as the process-buffer are sent the SIGHUP signal, which normally causes them to terminate. (The basic meaning of SIGHUP is that a dialup line has been disconnected.) See Section 33.5 [Deleting Processes], page 530. If the buffer is visiting a file and contains unsaved changes, kill-buffer asks the user to confirm before the buffer is killed. It does this even if not called interactively. To prevent the request for confirmation, clear the modified flag before calling kill-buffer. See Section 24.5 [Buffer Modification], page 374. Killing a buffer that is already dead has no effect.

     (kill-buffer "foo.unchanged")
          ⇒ nil
     (kill-buffer "foo.changed")
     ---------- Buffer: Minibuffer ----------
     Buffer foo.changed modified; kill anyway? (yes or no) yes

     ---------- Buffer: Minibuffer ----------

          ⇒ nil

Variable kill-buffer-query-functions

After confirming unsaved changes, kill-buffer calls the functions in the list kill-buffer-query-functions, in order of appearance, with no arguments. The buffer being killed is the current buffer when they are called. The idea is that these functions ask for confirmation from the user for various nonstandard reasons. If any of them returns nil, kill-buffer spares the buffer’s life.

Variable kill-buffer-hook

This is a normal hook run by kill-buffer after asking all the questions it is going to ask, just before actually killing the buffer. The buffer to be killed is current when the hook functions run. See Section 20.4 [Hooks], page 316.

Variable buffer-offer-save

This variable, if non-nil in a particular buffer, tells save-buffers-kill-emacs and save-some-buffers to offer to save that buffer, just as they offer to save file-visiting buffers. The variable buffer-offer-save automatically becomes buffer-local when set for any reason. See Section 10.10 [Buffer-Local Variables], page 134.

24.11 Indirect Buffers

An indirect buffer shares the text of some other buffer, which is called the base buffer of the indirect buffer. In some ways it is the analogue, for buffers, of a symbolic link among files. The base buffer may not itself be an indirect buffer.

The text of the indirect buffer is always identical to the text of its base buffer; changes made by editing either one are visible immediately in the other. This includes the text properties as well as the characters themselves.

But in all other respects, the indirect buffer and its base buffer are completely separate. They have different names, different values of point, different narrowing, different markers and overlays (though inserting or deleting text in either buffer relocates the markers and overlays for both), different major modes, and different local variables.

An indirect buffer cannot visit a file, but its base buffer can. If you try to save the indirect buffer, that actually works by saving the base buffer.

Killing an indirect buffer has no effect on its base buffer. Killing the base buffer effectively kills the indirect buffer in that it cannot ever again be the current buffer.

Command make-indirect-buffer base-buffer name

This creates an indirect buffer named name whose base buffer is base-buffer. The argument base-buffer may be a buffer or a string.

If base-buffer is an indirect buffer, its base buffer is used as the base for the new buffer.

Function buffer-base-buffer buffer

This function returns the base buffer of buffer. If buffer is not indirect, the value is nil. Otherwise, the value is another buffer, which is never an indirect buffer.

382 GNU Emacs Lisp Reference Manual

25 Windows

This chapter describes most of the functions and variables related to Emacs windows. See Chapter 35 [Display], page 567, for information on how text is displayed in windows.

25.1 Basic Concepts of Emacs Windows

A window in Emacs is the physical area of the screen in which a buffer is displayed. The term is also used to refer to a Lisp object that represents that screen area in Emacs Lisp. It should be clear from the context which is meant.

Emacs groups windows into frames. A frame represents an area of screen available for Emacs to use. Each frame always contains at least one window, but you can subdivide it vertically or horizontally into multiple nonoverlapping Emacs windows.

In each frame, at any time, one and only one window is designated as selected within the frame. The frame’s cursor appears in that window. At ant time, one frame is the selected frame; and the window selected within that frame is the selected window. The selected window’s buffer is usually the current buffer (except when set-buffer has been used). See Section 24.2 [Current Buffer], page 369.

For practical purposes, a window exists only while it is displayed in a frame. Once removed from the frame, the window is effectively deleted and should not be used, even though there may still be references to it from other Lisp objects. Restoring a saved window configuration is the only way for a window no longer on the screen to come back to life. (See Section 25.3 [Deleting Windows], page 386.)

Each window has the following attributes:

• containing frame

• window height

• window width

• window edges with respect to the screen or frame

• the buffer it displays

• position within the buffer at the upper left of the window

• amount of horizontal scrolling, in columns

• point

• the mark

• how recently the window was selected

Users create multiple windows so they can look at several buffers at once. Lisp libraries use multiple windows for a variety of reasons, but most often to display related information. In Rmail, for example, you can move through a summary buffer in one window while the other window shows messages one at a time as they are reached.

The meaning of “window” in Emacs is similar to what it means in the context of generalpurpose window systems such as X, but not identical. The X Window System places X windows on the screen; Emacs uses one or more X windows as frames, and subdivides them into Emacs windows. When you use Emacs on a character-only terminal, Emacs treats the whole terminal screen as one frame.

Most window systems support arbitrarily located overlapping windows. In contrast, Emacs windows are tiled; they never overlap, and together they fill the whole screen or frame. Because of the way in which Emacs creates new windows and resizes them, you can’t create every conceivable tiling of windows on an Emacs frame. See Section 25.2 [Splitting Windows], page 384, and Section 25.14 [Size of Window], page 402.

See Chapter 35 [Display], page 567, for information on how the contents of the window’s buffer are displayed in the window.

Function windowp object

This function returns t if object is a window.

25.2 Splitting Windows

The functions described here are the primitives used to split a window into two windows. Two higher level functions sometimes split a window, but not always: pop-to-buffer and display-buffer (see Section 25.7 [Displaying Buffers], page 391).

The functions described here do not accept a buffer as an argument. The two “halves” of the split window initially display the same buffer previously visible in the window that was split.

Command split-window &optional window size horizontal This function splits window into two windows. The original window window remains the selected window, but occupies only part of its former screen area. The rest is occupied by a newly created window which is returned as the value of this function.

If horizontal is non-nil, then window splits into two side by side windows. The original window window keeps the leftmost size columns, and gives the rest of the columns to the new window. Otherwise, it splits into windows one above the other, and window keeps the upper size lines and gives the rest of the lines to the new window. The original window is therefore the left-hand or upper of the two, and the new window is the right-hand or lower.

If window is omitted or nil, then the selected window is split. If size is omitted or nil, then window is divided evenly into two parts. (If there is an odd line, it is allocated to the new window.) When split-window is called interactively, all its arguments are nil.

The following example starts with one window on a screen that is 50 lines high by 80 columns wide; then the window is split.

     (setq w (selected-window))
          ⇒ #<window 8 on windows.texi>
     (window-edges)          ; Edges in order:

⇒ (0 0 80 50) ; left–top–right–bottom ;; Returns window created

     (setq w2 (split-window w 15))
          ⇒ #<window 28 on windows.texi>

(window-edges w2)

⇒ (0 15 80 50) ; Bottom window;

; top is line 15

(window-edges w)

⇒ (0 0 80 15) ; Top window

The screen looks like this:

 __________
|          |  line 0
|    w     |
|__________|
|          |  line 15
|    w2    |
|__________|
              line 50
column 0   column 80

Next, the top window is split horizontally:

(setq w3 (split-window w 35 t))
⇒ #<window 32 on windows.texi>
(window-edges w3)

⇒ (35 0 80 15) ; Left edge at column 35

(window-edges w)

⇒ (0 0 35 15) ; Right edge at column 35

(window-edges w2)

⇒ (0 15 80 50) ; Bottom window unchanged

Now, the screen looks like this:

column 35
 __________
|   |      |  line 0
| w |  w3  |
|___|______|
|          |  line 15
|    w2    |
|__________|
              line 50
column 0   column 80

Normally, Emacs indicates the border between two side-by-side windows with a scroll bar (see Section 26.3.3 [X Frame Parameters], page 412) or ‘|’ characters. The display table can specify alternative border characters; see Section 35.14 [Display Tables], page 583.

Command split-window-vertically size

This function splits the selected window into two windows, one above the other, leaving the selected window with size lines.

This function is simply an interface to split-windows. Here is the complete function definition for it:

     (defun split-window-vertically (&optional arg)
       "Split current window into two windows, . . ."
       (interactive "P")
       (split-window nil (and arg (prefix-numeric-value arg))))

Command split-window-horizontally size

This function splits the selected window into two windows side-by-side, leaving the selected window with size columns. This function is simply an interface to split-windows. Here is the complete definition for split-window-horizontally (except for part of the documentation string):

     (defun split-window-horizontally (&optional arg)
       "Split selected window into two windows, side by side..."
       (interactive "P")
       (split-window nil (and arg (prefix-numeric-value arg)) t))

Function one-window-p &optional no-mini all-frames This function returns non-nil if there is only one window. The argument nomini, if non-nil, means don’t count the minibuffer even if it is active; otherwise, the minibuffer window is included, if active, in the total number of windows, which is compared against one. The argument all-frames specifies which frames to consider. Here are the possible values and their meanings:

nil Count the windows in the selected frame, plus the minibuffer used by that frame even if it lies in some other frame.

t Count all windows in all existing frames.

visible Count all windows in all visible frames.

0 Count all windows in all visible or iconified frames.

anything else Count precisely the windows in the selected frame, and no others.

25.3 Deleting Windows

A window remains visible on its frame unless you delete it by calling certain functions that delete windows. A deleted window cannot appear on the screen, but continues to exist as a Lisp object until there are no references to it. There is no way to cancel the deletion of a window aside from restoring a saved window configuration (see Section 25.17 [Window Configurations], page 406). Restoring a window configuration also deletes any windows that aren’t part of that configuration.

When you delete a window, the space it took up is given to one adjacent sibling. (In Emacs version 18, the space was divided evenly among all the siblings.)

Function window-live-p window

This function returns nil if window is deleted, and t otherwise. Warning: Erroneous information or fatal errors may result from using a deleted window as if it were live.

Command delete-window &optional window This function removes window from the display. If window is omitted, then the selected window is deleted. An error is signaled if there is only one window

when delete-window is called.

This function returns nil. When delete-window is called interactively, window defaults to the selected window.

Command delete-other-windows &optional window

This function makes window the only window on its frame, by deleting the other windows in that frame. If window is omitted or nil, then the selected window is used by default. The result is nil.

Command delete-windows-on buffer &optional frame This function deletes all windows showing buffer. If there are no windows showing buffer, it does nothing. delete-windows-on operates frame by frame. If a frame has several windows showing different buffers, then those showing buffer are removed, and the others expand to fill the space. If all windows in some frame are showing buffer (including the case where there is only one window), then the frame reverts to having a single window showing another buffer chosen with other-buffer. See Section 24.8 [The Buffer List], page 377. The argument frame controls which frames to operate on:

• If it is nil, operate on the selected frame.

• If it is t, operate on all frames.

• If it is visible, operate on all visible frames.

• 0 If it is 0, operate on all visible or iconified frames.

• If it is a frame, operate on that frame.

This function always returns nil.

25.4 Selecting Windows

When a window is selected, the buffer in the window becomes the current buffer, and the cursor will appear in it.

Function selected-window

This function returns the selected window. This is the window in which the cursor appears and to which many commands apply.

Function select-window window

This function makes window the selected window. The cursor then appears in window (on redisplay). The buffer being displayed in window is immediately designated the current buffer. The return value is window.

     (setq w (next-window))
     (select-window w)
          ⇒ #<window 65 on windows.texi>

Macro save-selected-window forms…

This macro records the selected window, executes forms in sequence, then restores the earlier selected window. This macro does not save or restore anything about the sizes, arrangement or contents of windows; therefore, if the forms change them, the change persists. Each frame, at any time, has a window selected within the frame. This macro only saves the selected window; it does not save anything about other frames. If the forms select some other frame and alter the window selected within it, the change persists.

The following functions choose one of the windows on the screen, offering various criteria for the choice.

Function get-lru-window &optional frame

This function returns the window least recently “used” (that is, selected). The selected window is always the most recently used window. The selected window can be the least recently used window if it is the only window. A newly created window becomes the least recently used window until it is selected. A minibuffer window is never a candidate. The argument frame controls which windows are considered.

• If it is nil, consider windows on the selected frame.

• If it is t, consider windows on all frames.

• If it is visible, consider windows on all visible frames.

• If it is 0, consider windows on all visible or iconified frames.

• If it is a frame, consider windows on that frame.

Function get-largest-window &optional frame

This function returns the window with the largest area (height times width). If there are no side-by-side windows, then this is the window with the most lines. A minibuffer window is never a candidate. If there are two windows of the same size, then the function returns the window that is first in the cyclic ordering of windows (see following section), starting from the selected window. The argument frame controls which set of windows are considered. See get-

lru-window, above.

25.5 Cyclic Ordering of Windows

When you use the command C-x o (other-window) to select the next window, it moves through all the windows on the screen in a specific cyclic order. For any given configuration of windows, this order never varies. It is called the cyclic ordering of windows.

This ordering generally goes from top to bottom, and from left to right. But it may go down first or go right first, depending on the order in which the windows were split.

If the first split was vertical (into windows one above each other), and then the subwindows were split horizontally, then the ordering is left to right in the top of the frame, and then left to right in the next lower part of the frame, and so on. If the first split was horizontal, the ordering is top to bottom in the left part, and so on. In general, within each set of siblings at any level in the window tree, the order is left to right, or top to bottom.

Function next-window &optional window minibuf all-frames This function returns the window following window in the cyclic ordering of windows. This is the window that C-x o would select if typed when window is selected. If window is the only window visible, then this function returns window. If omitted, window defaults to the selected window.

The value of the argument minibuf determines whether the minibuffer is included in the window order. Normally, when minibuf is nil, the minibuffer is included if it is currently active; this is the behavior of C-x o. (The minibuffer window is active while the minibuffer is in use. See Chapter 17 [Minibuffers], page 223.)

If minibuf is t, then the cyclic ordering includes the minibuffer window even if it is not active.

If minibuf is neither t nor nil, then the minibuffer window is not included even if it is active.

The argument all-frames specifies which frames to consider. Here are the possible values and their meanings:

nil Consider all the windows in window’s frame, plus the minibuffer used by that frame even if it lies in some other frame.

t Consider all windows in all existing frames.

visible Consider all windows in all visible frames. (To get useful results, you must ensure window is in a visible frame.)

0 Consider all windows in all visible or iconified frames.

anything else Consider precisely the windows in window’s frame, and no others.

This example assumes there are two windows, both displaying the buffer

‘windows.texi’:
     (selected-window)
          ⇒ #<window 56 on windows.texi>
     (next-window (selected-window))
          ⇒ #<window 52 on windows.texi>
     (next-window (next-window (selected-window)))
          ⇒ #<window 56 on windows.texi>

Function previous-window &optional window minibuf all-frames This function returns the window preceding window in the cyclic ordering of windows. The other arguments specify which windows to include in the cycle,

as in next-window.

Command other-window count

This function selects the countth following window in the cyclic order. If count is negative, then it selects the −countth preceding window. It returns nil. In an interactive call, count is the numeric prefix argument.

Function walk-windows proc &optional minibuf all-frames This function cycles through all windows, calling proc once for each window with the window as its sole argument. The optional arguments minibuf and all-frames specify the set of windows to include in the scan. See next-window, above, for details.

25.6 Buffers and Windows

This section describes low-level functions to examine windows or to display buffers in windows in a precisely controlled fashion. See the following section for related functions that find a window to use and specify a buffer for it. The functions described there are easier to use than these, but they employ heuristics in choosing or creating a window; use these functions when you need complete control.

Function set-window-buffer window buffer-or-name This function makes window display buffer-or-name as its contents. It returns

nil.
     (set-window-buffer (selected-window) "foo")
          ⇒ nil

Function window-buffer &optional window This function returns the buffer that window is displaying. If window is omitted, this function returns the buffer for the selected window.

     (window-buffer)
          ⇒ #<buffer windows.texi>

Function get-buffer-window buffer-or-name &optional all-frames This function returns a window currently displaying buffer-or-name, or nil if there is none. If there are several such windows, then the function returns the first one in the cyclic ordering of windows, starting from the selected window. See Section 25.5 [Cyclic Window Ordering], page 388. The argument all-frames controls which windows to consider.

• If it is nil, consider windows on the selected frame.

• If it is t, consider windows on all frames.

• If it is visible, consider windows on all visible frames.

• If it is 0, consider windows on all visible or iconified frames.

• If it is a frame, consider windows on that frame.

Function get-buffer-window-list buffer-or-name &optional minibuf

all-frames This function returns a list of all the windows currently displaying buffer-or-name. The two optional arguments work like the optional arguments of next-window (see Section 25.5 [Cyclic Window Ordering], page 388); they are not like the single optional argument of get-buffer-window. Perhaps we should change get-buffer-window in the future to make it compatible with the other functions. The argument all-frames controls which windows to consider.

• If it is nil, consider windows on the selected frame.

• If it is t, consider windows on all frames.

• If it is visible, consider windows on all visible frames.

• If it is 0, consider windows on all visible or iconified frames.

• If it is a frame, consider windows on that frame.

25.7 Displaying Buffers in Windows

In this section we describe convenient functions that choose a window automatically and use it to display a specified buffer. These functions can also split an existing window in certain circumstances. We also describe variables that parameterize the heuristics used for choosing a window. See the preceding section for low-level functions that give you more precise control.

Do not use the functions in this section in order to make a buffer current so that a Lisp program can access or modify it; they are too drastic for that purpose, since they change the display of buffers in windows, which is gratuitous and will surprise the user. Instead, use set-buffer (see Section 24.2 [Current Buffer], page 369) and save-excursion (see Section 27.3 [Excursions], page 437), which designate buffers as current for programmed access without affecting the display of buffers in windows.

Command switch-to-buffer buffer-or-name &optional norecord This function makes buffer-or-name the current buffer, and also displays the buffer in the selected window. This means that a human can see the buffer and subsequent keyboard commands will apply to it. Contrast this with setbuffer, which makes buffer-or-name the current buffer but does not display it in the selected window. See Section 24.2 [Current Buffer], page 369. If buffer-or-name does not identify an existing buffer, then a new buffer by that name is created. The major mode for the new buffer is set according to the variable default-major-mode. See Section 20.1.3 [Auto Major Mode], page 305. Normally the specified buffer is put at the front of the buffer list. This affects the operation of other-buffer. However, if norecord is non-nil, this is not done. See Section 24.8 [The Buffer List], page 377. The switch-to-buffer function is often used interactively, as the binding of C-x b. It is also used frequently in programs. It always returns nil.

Command switch-to-buffer-other-window buffer-or-name

This function makes buffer-or-name the current buffer and displays it in a window not currently selected. It then selects that window. The handling of the buffer is the same as in switch-to-buffer.

The currently selected window is absolutely never used to do the job. If it is the only window, then it is split to make a distinct window for this purpose. If the selected window is already displaying the buffer, then it continues to do so, but another window is nonetheless found to display it in as well.

Function pop-to-buffer buffer-or-name &optional other-window This function makes buffer-or-name the current buffer and switches to it in some window, preferably not the window previously selected. The “popped-to” window becomes the selected window within its frame.

If the variable pop-up-frames is non-nil, pop-to-buffer looks for a window in any visible frame already displaying the buffer; if there is one, it returns that window and makes it be selected within its frame. If there is none, it creates a new frame and displays the buffer in it.

If pop-up-frames is nil, then pop-to-buffer operates entirely within the selected frame. (If the selected frame has just a minibuffer, pop-to-buffer operates within the most recently selected frame that was not just a minibuffer.)

If the variable pop-up-windows is non-nil, windows may be split to create a new window that is different from the original window. For details, see Section 25.8 [Choosing Window], page 393.

If other-window is non-nil, pop-to-buffer finds or creates another window even if buffer-or-name is already visible in the selected window. Thus bufferor-name could end up displayed in two windows. On the other hand, if bufferor-name is already displayed in the selected window and other-window is nil, then the selected window is considered sufficient display for buffer-or-name, so that nothing needs to be done.

All the variables that affect display-buffer affect pop-to-buffer as well. See Section 25.8 [Choosing Window], page 393.

If buffer-or-name is a string that does not name an existing buffer, a buffer by that name is created. The major mode for the new buffer is set according to the variable default-major-mode. See Section 20.1.3 [Auto Major Mode], page 305.

Command replace-buffer-in-windows buffer

This function replaces buffer with some other buffer in all windows displaying it. The other buffer used is chosen with other-buffer. In the usual applications of this function, you don’t care which other buffer is used; you just want to make sure that buffer is no longer displayed.

This function returns nil.

25.8 Choosing a Window for Display

This section describes the basic facility that chooses a window to display a buffer in— display-buffer. All the higher-level functions and commands use this subroutine. Here we describe how to use display-buffer and how to customize it.

Command display-buffer buffer-or-name &optional not-this-window This command makes buffer-or-name appear in some window, like pop-to-buffer, but it does not select that window and does not make the buffer current. The identity of the selected window is unaltered by this function. If not-this-window is non-nil, it means to display the specified buffer in a window other than the selected one, even if it is already on display in the selected window. This can cause the buffer to appear in two windows at once. Otherwise, if buffer-or-name is already being displayed in any window, that is good enough, so this function does nothing. display-buffer returns the window chosen to display buffer-or-name. Precisely how display-buffer finds or creates a window depends on the variables described below.

User Option pop-up-windows

This variable controls whether display-buffer makes new windows. If it is non-nil and there is only one window, then that window is split. If it is nil, then display-buffer does not split the single window, but uses it whole.

User Option split-height-threshold

This variable determines when display-buffer may split a window, if there are multiple windows. display-buffer always splits the largest window if it has at least this many lines. If the largest window is not this tall, it is split only if it is the sole window and pop-up-windows is non-nil.

User Option pop-up-frames

This variable controls whether display-buffer makes new frames. If it is non-nil, display-buffer looks for an existing window already displaying the desired buffer, on any visible frame. If it finds one, it returns that window. Otherwise it makes a new frame. The variables pop-up-windows and split-

height-threshold do not matter if pop-up-frames is non-nil.

If pop-up-frames is nil, then display-buffer either splits a window or reuses one. See Chapter 26 [Frames], page 409, for more information.

Variable pop-up-frame-function

This variable specifies how to make a new frame if pop-up-frames is non-nil. Its value should be a function of no arguments. When display-buffer makes a new frame, it does so by calling that function, which should return a frame. The default value of the variable is a function that creates a frame using parameters

from pop-up-frame-alist.

Variable pop-up-frame-alist

This variable holds an alist specifying frame parameters used when displaybuffer makes a new frame. See Section 26.3 [Frame Parameters], page 410, for more information about frame parameters.

Variable special-display-buffer-names

A list of buffer names for buffers that should be displayed specially. If the buffer’s name is in this list, display-buffer handles the buffer specially. By default, special display means to give the buffer a dedicated frame. If an element is a list, instead of a string, then the car of the list is the buffer name, and the rest of the list says how to create the frame. There are two possibilities for the rest of the list. It can be an alist, specifying frame parameters, or it can contain a function and arguments to give to it. (The function’s first argument is always the buffer to be displayed; the arguments from the list come after that.)

Variable special-display-regexps

A list of regular expressions that specify buffers that should be displayed specially. If the buffer’s name matches any of the regular expressions in this list, display-buffer handles the buffer specially. By default, special display means to give the buffer a dedicated frame. If an element is a list, instead of a string, then the car of the list is the regular expression, and the rest of the list says how to create the frame. See above,

under special-display-buffer-names.

Variable special-display-function

This variable holds the function to call to display a buffer specially. It receives the buffer as an argument, and should return the window in which it is displayed. The default value of this variable is special-display-popup-frame.

Function special-display-popup-frame buffer

This function makes buffer visible in a frame of its own. If buffer is already displayed in a window in some frame, it makes the frame visible and raises it, to use that window. Otherwise, it creates a frame that will be dedicated to buffer. This function uses an existing window displaying buffer whether or not it is in a frame of its own; but if you set up the above variables in your init file, before buffer was created, then presumably the window was previously made by this function.

User Option special-display-frame-alist

This variable holds frame parameters for special-display-popup-frame to use when it creates a frame.

User Option same-window-buffer-names

A list of buffer names for buffers that should be displayed in the selected window. If the buffer’s name is in this list, display-buffer handles the buffer by switching to it in the selected window.

User Option same-window-regexps

A list of regular expressions that specify buffers that should be displayed in the selected window. If the buffer’s name matches any of the regular expressions in this list, display-buffer handles the buffer by switching to it in the selected window.

Variable display-buffer-function

This variable is the most flexible way to customize the behavior of displaybuffer. If it is non-nil, it should be a function that display-buffer calls to do the work. The function should accept two arguments, the same two arguments that display-buffer received. It should choose or create a window, display the specified buffer, and then return the window.

This hook takes precedence over all the other options and hooks described above.

A window can be marked as “dedicated” to its buffer. Then display-buffer does not try to use that window.

Function window-dedicated-p window

This function returns t if window is marked as dedicated; otherwise nil.

Function set-window-dedicated-p window flag

This function marks window as dedicated if flag is non-nil, and nondedicated otherwise.

25.9 Windows and Point

Each window has its own value of point, independent of the value of point in other windows displaying the same buffer. This makes it useful to have multiple windows showing one buffer.

• The window point is established when a window is first created; it is initialized from the buffer’s point, or from the window point of another window opened on the buffer if such a window exists.

• Selecting a window sets the value of point in its buffer to the window’s value of point. Conversely, deselecting a window sets the window’s value of point from that of the buffer. Thus, when you switch between windows that display a given buffer, the point value for the selected window is in effect in the buffer, while the point values for the other windows are stored in those windows.

• As long as the selected window displays the current buffer, the window’s point and the buffer’s point always move together; they remain equal.

• See Chapter 27 [Positions], page 429, for more details on buffer positions.

As far as the user is concerned, point is where the cursor is, and when the user switches to another buffer, the cursor jumps to the position of point in that buffer.

Function window-point window

This function returns the current position of point in window. For a nonselected window, this is the value point would have (in that window’s buffer) if that window were selected. When window is the selected window and its buffer is also the current buffer, the value returned is the same as point in that buffer. Strictly speaking, it would be more correct to return the “top-level” value of point, outside of any save-excursion forms. But that value is hard to find.

Function set-window-point window position

This function positions point in window at position position in window’s buffer.

25.10 The Window Start Position

Each window contains a marker used to keep track of a buffer position that specifies where in the buffer display should start. This position is called the display-start position of the window (or just the start). The character after this position is the one that appears at the upper left corner of the window. It is usually, but not inevitably, at the beginning of a text line.

Function window-start &optional window This function returns the display-start position of window window. If window is nil, the selected window is used. For example,

     (window-start)
          ⇒ 7058

When you create a window, or display a different buffer in it, the display-start position is set to a display-start position recently used for the same buffer, or 1 if the buffer doesn’t have any. Redisplay updates the window-start position (if you have not specified it explicitly since the previous redisplay) so that point appears on the screen. Nothing except redisplay automatically changes the window-start position; if you move point, do not expect the window-start position to change in response until after the next redisplay. For a realistic example of using window-start, see the description of countlines in Section 27.2.4 [Text Lines], page 432.

Function window-end &optional window This function returns the position of the end of the display in window window. If window is nil, the selected window is used. Simply changing the buffer text or moving point does not update the value that window-end returns. The value is updated only when Emacs redisplays and redisplay actually finishes. If the last redisplay of window was preempted, and did not finish, Emacs does not know the position of the end of display in that window. In that case, this function returns a value that is not correct. In a future version, window-end will return nil in that case.

Function set-window-start window position &optional noforce This function sets the display-start position of window to position in window’s buffer. It returns position. The display routines insist that the position of point be visible when a buffer is displayed. Normally, they change the display-start position (that is, scroll the window) whenever necessary to make point visible. However, if you specify the start position with this function using nil for noforce, it means you want display to start at position even if that would put the location of point off the screen. If this does place point off screen, the display routines move point to the left margin on the middle line in the window. For example, if point is 1 and you set the start of the window to 2, then point would be “above” the top of the window. The display routines will automatically move point if it is still 1 when redisplay occurs. Here is an example:

;; Here is what ‘foo’ looks like before executing

;; the set-window-start expression.
---------- Buffer: foo ----------
⋆This is the contents of buffer foo.
2
3
4
5
6
---------- Buffer: foo ----------
(set-window-start
 (selected-window)
 (1+ (window-start)))
⇒ 2

;; Here is what ‘foo’ looks like after executing

;; the set-window-start expression.
---------- Buffer: foo ----------
his is the contents of buffer foo.
2
3
⋆4
5
6
---------- Buffer: foo ----------

If noforce is non-nil, and position would place point off screen at the next redisplay, then redisplay computes a new window-start position that works well with point, and thus position is not used.

Function pos-visible-in-window-p &optional position window

This function returns t if position is within the range of text currently visible on the screen in window. It returns nil if position is scrolled vertically out of view. The argument position defaults to the current position of point; window, to the selected window. Here is an example:

          (or (pos-visible-in-window-p
               (point) (selected-window))
              (recenter 0))

The pos-visible-in-window-p function considers only vertical scrolling. If position is out of view only because window has been scrolled horizontally, pos-visible-in-window-p returns t. See Section 25.13 [Horizontal Scrolling], page 401.

25.11 Vertical Scrolling

Vertical scrolling means moving the text up or down in a window. It works by changing the value of the window’s display-start location. It may also change the value of windowpoint to keep it on the screen.

In the commands scroll-up and scroll-down, the directions “up” and “down” refer to the motion of the text in the buffer at which you are looking through the window. Imagine that the text is written on a long roll of paper and that the scrolling commands move the paper up and down. Thus, if you are looking at text in the middle of a buffer and repeatedly call scroll-down, you will eventually see the beginning of the buffer.

Some people have urged that the opposite convention be used: they imagine that the window moves over text that remains in place. Then “down” commands would take you to the end of the buffer. This view is more consistent with the actual relationship between windows and the text in the buffer, but it is less like what the user sees. The position of a window on the terminal does not move, and short scrolling commands clearly move the text up or down on the screen. We have chosen names that fit the user’s point of view.

The scrolling functions (aside from scroll-other-window) have unpredictable results if the current buffer is different from the buffer that is displayed in the selected window. See Section 24.2 [Current Buffer], page 369.

Command scroll-up &optional count This function scrolls the text in the selected window upward count lines. If count is negative, scrolling is actually downward.

If count is nil (or omitted), then the length of scroll is next-screen-context-lines lines less than the usable height of the window (not counting its mode line).

     scroll-up returns nil.

Command scroll-down &optional count This function scrolls the text in the selected window downward count lines. If count is negative, scrolling is actually upward.

If count is omitted or nil, then the length of the scroll is next-screen-context-lines lines less than the usable height of the window (not counting its mode line).

     scroll-down returns nil.

Command scroll-other-window &optional count

This function scrolls the text in another window upward count lines. Negative values of count, or nil, are handled as in scroll-up. You can specify a buffer to scroll with the variable other-window-scroll-buffer. When the selected window is the minibuffer, the next window is normally the one at the top left corner. You can specify a different window to scroll with the variable minibuffer-scroll-window. This variable has no effect when any other window is selected. See Section 17.8 [Minibuffer Misc], page 240. When the minibuffer is active, it is the next window if the selected window is the one at the bottom right corner. In this case, scroll-other-window attempts to scroll the minibuffer. If the minibuffer contains just one line, it has nowhere to scroll to, so the line reappears after the echo area momentarily displays the message “Beginning of buffer”.

Variable other-window-scroll-buffer

If this variable is non-nil, it tells scroll-other-window which buffer to scroll.

User Option scroll-step

This variable controls how scrolling is done automatically when point moves off the screen. If the value is zero, then redisplay scrolls the text to center point vertically in the window. If the value is a positive integer n, then redisplay brings point back on screen by scrolling n lines in either direction, if possible; otherwise, it centers point. The default value is zero.

User Option next-screen-context-lines

The value of this variable is the number of lines of continuity to retain when scrolling by full screens. For example, scroll-up with an argument of nil scrolls so that this many lines at the bottom of the window appear instead at the top. The default value is 2.

Command recenter &optional count This function scrolls the selected window to put the text where point is located at a specified vertical position within the window. If count is a nonnegative number, it puts the line containing point count lines down from the top of the window. If count is a negative number, then it counts upward from the bottom of the window, so that −1 stands for the last usable line in the window. If count is a non-nil list, then it stands for the line in the middle of the window. If count is nil, recenter puts the line containing point in the middle of the window, then clears and redisplays the entire selected frame. When recenter is called interactively, count is the raw prefix argument. Thus, typing C-u as the prefix sets the count to a non-nil list, while typing C-u 4 sets count to 4, which positions the current line four lines from the top. With an argument of zero, recenter positions the current line at the top of the window. This action is so handy that some people make a separate key binding to do this. For example,

     (defun line-to-top-of-window ()
       "Scroll current line to top of window.
     Replaces three keystroke sequence C-u 0 C-l."
       (interactive)
       (recenter 0))
     (global-set-key [kp-multiply] 'line-to-top-of-window)

25.12 Hooks for Vertical Scrolling

This section describes how a Lisp program can take action whenever a window displays a different part of its buffer or a different buffer. There are three actions that can change this: scrolling the window, switching buffers in the window, and changing the size of the window. The first two actions run window-scroll-functions; the last runs window-size-change-functions. The paradigmatic use of these hooks is Lazy Lock mode; see section “Font Lock Support Modes” in The GNU Emacs Manual.

Variable window-scroll-functions

This variable holds a list of functions that Emacs should call before redisplaying a window with scrolling. It is not a normal hook, because each function is called with two arguments: the window, and its new display-start position. Displaying a different buffer in the window also runs these functions. These functions cannot expect window-end (see Section 25.10 [Window Start], page 396) to return a meaningful value, because that value is updated only by redisplaying the buffer. So if one of these functions needs to know the last character that will fit in the window with its current display-start position, it has to find that character using vertical-motion (see Section 27.2.5 [Screen Lines], page 433).

Variable window-size-change-functions

This variable holds a list of functions to be called if the size of any window changes for any reason. The functions are called just once per redisplay, and just once for each frame on which size changes have occurred. Each function receives the frame as its sole argument. There is no direct way to find out which windows on that frame have changed size, or precisely how. However, if a size-change function records, at each call, the existing windows and their sizes, it can also compare the present sizes and the previous sizes. Creating or deleting windows counts as a size change, and therefore causes these functions to be called. Changing the frame size also counts, because it changes the sizes of the existing windows. It is not a good idea to use save-window-excursion (see Section 25.17 [Window Configurations], page 406) in these functions, because that always counts as a size change, and it would cause these functions to be called over and over. In most cases, save-selected-window (see Section 25.4 [Selecting Windows], page 387) is what you need here.

25.13 Horizontal Scrolling

Because we read English first from top to bottom and second from left to right, horizontal scrolling is not like vertical scrolling. Vertical scrolling involves selection of a contiguous portion of text to display. Horizontal scrolling causes part of each line to go off screen. The amount of horizontal scrolling is therefore specified as a number of columns rather than as a position in the buffer. It has nothing to do with the display-start position returned by

window-start.

Usually, no horizontal scrolling is in effect; then the leftmost column is at the left edge of the window. In this state, scrolling to the right is meaningless, since there is no data to the left of the screen to be revealed by it; so this is not allowed. Scrolling to the left is allowed; it scrolls the first columns of text off the edge of the window and can reveal additional columns on the right that were truncated before. Once a window has a nonzero amount of leftward horizontal scrolling, you can scroll it back to the right, but only so far as to reduce the net horizontal scroll to zero. There is no limit to how far left you can scroll, but eventually all the text will disappear off the left edge.

Command scroll-left count

This function scrolls the selected window count columns to the left (or to the right if count is negative). The return value is the total amount of leftward horizontal scrolling in effect after the change—just like the value returned by

window-hscroll (below).

Command scroll-right count

This function scrolls the selected window count columns to the right (or to the left if count is negative). The return value is the total amount of leftward horizontal scrolling in effect after the change—just like the value returned by

window-hscroll (below).

Once you scroll a window as far right as it can go, back to its normal position where the total leftward scrolling is zero, attempts to scroll any farther right have no effect.

Function window-hscroll &optional window This function returns the total leftward horizontal scrolling of window—the number of columns by which the text in window is scrolled left past the left margin.

The value is never negative. It is zero when no horizontal scrolling has been done in window (which is usually the case).

If window is nil, the selected window is used.

     (window-hscroll)
          ⇒ 0
     (scroll-left 5)
          ⇒ 5
     (window-hscroll)
          ⇒ 5

Function set-window-hscroll window columns

This function sets the number of columns from the left margin that window is scrolled to the value of columns. The argument columns should be zero or positive; if not, it is taken as zero. The value returned is columns.

     (set-window-hscroll (selected-window) 10)
          ⇒ 10

Here is how you can determine whether a given position position is off the screen due to horizontal scrolling:

(defun hscroll-on-screen (window position)
  (save-excursion
    (goto-char position)
    (and
     (>= (- (current-column) (window-hscroll window)) 0)
     (< (- (current-column) (window-hscroll window))
        (window-width window)))))

25.14 The Size of a Window

An Emacs window is rectangular, and its size information consists of the height (the number of lines) and the width (the number of character positions in each line). The mode line is included in the height. But the width does not count the scroll bar or the column of ‘|’ characters that separates side-by-side windows.

The following three functions return size information about a window:

Function window-height &optional window This function returns the number of lines in window, including its mode line. If window fills its entire frame, this is one less than the value of frame-height on that frame (since the last line is always reserved for the minibuffer). If window is nil, the function uses the selected window.

     (window-height)
          ⇒ 23
     (split-window-vertically)
          ⇒ #<window 4 on windows.texi>
     (window-height)
          ⇒ 11

Function window-width &optional window This function returns the number of columns in window. If window fills its entire frame, this is the same as the value of frame-width on that frame. The width does not include the window’s scroll bar or the column of ‘|’ characters that separates side-by-side windows. If window is nil, the function uses the selected window.

     (window-width)
          ⇒ 80

Function window-edges &optional window This function returns a list of the edge coordinates of window. If window is nil, the selected window is used.

The order of the list is (left top right bottom), all elements relative to 0, 0 at the top left corner of the frame. The element right of the value is one more than the rightmost column used by window, and bottom is one more than the bottommost row used by window and its mode-line.

When you have side-by-side windows, the right edge value for a window with a neighbor on the right includes the width of the separator between the window and that neighbor. This separator may be a column of ‘|’ characters or it may be a scroll bar. Since the width of the window does not include this separator, the width does not equal the difference between the right and left edges in this case.

Here is the result obtained on a typical 24-line terminal with just one window:

     (window-edges (selected-window))
          ⇒ (0 0 80 23)

The bottom edge is at line 23 because the last line is the echo area.

If window is at the upper left corner of its frame, then bottom is the same as the value of (window-height), right is almost the same as the value of (windowwidth)^{1}, and top and left are zero. For example, the edges of the following window are ‘0 0 5 8’. Assuming that the frame has more than 8 columns, the last column of the window (column 7) holds a border rather than text. The last row (row 4) holds the mode line, shown here with ‘xxxxxxxxx’.

                0
                _______
             0 |       |
               |       |
               |       |
               |       |
               xxxxxxxxx  4
                       7

When there are side-by-side windows, any window not at the right edge of its frame has a separator in its last column or columns. The separator counts as one or two columns in the width of the window. A window never includes a separator on its left, since that belongs to the window to the left.

In the following example, let’s suppose that the frame is 7 columns wide. Then the edges of the left window are ‘0 0 4 3’ and the edges of the right window are

‘4 0 7 3’.

1 They are not exactly equal because right includes the vertical separator line or scroll bar, while (window-width) does not.

               ______|   |   | |   |   | xxxxxxxxx 0  34  7

25.15 Changing the Size of a Window

The window size functions fall into two classes: high-level commands that change the size of windows and low-level functions that access window size. Emacs does not permit overlapping windows or gaps between windows, so resizing one window affects other windows.

Command enlarge-window size &optional horizontal This function makes the selected window size lines taller, stealing lines from neighboring windows. It takes the lines from one window at a time until that window is used up, then takes from another. If a window from which lines are stolen shrinks below window-min-height lines, that window disappears. If horizontal is non-nil, this function makes window wider by size columns, stealing columns instead of lines. If a window from which columns are stolen shrinks below window-min-width columns, that window disappears. If the requested size would exceed that of the window’s frame, then the function makes the window occupy the entire height (or width) of the frame. If size is negative, this function shrinks the window by −size lines or columns. If that makes the window smaller than the minimum size (window-min-height

and window-min-width), enlarge-window deletes the window.
enlarge-window returns nil.

Command enlarge-window-horizontally columns

This function makes the selected window columns wider. It could be defined as follows:

     (defun enlarge-window-horizontally (columns)
       (enlarge-window columns t))

Command shrink-window size &optional horizontal This function is like enlarge-window but negates the argument size, making the selected window smaller by giving lines (or columns) to the other windows.

If the window shrinks below window-min-height or window-min-width, then

it disappears. If size is negative, the window is enlarged by −size lines or columns.

Command shrink-window-horizontally columns

This function makes the selected window columns narrower. It could be defined as follows:

     (defun shrink-window-horizontally (columns)
       (shrink-window columns t))

The following two variables constrain the window-size-changing functions to a minimum height and width.

User Option window-min-height

The value of this variable determines how short a window may become before it is automatically deleted. Making a window smaller than window-min-height automatically deletes it, and no window may be created shorter than this. The absolute minimum height is two (allowing one line for the mode line, and one line for the buffer display). Actions that change window sizes reset this variable to two if it is less than two. The default value is 4.

User Option window-min-width

The value of this variable determines how narrow a window may become before it automatically deleted. Making a window smaller than window-min-width automatically deletes it, and no window may be created narrower than this. The absolute minimum width is one; any value below that is ignored. The default value is 10.

25.16 Coordinates and Windows

This section describes how to relate screen coordinates to windows.

Function window-at x y &optional frame This function returns the window containing the specified cursor position in the frame frame. The coordinates x and y are measured in characters and count from the top left corner of the frame. If they are out of range, window-at returns nil. If you omit frame, the selected frame is used.

Function coordinates-in-window-p coordinates window

This function checks whether a particular frame position falls within the window window. The argument coordinates is a cons cell of this form:

     (x . y)

The coordinates x and y are measured in characters, and count from the top left corner of the screen or frame. The value of coordinates-in-window-p is non-nil if the coordinates are inside window. The value also indicates what part of the window the position is in, as follows:

(relx . rely)

The coordinates are inside window. The numbers relx and rely are the equivalent window-relative coordinates for the specified position, counting from 0 at the top left corner of the window.

mode-line

The coordinates are in the mode line of window.

vertical-split

The coordinates are in the vertical line between window and its neighbor to the right. This value occurs only if the window doesn’t have a scroll bar; positions in a scroll bar are considered outside the window.

nil The coordinates are not in any part of window.

The function coordinates-in-window-p does not require a frame as argument because it always uses the frame that window is on.

25.17 Window Configurations

A window configuration records the entire layout of a frame—all windows, their sizes, which buffers they contain, what part of each buffer is displayed, and the values of point and the mark. You can bring back an entire previous layout by restoring a window configuration previously saved.

If you want to record all frames instead of just one, use a frame configuration instead of a window configuration. See Section 26.12 [Frame Configurations], page 421.

Function current-window-configuration

This function returns a new object representing Emacs’s current window configuration, namely the number of windows, their sizes and current buffers, which window is the selected window, and for each window the displayed buffer, the display-start position, and the positions of point and the mark. An exception is made for point in the current buffer, whose value is not saved.

Function set-window-configuration configuration

This function restores the configuration of Emacs’s windows and buffers to the state specified by configuration. The argument configuration must be a value

that was previously returned by current-window-configuration.

This function always counts as a window size change and triggers execution of the window-size-change-functions. (It doesn’t know how to tell whether the new configuration actually differs from the old one.) Here is a way of using this function to get the same effect as save-window-

excursion:
     (let ((config (current-window-configuration)))
       (unwind-protect
           (progn (split-window-vertically nil)

…)

         (set-window-configuration config)))

Special Form save-window-excursion forms…

This special form records the window configuration, executes forms in sequence, then restores the earlier window configuration. The window configuration includes the value of point and the portion of the buffer that is visible. It also includes the choice of selected window. However, it does not include the value of point in the current buffer; use save-excursion if you wish to preserve that.

Don’t use this construct when save-selected-window is all you need. Exit from save-window-excursion always triggers execution of the windowsize-change-functions. (It doesn’t know how to tell whether the restored configuration actually differs from the one in effect at the end of the forms.) The return value is the value of the final form in forms. For example:

     (split-window)
          ⇒ #<window 25 on control.texi>
     (setq w (selected-window))
          ⇒ #<window 19 on control.texi>
     (save-window-excursion
       (delete-other-windows w)
       (switch-to-buffer "foo")
       'do-something)
          ⇒ do-something

;; The screen is now split again.

Function window-configuration-p object

This function returns t if object is a window configuration.

Primitives to look inside of window configurations would make sense, but none are implemented. It is not clear they are useful enough to be worth implementing.

408 GNU Emacs Lisp Reference Manual

26 Frames

A frame is a rectangle on the screen that contains one or more Emacs windows. A frame initially contains a single main window (plus perhaps a minibuffer window), which you can subdivide vertically or horizontally into smaller windows.

When Emacs runs on a text-only terminal, it starts with one terminal frame. If you create additional ones, Emacs displays one and only one at any given time—on the terminal screen, of course.

When Emacs communicates directly with an X server, it does not have a terminal frame; instead, it starts with a single X window frame. It can display multiple X window frames at the same time, each in its own X window.

Function framep object

This predicate returns t if object is a frame, and nil otherwise.

See Chapter 35 [Display], page 567, for related information.

26.1 Creating Frames

To create a new frame, call the function make-frame.

Function make-frame &optional alist This function creates a new frame. If you are using X, it makes an X window frame; otherwise, it makes a terminal frame. The argument is an alist specifying frame parameters. Any parameters not mentioned in alist default according to the value of the variable defaultframe-alist; parameters not specified even there default from the standard X defaults file and X resources. The set of possible parameters depends in principle on what kind of window system Emacs uses to display its frames. See Section 26.3.3 [X Frame Parameters], page 412, for documentation of individual parameters you can specify.

Variable before-make-frame-hook

A normal hook run by make-frame before it actually creates the frame.

Variable after-make-frame-hook

A normal hook run by make-frame after it creates the frame.

26.2 Multiple Displays

A single Emacs can talk to more than one X Windows display. Initially, Emacs uses just one display—the one chosen with the DISPLAY environment variable or with the ‘--display’ option (see section “Initial Options” in The GNU Emacs Manual). To connect to another display, use the command make-frame-on-display or specify the display frame parameter when you create the frame.

Emacs treats each X server as a separate terminal, giving each one its own selected frame and its own minibuffer windows. A few Lisp variables have values local to the current terminal (that is, the terminal corresponding to the currently selected frame): these are

default-minibuffer-frame, defining-kbd-macro, last-kbd-macro, and system-key-

alist. These variables are always terminal-local and can never be buffer-local.

A single X server can handle more than one screen. A display name ‘host.server.screen’ has three parts; the last part specifies the screen number for a given server. When you use two screens belonging to one server, Emacs knows by the similarity in their names that they share a single keyboard, and it treats them as a single terminal.

Command make-frame-on-display display &optional parameters This creates a new frame on display display, taking the other frame parameters from parameters. Aside from the display argument, it is like make-frame (see Section 26.1 [Creating Frames], page 409).

Function x-display-list

This returns a list that indicates which X displays Emacs has a connection to. The elements of the list are strings, and each one is a display name.

Function x-open-connection display &optional xrm-string This function opens a connection to the X display display. It does not create a frame on that display, but it permits you to check that communication can be established with that display.

The optional argument resource-string, if not nil, is a string of resource names and values, in the same format used in the ‘.Xresources’ file. The values you specify override the resource values recorded in the X server itself; they apply to all Emacs frames created on this display. Here’s an example of what this string might look like:

     "*BorderWidth: 3\n*InternalBorder: 2\n"

See Section 26.20 [Resources], page 426.

Function x-close-connection display

This function closes the connection to display display. Before you can do this, you must first delete all the frames that were open on that display (see Section 26.5 [Deleting Frames], page 417).

26.3 Frame Parameters

A frame has many parameters that control its appearance and behavior. Just what parameters a frame has depends on what display mechanism it uses.

Frame parameters exist for the sake of window systems. A terminal frame has a few parameters, mostly for compatibility’s sake; only the height, width and buffer-predicate parameters really do something.

26.3.1 Access to Frame Parameters

These functions let you read and change the parameter values of a frame.

Function frame-parameters frame

The function frame-parameters returns an alist listing all the parameters of frame and their values.

Function modify-frame-parameters frame alist

This function alters the parameters of frame frame based on the elements of alist. Each element of alist has the form (parm . value), where parm is a symbol naming a parameter. If you don’t mention a parameter in alist, its value doesn’t change.

26.3.2 Initial Frame Parameters

You can specify the parameters for the initial startup frame by setting initial-frame-alist in your ‘.emacs’ file.

Variable initial-frame-alist

This variable’s value is an alist of parameter values used when creating the initial X window frame. You can set this variable to specify the appearance of the initial frame without altering subsequent frames. Each element has the form:

(parameter . value) Emacs creates the initial frame before it reads your ‘~/.emacs’ file. After reading that file, Emacs checks initial-frame-alist, and applies the parameter settings in the altered value to the already created initial frame. If these settings affect the frame geometry and appearance, you’ll see the frame appear with the wrong ones and then change to the specified ones. If that bothers you, you can specify the same geometry and appearance with X resources; those do take affect before the frame is created. See section “X Resources” in The GNU Emacs Manual. X resource settings typically apply to all frames. If you want to specify some X resources solely for the sake of the initial frame, and you don’t want them to apply to subsequent frames, here’s how to achieve this. Specify parameters in default-frame-alist to override the X resources for subsequent frames; then, to prevent these from affecting the initial frame, specify the same parameters in initial-frame-alist with values that match the X resources.

If these parameters specify a separate minibuffer-only frame with (minibuffer . nil), and you have not created one, Emacs creates one for you.

Variable minibuffer-frame-alist

This variable’s value is an alist of parameter values used when creating an initial minibuffer-only frame—if such a frame is needed, according to the parameters for the main initial frame.

Variable default-frame-alist

This is an alist specifying default values of frame parameters for all Emacs frames—the first frame, and subsequent frames. In many cases, you can get the same results by means of X resources.

See also special-display-frame-alist, in Section 25.8 [Choosing Window], page 393. If you use options that specify window appearance when you invoke Emacs, they take

effect by adding elements to default-frame-alist. One exception is ‘-geometry’, which adds the specified position to initial-frame-alist instead. See section “Command Arguments” in The GNU Emacs Manual.

26.3.3 X Window Frame Parameters

Just what parameters a frame has depends on what display mechanism it uses. Here is a table of the parameters of an X window frame; of these, name, height, width, and buffer-predicate provide meaningful information in non-X frames.

name The name of the frame. Most window managers display the frame’s name in the frame’s border, at the top of the frame. If you don’t specify a name, and you have more than one frame, Emacs sets the frame name based on the buffer displayed in the frame’s selected window. If you specify the frame name explicitly when you create the frame, the name is also used (instead of the name of the Emacs executable) when looking up X resources for the frame.

display The display on which to open this frame. It should be a string of the form "host:dpy.screen", just like the DISPLAY environment variable.

left The screen position of the left edge, in pixels, with respect to the left edge of the screen. The value may be a positive number pos, or a list of the form (+ pos) which permits specifying a negative pos value. A negative number −pos, or a list of the form (- pos), actually specifies the position of the right edge of the window with respect to the right edge of the screen. A positive value of pos counts toward the left. If the parameter is a negative integer −pos then pos is positive! Some window managers ignore program-specified positions. If you want to be sure the position you specify is not ignored, specify a non-nil value for the user-position parameter as well.

top The screen position of the top edge, in pixels, with respect to the top edge of the screen. The value may be a positive number pos, or a list of the form (+ pos) which permits specifying a negative pos value. A negative number −pos, or a list of the form (- pos), actually specifies the position of the bottom edge of the window with respect to the bottom edge of the screen. A positive value of pos counts toward the top. If the parameter is a negative integer −pos then pos is positive! Some window managers ignore program-specified positions. If you want to be sure the position you specify is not ignored, specify a non-nil value for the user-position parameter as well.

icon-left

The screen position of the left edge of the frame’s icon, in pixels, counting from the left edge of the screen. This takes effect if and when the frame is iconified. icon-top The screen position of the top edge of the frame’s icon, in pixels, counting from

the top edge of the screen. This takes effect if and when the frame is iconified.

user-position

When you create a frame and specify its screen position with the left and top parameters, use this parameter to say whether the specified position was user-specified (explicitly requested in some way by a human user) or merely program-specified (chosen by a program). A non-nil value says the position was user-specified. Window managers generally heed user-specified positions, and some heed program-specified positions too. But many ignore program-specified positions, placing the window in a default fashion or letting the user place it with the mouse. Some window managers, including twm, let the user specify whether to obey program-specified positions or ignore them. When you call make-frame, you should specify a non-nil value for this parameter if the values of the left and top parameters represent the user’s stated preference; otherwise, use nil.

height The height of the frame contents, in characters. (To get the height in pixels, call frame-pixel-height; see Section 26.3.4 [Size and Position], page 415.)

width The width of the frame contents, in characters. (To get the height in pixels, call frame-pixel-width; see Section 26.3.4 [Size and Position], page 415.)

window-id

The number of the X window for the frame.

minibuffer

Whether this frame has its own minibuffer. The value t means yes, nil means no, only means this frame is just a minibuffer. If the value is a minibuffer window (in some other frame), the new frame uses that minibuffer.

buffer-predicate

The buffer-predicate function for this frame. The function other-buffer uses this predicate (from the selected frame) to decide which buffers it should consider, if the predicate is not nil. It calls the predicate with one arg, a buffer, once for each buffer; if the predicate returns a non-nil value, it considers that buffer.

font The name of the font for displaying text in the frame. This is a string.

auto-raise

Whether selecting the frame raises it (non-nil means yes).

auto-lower

Whether deselecting the frame lowers it (non-nil means yes).

vertical-scroll-bars

Whether the frame has scroll bars for vertical scrolling (non-nil means yes).

horizontal-scroll-bars

Whether the frame has scroll bars for horizontal scrolling (non-nil means yes). (Horizontal scroll bars are not currently implemented.)

scroll-bar-width

The width of the vertical scroll bar, in pixels.

icon-type

The type of icon to use for this frame when it is iconified. If the value is a string, that specifies a file containing a bitmap to use. Any other non-nil value specifies the default bitmap icon (a picture of a gnu); nil specifies a text icon.

icon-name

The name to use in the icon for this frame, when and if the icon appears. If this is nil, the frame’s title is used.

foreground-color

The color to use for the image of a character. This is a string; the X server defines the meaningful color names.

background-color

The color to use for the background of characters.

mouse-color

The color for the mouse pointer.

cursor-color

The color for the cursor that shows point.

border-color

The color for the border of the frame.

cursor-type

The way to display the cursor. The legitimate values are bar, box, and (bar . width). The symbol box specifies an ordinary black box overlaying the character after point; that is the default. The symbol bar specifies a vertical bar between characters as the cursor. (bar . width) specifies a bar width pixels wide.

border-width

The width in pixels of the window border.

internal-border-width

The distance in pixels between text and border.

unsplittable

If non-nil, this frame’s window is never split automatically.

visibility

The state of visibility of the frame. There are three possibilities: nil for invisible, t for visible, and icon for iconified. See Section 26.10 [Visibility of Frames], page 420.

menu-bar-lines

The number of lines to allocate at the top of the frame for a menu bar. The default is 1. See Section 19.12.5 [Menu Bar], page 297. (In Emacs versions that use the X toolkit, there is only one menu bar line; all that matters about the number you specify is whether it is greater than zero.)

parent-id

The X window number of the window that should be the parent of this one. Specifying this lets you create an Emacs window inside some other application’s window. (It is not certain this will be implemented; try it and see if it works.)

26.3.4 Frame Size And Position

You can read or change the size and position of a frame using the frame parameters left, top, height, and width. Whatever geometry parameters you don’t specify are chosen by the window manager in its usual fashion.

Here are some special features for working with sizes and positions:

Function set-frame-position frame left top

This function sets the position of the top left corner of frame to left and top. These arguments are measured in pixels, and count from the top left corner of the screen. Negative parameter values count up or rightward from the top left corner of the screen.

Function frame-height &optional frame Function frame-width &optional frame

These functions return the height and width of frame, measured in characters. If you don’t supply frame, they use the selected frame.

Function frame-pixel-height &optional frame Function frame-pixel-width &optional frame

These functions return the height and width of frame, measured in pixels. If you don’t supply frame, they use the selected frame.

Function frame-char-height &optional frame Function frame-char-width &optional frame

These functions return the height and width of a character in frame, measured in pixels. The values depend on the choice of font. If you don’t supply frame, these functions use the selected frame.

Function set-frame-size frame cols rows

This function sets the size of frame, measured in characters; cols and rows specify the new width and height. To set the size based on values measured in pixels, use frame-char-height and frame-char-width to convert them to units of characters.

The old-fashioned functions set-screen-height and set-screen-width, which were used to specify the height and width of the screen in Emacs versions that did not support multiple frames, are still usable. They apply to the selected frame. See Section 35.2 [Screen Size], page 567.

Function x-parse-geometry geom

The function x-parse-geometry converts a standard X windows geometry string to an alist that you can use as part of the argument to make-frame.

The alist describes which parameters were specified in geom, and gives the values specified for them. Each element looks like (parameter . value). The possible parameter values are left, top, width, and height. For the size parameters, the value must be an integer. The position parameter names left and top are not totally accurate, because some values indicate the position of the right or bottom edges instead. These are the value possibilities for the position parameters:

an integer A positive integer relates the left edge or top edge of the window to the left or top edge of the screen. A negative integer relates the right or bottom edge of the window to the right or bottom edge of the screen.

(+ position)

This specifies the position of the left or top edge of the window relative to the left or top edge of the screen. The integer position may be positive or negative; a negative value specifies a position outside the screen.

(- position)

This specifies the position of the right or bottom edge of the window relative to the right or bottom edge of the screen. The integer position may be positive or negative; a negative value specifies a position outside the screen.

Here is an example:

     (x-parse-geometry "35x70+0-0")
          ⇒ ((width . 35) (height . 70)
              (left . 0) (top - 0))

26.4 Frame Titles

Every frame has a title; most window managers display the frame title at the top of the frame. You can specify an explicit title with the name frame property. But normally you don’t specify this explicitly, and Emacs computes the title automatically.

Emacs computes the frame title based on a template stored in the variable frame-title-

format.

Variable frame-title-format

This variable specifies how to compute a title for a frame when you have not explicitly specified one. The variable’s value is actually a mode line construct, just like mode-line-format. See Section 20.3.1 [Mode Line Data], page 311.

Variable icon-title-format

This variable specifies how to compute the title for an iconified frame, when you have not explicitly specified the frame title. This title appears in the icon itself.

Variable multiple-frames

This variable is set automatically by Emacs. Its value is t when there are two or more frames (not counting minibuffer-only frames or invisible frames). The

default value of frame-title-format uses multiple-frames so as to put the

buffer name in the frame title only when there is more than one frame.

26.5 Deleting Frames

Frames remain potentially visible until you explicitly delete them. A deleted frame cannot appear on the screen, but continues to exist as a Lisp object until there are no references to it. There is no way to cancel the deletion of a frame aside from restoring a saved frame configuration (see Section 26.12 [Frame Configurations], page 421); this is similar to the way windows behave.

Command delete-frame &optional frame This function deletes the frame frame. By default, frame is the selected frame.

Function frame-live-p frame

The function frame-live-p returns non-nil if the frame frame has not been deleted.

Some window managers provide a command to delete a window. These work by sending a special message to the program that operates the window. When Emacs gets one of these commands, it generates a delete-frame event, whose normal definition is a command that calls the function delete-frame. See Section 18.5.10 [Misc Events], page 258.

26.6 Finding All Frames

Function frame-list

The function frame-list returns a list of all the frames that have not been deleted. It is analogous to buffer-list for buffers. The list that you get is newly created, so modifying the list doesn’t have any effect on the internals of Emacs.

Function visible-frame-list

This function returns a list of just the currently visible frames. See Section 26.10 [Visibility of Frames], page 420. (Terminal frames always count as “visible”, even though only the selected one is actually displayed.)

Function next-frame &optional frame minibuf The function next-frame lets you cycle conveniently through all the frames from an arbitrary starting point. It returns the “next” frame after frame in the cycle. If frame is omitted or nil, it defaults to the selected frame. The second argument, minibuf, says which frames to consider:

nil Exclude minibuffer-only frames.

visible Consider all visible frames.

0 Consider all visible or iconified frames.

a window Consider only the frames using that particular window as their minibuffer.

anything else Consider all frames.

Function previous-frame &optional frame minibuf Like next-frame, but cycles through all frames in the opposite direction.

See also next-window and previous-window, in Section 25.5 [Cyclic Window Ordering], page 388.

26.7 Frames and Windows

Each window is part of one and only one frame; you can get the frame with window-

frame.

Function window-frame window

This function returns the frame that window is on.

All the non-minibuffer windows in a frame are arranged in a cyclic order. The order runs from the frame’s top window, which is at the upper left corner, down and to the right, until it reaches the window at the lower right corner (always the minibuffer window, if the frame has one), and then it moves back to the top.

Function frame-top-window frame

This returns the topmost, leftmost window of frame frame.

At any time, exactly one window on any frame is selected within the frame. The significance of this designation is that selecting the frame also selects this window. You can get the frame’s current selected window with frame-selected-window.

Function frame-selected-window frame

This function returns the window on frame that is selected within frame.

Conversely, selecting a window for Emacs with select-window also makes that window selected within its frame. See Section 25.4 [Selecting Windows], page 387.

Another function that (usually) returns one of the windows in a frame is minibufferwindow. See Section 17.8 [Minibuffer Misc], page 240.

26.8 Minibuffers and Frames

Normally, each frame has its own minibuffer window at the bottom, which is used whenever that frame is selected. If the frame has a minibuffer, you can get it with minibufferwindow (see Section 17.8 [Minibuffer Misc], page 240).

However, you can also create a frame with no minibuffer. Such a frame must use the minibuffer window of some other frame. When you create the frame, you can specify explicitly the minibuffer window to use (in some other frame). If you don’t, then the minibuffer is found in the frame which is the value of the variable default-minibuffer-frame. Its value should be a frame that does have a minibuffer.

If you use a minibuffer-only frame, you might want that frame to raise when you enter the minibuffer. If so, set the variable minibuffer-auto-raise to t. See Section 26.11 [Raising and Lowering], page 421.

Variable default-minibuffer-frame

This variable specifies the frame to use for the minibuffer window, by default. It is always local to the current terminal and cannot be buffer-local. See Section 26.2 [Multiple Displays], page 409.

26.9 Input Focus

At any time, one frame in Emacs is the selected frame. The selected window always resides on the selected frame.

Function selected-frame

This function returns the selected frame.

The X server normally directs keyboard input to the X window that the mouse is in. Some window managers use mouse clicks or keyboard events to shift the focus to various X windows, overriding the normal behavior of the server.

Lisp programs can switch frames “temporarily” by calling the function select-frame. This does not override the window manager; rather, it escapes from the window manager’s control until that control is somehow reasserted.

When using a text-only terminal, there is no window manager; therefore, switch-frame is the only way to switch frames, and the effect lasts until overridden by a subsequent call to switch-frame. Only the selected terminal frame is actually displayed on the terminal. Each terminal screen except for the initial one has a number, and the number of the selected frame appears in the mode line after the word ‘Emacs’ (see Section 20.3.2 [Mode Line Variables], page 312).

Function select-frame frame

This function selects frame frame, temporarily disregarding the focus of the X server if any. The selection of frame lasts until the next time the user does something to select a different frame, or until the next time this function is called.

Emacs cooperates with the X server and the window managers by arranging to select frames according to what the server and window manager ask for. It does so by generating a special kind of input event, called a focus event. The command loop handles a focus event by calling handle-switch-frame. See Section 18.5.9 [Focus Events], page 258.

Command handle-switch-frame frame

This function handles a focus event by selecting frame frame.

Focus events normally do their job by invoking this command. Don’t call it for any other reason.

Function redirect-frame-focus frame focus-frame

This function redirects focus from frame to focus-frame. This means that focusframe will receive subsequent keystrokes intended for frame. After such an event, the value of last-event-frame will be focus-frame. Also, switch-frame events specifying frame will instead select focus-frame.

If focus-frame is nil, that cancels any existing redirection for frame, which therefore once again receives its own events.

One use of focus redirection is for frames that don’t have minibuffers. These frames use minibuffers on other frames. Activating a minibuffer on another frame redirects focus to that frame. This puts the focus on the minibuffer’s frame, where it belongs, even though the mouse remains in the frame that activated the minibuffer.

Selecting a frame can also change focus redirections. Selecting frame bar, when foo had been selected, changes any redirections pointing to foo so that they point to bar instead. This allows focus redirection to work properly when the user switches from one frame to another using select-window.

This means that a frame whose focus is redirected to itself is treated differently from a frame whose focus is not redirected. select-frame affects the former but not the latter.

The redirection lasts until redirect-frame-focus is called to change it.

26.10 Visibility of Frames

An X window frame may be visible, invisible, or iconified. If it is visible, you can see its contents. If it is iconified, the frame’s contents do not appear on the screen, but an icon does. If the frame is invisible, it doesn’t show on the screen, not even as an icon.

Visibility is meaningless for terminal frames, since only the selected one is actually displayed in any case.

Command make-frame-visible &optional frame

This function makes frame frame visible. If you omit frame, it makes the selected frame visible.

Command make-frame-invisible &optional frame

This function makes frame frame invisible. If you omit frame, it makes the selected frame invisible.

Command iconify-frame &optional frame This function iconifies frame frame. If you omit frame, it iconifies the selected frame.

Function frame-visible-p frame

This returns the visibility status of frame frame. The value is t if frame is visible, nil if it is invisible, and icon if it is iconified.

The visibility status of a frame is also available as a frame parameter. You can read or change it as such. See Section 26.3.3 [X Frame Parameters], page 412.

The user can iconify and deiconify frames with the window manager. This happens below the level at which Emacs can exert any control, but Emacs does provide events that you can use to keep track of such changes. See Section 18.5.10 [Misc Events], page 258.

26.11 Raising and Lowering Frames

The X Window System uses a desktop metaphor. Part of this metaphor is the idea that windows are stacked in a notional third dimension perpendicular to the screen surface, and thus ordered from “highest” to “lowest”. Where two windows overlap, the one higher up covers the one underneath. Even a window at the bottom of the stack can be seen if no other window overlaps it.

A window’s place in this ordering is not fixed; in fact, users tend to change the order frequently. Raising a window means moving it “up”, to the top of the stack. Lowering a window means moving it to the bottom of the stack. This motion is in the notional third dimension only, and does not change the position of the window on the screen.

You can raise and lower Emacs’s X windows with these functions:

Command raise-frame frame

This function raises frame frame.

Command lower-frame frame

This function lowers frame frame.

User Option minibuffer-auto-raise

If this is non-nil, activation of the minibuffer raises the frame that the minibuffer window is in.

You can also enable auto-raise (raising automatically when a frame is selected) or autolower (lowering automatically when it is deselected) for any frame using frame parameters. See Section 26.3.3 [X Frame Parameters], page 412.

26.12 Frame Configurations

A frame configuration records the current arrangement of frames, all their properties, and the window configuration of each one.

Function current-frame-configuration

This function returns a frame configuration list that describes the current arrangement of frames and their contents.

Function set-frame-configuration configuration

This function restores the state of frames described in configuration.

26.13 Mouse Tracking

Sometimes it is useful to track the mouse, which means to display something to indicate where the mouse is and move the indicator as the mouse moves. For efficient mouse tracking, you need a way to wait until the mouse actually moves.

The convenient way to track the mouse is to ask for events to represent mouse motion. Then you can wait for motion by waiting for an event. In addition, you can easily handle any other sorts of events that may occur. That is useful, because normally you don’t want to track the mouse forever—only until some other event, such as the release of a button.

Special Form track-mouse body…

Execute body, meanwhile generating input events for mouse motion. The code in body can read these events with read-event or read-key-sequence. See Section 18.5.8 [Motion Events], page 257, for the format of mouse motion events.

The value of track-mouse is that of the last form in body.

The usual purpose of tracking mouse motion is to indicate on the screen the consequences of pushing or releasing a button at the current position.

In many cases, you can avoid the need to track the mouse by using the mouse-face text property (see Section 29.18.4 [Special Properties], page 482). That works at a much lower level and runs more smoothly than Lisp-level mouse tracking.

26.14 Mouse Position

The functions mouse-position and set-mouse-position give access to the current position of the mouse.

Function mouse-position

This function returns a description of the position of the mouse. The value looks like (frame x . y), where x and y are integers giving the position in characters relative to the top left corner of the inside of frame.

Function set-mouse-position frame x y

This function warps the mouse to position x, y in frame frame. The arguments x and y are integers, giving the position in characters relative to the top left corner of the inside of frame.

Function mouse-pixel-position

This function is like mouse-position except that it returns coordinates in units of pixels rather than units of characters.

Function set-mouse-pixel-position frame x y

This function warps the mouse like set-mouse-position except that x and y are in units of pixels rather than units of characters. These coordinates are not required to be within the frame.

26.15 Pop-Up Menus

When using X windows, a Lisp program can pop up a menu which the user can choose from with the mouse.

Function x-popup-menu position menu

This function displays a pop-up menu and returns an indication of what selection the user makes.

The argument position specifies where on the screen to put the menu. It can be either a mouse button event (which says to put the menu where the user actuated the button) or a list of this form:

((xoffset yoffset) window)

where xoffset and yoffset are coordinates, measured in pixels, counting from the top left corner of window’s frame.

If position is t, it means to use the current mouse position. If position is nil, it means to precompute the key binding equivalents for the keymaps specified in menu, without actually displaying or popping up the menu.

The argument menu says what to display in the menu. It can be a keymap or a list of keymaps (see Section 19.12 [Menu Keymaps], page 294). Alternatively, it can have the following form:

(title pane1 pane2...)

where each pane is a list of form (title (line . item)...)

Each line should be a string, and each item should be the value to return if that line is chosen.

Usage note: Don’t use x-popup-menu to display a menu if a prefix key with a menu keymap would do the job. If you use a menu keymap to implement a menu, C-h c and C-h a can see the individual items in that menu and provide help for them. If instead you implement the menu by defining a command that calls x-popup-menu, the help facilities cannot know what happens inside that command, so they cannot give any help for the menu’s items.

The menu bar mechanism, which lets you switch between submenus by moving the mouse, cannot look within the definition of a command to see that it calls x-popup-menu. Therefore, if you try to implement a submenu using x-popup-menu, it cannot work with the menu bar in an integrated fashion. This is why all menu bar submenus are implemented with menu keymaps within the parent menu, and never with x-popup-menu. See Section 19.12.5 [Menu Bar], page 297,

If you want a menu bar submenu to have contents that vary, you should still use a menu keymap to implement it. To make the contents vary, add a hook function to menu-bar-update-hook to update the contents of the menu keymap as necessary.

26.16 Dialog Boxes

A dialog box is a variant of a pop-up menu. It looks a little different (if Emacs uses an X toolkit), it always appears in the center of a frame, and it has just one level and one pane. The main use of dialog boxes is for asking questions that the user can answer with “yes”, “no”, and a few other alternatives. The functions y-or-n-p and yes-or-no-p use dialog boxes instead of the keyboard, when called from commands invoked by mouse clicks.

Function x-popup-dialog position contents This function displays a pop-up dialog box and returns an indication of what selection the user makes. The argument contents specifies the alternatives to offer; it has this format:

(title (string . value)…)

which looks like the list that specifies a single pane for x-popup-menu.

The return value is value from the chosen alternative.

An element of the list may be just a string instead of a cons cell (string . value). That makes a box that cannot be selected.

If nil appears in the list, it separates the left-hand items from the right-hand items; items that precede the nil appear on the left, and items that follow the nil appear on the right. If you don’t include a nil in the list, then approximately half the items appear on each side.

Dialog boxes always appear in the center of a frame; the argument position specifies which frame. The possible values are as in x-popup-menu, but the precise coordinates don’t matter; only the frame matters.

If your Emacs executable does not use an X toolkit, then it cannot display a real dialog box; so instead it displays the same items in a pop-up menu in the center of the frame.

26.17 Pointer Shapes

These variables specify which shape to use for the mouse pointer in various situations:

x-pointer-shape

This variable specifies the pointer shape to use ordinarily in the Emacs frame.

x-sensitive-text-pointer-shape

This variable specifies the pointer shape to use when the mouse is over mousesensitive text.

These variables affect newly created frames. They do not normally affect existing frames; however, if you set the mouse color of a frame, that also updates its pointer shapes based on the current values of these variables. See Section 26.3.3 [X Frame Parameters], page 412.

The values you can use, to specify either of these pointer shapes, are defined in the file

‘lisp/term/x-win.el’. Use M-x apropos ^{⟨}\underline{\overline{RET}}^{⟩} x-pointer ^{⟨}\underline{\overline{RET}}^{⟩} to see a list of them.

26.18 X Selections

The X server records a set of selections which permit transfer of data between application programs. The various selections are distinguished by selection types, represented in Emacs by symbols. X clients including Emacs can read or set the selection for any given type.

Function x-set-selection type data

This function sets a “selection” in the X server. It takes two arguments: a selection type type, and the value to assign to it, data. If data is nil, it means to clear out the selection. Otherwise, data may be a string, a symbol, an integer (or a cons of two integers or list of two integers), an overlay, or a cons of two markers pointing to the same buffer. An overlay or a pair of markers stands for text in the overlay or between the markers. The data may also be a vector of valid non-vector selection values. Each possible type has its own selection value, which changes independently. The usual values of type are PRIMARY and SECONDARY; these are symbols with upper-case names, in accord with X Window System conventions. The default

is PRIMARY.

Function x-get-selection &optional type data-type This function accesses selections set up by Emacs or by other X clients. It takes two optional arguments, type and data-type. The default for type, the selection type, is PRIMARY. The data-type argument specifies the form of data conversion to use, to convert the raw data obtained from another X client into Lisp data. Meaningful val-

ues include TEXT, STRING, TARGETS, LENGTH, DELETE, FILE_NAME, CHARACTER_
POSITION, LINE_NUMBER, COLUMN_NUMBER, OWNER_OS, HOST_NAME, USER, CLASS,

NAME, ATOM, and INTEGER. (These are symbols with upper-case names in accord with X conventions.) The default for data-type is STRING.

The X server also has a set of numbered cut buffers which can store text or other data being moved between applications. Cut buffers are considered obsolete, but Emacs supports them for the sake of X clients that still use them.

Function x-get-cut-buffer n

This function returns the contents of cut buffer number n.

Function x-set-cut-buffer string

This function stores string into the first cut buffer (cut buffer 0), moving the other values down through the series of cut buffers, much like the way successive kills in Emacs move down the kill ring.

26.19 Color Names

Function x-color-defined-p color &optional frame This function reports whether a color name is meaningful. It returns t if so; otherwise, nil. The argument frame says which frame’s display to ask about; if frame is omitted or nil, the selected frame is used.

Note that this does not tell you whether the display you are using really supports that color. You can ask for any defined color on any kind of display, and you will get some result—that is how the X server works. Here’s an approximate way to test whether your display supports the color color:

     (defun x-color-supported-p (color &optional frame)
       (and (x-color-defined-p color frame)
            (or (x-display-color-p frame)
                (member color '("black" "white"))
                (and (> (x-display-planes frame) 1)
                     (equal color "gray")))))

Function x-color-values color &optional frame This function returns a value that describes what color should ideally look like. If color is defined, the value is a list of three integers, which give the amount of red, the amount of green, and the amount of blue. Each integer ranges in principle from 0 to 65535, but in practice no value seems to be above 65280. If color is not defined, the value is nil.

     (x-color-values "black")
          ⇒ (0 0 0)
     (x-color-values "white")
          ⇒ (65280 65280 65280)
     (x-color-values "red")
          ⇒ (65280 0 0)
     (x-color-values "pink")
          ⇒ (65280 49152 51968)
     (x-color-values "hungry")
          ⇒ nil

The color values are returned for frame’s display. If frame is omitted or nil, the information is return for the selected frame’s display.

26.20 X Resources

Function x-get-resource attribute class &optional component subclass The function x-get-resource retrieves a resource value from the X Windows defaults database.

Resources are indexed by a combination of a key and a class. This function searches using a key of the form ‘instance.attribute’ (where instance is the name under which Emacs was invoked), and using ‘Emacs.class’ as the class.

The optional arguments component and subclass add to the key and the class, respectively. You must specify both of them or neither. If you specify them, the key is ‘instance.component.attribute’, and the class is ‘Emacs.class.subclass’.

See section “X Resources” in The GNU Emacs Manual.

26.21 Data about the X Server

This section describes functions you can use to get information about the capabilities and origin of an X display that Emacs is using. Each of these functions lets you specify the display you are interested in: the display argument can be either a display name, or a frame (meaning use the display that frame is on). If you omit the display argument, or specify nil, that means to use the selected frame’s display.

Function x-display-screens &optional display

This function returns the number of screens associated with the display.

Function x-server-version &optional display

This function returns the list of version numbers of the X server running the display.

Function x-server-vendor &optional display This function returns the vendor that provided the X server software.

Function x-display-pixel-height &optional display

This function returns the height of the screen in pixels.

Function x-display-mm-height &optional display

This function returns the height of the screen in millimeters.

Function x-display-pixel-width &optional display

This function returns the width of the screen in pixels.

Function x-display-mm-width &optional display

This function returns the width of the screen in millimeters.

Function x-display-backing-store &optional display

This function returns the backing store capability of the screen. Values can be

the symbols always, when-mapped, or not-useful.

Function x-display-save-under &optional display

This function returns non-nil if the display supports the SaveUnder feature.

Function x-display-planes &optional display

This function returns the number of planes the display supports.

Function x-display-visual-class &optional display

This function returns the visual class for the screen. The value is one of the sym-

bols static-gray, gray-scale, static-color, pseudo-color, true-color,
and direct-color.

Function x-display-grayscale-p &optional display

This function returns t if the screen can display shades of gray.

Function x-display-color-p &optional display

This function returns t if the screen is a color screen.

Function x-display-color-cells &optional display

This function returns the number of color cells the screen supports.

428 GNU Emacs Lisp Reference Manual

27 Positions

A position is the index of a character in the text of a buffer. More precisely, a position identifies the place between two characters (or before the first character, or after the last character), so we can speak of the character before or after a given position. However, we often speak of the character “at” a position, meaning the character after that position.

Positions are usually represented as integers starting from 1, but can also be represented as markers—special objects that relocate automatically when text is inserted or deleted so they stay with the surrounding characters. See Chapter 28 [Markers], page 441.

27.1 Point

Point is a special buffer position used by many editing commands, including the selfinserting typed characters and text insertion functions. Other commands move point through the text to allow editing and insertion at different places.

Like other positions, point designates a place between two characters (or before the first character, or after the last character), rather than a particular character. Usually terminals display the cursor over the character that immediately follows point; point is actually before the character on which the cursor sits.

The value of point is a number between 1 and the buffer size plus 1. If narrowing is in effect (see Section 27.4 [Narrowing], page 438), then point is constrained to fall within the accessible portion of the buffer (possibly at one end of it).

Each buffer has its own value of point, which is independent of the value of point in other buffers. Each window also has a value of point, which is independent of the value of point in other windows on the same buffer. This is why point can have different values in various windows that display the same buffer. When a buffer appears in only one window, the buffer’s point and the window’s point normally have the same value, so the distinction is rarely important. See Section 25.9 [Window Point], page 395, for more details.

Function point

This function returns the value of point in the current buffer, as an integer.

          (point) ⇒ 175

Function point-min

This function returns the minimum accessible value of point in the current buffer. This is normally 1, but if narrowing is in effect, it is the position of the start of the region that you narrowed to. (See Section 27.4 [Narrowing], page 438.)

Function point-max

This function returns the maximum accessible value of point in the current buffer. This is (1+ (buffer-size)), unless narrowing is in effect, in which case it is the position of the end of the region that you narrowed to. (See Section 27.4 [Narrowing], page 438).

Function buffer-end flag

This function returns (point-min) if flag is less than 1, (point-max) otherwise. The argument flag must be a number.

Function buffer-size

This function returns the total number of characters in the current buffer. In the absence of any narrowing (see Section 27.4 [Narrowing], page 438), point-max returns a value one larger than this.

     (buffer-size)
          ⇒ 35
     (point-max) ⇒ 36

27.2 Motion

Motion functions change the value of point, either relative to the current value of point, relative to the beginning or end of the buffer, or relative to the edges of the selected window. See Section 27.1 [Point], page 429.

27.2.1 Motion by Characters

These functions move point based on a count of characters. goto-char is the fundamental primitive; the other functions use that.

Command goto-char position

This function sets point in the current buffer to the value position. If position is less than 1, it moves point to the beginning of the buffer. If position is greater than the length of the buffer, it moves point to the end. If narrowing is in effect, position still counts from the beginning of the buffer, but point cannot go outside the accessible portion. If position is out of range, goto-char moves point to the beginning or the end of the accessible portion. When this function is called interactively, position is the numeric prefix argument, if provided; otherwise it is read from the minibuffer. goto-char returns position.

Command forward-char &optional count This function moves point count characters forward, towards the end of the buffer (or backward, towards the beginning of the buffer, if count is negative). If the function attempts to move point past the beginning or end of the buffer (or the limits of the accessible portion, when narrowing is in effect), an error is

signaled with error code beginning-of-buffer or end-of-buffer.

In an interactive call, count is the numeric prefix argument.

Command backward-char &optional count This function moves point count characters backward, towards the beginning of the buffer (or forward, towards the end of the buffer, if count is negative). If the function attempts to move point past the beginning or end of the buffer (or the limits of the accessible portion, when narrowing is in effect), an error is

signaled with error code beginning-of-buffer or end-of-buffer.

In an interactive call, count is the numeric prefix argument.

27.2.2 Motion by Words

These functions for parsing words use the syntax table to decide whether a given character is part of a word. See Chapter 31 [Syntax Tables], page 509.

Command forward-word count

This function moves point forward count words (or backward if count is negative). Normally it returns t. If this motion encounters the beginning or end of the buffer, or the limits of the accessible portion when narrowing is in effect, point stops there and the value is nil. In an interactive call, count is set to the numeric prefix argument.

Command backward-word count

This function is just like forward-word, except that it moves backward until encountering the front of a word, rather than forward. In an interactive call, count is set to the numeric prefix argument. This function is rarely used in programs, as it is more efficient to call forwardword with a negative argument.

Variable words-include-escapes

This variable affects the behavior of forward-word and everything that uses it. If it is non-nil, then characters in the “escape” and “character quote” syntax classes count as part of words. Otherwise, they do not.

27.2.3 Motion to an End of the Buffer

To move point to the beginning of the buffer, write:

(goto-char (point-min))

Likewise, to move to the end of the buffer, use:

(goto-char (point-max))

Here are two commands that users use to do these things. They are documented here to warn you not to use them in Lisp programs, because they set the mark and display messages in the echo area.

Command beginning-of-buffer &optional n

This function moves point to the beginning of the buffer (or the limits of the accessible portion, when narrowing is in effect), setting the mark at the previous position. If n is non-nil, then it puts point n tenths of the way from the beginning of the buffer. In an interactive call, n is the numeric prefix argument, if provided; otherwise n defaults to nil. Don’t use this function in Lisp programs!

Command end-of-buffer &optional n

This function moves point to the end of the buffer (or the limits of the accessible portion, when narrowing is in effect), setting the mark at the previous position. If n is non-nil, then it puts point n tenths of the way from the end of the buffer. In an interactive call, n is the numeric prefix argument, if provided; otherwise n defaults to nil. Don’t use this function in Lisp programs!

27.2.4 Motion by Text Lines

Text lines are portions of the buffer delimited by newline characters, which are regarded as part of the previous line. The first text line begins at the beginning of the buffer, and the last text line ends at the end of the buffer whether or not the last character is a newline. The division of the buffer into text lines is not affected by the width of the window, by line continuation in display, or by how tabs and control characters are displayed.

Command goto-line line

This function moves point to the front of the lineth line, counting from line 1 at beginning of the buffer. If line is less than 1, it moves point to the beginning of the buffer. If line is greater than the number of lines in the buffer, it moves point to the end of the buffer—that is, the end of the last line of the buffer. This is the only case in which goto-line does not necessarily move to the beginning of a line. If narrowing is in effect, then line still counts from the beginning of the buffer, but point cannot go outside the accessible portion. So goto-line moves point to the beginning or end of the accessible portion, if the line number specifies an inaccessible position. The return value of goto-line is the difference between line and the line number of the line to which point actually was able to move (in the full buffer, before taking account of narrowing). Thus, the value is positive if the scan encounters the real end of the buffer. The value is zero if scan encounters the end of the accessible portion but not the real end of the buffer. In an interactive call, line is the numeric prefix argument if one has been provided. Otherwise line is read in the minibuffer.

Command beginning-of-line &optional count

This function moves point to the beginning of the current line. With an argument count not nil or 1, it moves forward count−1 lines and then to the beginning of the line. If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point there. No error is signaled.

Command end-of-line &optional count This function moves point to the end of the current line. With an argument count not nil or 1, it moves forward count−1 lines and then to the end of the line.

If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point there. No error is signaled.

Command forward-line &optional count This function moves point forward count lines, to the beginning of the line. If count is negative, it moves point −count lines backward, to the beginning of a line. If count is zero, it moves point to the beginning of the current line. If forward-line encounters the beginning or end of the buffer (or of the accessible portion) before finding that many lines, it sets point there. No error is signaled. forward-line returns the difference between count and the number of lines actually moved. If you attempt to move down five lines from the beginning of a buffer that has only three lines, point stops at the end of the last line, and the value will be 2. In an interactive call, count is the numeric prefix argument.

Function count-lines start end

This function returns the number of lines between the positions start and end in the current buffer. If start and end are equal, then it returns 0. Otherwise it returns at least 1, even if start and end are on the same line. This is because the text between them, considered in isolation, must contain at least one line unless it is empty. Here is an example of using count-lines:

     (defun current-line ()
       "Return the vertical position of point. . ."
       (+ (count-lines (window-start) (point))
          (if (= (current-column) 0) 1 0)
          -1))

Also see the functions bolp and eolp in Section 29.1 [Near Point], page 449. These functions do not move point, but test whether it is already at the beginning or end of a line.

27.2.5 Motion by Screen Lines

The line functions in the previous section count text lines, delimited only by newline characters. By contrast, these functions count screen lines, which are defined by the way the text appears on the screen. A text line is a single screen line if it is short enough to fit the width of the selected window, but otherwise it may occupy several screen lines.

In some cases, text lines are truncated on the screen rather than continued onto additional screen lines. In these cases, vertical-motion moves point much like forward-line. See Section 35.3 [Truncation], page 568.

Because the width of a given string depends on the flags that control the appearance of certain characters, vertical-motion behaves differently, for a given piece of text, depending on the buffer it is in, and even on the selected window (because the width, the truncation flag, and display table may vary between windows). See Section 35.13 [Usual Display], page 582.

These functions scan text to determine where screen lines break, and thus take time proportional to the distance scanned. If you intend to use them heavily, Emacs provides caches which may improve the performance of your code. See Section 27.2.4 [Text Lines], page 432.

Function vertical-motion count &optional window This function moves point to the start of the screen line count screen lines down from the screen line containing point. If count is negative, it moves up instead. vertical-motion returns the number of lines moved. The value may be less in absolute value than count if the beginning or end of the buffer was reached. The window window is used for obtaining parameters such as the width, the horizontal scrolling, and the display table. But vertical-motion always operates on the current buffer, even if window currently displays some other buffer.

Command move-to-window-line count

This function moves point with respect to the text currently displayed in the selected window. It moves point to the beginning of the screen line count screen lines from the top of the window. If count is negative, that specifies a position −count lines from the bottom (or the last line of the buffer, if the buffer ends above the specified screen position). If count is nil, then point moves to the beginning of the line in the middle of the window. If the absolute value of count is greater than the size of the window, then point moves to the place that would appear on that screen line if the window were tall enough. This will probably cause the next redisplay to scroll to bring that location onto the screen. In an interactive call, count is the numeric prefix argument. The value returned is the window line number point has moved to, with the top line in the window numbered 0.

Function compute-motion from frompos to topos width offsets window This function scans the current buffer, calculating screen positions. It scans the buffer forward from position from, assuming that is at screen coordinates frompos, to position to or coordinates topos, whichever comes first. It returns the ending buffer position and screen coordinates. The coordinate arguments frompos and topos are cons cells of the form (hpos . vpos). The argument width is the number of columns available to display text; this affects handling of continuation lines. Use the value returned by window-width for the window of your choice; normally, use (window-width window). The argument offsets is either nil or a cons cell of the form (hscroll . taboffset). Here hscroll is the number of columns not being displayed at the left margin; most callers get this from window-hscroll. Meanwhile, tab-offset is the offset between column numbers on the screen and column numbers in the buffer. This can be nonzero in a continuation line, when the previous screen lines’ widths do not add up to a multiple of tab-width. It is always zero in a non-continuation line.

The window window serves only to specify which display table to use. computemotion always operates on the current buffer, regardless of what buffer is displayed in window. The return value is a list of five elements:

(pos vpos hpos prevhpos contin) Here pos is the buffer position where the scan stopped, vpos is the vertical screen position, and hpos is the horizontal screen position. The result prevhpos is the horizontal position one character back from pos. The result contin is t if the last line was continued after (or within) the previous character. For example, to find the buffer position of column col of line line of a certain window, pass the window’s display start location as from and the window’s upper-left coordinates as frompos. Pass the buffer’s (point-max) as to, to limit the scan to the end of the accessible portion of the buffer, and pass line and col as topos. Here’s a function that does this:

     (defun coordinates-of-position (col line)
       (car (compute-motion (window-start)
                            '(0 . 0)
                            (point-max)
                            (cons col line)
                            (window-width)
                            (cons (window-hscroll) 0)
                            (selected-window))))

When you use compute-motion for the minibuffer, you need to use minibufferprompt-width to get the horizontal position of the beginning of the first screen line. See Section 17.8 [Minibuffer Misc], page 240.

27.2.6 Moving over Balanced Expressions

Here are several functions concerned with balanced-parenthesis expressions (also called sexps in connection with moving across them in Emacs). The syntax table controls how these functions interpret various characters; see Chapter 31 [Syntax Tables], page 509. See Section 31.5 [Parsing Expressions], page 515, for lower-level primitives for scanning sexps or parts of sexps. For user-level commands, see section “Lists Commands” in GNU Emacs Manual.

Command forward-list arg

This function moves forward across arg balanced groups of parentheses. (Other syntactic entities such as words or paired string quotes are ignored.)

Command backward-list arg

This function moves backward across arg balanced groups of parentheses. (Other syntactic entities such as words or paired string quotes are ignored.)

Command up-list arg

This function moves forward out of arg levels of parentheses. A negative argument means move backward but still to a less deep spot.

Command down-list arg

This function moves forward into arg levels of parentheses. A negative argument means move backward but still go deeper in parentheses (−arg levels).

Command forward-sexp arg

This function moves forward across arg balanced expressions. Balanced expressions include both those delimited by parentheses and other kinds, such as words and string constants. For example,

     ---------- Buffer: foo ----------
     (concat⋆ "foo " (car x) y z)
     ---------- Buffer: foo ----------
     (forward-sexp 3)
          ⇒ nil
     ---------- Buffer: foo ----------
     (concat "foo " (car x) y⋆ z)
     ---------- Buffer: foo ----------

Command backward-sexp arg

This function moves backward across arg balanced expressions.

Command beginning-of-defun arg

This function moves back to the argth beginning of a defun. If arg is negative, this actually moves forward, but it still moves to the beginning of a defun, not to the end of one.

Command end-of-defun arg

This function moves forward to the argth end of a defun. If arg is negative, this actually moves backward, but it still moves to the end of a defun, not to the beginning of one.

User Option defun-prompt-regexp

If non-nil, this variable holds a regular expression that specifies what text can appear before the open-parenthesis that starts a defun. That is to say, a defun begins on a line that starts with a match for this regular expression, followed by a character with open-parenthesis syntax.

27.2.7 Skipping Characters

The following two functions move point over a specified set of characters. For example, they are often used to skip whitespace. For related functions, see Section 31.4 [Motion and Syntax], page 515.

Function skip-chars-forward character-set &optional limit This function moves point in the current buffer forward, skipping over a given set of characters. It examines the character following point, then advances point if the character matches character-set. This continues until it reaches a character that does not match. The function returns nil.

The argument character-set is like the inside of a ‘[…]’ in a regular expression except that ‘]’ is never special and ‘\’ quotes ‘^’, ‘-’ or ‘\’. Thus, "a-zA-Z" skips over all letters, stopping before the first nonletter, and "^a-zA-Z" skips nonletters stopping before the first letter. See Section 30.2 [Regular Expressions], page 492.

If limit is supplied (it must be a number or a marker), it specifies the maximum position in the buffer that point can be skipped to. Point will stop at or before limit.

In the following example, point is initially located directly before the ‘T’. After the form is evaluated, point is located at the end of that line (between the ‘t’ of ‘hat’ and the newline). The function skips all letters and spaces, but not newlines.

     ---------- Buffer: foo ----------
     I read "⋆The cat in the hat
     comes back" twice.
     ---------- Buffer: foo ----------
     (skip-chars-forward "a-zA-Z ")
          ⇒ nil
     ---------- Buffer: foo ----------
     I read "The cat in the hat⋆
     comes back" twice.
     ---------- Buffer: foo ----------

Function skip-chars-backward character-set &optional limit This function moves point backward, skipping characters that match characterset, until limit. It just like skip-chars-forward except for the direction of motion.

27.3 Excursions

It is often useful to move point “temporarily” within a localized portion of the program, or to switch buffers temporarily. This is called an excursion, and it is done with the saveexcursion special form. This construct saves the current buffer and its values of point and the mark so they can be restored after the completion of the excursion.

The forms for saving and restoring the configuration of windows are described elsewhere (see Section 25.17 [Window Configurations], page 406, and see Section 26.12 [Frame Configurations], page 421).

Special Form save-excursion forms…

The save-excursion special form saves the identity of the current buffer and the values of point and the mark in it, evaluates forms, and finally restores the buffer and its saved values of point and the mark. All three saved values are restored even in case of an abnormal exit via throw or error (see Section 9.5 [Nonlocal Exits], page 110).

The save-excursion special form is the standard way to switch buffers or move point within one part of a program and avoid affecting the rest of the program. It is used more than 500 times in the Lisp sources of Emacs.

save-excursion does not save the values of point and the mark for other buffers, so changes in other buffers remain in effect after save-excursion exits.

Likewise, save-excursion does not restore window-buffer correspondences altered by functions such as switch-to-buffer. One way to restore these correspondences, and the selected window, is to use save-window-excursion inside save-excursion (see Section 25.17 [Window Configurations], page 406).

The value returned by save-excursion is the result of the last of forms, or nil if no forms are given.

     (save-excursion

forms) ≡

     (let ((old-buf (current-buffer))
           (old-pnt (point-marker))
           (old-mark (copy-marker (mark-marker))))
       (unwind-protect
           (progn forms)
         (set-buffer old-buf)
         (goto-char old-pnt)
         (set-marker (mark-marker) old-mark)))

27.4 Narrowing

Narrowing means limiting the text addressable by Emacs editing commands to a limited range of characters in a buffer. The text that remains addressable is called the accessible portion of the buffer.

Narrowing is specified with two buffer positions which become the beginning and end of the accessible portion. For most editing commands and most Emacs primitives, these positions replace the values of the beginning and end of the buffer. While narrowing is in effect, no text outside the accessible portion is displayed, and point cannot move outside the accessible portion.

Values such as positions or line numbers, which usually count from the beginning of the buffer, do so despite narrowing, but the functions which use them refuse to operate on text that is inaccessible.

The commands for saving buffers are unaffected by narrowing; they save the entire buffer regardless of any narrowing.

Command narrow-to-region start end

This function sets the accessible portion of the current buffer to start at start and end at end. Both arguments should be character positions.

In an interactive call, start and end are set to the bounds of the current region (point and the mark, with the smallest first).

Command narrow-to-page move-count

This function sets the accessible portion of the current buffer to include just the current page. An optional first argument move-count non-nil means to move forward or backward by move-count pages and then narrow. The variable page-delimiter specifies where pages start and end (see Section 30.8 [Standard Regexps], page 506).

In an interactive call, move-count is set to the numeric prefix argument.

Command widen

This function cancels any narrowing in the current buffer, so that the entire contents are accessible. This is called widening. It is equivalent to the following expression:

     (narrow-to-region 1 (1+ (buffer-size)))

Special Form save-restriction body…

This special form saves the current bounds of the accessible portion, evaluates the body forms, and finally restores the saved bounds, thus restoring the same state of narrowing (or absence thereof) formerly in effect. The state of narrowing is restored even in the event of an abnormal exit via throw or error (see Section 9.5 [Nonlocal Exits], page 110). Therefore, this construct is a clean way to narrow a buffer temporarily.

The value returned by save-restriction is that returned by the last form in body, or nil if no body forms were given.

Caution: it is easy to make a mistake when using the save-restriction construct. Read the entire description here before you try it.

If body changes the current buffer, save-restriction still restores the restrictions on the original buffer (the buffer whose restructions it saved from), but it does not restore the identity of the current buffer.

save-restriction does not restore point and the mark; use save-excursion for that. If you use both save-restriction and save-excursion together, save-excursion should come first (on the outside). Otherwise, the old point value would be restored with temporary narrowing still in effect. If the old point value were outside the limits of the temporary narrowing, this would fail to restore it accurately.

The save-restriction special form records the values of the beginning and end of the accessible portion as distances from the beginning and end of the buffer. In other words, it records the amount of inaccessible text before and after the accessible portion.

This method yields correct results if body does further narrowing. However, save-restriction can become confused if the body widens and then make changes outside the range of the saved narrowing. When this is what you want to do, save-restriction is not the right tool for the job. Here is what you must use instead:

(let ((beg (point-min-marker))
      (end (point-max-marker)))
  (unwind-protect
      (progn body)
    (save-excursion
      (set-buffer (marker-buffer beg))
      (narrow-to-region beg end))))

Here is a simple example of correct use of save-restriction:

---------- Buffer: foo ----------
This is the contents of foo
This is the contents of foo
This is the contents of foo⋆
---------- Buffer: foo ----------
(save-excursion
  (save-restriction
    (goto-char 1)
    (forward-line 2)
    (narrow-to-region 1 (point))
    (goto-char (point-min))
    (replace-string "foo" "bar")))
---------- Buffer: foo ----------
This is the contents of bar
This is the contents of bar
This is the contents of foo⋆
---------- Buffer: foo ----------

28 Markers

A marker is a Lisp object used to specify a position in a buffer relative to the surrounding text. A marker changes its offset from the beginning of the buffer automatically whenever text is inserted or deleted, so that it stays with the two characters on either side of it.

28.1 Overview of Markers

A marker specifies a buffer and a position in that buffer. The marker can be used to represent a position in the functions that require one, just as an integer could be used. See Chapter 27 [Positions], page 429, for a complete description of positions.

A marker has two attributes: the marker position, and the marker buffer. The marker position is an integer that is equivalent (at a given time) to the marker as a position in that buffer. But the marker’s position value can change often during the life of the marker. Insertion and deletion of text in the buffer relocate the marker. The idea is that a marker positioned between two characters remains between those two characters despite insertion and deletion elsewhere in the buffer. Relocation changes the integer equivalent of the marker.

Deleting text around a marker’s position leaves the marker between the characters immediately before and after the deleted text. Inserting text at the position of a marker normally leaves the marker in front of the new text—unless it is inserted with insertbefore-markers (see Section 29.4 [Insertion], page 452).

Insertion and deletion in a buffer must check all the markers and relocate them if necessary. This slows processing in a buffer with a large number of markers. For this reason, it is a good idea to make a marker point nowhere if you are sure you don’t need it any more. Unreferenced markers are garbage collected eventually, but until then will continue to use time if they do point somewhere.

Because it is common to perform arithmetic operations on a marker position, most of the arithmetic operations (including + and -) accept markers as arguments. In such cases, the marker stands for its current position.

Here are examples of creating markers, setting markers, and moving point to markers: ;; Make a new marker that initially does not point anywhere:

     (setq m1 (make-marker))
          ⇒ #<marker in no buffer>

;; Set m1 to point between the 99th and 100th characters ;; in the current buffer:

     (set-marker m1 100)
          ⇒ #<marker at 100 in markers.texi>

;; Now insert one character at the beginning of the buffer:

     (goto-char (point-min))
          ⇒ 1
     (insert "Q")
          ⇒ nil

;; m1 is updated appropriately.

m1
     ⇒ #<marker at 101 in markers.texi>

;; Two markers that point to the same position ;; are not eq, but they are equal.

(setq m2 (copy-marker m1))
     ⇒ #<marker at 101 in markers.texi>
(eq m1 m2)
     ⇒ nil
(equal m1 m2)
     ⇒ t

;; When you are finished using a marker, make it point nowhere.

(set-marker m1 nil)
     ⇒ #<marker in no buffer>

28.2 Predicates on Markers

You can test an object to see whether it is a marker, or whether it is either an integer or a marker. The latter test is useful in connection with the arithmetic functions that work with both markers and integers.

Function markerp object

This function returns t if object is a marker, nil otherwise. Note that integers are not markers, even though many functions will accept either a marker or an integer.

Function integer-or-marker-p object

This function returns t if object is an integer or a marker, nil otherwise.

Function number-or-marker-p object

This function returns t if object is a number (either kind) or a marker, nil otherwise.

28.3 Functions That Create Markers

When you create a new marker, you can make it point nowhere, or point to the present position of point, or to the beginning or end of the accessible portion of the buffer, or to the same place as another given marker.

Function make-marker

This functions returns a newly created marker that does not point anywhere.

     (make-marker)
          ⇒ #<marker in no buffer>

Function point-marker

This function returns a new marker that points to the present position of point in the current buffer. See Section 27.1 [Point], page 429. For an example, see

copy-marker, below.

Function point-min-marker

This function returns a new marker that points to the beginning of the accessible portion of the buffer. This will be the beginning of the buffer unless narrowing is in effect. See Section 27.4 [Narrowing], page 438.

Function point-max-marker

This function returns a new marker that points to the end of the accessible portion of the buffer. This will be the end of the buffer unless narrowing is in effect. See Section 27.4 [Narrowing], page 438. Here are examples of this function and point-min-marker, shown in a buffer containing a version of the source file for the text of this chapter.

     (point-min-marker)
          ⇒ #<marker at 1 in markers.texi>
     (point-max-marker)
          ⇒ #<marker at 15573 in markers.texi>
     (narrow-to-region 100 200)
          ⇒ nil
     (point-min-marker)
          ⇒ #<marker at 100 in markers.texi>
     (point-max-marker)
          ⇒ #<marker at 200 in markers.texi>

Function copy-marker marker-or-integer If passed a marker as its argument, copy-marker returns a new marker that points to the same place and the same buffer as does marker-or-integer. If passed an integer as its argument, copy-marker returns a new marker that points to position marker-or-integer in the current buffer. If passed an integer argument less than 1, copy-marker returns a new marker that points to the beginning of the current buffer. If passed an integer argument greater than the length of the buffer, copy-marker returns a new marker that points to the end of the buffer. An error is signaled if marker is neither a marker nor an integer.

     (setq p (point-marker))
          ⇒ #<marker at 2139 in markers.texi>
     (setq q (copy-marker p))
          ⇒ #<marker at 2139 in markers.texi>
     (eq p q) ⇒ nil
     (equal p q) ⇒ t
     (copy-marker 0)
          ⇒ #<marker at 1 in markers.texi>
     (copy-marker 20000)
          ⇒ #<marker at 7572 in markers.texi>

28.4 Information from Markers

This section describes the functions for accessing the components of a marker object.

Function marker-position marker

This function returns the position that marker points to, or nil if it points nowhere.

Function marker-buffer marker

This function returns the buffer that marker points into, or nil if it points nowhere.

     (setq m (make-marker))
          ⇒ #<marker in no buffer>
     (marker-position m)
          ⇒ nil
     (marker-buffer m)
          ⇒ nil
     (set-marker m 3770 (current-buffer))
          ⇒ #<marker at 3770 in markers.texi>
     (marker-buffer m)
          ⇒ #<buffer markers.texi>
     (marker-position m)
          ⇒ 3770

Two distinct markers are considered equal (even though not eq) to each other if they have the same position and buffer, or if they both point nowhere.

28.5 Changing Marker Positions

This section describes how to change the position of an existing marker. When you do this, be sure you know whether the marker is used outside of your program, and, if so, what effects will result from moving it—otherwise, confusing things may happen in other parts of Emacs.

Function set-marker marker position &optional buffer This function moves marker to position in buffer. If buffer is not provided, it defaults to the current buffer. If position is less than 1, set-marker moves marker to the beginning of the buffer. If position is greater than the size of the buffer, set-marker moves marker to the end of the buffer. If position is nil or a marker that points nowhere, then marker is set to point nowhere. The value returned is marker.

     (setq m (point-marker))
          ⇒ #<marker at 4714 in markers.texi>
     (set-marker m 55)
          ⇒ #<marker at 55 in markers.texi>

          (setq b (get-buffer "foo"))
               ⇒ #<buffer foo>
          (set-marker m 0 b)
               ⇒ #<marker at 1 in foo>

Function move-marker marker position &optional buffer This is another name for set-marker.

28.6 The Mark

One special marker in each buffer is designated the mark. It records a position for the user for the sake of commands such as C-w and C-x ^{⟨}\underline{\overline{TAB}}^{⟩}. Lisp programs should set the mark only to values that have a potential use to the user, and never for their own internal purposes. For example, the replace-regexp command sets the mark to the value of point before doing any replacements, because this enables the user to move back there conveniently after the replace is finished.

Many commands are designed so that when called interactively they operate on the text between point and the mark. If you are writing such a command, don’t examine the mark directly; instead, use interactive with the ‘r’ specification. This provides the values of point and the mark as arguments to the command in an interactive call, but permits other Lisp programs to specify arguments explicitly. See Section 18.2.2 [Interactive Codes], page 245.

Each buffer has its own value of the mark that is independent of the value of the mark in other buffers. When a buffer is created, the mark exists but does not point anywhere. We consider this state as “the absence of a mark in that buffer.”

Once the mark “exists” in a buffer, it normally never ceases to exist. However, it may become inactive, if Transient Mark mode is enabled. The variable mark-active, which is always local in all buffers, indicates whether the mark is active: non-nil means yes. A command can request deactivation of the mark upon return to the editor command loop by setting deactivate-mark to a non-nil value (but this causes deactivation only if Transient Mark mode is enabled).

The main motivation for using Transient Mark mode is that this mode also enables highlighting of the region when the mark is active. See Chapter 35 [Display], page 567.

In addition to the mark, each buffer has a mark ring which is a list of markers containing previous values of the mark. When editing commands change the mark, they should normally save the old value of the mark on the mark ring. The variable mark-ring-max specifies the maximum number of entries in the mark ring; once the list becomes this long, adding a new element deletes the last element.

Function mark &optional force This function returns the current buffer’s mark position as an integer.

If the mark is inactive, mark normally signals an error. However, if force is non-nil, then mark returns the mark position anyway—or nil, if the mark is not yet set for this buffer.

Function mark-marker

This function returns the current buffer’s mark. This is the very marker that records the mark location inside Emacs, not a copy. Therefore, changing this marker’s position will directly affect the position of the mark. Don’t do it unless that is the effect you want.

     (setq m (mark-marker))
          ⇒ #<marker at 3420 in markers.texi>
     (set-marker m 100)
          ⇒ #<marker at 100 in markers.texi>
     (mark-marker)
          ⇒ #<marker at 100 in markers.texi>

Like any marker, this marker can be set to point at any buffer you like. We don’t recommend that you make it point at any buffer other than the one of which it is the mark. If you do, it will yield perfectly consistent, but rather odd, results.

Function set-mark position

This function sets the mark to position, and activates the mark. The old value of the mark is not pushed onto the mark ring. Please note: Use this function only if you want the user to see that the mark has moved, and you want the previous mark position to be lost. Normally, when a new mark is set, the old one should go on the mark-ring. For this reason, most applications should use push-mark and pop-mark, not set-mark. Novice Emacs Lisp programmers often try to use the mark for the wrong purposes. The mark saves a location for the user’s convenience. An editing command should not alter the mark unless altering the mark is part of the user-level functionality of the command. (And, in that case, this effect should be documented.) To remember a location for internal use in the Lisp program, store it in a Lisp variable. For example:

     (let ((beg (point)))
       (forward-line 1)
       (delete-region beg (point))).

Function push-mark &optional position nomsg activate This function sets the current buffer’s mark to position, and pushes a copy of the previous mark onto mark-ring. If position is nil, then the value of point is used. push-mark returns nil. The function push-mark normally does not activate the mark. To do that, specify t for the argument activate. A ‘Mark set’ message is displayed unless nomsg is non-nil.

Function pop-mark

This function pops off the top element of mark-ring and makes that mark become the buffer’s actual mark. This does not move point in the buffer, and it does nothing if mark-ring is empty. It deactivates the mark. The return value is not meaningful.

User Option transient-mark-mode

This variable if non-nil enables Transient Mark mode, in which every buffermodifying primitive sets deactivate-mark. The consequence of this is that commands that modify the buffer normally make the mark inactive.

Variable deactivate-mark

If an editor command sets this variable non-nil, then the editor command loop deactivates the mark after the command returns, but only if Transient Mark mode is enabled.

Function deactivate-mark

This function deactivates the mark, but only if Transient Mark mode is enabled.

Variable mark-active

The mark is active when this variable is non-nil. This variable is always local in each buffer.

Variable activate-mark-hook Variable deactivate-mark-hook

These normal hooks are run, respectively, when the mark becomes active and when it becomes inactive. The hook activate-mark-hook is also run at the end of a command if the mark is active and the region may have changed.

Variable mark-ring

The value of this buffer-local variable is the list of saved former marks of the current buffer, most recent first.

     mark-ring
     ⇒ (#<marker at 11050 in markers.texi>
         #<marker at 10832 in markers.texi>

…)

User Option mark-ring-max

The value of this variable is the maximum size of mark-ring. If more marks than this are pushed onto the mark-ring, push-mark discards an old mark when it adds a new one.

28.7 The Region

The text between point and the mark is known as the region. Various functions operate on text delimited by point and the mark, but only those functions specifically related to the region itself are described here.

Function region-beginning

This function returns the position of the beginning of the region (as an integer). This is the position of either point or the mark, whichever is smaller.

If the mark does not point anywhere, an error is signaled.

Function region-end

This function returns the position of the end of the region (as an integer). This is the position of either point or the mark, whichever is larger. If the mark does not point anywhere, an error is signaled.

Few programs need to use the region-beginning and region-end functions. A command designed to operate on a region should normally use interactive with the ‘r’ specification to find the beginning and end of the region. This lets other Lisp programs specify the bounds explicitly as arguments. (See Section 18.2.2 [Interactive Codes], page 245.)

29 Text

This chapter describes the functions that deal with the text in a buffer. Most examine, insert, or delete text in the current buffer, often in the vicinity of point. Many are interactive. All the functions that change the text provide for undoing the changes (see Section 29.9 [Undo], page 461).

Many text-related functions operate on a region of text defined by two buffer positions passed in arguments named start and end. These arguments should be either markers (see Chapter 28 [Markers], page 441) or numeric character positions (see Chapter 27 [Positions], page 429). The order of these arguments does not matter; it is all right for start to be the end of the region and end the beginning. For example, (delete-region 1 10) and (delete-region 10 1) are equivalent. An args-out-of-range error is signaled if either start or end is outside the accessible portion of the buffer. In an interactive call, point and the mark are used for these arguments.

Throughout this chapter, “text” refers to the characters in the buffer, together with their properties (when relevant).

29.1 Examining Text Near Point

Many functions are provided to look at the characters around point. Several simple functions are described here. See also looking-at in Section 30.3 [Regexp Search], page 497.

Function char-after position

This function returns the character in the current buffer at (i.e., immediately after) position position. If position is out of range for this purpose, either before the beginning of the buffer, or at or beyond the end, then the value is nil. In the following example, assume that the first character in the buffer is ‘@’:

          (char-to-string (char-after 1))
               ⇒ "@"

Function following-char

This function returns the character following point in the current buffer. This is similar to (char-after (point)). However, if point is at the end of the buffer, then following-char returns 0. Remember that point is always between characters, and the terminal cursor normally appears over the character following point. Therefore, the character returned by following-char is the character the cursor is over. In this example, point is between the ‘a’ and the ‘c’.

          ---------- Buffer: foo ----------
          Gentlemen may cry ``Pea⋆ce! Peace!,''
          but there is no peace.
          ---------- Buffer: foo ----------
          (char-to-string (preceding-char))
               ⇒ "a"
          (char-to-string (following-char))
               ⇒ "c"

Function preceding-char

This function returns the character preceding point in the current buffer. See above, under following-char, for an example. If point is at the beginning of the buffer, preceding-char returns 0.

Function bobp

This function returns t if point is at the beginning of the buffer. If narrowing is in effect, this means the beginning of the accessible portion of the text. See also point-min in Section 27.1 [Point], page 429.

Function eobp

This function returns t if point is at the end of the buffer. If narrowing is in effect, this means the end of accessible portion of the text. See also point-max in See Section 27.1 [Point], page 429.

Function bolp

This function returns t if point is at the beginning of a line. See Section 27.2.4 [Text Lines], page 432. The beginning of the buffer (or its accessible portion) always counts as the beginning of a line.

Function eolp

This function returns t if point is at the end of a line. The end of the buffer (or of its accessible portion) is always considered the end of a line.

29.2 Examining Buffer Contents

This section describes two functions that allow a Lisp program to convert any portion of the text in the buffer into a string.

Function buffer-substring start end

This function returns a string containing a copy of the text of the region defined by positions start and end in the current buffer. If the arguments are not positions in the accessible portion of the buffer, buffer-substring signals an

args-out-of-range error.

It is not necessary for start to be less than end; the arguments can be given in either order. But most often the smaller argument is written first. If the text being copied has any text properties, these are copied into the string along with the characters they belong to. See Section 29.18 [Text Properties], page 478. However, overlays (see Section 35.9 [Overlays], page 575) in the buffer and their properties are ignored, not copied.

     ---------- Buffer: foo ----------
     This is the contents of buffer foo
     ---------- Buffer: foo ----------
     (buffer-substring 1 10)
     ⇒ "This is t"

     (buffer-substring (point-max) 10)
     ⇒ "he contents of buffer foo
     "

Function buffer-substring-no-properties start end

This is like buffer-substring, except that it does not copy text properties, just the characters themselves. See Section 29.18 [Text Properties], page 478. Here’s an example of using this function to get a word to look up in an alist:

     (setq flammable
           (assoc (buffer-substring start end)
                  '(("wood" . t) ("paper" . t)
                    ("steel" . nil) ("asbestos" . nil))))

If this were written using buffer-substring instead, it would not work reliably; any text properties that happened to be in the word copied from the buffer would make the comparisons fail.

Function buffer-string

This function returns the contents of the accessible portion of the current buffer as a string. This is the portion between (point-min) and (point-max) (see Section 27.4 [Narrowing], page 438).

     ---------- Buffer: foo ----------
     This is the contents of buffer foo
     ---------- Buffer: foo ----------
     (buffer-string)
          ⇒ "This is the contents of buffer foo
     "

29.3 Comparing Text

This function lets you compare portions of the text in a buffer, without copying them into strings first.

Function compare-buffer-substrings buffer1 start1 end1 buffer2 start2

end2 This function lets you compare two substrings of the same buffer or two different buffers. The first three arguments specify one substring, giving a buffer and two positions within the buffer. The last three arguments specify the other substring in the same way. You can use nil for buffer1, buffer2, or both to stand for the current buffer. The value is negative if the first substring is less, positive if the first is greater, and zero if they are equal. The absolute value of the result is one plus the index of the first differing characters within the substrings. This function ignores case when comparing characters if case-fold-search is non-nil. It always ignores text properties.

Suppose the current buffer contains the text ‘foobarbar haha!rara!’; then in this example the two substrings are ‘rbar ’ and ‘rara!’. The value is 2 because the first substring is greater at the second character.

     (compare-buffer-substring nil 6 11 nil 16 21)
          ⇒ 2

29.4 Inserting Text

Insertion means adding new text to a buffer. The inserted text goes at point—between the character before point and the character after point.

Insertion relocates markers that point at positions after the insertion point, so that they stay with the surrounding text (see Chapter 28 [Markers], page 441). When a marker points at the place of insertion, insertion normally doesn’t relocate the marker, so that it points to the beginning of the inserted text; however, certain special functions such as insert-before-markers relocate such markers to point after the inserted text.

Some insertion functions leave point before the inserted text, while other functions leave it after. We call the former insertion after point and the latter insertion before point.

Insertion functions signal an error if the current buffer is read-only.

These functions copy text characters from strings and buffers along with their properties. The inserted characters have exactly the same properties as the characters they were copied from. By contrast, characters specified as separate arguments, not part of a string or buffer, inherit their text properties from the neighboring text.

Function insert &rest args This function inserts the strings and/or characters args into the current buffer, at point, moving point forward. In other words, it inserts the text before point. An error is signaled unless all args are either strings or characters. The value

is nil.

Function insert-before-markers &rest args

This function inserts the strings and/or characters args into the current buffer, at point, moving point forward. An error is signaled unless all args are either strings or characters. The value is nil.

This function is unlike the other insertion functions in that it relocates markers initially pointing at the insertion point, to point after the inserted text.

Function insert-char character count &optional inherit This function inserts count instances of character into the current buffer before point. The argument count must be a number, and character must be a character. The value is nil.

If inherit is non-nil, then the inserted characters inherit sticky text properties from the two characters before and after the insertion point. See Section 29.18.6 [Sticky Properties], page 484.

Function insert-buffer-substring from-buffer-or-name &optional start

end This function inserts a portion of buffer from-buffer-or-name (which must already exist) into the current buffer before point. The text inserted is the region from start and end. (These arguments default to the beginning and end of the accessible portion of that buffer.) This function returns nil. In this example, the form is executed with buffer ‘bar’ as the current buffer. We assume that buffer ‘bar’ is initially empty.

     ---------- Buffer: foo ----------
     We hold these truths to be self-evident, that all
     ---------- Buffer: foo ----------
     (insert-buffer-substring "foo" 1 20)
          ⇒ nil
     ---------- Buffer: bar ----------
     We hold these truth⋆
     ---------- Buffer: bar ----------

See Section 29.18.6 [Sticky Properties], page 484, for other insertion functions that inherit text properties from the nearby text in addition to inserting it. Whitespace inserted by indentation functions also inherits text properties.

29.5 User-Level Insertion Commands

This section describes higher-level commands for inserting text, commands intended primarily for the user but useful also in Lisp programs.

Command insert-buffer from-buffer-or-name This command inserts the entire contents of from-buffer-or-name (which must exist) into the current buffer after point. It leaves the mark after the inserted text. The value is nil.

Command self-insert-command count

This command inserts the last character typed; it does so count times, before point, and returns nil. Most printing characters are bound to this command. In routine use, self-insert-command is the most frequently called function in Emacs, but programs rarely use it except to install it on a keymap. In an interactive call, count is the numeric prefix argument. This command calls auto-fill-function whenever that is non-nil and the character inserted is a space or a newline (see Section 29.13 [Auto Filling], page 467). This command performs abbrev expansion if Abbrev mode is enabled and the inserted character does not have word-constituent syntax. (See Chapter 32 [Abbrevs], page 519, and Section 31.2.1 [Syntax Class Table], page 510.) This is also responsible for calling blink-paren-function when the inserted character has close parenthesis syntax (see Section 35.11 [Blinking], page 581).

Command newline &optional number-of-newlines This command inserts newlines into the current buffer before point. If numberof-newlines is supplied, that many newline characters are inserted. This function calls auto-fill-function if the current column number is greater than the value of fill-column and number-of-newlines is nil. Typically what auto-fill-function does is insert a newline; thus, the overall result in this case is to insert two newlines at different places: one at point, and another earlier in the line. newline does not auto-fill if number-of-newlines is non-nil. This command indents to the left margin if that is not zero. See Section 29.12 [Margins], page 466. The value returned is nil. In an interactive call, count is the numeric prefix argument.

Command split-line

This command splits the current line, moving the portion of the line after point down vertically so that it is on the next line directly below where it was before. Whitespace is inserted as needed at the beginning of the lower line, using the indent-to function. split-line returns the position of point. Programs hardly ever use this function.

Variable overwrite-mode

This variable controls whether overwrite mode is in effect: a non-nil value enables the mode. It is automatically made buffer-local when set in any fashion.

29.6 Deleting Text

Deletion means removing part of the text in a buffer, without saving it in the kill ring (see Section 29.8 [The Kill Ring], page 457). Deleted text can’t be yanked, but can be reinserted using the undo mechanism (see Section 29.9 [Undo], page 461). Some deletion functions do save text in the kill ring in some special cases.

All of the deletion functions operate on the current buffer, and all return a value of nil.

Function erase-buffer

This function deletes the entire text of the current buffer, leaving it empty. If the buffer is read-only, it signals a buffer-read-only error. Otherwise, it deletes the text without asking for any confirmation. It returns nil. Normally, deleting a large amount of text from a buffer inhibits further autosaving of that buffer “because it has shrunk”. However, erase-buffer does not do this, the idea being that the future text is not really related to the former text, and its size should not be compared with that of the former text.

Command delete-region start end

This command deletes the text in the current buffer in the region defined by start and end. The value is nil. If point was inside the deleted region, its value afterward is start. Otherwise, point relocates with the surrounding text, as markers do.

Command delete-char count &optional killp This command deletes count characters directly after point, or before point if count is negative. If killp is non-nil, then it saves the deleted characters in the kill ring.

In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.

The value returned is always nil.

Command delete-backward-char count &optional killp

This command deletes count characters directly before point, or after point if count is negative. If killp is non-nil, then it saves the deleted characters in the kill ring.

In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.

The value returned is always nil.

Command backward-delete-char-untabify count &optional killp

This command deletes count characters backward, changing tabs into spaces. When the next character to be deleted is a tab, it is first replaced with the proper number of spaces to preserve alignment and then one of those spaces is deleted instead of the tab. If killp is non-nil, then the command saves the deleted characters in the kill ring.

Conversion of tabs to spaces happens only if count is positive. If it is negative, exactly −count characters after point are deleted.

In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.

The value returned is always nil.

29.7 User-Level Deletion Commands

This section describes higher-level commands for deleting text, commands intended primarily for the user but useful also in Lisp programs.

Command delete-horizontal-space

This function deletes all spaces and tabs around point. It returns nil.

In the following examples, we call delete-horizontal-space four times, once on each line, with point between the second and third characters on the line each time.

---------- Buffer: foo ----------
I ⋆thought
I ⋆  thought
We⋆ thought
Yo⋆u thought
---------- Buffer: foo ----------
(delete-horizontal-space)   ; Four times.
     ⇒ nil
---------- Buffer: foo ----------
Ithought
Ithought
Wethought
You thought
---------- Buffer: foo ----------

Command delete-indentation &optional join-following-p This function joins the line point is on to the previous line, deleting any whitespace at the join and in some cases replacing it with one space. If join-following-p is non-nil, delete-indentation joins this line to the following line instead. The value is nil. If there is a fill prefix, and the second of the lines being joined starts with the prefix, then delete-indentation deletes the fill prefix before joining the lines. See Section 29.12 [Margins], page 466. In the example below, point is located on the line starting ‘events’, and it makes no difference if there are trailing spaces in the preceding line.

---------- Buffer: foo ----------
When in the course of human
⋆  events, it becomes necessary
---------- Buffer: foo ----------
(delete-indentation)
     ⇒ nil
---------- Buffer: foo ----------
When in the course of human⋆ events, it becomes necessary
---------- Buffer: foo ----------

After the lines are joined, the function fixup-whitespace is responsible for deciding whether to leave a space at the junction.

Function fixup-whitespace

This function replaces all the white space surrounding point with either one space or no space, according to the context. It returns nil. At the beginning or end of a line, the appropriate amount of space is none. Before a character with close parenthesis syntax, or after a character with open parenthesis or expression-prefix syntax, no space is also appropriate. Otherwise, one space is appropriate. See Section 31.2.1 [Syntax Class Table], page 510.

In the example below, fixup-whitespace is called the first time with point before the word ‘spaces’ in the first line. For the second invocation, point is directly after the ‘(’.

          ---------- Buffer: foo ----------
          This has too many  ⋆spaces
          This has too many spaces at the start of (⋆ this list)
          ---------- Buffer: foo ----------
          (fixup-whitespace)
               ⇒ nil
          (fixup-whitespace)
               ⇒ nil
          ---------- Buffer: foo ----------
          This has too many spaces
          This has too many spaces at the start of (this list)
          ---------- Buffer: foo ----------

Command just-one-space

This command replaces any spaces and tabs around point with a single space.

It returns nil.

Command delete-blank-lines

This function deletes blank lines surrounding point. If point is on a blank line with one or more blank lines before or after it, then all but one of them are deleted. If point is on an isolated blank line, then it is deleted. If point is on a nonblank line, the command deletes all blank lines following it. A blank line is defined as a line containing only tabs and spaces.

     delete-blank-lines returns nil.

29.8 The Kill Ring

Kill functions delete text like the deletion functions, but save it so that the user can reinsert it by yanking. Most of these functions have ‘kill-’ in their name. By contrast, the functions whose names start with ‘delete-’ normally do not save text for yanking (though they can still be undone); these are “deletion” functions.

Most of the kill commands are primarily for interactive use, and are not described here. What we do describe are the functions provided for use in writing such commands. You can use these functions to write commands for killing text. When you need to delete text for internal purposes within a Lisp function, you should normally use deletion functions, so as not to disturb the kill ring contents. See Section 29.6 [Deletion], page 454.

Killed text is saved for later yanking in the kill ring. This is a list that holds a number of recent kills, not just the last text kill. We call this a “ring” because yanking treats it as having elements in a cyclic order. The list is kept in the variable kill-ring, and can be operated on with the usual functions for lists; there are also specialized functions, described in this section, that treat it as a ring.

Some people think this use of the word “kill” is unfortunate, since it refers to operations that specifically do not destroy the entities “killed”. This is in sharp contrast to ordinary life, in which death is permanent and “killed” entities do not come back to life. Therefore, other metaphors have been proposed. For example, the term “cut ring” makes sense to people who, in pre-computer days, used scissors and paste to cut up and rearrange manuscripts. However, it would be difficult to change the terminology now.

29.8.1 Kill Ring Concepts

The kill ring records killed text as strings in a list, most recent first. A short kill ring, for example, might look like this:

     ("some text" "a different piece of text" "even older text")

When the list reaches kill-ring-max entries in length, adding a new entry automatically deletes the last entry.

When kill commands are interwoven with other commands, each kill command makes a new entry in the kill ring. Multiple kill commands in succession build up a single entry in the kill ring, which would be yanked as a unit; the second and subsequent consecutive kill commands add text to the entry made by the first one.

For yanking, one entry in the kill ring is designated the “front” of the ring. Some yank commands “rotate” the ring by designating a different element as the “front.” But this virtual rotation doesn’t change the list itself—the most recent entry always comes first in the list.

29.8.2 Functions for Killing

kill-region is the usual subroutine for killing text. Any command that calls this function is a “kill command” (and should probably have ‘kill’ in its name). kill-region puts the newly killed text in a new element at the beginning of the kill ring or adds it to the most recent element. It uses the last-command variable to determine whether the previous command was a kill command, and if so appends the killed text to the most recent entry.

Command kill-region start end

This function kills the text in the region defined by start and end. The text is deleted but saved in the kill ring, along with its text properties. The value is always nil. In an interactive call, start and end are point and the mark. If the buffer is read-only, kill-region modifies the kill ring just the same, then signals an error without modifying the buffer. This is convenient because it lets the user use all the kill commands to copy text into the kill ring from a read-only buffer.

Command copy-region-as-kill start end

This command saves the region defined by start and end on the kill ring (including text properties), but does not delete the text from the buffer. It returns nil. It also indicates the extent of the text copied by moving the cursor momentarily, or by displaying a message in the echo area. The command does not set this-command to kill-region, so a subsequent kill command does not append to the same kill ring entry.

Don’t call copy-region-as-kill in Lisp programs unless you aim to support Emacs 18. For Emacs 19, it is better to use kill-new or kill-append instead. See Section 29.8.4 [Low-Level Kill Ring], page 459.

29.8.3 Functions for Yanking

Yanking means reinserting an entry of previously killed text from the kill ring. The text properties are copied too.

Command yank &optional arg This command inserts before point the text in the first entry in the kill ring. It positions the mark at the beginning of that text, and point at the end. If arg is a list (which occurs interactively when the user types C-u with no digits), then yank inserts the text as described above, but puts point before the yanked text and puts the mark after it. If arg is a number, then yank inserts the argth most recently killed text—the argth element of the kill ring list. yank does not alter the contents of the kill ring or rotate it. It returns nil.

Command yank-pop arg

This command replaces the just-yanked entry from the kill ring with a different entry from the kill ring. This is allowed only immediately after a yank or another yank-pop. At such a time, the region contains text that was just inserted by yanking. yank-pop deletes that text and inserts in its place a different piece of killed text. It does not add the deleted text to the kill ring, since it is already in the kill ring somewhere. If arg is nil, then the replacement text is the previous element of the kill ring. If arg is numeric, the replacement is the argth previous kill. If arg is negative, a more recent kill is the replacement. The sequence of kills in the kill ring wraps around, so that after the oldest one comes the newest one, and before the newest one goes the oldest. The value is always nil.

29.8.4 Low-Level Kill Ring

These functions and variables provide access to the kill ring at a lower level, but still convenient for use in Lisp programs. They take care of interaction with X Window selections. They do not exist in Emacs version 18.

Function current-kill n &optional do-not-move The function current-kill rotates the yanking pointer which designates the “front” of the kill ring by n places (from newer kills to older ones), and returns the text at that place in the ring. If the optional second argument do-not-move is non-nil, then current-kill doesn’t alter the yanking pointer; it just returns the nth kill, counting from the current yanking pointer.

If n is zero, indicating a request for the latest kill, current-kill calls the value of interprogram-paste-function (documented below) before consulting the kill ring.

Function kill-new string

This function puts the text string into the kill ring as a new entry at the front of the ring. It discards the oldest entry if appropriate. It also invokes the value

of interprogram-cut-function (see below).

Function kill-append string before-p This function appends the text string to the first entry in the kill ring. Normally string goes at the end of the entry, but if before-p is non-nil, it goes at the beginning. This function also invokes the value of interprogram-cut-function (see below).

Variable interprogram-paste-function

This variable provides a way of transferring killed text from other programs, when you are using a window system. Its value should be nil or a function of no arguments. If the value is a function, current-kill calls it to get the “most recent kill”. If the function returns a non-nil value, then that value is used as the “most recent kill”. If it returns nil, then the first element of kill-ring is used. The normal use of this hook is to get the X server’s primary selection as the most recent kill, even if the selection belongs to another X client. See Section 26.18 [X Selections], page 425.

Variable interprogram-cut-function

This variable provides a way of communicating killed text to other programs, when you are using a window system. Its value should be nil or a function of one argument. If the value is a function, kill-new and kill-append call it with the new first element of the kill ring as an argument. The normal use of this hook is to set the X server’s primary selection to the newly killed text.

29.8.5 Internals of the Kill Ring

The variable kill-ring holds the kill ring contents, in the form of a list of strings. The most recent kill is always at the front of the list.

The kill-ring-yank-pointer variable points to a link in the kill ring list, whose car is the text to yank next. We say it identifies the “front” of the ring. Moving kill-ring-yank-pointer to a different link is called rotating the kill ring. We call the kill ring a “ring” because the functions that move the yank pointer wrap around from the end of the list to the beginning, or vice-versa. Rotation of the kill ring is virtual; it does not change the value of kill-ring.

Both kill-ring and kill-ring-yank-pointer are Lisp variables whose values are normally lists. The word “pointer” in the name of the kill-ring-yank-pointer indicates that the variable’s purpose is to identify one element of the list for use by the next yank command.

The value of kill-ring-yank-pointer is always eq to one of the links in the kill ring list. The element it identifies is the car of that link. Kill commands, which change the kill ring, also set this variable to the value of kill-ring. The effect is to rotate the ring so that the newly killed text is at the front.

Here is a diagram that shows the variable kill-ring-yank-pointer pointing to the sec-

ond entry in the kill ring ("some text" "a different piece of text" "yet older text").
     kill-ring       kill-ring-yank-pointer
       |               |
       |     ______--->  ____________
        --> |___|___|------> |___|___|--> |___|___|--> nil
              |                |            |
              |                |            |
              |                |             -->"yet older text"
              |                |
              |                 --> "a different piece of text"
              |
               --> "some text"

This state of affairs might occur after C-y (yank) immediately followed by M-y (yank-pop).

Variable kill-ring

This variable holds the list of killed text sequences, most recently killed first.

Variable kill-ring-yank-pointer

This variable’s value indicates which element of the kill ring is at the “front” of the ring for yanking. More precisely, the value is a tail of the value of killring, and its car is the kill string that C-y should yank.

User Option kill-ring-max

The value of this variable is the maximum length to which the kill ring can grow, before elements are thrown away at the end. The default value for kill-

     ring-max is 30.

29.9 Undo

Most buffers have an undo list, which records all changes made to the buffer’s text so that they can be undone. (The buffers that don’t have one are usually special-purpose buffers for which Emacs assumes that undoing is not useful.) All the primitives that modify the text in the buffer automatically add elements to the front of the undo list, which is in the

variable buffer-undo-list.

Variable buffer-undo-list

This variable’s value is the undo list of the current buffer. A value of t disables the recording of undo information.

Here are the kinds of elements an undo list can have: integer This kind of element records a previous value of point. Ordinary cursor motion

does not get any sort of undo record, but deletion commands use these entries to record where point was before the command.

(beg . end)

This kind of element indicates how to delete text that was inserted. Upon insertion, the text occupied the range beg–end in the buffer.

(text . position)

This kind of element indicates how to reinsert text that was deleted. The deleted text itself is the string text. The place to reinsert it is (abs position).

(t high . low)

This kind of element indicates that an unmodified buffer became modified. The elements high and low are two integers, each recording 16 bits of the visited file’s modification time as of when it was previously visited or saved. primitiveundo uses those values to determine whether to mark the buffer as unmodified once again; it does so only if the file’s modification time matches those numbers.

(nil property value beg . end)

This kind of element records a change in a text property. Here’s how you might undo the change:

     (put-text-property beg end property value)

(marker . adjustment)

This kind of element records the fact that the marker marker was relocated due to deletion of surrounding text, and that it moved adjustment character positions. Undoing this element moves marker − adjustment characters.

position This element indicates where point was at an earlier time. Undoing this element sets point to position. Deletion normally creates an element of this kind as well as a reinsertion element.

nil This element is a boundary. The elements between two boundaries are called a change group; normally, each change group corresponds to one keyboard command, and undo commands normally undo an entire group as a unit.

Function undo-boundary

This function places a boundary element in the undo list. The undo command stops at such a boundary, and successive undo commands undo to earlier and earlier boundaries. This function returns nil. The editor command loop automatically creates an undo boundary before each key sequence is executed. Thus, each undo normally undoes the effects of one command. Self-inserting input characters are an exception. The command loop makes a boundary for the first such character; the next 19 consecutive self-inserting input characters do not make boundaries, and then the 20th does, and so on as long as self-inserting characters continue. All buffer modifications add a boundary whenever the previous undoable change was made in some other buffer. This way, a command that modifies several buffers makes a boundary in each buffer it changes.

Calling this function explicitly is useful for splitting the effects of a command into more than one unit. For example, query-replace calls undo-boundary after each replacement, so that the user can undo individual replacements one by one.

Function primitive-undo count list

This is the basic function for undoing elements of an undo list. It undoes the first count elements of list, returning the rest of list. You could write this function in Lisp, but it is convenient to have it in C. primitive-undo adds elements to the buffer’s undo list when it changes the buffer. Undo commands avoid confusion by saving the undo list value at the beginning of a sequence of undo operations. Then the undo operations use and update the saved value. The new elements added by undoing are not part of this saved value, so they don’t interfere with continuing to undo.

29.10 Maintaining Undo Lists

This section describes how to enable and disable undo information for a given buffer. It also explains how the undo list is truncated automatically so it doesn’t get too big.

Recording of undo information in a newly created buffer is normally enabled to start with; but if the buffer name starts with a space, the undo recording is initially disabled. You can explicitly enable or disable undo recording with the following two functions, or by

setting buffer-undo-list yourself.

Command buffer-enable-undo &optional buffer-or-name This command enables recording undo information for buffer buffer-or-name, so that subsequent changes can be undone. If no argument is supplied, then the current buffer is used. This function does nothing if undo recording is already enabled in the buffer. It returns nil. In an interactive call, buffer-or-name is the current buffer. You cannot specify any other buffer.

Function buffer-disable-undo &optional buffer Function buffer-flush-undo &optional buffer

This function discards the undo list of buffer, and disables further recording of undo information. As a result, it is no longer possible to undo either previous changes or any subsequent changes. If the undo list of buffer is already disabled, this function has no effect. This function returns nil. It cannot be called interactively. The name buffer-flush-undo is not considered obsolete, but the preferred name buffer-disable-undo is new as of Emacs versions 19.

As editing continues, undo lists get longer and longer. To prevent them from using up all available memory space, garbage collection trims them back to size limits you can set. (For this purpose, the “size” of an undo list measures the cons cells that make up the list, plus the strings of deleted text.) Two variables control the range of acceptable sizes:

undo-limit and undo-strong-limit.

Variable undo-limit

This is the soft limit for the acceptable size of an undo list. The change group at which this size is exceeded is the last one kept.

Variable undo-strong-limit

This is the upper limit for the acceptable size of an undo list. The change group at which this size is exceeded is discarded itself (along with all older change groups). There is one exception: the very latest change group is never discarded no matter how big it is.

29.11 Filling

Filling means adjusting the lengths of lines (by moving the line breaks) so that they are nearly (but no greater than) a specified maximum width. Additionally, lines can be justified, which means inserting spaces to make the left and/or right margins line up precisely. The width is controlled by the variable fill-column. For ease of reading, lines should be no longer than 70 or so columns.

You can use Auto Fill mode (see Section 29.13 [Auto Filling], page 467) to fill text automatically as you insert it, but changes to existing text may leave it improperly filled. Then you must fill the text explicitly.

Most of the commands in this section return values that are not meaningful. All the functions that do filling take note of the current left margin, current right margin, and current justification style (see Section 29.12 [Margins], page 466). If the current justification style is none, the filling functions don’t actually do anything.

Several of the filling functions have an argument justify. If it is non-nil, that requests some kind of justification. It can be left, right, full, or center, to request a specific style of justification. If it is t, that means to use the current justification style for this part

of the text (see current-justification, below).

When you call the filling functions interactively, using a prefix argument implies the value full for justify.

Command fill-paragraph justify

This command fills the paragraph at or after point. If justify is non-nil, each line is justified as well. It uses the ordinary paragraph motion commands to find paragraph boundaries. See section “Paragraphs” in The Emacs Manual.

Command fill-region start end &optional justify This command fills each of the paragraphs in the region from start to end. It justifies as well if justify is non-nil. The variable paragraph-separate controls how to distinguish paragraphs. See Section 30.8 [Standard Regexps], page 506.

Command fill-individual-paragraphs start end &optional justify

mail-flag This command fills each paragraph in the region according to its individual fill prefix. Thus, if the lines of a paragraph were indented with spaces, the filled paragraph will remain indented in the same fashion.

The first two arguments, start and end, are the beginning and end of the region to be filled. The third and fourth arguments, justify and mail-flag, are optional. If justify is non-nil, the paragraphs are justified as well as filled. If mail-flag is non-nil, it means the function is operating on a mail message and therefore should not fill the header lines. Ordinarily, fill-individual-paragraphs regards each change in indentation

as starting a new paragraph. If fill-individual-varying-indent is non-nil,

then only separator lines separate paragraphs. That mode can handle indented paragraphs with additional indentation on the first line.

User Option fill-individual-varying-indent

This variable alters the action of fill-individual-paragraphs as described above.

Command fill-region-as-paragraph start end &optional justify This command considers a region of text as a paragraph and fills it. If the region was made up of many paragraphs, the blank lines between paragraphs are removed. This function justifies as well as filling when justify is non-nil. In an interactive call, any prefix argument requests justification. In Adaptive Fill mode, which is enabled by default, calling the function fillregion-as-paragraph on an indented paragraph when there is no fill prefix uses the indentation of the second line of the paragraph as the fill prefix.

Command justify-current-line how eop nosqueeze

This command inserts spaces between the words of the current line so that the line ends exactly at fill-column. It returns nil. The argument how, if non-nil specifies explicitly the style of justification. It can be left, right, full, center, or none. If it is t, that means to do follow specified justification style (see current-justification, below). nil means to do full justification. If eop is non-nil, that means do left-justification if current-justification specifies full justification. This is used for the last line of a paragraph; even if the paragraph as a whole is fully justified, the last line should not be. If nosqueeze is non-nil, that means do not change interior whitespace.

User Option default-justification

This variable’s value specifies the style of justification to use for text that doesn’t specify a style with a text property. The possible values are left, right, full, center, or none. The default value is left.

Function current-justification

This function returns the proper justification style to use for filling the text around point.

Variable fill-paragraph-function

This variable provides a way for major modes to override the filling of paragraphs. If the value is non-nil, fill-paragraph calls this function to do the work. If the function returns a non-nil value, fill-paragraph assumes the job is done, and immediately returns that value. The usual use of this feature is to fill comments in programming language modes. If the function needs to fill a paragraph in the usual way, it can do so as follows:

     (let ((fill-paragraph-function nil))
       (fill-paragraph arg))

Variable use-hard-newlines

If this variable is non-nil, the filling functions do not delete newlines that have the hard text property. These “hard newlines” act as paragraph separators.

29.12 Margins for Filling

User Option fill-prefix

This variable specifies a string of text that appears at the beginning of normal text lines and should be disregarded when filling them. Any line that fails to start with the fill prefix is considered the start of a paragraph; so is any line that starts with the fill prefix followed by additional whitespace. Lines that start with the fill prefix but no additional whitespace are ordinary text lines that can be filled together. The resulting filled lines also start with the fill prefix. The fill prefix follows the left margin whitespace, if any.

User Option fill-column

This buffer-local variable specifies the maximum width of filled lines. Its value should be an integer, which is a number of columns. All the filling, justification and centering commands are affected by this variable, including Auto Fill mode (see Section 29.13 [Auto Filling], page 467). As a practical matter, if you are writing text for other people to read, you should set fill-column to no more than 70. Otherwise the line will be too long for people to read comfortably, and this can make the text seem clumsy.

Variable default-fill-column

The value of this variable is the default value for fill-column in buffers that do not override it. This is the same as (default-value 'fill-column). The default value for default-fill-column is 70.

Command set-left-margin from to margin

This sets the left-margin property on the text from from to to to the value margin. If Auto Fill mode is enabled, this command also refills the region to fit the new margin.

Command set-right-margin from to margin

This sets the right-margin property on the text from from to to to the value margin. If Auto Fill mode is enabled, this command also refills the region to fit the new margin.

Function current-left-margin

This function returns the proper left margin value to use for filling the text around point. The value is the sum of the left-margin property of the character at the start of the current line (or zero if none), and the value of the variable

left-margin.

Function current-fill-column

This function returns the proper fill column value to use for filling the text around point. The value is the value of the fill-column variable, minus the value of the right-margin property of the character after point.

Command move-to-left-margin &optional n force

This function moves point to the left margin of the current line. The column moved to is determined by calling the function current-left-margin. If the argument n is non-nil, move-to-left-margin moves forward n−1 lines first.

If force is non-nil, that says to fix the line’s indentation if that doesn’t match the left margin value.

Function delete-to-left-margin from to

This function removes left margin indentation from the text between from and to. The amount of indentation to delete is determined by calling currentleft-margin. In no case does this function delete non-whitespace.

Function indent-to-left-margin

This is the default indent-line-function, used in Fundamental mode, Text mode, etc. Its effect is to adjust the indentation at the beginning of the current line to the value specified by the variable left-margin. This may involve either inserting or deleting whitespace.

Variable left-margin

This variable specifies the base left margin column. In Fundamental mode, ⟨\underline{\overline{LFD}}^{⟩} indents to this column. This variable automatically becomes buffer-local when set in any fashion.

29.13 Auto Filling

Auto Fill mode is a minor mode that fills lines automatically as text is inserted. This section describes the hook used by Auto Fill mode. For a description of functions that you can call explicitly to fill and justify existing text, see Section 29.11 [Filling], page 464.

Auto Fill mode also enables the functions that change the margins and justification style to refill portions of the text. See Section 29.12 [Margins], page 466.

Variable auto-fill-function

The value of this variable should be a function (of no arguments) to be called after self-inserting a space or a newline. It may be nil, in which case nothing special is done in that case.

The value of auto-fill-function is do-auto-fill when Auto-Fill mode is enabled. That is a function whose sole purpose is to implement the usual strategy for breaking a line.

In older Emacs versions, this variable was named auto-fill-hook, but since it is not called with the standard convention for hooks, it was renamed to auto-fill-function in version 19.

Variable normal-auto-fill-function

This variable specifies the function to use for auto-fill-function, if and when Auto Fill is turned on. Major modes can set this locally to alter how Auto Fill works.

29.14 Sorting Text

The sorting functions described in this section all rearrange text in a buffer. This is in contrast to the function sort, which rearranges the order of the elements of a list (see Section 5.6.3 [Rearrangement], page 70). The values returned by these functions are not meaningful.

Function sort-subr reverse nextrecfun endrecfun &optional startkeyfun

endkeyfun This function is the general text-sorting routine that divides a buffer into records and sorts them. Most of the commands in this section use this function. To understand how sort-subr works, consider the whole accessible portion of the buffer as being divided into disjoint pieces called sort records. The records may or may not be contiguous; they may not overlap. A portion of each sort record (perhaps all of it) is designated as the sort key. Sorting rearranges the records in order by their sort keys. Usually, the records are rearranged in order of ascending sort key. If the first argument to the sort-subr function, reverse, is non-nil, the sort records are rearranged in order of descending sort key. The next four arguments to sort-subr are functions that are called to move point across a sort record. They are called many times from within sort-subr.

1. nextrecfun is called with point at the end of a record. This function moves point to the start of the next record. The first record is assumed to start at the position of point when sort-subr is called. Therefore, you should usually move point to the beginning of the buffer before calling sort-subr. This function can indicate there are no more sort records by leaving point at the end of the buffer.

2. endrecfun is called with point within a record. It moves point to the end of the record.

3. startkeyfun is called to move point from the start of a record to the start of the sort key. This argument is optional; if it is omitted, the whole record is the sort key. If supplied, the function should either return a non-nil value to be used as the sort key, or return nil to indicate that the sort key is in the buffer starting at point. In the latter case, endkeyfun is called to find the end of the sort key.

4. endkeyfun is called to move point from the start of the sort key to the end of the sort key. This argument is optional. If startkeyfun returns nil and this argument is omitted (or nil), then the sort key extends to the end of the record. There is no need for endkeyfun if startkeyfun returns a non-nil value.

As an example of sort-subr, here is the complete function definition for sort-

lines:

;; Note that the first two lines of doc string ;; are effectively one line when viewed by a user.

     (defun sort-lines (reverse beg end)
       "Sort lines in region alphabetically.
     Called from a program, there are three arguments:
     REVERSE (non-nil means reverse order),
     and BEG and END (the region to sort)."
       (interactive "P\nr")
       (save-restriction
         (narrow-to-region beg end)
         (goto-char (point-min))
         (sort-subr reverse
                    'forward-line
                    'end-of-line)))

Here forward-line moves point to the start of the next record, and endof-line moves point to the end of record. We do not pass the arguments startkeyfun and endkeyfun, because the entire record is used as the sort key. The sort-paragraphs function is very much the same, except that its sortsubr call looks like this:

     (sort-subr reverse
                (function
                 (lambda ()
                   (skip-chars-forward "\n \t\f")))
                'forward-paragraph)

Command sort-regexp-fields reverse record-regexp key-regexp start end This command sorts the region between start and end alphabetically as specified by record-regexp and key-regexp. If reverse is a negative integer, then sorting is in reverse order. Alphabetical sorting means that two sort keys are compared by comparing the first characters of each, the second characters of each, and so on. If a mismatch is found, it means that the sort keys are unequal; the sort key whose character is less at the point of first mismatch is the lesser sort key. The individual characters are compared according to their numerical values. Since Emacs uses the ASCII character set, the ordering in that set determines alphabetical order. The value of the record-regexp argument specifies how to divide the buffer into sort records. At the end of each record, a search is done for this regular expression, and the text that matches it is the next record. For example, the regular expression ‘^.+$’, which matches lines with at least one character besides a newline, would make each such line into a sort record. See Section 30.2 [Regular Expressions], page 492, for a description of the syntax and meaning of regular expressions. The value of the key-regexp argument specifies what part of each record is the sort key. The key-regexp could match the whole record, or only a part. In the latter case, the rest of the record has no effect on the sorted order of records, but it is carried along when the record moves to its new position. The key-regexp argument can refer to the text matched by a subexpression of record-regexp, or it can be a regular expression on its own. If key-regexp is:

‘\digit’ then the text matched by the digitth ‘\(...\)’ parenthesis grouping in record-regexp is the sort key.

‘\&’ then the whole record is the sort key.

a regular expression then sort-regexp-fields searches for a match for the regular expression within the record. If such a match is found, it is the sort key. If there is no match for key-regexp within a record then that record is ignored, which means its position in the buffer is not changed. (The other records may move around it.)

For example, if you plan to sort all the lines in the region by the first word on each line starting with the letter ‘f’, you should set record-regexp to ‘^.*$’ and set key-regexp to ‘\<f\w*\>’. The resulting expression looks like this:

     (sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
                         (region-beginning)
                         (region-end))

If you call sort-regexp-fields interactively, it prompts for record-regexp and key-regexp in the minibuffer.

Command sort-lines reverse start end This command alphabetically sorts lines in the region between start and end. If reverse is non-nil, the sort is in reverse order.

Command sort-paragraphs reverse start end

This command alphabetically sorts paragraphs in the region between start and end. If reverse is non-nil, the sort is in reverse order.

Command sort-pages reverse start end This command alphabetically sorts pages in the region between start and end. If reverse is non-nil, the sort is in reverse order.

Command sort-fields field start end This command sorts lines in the region between start and end, comparing them alphabetically by the fieldth field of each line. Fields are separated by whitespace and numbered starting from 1. If field is negative, sorting is by the −fieldth field from the end of the line. This command is useful for sorting tables.

Command sort-numeric-fields field start end

This command sorts lines in the region between start and end, comparing them numerically by the fieldth field of each line. The specified field must contain a number in each line of the region. Fields are separated by whitespace and numbered starting from 1. If field is negative, sorting is by the −fieldth field from the end of the line. This command is useful for sorting tables.

Command sort-columns reverse &optional beg end This command sorts the lines in the region between beg and end, comparing them alphabetically by a certain range of columns. The column positions of beg and end bound the range of columns to sort on.

If reverse is non-nil, the sort is in reverse order.

One unusual thing about this command is that the entire line containing position beg, and the entire line containing position end, are included in the region sorted.

Note that sort-columns uses the sort utility program, and so cannot work properly on text containing tab characters. Use M-x untabify to convert tabs to spaces before sorting.

29.15 Counting Columns

The column functions convert between a character position (counting characters from the beginning of the buffer) and a column position (counting screen characters from the beginning of a line).

A character counts according to the number of columns it occupies on the screen. This means control characters count as occupying 2 or 4 columns, depending upon the value of ctl-arrow, and tabs count as occupying a number of columns that depends on the value of tab-width and on the column where the tab begins. See Section 35.13 [Usual Display], page 582.

Column number computations ignore the width of the window and the amount of horizontal scrolling. Consequently, a column value can be arbitrarily high. The first (or leftmost) column is numbered 0.

Function current-column

This function returns the horizontal position of point, measured in columns, counting from 0 at the left margin. The column position is the sum of the widths of all the displayed representations of the characters between the start of the current line and point.

For an example of using current-column, see the description of count-lines in Section 27.2.4 [Text Lines], page 432.

Function move-to-column column &optional force This function moves point to column in the current line. The calculation of column takes into account the widths of the displayed representations of the characters between the start of the line and point.

If column column is beyond the end of the line, point moves to the end of the line. If column is negative, point moves to the beginning of the line.

If it is impossible to move to column column because that is in the middle of a multicolumn character such as a tab, point moves to the end of that character. However, if force is non-nil, and column is in the middle of a tab, then moveto-column converts the tab into spaces so that it can move precisely to column column. Other multicolumn characters can cause anomalies despite force, since there is no way to split them.

The argument force also has an effect if the line isn’t long enough to reach column column; in that case, it says to add whitespace at the end of the line to reach that column.

If column is not an integer, an error is signaled.

The return value is the column number actually moved to.

29.16 Indentation

The indentation functions are used to examine, move to, and change whitespace that is at the beginning of a line. Some of the functions can also change whitespace elsewhere on a line. Columns and indentation count from zero at the left margin.

29.16.1 Indentation Primitives

This section describes the primitive functions used to count and insert indentation. The functions in the following sections use these primitives.

Function current-indentation

This function returns the indentation of the current line, which is the horizontal position of the first nonblank character. If the contents are entirely blank, then this is the horizontal position of the end of the line.

Command indent-to column &optional minimum This function indents from point with tabs and spaces until column is reached. If minimum is specified and non-nil, then at least that many spaces are inserted even if this requires going beyond column. Otherwise the function does nothing if point is already beyond column. The value is the column at which the inserted indentation ends.

The inserted whitespace characters inherit text properties from the surrounding text (usually, from the preceding text only). See Section 29.18.6 [Sticky Properties], page 484.

User Option indent-tabs-mode

If this variable is non-nil, indentation functions can insert tabs as well as spaces. Otherwise, they insert only spaces. Setting this variable automatically makes it local to the current buffer.

29.16.2 Indentation Controlled by Major Mode

An important function of each major mode is to customize the ^{⟨}\underline{\overline{TAB}}^{⟩} key to indent properly for the language being edited. This section describes the mechanism of the ^{⟨}\underline{\overline{TAB}}^{⟩} key and how to control it. The functions in this section return unpredictable values.

Variable indent-line-function

This variable’s value is the function to be used by^{⟨}\underline{\overline{TAB}}^{⟩} (and various commands) to indent the current line. The command indent-according-to-mode does no more than call this function.

In Lisp mode, the value is the symbol lisp-indent-line; in C mode, cindent-line; in Fortran mode, fortran-indent-line. In Fundamental mode, Text mode, and many other modes with no standard for indentation, the value is indent-to-left-margin (which is the default value).

Command indent-according-to-mode

This command calls the function in indent-line-function to indent the current line in a way appropriate for the current major mode.

Command indent-for-tab-command

This command calls the function in indent-line-function to indent the current line; except that if that function is indent-to-left-margin, it calls insert-tab instead. (That is a trivial command that inserts a tab character.)

Command newline-and-indent

This function inserts a newline, then indents the new line (the one following the newline just inserted) according to the major mode.

It does indentation by calling the current indent-line-function. In programming language modes, this is the same thing^{⟨}\underline{\overline{TAB}}^{⟩} does, but in some text modes, where ^{⟨}\underline{\overline{TAB}}^{⟩} inserts a tab, newline-and-indent indents to the column specified

by left-margin.

Command reindent-then-newline-and-indent

This command reindents the current line, inserts a newline at point, and then reindents the new line (the one following the newline just inserted).

This command does indentation on both lines according to the current major mode, by calling the current value of indent-line-function. In programming language modes, this is the same thing ^{⟨}\underline{\overline{TAB}}^{⟩} does, but in some text modes, where ^{⟨}\underline{\overline{TAB}}^{⟩} inserts a tab, reindent-then-newline-and-indent indents to the column specified by left-margin.

29.16.3 Indenting an Entire Region

This section describes commands that indent all the lines in the region. They return unpredictable values.

Command indent-region start end to-column This command indents each nonblank line starting between start (inclusive) and end (exclusive). If to-column is nil, indent-region indents each nonblank line by calling the current mode’s indentation function, the value of indent-line-

function.

If to-column is non-nil, it should be an integer specifying the number of columns of indentation; then this function gives each line exactly that much indentation, by either adding or deleting whitespace. If there is a fill prefix, indent-region indents each line by making it start with the fill prefix.

Variable indent-region-function

The value of this variable is a function that can be used by indent-region as a short cut. You should design the function so that it will produce the same results as indenting the lines of the region one by one, but presumably faster. If the value is nil, there is no short cut, and indent-region actually works line by line. A short-cut function is useful in modes such as C mode and Lisp mode, where the indent-line-function must scan from the beginning of the function definition: applying it to each line would be quadratic in time. The short cut can update the scan information as it moves through the lines indenting them; this takes linear time. In a mode where indenting a line individually is fast, there is no need for a short cut. indent-region with a non-nil argument to-column has a different meaning and does not use this variable.

Command indent-rigidly start end count

This command indents all lines starting between start (inclusive) and end (exclusive) sideways by count columns. This “preserves the shape” of the affected region, moving it as a rigid unit. Consequently, this command is useful not only for indenting regions of unindented text, but also for indenting regions of formatted code. For example, if count is 3, this command adds 3 columns of indentation to each of the lines beginning in the region specified.

In Mail mode, C-c C-y (mail-yank-original) uses indent-rigidly to indent

the text copied from the message being replied to.

Function indent-code-rigidly start end columns &optional

nochange-regexp This is like indent-rigidly, except that it doesn’t alter lines that start within strings or comments.

In addition, it doesn’t alter a line if nochange-regexp matches at the beginning of the line (if nochange-regexp is non-nil).

29.16.4 Indentation Relative to Previous Lines

This section describes two commands that indent the current line based on the contents of previous lines.

Command indent-relative &optional unindented-ok This command inserts whitespace at point, extending to the same column as the next indent point of the previous nonblank line. An indent point is a nonwhitespace character following whitespace. The next indent point is the first one at a column greater than the current column of point. For example, if point is underneath and to the left of the first non-blank character of a line of text, it moves to that column by inserting whitespace. If the previous nonblank line has no next indent point (i.e., none at a great enough column position), indent-relative either does nothing (if unindentedok is non-nil) or calls tab-to-tab-stop. Thus, if point is underneath and to the right of the last column of a short line of text, this command ordinarily moves point to the next tab stop by inserting whitespace. The return value of indent-relative is unpredictable. In the following example, point is at the beginning of the second line:

                 This line is indented twelve spaces.
     ⋆The quick brown fox jumped.

Evaluation of the expression (indent-relative nil) produces the following:

                 This line is indented twelve spaces.
                 ⋆The quick brown fox jumped.

In this example, point is between the ‘m’ and ‘p’ of ‘jumped’:

                 This line is indented twelve spaces.
     The quick brown fox jum⋆ped.

Evaluation of the expression (indent-relative nil) produces the following:

                 This line is indented twelve spaces.
     The quick brown fox jum ⋆ped.

Command indent-relative-maybe

This command indents the current line like the previous nonblank line. It calls indent-relative with t as the unindented-ok argument. The return value is unpredictable. If the previous nonblank line has no indent points beyond the current column, this command does nothing.

29.16.5 Adjustable “Tab Stops”

This section explains the mechanism for user-specified “tab stops” and the mechanisms that use and set them. The name “tab stops” is used because the feature is similar to that of the tab stops on a typewriter. The feature works by inserting an appropriate number of spaces and tab characters to reach the next tab stop column; it does not affect the display of tab characters in the buffer (see Section 35.13 [Usual Display], page 582). Note that the ⟨\underline{\overline{TAB}}^{⟩} character as input uses this tab stop feature only in a few major modes, such as Text mode.

Command tab-to-tab-stop

This command inserts spaces or tabs up to the next tab stop column defined by tab-stop-list. It searches the list for an element greater than the current column number, and uses that element as the column to indent to. It does nothing if no such element is found.

User Option tab-stop-list

This variable is the list of tab stop columns used by tab-to-tab-stops. The elements should be integers in increasing order. The tab stop columns need not be evenly spaced. Use M-x edit-tab-stops to edit the location of tab stops interactively.

29.16.6 Indentation-Based Motion Commands

These commands, primarily for interactive use, act based on the indentation in the text.

Command back-to-indentation

This command moves point to the first non-whitespace character in the current line (which is the line in which point is located). It returns nil.

Command backward-to-indentation arg

This command moves point backward arg lines and then to the first nonblank character on that line. It returns nil.

Command forward-to-indentation arg

This command moves point forward arg lines and then to the first nonblank character on that line. It returns nil.

29.17 Case Changes

The case change commands described here work on text in the current buffer. See Section 4.7 [Character Case], page 57, for case conversion commands that work on strings and characters. See Section 4.8 [Case Table], page 58, for how to customize which characters are upper or lower case and how to convert them.

Command capitalize-region start end

This function capitalizes all words in the region defined by start and end. To capitalize means to convert each word’s first character to upper case and convert the rest of each word to lower case. The function returns nil. If one end of the region is in the middle of a word, the part of the word within the region is treated as an entire word. When capitalize-region is called interactively, start and end are point and the mark, with the smallest first.

     ---------- Buffer: foo ----------
     This is the contents of the 5th foo.
     ---------- Buffer: foo ----------
     (capitalize-region 1 44)
     ⇒ nil
     ---------- Buffer: foo ----------
     This Is The Contents Of The 5th Foo.
     ---------- Buffer: foo ----------

Command downcase-region start end

This function converts all of the letters in the region defined by start and end to lower case. The function returns nil. When downcase-region is called interactively, start and end are point and the mark, with the smallest first.

Command upcase-region start end

This function converts all of the letters in the region defined by start and end to upper case. The function returns nil. When upcase-region is called interactively, start and end are point and the mark, with the smallest first.

Command capitalize-word count

This function capitalizes count words after point, moving point over as it does. To capitalize means to convert each word’s first character to upper case and convert the rest of each word to lower case. If count is negative, the function capitalizes the −count previous words but does not move point. The value is

nil.

If point is in the middle of a word, the part of the word before point is ignored when moving forward. The rest is treated as an entire word. When capitalize-word is called interactively, count is set to the numeric prefix argument.

Command downcase-word count

This function converts the count words after point to all lower case, moving point over as it does. If count is negative, it converts the −count previous words but does not move point. The value is nil. When downcase-word is called interactively, count is set to the numeric prefix argument.

Command upcase-word count

This function converts the count words after point to all upper case, moving point over as it does. If count is negative, it converts the −count previous words but does not move point. The value is nil. When upcase-word is called interactively, count is set to the numeric prefix argument.

29.18 Text Properties

Each character position in a buffer or a string can have a text property list, much like the property list of a symbol (see Section 7.4 [Property Lists], page 92). The properties belong to a particular character at a particular place, such as, the letter ‘T’ at the beginning of this sentence or the first ‘o’ in ‘foo’—if the same character occurs in two different places, the two occurrences generally have different properties.

Each property has a name and a value. Both of these can be any Lisp object, but the name is normally a symbol. The usual way to access the property list is to specify a name and ask what value corresponds to it.

If a character has a category property, we call it the category of the character. It should be a symbol. The properties of the symbol serve as defaults for the properties of the character.

Copying text between strings and buffers preserves the properties along with the characters; this includes such diverse functions as substring, insert, and buffer-substring.

29.18.1 Examining Text Properties

The simplest way to examine text properties is to ask for the value of a particular property of a particular character. For that, use get-text-property. Use text-properties-at to get the entire property list of a character. See Section 29.18.3 [Property Search], page 480, for functions to examine the properties of a number of characters at once.

These functions handle both strings and buffers. Keep in mind that positions in a string start from 0, whereas positions in a buffer start from 1.

Function get-text-property pos prop &optional object This function returns the value of the prop property of the character after position pos in object (a buffer or string). The argument object is optional and defaults to the current buffer. If there is no prop property strictly speaking, but the character has a category that is a symbol, then get-text-property returns the prop property of that symbol.

Function get-char-property pos prop &optional object This function is like get-text-property, except that it checks overlays first and then text properties. See Section 35.9 [Overlays], page 575. The argument object may be a string, a buffer, or a window. If it is a window, then the buffer displayed in that window is used for text properties and overlays, but only the overlays active for that window are considered. If object is a buffer, then all overlays in that buffer are considered, as well as text properties. If object is a string, only text properties are considered, since strings never have overlays.

Function text-properties-at position &optional object This function returns the entire property list of the character at position in the string or buffer object. If object is nil, it defaults to the current buffer.

Variable default-text-properties

This variable holds a property list giving default values for text properties. Whenever a character does not specify a value for a property, neither directly nor through a category symbol, the value stored in this list is used instead. Here is an example:

     (setq default-text-properties '(foo 69))

;; Make sure character 1 has no properties of its own.

     (set-text-properties 1 2 nil)

;; What we get, when we ask, is the default value.

     (get-text-property 1 'foo)
          ⇒ 69

29.18.2 Changing Text Properties

The primitives for changing properties apply to a specified range of text. The function set-text-properties (see end of section) sets the entire property list of the text in that range; more often, it is useful to add, change, or delete just certain properties specified by name.

Since text properties are considered part of the buffer’s contents, and can affect how the buffer looks on the screen, any change in the text properties is considered a buffer modification. Buffer text property changes are undoable (see Section 29.9 [Undo], page 461).

Function put-text-property start end prop value &optional object This function sets the prop property to value for the text between start and end in the string or buffer object. If object is nil, it defaults to the current buffer.

Function add-text-properties start end props &optional object This function modifies the text properties for the text between start and end in the string or buffer object. If object is nil, it defaults to the current buffer. The argument props specifies which properties to change. It should have the form of a property list (see Section 7.4 [Property Lists], page 92): a list whose elements include the property names followed alternately by the corresponding values. The return value is t if the function actually changed some property’s value; nil otherwise (if props is nil or its values agree with those in the text). For example, here is how to set the comment and face properties of a range of text:

     (add-text-properties start end
                          '(comment t face highlight))

Function remove-text-properties start end props &optional object This function deletes specified text properties from the text between start and end in the string or buffer object. If object is nil, it defaults to the current buffer. The argument props specifies which properties to delete. It should have the form of a property list (see Section 7.4 [Property Lists], page 92): a list whose elements are property names alternating with corresponding values. But only the names matter—the values that accompany them are ignored. For example, here’s how to remove the face property.

     (remove-text-properties start end '(face nil))

The return value is t if the function actually changed some property’s value; nil otherwise (if props is nil or if no character in the specified text had any of those properties).

Function set-text-properties start end props &optional object This function completely replaces the text property list for the text between start and end in the string or buffer object. If object is nil, it defaults to the current buffer. The argument props is the new property list. It should be a list whose elements are property names alternating with corresponding values. After set-text-properties returns, all the characters in the specified range have identical properties. If props is nil, the effect is to get rid of all properties from the specified range of text. Here’s an example:

     (set-text-properties start end nil)

See also the function buffer-substring-no-properties (see Section 29.2 [Buffer Contents], page 450) which copies text from the buffer but does not copy its properties.

29.18.3 Property Search Functions

In typical use of text properties, most of the time several or many consecutive characters have the same value for a property. Rather than writing your programs to examine characters one by one, it is much faster to process chunks of text that have the same property value.

Here are functions you can use to do this. They use eq for comparing property values. In all cases, object defaults to the current buffer.

For high performance, it’s very important to use the limit argument to these functions, especially the ones that search for a single property—otherwise, they may spend a long time scanning to the end of the buffer, if the property you are interested in does not change.

Remember that a position is always between two characters; the position returned by these functions is between two characters with different properties.

Function next-property-change pos &optional object limit The function scans the text forward from position pos in the string or buffer object till it finds a change in some text property, then returns the position of the change. In other words, it returns the position of the first character beyond pos whose properties are not identical to those of the character just after pos. If limit is non-nil, then the scan ends at position limit. If there is no property change before that point, next-property-change returns limit.

The value is nil if the properties remain unchanged all the way to the end of object and limit is nil. If the value is non-nil, it is a position greater than or equal to pos. The value equals pos only when limit equals pos. Here is an example of how to scan the buffer by chunks of text within which all properties are constant:

     (while (not (eobp))
       (let ((plist (text-properties-at (point)))
             (next-change
              (or (next-property-change (point) (current-buffer))
                  (point-max))))

Process text from point to next-change…

         (goto-char next-change)))

Function next-single-property-change pos prop &optional object limit

The function scans the text forward from position pos in the string or buffer object till it finds a change in the prop property, then returns the position of the change. In other words, it returns the position of the first character beyond pos whose prop property differs from that of the character just after pos. If limit is non-nil, then the scan ends at position limit. If there is no property change before that point, next-single-property-change returns limit. The value is nil if the property remains unchanged all the way to the end of object and limit is nil. If the value is non-nil, it is a position greater than or equal to pos; it equals pos only if limit equals pos.

Function previous-property-change pos &optional object limit

This is like next-property-change, but scans back from pos instead of forward. If the value is non-nil, it is a position less than or equal to pos; it equals pos only if limit equals pos.

Function previous-single-property-change pos prop &optional object

limit This is like next-single-property-change, but scans back from pos instead of forward. If the value is non-nil, it is a position less than or equal to pos; it equals pos only if limit equals pos.

Function text-property-any start end prop value &optional object This function returns non-nil if at least one character between start and end has a property prop whose value is value. More precisely, it returns the position of the first such character. Otherwise, it returns nil. The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object. The default for object is the current buffer.

Function text-property-not-all start end prop value &optional object This function returns non-nil if at least one character between start and end has a property prop whose value differs from value. More precisely, it returns the position of the first such character. Otherwise, it returns nil. The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object. The default for object is the current buffer.

29.18.4 Properties with Special Meanings

Here is a table of text property names that have special built-in meanings. The following section lists a few more special property names that are used to control filling. All other names have no standard meaning, and you can use them as you like.

category If a character has a category property, we call it the category of the character. It should be a symbol. The properties of the symbol serve as defaults for the properties of the character.

face You can use the property face to control the font and color of text. Its value is a face name or a list of face names. See Section 35.10 [Faces], page 578, for more information. This feature may be temporary; in the future, we may replace it with other ways of specifying how to display text.

mouse-face

The property mouse-face is used instead of face when the mouse is on or near the character. For this purpose, “near” means that all text between the character and where the mouse is have the same mouse-face property value.

local-map

You can specify a different keymap for a portion of the text by means of a local-map property. The property’s value for the character after point, if non-nil, replaces the buffer’s local map. See Section 19.6 [Active Keymaps], page 281.

read-only

If a character has the property read-only, then modifying that character is not allowed. Any command that would do so gets an error. Insertion next to a read-only character is an error if inserting ordinary text there would inherit the read-only property due to stickiness. Thus, you can control permission to insert next to read-only text by controlling the stickiness. See Section 29.18.6 [Sticky Properties], page 484. Since changing properties counts as modifying the buffer, it is not possible to remove a read-only property unless you know the special trick: bind inhibitread-only to a non-nil value and then remove the property. See Section 24.7 [Read Only Buffers], page 376.

invisible

A non-nil invisible property can make a character invisible on the screen. See Section 35.5 [Invisible Text], page 570, for details.

intangible

If a group of consecutive characters have equal and non-nil intangible properties, then you cannot place point between them. If you try to move point forward into the group, point actually moves to the end of the group. If you try to move point backward into the group, point actually moves to the start of the group.

When the variable inhibit-point-motion-hooks is non-nil, the intangible

property is ignored.

modification-hooks

If a character has the property modification-hooks, then its value should be a list of functions; modifying that character calls all of those functions. Each function receives two arguments: the beginning and end of the part of the buffer being modified. Note that if a particular modification hook function appears on several characters being modified by a single primitive, you can’t predict how many times the function will be called.

insert-in-front-hooks
insert-behind-hooks

The operation of inserting text in a buffer also calls the functions listed in the insert-in-front-hooks property of the following character and in the insert-behind-hooks property of the preceding character. These functions receive two arguments, the beginning and end of the inserted text. The functions are called after the actual insertion takes place. See also Section 29.22 [Change Hooks], page 489, for other hooks that are called when you change text in a buffer.

point-entered
point-left

The special properties point-entered and point-left record hook functions that report motion of point. Each time point moves, Emacs compares these two property values:

• the point-left property of the character after the old location, and

• the point-entered property of the character after the new location.

If these two values differ, each of them is called (if not nil) with two arguments: the old value of point, and the new one. The same comparison is made for the characters before the old and new locations. The result may be to execute two point-left functions (which may be the same function) and/or two point-entered functions (which may be the same function). In any case, all the point-left functions are called first, followed by all the point-entered functions. A primitive function may examine characters at various positions without moving point to those positions. Only an actual change in the value of point runs these hook functions.

Variable inhibit-point-motion-hooks

When this variable is non-nil, point-left and point-entered hooks are not run, and the intangible property has no effect.

29.18.5 Formatted Text Properties

These text properties affect the behavior of the fill commands. They are used for representing formatted text. See Section 29.11 [Filling], page 464, and Section 29.12 [Margins], page 466. hard If a newline character has this property, it is a “hard” newline. The fill com-

mands do not alter hard newlines and do not move words across them. However, this property takes effect only if the variable use-hard-newlines is non-nil.

right-margin

This property specifies an extra right margin for filling this part of the text.

left-margin

This property specifies an extra left margin for filling this part of the text.

justification

This property specifies the style of justification for filling this part of the text.

29.18.6 Stickiness of Text Properties

Self-inserting characters normally take on the same properties as the preceding character. This is called inheritance of properties.

In a Lisp program, you can do insertion with inheritance or without, depending on your choice of insertion primitive. The ordinary text insertion functions such as insert do not inherit any properties. They insert text with precisely the properties of the string being inserted, and no others. This is correct for programs that copy text from one context to another—for example, into or out of the kill ring. To insert with inheritance, use the special primitives described in this section. Self-inserting characters inherit properties because they work using these primitives.

When you do insertion with inheritance, which properties are inherited depends on two

specific properties: front-sticky and rear-nonsticky.

Insertion after a character inherits those of its properties that are rear-sticky. Insertion before a character inherits those of its properties that are front-sticky. By default, a text property is rear-sticky but not front-sticky. Thus, the default is to inherit all the properties of the preceding character, and nothing from the following character. You can request different behavior by specifying the stickiness of certain properties.

If a character’s front-sticky property is t, then all its properties are front-sticky. If the front-sticky property is a list, then the sticky properties of the character are those whose names are in the list. For example, if a character has a front-sticky property whose value is (face read-only), then insertion before the character can inherit its face property and its read-only property, but no others.

The rear-nonsticky works the opposite way. Every property is rear-sticky by default, so the rear-nonsticky property says which properties are not rear-sticky. If a character’s rear-nonsticky property is t, then none of its properties are rear-sticky. If the rearnonsticky property is a list, properties are rear-sticky unless their names are in the list.

When you insert text with inheritance, it inherits all the rear-sticky properties of the preceding character, and all the front-sticky properties of the following character. The previous character’s properties take precedence when both sides offer different sticky values for the same property.

Here are the functions that insert text with inheritance of properties:

Function insert-and-inherit &rest strings

Insert the strings strings, just like the function insert, but inherit any sticky properties from the adjoining text.

Function insert-before-markers-and-inherit &rest strings

Insert the strings strings, just like the function insert-before-markers, but inherit any sticky properties from the adjoining text.

29.18.7 Saving Text Properties in Files

You can save text properties in files, and restore text properties when inserting the files, using these two hooks:

Variable write-region-annotate-functions

This variable’s value is a list of functions for write-region to run to encode text properties in some fashion as annotations to the text being written in the file. See Section 22.4 [Writing to Files], page 335. Each function in the list is called with two arguments: the start and end of the region to be written. These functions should not alter the contents of the buffer. Instead, they should return lists indicating annotations to write in the file in addition to the text in the buffer. Each function should return a list of elements of the form (position . string), where position is an integer specifying the relative position in the text to be written, and string is the annotation to add there. Each list returned by one of these functions must be already sorted in increasing order by position. If there is more than one function, write-region merges the lists destructively into one sorted list. When write-region actually writes the text from the buffer to the file, it intermixes the specified annotations at the corresponding positions. All this takes place without modifying the buffer.

Variable after-insert-file-functions

This variable holds a list of functions for insert-file-contents to call after inserting a file’s contents. These functions should scan the inserted text for annotations, and convert them to the text properties they stand for. Each function receives one argument, the length of the inserted text; point indicates the start of that text. The function should scan that text for annotations, delete them, and create the text properties that the annotations specify. The function should return the updated length of the inserted text, as it stands after those changes. The value returned by one function becomes the argument to the next function. These functions should always return with point at the beginning of the inserted text. The intended use of after-insert-file-functions is for converting some sort of textual annotations into actual text properties. But other uses may be possible.

We invite users to write Lisp programs to store and retrieve text properties in files, using these hooks, and thus to experiment with various data formats and find good ones. Eventually we hope users will produce good, general extensions we can install in Emacs.

We suggest not trying to handle arbitrary Lisp objects as property names or property values—because a program that general is probably difficult to write, and slow. Instead, choose a set of possible data types that are reasonably flexible, and not too hard to encode.

See Section 22.12 [Format Conversion], page 354, for a related feature.

29.18.8 Lazy Computation of Text Properties

Instead of computing text properties for all the text in the buffer, you can arrange to compute the text properties for parts of the text when and if something depends on them.

The primitive that extracts text from the buffer along with its properties is buffersubstring. Before examining the properties, this function runs the abnormal hook buffer-

access-fontify-functions.

Variable buffer-access-fontify-functions

This variable holds a list of functions for computing text properties. Before buffer-substring copies the text and text properties for a portion of the buffer, it calls all the functions in this list. Each of the functions receives two arguments that specify the range of the buffer being accessed. (The buffer itself is always the current buffer.)

The function buffer-substring-no-properties does not call these functions, since it ignores text properties anyway.

In order to prevent the hook functions from being called more than once for the same part of the buffer, you can use the variable buffer-access-fontified-property.

Variable buffer-access-fontified-property

If this value’s variable is non-nil, it is a symbol which is used as a text property name. A non-nil value for that text property means, “the other text properties for this character have already been computed.” If all the characters in the range specified for buffer-substring have a non-nil value for this property, buffer-substring does not call the buffer-access-fontify-functions functions. It assumes these characters already have the right text properties, and just copies the properties they already have. The normal way to use this feature is that the buffer-access-fontify-functions functions add this property, as well as others, to the characters they operate on. That way, they avoid being called over and over for the same text.

29.18.9 Why Text Properties are not Intervals

Some editors that support adding attributes to text in the buffer do so by letting the user specify “intervals” within the text, and adding the properties to the intervals. Those editors permit the user or the programmer to determine where individual intervals start and end. We deliberately provided a different sort of interface in Emacs Lisp to avoid certain paradoxical behavior associated with text modification.

If the actual subdivision into intervals is meaningful, that means you can distinguish between a buffer that is just one interval with a certain property, and a buffer containing the same text subdivided into two intervals, both of which have that property.

Suppose you take the buffer with just one interval and kill part of the text. The text remaining in the buffer is one interval, and the copy in the kill ring (and the undo list) becomes a separate interval. Then if you yank back the killed text, you get two intervals with the same properties. Thus, editing does not preserve the distinction between one interval and two.

Suppose we “fix” this problem by coalescing the two intervals when the text is inserted. That works fine if the buffer originally was a single interval. But suppose instead that we have two adjacent intervals with the same properties, and we kill the text of one interval and yank it back. The same interval-coalescence feature that rescues the other case causes trouble in this one: after yanking, we have just one interval. One again, editing does not preserve the distinction between one interval and two.

Insertion of text at the border between intervals also raises questions that have no satisfactory answer.

However, it is easy to arrange for editing to behave consistently for questions of the form, “What are the properties of this character?” So we have decided these are the only questions that make sense; we have not implemented asking questions about where intervals start or end.

In practice, you can usually use the property search functions in place of explicit interval boundaries. You can think of them as finding the boundaries of intervals, assuming that intervals are always coalesced whenever possible. See Section 29.18.3 [Property Search], page 480.

Emacs also provides explicit intervals as a presentation feature; see Section 35.9 [Overlays], page 575.

29.19 Substituting for a Character Code

The following functions replace characters within a specified region based on their character codes.

Function subst-char-in-region start end old-char new-char &optional

noundo This function replaces all occurrences of the character old-char with the character new-char in the region of the current buffer defined by start and end.

If noundo is non-nil, then subst-char-in-region does not record the change for undo and does not mark the buffer as modified. This feature is used for controlling selective display (see Section 35.6 [Selective Display], page 571).

subst-char-in-region does not move point and returns nil.

          ---------- Buffer: foo ----------
          This is the contents of the buffer before.
          ---------- Buffer: foo ----------

     (subst-char-in-region 1 20 ?i ?X)
          ⇒ nil
     ---------- Buffer: foo ----------
     ThXs Xs the contents of the buffer before.
     ---------- Buffer: foo ----------

Function translate-region start end table

This function applies a translation table to the characters in the buffer between positions start and end. The translation table table is a string; (aref table ochar) gives the translated character corresponding to ochar. If the length of table is less than 256, any characters with codes larger than the length of table are not altered by the translation. The return value of translate-region is the number of characters that were actually changed by the translation. This does not count characters that were mapped into themselves in the translation table.

29.20 Registers

A register is a sort of variable used in Emacs editing that can hold a marker, a string, a rectangle, a window configuration (of one frame), or a frame configuration (of all frames). Each register is named by a single character. All characters, including control and meta characters (but with the exception of C-g), can be used to name registers. Thus, there are 255 possible registers. A register is designated in Emacs Lisp by a character that is its name.

The functions in this section return unpredictable values unless otherwise stated.

Variable register-alist

This variable is an alist of elements of the form (name . contents). Normally, there is one element for each Emacs register that has been used. The object name is a character (an integer) identifying the register. The object contents is a string, marker, or list representing the register contents. A string represents text stored in the register. A marker represents a position. A list represents a rectangle; its elements are strings, one per line of the rectangle.

Function get-register reg

This function returns the contents of the register reg, or nil if it has no contents.

Function set-register reg value

This function sets the contents of register reg to value. A register can be set to any value, but the other register functions expect only certain data types. The return value is value.

Command view-register reg

This command displays what is contained in register reg.

Command insert-register reg &optional beforep This command inserts contents of register reg into the current buffer. Normally, this command puts point before the inserted text, and the mark after it. However, if the optional second argument beforep is non-nil, it puts the mark before and point after. You can pass a non-nil second argument beforep to this function interactively by supplying any prefix argument. If the register contains a rectangle, then the rectangle is inserted with its upper left corner at point. This means that text is inserted in the current line and underneath it on successive lines. If the register contains something other than saved text (a string) or a rectangle (a list), currently useless things happen. This may be changed in the future.

29.21 Transposition of Text

This subroutine is used by the transposition commands.

Function transpose-regions start1 end1 start2 end2 &optional

leave-markers This function exchanges two nonoverlapping portions of the buffer. Arguments start1 and end1 specify the bounds of one portion and arguments start2 and end2 specify the bounds of the other portion. Normally, transpose-regions relocates markers with the transposed text; a marker previously positioned within one of the two transposed portions moves along with that portion, thus remaining between the same two characters in their new position. However, if leave-markers is non-nil, transpose-regions does not do this—it leaves all markers unrelocated.

29.22 Change Hooks

These hook variables let you arrange to take notice of all changes in all buffers (or in a particular buffer, if you make them buffer-local). See also Section 29.18.4 [Special Properties], page 482, for how to detect changes to specific parts of the text.

The functions you use in these hooks should save and restore the match data if they do anything that uses regular expressions; otherwise, they will interfere in bizarre ways with the editing operations that call them.

Variable before-change-functions

This variable holds a list of a functions to call before any buffer modification. Each function gets two arguments, the beginning and end of the region that is about to change, represented as integers. The buffer that is about to change is always the current buffer.

Variable after-change-functions

This variable holds a list of a functions to call after any buffer modification. Each function receives three arguments: the beginning and end of the region just changed, and the length of the text that existed before the change. (To get the current length, subtract the region beginning from the region end.) All three arguments are integers. The buffer that’s about to change is always the current buffer.

Variable before-change-function

This obsolete variable holds one function to call before any buffer modification (or nil for no function). It is called just like the functions in before-change-

functions.

Variable after-change-function

This obsolete variable holds one function to call after any buffer modification (or nil for no function). It is called just like the functions in after-change-

functions.

The four variables above are temporarily bound to nil during the time that any of these functions is running. This means that if one of these functions changes the buffer, that change won’t run these functions. If you do want a hook function to make changes that run these functions, make it bind these variables back to their usual values.

One inconvenient result of this protective feature is that you cannot have a function in

after-change-functions or before-change-functions which changes the value of that

variable. But that’s not a real limitation. If you want those functions to change the list of functions to run, simply add one fixed function to the hook, and code that function to look in another variable for other functions to call. Here is an example:

(setq my-own-after-change-functions nil)
(defun indirect-after-change-function (beg end len)
  (let ((list my-own-after-change-functions))
    (while list
      (funcall (car list) beg end len)
      (setq list (cdr list)))))
(add-hooks 'after-change-functions
           'indirect-after-change-function)

Variable first-change-hook

This variable is a normal hook that is run whenever a buffer is changed that was previously in the unmodified state.

30 Searching and Matching

GNU Emacs provides two ways to search through a buffer for specified text: exact string searches and regular expression searches. After a regular expression search, you can examine the match data to determine which text matched the whole regular expression or various portions of it.

The ‘skip-chars…’ functions also perform a kind of searching. See Section 27.2.7 [Skipping Characters], page 436.

30.1 Searching for Strings

These are the primitive functions for searching through the text in a buffer. They are meant for use in programs, but you may call them interactively. If you do so, they prompt for the search string; limit and noerror are set to nil, and repeat is set to 1.

Command search-forward string &optional limit noerror repeat This function searches forward from point for an exact match for string. If successful, it sets point to the end of the occurrence found, and returns the new value of point. If no match is found, the value and side effects depend on noerror (see below). In the following example, point is initially at the beginning of the line. Then (search-forward "fox") moves point after the last letter of ‘fox’:

     ---------- Buffer: foo ----------
     ⋆The quick brown fox jumped over the lazy dog.
     ---------- Buffer: foo ----------
     (search-forward "fox")
          ⇒ 20
     ---------- Buffer: foo ----------
     The quick brown fox⋆ jumped over the lazy dog.
     ---------- Buffer: foo ----------

The argument limit specifies the upper bound to the search. (It must be a position in the current buffer.) No match extending after that position is accepted. If limit is omitted or nil, it defaults to the end of the accessible portion of the buffer. What happens when the search fails depends on the value of noerror. If noerror is nil, a search-failed error is signaled. If noerror is t, search-forward returns nil and does nothing. If noerror is neither nil nor t, then searchforward moves point to the upper bound and returns nil. (It would be more consistent now to return the new position of point in that case, but some programs may depend on a value of nil.) If repeat is supplied (it must be a positive number), then the search is repeated that many times (each time starting at the end of the previous time’s match). If these successive searches succeed, the function succeeds, moving point and returning its new value. Otherwise the search fails.

Command search-backward string &optional limit noerror repeat This function searches backward from point for string. It is just like searchforward except that it searches backwards and leaves point at the beginning of the match.

Command word-search-forward string &optional limit noerror repeat This function searches forward from point for a “word” match for string. If it finds a match, it sets point to the end of the match found, and returns the new value of point. Word matching regards string as a sequence of words, disregarding punctuation that separates them. It searches the buffer for the same sequence of words. Each word must be distinct in the buffer (searching for the word ‘ball’ does not match the word ‘balls’), but the details of punctuation and spacing are ignored (searching for ‘ball boy’ does match ‘ball. Boy!’). In this example, point is initially at the beginning of the buffer; the search leaves it between the ‘y’ and the ‘!’.

     ---------- Buffer: foo ----------
     ⋆He said "Please!  Find
     the ball boy!"
     ---------- Buffer: foo ----------
     (word-search-forward "Please find the ball, boy.")
          ⇒ 35
     ---------- Buffer: foo ----------
     He said "Please!  Find
     the ball boy⋆!"
     ---------- Buffer: foo ----------

If limit is non-nil (it must be a position in the current buffer), then it is the upper bound to the search. The match found must not extend after that position. If noerror is nil, then word-search-forward signals an error if the search fails. If noerror is t, then it returns nil instead of signaling an error. If noerror is neither nil nor t, it moves point to limit (or the end of the buffer) and returns

nil.

If repeat is non-nil, then the search is repeated that many times. Point is positioned at the end of the last match.

Command word-search-backward string &optional limit noerror repeat This function searches backward from point for a word match to string. This function is just like word-search-forward except that it searches backward and normally leaves point at the beginning of the match.

30.2 Regular Expressions

A regular expression (regexp, for short) is a pattern that denotes a (possibly infinite) set of strings. Searching for matches for a regexp is a very powerful operation. This section explains how to write regexps; the following section says how to search for them.

30.2.1 Syntax of Regular Expressions

Regular expressions have a syntax in which a few characters are special constructs and the rest are ordinary. An ordinary character is a simple regular expression that matches that character and nothing else. The special characters are ‘.’, ‘*’, ‘+’, ‘?’, ‘[’, ‘]’, ‘^’, ‘$’, and ‘\’; no new special characters will be defined in the future. Any other character appearing in a regular expression is ordinary, unless a ‘\’ precedes it.

For example, ‘f’ is not a special character, so it is ordinary, and therefore ‘f’ is a regular expression that matches the string ‘f’ and no other string. (It does not match the string ‘ff’.) Likewise, ‘o’ is a regular expression that matches only ‘o’.

Any two regular expressions a and b can be concatenated. The result is a regular expression that matches a string if a matches some amount of the beginning of that string and b matches the rest of the string.

As a simple example, we can concatenate the regular expressions ‘f’ and ‘o’ to get the regular expression ‘fo’, which matches only the string ‘fo’. Still trivial. To do something more powerful, you need to use one of the special characters. Here is a list of them:

. (Period) is a special character that matches any single character except a newline. Using concatenation, we can make regular expressions like ‘a.b’, which matches any three-character string that begins with ‘a’ and ends with ‘b’.

* is not a construct by itself; it is a suffix operator that means to repeat the preceding regular expression as many times as possible. In ‘fo*’, the ‘*’ applies to the ‘o’, so ‘fo*’ matches one ‘f’ followed by any number of ‘o’s. The case of zero ‘o’s is allowed: ‘fo*’ does match ‘f’.

‘*’ always applies to the smallest possible preceding expression. Thus, ‘fo*’ has a repeating ‘o’, not a repeating ‘fo’.

The matcher processes a ‘*’ construct by matching, immediately, as many repetitions as can be found. Then it continues with the rest of the pattern. If that fails, backtracking occurs, discarding some of the matches of the ‘*’-modified construct in case that makes it possible to match the rest of the pattern. For example, in matching ‘ca*ar’ against the string ‘caaar’, the ‘a*’ first tries to match all three ‘a’s; but the rest of the pattern is ‘ar’ and there is only ‘r’ left to match, so this try fails. The next alternative is for ‘a*’ to match only two ‘a’s. With this choice, the rest of the regexp matches successfully.

Nested repetition operators can be extremely slow if they specify backtracking loops. For example, it could take hours for the regular expression ‘\(x+y*\)*a’

to match the sequence ‘xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz’. The slow-

ness is because Emacs must try each imaginable way of grouping the 35 ‘x’’s before concluding that none of them can work. To make sure your regular expressions run fast, check nested repetitions carefully.

+ is a suffix operator similar to ‘*’ except that the preceding expression must match at least once. So, for example, ‘ca+r’ matches the strings ‘car’ and ‘caaaar’ but not the string ‘cr’, whereas ‘ca*r’ matches all three strings.

? is a suffix operator similar to ‘*’ except that the preceding expression can match either once or not at all. For example, ‘ca?r’ matches ‘car’ or ‘cr’, but does not match anyhing else.

[ …] ‘[’ begins a character set, which is terminated by a ‘]’. In the simplest case, the characters between the two brackets form the set. Thus, ‘[ad]’ matches either one ‘a’ or one ‘d’, and ‘[ad]*’ matches any string composed of just ‘a’s and ‘d’s (including the empty string), from which it follows that ‘c[ad]*r’ matches ‘cr’, ‘car’, ‘cdr’, ‘caddaar’, etc. The usual regular expression special characters are not special inside a character set. A completely different set of special characters exists inside character sets: ‘]’, ‘-’ and ‘^’. ‘-’ is used for ranges of characters. To write a range, write two characters with a ‘-’ between them. Thus, ‘[a-z]’ matches any lower case letter. Ranges may be intermixed freely with individual characters, as in ‘[a-z$%.]’, which matches any lower case letter or ‘$’, ‘%’, or a period. To include a ‘]’ in a character set, make it the first character. For example, ‘[]a]’ matches ‘]’ or ‘a’. To include a ‘-’, write ‘-’ as the first character in the set, or put it immediately after a range. (You can replace one individual character c with the range ‘c-c’ to make a place to put the ‘-’.) There is no way to write a set containing just ‘-’ and ‘]’. To include ‘^’ in a set, put it anywhere but at the beginning of the set.

[^…] ‘[^’ begins a complement character set, which matches any character except the ones specified. Thus, ‘[^a-z0-9A-Z]’ matches all characters except letters and digits. ‘^’ is not special in a character set unless it is the first character. The character following the ‘^’ is treated as if it were first (thus, ‘-’ and ‘]’ are not special there). Note that a complement character set can match a newline, unless newline is mentioned as one of the characters not to match.

^is a special character that matches the empty string, but only at the beginning of a line in the text being matched. Otherwise it fails to match anything. Thus, ‘^foo’ matches a ‘foo’ that occurs at the beginning of a line. When matching a string instead of a buffer, ‘^’ matches at the beginning of the string or after a newline character ‘\n’.

$ is similar to ‘^’ but matches only at the end of a line. Thus, ‘x+$’ matches a string of one ‘x’ or more at the end of a line. When matching a string instead of a buffer, ‘$’ matches at the end of the string or before a newline character ‘\n’.

\ has two functions: it quotes the special characters (including ‘\’), and it introduces additional special constructs. Because ‘\’ quotes special characters, ‘\$’ is a regular expression that matches only ‘$’, and ‘\[’ is a regular expression that matches only ‘[’, and so on.

Note that ‘\’ also has special meaning in the read syntax of Lisp strings (see Section 2.3.8 [String Type], page 23), and must be quoted with ‘\’. For example, the regular expression that matches the ‘\’ character is ‘\\’. To write a Lisp string that contains the characters ‘\\’, Lisp syntax requires you to quote each ‘\’ with another ‘\’. Therefore, the read syntax for a regular expression matching ‘\’ is "\\\\".

Please note: For historical compatibility, special characters are treated as ordinary ones if they are in contexts where their special meanings make no sense. For example, ‘*foo’ treats ‘*’ as ordinary since there is no preceding expression on which the ‘*’ can act. It is poor practice to depend on this behavior; quote the special character anyway, regardless of where it appears.

For the most part, ‘\’ followed by any character matches only that character. However, there are several exceptions: characters that, when preceded by ‘\’, are special constructs. Such characters are always ordinary when encountered on their own. Here is a table of ‘\’ constructs:

\| specifies an alternative. Two regular expressions a and b with ‘\|’ in between form an expression that matches anything that either a or b matches. Thus, ‘foo\|bar’ matches either ‘foo’ or ‘bar’ but no other string. ‘\|’ applies to the largest possible surrounding expressions. Only a surrounding ‘\( … \)’ grouping can limit the grouping power of ‘\|’. Full backtracking capability exists to handle multiple uses of ‘\|’.

\( … \) is a grouping construct that serves three purposes:

1. To enclose a set of ‘\|’ alternatives for other operations. Thus, the regular expression ‘\(foo\|bar\)x’ matches either ‘foox’ or ‘barx’.

2. To enclose an expression for a suffix operator such as ‘*’ to act on. Thus, ‘ba\(na\)*’ matches ‘bananana’, etc., with any (zero or more) number of ‘na’ strings.

3. To record a matched substring for future reference.

This last application is not a consequence of the idea of a parenthetical grouping; it is a separate feature that happens to be assigned as a second meaning to the same ‘\( … \)’ construct because there is no conflict in practice between the two meanings. Here is an explanation of this feature:

\digit matches the same text that matched the digitth occurrence of a ‘\( … \)’ construct. In other words, after the end of a ‘\( … \)’ construct. the matcher remembers the beginning and end of the text matched by that construct. Then, later on in the regular expression, you can use ‘\’ followed by digit to match that same text, whatever it may have been. The strings matching the first nine ‘\( … \)’ constructs appearing in a regular expression are assigned numbers 1 through 9 in the order that the open parentheses appear in the regular expression. So you can use ‘\1’ through ‘\9’ to refer to the text matched by the corresponding ‘\( … \)’ constructs.

For example, ‘\(.*\)\1’ matches any newline-free string that is composed of two identical halves. The ‘\(.*\)’ matches the first half, which may be anything, but the ‘\1’ that follows must match the same exact text.

\w matches any word-constituent character. The editor syntax table determines which characters these are. See Chapter 31 [Syntax Tables], page 509.

\W matches any character that is not a word constituent.

\scode matches any character whose syntax is code. Here code is a character that represents a syntax code: thus, ‘w’ for word constituent, ‘-’ for whitespace, ‘(’ for open parenthesis, etc. See Chapter 31 [Syntax Tables], page 509, for a list of syntax codes and the characters that stand for them.

\Scode matches any character whose syntax is not code.

The following regular expression constructs match the empty string—that is, they don’t use up any characters—but whether they match depends on the context.

\` matches the empty string, but only at the beginning of the buffer or string being matched against.

\' matches the empty string, but only at the end of the buffer or string being matched against.

\= matches the empty string, but only at point. (This construct is not defined when matching against a string.)

\b matches the empty string, but only at the beginning or end of a word. Thus, ‘\bfoo\b’ matches any occurrence of ‘foo’ as a separate word. ‘\bballs?\b’ matches ‘ball’ or ‘balls’ as a separate word.

\B matches the empty string, but not at the beginning or end of a word.

\< matches the empty string, but only at the beginning of a word.

\> matches the empty string, but only at the end of a word.

Not every string is a valid regular expression. For example, a string with unbalanced square brackets is invalid (with a few exceptions, such as ‘[]]’), and so is a string that ends with a single ‘\’. If an invalid regular expression is passed to any of the search functions, an invalid-regexp error is signaled.

Function regexp-quote string

This function returns a regular expression string that matches exactly string and nothing else. This allows you to request an exact string match when calling a function that wants a regular expression.

          (regexp-quote "^The cat$")
               ⇒ "\\^The cat\\$"

One use of regexp-quote is to combine an exact string match with context described as a regular expression. For example, this searches for the string that is the value of string, surrounded by whitespace:

          (re-search-forward
           (concat "\\s-" (regexp-quote string) "\\s-"))

30.2.2 Complex Regexp Example

Here is a complicated regexp, used by Emacs to recognize the end of a sentence together with any whitespace that follows. It is the value of the variable sentence-end.

First, we show the regexp as a string in Lisp syntax to distinguish spaces from tab characters. The string constant begins and ends with a double-quote. ‘\"’ stands for a double-quote as part of the string, ‘\\’ for a backslash as part of the string, ‘\t’ for a tab and ‘\n’ for a newline.

     "[.?!][]\"')}]*\\($\\| $\\|\t\\|  \\)[ \t\n]*"

In contrast, if you evaluate the variable sentence-end, you will see the following:

     sentence-end

⇒

     "[.?!][]\"')}]*\\($\\| $\\|  \\|  \\)[
     ]*"

In this output, tab and newline appear as themselves.

This regular expression contains four parts in succession and can be deciphered as follows:

[.?!] The first part of the pattern is a character set that matches any one of three characters: period, question mark, and exclamation mark. The match must begin with one of these three characters.

[]\"')}]*

The second part of the pattern matches any closing braces and quotation marks, zero or more of them, that may follow the period, question mark or exclamation mark. The \" is Lisp syntax for a double-quote in a string. The ‘*’ at the end indicates that the immediately preceding regular expression (a character set, in this case) may be repeated zero or more times.

\\($\\| $\\|\t\\|  \\)

The third part of the pattern matches the whitespace that follows the end of a sentence: the end of a line, or a tab, or two spaces. The double backslashes mark the parentheses and vertical bars as regular expression syntax; the parentheses delimit a group and the vertical bars separate alternatives. The dollar sign is used to match the end of a line.

[ \t\n]* Finally, the last part of the pattern matches any additional whitespace beyond the minimum needed to end a sentence.

30.3 Regular Expression Searching

In GNU Emacs, you can search for the next match for a regexp either incrementally or not. For incremental search commands, see section “Regular Expression Search” in The GNU Emacs Manual. Here we describe only the search functions useful in programs. The

principal one is re-search-forward.

Command re-search-forward regexp &optional limit noerror repeat This function searches forward in the current buffer for a string of text that is matched by the regular expression regexp. The function skips over any amount of text that is not matched by regexp, and leaves point at the end of the first match found. It returns the new value of point. If limit is non-nil (it must be a position in the current buffer), then it is the upper bound to the search. No match extending after that position is accepted. What happens when the search fails depends on the value of noerror. If noerror

is nil, a search-failed error is signaled. If noerror is t, re-search-forward

does nothing and returns nil. If noerror is neither nil nor t, then re-search-forward moves point to limit (or the end of the buffer) and returns nil. If repeat is supplied (it must be a positive number), then the search is repeated that many times (each time starting at the end of the previous time’s match). If these successive searches succeed, the function succeeds, moving point and returning its new value. Otherwise the search fails. In the following example, point is initially before the ‘T’. Evaluating the search call moves point to the end of that line (between the ‘t’ of ‘hat’ and the newline).

     ---------- Buffer: foo ----------
     I read "⋆The cat in the hat
     comes back" twice.
     ---------- Buffer: foo ----------
     (re-search-forward "[a-z]+" nil t 5)
          ⇒ 27
     ---------- Buffer: foo ----------
     I read "The cat in the hat⋆
     comes back" twice.
     ---------- Buffer: foo ----------

Command re-search-backward regexp &optional limit noerror repeat This function searches backward in the current buffer for a string of text that is matched by the regular expression regexp, leaving point at the beginning of the first text found. This function is analogous to re-search-forward, but they are not simple mirror images. re-search-forward finds the match whose beginning is as close as possible to the starting point. If re-search-backward were a perfect mirror image, it would find the match whose end is as close as possible. However, in fact it finds the match whose beginning is as close as possible. The reason is that matching a regular expression at a given spot always works from beginning to end, and starts at a specified beginning position. A true mirror-image of re-search-forward would require a special feature for matching regexps from end to beginning. It’s not worth the trouble of implementing that.

Function string-match regexp string &optional start This function returns the index of the start of the first match for the regular expression regexp in string, or nil if there is no match. If start is non-nil, the search starts at that index in string. For example,

     (string-match
      "quick" "The quick brown fox jumped quickly.")
          ⇒ 4
     (string-match
      "quick" "The quick brown fox jumped quickly." 8)
          ⇒ 27

The index of the first character of the string is 0, the index of the second character is 1, and so on. After this function returns, the index of the first character beyond the match is available as (match-end 0). See Section 30.6 [Match Data], page 501.

     (string-match
      "quick" "The quick brown fox jumped quickly." 8)
          ⇒ 27
     (match-end 0)
          ⇒ 32

Function looking-at regexp

This function determines whether the text in the current buffer directly following point matches the regular expression regexp. “Directly following” means precisely that: the search is “anchored” and it can succeed only starting with the first character following point. The result is t if so, nil otherwise. This function does not move point, but it updates the match data, which you can access using match-beginning and match-end. See Section 30.6 [Match Data], page 501. In this example, point is located directly before the ‘T’. If it were anywhere else, the result would be nil.

     ---------- Buffer: foo ----------
     I read "⋆The cat in the hat
     comes back" twice.
     ---------- Buffer: foo ----------
     (looking-at "The cat in the hat$")
          ⇒ t

30.4 POSIX Regular Expression Searching

The usual regular expression functions do backtracking when necessary to handle the ‘\|’ and repetition constructs, but they continue this only until they find some match. Then they succeed and report the first match found.

This section describes alternative search functions which perform the full backtracking specified by the POSIX standard for regular expression matching. They continue backtracking until they have tried all possibilities and found all matches, so they can report the longest match, as required by POSIX. This is much slower, so use these functions only when you really need the longest match.

In Emacs versions prior to 19.29, these functions did not exist, and the functions described above implemented full POSIX backtracking.

Function posix-search-forward regexp &optional limit noerror repeat This is like re-search-forward except that it performs the full backtracking specified by the POSIX standard for regular expression matching.

Function posix-search-backward regexp &optional limit noerror repeat This is like re-search-backward except that it performs the full backtracking specified by the POSIX standard for regular expression matching.

Function posix-looking-at regexp

This is like looking-at except that it performs the full backtracking specified by the POSIX standard for regular expression matching.

Function posix-string-match regexp string &optional start This is like string-match except that it performs the full backtracking specified by the POSIX standard for regular expression matching.

30.5 Search and Replace

Function perform-replace from-string replacements query-flag regexp-flag

delimited-flag &optional repeat-count map This function is the guts of query-replace and related commands. It searches for occurrences of from-string and replaces some or all of them. If query-flag is nil, it replaces all occurrences; otherwise, it asks the user what to do about each one. If regexp-flag is non-nil, then from-string is considered a regular expression; otherwise, it must match literally. If delimited-flag is non-nil, then only replacements surrounded by word boundaries are considered. The argument replacements specifies what to replace occurrences with. If it is a string, that string is used. It can also be a list of strings, to be used in cyclic order. If repeat-count is non-nil, it should be an integer. Then it specifies how many times to use each of the strings in the replacements list before advancing cyclicly to the next one. Normally, the keymap query-replace-map defines the possible user responses for queries. The argument map, if non-nil, is a keymap to use instead of

query-replace-map.

Variable query-replace-map

This variable holds a special keymap that defines the valid user responses for

query-replace and related functions, as well as y-or-n-p and map-y-or-n-p.

It is unusual in two ways:

• The “key bindings” are not commands, just symbols that are meaningful to the functions that use this map.

• Prefix keys are not supported; each key binding must be for a single event key sequence. This is because the functions don’t use read key sequence to get the input; instead, they read a single event and look it up “by hand.”

Here are the meaningful “bindings” for query-replace-map. Several of them are meaningful only for query-replace and friends.

act Do take the action being considered—in other words, “yes.”

skip Do not take action for this question—in other words, “no.”

exit Answer this question “no,” and give up on the entire series of questions, assuming that the answers will be “no.”

act-and-exit

Answer this question “yes,” and give up on the entire series of questions, assuming that subsequent answers will be “no.”

act-and-show

Answer this question “yes,” but show the results—don’t advance yet to the next question.

automatic

Answer this question and all subsequent questions in the series with “yes,” without further user interaction.

backup Move back to the previous place that a question was asked about.

edit Enter a recursive edit to deal with this question—instead of any other action that would normally be taken.

delete-and-edit

Delete the text being considered, then enter a recursive edit to replace it.

recenter Redisplay and center the window, then ask the same question again.

quit Perform a quit right away. Only y-or-n-p and related functions use this answer.

help Display some help, then ask again.

30.6 The Match Data

Emacs keeps track of the positions of the start and end of segments of text found during a regular expression search. This means, for example, that you can search for a complex pattern, such as a date in an Rmail message, and then extract parts of the match under control of the pattern.

Because the match data normally describe the most recent search only, you must be careful not to do another search inadvertently between the search you wish to refer back to and the use of the match data. If you can’t avoid another intervening search, you must save and restore the match data around it, to prevent it from being overwritten.

30.6.1 Simple Match Data Access

This section explains how to use the match data to find out what was matched by the last search or match operation.

You can ask about the entire matching text, or about a particular parenthetical subexpression of a regular expression. The count argument in the functions below specifies which.

If count is zero, you are asking about the entire match. If count is positive, it specifies which subexpression you want.

Recall that the subexpressions of a regular expression are those expressions grouped with escaped parentheses, ‘\(…\)’. The countth subexpression is found by counting occurrences of ‘\(’ from the beginning of the whole regular expression. The first subexpression is numbered 1, the second 2, and so on. Only regular expressions can have subexpressions— after a simple string search, the only information available is about the entire match.

Function match-string count &optional in-string This function returns, as a string, the text matched in the last search or match operation. It returns the entire text if count is zero, or just the portion corresponding to the countth parenthetical subexpression, if count is positive. If count is out of range, or if that subexpression didn’t match anything, the value

is nil.

If the last such operation was done against a string with string-match, then you should pass the same string as the argument in-string. Otherwise, after a buffer search or match, you should omit in-string or pass nil for it; but you should make sure that the current buffer when you call match-string is the one in which you did the searching or matching.

Function match-beginning count

This function returns the position of the start of text matched by the last regular expression searched for, or a subexpression of it. If count is zero, then the value is the position of the start of the entire match. Otherwise, count specifies a subexpression in the regular expresion, and the value of the function is the starting position of the match for that subexpression. The value is nil for a subexpression inside a ‘\|’ alternative that wasn’t used in the match.

Function match-end count

This function is like match-beginning except that it returns the position of the end of the match, rather than the position of the beginning.

Here is an example of using the match data, with a comment showing the positions within the text:

(string-match "\\(qu\\)\\(ick\\)"
              "The quick fox jumped quickly.")
              ;0123456789
     ⇒ 4
(match-string 0 "The quick fox jumped quickly.")
     ⇒ "quick"
(match-string 1 "The quick fox jumped quickly.")
     ⇒ "qu"
(match-string 2 "The quick fox jumped quickly.")
     ⇒ "ick"

(match-beginning 1) ; The beginning of the match ⇒ 4 ; with ‘qu’ is at index 4.

(match-beginning 2) ; The beginning of the match

⇒ 6 ; with ‘ick’ is at index 6. (match-end 1) ; The end of the match

⇒ 6 ; with ‘qu’ is at index 6.

(match-end 2) ; The end of the match

⇒ 9 ; with ‘ick’ is at index 9. Here is another example. Point is initially located at the beginning of the line. Searching

moves point to between the space and the word ‘in’. The beginning of the entire match is at the 9th character of the buffer (‘T’), and the beginning of the match for the first subexpression is at the 13th character (‘c’).

(list
  (re-search-forward "The \\(cat \\)")
  (match-beginning 0)
  (match-beginning 1))
    ⇒ (9 9 13)
---------- Buffer: foo ----------
I read "The cat ⋆in the hat comes back" twice.
        ^^
        9  13
---------- Buffer: foo ----------

(In this case, the index returned is a buffer position; the first character of the buffer counts as 1.)

30.6.2 Replacing the Text That Matched

This function replaces the text matched by the last search with replacement.

Function replace-match replacement &optional fixedcase literal string

subexp This function replaces the text in the buffer (or in string) that was matched by the last search. It replaces that text with replacement. If you did the last search in a buffer, you should specify nil for string. Then replace-match does the replacement by editing the buffer; it leaves point at the end of the replacement text, and returns t. If you did the search in a string, pass the same string as string. Then replacematch does the replacement by constructing and returning a new string. If fixedcase is non-nil, then the case of the replacement text is not changed; otherwise, the replacement text is converted to a different case depending upon the capitalization of the text to be replaced. If the original text is all upper case, the replacement text is converted to upper case. If the first word of the original text is capitalized, then the first word of the replacement text is capitalized. If the original text contains just one word, and that word is a capital letter, replace-match considers this a capitalized first word rather than all upper case.

If case-replace is nil, then case conversion is not done, regardless of the value of fixed-case. See Section 30.7 [Searching and Case], page 505. If literal is non-nil, then replacement is inserted exactly as it is, the only alterations being case changes as needed. If it is nil (the default), then the character ‘\’ is treated specially. If a ‘\’ appears in replacement, then it must be part of one of the following sequences:

‘\&’ ‘\&’ stands for the entire text being replaced.

‘\n’ ‘\n’, where n is a digit, stands for the text that matched the nth subexpression in the original regexp. Subexpressions are those expressions grouped inside ‘\(…\)’.

‘\\’ ‘\\’ stands for a single ‘\’ in the replacement text.

If subexp is non-nil, that says to replace just subexpression number subexp of the regexp that was matched, not the entire match. For example, after matching ‘foo \(ba*r\)’, calling replace-match with 1 as subexp means to replace just the text that matched ‘\(ba*r\)’.

30.6.3 Accessing the Entire Match Data

The functions match-data and set-match-data read or write the entire match data, all at once.

Function match-data

This function returns a newly constructed list containing all the information on what text the last search matched. Element zero is the position of the beginning of the match for the whole expression; element one is the position of the end of the match for the expression. The next two elements are the positions of the beginning and end of the match for the first subexpression, and so on. In general, element number 2n corresponds to (match-beginning n); and element number 2n + 1 corresponds to (match-end n). All the elements are markers or nil if matching was done on a buffer, and all are integers or nil if matching was done on a string with string-match. (In Emacs 18 and earlier versions, markers were used even for matching on a string, except in the case of the integer 0.) As always, there must be no possibility of intervening searches between the call to a search function and the call to match-data that is intended to access the match data for that search.

     (match-data)
          ⇒ (#<marker at 9 in foo>
               #<marker at 17 in foo>
               #<marker at 13 in foo>
               #<marker at 17 in foo>)

Function set-match-data match-list

This function sets the match data from the elements of match-list, which should be a list that was the value of a previous call to match-data.

If match-list refers to a buffer that doesn’t exist, you don’t get an error; that sets the match data in a meaningless but harmless way.

     store-match-data is an alias for set-match-data.

30.6.4 Saving and Restoring the Match Data

When you call a function that may do a search, you may need to save and restore the match data around that call, if you want to preserve the match data from an earlier search for later use. Here is an example that shows the problem that arises if you fail to save the match data:

     (re-search-forward "The \\(cat \\)")
          ⇒ 48

(foo) ; Perhaps foo does

; more searching.

     (match-end 0)

⇒ 61 ; Unexpected result—not 48! You can save and restore the match data with save-match-data:

Macro save-match-data body…

This special form executes body, saving and restoring the match data around it.

You can use set-match-data together with match-data to imitate the effect of the special form save-match-data. This is useful for writing code that can run in Emacs 18. Here is how:

     (let ((data (match-data)))
       (unwind-protect

…; May change the original match data.

         (set-match-data data)))

Emacs automatically saves and restores the match data when it runs process filter functions (see Section 33.9.2 [Filter Functions], page 536) and process sentinels (see Section 33.10 [Sentinels], page 539).

30.7 Searching and Case

By default, searches in Emacs ignore the case of the text they are searching through; if you specify searching for ‘FOO’, then ‘Foo’ or ‘foo’ is also considered a match. Regexps, and in particular character sets, are included: thus, ‘[aB]’ would match ‘a’ or ‘A’ or ‘b’ or ‘B’.

If you do not want this feature, set the variable case-fold-search to nil. Then all letters must match exactly, including case. This is a buffer-local variable; altering the variable affects only the current buffer. (See Section 10.10.1 [Intro to Buffer-Local], page 134.) Alternatively, you may change the value of default-case-fold-search, which is the default value of case-fold-search for buffers that do not override it.

Note that the user-level incremental search feature handles case distinctions differently. When given a lower case letter, it looks for a match of either case, but when given an upper case letter, it looks for an upper case letter only. But this has nothing to do with the searching functions Lisp functions use.

User Option case-replace

This variable determines whether the replacement functions should preserve case. If the variable is nil, that means to use the replacement text verbatim. A non-nil value means to convert the case of the replacement text according to the text being replaced. The function replace-match is where this variable actually has its effect. See Section 30.6.2 [Replacing Match], page 503.

User Option case-fold-search

This buffer-local variable determines whether searches should ignore case. If the variable is nil they do not ignore case; otherwise they do ignore case.

Variable default-case-fold-search

The value of this variable is the default value for case-fold-search in buffers that do not override it. This is the same as (default-value 'case-fold-

search).

30.8 Standard Regular Expressions Used in Editing

This section describes some variables that hold regular expressions used for certain purposes in editing:

Variable page-delimiter

This is the regexp describing line-beginnings that separate pages. The default value is "^\014" (i.e., "^^L" or "^\C-l"); this matches a line that starts with a formfeed character.

The following two regular expressions should not assume the match always starts at the beginning of a line; they should not use ‘^’ to anchor the match. Most often, the paragraph commands do check for a match only at the beginning of a line, which means that ‘^’ would be superfluous. When there is a nonzero left margin, they accept matches that start after the left margin. In that case, a ‘^’ would be incorrect. However, a ‘^’ is harmless in modes where a left margin is never used.

Variable paragraph-separate

This is the regular expression for recognizing the beginning of a line that separates paragraphs. (If you change this, you may have to change paragraphstart also.) The default value is "[ \t\f]*$", which matches a line that consists entirely of spaces, tabs, and form feeds (after its left margin).

Variable paragraph-start

This is the regular expression for recognizing the beginning of a line that starts or separates paragraphs. The default value is "[ \t\n\f]", which matches a line starting with a space, tab, newline, or form feed (after its left margin).

Variable sentence-end

This is the regular expression describing the end of a sentence. (All paragraph boundaries also end sentences, regardless.) The default value is:

     "[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"

This means a period, question mark or exclamation mark, followed optionally by a closing parenthetical character, followed by tabs, spaces or new lines. For a detailed explanation of this regular expression, see Section 30.2.2 [Regexp Example], page 497.

508 GNU Emacs Lisp Reference Manual

31 Syntax Tables

A syntax table specifies the syntactic textual function of each character. This information is used by the parsing commands, the complex movement commands, and others to determine where words, symbols, and other syntactic constructs begin and end. The current syntax table controls the meaning of the word motion functions (see Section 27.2.2 [Word Motion], page 431) and the list motion functions (see Section 27.2.6 [List Motion], page 435) as well as the functions in this chapter.

31.1 Syntax Table Concepts

A syntax table is a vector of 256 elements; it contains one entry for each of the 256 possible characters in an 8-bit byte. Each element is an integer that encodes the syntax of the character in question.

Syntax tables are used only for moving across text, not for the Emacs Lisp reader. Emacs Lisp uses built-in syntactic rules when reading Lisp expressions, and these rules cannot be changed.

Each buffer has its own major mode, and each major mode has its own idea of the syntactic class of various characters. For example, in Lisp mode, the character ‘;’ begins a comment, but in C mode, it terminates a statement. To support these variations, Emacs makes the choice of syntax table local to each buffer. Typically, each major mode has its own syntax table and installs that table in each buffer that uses that mode. Changing this table alters the syntax in all those buffers as well as in any buffers subsequently put in that mode. Occasionally several similar modes share one syntax table. See Section 20.1.2 [Example Major Modes], page 302, for an example of how to set up a syntax table.

A syntax table can inherit the data for some characters from the standard syntax table, while specifying other characters itself. The “inherit” syntax class means “inherit this character’s syntax from the standard syntax table.” Most major modes’ syntax tables inherit the syntax of character codes 0 through 31 and 128 through 255. This is useful with character sets such as ISO Latin-1 that have additional alphabetic characters in the range 128 to 255. Just changing the standard syntax for these characters affects all major modes.

Function syntax-table-p object

This function returns t if object is a vector of length 256 elements. This means that the vector may be a syntax table. However, according to this test, any vector of length 256 is considered to be a syntax table, no matter what its contents.

31.2 Syntax Descriptors

This section describes the syntax classes and flags that denote the syntax of a character, and how they are represented as a syntax descriptor, which is a Lisp string that you pass to modify-syntax-entry to specify the desired syntax.

Emacs defines a number of syntax classes. Each syntax table puts each character into one class. There is no necessary relationship between the class of a character in one syntax table and its class in any other table.

Each class is designated by a mnemonic character, which serves as the name of the class when you need to specify a class. Usually the designator character is one that is frequently in that class; however, its meaning as a designator is unvarying and independent of what syntax that character currently has.

A syntax descriptor is a Lisp string that specifies a syntax class, a matching character (used only for the parenthesis classes) and flags. The first character is the designator for a syntax class. The second character is the character to match; if it is unused, put a space there. Then come the characters for any desired flags. If no matching character or flags are needed, one character is sufficient.

For example, the descriptor for the character ‘*’ in C mode is ‘. 23’ (i.e., punctuation, matching character slot unused, second character of a comment-starter, first character of an comment-ender), and the entry for ‘/’ is ‘. 14’ (i.e., punctuation, matching character slot unused, first character of a comment-starter, second character of a comment-ender).

31.2.1 Table of Syntax Classes

Here is a table of syntax classes, the characters that stand for them, their meanings, and examples of their use.

whitespace character Syntax class

Whitespace characters (designated with ‘ ’ or ‘-’) separate symbols and words from each other. Typically, whitespace characters have no other syntactic significance, and multiple whitespace characters are syntactically equivalent to a single one. Space, tab, newline and formfeed are almost always classified as whitespace.

word constituent Syntax class

Word constituents (designated with ‘w’) are parts of normal English words and are typically used in variable and command names in programs. All upper- and lower-case letters, and the digits, are typically word constituents.

symbol constituent Syntax class

Symbol constituents (designated with ‘_’) are the extra characters that are used in variable and command names along with word constituents. For example, the symbol constituents class is used in Lisp mode to indicate that certain characters may be part of symbol names even though they are not part of English words. These characters are ‘$&*+-_<>’. In standard C, the only non-word-constituent character that is valid in symbols is underscore (‘_’).

punctuation character Syntax class

Punctuation characters (‘.’) are those characters that are used as punctuation in English, or are used in some way in a programming language to separate symbols from one another. Most programming language modes, including Emacs Lisp mode, have no characters in this class since the few characters that are not symbol or word constituents all have other uses.

open parenthesis character Syntax class close parenthesis character Syntax class

Open and close parenthesis characters are characters used in dissimilar pairs to surround sentences or expressions. Such a grouping is begun with an open parenthesis character and terminated with a close. Each open parenthesis character matches a particular close parenthesis character, and vice versa. Normally, Emacs indicates momentarily the matching open parenthesis when you insert a close parenthesis. See Section 35.11 [Blinking], page 581. The class of open parentheses is designated with ‘(’, and that of close parentheses with ‘)’. In English text, and in C code, the parenthesis pairs are ‘()’, ‘[]’, and ‘{}’. In Emacs Lisp, the delimiters for lists and vectors (‘()’ and ‘[]’) are classified as parenthesis characters.

string quote Syntax class

String quote characters (designated with ‘"’) are used in many languages, including Lisp and C, to delimit string constants. The same string quote character appears at the beginning and the end of a string. Such quoted strings do not nest. The parsing facilities of Emacs consider a string as a single token. The usual syntactic meanings of the characters in the string are suppressed. The Lisp modes have two string quote characters: double-quote (‘"’) and vertical bar (‘|’). ‘|’ is not used in Emacs Lisp, but it is used in Common Lisp. C also has two string quote characters: double-quote for strings, and single-quote (‘'’) for character constants. English text has no string quote characters because English is not a programming language. Although quotation marks are used in English, we do not want them to turn off the usual syntactic properties of other characters in the quotation.

Syntax class escape

An escape character (designated with ‘\’) starts an escape sequence such as is used in C string and character constants. The character ‘\’ belongs to this class in both C and Lisp. (In C, it is used thus only inside strings, but it turns out to cause no trouble to treat it this way throughout C code.) Characters in this class count as part of words if words-include-escapes is non-nil. See Section 27.2.2 [Word Motion], page 431.

character quote Syntax class

A character quote character (designated with ‘/’) quotes the following character so that it loses its normal syntactic meaning. This differs from an escape character in that only the character immediately following is ever affected. Characters in this class count as part of words if words-include-escapes is non-nil. See Section 27.2.2 [Word Motion], page 431. This class is used for backslash in TEX mode.

paired delimiter Syntax class

Paired delimiter characters (designated with ‘$’) are like string quote characters except that the syntactic properties of the characters between the delimiters are not suppressed. Only TEX mode uses a paired delimiter presently—the ‘$’ that both enters and leaves math mode.

expression prefix Syntax class

An expression prefix operator (designated with ‘'’) is used for syntactic operators that are part of an expression if they appear next to one. These characters in Lisp include the apostrophe, ‘'’ (used for quoting), the comma, ‘,’ (used in macros), and ‘#’ (used in the read syntax for certain data types).

comment starter Syntax class comment ender Syntax class

The comment starter and comment ender characters are used in various languages to delimit comments. These classes are designated with ‘<’ and ‘>’, respectively. English text has no comment characters. In Lisp, the semicolon (‘;’) starts a comment and a newline or formfeed ends one.

Syntax class inherit

This syntax class does not specify a syntax. It says to look in the standard syntax table to find the syntax of this character. The designator for this syntax code is ‘@’.

31.2.2 Syntax Flags

In addition to the classes, entries for characters in a syntax table can include flags. There are six possible flags, represented by the characters ‘1’, ‘2’, ‘3’, ‘4’, ‘b’ and ‘p’.

All the flags except ‘p’ are used to describe multi-character comment delimiters. The digit flags indicate that a character can also be part of a comment sequence, in addition to the syntactic properties associated with its character class. The flags are independent of the class and each other for the sake of characters such as ‘*’ in C mode, which is a punctuation character, and the second character of a start-of-comment sequence (‘/*’), and the first character of an end-of-comment sequence (‘*/’).

The flags for a character c are:

• ‘1’ means c is the start of a two-character comment-start sequence.

• ‘2’ means c is the second character of such a sequence.

• ‘3’ means c is the start of a two-character comment-end sequence.

• ‘4’ means c is the second character of such a sequence.

• ‘b’ means that c as a comment delimiter belongs to the alternative “b” comment style. Emacs supports two comment styles simultaneously in any one syntax table. This is for the sake of C++. Each style of comment syntax has its own comment-start sequence and its own comment-end sequence. Each comment must stick to one style or the other; thus, if it starts with the comment-start sequence of style “b”, it must also end with the comment-end sequence of style “b”.

The two comment-start sequences must begin with the same character; only the second character may differ. Mark the second character of the “b”-style comment-start sequence with the ‘b’ flag. A comment-end sequence (one or two characters) applies to the “b” style if its first character has the ‘b’ flag set; otherwise, it applies to the “a” style. The appropriate comment syntax settings for C++ are as follows:

‘/’  ‘124b’

‘*’ ‘23’

newline ‘>b’

This defines four comment-delimiting sequences:

‘/*’ This is a comment-start sequence for “a” style because the second character, ‘*’, does not have the ‘b’ flag.

‘//’ This is a comment-start sequence for “b” style because the second character, ‘/’, does have the ‘b’ flag.

‘*/’ This is a comment-end sequence for “a” style because the first character, ‘*’, does not have the ‘b’ flag

newline This is a comment-end sequence for “b” style, because the newline charac-

ter has the ‘b’ flag.

• ‘p’ identifies an additional “prefix character” for Lisp syntax. These characters are treated as whitespace when they appear between expressions. When they appear within an expression, they are handled according to their usual syntax codes. The function backward-prefix-chars moves back over these characters, as well as over characters whose primary syntax class is prefix (‘'’). See Section 31.4 [Motion and Syntax], page 515.

31.3 Syntax Table Functions

In this section we describe functions for creating, accessing and altering syntax tables.

Function make-syntax-table

This function creates a new syntax table. Character codes 0 through 31 and 128 through 255 are set up to inherit from the standard syntax table. The other character codes are set up by copying what the standard syntax table says about them.

Most major mode syntax tables are created in this way.

Function copy-syntax-table &optional table

This function constructs a copy of table and returns it. If table is not supplied (or is nil), it returns a copy of the current syntax table. Otherwise, an error is signaled if table is not a syntax table.

Command modify-syntax-entry char syntax-descriptor &optional table This function sets the syntax entry for char according to syntax-descriptor. The syntax is changed only for table, which defaults to the current buffer’s syntax table, and not in any other syntax table. The argument syntax-descriptor specifies the desired syntax; this is a string beginning with a class designator character, and optionally containing a matching character and flags as well. See Section 31.2 [Syntax Descriptors], page 509. This function always returns nil. The old syntax information in the table for this character is discarded. An error is signaled if the first character of the syntax descriptor is not one of the twelve syntax class designator characters. An error is also signaled if char is not a character. Examples:

;; Put the space character in class whitespace.

     (modify-syntax-entry ?\  " ")
          ⇒ nil

;; Make ‘$’ an open parenthesis character,

;; with ‘^’ as its matching close.

     (modify-syntax-entry ?$ "(^")
          ⇒ nil

;; Make ‘^’ a close parenthesis character,

;; with ‘$’ as its matching open.

     (modify-syntax-entry ?^")$")
          ⇒ nil

;; Make ‘/’ a punctuation character,

;; the first character of a start-comment sequence, ;; and the second character of an end-comment sequence. ;; This is used in C mode.

     (modify-syntax-entry ?/ ". 14")
          ⇒ nil

Function char-syntax character

This function returns the syntax class of character, represented by its mnemonic designator character. This only returns the class, not any matching parenthesis or flags. An error is signaled if char is not a character. The following examples apply to C mode. The first example shows that the syntax class of space is whitespace (represented by a space). The second example shows that the syntax of ‘/’ is punctuation. This does not show the fact that it is also part of comment-start and -end sequences. The third example shows that open parenthesis is in the class of open parentheses. This does not show the fact that it has a matching character, ‘)’.

     (char-to-string (char-syntax ?\ ))
          ⇒ " "

     (char-to-string (char-syntax ?/))
          ⇒ "."
     (char-to-string (char-syntax ?\())
          ⇒ "("

Function set-syntax-table table

This function makes table the syntax table for the current buffer. It returns table.

Function syntax-table

This function returns the current syntax table, which is the table for the current buffer.

31.4 Motion and Syntax

This section describes functions for moving across characters in certain syntax classes. None of these functions exists in Emacs version 18 or earlier.

Function skip-syntax-forward syntaxes &optional limit This function moves point forward across characters having syntax classes mentioned in syntaxes. It stops when it encounters the end of the buffer, or position limit (if specified), or a character it is not supposed to skip.

Function skip-syntax-backward syntaxes &optional limit This function moves point backward across characters whose syntax classes are mentioned in syntaxes. It stops when it encounters the beginning of the buffer, or position limit (if specified), or a character it is not supposed to skip.

Function backward-prefix-chars

This function moves point backward over any number of characters with expression prefix syntax. This includes both characters in the expression prefix syntax class, and characters with the ‘p’ flag.

31.5 Parsing Balanced Expressions

Here are several functions for parsing and scanning balanced expressions, also known as sexps, in which parentheses match in pairs. The syntax table controls the interpretation of characters, so these functions can be used for Lisp expressions when in Lisp mode and for C expressions when in C mode. See Section 27.2.6 [List Motion], page 435, for convenient higher-level functions for moving over balanced expressions.

Function parse-partial-sexp start limit &optional target-depth stop-before

state stop-comment This function parses a sexp in the current buffer starting at start, not scanning past limit. It stops at position limit or when certain criteria described below are met, and sets point to the location where parsing stops. It returns a value describing the status of the parse at the point where it stops.

If state is nil, start is assumed to be at the top level of parenthesis structure, such as the beginning of a function definition. Alternatively, you might wish to resume parsing in the middle of the structure. To do this, you must provide a state argument that describes the initial status of parsing. If the third argument target-depth is non-nil, parsing stops if the depth in parentheses becomes equal to target-depth. The depth starts at 0, or at whatever is given in state. If the fourth argument stop-before is non-nil, parsing stops when it comes to any character that starts a sexp. If stop-comment is non-nil, parsing stops when it comes to the start of a comment. The fifth argument state is an eight-element list of the same form as the value of this function, described below. The return value of one call may be used to initialize the state of the parse on another call to parse-partial-sexp. The result is a list of eight elements describing the final state of the parse:

0. The depth in parentheses, counting from 0.

1. The character position of the start of the innermost parenthetical grouping containing the stopping point; nil if none.

2. The character position of the start of the last complete subexpression terminated; nil if none.

3. Non-nil if inside a string. More precisely, this is the character that will terminate the string.

4. t if inside a comment (of either style).

5. t if point is just after a quote character.

6. The minimum parenthesis depth encountered during this scan.

7. t if inside a comment of style “b”.

Elements 0, 3, 4, 5 and 7 are significant in the argument state. This function is most often used to compute indentation for languages that have nested parentheses.

Function scan-lists from count depth This function scans forward count balanced parenthetical groupings from character number from. It returns the character position where the scan stops. If depth is nonzero, parenthesis depth counting begins from that value. The only candidates for stopping are places where the depth in parentheses becomes zero; scan-lists counts count such places and then stops. Thus, a positive value for depth means go out depth levels of parenthesis. Scanning ignores comments if parse-sexp-ignore-comments is non-nil. If the scan reaches the beginning or end of the buffer (or its accessible portion), and the depth is not zero, an error is signaled. If the depth is zero but the count is not used up, nil is returned.

Function scan-sexps from count

This function scans forward count sexps from character position from. It returns the character position where the scan stops.

Scanning ignores comments if parse-sexp-ignore-comments is non-nil.

If the scan reaches the beginning or end of (the accessible part of) the buffer in the middle of a parenthetical grouping, an error is signaled. If it reaches the beginning or end between groupings but before count is used up, nil is returned.

Variable parse-sexp-ignore-comments

If the value is non-nil, then comments are treated as whitespace by the functions in this section and by forward-sexp.

In older Emacs versions, this feature worked only when the comment terminator is something like ‘*/’, and appears only to end a comment. In languages where newlines terminate comments, it was necessary make this variable nil, since not every newline is the end of a comment. This limitation no longer exists.

You can use forward-comment to move forward or backward over one comment or several comments.

Function forward-comment count

This function moves point forward across count comments (backward, if count is negative). If it finds anything other than a comment or whitespace, it stops, leaving point at the place where it stopped. It also stops after satisfying count.

To move forward over all comments and whitespace following point, use (forwardcomment (buffer-size)). (buffer-size) is a good argument to use, because the number of comments in the buffer cannot exceed that many.

31.6 Some Standard Syntax Tables

Most of the major modes in Emacs have their own syntax tables. Here are several of them:

Function standard-syntax-table

This function returns the standard syntax table, which is the syntax table used in Fundamental mode.

Variable text-mode-syntax-table

The value of this variable is the syntax table used in Text mode.

Variable c-mode-syntax-table

The value of this variable is the syntax table for C-mode buffers.

Variable emacs-lisp-mode-syntax-table

The value of this variable is the syntax table used in Emacs Lisp mode by editing commands. (It has no effect on the Lisp read function.)

31.7 Syntax Table Internals

Each element of a syntax table is an integer that encodes the syntax of one character: the syntax class, possible matching character, and flags. Lisp programs don’t usually work with the elements directly; the Lisp-level syntax table functions usually work with syntax descriptors (see Section 31.2 [Syntax Descriptors], page 509).

The low 8 bits of each element of a syntax table indicate the syntax class. Integer Class 0 whitespace 1 punctuation 2 word 3 symbol 4 open parenthesis 5 close parenthesis 6 expression prefix 7 string quote 8 paired delimiter 9 escape 10 character quote 11 comment-start 12 comment-end 13 inherit

The next 8 bits are the matching opposite parenthesis (if the character has parenthesis syntax); otherwise, they are not meaningful. The next 6 bits are the flags.

32 Abbrevs And Abbrev Expansion

An abbreviation or abbrev is a string of characters that may be expanded to a longer string. The user can insert the abbrev string and find it replaced automatically with the expansion of the abbrev. This saves typing.

The set of abbrevs currently in effect is recorded in an abbrev table. Each buffer has a local abbrev table, but normally all buffers in the same major mode share one abbrev table. There is also a global abbrev table. Normally both are used.

An abbrev table is represented as an obarray containing a symbol for each abbreviation. The symbol’s name is the abbreviation; its value is the expansion; its function definition is the hook function to do the expansion (see Section 32.3 [Defining Abbrevs], page 520); its property list cell contains the use count, the number of times the abbreviation has been expanded. Because these symbols are not interned in the usual obarray, they will never appear as the result of reading a Lisp expression; in fact, normally they are never used except by the code that handles abbrevs. Therefore, it is safe to use them in an extremely nonstandard way. See Section 7.3 [Creating Symbols], page 89.

For the user-level commands for abbrevs, see section “Abbrev Mode” in The GNU Emacs Manual.

32.1 Setting Up Abbrev Mode

Abbrev mode is a minor mode controlled by the value of the variable abbrev-mode.

Variable abbrev-mode

A non-nil value of this variable turns on the automatic expansion of abbrevs when their abbreviations are inserted into a buffer. If the value is nil, abbrevs may be defined, but they are not expanded automatically.

This variable automatically becomes local when set in any fashion.

Variable default-abbrev-mode

This is the value of abbrev-mode for buffers that do not override it. This is the

     same as (default-value 'abbrev-mode).

32.2 Abbrev Tables

This section describes how to create and manipulate abbrev tables.

Function make-abbrev-table

This function creates and returns a new, empty abbrev table—an obarray containing no symbols. It is a vector filled with zeros.

Function clear-abbrev-table table

This function undefines all the abbrevs in abbrev table table, leaving it empty.

The function returns nil.

Function define-abbrev-table tabname definitions

This function defines tabname (a symbol) as an abbrev table name, i.e., as a variable whose value is an abbrev table. It defines abbrevs in the table according to definitions, a list of elements of the form (abbrevname expansion hook usecount). The value is always nil.

Variable abbrev-table-name-list

This is a list of symbols whose values are abbrev tables. define-abbrev-table adds the new abbrev table name to this list.

Function insert-abbrev-table-description name &optional human

This function inserts before point a description of the abbrev table named name. The argument name is a symbol whose value is an abbrev table. The value is always nil. If human is non-nil, the description is human-oriented. Otherwise the description is a Lisp expression—a call to define-abbrev-table that would define name exactly as it is currently defined.

32.3 Defining Abbrevs

These functions define an abbrev in a specified abbrev table. define-abbrev is the low-level basic function, while add-abbrev is used by commands that ask for information from the user.

Function add-abbrev table type arg This function adds an abbreviation to abbrev table table based on information from the user. The argument type is a string describing in English the kind of abbrev this will be (typically, "global" or "mode-specific"); this is used in prompting the user. The argument arg is the number of words in the expansion. The return value is the symbol that internally represents the new abbrev, or nil if the user declines to confirm redefining an existing abbrev.

Function define-abbrev table name expansion hook This function defines an abbrev in table named name, to expand to expansion, and call hook. The return value is an uninterned symbol that represents the abbrev inside Emacs; its name is name. The argument name should be a string. The argument expansion should be a string, or nil to undefine the abbrev. The argument hook is a function or nil. If hook is non-nil, then it is called with no arguments after the abbrev is replaced with expansion; point is located at the end of expansion when hook is called. The use count of the abbrev is initialized to zero.

User Option only-global-abbrevs

If this variable is non-nil, it means that the user plans to use global abbrevs only. This tells the commands that define mode-specific abbrevs to define global ones instead. This variable does not alter the behavior of the functions in this section; it is examined by their callers.

32.4 Saving Abbrevs in Files

A file of saved abbrev definitions is actually a file of Lisp code. The abbrevs are saved in the form of a Lisp program to define the same abbrev tables with the same contents. Therefore, you can load the file with load (see Section 13.1 [How Programs Do Loading], page 161). However, the function quietly-read-abbrev-file is provided as a more convenient interface.

User-level facilities such as save-some-buffers can save abbrevs in a file automatically, under the control of variables described here.

User Option abbrev-file-name

This is the default file name for reading and saving abbrevs.

Function quietly-read-abbrev-file filename

This function reads abbrev definitions from a file named filename, previously written with write-abbrev-file. If filename is nil, the file specified in abbrev-file-name is used. save-abbrevs is set to t so that changes will be saved. This function does not display any messages. It returns nil.

User Option save-abbrevs

A non-nil value for save-abbrev means that Emacs should save abbrevs when files are saved. abbrev-file-name specifies the file to save the abbrevs in.

Variable abbrevs-changed

This variable is set non-nil by defining or altering any abbrevs. This serves as a flag for various Emacs commands to offer to save your abbrevs.

Command write-abbrev-file filename

Save all abbrev definitions, in all abbrev tables, in the file filename, in the form of a Lisp program that when loaded will define the same abbrevs. This function returns nil.

32.5 Looking Up and Expanding Abbreviations

Abbrevs are usually expanded by commands for interactive use, including self-insert-command. This section describes the subroutines used in writing such functions, as well as the variables they use for communication.

Function abbrev-symbol abbrev &optional table This function returns the symbol representing the abbrev named abbrev. The value returned is nil if that abbrev is not defined. The optional second argument table is the abbrev table to look it up in. If table is nil, this function tries first the current buffer’s local abbrev table, and second the global abbrev table.

Function abbrev-expansion abbrev &optional table This function returns the string that abbrev would expand into (as defined by the abbrev tables used for the current buffer). The optional argument table specifies the abbrev table to use, as in abbrev-symbol.

Command expand-abbrev

This command expands the abbrev before point, if any. If point does not follow an abbrev, this command does nothing. The command returns t if it did expansion, nil otherwise.

Command abbrev-prefix-mark &optional arg

Mark current point as the beginning of an abbrev. The next call to expandabbrev will use the text from here to point (where it is then) as the abbrev to expand, rather than using the previous word as usual.

User Option abbrev-all-caps

When this is set non-nil, an abbrev entered entirely in upper case is expanded using all upper case. Otherwise, an abbrev entered entirely in upper case is expanded by capitalizing each word of the expansion.

Variable abbrev-start-location

This is the buffer position for expand-abbrev to use as the start of the next abbrev to be expanded. (nil means use the word before point instead.) abbrevstart-location is set to nil each time expand-abbrev is called. This variable

is also set by abbrev-prefix-mark.

Variable abbrev-start-location-buffer

The value of this variable is the buffer for which abbrev-start-location has been set. Trying to expand an abbrev in any other buffer clears abbrev-start-

location. This variable is set by abbrev-prefix-mark.

Variable last-abbrev

This is the abbrev-symbol of the last abbrev expanded. This information is left by expand-abbrev for the sake of the unexpand-abbrev command.

Variable last-abbrev-location

This is the location of the last abbrev expanded. This contains information left

by expand-abbrev for the sake of the unexpand-abbrev command.

Variable last-abbrev-text

This is the exact expansion text of the last abbrev expanded, after case conversion (if any). Its value is nil if the abbrev has already been unexpanded. This contains information left by expand-abbrev for the sake of the unexpandabbrev command.

Variable pre-abbrev-expand-hook

This is a normal hook whose functions are executed, in sequence, just before any expansion of an abbrev. See Section 20.4 [Hooks], page 316. Since it is a normal hook, the hook functions receive no arguments. However, they can find the abbrev to be expanded by looking in the buffer before point.

The following sample code shows a simple use of pre-abbrev-expand-hook. If the user terminates an abbrev with a punctuation character, the hook function asks for confirmation. Thus, this hook allows the user to decide whether to expand the abbrev, and aborts expansion if it is not confirmed.

(add-hook 'pre-abbrev-expand-hook 'query-if-not-space)

;; This is the function invoked by pre-abbrev-expand-hook.

;; If the user terminated the abbrev with a space, the function does ;; nothing (that is, it returns so that the abbrev can expand). If the ;; user entered some other character, this function asks whether ;; expansion should continue.

;; If the user answers the prompt with y, the function returns ;; nil (because of the not function), but that is ;; acceptable; the return value has no effect on expansion.

(defun query-if-not-space ()
  (if (/= ?\  (preceding-char))
      (if (not (y-or-n-p "Do you want to expand this abbrev? "))
          (error "Not expanding this abbrev"))))

32.6 Standard Abbrev Tables

Here we list the variables that hold the abbrev tables for the preloaded major modes of Emacs.

Variable global-abbrev-table

This is the abbrev table for mode-independent abbrevs. The abbrevs defined in it apply to all buffers. Each buffer may also have a local abbrev table, whose abbrev definitions take precedence over those in the global table.

Variable local-abbrev-table

The value of this buffer-local variable is the (mode-specific) abbreviation table of the current buffer.

Variable fundamental-mode-abbrev-table

This is the local abbrev table used in Fundamental mode; in other words, it is the local abbrev table in all buffers in Fundamental mode.

Variable text-mode-abbrev-table

This is the local abbrev table used in Text mode.

Variable c-mode-abbrev-table

This is the local abbrev table used in C mode.

Variable lisp-mode-abbrev-table

This is the local abbrev table used in Lisp mode and Emacs Lisp mode.

524 GNU Emacs Lisp Reference Manual

33 Processes

In the terminology of operating systems, a process is a space in which a program can execute. Emacs runs in a process. Emacs Lisp programs can invoke other programs in processes of their own. These are called subprocesses or child processes of the Emacs process, which is their parent process.

A subprocess of Emacs may be synchronous or asynchronous, depending on how it is created. When you create a synchronous subprocess, the Lisp program waits for the subprocess to terminate before continuing execution. When you create an asynchronous subprocess, it can run in parallel with the Lisp program. This kind of subprocess is represented within Emacs by a Lisp object which is also called a “process”. Lisp programs can use this object to communicate with the subprocess or to control it. For example, you can send signals, obtain status information, receive output from the process, or send input to it.

Function processp object

This function returns t if object is a process, nil otherwise.

33.1 Functions that Create Subprocesses

There are three functions that create a new subprocess in which to run a program. One of them, start-process, creates an asynchronous process and returns a process object (see Section 33.4 [Asynchronous Processes], page 529). The other two, call-process and call-process-region, create a synchronous process and do not return a process object (see Section 33.2 [Synchronous Processes], page 526).

Synchronous and asynchronous processes are explained in following sections. Since the three functions are all called in a similar fashion, their common arguments are described here.

In all cases, the function’s program argument specifies the program to be run. An error is signaled if the file is not found or cannot be executed. If the file name is relative, the variable exec-path contains a list of directories to search. Emacs initializes exec-path when it starts up, based on the value of the environment variable PATH. The standard file name constructs, ‘~’, ‘.’, and ‘..’, are interpreted as usual in exec-path, but environment variable substitutions (‘$HOME’, etc.) are not recognized; use substitute-in-file-name to perform them (see Section 22.8.4 [File Name Expansion], page 347).

Each of the subprocess-creating functions has a buffer-or-name argument which specifies where the standard output from the program will go. If buffer-or-name is nil, that says to discard the output unless a filter function handles it. (See Section 33.9.2 [Filter Functions], page 536, and Chapter 16 [Read and Print], page 213.) Normally, you should avoid having multiple processes send output to the same buffer because their output would be intermixed randomly.

All three of the subprocess-creating functions have a &rest argument, args. The args must all be strings, and they are supplied to program as separate command line arguments. Wildcard characters and other shell constructs are not allowed in these strings, since they are passed directly to the specified program.

Please note: The argument program contains only the name of the program; it may not contain any command-line arguments. You must use args to provide those.

The subprocess gets its current directory from the value of default-directory (see Section 22.8.4 [File Name Expansion], page 347).

The subprocess inherits its environment from Emacs; but you can specify overrides for it with process-environment. See Section 34.3 [System Environment], page 549.

Variable exec-directory

The value of this variable is the name of a directory (a string) that contains programs that come with GNU Emacs, that are intended for Emacs to invoke. The program wakeup is an example of such a program; the display-time command uses it to get a reminder once per minute.

User Option exec-path

The value of this variable is a list of directories to search for programs to run in subprocesses. Each element is either the name of a directory (i.e., a string), or nil, which stands for the default directory (which is the value of default-

directory).
The value of exec-path is used by call-process and start-process when

the program argument is not an absolute file name.

33.2 Creating a Synchronous Process

After a synchronous process is created, Emacs waits for the process to terminate before continuing. Starting Dired is an example of this: it runs ls in a synchronous process, then modifies the output slightly. Because the process is synchronous, the entire directory listing arrives in the buffer before Emacs tries to do anything with it.

While Emacs waits for the synchronous subprocess to terminate, the user can quit by typing C-g. The first C-g tries to kill the subprocess with a SIGINT signal; but it waits until the subprocess actually terminates before quitting. If during that time the user types another C-g, that kills the subprocess instantly with SIGKILL and quits immediately. See Section 18.8 [Quitting], page 268.

The synchronous subprocess functions returned nil in version 18. In version 19, they return an indication of how the process terminated.

Function call-process program &optional infile destination display &rest

args This function calls program in a separate process and waits for it to finish.

The standard input for the process comes from file infile if infile is not nil and from ‘/dev/null’ otherwise. The argument destination says where to put the process output. Here are the possibilities:

a buffer Insert the output in that buffer, before point. This includes both the standard output stream and the standard error stream of the process. a string Find the buffer with that name, then insert the output in that

buffer, before point.

t Insert the output in the current buffer, before point.

nil Discard the output.

0 Discard the output, and return immediately without waiting for the subprocess to finish.

In this case, the process is not truly synchronous, since it can run in parallel with Emacs; but you can think of it as synchronous in that Emacs is essentially finished with the subprocess as soon as this function returns.

(real-destination error-destination)

Keep the standard output stream separate from the standard error stream; deal with the ordinary output as specified by realdestination, and dispose of the error output according to errordestination. The value nil means discard it, t means mix it with the ordinary output, and a string specifies a file name to redirect error output into.

You can’t directly specify a buffer to put the error output in; that is too difficult to implement. But you can achieve this result by sending the error output to a temporary file and then inserting the file into a buffer.

If display is non-nil, then call-process redisplays the buffer as output is inserted. Otherwise the function does no redisplay, and the results become visible on the screen only when Emacs redisplays that buffer in the normal course of events.

The remaining arguments, args, are strings that specify command line arguments for the program.

The value returned by call-process (unless you told it not to wait) indicates the reason for process termination. A number gives the exit status of the subprocess; 0 means success, and any other value means failure. If the process terminated with a signal, call-process returns a string describing the signal.

In the examples below, the buffer ‘foo’ is current.

     (call-process "pwd" nil t)
          ⇒ nil
     ---------- Buffer: foo ----------
     /usr/user/lewis/manual
     ---------- Buffer: foo ----------

     (call-process "grep" nil "bar" nil "lewis" "/etc/passwd")
          ⇒ nil
     ---------- Buffer: bar ----------
     lewis:5LTsHm66CSWKg:398:21:Bil Lewis:/user/lewis:/bin/csh
     ---------- Buffer: bar ----------

The insert-directory function contains a good example of the use of call-

process:
     (call-process insert-directory-program nil t nil switches
                   (if full-directory-p
                       (concat (file-name-as-directory file) ".")
                     file))

Function call-process-region start end program &optional delete

destination display &rest args This function sends the text between start to end as standard input to a process running program. It deletes the text sent if delete is non-nil; this is useful when buffer is t, to insert the output in the current buffer.

The arguments destination and display control what to do with the output from the subprocess, and whether to update the display as it comes in. For details, see the description of call-process, above. If destination is the integer 0, callprocess-region discards the output and returns nil immediately, without waiting for the subprocess to finish.

The remaining arguments, args, are strings that specify command line arguments for the program.

The return value of call-process-region is just like that of call-process: nil if you told it to return without waiting; otherwise, a number or string which indicates how the subprocess terminated.

In the following example, we use call-process-region to run the cat utility, with standard input being the first five characters in buffer ‘foo’ (the word ‘input’). cat copies its standard input into its standard output. Since the argument destination is t, this output is inserted in the current buffer.

     ---------- Buffer: foo ----------
     input⋆
     ---------- Buffer: foo ----------
     (call-process-region 1 6 "cat" nil t)
          ⇒ nil
     ---------- Buffer: foo ----------
     inputinput⋆
     ---------- Buffer: foo ----------
The shell-command-on-region command uses call-process-region like

this:

     (call-process-region
      start end
      shell-file-name      ; Name of program.

nil ; Do not delete region.

      buffer               ; Send output to buffer.

nil ; No redisplay during output. "-c" command) ; Arguments for the shell.

33.3 MS-DOS Subprocesses

On MS-DOS, you must indicate whether the data going to and from a synchronous subprocess are text or binary. Text data requires translation between the end-of-line convention used within Emacs (a single newline character) and the convention used outside Emacs (the two-character sequence, crlf).

The variable binary-process-input applies to input sent to the subprocess, and binary-process-output applies to output received from it. A non-nil value means the data is non-text; nil means the data is text, and calls for conversion.

Variable binary-process-input

If this variable is nil, convert newlines to crlf sequences in the input to a synchronous subprocess.

Variable binary-process-output

If this variable is nil, convert crlf sequences to newlines in the output from a synchronous subprocess.

See Section 22.13 [Files and MS-DOS], page 356, for related information.

33.4 Creating an Asynchronous Process

After an asynchronous process is created, Emacs and the Lisp program both continue running immediately. The process may thereafter run in parallel with Emacs, and the two may communicate with each other using the functions described in following sections. Here we describe how to create an asynchronous process with start-process.

Function start-process name buffer-or-name program &rest args This function creates a new asynchronous subprocess and starts the program program running in it. It returns a process object that stands for the new subprocess in Lisp. The argument name specifies the name for the process object; if a process with this name already exists, then name is modified (by adding ‘<1>’, etc.) to be unique. The buffer buffer-or-name is the buffer to associate with the process. The remaining arguments, args, are strings that specify command line arguments for the program. In the example below, the first process is started and runs (rather, sleeps) for 100 seconds. Meanwhile, the second process is started, and given the name ‘my-process<1>’ for the sake of uniqueness. It inserts the directory listing at the end of the buffer ‘foo’, before the first process finishes. Then it finishes, and a message to that effect is inserted in the buffer. Much later, the first process finishes, and another message is inserted in the buffer for it.

     (start-process "my-process" "foo" "sleep" "100")
          ⇒ #<process my-process>
     (start-process "my-process" "foo" "ls" "-l" "/user/lewis/bin")
          ⇒ #<process my-process<1>>
     ---------- Buffer: foo ----------
     total 2
     lrwxrwxrwx  1 lewis     14 Jul 22 10:12 gnuemacs --> /emacs
     -rwxrwxrwx  1 lewis     19 Jul 30 21:02 lemon
     Process my-process<1> finished
     Process my-process finished
     ---------- Buffer: foo ----------

Function start-process-shell-command name buffer-or-name command

&rest command-args This function is like start-process except that it uses a shell to execute the specified command. The argument command is a shell command name, and command-args are the arguments for the shell command.

Variable process-connection-type

This variable controls the type of device used to communicate with asynchronous subprocesses. If it is non-nil, then ptys are used, when available. Otherwise, pipes are used. ptys are usually preferable for processes visible to the user, as in Shell mode, because they allow job control (C-c, C-z, etc.) to work between the process and its children whereas pipes do not. For subprocesses used for internal purposes by programs, it is often better to use a pipe, because they are more efficient. In addition, the total number of ptys is limited on many systems and it is good not to waste them.

The value process-connection-type is used when start-process is called.

So you can specify how to communicate with one subprocess by binding the variable around the call to start-process.

     (let ((process-connection-type nil))  ; Use a pipe.
       (start-process . . .))

To determine whether a given subprocess actually got a pipe or a pty, use the function process-tty-name (see Section 33.6 [Process Information], page 531).

33.5 Deleting Processes

Deleting a process disconnects Emacs immediately from the subprocess, and removes it from the list of active processes. It sends a signal to the subprocess to make the subprocess terminate, but this is not guaranteed to happen immediately. The process object itself continues to exist as long as other Lisp objects point to it. The process mark continues to point to the same place as before (usually into a buffer where output from the process was being inserted).

You can delete a process explicitly at any time. Processes are deleted automatically after they terminate, but not necessarily right away. If you delete a terminated process explicitly before it is deleted automatically, no harm results.

Variable delete-exited-processes

This variable controls automatic deletion of processes that have terminated (due to calling exit or to a signal). If it is nil, then they continue to exist until the user runs list-processes. Otherwise, they are deleted immediately after they exit.

Function delete-process name

This function deletes the process associated with name, killing it with a SIGHUP signal. The argument name may be a process, the name of a process, a buffer, or the name of a buffer.

     (delete-process "*shell*")
          ⇒ nil

Function process-kill-without-query process

This function declares that Emacs need not query the user if process is still running when Emacs is exited. The process will be deleted silently. The value is t.

     (process-kill-without-query (get-process "shell"))
          ⇒ t

33.6 Process Information

Several functions return information about processes. list-processes is provided for interactive use.

Command list-processes

This command displays a listing of all living processes. In addition, it finally deletes any process whose status was ‘Exited’ or ‘Signaled’. It returns nil.

Function process-list

This function returns a list of all processes that have not been deleted.

     (process-list)
          ⇒ (#<process display-time> #<process shell>)

Function get-process name

This function returns the process named name, or nil if there is none. An error is signaled if name is not a string.

     (get-process "shell")
          ⇒ #<process shell>

Function process-command process

This function returns the command that was executed to start process. This is a list of strings, the first string being the program executed and the rest of the strings being the arguments that were given to the program.

     (process-command (get-process "shell"))
          ⇒ ("/bin/csh" "-i")

Function process-id process

This function returns the pid of process. This is an integer that distinguishes the process process from all other processes running on the same computer at the current time. The pid of a process is chosen by the operating system kernel when the process is started and remains constant as long as the process exists.

Function process-name process

This function returns the name of process.

Function process-status process-name

This function returns the status of process-name as a symbol. The argument process-name must be a process, a buffer, a process name (string) or a buffer name (string). The possible values for an actual subprocess are:

run for a process that is running.

stop for a process that is stopped but continuable.

exit for a process that has exited.

signal for a process that has received a fatal signal.

open for a network connection that is open.

closed for a network connection that is closed. Once a connection is closed, you cannot reopen it, though you might be able to open a new connection to the same place.

nil if process-name is not the name of an existing process.

     (process-status "shell")
          ⇒ run
     (process-status (get-buffer "*shell*"))
          ⇒ run
     x
          ⇒ #<process xx<1>>
     (process-status x)
          ⇒ exit

For a network connection, process-status returns one of the symbols open or closed. The latter means that the other side closed the connection, or Emacs

did delete-process.

In earlier Emacs versions (prior to version 19), the status of a network connection was run if open, and exit if closed.

Function process-exit-status process

This function returns the exit status of process or the signal number that killed it. (Use the result of process-status to determine which of those it is.) If process has not yet terminated, the value is 0.

Function process-tty-name process

This function returns the terminal name that process is using for its communication with Emacs—or nil if it is using pipes instead of a terminal (see processconnection-type in Section 33.4 [Asynchronous Processes], page 529).

33.7 Sending Input to Processes

Asynchronous subprocesses receive input when it is sent to them by Emacs, which is done with the functions in this section. You must specify the process to send input to, and the input data to send. The data appears on the “standard input” of the subprocess.

Some operating systems have limited space for buffered input in a pty. On these systems, Emacs sends an eof periodically amidst the other characters, to force them through. For most programs, these eofs do no harm.

Function process-send-string process-name string

This function sends process-name the contents of string as standard input. The argument process-name must be a process or the name of a process. If it is nil, the current buffer’s process is used. The function returns nil.

     (process-send-string "shell<1>" "ls\n")
          ⇒ nil
     ---------- Buffer: *shell* ----------
     ...
     introduction.texi               syntax-tables.texi~
     introduction.texi~              text.texi
     introduction.txt                text.texi~
     ...
     ---------- Buffer: *shell* ----------

Command process-send-region process-name start end This function sends the text in the region defined by start and end as standard input to process-name, which is a process or a process name. (If it is nil, the current buffer’s process is used.) An error is signaled unless both start and end are integers or markers that indicate positions in the current buffer. (It is unimportant which number is larger.)

Function process-send-eof &optional process-name This function makes process-name see an end-of-file in its input. The eof comes after any text already sent to it.

If process-name is not supplied, or if it is nil, then this function sends the eof to the current buffer’s process. An error is signaled if the current buffer has no process.

The function returns process-name.

          (process-send-eof "shell")
               ⇒ "shell"

33.8 Sending Signals to Processes

Sending a signal to a subprocess is a way of interrupting its activities. There are several different signals, each with its own meaning. The set of signals and their names is defined by the operating system. For example, the signal SIGINT means that the user has typed C-c, or that some analogous thing has happened.

Each signal has a standard effect on the subprocess. Most signals kill the subprocess, but some stop or resume execution instead. Most signals can optionally be handled by programs; if the program handles the signal, then we can say nothing in general about its effects.

You can send signals explicitly by calling the functions in this section. Emacs also sends signals automatically at certain times: killing a buffer sends a SIGHUP signal to all its associated processes; killing Emacs sends a SIGHUP signal to all remaining processes. (SIGHUP is a signal that usually indicates that the user hung up the phone.)

Each of the signal-sending functions takes two optional arguments: process-name and current-group.

The argument process-name must be either a process, the name of one, or nil. If it is nil, the process defaults to the process associated with the current buffer. An error is signaled if process-name does not identify a process.

The argument current-group is a flag that makes a difference when you are running a job-control shell as an Emacs subprocess. If it is non-nil, then the signal is sent to the current process-group of the terminal that Emacs uses to communicate with the subprocess. If the process is a job-control shell, this means the shell’s current subjob. If it is nil, the signal is sent to the process group of the immediate subprocess of Emacs. If the subprocess is a job-control shell, this is the shell itself.

The flag current-group has no effect when a pipe is used to communicate with the subprocess, because the operating system does not support the distinction in the case of pipes. For the same reason, job-control shells won’t work when a pipe is used. See processconnection-type in Section 33.4 [Asynchronous Processes], page 529.

Function interrupt-process &optional process-name current-group This function interrupts the process process-name by sending the signal SIGINT. Outside of Emacs, typing the “interrupt character” (normally C-c on some systems, and DEL on others) sends this signal. When the argument currentgroup is non-nil, you can think of this function as “typing C-c” on the terminal by which Emacs talks to the subprocess.

Function kill-process &optional process-name current-group This function kills the process process-name by sending the signal SIGKILL. This signal kills the subprocess immediately, and cannot be handled by the subprocess.

Function quit-process &optional process-name current-group This function sends the signal SIGQUIT to the process process-name. This signal is the one sent by the “quit character” (usually C-b or C-\) when you are not inside Emacs.

Function stop-process &optional process-name current-group This function stops the process process-name by sending the signal SIGTSTP. Use continue-process to resume its execution. On systems with job control, the “stop character” (usually C-z) sends this signal (outside of Emacs). When current-group is non-nil, you can think of this function as “typing C-z” on the terminal Emacs uses to communicate with the subprocess.

Function continue-process &optional process-name current-group This function resumes execution of the process process by sending it the signal SIGCONT. This presumes that process-name was stopped previously.

Function signal-process pid signal

This function sends a signal to process pid, which need not be a child of Emacs. The argument signal specifies which signal to send; it should be an integer.

33.9 Receiving Output from Processes

There are two ways to receive the output that a subprocess writes to its standard output stream. The output can be inserted in a buffer, which is called the associated buffer of the process, or a function called the filter function can be called to act on the output. If the process has no buffer and no filter function, its output is discarded.

33.9.1 Process Buffers

A process can (and usually does) have an associated buffer, which is an ordinary Emacs buffer that is used for two purposes: storing the output from the process, and deciding when to kill the process. You can also use the buffer to identify a process to operate on, since in normal practice only one process is associated with any given buffer. Many applications of processes also use the buffer for editing input to be sent to the process, but this is not built into Emacs Lisp.

Unless the process has a filter function (see Section 33.9.2 [Filter Functions], page 536), its output is inserted in the associated buffer. The position to insert the output is determined by the process-mark, which is then updated to point to the end of the text just inserted. Usually, but not always, the process-mark is at the end of the buffer.

Function process-buffer process

This function returns the associated buffer of the process process.

     (process-buffer (get-process "shell"))
          ⇒ #<buffer *shell*>

Function process-mark process

This function returns the process marker for process, which is the marker that says where to insert output from the process. If process does not have a buffer, process-mark returns a marker that points nowhere. Insertion of process output in a buffer uses this marker to decide where to insert, and updates it to point after the inserted text. That is why successive batches of output are inserted consecutively. Filter functions normally should use this marker in the same fashion as is done by direct insertion of output in the buffer. A good example of a filter function that uses process-mark is found at the end of the following section. When the user is expected to enter input in the process buffer for transmission to the process, the process marker is useful for distinguishing the new input from previous output.

Function set-process-buffer process buffer

This function sets the buffer associated with process to buffer. If buffer is nil, the process becomes associated with no buffer.

Function get-buffer-process buffer-or-name

This function returns the process associated with buffer-or-name. If there are several processes associated with it, then one is chosen. (Presently, the one chosen is the one most recently created.) It is usually a bad idea to have more than one process associated with the same buffer.

     (get-buffer-process "*shell*")
          ⇒ #<process shell>

Killing the process’s buffer deletes the process, which kills the subprocess with a SIGHUP signal (see Section 33.8 [Signals to Processes], page 534).

33.9.2 Process Filter Functions

A process filter function is a function that receives the standard output from the associated process. If a process has a filter, then all output from that process is passed to the filter. The process buffer is used directly for output from the process only when there is no filter.

A filter function must accept two arguments: the associated process and a string, which is the output. The function is then free to do whatever it chooses with the output.

A filter function runs only while Emacs is waiting (e.g., for terminal input, or for time to elapse, or for process output). This avoids the timing errors that could result from running filters at random places in the middle of other Lisp programs. You may explicitly cause Emacs to wait, so that filter functions will run, by calling sit-for or sleep-for (see Section 18.7 [Waiting], page 267), or accept-process-output (see Section 33.9.3 [Accepting Output], page 538). Emacs is also waiting when the command loop is reading input.

Quitting is normally inhibited within a filter function—otherwise, the effect of typing C-g at command level or to quit a user command would be unpredictable. If you want to permit quitting inside a filter function, bind inhibit-quit to nil. See Section 18.8 [Quitting], page 268.

If an error happens during execution of a filter function, it is caught automatically, so that it doesn’t stop the execution of whatever program was running when the filter function was started. However, if debug-on-error is non-nil, the error-catching is turned off. This makes it possible to use the Lisp debugger to debug the filter function. See Section 15.1 [Debugger], page 181.

Many filter functions sometimes or always insert the text in the process’s buffer, mimicking the actions of Emacs when there is no filter. Such filter functions need to use set-buffer in order to be sure to insert in that buffer. To avoid setting the current buffer semipermanently, these filter functions must use unwind-protect to make sure to restore the previous current buffer. They should also update the process marker, and in some cases update the value of point. Here is how to do these things:

     (defun ordinary-insertion-filter (proc string)
       (let ((old-buffer (current-buffer)))
         (unwind-protect
             (let (moving)
               (set-buffer (process-buffer proc))
               (setq moving (= (point) (process-mark proc)))
               (save-excursion

;; Insert the text, moving the process-marker.

                 (goto-char (process-mark proc))
                 (insert string)
                 (set-marker (process-mark proc) (point)))
               (if moving (goto-char (process-mark proc))))
           (set-buffer old-buffer))))

The reason to use an explicit unwind-protect rather than letting save-excursion restore the current buffer is so as to preserve the change in point made by goto-char.

To make the filter force the process buffer to be visible whenever new text arrives, insert the following line just before the unwind-protect:

     (display-buffer (process-buffer proc))

To force point to move to the end of the new output no matter where it was previously, eliminate the variable moving and call goto-char unconditionally.

In earlier Emacs versions, every filter function that did regexp searching or matching had to explicitly save and restore the match data. Now Emacs does this automatically; filter functions never need to do it explicitly. See Section 30.6 [Match Data], page 501.

A filter function that writes the output into the buffer of the process should check whether the buffer is still alive. If it tries to insert into a dead buffer, it will get an error.

If the buffer is dead, (buffer-name (process-buffer process)) returns nil.

The output to the function may come in chunks of any size. A program that produces the same output twice in a row may send it as one batch of 200 characters one time, and five batches of 40 characters the next.

Function set-process-filter process filter

This function gives process the filter function filter. If filter is nil, it gives the process no filter.

Function process-filter process

This function returns the filter function of process, or nil if it has none.

Here is an example of use of a filter function:

(defun keep-output (process output)
   (setq kept (cons output kept)))
     ⇒ keep-output
(setq kept nil)
     ⇒ nil
(set-process-filter (get-process "shell") 'keep-output)
     ⇒ keep-output
(process-send-string "shell" "ls ~/other\n")
     ⇒ nil
kept
     ⇒ ("lewis@slug[8] % "
"FINAL-W87-SHORT.MSS    backup.otl              kolstad.mss~
address.txt             backup.psf              kolstad.psf
backup.bib~             david.mss               resume-Dec-86.mss~
backup.err              david.psf               resume-Dec.psf
backup.mss              dland                   syllabus.mss
"
"#backups.mss#          backup.mss~             kolstad.mss
")

33.9.3 Accepting Output from Processes

Output from asynchronous subprocesses normally arrives only while Emacs is waiting for some sort of external event, such as elapsed time or terminal input. Occasionally it is useful in a Lisp program to explicitly permit output to arrive at a specific point, or even to wait until output arrives from a process.

Function accept-process-output &optional process seconds millisec This function allows Emacs to read pending output from processes. The output is inserted in the associated buffers or given to their filter functions. If process is non-nil then this function does not return until some output has been received from process. The arguments seconds and millisec let you specify timeout periods. The former specifies a period measured in seconds and the latter specifies one measured in milliseconds. The two time periods thus specified are added together, and accept-process-output returns after that much time whether or not there has been any subprocess output. The argument seconds need not be an integer. If it is a floating point number, this function waits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down.

If the system doesn’t support waiting fractions of a second, you get an error if you specify nonzero millisec. Not all operating systems support waiting periods other than multiples of a second; on those that do not, you get an error if you specify nonzero millisec. The function accept-process-output returns non-nil if it did get some output, or nil if the timeout expired before output arrived.

33.10 Sentinels: Detecting Process Status Changes

A process sentinel is a function that is called whenever the associated process changes status for any reason, including signals (whether sent by Emacs or caused by the process’s own actions) that terminate, stop, or continue the process. The process sentinel is also called if the process exits. The sentinel receives two arguments: the process for which the event occurred, and a string describing the type of event.

The string describing the event looks like one of the following:

  • "finished\n".
  • "exited abnormally with code exitcode\n".

• "name-of-signal\n".

  • "name-of-signal (core dumped)\n".

A sentinel runs only while Emacs is waiting (e.g., for terminal input, or for time to elapse, or for process output). This avoids the timing errors that could result from running them at random places in the middle of other Lisp programs. A program can wait, so that sentinels will run, by calling sit-for or sleep-for (see Section 18.7 [Waiting], page 267), or accept-process-output (see Section 33.9.3 [Accepting Output], page 538). Emacs is also waiting when the command loop is reading input.

Quitting is normally inhibited within a sentinel—otherwise, the effect of typing C-g at command level or to quit a user command would be unpredictable. If you want to permit quitting inside a sentinel, bind inhibit-quit to nil. See Section 18.8 [Quitting], page 268.

A sentinel that writes the output into the buffer of the process should check whether the buffer is still alive. If it tries to insert into a dead buffer, it will get an error. If the buffer

is dead, (buffer-name (process-buffer process)) returns nil.

If an error happens during execution of a sentinel, it is caught automatically, so that it doesn’t stop the execution of whatever programs was running when the sentinel was started. However, if debug-on-error is non-nil, the error-catching is turned off. This makes it possible to use the Lisp debugger to debug the sentinel. See Section 15.1 [Debugger], page 181.

In earlier Emacs versions, every sentinel that did regexp searching or matching had to explicitly save and restore the match data. Now Emacs does this automatically; sentinels never need to do it explicitly. See Section 30.6 [Match Data], page 501.

Function set-process-sentinel process sentinel

This function associates sentinel with process. If sentinel is nil, then the process will have no sentinel. The default behavior when there is no sentinel is to insert a message in the process’s buffer when the process status changes.

     (defun msg-me (process event)
        (princ
          (format "Process: %s had the event `%s'" process event)))
     (set-process-sentinel (get-process "shell") 'msg-me)
          ⇒ msg-me
     (kill-process (get-process "shell"))
          ⊣ Process: #<process shell> had the event `killed'
          ⇒ #<process shell>

Function process-sentinel process

This function returns the sentinel of process, or nil if it has none.

Function waiting-for-user-input-p

While a sentinel or filter function is running, this function returns non-nil if Emacs was waiting for keyboard input from the user at the time the sentinel or filter function was called, nil if it was not.

33.11 Transaction Queues

You can use a transaction queue for more convenient communication with subprocesses using transactions. First use tq-create to create a transaction queue communicating with a specified process. Then you can call tq-enqueue to send a transaction.

Function tq-create process

This function creates and returns a transaction queue communicating with process. The argument process should be a subprocess capable of sending and receiving streams of bytes. It may be a child process, or it may be a TCP connection to a server, possibly on another machine.

Function tq-enqueue queue question regexp closure fn This function sends a transaction to queue queue. Specifying the queue has the effect of specifying the subprocess to talk to.

The argument question is the outgoing message that starts the transaction. The argument fn is the function to call when the corresponding answer comes back; it is called with two arguments: closure, and the answer received.

The argument regexp is a regular expression that should match the entire answer, but nothing less; that’s how tq-enqueue determines where the answer ends.

The return value of tq-enqueue itself is not meaningful.

Function tq-close queue

Shut down transaction queue queue, waiting for all pending transactions to complete, and then terminate the connection or child process.

Transaction queues are implemented by means of a filter function. See Section 33.9.2 [Filter Functions], page 536.

33.12 Network Connections

Emacs Lisp programs can open TCP network connections to other processes on the same machine or other machines. A network connection is handled by Lisp much like a subprocess, and is represented by a process object. However, the process you are communicating with is not a child of the Emacs process, so you can’t kill it or send it signals. All you can do is send and receive data. delete-process closes the connection, but does not kill the process at the other end; that process must decide what to do about closure of the connection.

You can distinguish process objects representing network connections from those representing subprocesses with the process-status function. It always returns either open or closed for a network connection, and it never returns either of those values for a real subprocess. See Section 33.6 [Process Information], page 531.

Function open-network-stream name buffer-or-name host service This function opens a TCP connection for a service to a host. It returns a process object to represent the connection. The name argument specifies the name for the process object. It is modified as necessary to make it unique. The buffer-or-name argument is the buffer to associate with the connection. Output from the connection is inserted in the buffer, unless you specify a filter function to handle the output. If buffer-or-name is nil, it means that the connection is not associated with any buffer. The arguments host and service specify where to connect to; host is the host name (a string), and service is the name of a defined network service (a string) or a port number (an integer).

542 GNU Emacs Lisp Reference Manual

34 Operating System Interface

This chapter is about starting and getting out of Emacs, access to values in the operating system environment, and terminal input, output, and flow control.

See Section B.1 [Building Emacs], page 609, for related information. See also Chapter 35 [Display], page 567, for additional operating system status information pertaining to the terminal and the screen.

34.1 Starting Up Emacs

This section describes what Emacs does when it is started, and how you can customize these actions.

34.1.1 Summary: Sequence of Actions at Start Up

The order of operations performed (in ‘startup.el’) by Emacs when it is started up is as follows:

1. It loads the initialization library for the window system, if you are using a window system. This library’s name is ‘term/windowsystem-win.el’.

2. It processes the initial options. (Some of them are handled even earlier than this.)

3. It initializes the X window frame and faces, if appropriate.

4. It runs the normal hook before-init-hook.

5. It loads the library ‘site-start’, unless the option ‘-no-site-file’ was specified. The library’s file name is usually ‘site-start.el’.

6. It loads the file ‘~/.emacs’ unless ‘-q’ was specified on the command line. (This is not done in ‘-batch’ mode.) The ‘-u’ option can specify the user name whose home directory should be used instead of ‘~’.

7. It loads the library ‘default’ unless inhibit-default-init is non-nil. (This is not done in ‘-batch’ mode or if ‘-q’ was specified on the command line.) The library’s file name is usually ‘default.el’.

8. It runs the normal hook after-init-hook.

9. It sets the major mode according to initial-major-mode, provided the buffer ‘*scratch*’ is still current and still in Fundamental mode.

10. It loads the terminal-specific Lisp file, if any, except when in batch mode or using a window system.

11. It displays the initial echo area message, unless you have suppressed that with inhibit-

startup-echo-area-message.

12. It processes the action arguments from the command line.

13. It runs term-setup-hook.

14. It calls frame-notice-user-settings, which modifies the parameters of the selected frame according to whatever the init files specify.

15. It runs window-setup-hook. See Section 35.16 [Window Systems], page 586.

16. It displays copyleft, nonwarranty, and basic use information, provided there were no remaining command line arguments (a few steps above) and the value of inhibit-

startup-message is nil.

User Option inhibit-startup-message

This variable inhibits the initial startup messages (the nonwarranty, etc.). If it is non-nil, then the messages are not printed. This variable exists so you can set it in your personal init file, once you are familiar with the contents of the startup message. Do not set this variable in the init file of a new user, or in a way that affects more than one user, because that would prevent new users from receiving the information they are supposed to see.

User Option inhibit-startup-echo-area-message

This variable controls the display of the startup echo area message. You can suppress the startup echo area message by adding text with this form to your

‘.emacs’ file:
     (setq inhibit-startup-echo-area-message

"your-login-name")

Simply setting inhibit-startup-echo-area-message to your login name is

not sufficient to inhibit the message; Emacs explicitly checks whether ‘.emacs’ contains an expression as shown above. Your login name must appear in the expression as a Lisp string constant. This way, you can easily inhibit the message for yourself if you wish, but thoughtless copying of your ‘.emacs’ file will not inhibit the message for someone else.

34.1.2 The Init File: ‘.emacs’

When you start Emacs, it normally attempts to load the file ‘.emacs’ from your home directory. This file, if it exists, must contain Lisp code. It is called your init file. The command line switches ‘-q’ and ‘-u’ affect the use of the init file; ‘-q’ says not to load an init file, and ‘-u’ says to load a specified user’s init file instead of yours. See section “Entering Emacs” in The GNU Emacs Manual.

A site may have a default init file, which is the library named ‘default.el’. Emacs finds the ‘default.el’ file through the standard search path for libraries (see Section 13.1 [How Programs Do Loading], page 161). The Emacs distribution does not come with this file; sites may provide one for local customizations. If the default init file exists, it is loaded whenever you start Emacs, except in batch mode or if ‘-q’ is specified. But your own personal init file, if any, is loaded first; if it sets inhibit-default-init to a non-nil value, then Emacs does not subsequently load the ‘default.el’ file.

Another file for site-customization is ‘site-start.el’. Emacs loads this before the user’s init file. You can inhibit the loading of this file with the option ‘-no-site-file’.

Variable site-run-file

This variable specifies the site-customization file to load before the user’s init file. Its normal value is "site-start".

If there is a great deal of code in your ‘.emacs’ file, you should move it into another file named ‘something.el’, byte-compile it (see Chapter 14 [Byte Compilation], page 171), and make your ‘.emacs’ file load the other file using load (see Chapter 13 [Loading], page 161).

See section “Init File Examples” in The GNU Emacs Manual, for examples of how to make various commonly desired customizations in your ‘.emacs’ file.

User Option inhibit-default-init

This variable prevents Emacs from loading the default initialization library file for your session of Emacs. If its value is non-nil, then the default library is not loaded. The default value is nil.

Variable before-init-hook Variable after-init-hook

These two normal hooks are run just before, and just after, loading of the user’s

     init file, ‘default.el’, and/or ‘site-start.el’.

34.1.3 Terminal-Specific Initialization

Each terminal type can have its own Lisp library that Emacs loads when run on that type of terminal. For a terminal type named termtype, the library is called ‘term/termtype’. Emacs finds the file by searching the load-path directories as it does for other files, and trying the ‘.elc’ and ‘.el’ suffixes. Normally, terminal-specific Lisp library is located in ‘emacs/lisp/term’, a subdirectory of the ‘emacs/lisp’ directory in which most Emacs Lisp libraries are kept.

The library’s name is constructed by concatenating the value of the variable termfile-prefix and the terminal type. Normally, term-file-prefix has the value "term/"; changing this is not recommended.

The usual function of a terminal-specific library is to enable special keys to send sequences that Emacs can recognize. It may also need to set or add to function-key-map if the Termcap entry does not specify all the terminal’s function keys. See Section 34.8 [Terminal Input], page 558.

When the name of the terminal type contains a hyphen, only the part of the name before the first hyphen is significant in choosing the library name. Thus, terminal types ‘aaa-48’ and ‘aaa-30-rv’ both use the ‘term/aaa’ library. If necessary, the library can evaluate (getenv "TERM") to find the full name of the terminal type.

Your ‘.emacs’ file can prevent the loading of the terminal-specific library by setting the variable term-file-prefix to nil. This feature is useful when experimenting with your own peculiar customizations.

You can also arrange to override some of the actions of the terminal-specific library by setting the variable term-setup-hook. This is a normal hook which Emacs runs using run-hooks at the end of Emacs initialization, after loading both your ‘.emacs’ file and any terminal-specific libraries. You can use this variable to define initializations for terminals that do not have their own libraries. See Section 20.4 [Hooks], page 316.

Variable term-file-prefix

If the term-file-prefix variable is non-nil, Emacs loads a terminal-specific initialization file as follows:

     (load (concat term-file-prefix (getenv "TERM")))

You may set the term-file-prefix variable to nil in your ‘.emacs’ file if you do not wish to load the terminal-initialization file. To do this, put the following

in your ‘.emacs’ file: (setq term-file-prefix nil).

Variable term-setup-hook

This variable is a normal hook that Emacs runs after loading your ‘.emacs’ file, the default initialization file (if any) and the terminal-specific Lisp file. You can use term-setup-hook to override the definitions made by a terminalspecific file.

See window-setup-hook in Section 35.16 [Window Systems], page 586, for a related feature.

34.1.4 Command Line Arguments

You can use command line arguments to request various actions when you start Emacs. Since you do not need to start Emacs more than once per day, and will often leave your Emacs session running longer than that, command line arguments are hardly ever used. As a practical matter, it is best to avoid making the habit of using them, since this habit would encourage you to kill and restart Emacs unnecessarily often. These options exist for two reasons: to be compatible with other editors (for invocation by other programs) and to enable shell scripts to run specific Lisp programs.

This section describes how Emacs processes command line arguments, and how you can customize them.

Function command-line

This function parses the command line that Emacs was called with, processes it, loads the user’s ‘.emacs’ file and displays the startup messages.

Variable command-line-processed

The value of this variable is t once the command line has been processed. If you redump Emacs by calling dump-emacs, you may wish to set this variable to nil first in order to cause the new dumped Emacs to process its new command line arguments.

Variable command-switch-alist

The value of this variable is an alist of user-defined command-line options and associated handler functions. This variable exists so you can add elements to it. A command line option is an argument on the command line of the form:

-option The elements of the command-switch-alist look like this:

(option . handler-function) The handler-function is called to handle option and receives the option name as its sole argument.

In some cases, the option is followed in the command line by an argument. In these cases, the handler-function can find all the remaining command-line arguments in the variable command-line-args-left. (The entire list of commandline arguments is in command-line-args.) The command line arguments are parsed by the command-line-1 function in the ‘startup.el’ file. See also section “Command Line Switches and Arguments” in The GNU Emacs Manual.

Variable command-line-args

The value of this variable is the list of command line arguments passed to Emacs.

Variable command-line-functions

This variable’s value is a list of functions for handling an unrecognized command-line argument. Each time the next argument to be processed has no special meaning, the functions in this list are called, in order of appearance, until one of them returns a non-nil value. These functions are called with no arguments. They can access the commandline argument under consideration through the variable argi. The remaining arguments (not including the current one) are in the variable command-line-

args-left.

When a function recognizes and processes the argument in argi, it should return a non-nil value to say it has dealt with that argument. If it has also dealt with some of the following arguments, it can indicate that by deleting

them from command-line-args-left.

If all of these functions return nil, then the argument is used as a file name to visit.

34.2 Getting Out of Emacs

There are two ways to get out of Emacs: you can kill the Emacs job, which exits permanently, or you can suspend it, which permits you to reenter the Emacs process later. As a practical matter, you seldom kill Emacs—only when you are about to log out. Suspending is much more common.

34.2.1 Killing Emacs

Killing Emacs means ending the execution of the Emacs process. The parent process normally resumes control. The low-level primitive for killing Emacs is kill-emacs.

Function kill-emacs &optional exit-data This function exits the Emacs process and kills it. If exit-data is an integer, then it is used as the exit status of the Emacs process. (This is useful primarily in batch operation; see Section 34.12 [Batch Mode], page 565.) If exit-data is a string, its contents are stuffed into the terminal input buffer so that the shell (or whatever program next reads input) can read them.

All the information in the Emacs process, aside from files that have been saved, is lost when the Emacs is killed. Because killing Emacs inadvertently can lose a lot of work, Emacs queries for confirmation before actually terminating if you have buffers that need saving or subprocesses that are running. This is done in the function save-buffers-kill-emacs.

Variable kill-emacs-query-functions

After asking the standard questions, save-buffers-kill-emacs calls the functions in the list kill-buffer-query-functions, in order of appearance, with no arguments. These functions can ask for additional confirmation from the user. If any of them returns non-nil, Emacs is not killed.

Variable kill-emacs-hook

This variable is a normal hook; once save-buffers-kill-emacs is finished with all file saving and confirmation, it runs the functions in this hook.

34.2.2 Suspending Emacs

Suspending Emacs means stopping Emacs temporarily and returning control to its superior process, which is usually the shell. This allows you to resume editing later in the same Emacs process, with the same buffers, the same kill ring, the same undo history, and so on. To resume Emacs, use the appropriate command in the parent shell—most likely fg.

Some operating systems do not support suspension of jobs; on these systems, “suspension” actually creates a new shell temporarily as a subprocess of Emacs. Then you would exit the shell to return to Emacs.

Suspension is not useful with window systems such as X, because the Emacs job may not have a parent that can resume it again, and in any case you can give input to some other job such as a shell merely by moving to a different window. Therefore, suspending is not allowed when Emacs is an X client.

Function suspend-emacs string

This function stops Emacs and returns control to the superior process. If and when the superior process resumes Emacs, suspend-emacs returns nil to its caller in Lisp. If string is non-nil, its characters are sent to be read as terminal input by Emacs’s superior shell. The characters in string are not echoed by the superior shell; only the results appear. Before suspending, suspend-emacs runs the normal hook suspend-hook. In Emacs version 18, suspend-hook was not a normal hook; its value was a single function, and if its value was non-nil, then suspend-emacs returned immediately without actually suspending anything. After the user resumes Emacs, suspend-emacs runs the normal hook suspendresume-hook. See Section 20.4 [Hooks], page 316. The next redisplay after resumption will redraw the entire screen, unless the variable no-redraw-on-reenter is non-nil (see Section 35.1 [Refresh Screen], page 567). In the following example, note that ‘pwd’ is not echoed after Emacs is suspended. But it is read and executed by the shell.

(suspend-emacs)
     ⇒ nil
(add-hook 'suspend-hook
          (function (lambda ()
                      (or (y-or-n-p
                            "Really suspend? ")
                          (error "Suspend cancelled")))))
     ⇒ (lambda nil
          (or (y-or-n-p "Really suspend? ")
              (error "Suspend cancelled")))
(add-hook 'suspend-resume-hook
          (function (lambda () (message "Resumed!"))))
     ⇒ (lambda nil (message "Resumed!"))
(suspend-emacs "pwd")
     ⇒ nil
---------- Buffer: Minibuffer ----------
Really suspend? y
---------- Buffer: Minibuffer ----------
---------- Parent Shell ----------
lewis@slug[23] % /user/lewis/manual
lewis@slug[24] % fg
---------- Echo Area ----------
Resumed!

Variable suspend-hook

This variable is a normal hook run before suspending.

Variable suspend-resume-hook

This variable is a normal hook run after suspending.

34.3 Operating System Environment

Emacs provides access to variables in the operating system environment through various functions. These variables include the name of the system, the user’s uid, and so on.

Variable system-type

The value of this variable is a symbol indicating the type of operating system Emacs is operating on. Here is a table of the possible values:

aix-v3  AIX.
berkeley-unix

Berkeley BSD.

dgux Data General DGUX operating system.

gnu A GNU system (using the GNU kernel, which consists of the HURD and Mach).

gnu/linux

A variant GNU system using the Linux kernel.

hpux Hewlett-Packard HPUX operating system.

irix Silicon Graphics Irix system.

ms-dos Microsoft MS-DOS “operating system.”

next-mach

NeXT Mach-based system.

rtu Masscomp RTU, UCB universe.

unisoft-unix

UniSoft UniPlus.

usg-unix-v

AT&T System V.

vax-vms VAX VMS.
windows-nt

Microsoft windows NT.

xenix SCO Xenix 386.

We do not wish to add new symbols to make finer distinctions unless it is absolutely necessary! In fact, we hope to eliminate some of these alternatives in the future. We recommend using system-configuration to distinguish between different operating systems.

Variable system-configuration

This variable holds the three-part configuration name for the hardware/software configuration of your system, as a string. The convenient way to test parts of this string is with string-match.

Function system-name

This function returns the name of the machine you are running on.

     (system-name)
          ⇒ "prep.ai.mit.edu"

The symbol system-name is a variable as well as a function. In fact, the function returns whatever value the variable system-name currently holds. Thus, you can set the variable system-name in case Emacs is confused about the name of your system. The variable is also useful for constructing frame titles (see Section 26.4 [Frame Titles], page 416).

Variable mail-host-address

If this variable is non-nil, it is used instead of system-name for purposes of generating email addresses. For example, it is used when constructing the default value of user-mail-address. See Section 34.4 [User Identification], page 552. (Since this is done when Emacs starts up, the value actually used is the one saved when Emacs was dumped. See Section B.1 [Building Emacs], page 609.)

Function getenv var

This function returns the value of the environment variable var, as a string. Within Emacs, the environment variable values are kept in the Lisp variable

process-environment.
     (getenv "USER")
          ⇒ "lewis"
     lewis@slug[10] % printenv
     PATH=.:/user/lewis/bin:/usr/bin:/usr/local/bin
     USER=lewis
     TERM=ibmapa16
     SHELL=/bin/csh
     HOME=/user/lewis

Command setenv variable value This command sets the value of the environment variable named variable to value. Both arguments should be strings. This function works by modifying process-environment; binding that variable with let is also reasonable practice.

Variable process-environment

This variable is a list of strings, each describing one environment variable. The functions getenv and setenv work by means of this variable.

     process-environment
     ⇒ ("l=/usr/stanford/lib/gnuemacs/lisp"
         "PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin"
         "USER=lewis"
         "TERM=ibmapa16"
         "SHELL=/bin/csh"
         "HOME=/user/lewis")

Variable path-separator

This variable holds a string which says which character separates directories in a search path (as found in an environment variable). Its value is ":" for Unix and GNU systems, and ";" for MS-DOS and Windows NT.

Variable invocation-name

This variable holds the program name under which Emacs was invoked. The value is a string, and does not include a directory name.

Variable invocation-directory

This variable holds the directory from which the Emacs executable was invoked, or perhaps nil if that directory cannot be determined.

Variable installation-directory

If non-nil, this is a directory within which to look for the ‘lib-src’ and ‘etc’ subdirectories. This is non-nil when Emacs can’t find those directories in their standard installed locations, but can find them in a directory related somehow to the one containing the Emacs executable.

Function load-average

This function returns the current 1-minute, 5-minute and 15-minute load averages in a list. The values are integers that are 100 times the system load averages. (The load averages indicate the number of processes trying to run.)

     (load-average)
          ⇒ (169 48 36)
     lewis@rocky[5] % uptime
      11:55am  up 1 day, 19:37,  3 users,
      load average: 1.69, 0.48, 0.36

Function emacs-pid

This function returns the process id of the Emacs process.

Function setprv privilege-name &optional setp getprv This function sets or resets a VMS privilege. (It does not exist on Unix.) The first arg is the privilege name, as a string. The second argument, setp, is t or nil, indicating whether the privilege is to be turned on or off. Its default is nil. The function returns t if successful, nil otherwise. If the third argument, getprv, is non-nil, setprv does not change the privilege, but returns t or nil indicating whether the privilege is currently enabled.

34.4 User Identification

Variable user-mail-address

This holds the nominal email address of the user who is using Emacs. Emacs normally sets this variable to a default value after reading your init files, but not if you have already set it. So you can set the variable to some other value in your ‘~/.emacs’ file if you do not want to use the default value.

Function user-login-name &optional uid

If you don’t specify uid, this function returns the name under which the user is logged in. If the environment variable LOGNAME is set, that value is used. Otherwise, if the environment variable USER is set, that value is used. Otherwise, the value is based on the effective uid, not the real uid. If you specify uid, the value is the user name that corresponds to uid (which should be an integer).

     (user-login-name)
          ⇒ "lewis"

Function user-real-login-name

This function returns the user name corresponding to Emacs’s real uid. This ignores the effective uid and ignores the environment variables LOGNAME and

USER.

Function user-full-name

This function returns the full name of the user.

     (user-full-name)
          ⇒ "Bil Lewis"

The symbols user-login-name, user-real-login-name and user-full-name are vari-

ables as well as functions. The functions return the same values that the variables hold. These variables allow you to “fake out” Emacs by telling the functions what to return. The variables are also useful for constructing frame titles (see Section 26.4 [Frame Titles], page 416).

Function user-real-uid

This function returns the real uid of the user.

     (user-real-uid)
          ⇒ 19

Function user-uid

This function returns the effective uid of the user.

34.5 Time of Day

This section explains how to determine the current time and the time zone.

Function current-time-string &optional time-value

This function returns the current time and date as a humanly-readable string. The format of the string is unvarying; the number of characters used for each part is always the same, so you can reliably use substring to extract pieces of it. It is wise to count the characters from the beginning of the string rather than from the end, as additional information may be added at the end. The argument time-value, if given, specifies a time to format instead of the current time. The argument should be a list whose first two elements are integers. Thus, you can use times obtained from current-time (see below) and from file-attributes (see Section 22.6.4 [File Attributes], page 340).

     (current-time-string)
          ⇒ "Wed Oct 14 22:21:05 1987"

Function current-time

This function returns the system’s time value as a list of three integers: (high low microsec). The integers high and low combine to give the number of seconds since 0:00 January 1, 1970, which is high ∗ 2^{16} + low. The third element, microsec, gives the microseconds since the start of the current second (or 0 for systems that return time only on the resolution of a second). The first two elements can be compared with file time values such as you get with the function file-attributes. See Section 22.6.4 [File Attributes], page 340.

Function current-time-zone &optional time-value This function returns a list describing the time zone that the user is in. The value has the form (offset name). Here offset is an integer giving the number of seconds ahead of UTC (east of Greenwich). A negative value means west of Greenwich. The second element, name is a string giving the name of the time zone. Both elements change when daylight savings time begins or ends; if the user has specified a time zone that does not use a seasonal time adjustment, then the value is constant through time. If the operating system doesn’t supply all the information necessary to compute the value, both elements of the list are nil. The argument time-value, if given, specifies a time to analyze instead of the current time. The argument should be a cons cell containing two integers, or a list whose first two elements are integers. Thus, you can use times obtained from current-time (see above) and from file-attributes (see Section 22.6.4 [File Attributes], page 340).

34.6 Time Conversion

These functions convert time values (lists of two or three integers) to strings or to calendrical information. There is also a function to convert calendrical information to a time value. You can get time values from the functions current-time (see Section 34.5 [Time of Day], page 553) and file-attributes (see Section 22.6.4 [File Attributes], page 340).

Many operating systems are limited to time values that contain 32 bits of information; these systems typically handle only the times from 1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC. However, some operating systems have larger time values, and can represent times far in the past or future.

Time conversion functions always use the Gregorian calendar, even for dates before the Gregorian calendar was introduced. Year numbers count the number of years since the year 1 B.C., and do not skip zero as traditional Gregorian years do; for example, the year number -37 represents the Gregorian year 38 B.C.

Function format-time-string format-string time

This function converts time to a string according to format-string. The argument format-string may contain ‘%’-sequences which say to substitute parts of the time. Here is a table of what the ‘%’-sequences mean:

‘%a’ This stands for the abbreviated name of the day of week.

‘%A’ This stands for the full name of the day of week.

‘%b’ This stands for the abbreviated name of the month.

‘%B’ This stands for the full name of the month.

‘%c’ This is a synonym for ‘%x %X’.

‘%C’ This has a locale-specific meaning. In the default locale (named C), it is equivalent to ‘%A, %B %e, %Y’.

‘%d’ This stands for the day of month, zero-padded.

‘%D’ This is a synonym for ‘%m/%d/%y’.

‘%e’ This stands for the day of month, blank-padded.

‘%h’ This is a synonym for ‘%b’.

‘%H’ This stands for the hour (00-23).

‘%I’ This stands for the hour (00-12). ‘%j’ This stands for the day of the year (001-366). ‘%k’ This stands for the hour (0-23), blank padded. ‘%l’ This stands for the hour (1-12), blank padded. ‘%m’ This stands for the month (01-12). ‘%M’ This stands for the minute (00-59). ‘%n’ This stands for a newline. ‘%p’ This stands for ‘AM’ or ‘PM’, as appropriate. ‘%r’ This is a synonym for ‘%I:%M:%S %p’. ‘%R’ This is a synonym for ‘%H:%M’. ‘%S’ This stands for the seconds (00-60). ‘%t’ This stands for a tab character. ‘%T’ This is a synonym for ‘%H:%M:%S’. ‘%U’ This stands for the week of the year (01-52), assuming that weeks

start on Sunday.

‘%w’ This stands for the numeric day of week (0-6). Sunday is day 0. ‘%W’ This stands for the week of the year (01-52), assuming that weeks

start on Monday.

‘%x’ This has a locale-specific meaning. In the default locale (named

C), it is equivalent to ‘%D’.

‘%X’ This has a locale-specific meaning. In the default locale (named

C), it is equivalent to ‘%T’.

‘%y’ This stands for the year without century (00-99). ‘%Y’ This stands for the year with century. ‘%Z’ This stands for the time zone abbreviation.

Function decode-time time

This function converts a time value into calendrical information. The return value is a list of nine elements, as follows:

(seconds minutes hour day month year dow dst zone) Here is what the elements mean: sec The number of seconds past the minute, as an integer between 0

and 59.

minute The number of minutes past the hour, as an integer between 0 and

59.

hour The hour of the day, as an integer between 0 and 23. day The day of the month, as an integer between 1 and 31.

month The month of the year, as an integer between 1 and 12.

year The year, an integer typically greater than 1900.

dow The day of week, as an integer between 0 and 6, where 0 stands for Sunday.

dst t if daylight savings time is effect, otherwise nil.

zone An integer indicating the time zone, as the number of seconds east of Greenwich.

Note that Common Lisp has different meanings for dow and zone.

Function encode-time seconds minutes hour day month year &optional

…zone This function is the inverse of decode-time. It converts seven items of calendrical data into a time value. For the meanings of the arguments, see the table

above under decode-time.

Year numbers less than 100 are treated just like other year numbers. If you want them to stand for years above 1900, you must alter them yourself before

you call encode-time.

The optional argument zone defaults to the current time zone and its daylight savings time rules. If specified, it can be either a list (as you would get from current-time-zone) or an integer (as you would get from decode-time). The specified zone is used without any further alteration for daylight savings time. If you pass more than seven arguments to encode-time, the first six are used as seconds through year, the last argument is used as zone, and the arguments in between are ignored. This feature makes it possible to use the elements of a list returned by decode-time as the arguments to encode-time, like this:

     (apply 'encode-time (decode-time . . .))

34.7 Timers for Delayed Execution

You can set up a timer to call a function at a specified future time or after a certain length of idleness.

Emacs cannot run a timer at any arbitrary point in a Lisp program; it can run them only when Emacs could accept output from a subprocess: namely, while waiting or inside certain primitive functions such as sit-for or read-char which can wait. Therefore, a timer’s execution may be delayed if Emacs is busy. However, the time of execution is very precise if Emacs is idle.

Function run-at-time time repeat function &rest args This function arranges to call function with arguments args at time time. The argument function is a function to call later, and args are the arguments to give it when it is called. The time time is specified as a string.

Absolute times may be specified in a variety of formats; The form ‘hour:min:sec timezone month/day/year’, where all fields are numbers, works; the format that current-time-string returns is also allowed. To specify a relative time, use numbers followed by units. For example:

‘1 min’ denotes 1 minute from now.

‘1 min 5 sec’

denotes 65 seconds from now.

‘1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year’

denotes exactly 103 months, 123 days, and 10862 seconds from now.

If time is a number (integer or floating point), that specifies a relative time measured in seconds. The argument repeat specifies how often to repeat the call. If repeat is nil, there are no repetitions; function is called just once, at time. If repeat is a number, it specifies a repetition period measured in seconds. In any case, repeat has no effect on when first call takes place—time alone specifies that. The function run-at-time returns a timer value that identifies the particular scheduled future action. You can use this value to call cancel-timer (see below).

Macro with-timeout (seconds timeout-forms…) body… Execute body, but give up after seconds seconds. If body finishes before the time is up, with-timeout returns the value of the last form in body. If, however, the execution of body is cut short by the timeout, then with-timeout executes all the timeout-forms and returns the value of the last of them. This macro works by set a timer to run after seconds seconds. If body finishes before that time, it cancels the timer. If the timer actually runs, it terminates execution of body, then executes timeout-forms. Since timers can run within a Lisp program only when the program calls a primitive that can wait, with-timeout cannot stop executing body while it is in the midst of a computation—only when it calls one of those primitives. So use with-timeout only with a body that waits for input, not one that does a long computation.

The function y-or-n-p-with-timeout provides a simple way to use a timer to avoid waiting too long for an answer. See Section 17.6 [Yes-or-No Queries], page 237.

Function run-with-idle-timer secs repeat function &rest args Set up a timer which runs when Emacs has been idle for secs seconds. The value of secs may be an integer or a floating point number. If repeat is nil, the timer runs just once, the first time Emacs remains idle for a long enough time. More often repeat is non-nil, which means to run the timer each time Emacs remains idle for secs seconds. The function run-with-idle-timer returns a timer value which you can use in calling cancel-timer (see below).

Emacs becomes “idle” when it starts waiting for user input, and it remains idle until the user provides some input. If a timer is set for five seconds of idleness, it runs approximately five seconds after Emacs first became idle. Even if its repeat is true, this timer will not run again as long as Emacs remains idle, because the duration of idleness will continue to increase and will not go down to five seconds again.

Emacs can do various things while idle: garbage collect, autosave or handle data from a subprocess. But these interludes during idleness have little effect on idle timers. An idle timer set for 600 seconds will run when ten minutes have elapsed since the last user command was finished, even if subprocess output has been accepted thousands of times within those ten minutes, even if there have been garbage collections and autosaves.

When the user supplies input, Emacs becomes non-idle while executing the input. Then it becomes idle again, and all the idle timers that are set up to repeat will subsequently run another time, one by one.

Function cancel-timer timer

Cancel the requested action for timer, which should be a value previously returned by run-at-time or run-with-idle-timer. This cancels the effect of that call to run-at-time; the arrival of the specified time will not cause anything special to happen.

34.8 Terminal Input

This section describes functions and variables for recording or manipulating terminal input. See Chapter 35 [Display], page 567, for related functions.

34.8.1 Input Modes

Function set-input-mode interrupt flow meta quit-char This function sets the mode for reading keyboard input. If interrupt is nonnull, then Emacs uses input interrupts. If it is nil, then it uses cbreak mode. When Emacs communicates directly with X, it ignores this argument and uses interrupts if that is the way it knows how to communicate. If flow is non-nil, then Emacs uses xon/xoff (C-q, C-s) flow control for output to the terminal. This has no effect except in cbreak mode. See Section 34.11 [Flow Control], page 564. The default setting is system dependent. Some systems always use cbreak mode regardless of what is specified. The argument meta controls support for input character codes above 127. If meta is t, Emacs converts characters with the 8th bit set into Meta characters. If meta is nil, Emacs disregards the 8th bit; this is necessary when the terminal uses it as a parity bit. If meta is neither t nor nil, Emacs uses all 8 bits of input unchanged. This is good for terminals using European 8-bit character sets. If quit-char is non-nil, it specifies the character to use for quitting. Normally this character is C-g. See Section 18.8 [Quitting], page 268.

The current-input-mode function returns the input mode settings Emacs is currently using.

Function current-input-mode

This function returns current mode for reading keyboard input. It returns a list, corresponding to the arguments of set-input-mode, of the form (interrupt flow meta quit) in which:

interrupt is non-nil when Emacs is using interrupt-driven input. If nil, Emacs is using cbreak mode.

flow is non-nil if Emacs uses xon/xoff (C-q, C-s) flow control for output to the terminal. This value has no effect unless interrupt is non-nil.

meta is t if Emacs treats the eighth bit of input characters as the meta bit; nil means Emacs clears the eighth bit of every input character; any other value means Emacs uses all eight bits as the basic character code.

quit is the character Emacs currently uses for quitting, usually C-g.

34.8.2 Translating Input Events

This section describes features for translating input events into other input events before they become part of key sequences. These features apply to each event in the order they are described here: each event is first modified according to extra-keyboard-modifiers, then translated through keyboard-translate-table (if applicable). If it is being read as part of a key sequence, it is then added to the sequece being read; then subsequences containing

it are checked first with function-key-map and then with key-translation-map.

Variable extra-keyboard-modifiers

This variable lets Lisp programs “press” the modifier keys on the keyboard. The value is a bit mask:

1 The ^{⟨}\underline{\overline{SHIFT}}^{⟩} key.

2 The ^{⟨}\underline{\overline{LOCK}}^{⟩} key.

4 The ^{⟨}\underline{\overline{CTL}}^{⟩} key.

8 The ^{⟨}\underline{\overline{META}}^{⟩} key.

Each time the user types a keyboard key, it is altered as if the modifier keys specified in the bit mask were held down. When using X windows, the program can “press” any of the modifier keys in this way. Otherwise, only the ^{⟨}\underline{\overline{CTL}}^{⟩} and ^{⟨}\underline{\overline{META}}^{⟩} keys can be virtually pressed.

Variable keyboard-translate-table

This variable is the translate table for keyboard characters. It lets you reshuffle the keys on the keyboard without changing any command bindings. Its value must be a string or nil.

If keyboard-translate-table is a string, then each character read from the keyboard is looked up in this string and the character in the string is used instead. If the string is of length n, character codes n and up are untranslated. In the example below, we set keyboard-translate-table to a string of 128 characters. Then we fill it in to swap the characters C-s and C-\ and the characters C-q and C-^. Subsequently, typing C-\ has all the usual effects of typing C-s, and vice versa. (See Section 34.11 [Flow Control], page 564 for more information on this subject.)

     (defun evade-flow-control ()
       "Replace C-s with C-\ and C-q with C-^."
       (interactive)
       (let ((the-table (make-string 128 0)))
         (let ((i 0))
           (while (< i 128)
             (aset the-table i i)
             (setq i (1+ i))))
         ;; Swap C-s and C-\.
         (aset the-table ?\034 ?\^s)
         (aset the-table ?\^s ?\034)
         ;; Swap C-q and C-^.
         (aset the-table ?\036 ?\^q)
         (aset the-table ?\^q ?\036)
         (setq keyboard-translate-table the-table)))

Note that this translation is the first thing that happens to a character after it is read from the terminal. Record-keeping features such as recent-keys and dribble files record the characters after translation.

Function keyboard-translate from to

This function modifies keyboard-translate-table to translate character code from into character code to. It creates or enlarges the translate table if necessary.

The remaining translation features translate subsequences of key sequences being read. They are implemented in read-key-sequence and have no effect on read-char.

Variable function-key-map

This variable holds a keymap that describes the character sequences sent by function keys on an ordinary character terminal. This keymap uses the same data structure as other keymaps, but is used differently: it specifies translations to make while reading event sequences. If function-key-map “binds” a key sequence k to a vector v, then when k appears as a subsequence anywhere in a key sequence, it is replaced with the events in v. For example, VT100 terminals send ^{⟨}\underline{\overline{ESC}}^{⟩} O P when the keypad PF1 key is pressed. Therefore, we want Emacs to translate that sequence of events into the single event pf1. We accomplish this by “binding” ^{⟨}\underline{\overline{ESC}}^{⟩} O P to [pf1] in function-key-map, when using a VT100.

Thus, typing C-c ^{⟨}\underline{\overline{PF1}}^{⟩} sends the character sequence C-c ^{⟨}\underline{\overline{ESC}}^{⟩} O P; later the function read-key-sequence translates this back into C-c ^{⟨}\underline{\overline{PF1}}^{⟩}, which it returns as the vector [?\C-c pf1].

Entries in function-key-map are ignored if they conflict with bindings made in the minor mode, local, or global keymaps. The intent is that the character sequences that function keys send should not have command bindings in their own right.

The value of function-key-map is usually set up automatically according to the terminal’s Terminfo or Termcap entry, but sometimes those need help from terminal-specific Lisp files. Emacs comes with terminal-specific files for many common terminals; their main purpose is to make entries in function-key-map beyond those that can be deduced from Termcap and Terminfo. See Section 34.1.3 [Terminal-Specific], page 545.

Emacs versions 18 and earlier used totally different means of detecting the character sequences that represent function keys.

Variable key-translation-map

This variable is another keymap used just like function-key-map to translate input events into other events. It differs from function-key-map in two ways:

  • key-translation-map goes to work after function-key-map is finished;

it receives the results of translation by function-key-map.

• key-translation-map overrides actual key bindings. For example, if Cx f has a binding in key-translation-map, that translation takes effect even though C-x f also has a key binding in the global map.

The intent of key-translation-map is for users to map one character set to another, including ordinary characters normally bound to self-insert-command.

You can use function-key-map or key-translation-map for more than simple aliases, by using a function, instead of a key sequence, as the “translation” of a key. Then this function is called to compute the translation of that key.

The key translation function receives one argument, which is the prompt that was specified in read-key-sequence—or nil if the key sequence is being read by the editor command loop. In most cases you can ignore the prompt value.

If the function reads input itself, it can have the effect of altering the event that follows. For example, here’s how to define C-c h to turn the character that follows into a Hyper character:

(defun hyperify (prompt)
  (let ((e (read-event)))
    (vector (if (numberp e)
                (logior (lsh 1 20) e)
              (if (memq 'hyper (event-modifiers e))
                  e
                (add-event-modifier "H-" e))))))
(defun add-event-modifier (string e)
  (let ((symbol (if (symbolp e) e (car e))))
    (setq symbol (intern (concat string
                                 (symbol-name symbol))))
    (if (symbolp e)
        symbol
      (cons symbol (cdr e)))))
(define-key function-key-map "\C-ch" 'hyperify)

The ‘iso-transl’ library uses this feature to provide a way of inputting non-ASCII Latin-1 characters.

34.8.3 Recording Input

Function recent-keys

This function returns a vector containing the last 100 input events from the keyboard or mouse. All input events are included, whether or not they were used as parts of key sequences. Thus, you always get the last 100 inputs, not counting keyboard macros. (Events from keyboard macros are excluded because they are less interesting for debugging; it should be enough to see the events that invoked the macros.)

Command open-dribble-file filename

This function opens a dribble file named filename. When a dribble file is open, each input event from the keyboard or mouse (but not those from keyboard macros) is written in that file. A non-character event is expressed using its printed representation surrounded by ‘<…>’. You close the dribble file by calling this function with an argument of nil. This function is normally used to record the input necessary to trigger an Emacs bug, for the sake of a bug report.

     (open-dribble-file "~/dribble")
          ⇒ nil

See also the open-termscript function (see Section 34.9 [Terminal Output], page 562).

34.9 Terminal Output

The terminal output functions send output to the terminal or keep track of output sent to the terminal. The variable baud-rate tells you what Emacs thinks is the output speed of the terminal.

Variable baud-rate

This variable’s value is the output speed of the terminal, as far as Emacs knows. Setting this variable does not change the speed of actual data transmission, but the value is used for calculations such as padding. It also affects decisions about whether to scroll part of the screen or repaint—even when using a window system. (We designed it this way despite the fact that a window system has no true “output speed”, to give you a way to tune these decisions.)

The value is measured in baud.

If you are running across a network, and different parts of the network work at different baud rates, the value returned by Emacs may be different from the value used by your local terminal. Some network protocols communicate the local terminal speed to the remote machine, so that Emacs and other programs can get the proper value, but others do not. If Emacs has the wrong value, it makes decisions that are less than optimal. To fix the problem, set baud-rate.

Function baud-rate

This function returns the value of the variable baud-rate. In Emacs versions 18 and earlier, this was the only way to find out the terminal speed.

Function send-string-to-terminal string

This function sends string to the terminal without alteration. Control characters in string have terminal-dependent effects.

One use of this function is to define function keys on terminals that have downloadable function key definitions. For example, this is how on certain terminals to define function key 4 to move forward four characters (by transmitting the characters C-u C-f to the computer):

     (send-string-to-terminal "\eF4\^U\^F")
          ⇒ nil

Command open-termscript filename

This function is used to open a termscript file that will record all the characters sent by Emacs to the terminal. It returns nil. Termscript files are useful for investigating problems where Emacs garbles the screen, problems that are due to incorrect Termcap entries or to undesirable settings of terminal options more often than to actual Emacs bugs. Once you are certain which characters were actually output, you can determine reliably whether they correspond to the Termcap specifications in use.

See also open-dribble-file in Section 34.8 [Terminal Input], page 558.

     (open-termscript "../junk/termscript")
          ⇒ nil

34.10 System-Specific X11 Keysyms

To define system-specific X11 keysyms, set the variable system-key-alist.

Variable system-key-alist

This variable’s value should be an alist with one element for each system-specific keysym. An element has this form: (code . symbol), where code is the numeric keysym code (not including the “vendor specific” bit, 1 << 28), and symbol is the name for the function key. For example (168 . mute-acute) defines a system-specific key used by HP X servers whose numeric code is (1 << 28) + 168. It is not a problem if the alist defines keysyms for other X servers, as long as they don’t conflict with the ones used by the X server actually in use. The variable is always local to the current X terminal and cannot be buffer-local. See Section 26.2 [Multiple Displays], page 409.

34.11 Flow Control

This section attempts to answer the question “Why does Emacs choose to use flowcontrol characters in its command character set?” For a second view on this issue, read the comments on flow control in the ‘emacs/INSTALL’ file from the distribution; for help with Termcap entries and DEC terminal concentrators, see ‘emacs/etc/TERMS’.

At one time, most terminals did not need flow control, and none used C-s and C-q for flow control. Therefore, the choice of C-s and C-q as command characters was uncontroversial. Emacs, for economy of keystrokes and portability, used nearly all the ASCII control characters, with mnemonic meanings when possible; thus, C-s for search and C-q for quote.

Later, some terminals were introduced which required these characters for flow control. They were not very good terminals for full-screen editing, so Emacs maintainers did not pay attention. In later years, flow control with C-s and C-q became widespread among terminals, but by this time it was usually an option. And the majority of users, who can turn flow control off, were unwilling to switch to less mnemonic key bindings for the sake of flow control.

So which usage is “right”, Emacs’s or that of some terminal and concentrator manufacturers? This question has no simple answer.

One reason why we are reluctant to cater to the problems caused by C-s and C-q is that they are gratuitous. There are other techniques (albeit less common in practice) for flow control that preserve transparency of the character stream. Note also that their use for flow control is not an official standard. Interestingly, on the model 33 teletype with a paper tape punch (which is very old), C-s and C-q were sent by the computer to turn the punch on and off!

As X servers and other window systems replace character-only terminals, this problem is gradually being cured. For the mean time, Emacs provides a convenient way of enabling flow control if you want it: call the function enable-flow-control.

Function enable-flow-control

This function enables use of C-s and C-q for output flow control, and provides the characters C-\ and C-^as aliases for them using keyboard-translate-table (see Section 34.8.2 [Translating Input], page 559).

You can use the function enable-flow-control-on in your ‘.emacs’ file to enable flow control automatically on certain terminal types.

Function enable-flow-control-on &rest termtypes

This function enables flow control, and the aliases C-\ and C-^, if the terminal type is one of termtypes. For example:

          (enable-flow-control-on "vt200" "vt300" "vt101" "vt131")

Here is how enable-flow-control does its job:

1. It sets cbreak mode for terminal input, and tells the operating system to handle flow

    control, with (set-input-mode nil t).
 2. It sets up keyboard-translate-table to translate C-\ and C-^into C-s and C-q.

Except at its very lowest level, Emacs never knows that the characters typed were anything but C-s and C-q, so you can in effect type them as C-\ and C-^even when they are input for other commands. See Section 34.8.2 [Translating Input], page 559.

If the terminal is the source of the flow control characters, then once you enable kernel flow control handling, you probably can make do with less padding than normal for that terminal. You can reduce the amount of padding by customizing the Termcap entry. You can also reduce it by setting baud-rate to a smaller value so that Emacs uses a smaller speed when calculating the padding needed. See Section 34.9 [Terminal Output], page 562.

34.12 Batch Mode

The command line option ‘-batch’ causes Emacs to run noninteractively. In this mode, Emacs does not read commands from the terminal, it does not alter the terminal modes, and it does not expect to be outputting to an erasable screen. The idea is that you specify Lisp programs to run; when they are finished, Emacs should exit. The way to specify the programs to run is with ‘-l file’, which loads the library named file, and ‘-f function’, which calls function with no arguments.

Any Lisp program output that would normally go to the echo area, either using message or using prin1, etc., with t as the stream, goes instead to Emacs’s standard error descriptor when in batch mode. Thus, Emacs behaves much like a noninteractive application program. (The echo area output that Emacs itself normally generates, such as command echoing, is suppressed entirely.)

Variable noninteractive

This variable is non-nil when Emacs is running in batch mode.

566 GNU Emacs Lisp Reference Manual

35 Emacs Display

This chapter describes a number of features related to the display that Emacs presents to the user.

35.1 Refreshing the Screen

The function redraw-frame redisplays the entire contents of a given frame. See Chapter 26 [Frames], page 409.

Function redraw-frame frame

This function clears and redisplays frame frame.

Even more powerful is redraw-display:

Command redraw-display

This function clears and redisplays all visible frames.

Processing user input takes absolute priority over redisplay. If you call these functions when input is available, they do nothing immediately, but a full redisplay does happen eventually—after all the input has been processed.

Normally, suspending and resuming Emacs also refreshes the screen. Some terminal emulators record separate contents for display-oriented programs such as Emacs and for ordinary sequential display. If you are using such a terminal, you might want to inhibit the redisplay on resumption.

Variable no-redraw-on-reenter

This variable controls whether Emacs redraws the entire screen after it has been suspended and resumed. Non-nil means yes, nil means no.

35.2 Screen Size

The screen size functions access or specify the height or width of the terminal. When you are using multiple frames, they apply to the selected frame (see Chapter 26 [Frames], page 409).

Function screen-height

This function returns the number of lines on the screen that are available for display.

          (screen-height)
               ⇒ 50

Function screen-width

This function returns the number of columns on the screen that are available for display.

          (screen-width)
               ⇒ 80

Function set-screen-height lines &optional not-actual-size This function declares that the terminal can display lines lines. The sizes of existing windows are altered proportionally to fit. If not-actual-size is non-nil, then Emacs displays lines lines of output, but does not change its value for the actual height of the screen. (Knowing the correct actual size may be necessary for correct cursor positioning.) Using a smaller height than the terminal actually implements may be useful to reproduce behavior observed on a smaller screen, or if the terminal malfunctions when using its whole screen. If lines is different from what it was previously, then the entire screen is cleared and redisplayed using the new size. This function returns nil.

Function set-screen-width columns &optional not-actual-size This function declares that the terminal can display columns columns. The

details are as in set-screen-height.

35.3 Truncation

When a line of text extends beyond the right edge of a window, the line can either be continued on the next screen line, or truncated to one screen line. The additional screen lines used to display a long text line are called continuation lines. Normally, a ‘$’ in the rightmost column of the window indicates truncation; a ‘\’ on the rightmost column indicates a line that “wraps” or is continued onto the next line. (The display table can specify alternative indicators; see Section 35.14 [Display Tables], page 583.)

Note that continuation is different from filling; continuation happens on the screen only, not in the buffer contents, and it breaks a line precisely at the right margin, not at a word boundary. See Section 29.11 [Filling], page 464.

User Option truncate-lines

This buffer-local variable controls how Emacs displays lines that extend beyond the right edge of the window. The default is nil, which specifies continuation. If the value is non-nil, then these lines are truncated. If the variable truncate-partial-width-windows is non-nil, then truncation is always used for side-by-side windows (within one frame) regardless of the

value of truncate-lines.

User Option default-truncate-lines

This variable is the default value for truncate-lines, for buffers that do not have local values for it.

User Option truncate-partial-width-windows

This variable controls display of lines that extend beyond the right edge of the window, in side-by-side windows (see Section 25.2 [Splitting Windows], page 384). If it is non-nil, these lines are truncated; otherwise, truncatelines says what to do with them.

You can override the images that indicate continuation or truncation with the display table; see Section 35.14 [Display Tables], page 583.

If your buffer contains very long lines, and you use continuation to display them, just thinking about them can make Emacs redisplay slow. The column computation and indentation functions also become slow. Then you might find it advisable to set cache-long-

line-scans to t.

Variable cache-long-line-scans

If this variable is non-nil, various indentation and motion functions, and Emacs redisplay, cache the results of scanning the buffer, and consult the cache to avoid rescanning regions of the buffer unless they are modified.

Turning on the cache slows down processing of short lines somewhat.

This variable is automatically local in every buffer.

35.4 The Echo Area

The echo area is used for displaying messages made with the message primitive, and for echoing keystrokes. It is not the same as the minibuffer, despite the fact that the minibuffer appears (when active) in the same place on the screen as the echo area. The GNU Emacs Manual specifies the rules for resolving conflicts between the echo area and the minibuffer for use of that screen space (see section “The Minibuffer” in The GNU Emacs Manual). Error messages appear in the echo area; see Section 9.5.3 [Errors], page 112.

You can write output in the echo area by using the Lisp printing functions with t as the stream (see Section 16.5 [Output Functions], page 218), or as follows:

Function message string &rest arguments This function displays a one-line message in the echo area. The argument string is similar to a C language printf control string. See format in Section 4.5 [String Conversion], page 53, for the details on the conversion specifications. message returns the constructed string.

In batch mode, message prints the message text on the standard error stream, followed by a newline.

If string is nil, message clears the echo area. If the minibuffer is active, this brings the minibuffer contents back onto the screen immediately.

          (message "Minibuffer depth is %d."
                   (minibuffer-depth))
           ⊣ Minibuffer depth is 0.
          ⇒ "Minibuffer depth is 0."
          ---------- Echo Area ----------
          Minibuffer depth is 0.
          ---------- Echo Area ----------

Almost all the messages displayed in the echo area are also recorded in the ‘*Messages*’ buffer.

User Option message-log-max

This variable specifies how many lines to keep in the ‘*Messages*’ buffer. The value t means there is no limit on how many lines to keep. The value nil disables message logging entirely. Here’s how to display a message and prevent it from being logged:

     (let (message-log-max)
       (message . . .))

Variable echo-keystrokes

This variable determines how much time should elapse before command characters echo. Its value must be an integer, which specifies the number of seconds to wait before echoing. If the user types a prefix key (such as C-x) and then delays this many seconds before continuing, the prefix key is echoed in the echo area. Any subsequent characters in the same command will be echoed as well. If the value is zero, then command input is not echoed.

Variable cursor-in-echo-area

This variable controls where the cursor appears when a message is displayed in the echo area. If it is non-nil, then the cursor appears at the end of the message. Otherwise, the cursor appears at point—not in the echo area at all. The value is normally nil; Lisp programs bind it to t for brief periods of time.

35.5 Invisible Text

You can make characters invisible, so that they do not appear on the screen, with the invisible property. This can be either a text property or a property of an overlay.

In the simplest case, any non-nil invisible property makes a character invisible. This is the default case—if you don’t alter the default value of buffer-invisibility-spec, this is how the invisibility property works. This feature is much like selective display (see Section 35.6 [Selective Display], page 571), but more general and cleaner.

More generally, you can use the variable buffer-invisibility-spec to control which values of the invisible property make text invisible. This permits you to classify the text into different subsets in advance, by giving them different invisible values, and subsequently make various subsets visible or invisible by changing the value of buffer-

invisibility-spec.

Controlling visibility with buffer-invisibility-spec is especially useful in a program to display the list of entries in a data base. It permits the implementation of convenient filtering commands to view just a part of the entries in the data base. Setting this variable is very fast, much faster than scanning all the text in the buffer looking for properties to change.

Variable buffer-invisibility-spec

This variable specifies which kinds of invisible properties actually make a character invisible.

t A character is invisible if its invisible property is non-nil. This is the default. a list Each element of the list makes certain characters invisible. Ulti-

mately, a character is invisible if any of the elements of this list applies to it. The list can have two kinds of elements:

atom A character is invisible if its invisible propery value is atom or if it is a list with atom as a member.

               (atom . t)

A character is invisible if its invisible propery value is atom or if it is a list with atom as a member. Moreover, if this character is at the end of a line and is followed by a visible newline, it displays an ellipsis.

Ordinarily, commands that operate on text or move point do not care whether the text is invisible. The user-level line motion commands explicitly ignore invisible newlines if linemove-ignore-invisible is non-nil, but only because they are explicitly programmed to do so.

35.6 Selective Display

Selective display is a pair of features that hide certain lines on the screen.

The first variant, explicit selective display, is designed for use in a Lisp program. The program controls which lines are hidden by altering the text. Outline mode has traditionally used this variant. It has been partially replaced by the invisible text feature (see Section 35.5 [Invisible Text], page 570); there is a new version of Outline mode which uses that instead.

In the second variant, the choice of lines to hide is made automatically based on indentation. This variant is designed to be a user-level feature.

The way you control explicit selective display is by replacing a newline (control-j) with a carriage return (control-m). The text that was formerly a line following that newline is now invisible. Strictly speaking, it is temporarily no longer a line at all, since only newlines can separate lines; it is now part of the previous line.

Selective display does not directly affect editing commands. For example, C-f (forwardchar) moves point unhesitatingly into invisible text. However, the replacement of newline characters with carriage return characters affects some editing commands. For example, next-line skips invisible lines, since it searches only for newlines. Modes that use selective display can also define commands that take account of the newlines, or that make parts of the text visible or invisible.

When you write a selectively displayed buffer into a file, all the control-m’s are output as newlines. This means that when you next read in the file, it looks OK, with nothing invisible. The selective display effect is seen only within Emacs.

Variable selective-display

This buffer-local variable enables selective display. This means that lines, or portions of lines, may be made invisible.

• If the value of selective-display is t, then any portion of a line that follows a control-m is not displayed.

• If the value of selective-display is a positive integer, then lines that start with more than that many columns of indentation are not displayed.

When some portion of a buffer is invisible, the vertical movement commands operate as if that portion did not exist, allowing a single next-line command to skip any number of invisible lines. However, character movement commands (such as forward-char) do not skip the invisible portion, and it is possible (if tricky) to insert or delete text in an invisible portion. In the examples below, we show the display appearance of the buffer foo, which changes with the value of selective-display. The contents of the buffer do not change.

(setq selective-display nil)
     ⇒ nil
---------- Buffer: foo ----------
1 on this column
 2on this column
  3n this column
  3n this column
 2on this column
1 on this column
---------- Buffer: foo ----------
(setq selective-display 2)
     ⇒ 2
---------- Buffer: foo ----------
1 on this column
 2on this column
 2on this column
1 on this column
---------- Buffer: foo ----------

Variable selective-display-ellipses

If this buffer-local variable is non-nil, then Emacs displays ‘…’ at the end of a line that is followed by invisible text. This example is a continuation of the previous one.

(setq selective-display-ellipses t)
     ⇒ t
---------- Buffer: foo ----------
1 on this column
 2on this column ...
 2on this column
1 on this column
---------- Buffer: foo ----------

You can use a display table to substitute other text for the ellipsis (‘…’). See Section 35.14 [Display Tables], page 583.

35.7 The Overlay Arrow

The overlay arrow is useful for directing the user’s attention to a particular line in a buffer. For example, in the modes used for interface to debuggers, the overlay arrow indicates the line of code about to be executed.

Variable overlay-arrow-string

This variable holds the string to display to call attention to a particular line, or nil if the arrow feature is not in use.

Variable overlay-arrow-position

This variable holds a marker that indicates where to display the overlay arrow. It should point at the beginning of a line. The arrow text appears at the beginning of that line, overlaying any text that would otherwise appear. Since the arrow is usually short, and the line usually begins with indentation, normally nothing significant is overwritten.

The overlay string is displayed only in the buffer that this marker points into. Thus, only one buffer can have an overlay arrow at any given time.

You can do the same job by creating an overlay with a before-string property. See Section 35.9.1 [Overlay Properties], page 575.

35.8 Temporary Displays

Temporary displays are used by commands to put output into a buffer and then present it to the user for perusal rather than for editing. Many of the help commands use this feature.

Special Form with-output-to-temp-buffer buffer-name forms…

This function executes forms while arranging to insert any output they print into the buffer named buffer-name. The buffer is then shown in some window for viewing, displayed but not selected.

The string buffer-name specifies the temporary buffer, which need not already exist. The argument must be a string, not a buffer. The buffer is erased initially (with no questions asked), and it is marked as unmodified after with-output-

to-temp-buffer exits.
with-output-to-temp-buffer binds standard-output to the temporary

buffer, then it evaluates the forms in forms. Output using the Lisp output functions within forms goes by default to that buffer (but screen display and messages in the echo area, although they are “output” in the general sense of the word, are not affected). See Section 16.5 [Output Functions], page 218.

The value of the last form in forms is returned.

     ---------- Buffer: foo ----------
      This is the contents of foo.
     ---------- Buffer: foo ----------

     (with-output-to-temp-buffer "foo"
         (print 20)
         (print standard-output))
     ⇒ #<buffer foo>
     ---------- Buffer: foo ----------
     20
     #<buffer foo>
     ---------- Buffer: foo ----------

Variable temp-buffer-show-function

If this variable is non-nil, with-output-to-temp-buffer calls it as a function to do the job of displaying a help buffer. The function gets one argument, which is the buffer it should display. In Emacs versions 18 and earlier, this variable was called temp-buffer-show-

hook.

Function momentary-string-display string position &optional char

message This function momentarily displays string in the current buffer at position. It has no effect on the undo list or on the buffer’s modification status. The momentary display remains until the next input event. If the next input event is char, momentary-string-display ignores it and returns. Otherwise, that event remains buffered for subsequent use as input. Thus, typing char will simply remove the string from the display, while typing (say) C-f will remove the string from the display and later (presumably) move point forward. The argument char is a space by default. The return value of momentary-string-display is not meaningful. If the string string does not contain control characters, you can do the same job in a more general way by creating an overlay with a before-string property. See Section 35.9.1 [Overlay Properties], page 575. If message is non-nil, it is displayed in the echo area while string is displayed in the buffer. If it is nil, a default message says to type char to continue. In this example, point is initially located at the beginning of the second line:

     ---------- Buffer: foo ----------
     This is the contents of foo.
     ⋆Second line.
     ---------- Buffer: foo ----------
     (momentary-string-display
       "**** Important Message! ****"
       (point) ?\r
       "Type RET when done reading")
     ⇒ t

---------- Buffer: foo ----------
This is the contents of foo.
**** Important Message! ****Second line.
---------- Buffer: foo ----------
---------- Echo Area ----------
Type RET when done reading
---------- Echo Area ----------

35.9 Overlays

You can use overlays to alter the appearance of a buffer’s text on the screen, for the sake of presentation features. An overlay is an object that belongs to a particular buffer, and has a specified beginning and end. It also has properties that you can examine and set; these affect the display of the text within the overlay.

35.9.1 Overlay Properties

Overlay properties are like text properties in some respects, but the differences are more important than the similarities. Text properties are considered a part of the text; overlays are specifically considered not to be part of the text. Thus, copying text between various buffers and strings preserves text properties, but does not try to preserve overlays. Changing a buffer’s text properties marks the buffer as modified, while moving an overlay or changing its properties does not. Unlike text propery changes, overlay changes are not recorded in the buffer’s undo list.

priority This property’s value (which should be a nonnegative number) determines the priority of the overlay. The priority matters when two or more overlays cover the same character and both specify a face for display; the one whose priority value is larger takes priority over the other, and its face attributes override the face attributes of the lower priority overlay. Currently, all overlays take priority over text properties. Please avoid using negative priority values, as we have not yet decided just what they should mean.

window If the window property is non-nil, then the overlay applies only on that window.

category If an overlay has a category property, we call it the category of the overlay. It should be a symbol. The properties of the symbol serve as defaults for the properties of the overlay.

face This property controls the font and color of text. Its value is a face name or a list of face names. See Section 35.10 [Faces], page 578, for more information. This feature may be temporary; in the future, we may replace it with other ways of specifying how to display text.

mouse-face

This property is used instead of face when the mouse is within the range of the overlay. This feature may be temporary, like face.

modification-hooks

This property’s value is a list of functions to be called if any character within the overlay is changed or if text is inserted strictly within the overlay. The hook functions are called both before and after each change. If the functions save the information they receive, and compare notes between calls, they can determine exactly what change has been made in the buffer text. When called before a change, each function receives four arguments: the overlay, nil, and the beginning and end of the text range to be modified. When called after a change, each function receives five arguments: the overlay, t, the beginning and end of the text range just modified, and the length of the pre-change text replaced by that range. (For an insertion, the pre-change length is zero; for a deletion, that length is the number of characters deleted, and the post-change beginning and end are equal.)

insert-in-front-hooks

This property’s value is a list of functions to be called before and after inserting text right at the beginning of the overlay. The calling conventions are the same

as for the modification-hooks functions.
insert-behind-hooks

This property’s value is a list of functions to be called before and after inserting text right at the end of the overlay. The calling conventions are the same as for

the modification-hooks functions.
invisible

The invisible property can make the text in the overlay invisible, which means that it does not appear on the screen. See Section 35.5 [Invisible Text], page 570, for details.

before-string

This property’s value is a string to add to the display at the beginning of the overlay. The string does not appear in the buffer in any sense—only on the screen. The string should contain only characters that display as a single column—control characters, including tabs or newlines, will give strange results.

after-string

This property’s value is a string to add to the display at the end of the overlay. The string does not appear in the buffer in any sense—only on the screen. The string should contain only characters that display as a single column—control characters, including tabs or newlines, will give strange results.

evaporate

If this property is non-nil, the overlay is deleted automatically if it ever becomes empty (i.e., if it spans no characters).

local-map

If this property is non-nil, it specifies a keymap for a portion of the text. The property’s value replaces the buffer’s local map, when the character after point is within the overlay. See Section 19.6 [Active Keymaps], page 281.

These are the functions for reading and writing the properties of an overlay.

Function overlay-get overlay prop

This function returns the value of property prop recorded in overlay, if any. If overlay does not record any value for that property, but it does have a category property which is a symbol, that symbol’s prop property is used. Otherwise, the value is nil.

Function overlay-put overlay prop value This function sets the value of property prop recorded in overlay to value. It returns value.

See also the function get-char-property which checks both overlay properties and text properties for a given character. See Section 29.18.1 [Examining Properties], page 478.

35.9.2 Managing Overlays

This section describes the functions to create, delete and move overlays, and to examine their contents.

Function make-overlay start end &optional buffer This function creates and returns an overlay that belongs to buffer and ranges from start to end. Both start and end must specify buffer positions; they may be integers or markers. If buffer is omitted, the overlay is created in the current buffer.

Function overlay-start overlay

This function returns the position at which overlay starts.

Function overlay-end overlay

This function returns the position at which overlay ends.

Function overlay-buffer overlay

This function returns the buffer that overlay belongs to.

Function delete-overlay overlay

This function deletes overlay. The overlay continues to exist as a Lisp object, but ceases to be part of the buffer it belonged to, and ceases to have any effect on display.

Function move-overlay overlay start end &optional buffer This function moves overlay to buffer, and places its bounds at start and end. Both arguments start and end must specify buffer positions; they may be integers or markers. If buffer is omitted, the overlay stays in the same buffer. The return value is overlay. This is the only valid way to change the endpoints of an overlay. Do not try modifying the markers in the overlay by hand, as that fails to update other vital data structures and can cause some overlays to be “lost”.

Function overlays-at pos

This function returns a list of all the overlays that contain position pos in the current buffer. The list is in no particular order. An overlay contains position pos if it begins at or before pos, and ends after pos.

Function next-overlay-change pos

This function returns the buffer position of the next beginning or end of an overlay, after pos.

Function previous-overlay-change pos

This function returns the buffer position of the previous beginning or end of an overlay, before pos.

35.10 Faces

A face is a named collection of graphical attributes: font, foreground color, background color and optional underlining. Faces control the display of text on the screen.

Each face has its own face id number which distinguishes faces at low levels within Emacs. However, for most purposes, you can refer to faces in Lisp programs by their names.

Function facep object This function returns t if object is a face name symbol (or if it is a vector of the kind used internally to record face data). It returns nil otherwise.

Each face name is meaningful for all frames, and by default it has the same meaning in all frames. But you can arrange to give a particular face name a special meaning in one frame if you wish.

35.10.1 Standard Faces

This table lists all the standard faces and their uses.

default This face is used for ordinary text.

modeline This face is used for mode lines and menu bars.

region This face is used for highlighting the region in Transient Mark mode.

secondary-selection

This face is used to show any secondary selection you have made.

highlight

This face is meant to be used for highlighting for various purposes.

underline

This face underlines text.

bold This face uses a bold font, if possible. It uses the bold variant of the frame’s font, if it has one. It’s up to you to choose a default font that has a bold variant, if you want to use one.

italic This face uses the italic variant of the frame’s font, if it has one.

bold-italic

This face uses the bold italic variant of the frame’s font, if it has one.

35.10.2 Merging Faces for Display

Here are all the ways to specify which face to use for display of text:

• With defaults. Each frame has a default face, whose id number is zero, which is used for all text that doesn’t somehow specify another face.

• With text properties. A character may have a face property; if so, it is displayed with that face. See Section 29.18.4 [Special Properties], page 482. If the character has a mouse-face property, that is used instead of the face property when the mouse is “near enough” to the character.

• With overlays. An overlay may have face and mouse-face properties too; they apply to all the text covered by the overlay.

• With a region that is active. In Transient Mark mode, the region is highlighted with a particular face (see region-face, below).

• With special glyphs. Each glyph can specify a particular face id number. See Section 35.14.3 [Glyphs], page 585.

If these various sources together specify more than one face for a particular character, Emacs merges the attributes of the various faces specified. The attributes of the faces of special glyphs come first; then comes the face for region highlighting, if appropriate; then come attributes of faces from overlays, followed by those from text properties, and last the default face.

When multiple overlays cover one character, an overlay with higher priority overrides those with lower priority. See Section 35.9 [Overlays], page 575.

If an attribute such as the font or a color is not specified in any of the above ways, the frame’s own font or color is used.

35.10.3 Functions for Working with Faces

The attributes a face can specify include the font, the foreground color, the background color, and underlining. The face can also leave these unspecified by giving the value nil for them.

Here are the primitives for creating and changing faces.

Function make-face name

This function defines a new face named name, initially with all attributes nil.

It does nothing if there is already a face named name.

Function face-list

This function returns a list of all defined face names.

Function copy-face old-face new-name &optional frame new-frame This function defines the face new-name as a copy of the existing face named old-face. It creates the face new-name if that doesn’t already exist. If the optional argument frame is given, this function applies only to that frame. Otherwise it applies to each frame individually, copying attributes from old-face in each frame to new-face in the same frame.

If the optional argument new-frame is given, then copy-face copies the attributes of old-face in frame to new-name in new-frame.

You can modify the attributes of an existing face with the following functions. If you specify frame, they affect just that frame; otherwise, they affect all frames as well as the defaults that apply to new frames.

Function set-face-foreground face color &optional frame Function set-face-background face color &optional frame

These functions set the foreground (or background, respectively) color of face face to color. The argument color should be a string, the name of a color. Certain shades of gray are implemented by stipple patterns on black-and-white screens.

Function set-face-stipple face pattern &optional frame This function sets the background stipple pattern of face face to pattern. The argument pattern should be the name of a stipple pattern defined by the X server, or nil meaning don’t use stipple. Normally there is no need to pay attention to stipple patterns, because they are used automatically to handle certain shades of gray.

Function set-face-font face font &optional frame This function sets the font of face face. The argument font should be a string.

Function set-face-underline-p face underline-p &optional frame This function sets the underline attribute of face face. Non-nil means do underline; nil means don’t.

Function invert-face face &optional frame Swap the foreground and background colors of face face. If the face doesn’t specify both foreground and background, then its foreground and background are set to the default background and foreground, respectively.

These functions examine the attributes of a face. If you don’t specify frame, they refer to the default data for new frames.

Function face-foreground face &optional frame Function face-background face &optional frame

These functions return the foreground color (or background color, respectively) of face face, as a string.

Function face-stipple face &optional frame This function returns the name of the background stipple pattern of face face, or nil if it doesn’t have one.

Function face-font face &optional frame This function returns the name of the font of face face.

Function face-underline-p face &optional frame This function returns the underline attribute of face face.

Function face-id face

This function returns the face id number of face face.

Function face-equal face1 face2 &optional frame This returns t if the faces face1 and face2 have the same attributes for display.

Function face-differs-from-default-p face &optional frame

This returns t if the face face displays differently from the default face. A face is considered to be “the same” as the normal face if each attribute is either the same as that of the default face or nil (meaning to inherit from the default).

Variable region-face

This variable’s value specifies the face id to use to display characters in the region when it is active (in Transient Mark mode only). The face thus specified takes precedence over all faces that come from text properties and overlays, for characters in the region. See Section 28.6 [The Mark], page 445, for more information about Transient Mark mode. Normally, the value is the id number of the face named region.

35.11 Blinking Parentheses

This section describes the mechanism by which Emacs shows a matching open parenthesis when the user inserts a close parenthesis.

Variable blink-paren-function

The value of this variable should be a function (of no arguments) to be called whenever a character with close parenthesis syntax is inserted. The value of blink-paren-function may be nil, in which case nothing is done.

Please note: This variable was named blink-paren-hook in older Emacs versions, but since it is not called with the standard convention for hooks, it was renamed to blink-paren-function in version 19.

Variable blink-matching-paren

If this variable is nil, then blink-matching-open does nothing.

Variable blink-matching-paren-distance

This variable specifies the maximum distance to scan for a matching parenthesis before giving up.

Variable blink-matching-paren-delay

This variable specifies the number of seconds for the cursor to remain at the matching parenthesis. A fraction of a second often gives good results, but the default is 1, which works on all systems.

Function blink-matching-open

This function is the default value of blink-paren-function. It assumes that point follows a character with close parenthesis syntax and moves the cursor momentarily to the matching opening character. If that character is not already on the screen, it displays the character’s context in the echo area. To avoid long delays, this function does not search farther than blink-matching-paren-distance characters.

Here is an example of calling this function explicitly.

     (defun interactive-blink-matching-open ()
       "Indicate momentarily the start of sexp before point."
       (interactive)
       (let ((blink-matching-paren-distance
              (buffer-size))
             (blink-matching-paren t))
         (blink-matching-open)))

35.12 Inverse Video

User Option inverse-video

This variable controls whether Emacs uses inverse video for all text on the screen. Non-nil means yes, nil means no. The default is nil.

User Option mode-line-inverse-video

This variable controls the use of inverse video for mode lines. If it is nonnil, then mode lines are displayed in inverse video. Otherwise, mode lines are displayed normally, just like text. The default is t.

For X window frames, this displays mode lines using the face named modeline, which is normally the inverse of the default face unless you change it.

35.13 Usual Display Conventions

The usual display conventions define how to display each character code. You can override these conventions by setting up a display table (see Section 35.14 [Display Tables], page 583). Here are the usual display conventions:

• Character codes 32 through 126 map to glyph codes 32 through 126. Normally this means they display as themselves.

• Character code 9 is a horizontal tab. It displays as whitespace up to a position deter-

mined by tab-width.

• Character code 10 is a newline.

• All other codes in the range 0 through 31, and code 127, display in one of two ways according to the value of ctl-arrow. If it is non-nil, these codes map to sequences of two glyphs, where the first glyph is the ASCII code for ‘^’. (A display table can specify a glyph to use instead of ‘^’.) Otherwise, these codes map just like the codes in the range 128 to 255.

• Character codes 128 through 255 map to sequences of four glyphs, where the first glyph is the ASCII code for ‘\’, and the others are digit characters representing the code in octal. (A display table can specify a glyph to use instead of ‘\’.)

The usual display conventions apply even when there is a display table, for any character whose entry in the active display table is nil. Thus, when you set up a display table, you need only specify the characters for which you want unusual behavior.

These variables affect the way certain characters are displayed on the screen. Since they change the number of columns the characters occupy, they also affect the indentation functions.

User Option ctl-arrow

This buffer-local variable controls how control characters are displayed. If it is non-nil, they are displayed as a caret followed by the character: ‘^A’. If it is nil, they are displayed as a backslash followed by three octal digits: ‘\001’.

Variable default-ctl-arrow

The value of this variable is the default value for ctl-arrow in buffers that do not override it. See Section 10.10.3 [Default Value], page 137.

User Option tab-width

The value of this variable is the spacing between tab stops used for displaying tab characters in Emacs buffers. The default is 8. Note that this feature is completely independent from the user-settable tab stops used by the command tab-to-tab-stop. See Section 29.16.5 [Indent Tabs], page 475.

35.14 Display Tables

You can use the display table feature to control how all 256 possible character codes display on the screen. This is useful for displaying European languages that have letters not in the ASCII character set.

The display table maps each character code into a sequence of glyphs, each glyph being an image that takes up one character position on the screen. You can also define how to display each glyph on your terminal, using the glyph table.

35.14.1 Display Table Format

A display table is actually an array of 262 elements.

Function make-display-table

This creates and returns a display table. The table initially has nil in all elements.

The first 256 elements correspond to character codes; the nth element says how to display the character code n. The value should be nil or a vector of glyph values (see Section 35.14.3 [Glyphs], page 585). If an element is nil, it says to display that character according to the usual display conventions (see Section 35.13 [Usual Display], page 582).

If you use the display table to change the display of newline characters, the whole buffer will be displayed as one long “line.”

The remaining six elements of a display table serve special purposes, and nil means use the default stated below.

256 The glyph for the end of a truncated screen line (the default for this is ‘$’). See Section 35.14.3 [Glyphs], page 585.

257 The glyph for the end of a continued line (the default is ‘\’).

258 The glyph for indicating a character displayed as an octal character code (the default is ‘\’).

259 The glyph for indicating a control character (the default is ‘^’).

260 A vector of glyphs for indicating the presence of invisible lines (the default is ‘...’). See Section 35.6 [Selective Display], page 571.

261 The glyph used to draw the border between side-by-side windows (the default is ‘|’). See Section 25.2 [Splitting Windows], page 384.

For example, here is how to construct a display table that mimics the effect of setting ctl-arrow to a non-nil value:

(setq disptab (make-display-table))
(let ((i 0))
  (while (< i 32)
    (or (= i ?\t) (= i ?\n)
        (aset disptab i (vector ?^(+ i 64))))
    (setq i (1+ i)))
  (aset disptab 127 (vector ?^??)))

35.14.2 Active Display Table

Each window can specify a display table, and so can each buffer. When a buffer b is displayed in window w, display uses the display table for window w if it has one; otherwise, the display table for buffer b if it has one; otherwise, the standard display table if any. The display table chosen is called the active display table.

Function window-display-table window

This function returns window’s display table, or nil if window does not have an assigned display table.

Function set-window-display-table window table

This function sets the display table of window to table. The argument table should be either a display table or nil.

Variable buffer-display-table

This variable is automatically local in all buffers; its value in a particular buffer is the display table for that buffer, or nil if the buffer does not have an assigned display table.

Variable standard-display-table

This variable’s value is the default display table, used whenever a window has no display table and neither does the buffer displayed in that window. This variable is nil by default.

If there is no display table to use for a particular window—that is, if the window has none, its buffer has none, and standard-display-table has none—then Emacs uses the usual display conventions for all character codes in that window. See Section 35.13 [Usual Display], page 582.

35.14.3 Glyphs

A glyph is a generalization of a character; it stands for an image that takes up a single character position on the screen. Glyphs are represented in Lisp as integers, just as characters are.

The meaning of each integer, as a glyph, is defined by the glyph table, which is the value of the variable glyph-table.

Variable glyph-table

The value of this variable is the current glyph table. It should be a vector; the gth element defines glyph code g. If the value is nil instead of a vector, then all glyphs are simple (see below).

Here are the possible types of elements in the glyph table:

string Send the characters in string to the terminal to output this glyph. This alternative is available on character terminals, but not under X.

integer Define this glyph code as an alias for code integer. You can use an alias to specify a face code for the glyph; see below.

nil This glyph is simple. On an ordinary terminal, the glyph code mod 256 is the character to output. With X, the glyph code mod 256 is the character to output, and the glyph code divided by 256 specifies the face id number to use while outputting it. See Section 35.10 [Faces], page 578.

If a glyph code is greater than or equal to the length of the glyph table, that code is automatically simple.

35.14.4 ISO Latin 1

If you have a terminal that can handle the entire ISO Latin 1 character set, you can arrange to use that character set as follows:

     (require 'disp-table)

;; Set char codes 160–255 to display as themselves.

;; (Codes 128–159 are the additional control characters.)

     (standard-display-8bit 160 255)

If you are editing buffers written in the ISO Latin 1 character set and your terminal doesn’t handle anything but ASCII, you can load the file ‘iso-ascii’ to set up a display table that displays the other ISO characters as explanatory sequences of ASCII characters. For example, the character “o with umlaut” displays as ‘{"o}’.

Some European countries have terminals that don’t support ISO Latin 1 but do support the special characters for that country’s language. You can define a display table to work one language using such terminals. For an example, see ‘lisp/iso-swed.el’, which handles certain Swedish terminals.

You can load the appropriate display table for your terminal automatically by writing a terminal-specific Lisp file for the terminal type.

35.15 Beeping

You can make Emacs ring a bell (or blink the screen) to attract the user’s attention. Be conservative about how often you do this; frequent bells can become irritating. Also be careful not to use beeping alone when signaling an error is appropriate. (See Section 9.5.3 [Errors], page 112.)

Function ding &optional dont-terminate This function beeps, or flashes the screen (see visible-bell below). It also terminates any keyboard macro currently executing unless dont-terminate is non-nil.

Function beep &optional dont-terminate This is a synonym for ding.

Variable visible-bell

This variable determines whether Emacs should flash the screen to represent a bell. Non-nil means yes, nil means no. This is effective under X windows, and on a character-only terminal provided the terminal’s Termcap entry defines the visible bell capability (‘vb’).

35.16 Window Systems

Emacs works with several window systems, most notably the X Window System. Both Emacs and X use the term “window”, but use it differently. An Emacs frame is a single window as far as X is concerned; the individual Emacs windows are not known to X at all.

Variable window-system

This variable tells Lisp programs what window system Emacs is running under. Its value should be a symbol such as x (if Emacs is running under X) or nil (if Emacs is running on an ordinary terminal).

Variable window-setup-hook

This variable is a normal hook which Emacs runs after loading your ‘.emacs’ file and the default initialization file (if any), after loading terminal-specific Lisp code, and after running the hook term-setup-hook. This hook is used for internal purposes: setting up communication with the window system, and creating the initial window. Users should not interfere with it.

36 Customizing the Calendar and Diary

There are many customizations that you can use to make the calendar and diary suit your personal tastes.

36.1 Customizing the Calendar

If you set the variable view-diary-entries-initially to t, calling up the calendar automatically displays the diary entries for the current date as well. The diary dates appear only if the current date is visible. If you add both of the following lines to your ‘.emacs’ file:

     (setq view-diary-entries-initially t)
     (calendar)

this displays both the calendar and diary windows whenever you start Emacs.

Similarly, if you set the variable view-calendar-holidays-initially to t, entering the calendar automatically displays a list of holidays for the current three-month period. The holiday list appears in a separate window.

You can set the variable mark-diary-entries-in-calendar to t in order to mark any dates with diary entries. This takes effect whenever the calendar window contents are recomputed. There are two ways of marking these dates: by changing the face (see Section 35.10 [Faces], page 578), if the display supports that, or by placing a plus sign (‘+’) beside the date otherwise.

Similarly, setting the variable mark-holidays-in-calendar to t marks holiday dates, either with a change of face or with an asterisk (‘*’).

The variable calendar-holiday-marker specifies how to mark a date as being a holiday. Its value may be a character to insert next to the date, or a face name to use for displaying the date. Likewise, the variable diary-entry-marker specifies how to mark a date that has diary entries. The calendar creates faces named holiday-face and diary-face for these purposes; those symbols are the default values of these variables, when Emacs supports multiple faces on your terminal.

The variable calendar-load-hook is a normal hook run when the calendar package is first loaded (before actually starting to display the calendar).

Starting the calendar runs the normal hook initial-calendar-window-hook. Recomputation of the calendar display does not run this hook. But if you leave the calendar with the q command and reenter it, the hook runs again.

The variable today-visible-calendar-hook is a normal hook run after the calendar buffer has been prepared with the calendar when the current date is visible in the window. One use of this hook is to replace today’s date with asterisks; to do that, use the hook

function calendar-star-date.
     (add-hook 'today-visible-calendar-hook 'calendar-star-date)

Another standard hook function marks the current date, either by changing its face or by adding an asterisk. Here’s how to use it:

     (add-hook 'today-visible-calendar-hook 'calendar-mark-today)

The variable calendar-today-marker specifies how to mark today’s date. Its value should be a character to insert next to the date or a face name to use for displaying the date. A face named calendar-today-face is provided for this purpose; that symbol is the default for this variable when Emacs supports multiple faces on your terminal. A similar normal hook, today-invisible-calendar-hook is run if the current date is not visible in the window.

36.2 Customizing the Holidays

Emacs knows about holidays defined by entries on one of several lists. You can customize these lists of holidays to your own needs, adding or deleting holidays. The lists of holidays that Emacs uses are for general holidays (general-holidays), local holidays (local-holidays), Christian holidays (christian-holidays), Hebrew (Jewish) holidays (hebrew-holidays), Islamic (Moslem) holidays (islamic-holidays), and other holidays

(other-holidays).

The general holidays are, by default, holidays common throughout the United States. To eliminate these holidays, set general-holidays to nil.

There are no default local holidays (but sites may supply some). You can set the variable local-holidays to any list of holidays, as described below.

By default, Emacs does not include all the holidays of the religions that it knows, only those commonly found in secular calendars. For a more extensive collection of religious holidays, you can set any (or all) of the variables all-christian-calendar-holidays,

all-hebrew-calendar-holidays, or all-islamic-calendar-holidays to t. If you want

to eliminate the religious holidays, set any or all of the corresponding variables christian-

holidays, hebrew-holidays, and islamic-holidays to nil.

You can set the variable other-holidays to any list of holidays. This list, normally empty, is intended for individual use.

   Each of the lists (general-holidays, local-holidays, christian-holidays, hebrew-

holidays, islamic-holidays, and other-holidays) is a list of holiday forms, each holiday form describing a holiday (or sometimes a list of holidays).

Here is a table of the possible kinds of holiday form. Day numbers and month numbers count starting from 1, but “dayname” numbers count Sunday as 0. The element string is always the name of the holiday, as a string.

(holiday-fixed month day string)

A fixed date on the Gregorian calendar.

(holiday-float month dayname k string)

The kth dayname in month on the Gregorian calendar (dayname=0 for Sunday, and so on); negative k means count back from the end of the month.

(holiday-hebrew month day string)

A fixed date on the Hebrew calendar.

(holiday-islamic month day string)

A fixed date on the Islamic calendar.

(holiday-julian month day string)

A fixed date on the Julian calendar.

(holiday-sexp sexp string)

A date calculated by the Lisp expression sexp. The expression should use the variable year to compute and return the date of a holiday, or nil if the holiday doesn’t happen this year. The value of sexp must represent the date as a list of the form (month day year).

(if condition holiday-form)

A holiday that happens only if condition is true.

(function [args])

A list of dates calculated by the function function, called with arguments args.

For example, suppose you want to add Bastille Day, celebrated in France on July 14. You can do this as follows:

     (setq other-holidays '((holiday-fixed 7 14 "Bastille Day")))

The holiday form (holiday-fixed 7 14 "Bastille Day") specifies the fourteenth day of the seventh month (July).

Many holidays occur on a specific day of the week, at a specific time of month. Here is a holiday form describing Hurricane Supplication Day, celebrated in the Virgin Islands on the fourth Monday in August:

     (holiday-float 8 1 4 "Hurricane Supplication Day")

Here the 8 specifies August, the 1 specifies Monday (Sunday is 0, Tuesday is 2, and so on), and the 4 specifies the fourth occurrence in the month (1 specifies the first occurrence, 2 the second occurrence, −1 the last occurrence, −2 the second-to-last occurrence, and so on).

You can specify holidays that occur on fixed days of the Hebrew, Islamic, and Julian calendars too. For example,

     (setq other-holidays
           '((holiday-hebrew 10 2 "Last day of Hanukkah")
             (holiday-islamic 3 12 "Mohammed's Birthday")
             (holiday-julian 4 2 "Jefferson's Birthday")))

adds the last day of Hanukkah (since the Hebrew months are numbered with 1 starting from Nisan), the Islamic feast celebrating Mohammed’s birthday (since the Islamic months are numbered from 1 starting with Muharram), and Thomas Jefferson’s birthday, which is 2 April 1743 on the Julian calendar.

To include a holiday conditionally, use either Emacs Lisp’s if or the holiday-sexp form. For example, American presidential elections occur on the first Tuesday after the first Monday in November of years divisible by 4:

     (holiday-sexp (if (= 0 (% year 4))
                        (calendar-gregorian-from-absolute
                         (1+ (calendar-dayname-on-or-before
                               1 (+ 6 (calendar-absolute-from-gregorian
                                       (list 11 1 year))))))
                   "US Presidential Election"))

or

     (if (= 0 (% displayed-year 4))
         (fixed 11
                (extract-calendar-day
                  (calendar-gregorian-from-absolute
                    (1+ (calendar-dayname-on-or-before
                          1 (+ 6 (calendar-absolute-from-gregorian
                                   (list 11 1 displayed-year)))))))
                "US Presidential Election"))

Some holidays just don’t fit into any of these forms because special calculations are involved in their determination. In such cases you must write a Lisp function to do the calculation. To include eclipses, for example, add (eclipses) to other-holidays and write an Emacs Lisp function eclipses that returns a (possibly empty) list of the relevant Gregorian dates among the range visible in the calendar window, with descriptive strings, like this:

     (((6 27 1991) "Lunar Eclipse") ((7 11 1991) "Solar Eclipse") ... )

36.3 Date Display Format

You can customize the manner of displaying dates in the diary, in mode lines, and in messages by setting calendar-date-display-form. This variable holds a list of expressions that can involve the variables month, day, and year, which are all numbers in string form, and monthname and dayname, which are both alphabetic strings. In the American style, the default value of this list is as follows:

     ((if dayname (concat dayname ", ")) monthname " " day ", " year)

while in the European style this value is the default:

     ((if dayname (concat dayname ", ")) day " " monthname " " year)

The ISO standard date representation is this:

     (year "-" month "-" day)

This specifies a typical American format:

     (month "/" day "/" (substring year -2))

36.4 Time Display Format

The calendar and diary by default display times of day in the conventional American style with the hours from 1 through 12, minutes, and either ‘am’ or ‘pm’. If you prefer the European style, also known in the US as military, in which the hours go from 00 to 23, you can alter the variable calendar-time-display-form. This variable is a list of expressions that can involve the variables 12-hours, 24-hours, and minutes, which are all numbers in string form, and am-pm and time-zone, which are both alphabetic strings. The default

value of calendar-time-display-form is as follows:
     (12-hours ":" minutes am-pm
               (if time-zone " (") time-zone (if time-zone ")"))

Here is a value that provides European style times:

     (24-hours ":" minutes
               (if time-zone " (") time-zone (if time-zone ")"))

36.5 Daylight Savings Time

Emacs understands the difference between standard time and daylight savings time—the times given for sunrise, sunset, solstices, equinoxes, and the phases of the moon take that into account. The rules for daylight savings time vary from place to place and have also varied historically from year to year. To do the job properly, Emacs needs to know which rules to use.

Some operating systems keep track of the rules that apply to the place where you are; on these systems, Emacs gets the information it needs from the system automatically. If some or all of this information is missing, Emacs fills in the gaps with the rules currently used in Cambridge, Massachusetts, which is the center of GNU’s world.

If the default choice of rules is not appropriate for your location, you can tell Emacs the

rules to use by setting the variables calendar-daylight-savings-starts and calendar-

daylight-savings-ends. Their values should be Lisp expressions that refer to the variable year, and evaluate to the Gregorian date on which daylight savings time starts or (respectively) ends, in the form of a list (month day year). The values should be nil if your area does not use daylight savings time.

Emacs uses these expressions to determine the start and end dates of daylight savings time as holidays and for correcting times of day in the solar and lunar calculations.

The values for Cambridge, Massachusetts are as follows:

     (calendar-nth-named-day 1 0 4 year)
     (calendar-nth-named-day -1 0 10 year)

i.e., the first 0th day (Sunday) of the fourth month (April) in the year specified by year, and the last Sunday of the tenth month (October) of that year. If daylight savings time were changed to start on October 1, you would set calendar-daylight-savings-starts to this:

     (list 10 1 year)

For a more complex example, suppose daylight savings time begins on the first of Nisan on the Hebrew calendar. You should set calendar-daylight-savings-starts to this value:

     (calendar-gregorian-from-absolute
       (calendar-absolute-from-hebrew
         (list 1 1 (+ year 3760))))

because Nisan is the first month in the Hebrew calendar and the Hebrew year differs from the Gregorian year by 3760 at Nisan.

If there is no daylight savings time at your location, or if you want all times in standard

time, set calendar-daylight-savings-starts and calendar-daylight-savings-ends
to nil.

The variable calendar-daylight-time-offset specifies the difference between daylight savings time and standard time, measured in minutes. The value for Cambridge is 60.

   The variable calendar-daylight-savings-starts-time and the variable calendar-

daylight-savings-ends-time specify the number of minutes after midnight local time when the transition to and from daylight savings time should occur. For Cambridge, both variables’ values are 120.

36.6 Customizing the Diary

Ordinarily, the mode line of the diary buffer window indicates any holidays that fall on the date of the diary entries. The process of checking for holidays can take several seconds, so including holiday information delays the display of the diary buffer noticeably. If you’d prefer to have a faster display of the diary buffer but without the holiday information, set

the variable holidays-in-diary-buffer to nil.

The variable number-of-diary-entries controls the number of days of diary entries to be displayed at one time. It affects the initial display when view-diary-entries-initially is t, as well as the command M-x diary. For example, the default value is 1, which says to display only the current day’s diary entries. If the value is 2, both the current day’s and the next day’s entries are displayed. The value can also be a vector of seven elements: for example, if the value is [0 2 2 2 2 4 1] then no diary entries appear on Sunday, the current date’s and the next day’s diary entries appear Monday through Thursday, Friday through Monday’s entries appear on Friday, while on Saturday only that day’s entries appear.

The variable print-diary-entries-hook is a normal hook run after preparation of a temporary buffer containing just the diary entries currently visible in the diary buffer. (The other, irrelevant diary entries are really absent from the temporary buffer; in the diary buffer, they are merely hidden.) The default value of this hook does the printing with the command lpr-buffer. If you want to use a different command to do the printing, just change the value of this hook. Other uses might include, for example, rearranging the lines into order by day and time.

You can customize the form of dates in your diary file, if neither the standard American nor European styles suits your needs, by setting the variable diary-date-forms. This variable is a list of patterns for recognizing a date. Each date pattern is a list whose elements may be regular expressions (see Section 30.2 [Regular Expressions], page 492) or the symbols month, day, year, monthname, and dayname. All these elements serve as patterns that match certain kinds of text in the diary file. In order for the date pattern, as a whole, to match, all of its elements must match consecutively.

A regular expression in a date pattern matches in its usual fashion, using the standard syntax table altered so that ‘*’ is a word constituent.

The symbols month, day, year, monthname, and dayname match the month number, day number, year number, month name, and day name of the date being considered. The symbols that match numbers allow leading zeros; those that match names allow three-letter abbreviations and capitalization. All the symbols can match ‘*’; since ‘*’ in a diary entry means “any day”, “any month”, and so on, it should match regardless of the date being considered.

The default value of diary-date-forms in the American style is this:

     ((month "/" day "[^/0-9]")
      (month "/" day "/" year "[^0-9]")
      (monthname " *" day "[^,0-9]")
      (monthname " *" day ", *" year "[^0-9]")
      (dayname "\\W"))

The date patterns in the list must be mutually exclusive and must not match any portion of the diary entry itself, just the date and one character of whitespace. If, to be mutually exclusive, the pattern must match a portion of the diary entry text—beyond the whitespace that ends the date—then the first element of the date pattern must be backup. This causes the date recognizer to back up to the beginning of the current word of the diary entry, after finishing the match. Even if you use backup, the date pattern must absolutely not match more than a portion of the first word of the diary entry. The default value of diary-date-forms in the European style is this list:

     ((day "/" month "[^/0-9]")
      (day "/" month "/" year "[^0-9]")
      (backup day " *" monthname "\\W+\\<[^*0-9]")
      (day " *" monthname " *" year "[^0-9]")
      (dayname "\\W"))

Notice the use of backup in the third pattern, because it needs to match part of a word beyond the date itself to distinguish it from the fourth pattern.

36.7 Hebrew- and Islamic-Date Diary Entries

Your diary file can have entries based on Hebrew or Islamic dates, as well as entries based on the world-standard Gregorian calendar. However, because recognition of such entries is time-consuming and most people don’t use them, you must explicitly enable their use. If you want the diary to recognize Hebrew-date diary entries, for example, you must do this:

     (add-hook 'nongregorian-diary-listing-hook 'list-hebrew-diary-entries)
     (add-hook 'nongregorian-diary-marking-hook 'mark-hebrew-diary-entries)

If you want Islamic-date entries, do this:

     (add-hook 'nongregorian-diary-listing-hook 'list-islamic-diary-entries)
     (add-hook 'nongregorian-diary-marking-hook 'mark-islamic-diary-entries)

Hebrew- and Islamic-date diary entries have the same formats as Gregorian-date diary entries, except that ‘H’ precedes a Hebrew date and ‘I’ precedes an Islamic date. Moreover, because the Hebrew and Islamic month names are not uniquely specified by the first three letters, you may not abbreviate them. For example, a diary entry for the Hebrew date Heshvan 25 could look like this:

     HHeshvan 25 Happy Hebrew birthday!

and would appear in the diary for any date that corresponds to Heshvan 25 on the Hebrew calendar. And here is Islamic-date diary entry that matches Dhu al-Qada 25:

     IDhu al-Qada 25 Happy Islamic birthday!

As with Gregorian-date diary entries, Hebrew- and Islamic-date entries are nonmarking if they are preceded with an ampersand (‘&’).

Here is a table of commands used in the calendar to create diary entries that match the selected date and other dates that are similar in the Hebrew or Islamic calendar:

i h d Add a diary entry for the Hebrew date corresponding to the selected date

          (insert-hebrew-diary-entry).

i h m Add a diary entry for the day of the Hebrew month corresponding to the selected

          date (insert-monthly-hebrew-diary-entry). This diary entry matches any

date that has the same Hebrew day-within-month as the selected date.

i h y Add a diary entry for the day of the Hebrew year corresponding to the selected

          date (insert-yearly-hebrew-diary-entry). This diary entry matches any

date which has the same Hebrew month and day-within-month as the selected date.

i i d Add a diary entry for the Islamic date corresponding to the selected date

          (insert-islamic-diary-entry).

i i m Add a diary entry for the day of the Islamic month corresponding to the selected

          date (insert-monthly-islamic-diary-entry).

i i y Add a diary entry for the day of the Islamic year corresponding to the selected

          date (insert-yearly-islamic-diary-entry).

These commands work much like the corresponding commands for ordinary diary entries: they apply to the date that point is on in the calendar window, and what they do is insert just the date portion of a diary entry at the end of your diary file. You must then insert the rest of the diary entry.

36.8 Fancy Diary Display

Diary display works by preparing the diary buffer and then running the hook diarydisplay-hook. The default value of this hook (simple-diary-display) hides the irrelevant diary entries and then displays the buffer. However, if you specify the hook as follows,

     (add-hook 'diary-display-hook 'fancy-diary-display)

this enables fancy diary display. It displays diary entries and holidays by copying them into a special buffer that exists only for the sake of display. Copying to a separate buffer provides an opportunity to change the displayed text to make it prettier—for example, to sort the entries by the dates they apply to.

As with simple diary display, you can print a hard copy of the buffer with print-diary-entries. To print a hard copy of a day-by-day diary for a week by positioning point on Sunday of that week, type 7 d and then do M-x print-diary-entries. As usual, the inclusion of the holidays slows down the display slightly; you can speed things up by setting

the variable holidays-in-diary-buffer to nil.

Ordinarily, the fancy diary buffer does not show days for which there are no diary entries, even if that day is a holiday. If you want such days to be shown in the fancy diary buffer,

set the variable diary-list-include-blanks to t.

If you use the fancy diary display, you can use the normal hook list-diary-entries-hook to sort each day’s diary entries by their time of day. Here’s how

     (add-hook 'list-diary-entries-hook 'sort-diary-entries t)

For each day, this sorts diary entries that begin with a recognizable time of day according to their times. Diary entries without times come first within each day.

Fancy diary display also has the ability to process included diary files. This permits a group of people to share a diary file for events that apply to all of them. Lines in the diary file of this form:

     #include "filename"

includes the diary entries from the file filename in the fancy diary buffer. The include mechanism is recursive, so that included files can include other files, and so on; you must be careful not to have a cycle of inclusions, of course. Here is how to enable the include facility:

     (add-hook 'list-diary-entries-hook 'include-other-diary-files)
     (add-hook 'mark-diary-entries-hook 'mark-included-diary-files)

The include mechanism works only with the fancy diary display, because ordinary diary display shows the entries directly from your diary file.

36.9 Sexp Entries and the Fancy Diary Display

Sexp diary entries allow you to do more than just have complicated conditions under which a diary entry applies. If you use the fancy diary display, sexp entries can generate the text of the entry depending on the date itself. For example, an anniversary diary entry can insert the number of years since the anniversary date into the text of the diary entry. Thus the ‘%d’ in this dairy entry:

     %%(diary-anniversary 10 31 1948) Arthur's birthday (%d years old)

gets replaced by the age, so on October 31, 1990 the entry appears in the fancy diary buffer like this:

     Arthur's birthday (42 years old)

If the diary file instead contains this entry:

     %%(diary-anniversary 10 31 1948) Arthur's %d%s birthday

the entry in the fancy diary buffer for October 31, 1990 appears like this:

     Arthur's 42nd birthday

Similarly, cyclic diary entries can interpolate the number of repetitions that have occurred:

     %%(diary-cyclic 50 1 1 1990) Renew medication (%d%s time)

looks like this:

     Renew medication (5th time)

in the fancy diary display on September 8, 1990.

The generality of sexp diary entries lets you specify any diary entry that you can describe algorithmically. A sexp diary entry contains an expression that computes whether the entry applies to any given date. If its value is non-nil, the entry applies to that date; otherwise, it does not. The expression can use the variable date to find the date being considered; its value is a list (month day year) that refers to the Gregorian calendar.

Suppose you get paid on the 21st of the month if it is a weekday, and on the Friday before if the 21st is on a weekend. Here is how to write a sexp diary entry that matches those dates:

     &%%(let ((dayname (calendar-day-of-week date))
              (day (car (cdr date))))
           (or (and (= day 21) (memq dayname '(1 2 3 4 5)))
               (and (memq day '(19 20)) (= dayname 5)))
              ) Pay check deposited

The following sexp diary entries take advantage of the ability (in the fancy diary display) to concoct diary entries whose text varies based on the date:

%%(diary-sunrise-sunset)

Make a diary entry for the local times of today’s sunrise and sunset.

%%(diary-phases-of-moon)

Make a diary entry for the phases (quarters) of the moon.

%%(diary-day-of-year)

Make a diary entry with today’s day number in the current year and the number of days remaining in the current year.

%%(diary-iso-date)

Make a diary entry with today’s equivalent ISO commercial date.

%%(diary-julian-date)

Make a diary entry with today’s equivalent date on the Julian calendar.

%%(diary-astro-day-number)

Make a diary entry with today’s equivalent astronomical (Julian) day number.

%%(diary-hebrew-date)

Make a diary entry with today’s equivalent date on the Hebrew calendar.

%%(diary-islamic-date)

Make a diary entry with today’s equivalent date on the Islamic calendar.

%%(diary-french-date)

Make a diary entry with today’s equivalent date on the French Revolutionary calendar.

%%(diary-mayan-date)

Make a diary entry with today’s equivalent date on the Mayan calendar.

Thus including the diary entry

     &%%(diary-hebrew-date)

causes every day’s diary display to contain the equivalent date on the Hebrew calendar, if you are using the fancy diary display. (With simple diary display, the line ‘&%%(diary-hebrew-date)’ appears in the diary for any date, but does nothing particularly useful.)

These functions can be used to construct sexp diary entries based on the Hebrew calendar in certain standard ways:

%%(diary-rosh-hodesh)

Make a diary entry that tells the occurrence and ritual announcement of each new Hebrew month.

%%(diary-parasha)

Make a Saturday diary entry that tells the weekly synagogue scripture reading.

%%(diary-sabbath-candles)

Make a Friday diary entry that tells the local time of Sabbath candle lighting.

%%(diary-omer)

Make a diary entry that gives the omer count, when appropriate.

%%(diary-yahrzeit month day year) name

Make a diary entry marking the anniversary of a date of death. The date is the Gregorian (civil) date of death. The diary entry appears on the proper Hebrew calendar anniversary and on the day before. (In the European style, the order of the parameters is changed to day, month, year.)

36.10 Customizing Appointment Reminders

You can specify exactly how Emacs reminds you of an appointment, and how far in advance it begins doing so, by setting these variables:

appt-message-warning-time

The time in minutes before an appointment that the reminder begins. The default is 10 minutes.

appt-audible

If this is non-nil, Emacs rings the terminal bell for appointment reminders. The default is t.

appt-visible

If this is non-nil, Emacs displays the appointment message in the echo area. The default is t.

appt-display-mode-line

If this is non-nil, Emacs displays the number of minutes to the appointment on the mode line. The default is t.

appt-msg-window

If this is non-nil, Emacs displays the appointment message in another window. The default is t.

appt-disp-window-function

This variable holds a function to use to create the other window for the appointment message.

appt-delete-window-function

This variable holds a function to use to get rid of the appointment message window, when its time is up.

appt-display-duration

The number of seconds to display an appointment message. The default is 5 seconds.

598 GNU Emacs Lisp Reference Manual

Appendix A Tips and Standards

This chapter describes no additional features of Emacs Lisp. Instead it gives advice on making effective use of the features described in the previous chapters.

A.1 Writing Clean Lisp Programs

Here are some tips for avoiding common errors in writing Lisp code intended for widespread use:

• Since all global variables share the same name space, and all functions share another name space, you should choose a short word to distinguish your program from other Lisp programs. Then take care to begin the names of all global variables, constants, and functions with the chosen prefix. This helps avoid name conflicts. This recommendation applies even to names for traditional Lisp primitives that are not primitives in Emacs Lisp—even to cadr. Believe it or not, there is more than one plausible way to define cadr. Play it safe; append your name prefix to produce a name

like foo-cadr or mylib-cadr instead.

If you write a function that you think ought to be added to Emacs under a certain name, such as twiddle-files, don’t call it by that name in your program. Call it mylib-

twiddle-files in your program, and send mail to ‘bug-gnu-emacs@prep.ai.mit.edu’

suggesting we add it to Emacs. If and when we do, we can change the name easily enough. If one prefix is insufficient, your package may use two or three alternative common prefixes, so long as they make sense. Separate the prefix from the rest of the symbol name with a hyphen, ‘-’. This will be consistent with Emacs itself and with most Emacs Lisp programs.

• It is often useful to put a call to provide in each separate library program, at least if there is more than one entry point to the program.

• If a file requires certain other library programs to be loaded beforehand, then the comments at the beginning of the file should say so. Also, use require to make sure they are loaded.

• If one file foo uses a macro defined in another file bar, foo should contain this expression

before the first use of the macro:

     (eval-when-compile (require 'bar))

(And bar should contain (provide 'bar), to make the require work.) This will cause bar to be loaded when you byte-compile foo. Otherwise, you risk compiling foo without the necessary macro loaded, and that would produce compiled code that won’t work right. See Section 12.3 [Compiling Macros], page 154. Using eval-when-compile avoids loading bar when the compiled version of foo is used.

• If you define a major mode, make sure to run a hook variable using run-hooks, just as the existing major modes do. See Section 20.4 [Hooks], page 316.

• If the purpose of a function is to tell you whether a certain condition is true or false, give the function a name that ends in ‘p’. If the name is one word, add just ‘p’; if the name is multiple words, add ‘-p’. Examples are framep and frame-live-p.

• If a user option variable records a true-or-false condition, give it a name that ends in

‘-flag’.

• Please do not define C-c letter as a key in your major modes. These sequences are reserved for users; they are the only sequences reserved for users, so we cannot do without them.

Instead, define sequences consisting of C-c followed by a control character, a digit, or certain punctuation characters. These sequences are reserved for major modes.

Changing all the major modes in Emacs 18 so they would follow this convention was a lot of work. Abandoning this convention would make that work go to waste, and inconvenience users.

• Sequences consisting of C-c followed by {, }, <, >, : or ; are also reserved for major modes.

• Sequences consisting of C-c followed by any other punctuation character are allocated for minor modes. Using them in a major mode is not absolutely prohibited, but if you do that, the major mode binding may be shadowed from time to time by minor modes.

• You should not bind C-h following any prefix character (including C-c). If you don’t bind C-h, it is automatically available as a help character for listing the subcommands of the prefix character.

• You should not bind a key sequence ending in ^{⟨}\underline{\overline{ESC}}^{⟩} except following another ^{⟨}\underline{\overline{ESC}}^{⟩}. (That is, it is ok to bind a sequence ending in ^{⟨}\underline{\overline{ESC}}^{⟩} ^{⟨}\underline{\overline{ESC}}^{⟩}.)

The reason for this rule is that a non-prefix binding for ^{⟨}\underline{\overline{ESC}}^{⟩} in any context prevents recognition of escape sequences as function keys in that context.

• Applications should not bind mouse events based on button 1 with the shift key held down. These events include S-mouse-1, M-S-mouse-1, C-S-mouse-1, and so on. They are reserved for users.

• Modes should redefine mouse-2 as a command to follow some sort of reference in the text of a buffer, if users usually would not want to alter the text in that buffer by hand. Modes such as Dired, Info, Compilation, and Occur redefine it in this way.

• When a package provides a modification of ordinary Emacs behavior, it is good to include a command to enable and disable the feature, Provide a command named whatever-mode which turns the feature on or off, and make it autoload (see Section 13.2 [Autoload], page 164). Design the package so that simply loading it has no visible effect—that should not enable the feature. Users will request the feature by invoking the command.

• It is a bad idea to define aliases for the Emacs primitives. Use the standard names instead.

• Redefining an Emacs primitive is an even worse idea. It may do the right thing for a particular program, but there is no telling what other programs might break as a result.

• If a file does replace any of the functions or library programs of standard Emacs, prominent comments at the beginning of the file should say which functions are replaced, and how the behavior of the replacements differs from that of the originals.

• Please keep the names of your Emacs Lisp source files to 13 characters or less. This way, if the files are compiled, the compiled files’ names will be 14 characters or less, which is short enough to fit on all kinds of Unix systems.

• Don’t use next-line or previous-line in programs; nearly always, forward-line is more convenient as well as more predictable and robust. See Section 27.2.4 [Text Lines], page 432.

• Don’t call functions that set the mark, unless setting the mark is one of the intended features of your program. The mark is a user-level feature, so it is incorrect to change the mark except to supply a value for the user’s benefit. See Section 28.6 [The Mark], page 445. In particular, don’t use these functions:

  • beginning-of-buffer, end-of-buffer
  • replace-string, replace-regexp

If you just want to move point, or replace a certain string, without any of the other features intended for interactive users, you can replace these functions with one or two lines of simple Lisp code.

• Use lists rather than vectors, except when there is a particular reason to use a vector. Lisp has more facilities for manipulating lists than for vectors, and working with lists is usually more convenient. Vectors are advantageous for tables that are substantial in size and are accessed in random order (not searched front to back), provided there is no need to insert or delete elements (only lists allow that).

• The recommended way to print a message in the echo area is with the message function, not princ. See Section 35.4 [The Echo Area], page 569.

• When you encounter an error condition, call the function error (or signal). The function error does not return. See Section 9.5.3.1 [Signaling Errors], page 113. Do not use message, throw, sleep-for, or beep to report errors.

• An error message should start with a capital letter but should not end with a period.

• Many commands that take a long time to execute display a message that says ‘Operating...’ when they start, and change it to ‘Operating...done’ when they finish. Please keep the style of these messages uniform: no space around the ellipsis, and no period at the end.

• Try to avoid using recursive edits. Instead, do what the Rmail e command does: use a new local keymap that contains one command defined to switch back to the old local keymap. Or do what the edit-options command does: switch to another buffer and let the user switch back at will. See Section 18.10 [Recursive Editing], page 271.

• In some other systems there is a convention of choosing variable names that begin and end with ‘*’. We don’t use that convention in Emacs Lisp, so please don’t use it in your programs. (Emacs uses such names only for program-generated buffers.) The users will find Emacs more coherent if all libraries use the same conventions.

• Try to avoid compiler warnings about undefined free variables, by adding defvar definitions for these variables.

If you bind a variable in one function, and use it or set it in another function, the compiler warns about the latter function unless the variable has a definition. But often these variables have short names, and it is not clean for Lisp packages to define such variables names. Therefore, you should rename the variable to start with the name prefix used for the other functions and variables in your package.

• Indent each function with C-M-q (indent-sexp) using the default indentation parameters.

• Don’t make a habit of putting close-parentheses on lines by themselves; Lisp programmers find this disconcerting. Once in a while, when there is a sequence of many consecutive close-parentheses, it may make sense to split them in one or two significant places.

• Please put a copyright notice on the file if you give copies to anyone. Use the same lines that appear at the top of the Lisp files in Emacs itself. If you have not signed papers to assign the copyright to the Foundation, then place your name in the copyright notice in place of the Foundation’s name.

A.2 Tips for Making Compiled Code Fast

Here are ways of improving the execution speed of byte-compiled Lisp programs.

• Use the ‘profile’ library to profile your program. See the file ‘profile.el’ for instructions.

• Use iteration rather than recursion whenever possible. Function calls are slow in Emacs Lisp even when a compiled function is calling another compiled function.

• Using the primitive list-searching functions memq, member, assq, or assoc is even faster than explicit iteration. It may be worth rearranging a data structure so that one of these primitive search functions can be used.

• Certain built-in functions are handled specially in byte-compiled code, avoiding the need for an ordinary function call. It is a good idea to use these functions rather than alternatives. To see whether a function is handled specially by the compiler, examine its byte-compile property. If the property is non-nil, then the function is handled specially. For example, the following input will show you that aref is compiled specially (see Section 6.3 [Array Functions], page 82) while elt is not (see Section 6.1 [Sequence Functions], page 79):

     (get 'aref 'byte-compile)
          ⇒ byte-compile-two-args
     (get 'elt 'byte-compile)
          ⇒ nil

• If calling a small function accounts for a substantial part of your program’s running time, make the function inline. This eliminates the function call overhead. Since making a function inline reduces the flexibility of changing the program, don’t do it unless it gives a noticeable speedup in something slow enough that users care about the speed. See Section 11.9 [Inline Functions], page 151.

A.3 Tips for Documentation Strings

Here are some tips for the writing of documentation strings.

• Every command, function, or variable intended for users to know about should have a documentation string.

• An internal variable or subroutine of a Lisp program might as well have a documentation string. In earlier Emacs versions, you could save space by using a comment instead of a documentation string, but that is no longer the case.

• The first line of the documentation string should consist of one or two complete sentences that stand on their own as a summary. M-x apropos displays just the first line, and if it doesn’t stand on its own, the result looks bad. In particular, start the first line with a capital letter and end with a period. The documentation string can have additional lines that expand on the details of how to use the function or variable. The additional lines should be made up of complete sentences also, but they may be filled if that looks good.

• For consistency, phrase the verb in the first sentence of a documentation string as an infinitive with “to” omitted. For instance, use “Return the cons of A and B.” in preference to “Returns the cons of A and B.” Usually it looks good to do likewise for the rest of the first paragraph. Subsequent paragraphs usually look better if they have proper subjects.

• Write documentation strings in the active voice, not the passive, and in the present tense, not the future. For instance, use “Return a list containing A and B.” instead of “A list containing A and B will be returned.”

• Avoid using the word “cause” (or its equivalents) unnecessarily. Instead of, “Cause Emacs to display text in boldface,” write just “Display text in boldface.”

• Do not start or end a documentation string with whitespace.

• Format the documentation string so that it fits in an Emacs window on an 80-column screen. It is a good idea for most lines to be no wider than 60 characters. The first line can be wider if necessary to fit the information that ought to be there. However, rather than simply filling the entire documentation string, you can make it much more readable by choosing line breaks with care. Use blank lines between topics if the documentation string is long.

• Do not indent subsequent lines of a documentation string so that the text is lined up in the source code with the text of the first line. This looks nice in the source code, but looks bizarre when users view the documentation. Remember that the indentation before the starting double-quote is not part of the string!

• When the user tries to use a disabled command, Emacs displays just the first paragraph of its documentation string—everything through the first blank line. If you wish, you can choose which information to include before the first blank line so as to make this display useful.

• A variable’s documentation string should start with ‘*’ if the variable is one that users would often want to set interactively. If the value is a long list, or a function, or if the variable would be set only in init files, then don’t start the documentation string with ‘*’. See Section 10.5 [Defining Variables], page 125.

• The documentation string for a variable that is a yes-or-no flag should start with words such as “Non-nil means…”, to make it clear that all non-nil values are equivalent and indicate explicitly what nil and non-nil mean.

• When a function’s documentation string mentions the value of an argument of the function, use the argument name in capital letters as if it were a name for that value. Thus, the documentation string of the function / refers to its second argument as ‘DIVISOR’, because the actual argument name is divisor. Also use all caps for meta-syntactic variables, such as when you show the decomposition of a list or vector into subunits, some of which may vary.

• When a documentation string refers to a Lisp symbol, write it as it would be printed (which usually means in lower case), with single-quotes around it. For example: ‘`lambda'’. There are two exceptions: write t and nil without single-quotes.

• Don’t write key sequences directly in documentation strings. Instead, use the ‘\\[…]’ construct to stand for them. For example, instead of writing ‘C-f’, write the construct ‘\\[forward-char]’. When Emacs displays the documentation string, it substitutes whatever key is currently bound to forward-char. (This is normally ‘C-f’, but it may be some other character if the user has moved key bindings.) See Section 21.3 [Keys in Documentation], page 322.

• In documentation strings for a major mode, you will want to refer to the key bindings of that mode’s local map, rather than global ones. Therefore, use the construct ‘\\<…>’ once in the documentation string to specify which key map to use. Do this before the first use of ‘\\[…]’. The text inside the ‘\\<…>’ should be the name of the variable containing the local keymap for the major mode. It is not practical to use ‘\\[…]’ very many times, because display of the documentation string will become slow. So use this to describe the most important commands in your major mode, and then use ‘\\{…}’ to display the rest of the mode’s keymap.

A.4 Tips on Writing Comments

We recommend these conventions for where to put comments and how to indent them:

‘;’ Comments that start with a single semicolon, ‘;’, should all be aligned to the same column on the right of the source code. Such comments usually explain how the code on the same line does its job. In Lisp mode and related modes, the M-; (indent-for-comment) command automatically inserts such a ‘;’ in the right place, or aligns such a comment if it is already present. This and following examples are taken from the Emacs sources.

           (setq base-version-list                 ; there was a base
                 (assoc (substring fn 0 start-vn)  ; version to which
                        file-version-assoc-list))  ; this looks like
                                                   ; a subversion

‘;;’ Comments that start with two semicolons, ‘;;’, should be aligned to the same level of indentation as the code. Such comments usually describe the purpose of the following lines or the state of the program at that point. For example:

     (prog1 (setq auto-fill-function

…

…

       ;; update mode line
       (force-mode-line-update)))

Every function that has no documentation string (because it is use only internally within the package it belongs to), should have instead a two-semicolon comment right before the function, explaining what the function does and how to call it properly. Explain precisely what each argument means and how the function interprets its possible values.

‘;;;’ Comments that start with three semicolons, ‘;;;’, should start at the left margin. Such comments are used outside function definitions to make general statements explaining the design principles of the program. For example:

     ;;; This Lisp code is run in Emacs
     ;;; when it is to operate as a server
     ;;; for other processes.

Another use for triple-semicolon comments is for commenting out lines within a function. We use triple-semicolons for this precisely so that they remain at the left margin.

     (defun foo (a)
     ;;; This is no longer necessary.
     ;;;  (force-mode-line-update)
       (message "Finished with %s" a))

‘;;;;’ Comments that start with four semicolons, ‘;;;;’, should be aligned to the left

margin and are used for headings of major sections of a program. For example:

     ;;;; The kill ring

The indentation commands of the Lisp modes in Emacs, such as M-; (indent-for-comment) and ^{⟨}\underline{\overline{TAB}}^{⟩} (lisp-indent-line) automatically indent comments according to these conventions, depending on the number of semicolons. See section “Manipulating Comments” in The GNU Emacs Manual.

A.5 Conventional Headers for Emacs Libraries

Emacs 19 has conventions for using special comments in Lisp libraries to divide them into sections and give information such as who wrote them. This section explains these conventions. First, an example:

;;; lisp-mnt.el --- minor mode for Emacs Lisp maintainers
;; Copyright (C) 1992 Free Software Foundation, Inc.
;; Author: Eric S. Raymond <esr@snark.thyrsus.com>
;; Maintainer: Eric S. Raymond <esr@snark.thyrsus.com>
;; Created: 14 Jul 1992
;; Version: 1.2

;; Keywords: docs
;; This file is part of GNU Emacs.

copying permissions… The very first line should have this format:

;;; filename --- description The description should be complete in one line.

After the copyright notice come several header comment lines, each beginning with ‘;; header-name:’. Here is a table of the conventional possibilities for header-name:

‘Author’ This line states the name and net address of at least the principal author of the library. If there are multiple authors, you can list them on continuation lines led by ;; and a tab character, like this:

     ;; Author: Ashwin Ram <Ram-Ashwin@cs.yale.edu>
     ;;      Dave Sill <de5@ornl.gov>
     ;;      Dave Brennan <brennan@hal.com>
     ;;      Eric Raymond <esr@snark.thyrsus.com>
‘Maintainer’

This line should contain a single name/address as in the Author line, or an address only, or the string ‘FSF’. If there is no maintainer line, the person(s) in the Author field are presumed to be the maintainers. The example above is mildly bogus because the maintainer line is redundant. The idea behind the ‘Author’ and ‘Maintainer’ lines is to make possible a Lisp function to “send mail to the maintainer” without having to mine the name out by hand. Be sure to surround the network address with ‘<…>’ if you include the person’s full name as well as the network address.

‘Created’ This optional line gives the original creation date of the file. For historical interest only.

‘Version’ If you wish to record version numbers for the individual Lisp program, put them in this line.

‘Adapted-By’

In this header line, place the name of the person who adapted the library for installation (to make it fit the style conventions, for example).

‘Keywords’

This line lists keywords for the finder-by-keyword help command. This field is important; it’s how people will find your package when they’re looking for things by topic area. To separate the keywords, you can use spaces, commas, or both.

Just about every Lisp library ought to have the ‘Author’ and ‘Keywords’ header comment lines. Use the others if they are appropriate. You can also put in header lines with other header names—they have no standard meanings, so they can’t do any harm.

We use additional stylized comments to subdivide the contents of the library file. Here is a table of them:

‘;;; Commentary:’

This begins introductory comments that explain how the library works. It should come right after the copying permissions.

‘;;; Change log:’

This begins change log information stored in the library file (if you store the change history there). For most of the Lisp files distributed with Emacs, the change history is kept in the file ‘ChangeLog’ and not in the source file at all; these files do not have a ‘;;; Change log:’ line.

‘;;; Code:’

This begins the actual code of the program.

‘;;; filename ends here’

This is the footer line; it appears at the very end of the file. Its purpose is to enable people to detect truncated versions of the file from the lack of a footer line.

608 GNU Emacs Lisp Reference Manual

Appendix B GNU Emacs Internals

This chapter describes how the runnable Emacs executable is dumped with the preloaded Lisp libraries in it, how storage is allocated, and some internal aspects of GNU Emacs that may be of interest to C programmers.

B.1 Building Emacs

This section explains the steps involved in building the Emacs executable. You don’t have to know this material to build and install Emacs, since the makefiles do all these things automatically. This information is pertinent to Emacs maintenance.

Compilation of the C source files in the ‘src’ directory produces an executable file called ‘temacs’, also called a bare impure Emacs. It contains the Emacs Lisp interpreter and I/O routines, but not the editing commands.

The command ‘temacs -l loadup’ uses ‘temacs’ to create the real runnable Emacs executable. These arguments direct ‘temacs’ to evaluate the Lisp files specified in the file ‘loadup.el’. These files set up the normal Emacs editing environment, resulting in an Emacs that is still impure but no longer bare.

It takes a substantial time to load the standard Lisp files. Luckily, you don’t have to do this each time you run Emacs; ‘temacs’ can dump out an executable program called ‘emacs’ that has these files preloaded. ‘emacs’ starts more quickly because it does not need to load the files. This is the Emacs executable that is normally installed.

To create ‘emacs’, use the command ‘temacs -batch -l loadup dump’. The purpose of ‘-batch’ here is to prevent ‘temacs’ from trying to initialize any of its data on the terminal; this ensures that the tables of terminal information are empty in the dumped Emacs. The argument ‘dump’ tells ‘loadup.el’ to dump a new executable named ‘emacs’.

Some operating systems don’t support dumping. On those systems, you must start Emacs with the ‘temacs -l loadup’ command each time you use it. This takes a substantial time, but since you need to start Emacs once a day at most—or once a week if you never log out—the extra time is not too severe a problem.

You can specify additional files to preload by writing a library named ‘site-load.el’ that loads them. You may need to increase the value of PURESIZE, in ‘src/puresize.h’, to make room for the additional data. (Try adding increments of 20000 until it is big enough.) However, the advantage of preloading additional files decreases as machines get faster. On modern machines, it is usually not advisable.

After ‘loadup.el’ reads ‘site-load.el’, it finds the documentation strings for primitive and preloaded functions (and variables) in the file ‘etc/DOC’ where they are stored, by calling Snarf-documentation (see Section 21.2 [Accessing Documentation], page 320).

You can specify other Lisp expressions to execute just before dumping by putting them in a library named ‘site-init.el’. This file is executed after the documentation strings are found.

If you want to preload function or variable definitions, there are three ways you can do this and make their documentation strings accessible when you subsequently run Emacs:

• Arrange to scan these files when producing the ‘etc/DOC’ file, and load them with

‘site-load.el’.

• Load the files with ‘site-init.el’, then copy the files into the installation directory for Lisp files when you install Emacs.

• Specify a non-nil value for byte-compile-dynamic-docstrings as a local variable in each these files, and load them with either ‘site-load.el’ or ‘site-init.el’. (This method has the drawback that the documentation strings take up space in Emacs all the time.)

It is not advisable to put anything in ‘site-load.el’ or ‘site-init.el’ that would alter any of the features that users expect in an ordinary unmodified Emacs. If you feel you must override normal features for your site, do it with ‘default.el’, so that users can override your changes if they wish. See Section 34.1.1 [Start-up Summary], page 543.

Function dump-emacs to-file from-file This function dumps the current state of Emacs into an executable file to-file. It takes symbols from from-file (this is normally the executable file ‘temacs’). If you use this function in an Emacs that was already dumped, you must set command-line-processed to nil first for good results. See Section 34.1.4 [Command Line Arguments], page 546.

Command emacs-version

This function returns a string describing the version of Emacs that is running. It is useful to include this string in bug reports.

     (emacs-version)
       ⇒ "GNU Emacs 19.29.1 (i386-debian-linux) \
      of Tue Jun  6 1995 on balloon"

Called interactively, the function prints the same information in the echo area.

Variable emacs-build-time

The value of this variable is the time at which Emacs was built at the local site.

     emacs-build-time
          ⇒ "Tue Jun  6 14:55:57 1995"

Variable emacs-version

The value of this variable is the version of Emacs being run. It is a string such

as "19.29.1".

The following two variables did not exist before Emacs version 19.23, which reduces their usefulness at present, but we hope they will be convenient in the future.

Variable emacs-major-version

The major version number of Emacs, as an integer. For Emacs version 19.29, the value is 19.

Variable emacs-minor-version

The minor version number of Emacs, as an integer. For Emacs version 19.29, the value is 29.

B.2 Pure Storage

Emacs Lisp uses two kinds of storage for user-created Lisp objects: normal storage and pure storage. Normal storage is where all the new data created during an Emacs session is kept; see the following section for information on normal storage. Pure storage is used for certain data in the preloaded standard Lisp files—data that should never change during actual use of Emacs.

Pure storage is allocated only while ‘temacs’ is loading the standard preloaded Lisp libraries. In the file ‘emacs’, it is marked as read-only (on operating systems that permit this), so that the memory space can be shared by all the Emacs jobs running on the machine at once. Pure storage is not expandable; a fixed amount is allocated when Emacs is compiled, and if that is not sufficient for the preloaded libraries, ‘temacs’ crashes. If that happens, you must increase the compilation parameter PURESIZE in the file ‘src/puresize.h’. This normally won’t happen unless you try to preload additional libraries or add features to the standard ones.

Function purecopy object

This function makes a copy of object in pure storage and returns it. It copies strings by simply making a new string with the same characters in pure storage. It recursively copies the contents of vectors and cons cells. It does not make copies of other objects such as symbols, but just returns them unchanged. It signals an error if asked to copy markers. This function is a no-op except while Emacs is being built and dumped; it is usually called only in the file ‘emacs/lisp/loaddefs.el’, but a few packages call it just in case you decide to preload them.

Variable pure-bytes-used

The value of this variable is the number of bytes of pure storage allocated so far. Typically, in a dumped Emacs, this number is very close to the total amount of pure storage available—if it were not, we would preallocate less.

Variable purify-flag

This variable determines whether defun should make a copy of the function definition in pure storage. If it is non-nil, then the function definition is copied into pure storage. This flag is t while loading all of the basic functions for building Emacs initially (allowing those functions to be sharable and non-collectible). Dumping Emacs as an executable always writes nil in this variable, regardless of the value it actually has before and after dumping. You should not change this flag in a running Emacs.

B.3 Garbage Collection

When a program creates a list or the user defines a new function (such as by loading a library), that data is placed in normal storage. If normal storage runs low, then Emacs asks the operating system to allocate more memory in blocks of 1k bytes. Each block is used for one type of Lisp object, so symbols, cons cells, markers, etc., are segregated in distinct blocks in memory. (Vectors, long strings, buffers and certain other editing types, which are fairly large, are allocated in individual blocks, one per object, while small strings are packed into blocks of 8k bytes.)

It is quite common to use some storage for a while, then release it by (for example) killing a buffer or deleting the last pointer to an object. Emacs provides a garbage collector to reclaim this abandoned storage. (This name is traditional, but “garbage recycler” might be a more intuitive metaphor for this facility.)

The garbage collector operates by finding and marking all Lisp objects that are still accessible to Lisp programs. To begin with, it assumes all the symbols, their values and associated function definitions, and any data presently on the stack, are accessible. Any objects that can be reached indirectly through other accessible objects are also accessible.

When marking is finished, all objects still unmarked are garbage. No matter what the Lisp program or the user does, it is impossible to refer to them, since there is no longer a way to reach them. Their space might as well be reused, since no one will miss them. The second (“sweep”) phase of the garbage collector arranges to reuse them.

The sweep phase puts unused cons cells onto a free list for future allocation; likewise for symbols and markers. It compacts the accessible strings so they occupy fewer 8k blocks; then it frees the other 8k blocks. Vectors, buffers, windows, and other large objects are individually allocated and freed using malloc and free.

Common Lisp note: Unlike other Lisps, GNU Emacs Lisp does not call the garbage collector when the free list is empty. Instead, it simply requests the operating system to allocate more storage, and processing continues until gccons-threshold bytes have been used. This means that you can make sure that the garbage collector will not run during a certain portion of a Lisp program by calling the garbage collector explicitly just before it (provided that portion of the program does not use so much space as to force a second garbage collection).

Command garbage-collect

This command runs a garbage collection, and returns information on the amount of space in use. (Garbage collection can also occur spontaneously if you use more than gc-cons-threshold bytes of Lisp data since the previous garbage collection.) garbage-collect returns a list containing the following information:

((used-conses . free-conses) (used-syms . free-syms) (used-markers . free-markers) used-string-chars used-vector-slots (used-floats . free-floats))

          (garbage-collect)
               ⇒ ((3435 . 2332) (1688 . 0)
                     (57 . 417) 24510 3839 (4 . 1))

Here is a table explaining each element: used-conses

The number of cons cells in use.

free-conses The number of cons cells for which space has been obtained from the operating system, but that are not currently being used.

used-syms The number of symbols in use.

free-syms The number of symbols for which space has been obtained from the operating system, but that are not currently being used.

used-markers The number of markers in use.

free-markers The number of markers for which space has been obtained from the operating system, but that are not currently being used.

used-string-chars The total size of all strings, in characters.

used-vector-slots The total number of elements of existing vectors.

used-floats The number of floats in use.

free-floats The number of floats for which space has been obtained from the operating system, but that are not currently being used.

User Option garbage-collection-messages

If this variable is non-nil, Emacs displays a message at the beginning and end of garbage collection. The default value is nil, meaning there are no such messages.

User Option gc-cons-threshold

The value of this variable is the number of bytes of storage that must be allocated for Lisp objects after one garbage collection in order to trigger another garbage collection. A cons cell counts as eight bytes, a string as one byte per character plus a few bytes of overhead, and so on; space allocated to the contents of buffers does not count. Note that the subsequent garbage collection does not happen immediately when the threshold is exhausted, but only the next time the Lisp evaluator is called. The initial threshold value is 300,000. If you specify a larger value, garbage collection will happen less often. This reduces the amount of time spent garbage collecting, but increases total memory use. You may want to do this when running a program that creates lots of Lisp data. You can make collections more frequent by specifying a smaller value, down to 10,000. A value less than 10,000 will remain in effect only until the subsequent garbage collection, at which time garbage-collect will set the threshold back to 10,000.

Function memory-limit

This function returns the address of the last byte Emacs has allocated, divided by 1024. We divide the value by 1024 to make sure it fits in a Lisp integer. You can use this to get a general idea of how your actions affect the memory usage.

B.4 Writing Emacs Primitives

Lisp primitives are Lisp functions implemented in C. The details of interfacing the C function so that Lisp can call it are handled by a few C macros. The only way to really understand how to write new C code is to read the source, but we can explain some things here.

An example of a special form is the definition of or, from ‘eval.c’. (An ordinary function would have the same general appearance.)

DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
  "Eval args until one of them yields non-nil; return that value.\n\
The remaining args are not evalled at all.\n\
If all args return nil, return nil.")
  (args)
     Lisp_Object args;
{
  register Lisp_Object val;
  Lisp_Object args_left;
  struct gcpro gcpro1;
  if (NULL (args))
    return Qnil;
  args_left = args;
  GCPRO1 (args_left);
  do
    {
      val = Feval (Fcar (args_left));
      if (!NULL (val))
        break;
      args_left = Fcdr (args_left);
    }
  while (!NULL (args_left));
UNGCPRO; return val; }

Let’s start with a precise explanation of the arguments to the DEFUN macro. Here is a template for them:

DEFUN (lname, fname, sname, min, max, interactive, doc)

lname This is the name of the Lisp symbol to define as the function name; in the example above, it is or. fname This is the C function name for this function. This is the name that is used in

C code for calling the function. The name is, by convention, ‘F’ prepended to the Lisp name, with all dashes (‘-’) in the Lisp name changed to underscores. Thus, to call this function from C code, call For. Remember that the arguments must be of type Lisp_Object; various macros and functions for creating values of type Lisp_Object are declared in the file ‘lisp.h’.

sname This is a C variable name to use for a structure that holds the data for the subr object that represents the function in Lisp. This structure conveys the Lisp symbol name to the initialization routine that will create the symbol and store the subr object as its definition. By convention, this name is always fname with ‘F’ replaced with ‘S’.

min This is the minimum number of arguments that the function requires. The function or allows a minimum of zero arguments.

max This is the maximum number of arguments that the function accepts, if there is a fixed maximum. Alternatively, it can be UNEVALLED, indicating a special form that receives unevaluated arguments, or MANY, indicating an unlimited number of evaluated arguments (the equivalent of &rest). Both UNEVALLED and MANY are macros. If max is a number, it may not be less than min and it may not be greater than seven.

interactive This is an interactive specification, a string such as might be used as the argument of interactive in a Lisp function. In the case of or, it is 0 (a null pointer), indicating that or cannot be called interactively. A value of "" indicates a function that should receive no arguments when called interactively.

doc This is the documentation string. It is written just like a documentation string for a function defined in Lisp, except you must write ‘\n\’ at the end of each line. In particular, the first line should be a single sentence.

After the call to the DEFUN macro, you must write the argument name list that every C function must have, followed by ordinary C declarations for the arguments. For a function with a fixed maximum number of arguments, declare a C argument for each Lisp argument, and give them all type Lisp_Object. When a Lisp function has no upper limit on the number of arguments, its implementation in C actually receives exactly two arguments: the first is the number of Lisp arguments, and the second is the address of a block containing their values. They have types int and Lisp_Object *.

Within the function For itself, note the use of the macros GCPRO1 and UNGCPRO. GCPRO1 is used to “protect” a variable from garbage collection—to inform the garbage collector that it must look in that variable and regard its contents as an accessible object. This is necessary whenever you call Feval or anything that can directly or indirectly call Feval. At such a time, any Lisp object that you intend to refer to again must be protected somehow. UNGCPRO cancels the protection of the variables that are protected in the current function. It is necessary to do this explicitly.

For most data types, it suffices to protect at least one pointer to the object; as long as the object is not recycled, all pointers to it remain valid. This is not so for strings, because the garbage collector can move them. When the garbage collector moves a string, it relocates all the pointers it knows about; any other pointers become invalid. Therefore, you must protect all pointers to strings across any point where garbage collection may be possible.

The macro GCPRO1 protects just one local variable. If you want to protect two, use GCPRO2 instead; repeating GCPRO1 will not work. Macros GCPRO3 and GCPRO4 also exist.

These macros implicitly use local variables such as gcpro1; you must declare these explicitly, with type struct gcpro. Thus, if you use GCPRO2, you must declare gcpro1 and gcpro2. Alas, we can’t explain all the tricky details here.

You must not use C initializers for static or global variables unless they are never written once Emacs is dumped. These variables with initializers are allocated in an area of memory that becomes read-only (on certain operating systems) as a result of dumping Emacs. See Section B.2 [Pure Storage], page 611.

Do not use static variables within functions—place all static variables at top level in the file. This is necessary because Emacs on some operating systems defines the keyword static as a null macro. (This definition is used because those systems put all variables declared static in a place that becomes read-only after dumping, whether they have initializers or not.)

Defining the C function is not enough to make a Lisp primitive available; you must also create the Lisp symbol for the primitive and store a suitable subr object in its function cell. The code looks like this:

defsubr (&subr-structure-name);

Here subr-structure-name is the name you used as the third argument to DEFUN.

If you add a new primitive to a file that already has Lisp primitives defined in it, find the function (near the end of the file) named syms_of_something, and add the call to defsubr there. If the file doesn’t have this function, or if you create a new file, add to it a syms_ of_filename (e.g., syms_of_myfile). Then find the spot in ‘emacs.c’ where all of these functions are called, and add a call to syms_of_filename there.

The function syms_of_filename is also the place to define any C variables that are to be visible as Lisp variables. DEFVAR_LISP makes a C variable of type Lisp_Object visible in Lisp. DEFVAR_INT makes a C variable of type int visible in Lisp with a value that is always an integer. DEFVAR_BOOL makes a C variable of type int visible in Lisp with a value that is either t or nil.

Here is another example function, with more complicated arguments. This comes from the code for the X Window System, and it demonstrates the use of macros and functions to manipulate Lisp objects.

     DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
       Scoordinates_in_window_p, 2, 2,
       "xSpecify coordinate pair: \nXExpression which evals to window: ",
       "Return non-nil if POSITIONS is in WINDOW.\n\
       \(POSITIONS is a list, (SCREEN-X SCREEN-Y)\)\n\

Returned value is list of positions expressed\n\
relative to window upper left corner.")
(coordinate, window)
   register Lisp_Object coordinate, window;
{
register Lisp_Object xcoord, ycoord;
if (!CONSP (coordinate)) wrong_type_argument (Qlistp, coordinate);
CHECK_WINDOW (window, 2);
xcoord = Fcar (coordinate);
ycoord = Fcar (Fcdr (coordinate));
CHECK_NUMBER (xcoord, 0);
CHECK_NUMBER (ycoord, 1);
if ((XINT (xcoord) < XINT (XWINDOW (window)->left))
    || (XINT (xcoord) >= (XINT (XWINDOW (window)->left)
                          + XINT (XWINDOW (window)->width))))
  return Qnil;
XFASTINT (xcoord) -= XFASTINT (XWINDOW (window)->left);
if (XINT (ycoord) == (screen_height - 1))
  return Qnil;
if ((XINT (ycoord) < XINT (XWINDOW (window)->top))
    || (XINT (ycoord) >= (XINT (XWINDOW (window)->top)
                          + XINT (XWINDOW (window)->height)) - 1))
  return Qnil;
XFASTINT (ycoord) -= XFASTINT (XWINDOW (window)->top);
return (Fcons (xcoord, Fcons (ycoord, Qnil)));
}

Note that C code cannot call functions by name unless they are defined in C. The way to call a function written in Lisp is to use Ffuncall, which embodies the Lisp function funcall. Since the Lisp function funcall accepts an unlimited number of arguments, in C it takes two: the number of Lisp-level arguments, and a one-dimensional array containing their values. The first Lisp-level argument is the Lisp function to call, and the rest are the arguments to pass to it. Since Ffuncall can call the evaluator, you must protect pointers from garbage collection around the call to Ffuncall.

The C functions call0, call1, call2, and so on, provide handy ways to call a Lisp function conveniently with a fixed number of arguments. They work by calling Ffuncall.

‘eval.c’ is a very good file to look through for examples; ‘lisp.h’ contains the definitions for some important macros and functions.

B.5 Object Internals

GNU Emacs Lisp manipulates many different types of data. The actual data are stored in a heap and the only access that programs have to it is through pointers. Pointers are thirty-two bits wide in most implementations. Depending on the operating system and type of machine for which you compile Emacs, twenty-four to twenty-six bits are used to address the object, and the remaining six to eight bits are used for a tag that identifies the object’s type.

Because Lisp objects are represented as tagged pointers, it is always possible to determine the Lisp data type of any object. The C data type Lisp_Object can hold any Lisp object of any data type. Ordinary variables have type Lisp_Object, which means they can hold any type of Lisp value; you can determine the actual data type only at run time. The same is true for function arguments; if you want a function to accept only a certain type of argument, you must check the type explicitly using a suitable predicate (see Section 2.5 [Type Predicates], page 29).

B.5.1 Buffer Internals

Buffers contain fields not directly accessible by the Lisp programmer. We describe them here, naming them by the names used in the C code. Many are accessible indirectly in Lisp programs via Lisp primitives.

name The buffer name is a string that names the buffer. It is guaranteed to be unique. See Section 24.3 [Buffer Names], page 371.

save_modified

This field contains the time when the buffer was last saved, as an integer. See Section 24.5 [Buffer Modification], page 374.

modtime This field contains the modification time of the visited file. It is set when the file is written or read. Every time the buffer is written to the file, this field is compared to the modification time of the file. See Section 24.5 [Buffer Modification], page 374.

auto_save_modified

This field contains the time when the buffer was last auto-saved.

last_window_start

This field contains the window-start position in the buffer as of the last time the buffer was displayed in a window.

undo_list

This field points to the buffer’s undo list. See Section 29.9 [Undo], page 461.

syntax_table_v

This field contains the syntax table for the buffer. See Chapter 31 [Syntax Tables], page 509.

downcase_table

This field contains the conversion table for converting text to lower case. See Section 4.8 [Case Table], page 58.

upcase_table

This field contains the conversion table for converting text to upper case. See Section 4.8 [Case Table], page 58.

case_canon_table

This field contains the conversion table for canonicalizing text for case-folding search. See Section 4.8 [Case Table], page 58.

case_eqv_table

This field contains the equivalence table for case-folding search. See Section 4.8 [Case Table], page 58.

display_table

This field contains the buffer’s display table, or nil if it doesn’t have one. See Section 35.14 [Display Tables], page 583.

markers This field contains the chain of all markers that currently point into the buffer. Deletion of text in the buffer, and motion of the buffer’s gap, must check each of these markers and perhaps update it. See Chapter 28 [Markers], page 441.

backed_up

This field is a flag that tells whether a backup file has been made for the visited file of this buffer.

mark This field contains the mark for the buffer. The mark is a marker, hence it is also included on the list markers. See Section 28.6 [The Mark], page 445.

mark_active

This field is non-nil if the buffer’s mark is active.

local_var_alist

This field contains the association list describing the variables local in this buffer, and their values, with the exception of local variables that have special slots in the buffer object. (Those slots are omitted from this table.) See Section 10.10 [Buffer-Local Variables], page 134.

base_buffer

This field holds the buffer’s base buffer (if it is an indirect buffer), or nil.

keymap This field holds the buffer’s local keymap. See Chapter 19 [Keymaps], page 277.

overlay_center

This field holds the current overlay center position. See Section 35.9 [Overlays], page 575.

overlays_before

This field holds a list of the overlays in this buffer that end at or before the current overlay center position. They are sorted in order of decreasing end position.

overlays_after

This field holds a list of the overlays in this buffer that end after the current overlay center position. They are sorted in order of increasing beginning position.

B.5.2 Window Internals

Windows have the following accessible fields:

frame The frame that this window is on.

mini_p Non-nil if this window is a minibuffer window. buffer The buffer that the window is displaying. This may change often during the

life of the window.

dedicated

Non-nil if this window is dedicated to its buffer.

pointm This is the value of point in the current buffer when this window is selected; when it is not selected, it retains its previous value.

start The position in the buffer that is the first character to be displayed in the window.

force_start

If this flag is non-nil, it says that the window has been scrolled explicitly by the Lisp program. This affects what the next redisplay does if point is off the screen: instead of scrolling the window to show the text around point, it moves point to a location that is on the screen.

last_modified

The modified field of the window’s buffer, as of the last time a redisplay completed in this window.

last_point

The buffer’s value of point, as of the last time a redisplay completed in this window.

left This is the left-hand edge of the window, measured in columns. (The leftmost column on the screen is column 0.)

top This is the top edge of the window, measured in lines. (The top line on the screen is line 0.)

height The height of the window, measured in lines.

width The width of the window, measured in columns.

next This is the window that is the next in the chain of siblings. It is nil in a window that is the rightmost or bottommost of a group of siblings.

prev This is the window that is the previous in the chain of siblings. It is nil in a window that is the leftmost or topmost of a group of siblings.

parent Internally, Emacs arranges windows in a tree; each group of siblings has a parent window whose area includes all the siblings. This field points to a window’s parent. Parent windows do not display buffers, and play little role in display except to shape their child windows. Emacs Lisp programs usually have no access to the parent windows; they operate on the windows at the leaves of the tree, which actually display buffers.

hscroll This is the number of columns that the display in the window is scrolled horizontally to the left. Normally, this is 0.

use_time This is the last time that the window was selected. The function get-lru-window uses this field.

display_table

The window’s display table, or nil if none is specified for it.

update_mode_line

Non-nil means this window’s mode line needs to be updated.

base_line_number

The line number of a certain position in the buffer, or nil. This is used for displaying the line number of point in the mode line.

base_line_pos

The position in the buffer for which the line number is known, or nil meaning none is known.

region_showing

If the region (or part of it) is highlighted in this window, this field holds the mark position that made one end of that region. Otherwise, this field is nil.

B.5.3 Process Internals

The fields of a process are:

name A string, the name of the process.

command A list containing the command arguments that were used to start this process.

filter A function used to accept output from the process instead of a buffer, or nil.

sentinel A function called whenever the process receives a signal, or nil.

buffer The associated buffer of the process.

pid An integer, the Unix process id.

childp A flag, non-nil if this is really a child process. It is nil for a network connection.

mark A marker indicating the position of the end of the last output from this process inserted into the buffer. This is often but not always the end of the buffer.

kill_without_query

If this is non-nil, killing Emacs while this process is still running does not ask for confirmation about killing the process.

raw_status_low
raw_status_high

These two fields record 16 bits each of the process status returned by the wait system call.

status The process status, as process-status should return it.

tick
update_tick

If these two fields are not equal, a change in the status of the process needs to be reported, either by running the sentinel or by inserting a message in the process buffer. pty_flag Non-nil if communication with the subprocess uses a pty; nil if it uses a pipe. infd The file descriptor for input from the process. outfd The file descriptor for output to the process. subtty The file descriptor for the terminal that the subprocess is using. (On some

systems, there is no need to record this, so the value is nil.)

tty_name The name of the terminal that the subprocess is using, or nil if it is using pipes.

Appendix C Standard Errors

Here is the complete list of the error symbols in standard Emacs, grouped by concept. The list includes each symbol’s message (on the error-message property of the symbol) and a cross reference to a description of how the error can occur.

Each error symbol has an error-conditions property that is a list of symbols. Normally this list includes the error symbol itself and the symbol error. Occasionally it includes additional symbols, which are intermediate classifications, narrower than error but broader than a single error symbol. For example, all the errors in accessing files have the condition

file-error.

As a special exception, the error symbol quit does not have the condition error, because quitting is not considered an error.

See Section 9.5.3 [Errors], page 112, for an explanation of how errors are generated and handled.

symbol string; reference.

error     "error"

See Section 9.5.3 [Errors], page 112.

quit      "Quit"

See Section 18.8 [Quitting], page 268.

args-out-of-range
          "Args out of range"

See Chapter 6 [Sequences Arrays Vectors], page 79.

arith-error
          "Arithmetic error"

See / and % in Chapter 3 [Numbers], page 35.

beginning-of-buffer
          "Beginning of buffer"

See Section 27.2 [Motion], page 430.

buffer-read-only
          "Buffer is read-only"

See Section 24.7 [Read Only Buffers], page 376.

cyclic-function-indirection
          "Symbol's chain of function indirections contains a
          loop"

See Section 8.2.4 [Function Indirection], page 99.

end-of-buffer
          "End of buffer"

See Section 27.2 [Motion], page 430.

end-of-file
          "End of file during parsing"

This is not a file-error.

See Section 16.3 [Input Functions], page 216.

file-error

This error and its subcategories do not have error-strings, because the error message is constructed from the data items alone when the error condition

file-error is present.

See Chapter 22 [Files], page 329.

file-locked
This is a file-error.

See Section 22.5 [File Locks], page 336.

file-already-exists
This is a file-error.

See Section 22.4 [Writing to Files], page 335.

file-supersession
This is a file-error.

See Section 24.6 [Modification Time], page 375.

invalid-function
"Invalid function"

See Section 8.2.3 [Classifying Lists], page 99.

invalid-read-syntax
"Invalid read syntax"

See Section 16.3 [Input Functions], page 216.

invalid-regexp
"Invalid regexp"

See Section 30.2 [Regular Expressions], page 492.

no-catch  "No catch for tag"

See Section 9.5.1 [Catch and Throw], page 110.

search-failed
"Search failed"

See Chapter 30 [Searching and Matching], page 491.

setting-constant
"Attempt to set a constant symbol"

The values of the symbols nil and t may not be changed. See Section 10.2 [Variables that Never Change], page 121.

undefined-color
"Undefined color"

See Section 26.19 [Color Names], page 425.

void-function
"Symbol's function definition is void"

See Section 11.8 [Function Cells], page 149.

void-variable
"Symbol's value as variable is void"

See Section 10.7 [Accessing Variables], page 128.

wrong-number-of-arguments
"Wrong number of arguments"

See Section 8.2.3 [Classifying Lists], page 99.

wrong-type-argument
"Wrong type argument"

See Section 2.5 [Type Predicates], page 29.

These error types, which are all classified as special cases of arith-error, can occur on certain systems for invalid use of mathematical functions.

domain-error
"Arithmetic domain error"

See Section 3.9 [Math Functions], page 46.

overflow-error
"Arithmetic overflow error"

See Section 3.9 [Math Functions], page 46.

range-error
"Arithmetic range error"

See Section 3.9 [Math Functions], page 46.

singularity-error
"Arithmetic singularity error"

See Section 3.9 [Math Functions], page 46.

underflow-error
"Arithmetic underflow error"

See Section 3.9 [Math Functions], page 46.

626 GNU Emacs Lisp Reference Manual

Appendix D Buffer-Local Variables

The table below lists the general-purpose Emacs variables that are automatically local (when set) in each buffer. Many Lisp packages define such variables for their internal use; we don’t list them here.

abbrev-mode

see Chapter 32 [Abbrevs], page 519

auto-fill-function

see Section 29.13 [Auto Filling], page 467

buffer-auto-save-file-name

see Section 23.2 [Auto-Saving], page 363

buffer-backed-up

see Section 23.1 [Backup Files], page 359

buffer-display-table

see Section 35.14 [Display Tables], page 583

buffer-file-format

see Section 22.12 [Format Conversion], page 354

buffer-file-name

see Section 24.4 [Buffer File Name], page 372

buffer-file-number

see Section 24.4 [Buffer File Name], page 372

buffer-file-truename

see Section 24.4 [Buffer File Name], page 372

buffer-file-type

see Section 22.13 [Files and MS-DOS], page 356

buffer-invisibility-spec

see Section 35.5 [Invisible Text], page 570

buffer-offer-save

see Section 22.2 [Saving Buffers], page 332

buffer-read-only

see Section 24.7 [Read Only Buffers], page 376

buffer-saved-size

see Section 27.1 [Point], page 429

buffer-undo-list

see Section 29.9 [Undo], page 461

cache-long-line-scans

see Section 27.2.4 [Text Lines], page 432

case-fold-search

see Section 30.7 [Searching and Case], page 505

ctl-arrow

see Section 35.13 [Usual Display], page 582

comment-column

see section “Comments” in The GNU Emacs Manual

default-directory

see Section 34.3 [System Environment], page 549

defun-prompt-regexp

see Section 27.2.6 [List Motion], page 435

fill-column

see Section 29.13 [Auto Filling], page 467

goal-column

see section “Moving Point” in The GNU Emacs Manual

left-margin

see Section 29.16 [Indentation], page 472

local-abbrev-table

see Chapter 32 [Abbrevs], page 519

local-write-file-hooks

see Section 22.2 [Saving Buffers], page 332

major-mode

see Section 20.1.4 [Mode Help], page 307

mark-active

see Section 28.6 [The Mark], page 445

mark-ring

see Section 28.6 [The Mark], page 445

minor-modes

see Section 20.2 [Minor Modes], page 309

mode-line-buffer-identification

see Section 20.3.2 [Mode Line Variables], page 312

mode-line-format

see Section 20.3.1 [Mode Line Data], page 311

mode-line-modified

see Section 20.3.2 [Mode Line Variables], page 312

mode-line-process

see Section 20.3.2 [Mode Line Variables], page 312

mode-name

see Section 20.3.2 [Mode Line Variables], page 312

overwrite-mode

see Section 29.4 [Insertion], page 452

paragraph-separate

see Section 30.8 [Standard Regexps], page 506

paragraph-start

see Section 30.8 [Standard Regexps], page 506

point-before-scroll

Used for communication between mouse commands and scroll-bar commands.

require-final-newline

see Section 29.4 [Insertion], page 452

selective-display

see Section 35.6 [Selective Display], page 571

selective-display-ellipses

see Section 35.6 [Selective Display], page 571

tab-width

see Section 35.13 [Usual Display], page 582

truncate-lines

see Section 35.3 [Truncation], page 568

vc-mode see Section 20.3.2 [Mode Line Variables], page 312 630 GNU Emacs Lisp Reference Manual

Appendix E Standard Keymaps

The following symbols are used as the names for various keymaps. Some of these exist when Emacs is first started, others are loaded only when their respective mode is used. This is not an exhaustive list.

Almost all of these maps are used as local maps. Indeed, of the modes that presently exist, only Vip mode and Terminal mode ever change the global keymap.

Buffer-menu-mode-map

A full keymap used by Buffer Menu mode.

c-mode-map

A sparse keymap used by C mode.

command-history-map

A full keymap used by Command History mode.

ctl-x-4-map

A sparse keymap for subcommands of the prefix C-x 4.

ctl-x-5-map

A sparse keymap for subcommands of the prefix C-x 5.

ctl-x-map

A full keymap for C-x commands.

debugger-mode-map

A full keymap used by Debugger mode.

dired-mode-map

A full keymap for dired-mode buffers.

edit-abbrevs-map

A sparse keymap used in edit-abbrevs.

edit-tab-stops-map

A sparse keymap used in edit-tab-stops.

electric-buffer-menu-mode-map

A full keymap used by Electric Buffer Menu mode.

electric-history-map

A full keymap used by Electric Command History mode.

emacs-lisp-mode-map

A sparse keymap used by Emacs Lisp mode.

facemenu-menu

The keymap that displays the Text Properties menu.

facemenu-background-menu

The keymap that displays the Background Color submenu of the Text Properties menu.

facemenu-face-menu

The keymap that displays the Face submenu of the Text Properties menu.

facemenu-foreground-menu

The keymap that displays the Foreground Color submenu of the Text Properties menu.

facemenu-indentation-menu

The keymap that displays the Indentation submenu of the Text Properties menu.

facemenu-justification-menu

The keymap that displays the Justification submenu of the Text Properties menu.

facemenu-special-menu

The keymap that displays the Special Props submenu of the Text Properties menu.

function-key-map

The keymap for translating keypad and function keys. If there are none, then it contains an empty sparse keymap.

fundamental-mode-map

The local keymap for Fundamental mode. It is empty and should not be changed.

Helper-help-map

A full keymap used by the help utility package. It has the same keymap in its value cell and in its function cell.

Info-edit-map

A sparse keymap used by the e command of Info.

Info-mode-map

A sparse keymap containing Info commands.

isearch-mode-map

A keymap that defines the characters you can type within incremental search.

key-translation-map

A keymap for translating keys. This one overrides ordinary key bindings, unlike

function-key-map.
lisp-interaction-mode-map

A sparse keymap used by Lisp mode.

lisp-mode-map

A sparse keymap used by Lisp mode.

menu-bar-edit-menu

The keymap which displays the Edit menu in the menu bar.

menu-bar-files-menu

The keymap which displays the Files menu in the menu bar.

menu-bar-help-menu

The keymap which displays the Help menu in the menu bar.

menu-bar-search-menu

The keymap which displays the Search menu in the menu bar.

menu-bar-tools-menu

The keymap which displays the Tools menu in the menu bar.

mode-specific-map

The keymap for characters following C-c. Note, this is in the global map. This map is not actually mode specific: its name was chosen to be informative for the user in C-h b (display-bindings), where it describes the main use of the C-c prefix key.

occur-mode-map

A local keymap used by Occur mode.

query-replace-map

A local keymap used for responses in query-replace and related commands; also for y-or-n-p and map-y-or-n-p. The functions that use this map do not support prefix keys; they look up one event at a time.

text-mode-map

A sparse keymap used by Text mode.

view-mode-map

A full keymap used by View mode.

634 GNU Emacs Lisp Reference Manual

Appendix F Standard Hooks

The following is a list of hook variables that let you provide functions to be called from within Emacs on suitable occasions.

Most of these variables have names ending with ‘-hook’. They are normal hooks, run by means of run-hooks. The value of such a hook is a list of functions; the functions are called with no arguments and their values are completely ignored. The recommended way to put a new function on such a hook is to call add-hook. See Section 20.4 [Hooks], page 316, for more information about using hooks.

The variables whose names end in ‘-hooks’ or ‘-functions’ are usually abnormal hooks; their values are lists of functions, but these functions are called in a special way (they are passed arguments, or their values are used). A few of these variables are actually normal hooks which were named before we established the convention that normal hooks’ names should end in ‘-hook’.

The variables whose names end in ‘-function’ have single functions as their values. (In older Emacs versions, some of these variables had names ending in ‘-hook’ even though they were not normal hooks; however, we have renamed all of those.)

activate-mark-hook
after-change-function
after-change-functions
after-init-hook
after-insert-file-functions
after-make-frame-hook
auto-fill-function
auto-save-hook
before-change-function
before-change-functions
before-init-hook
before-make-frame-hook
blink-paren-function
c-mode-hook
calendar-load-hook
command-history-hook
comment-indent-function
deactivate-mark-hook
diary-display-hook
diary-hook
dired-mode-hook
disabled-command-hook
edit-picture-hook

electric-buffer-menu-mode-hook
electric-command-history-hook
electric-help-mode-hook
emacs-lisp-mode-hook
find-file-hooks
find-file-not-found-hooks
first-change-hook
fortran-comment-hook
fortran-mode-hook
ftp-setup-write-file-hooks
ftp-write-file-hook
indent-mim-hook
initial-calendar-window-hook
kill-buffer-query-functions
kill-emacs-query-functions
LaTeX-mode-hook
ledit-mode-hook
lisp-indent-function
lisp-interaction-mode-hook
lisp-mode-hook
list-diary-entries-hook
m2-mode-hook
mail-mode-hook
mail-setup-hook
mark-diary-entries-hook
medit-mode-hook
mh-compose-letter-hook
mh-folder-mode-hook
mh-letter-mode-hook
mim-mode-hook
minibuffer-setup-hook
minibuffer-exit-hook
news-mode-hook
news-reply-mode-hook
news-setup-hook
nongregorian-diary-listing-hook
nongregorian-diary-marking-hook
nroff-mode-hook

outline-mode-hook
plain-TeX-mode-hook
post-command-hook
pre-abbrev-expand-hook
pre-command-hook
print-diary-entries-hook
prolog-mode-hook
protect-innocence-hook
rmail-edit-mode-hook
rmail-mode-hook
rmail-summary-mode-hook
scheme-indent-hook
scheme-mode-hook
scribe-mode-hook
shell-mode-hook
shell-set-directory-error-hook
suspend-hook
suspend-resume-hook
temp-buffer-show-function
term-setup-hook
terminal-mode-hook
terminal-mode-break-hook
TeX-mode-hook
text-mode-hook
today-visible-calendar-hook
today-invisible-calendar-hook
vi-mode-hook
view-hook
window-setup-hook
write-contents-hooks
write-file-hooks
write-region-annotate-functions

638 GNU Emacs Lisp Reference Manual

Index 639

Index

#

‘#$’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 ‘#@count’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

$

‘$’ in display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568 ‘$’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494

%

% . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 ‘%’ in format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

&

‘&’ in replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504 &define (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 &not (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 &optional. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 &optional (Edebug). . . . . . . . . . . . . . . . . . . . . . . . . . 205 &or (Edebug). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 &rest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 &rest (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205

’

‘'’ for quoting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

(

‘(’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495 ‘(…)’ in lists. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

)

‘)’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495

*

* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 ‘*’ in interactive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 ‘*’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493 ‘*scratch*’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

,

, (with Backquote) . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 ,@ (with Backquote) . . . . . . . . . . . . . . . . . . . . . . . . . . 155

-

- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

.

‘.’ in lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 ‘.’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493 ‘.emacs’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544 ‘.emacs’ customization . . . . . . . . . . . . . . . . . . . . . . . 301

/

/ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 /= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

;

‘;’ in comment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

?

‘?’ in character constant . . . . . . . . . . . . . . . . . . . . . . . 19 ? in minibuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 ‘?’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494

@

‘@’ in interactive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

[

‘[’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494 […] (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206

]

‘]’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494

‘

` . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 ‘ (list substitution) . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

                              "

‘"’ in printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 ‘"’ in strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

                              |

‘|’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495

                              +

+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 ‘+’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493

                              =

= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

>

> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 >= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

^

‘^’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494

\

‘\’ in character constant . . . . . . . . . . . . . . . . . . . . . . . 19 ‘\’ in display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568 ‘\’ in printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 ‘\’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494 ‘\’ in replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504 ‘\’ in strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 ‘\’ in symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 ‘\'’ in regexp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496 ‘\=’ in regexp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496 ‘\`’ in regexp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496 ‘\>’ in regexp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496 ‘\<’ in regexp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496 ‘\a’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 ‘\b’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 ‘\b’ in regexp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496 ‘\B’ in regexp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496 ‘\e’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 ‘\f’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 ‘\n’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 ‘\n’ in print . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 ‘\n’ in replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . 504 ‘\r’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 ‘\s’ in regexp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496 ‘\S’ in regexp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496 ‘\t’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 ‘\v’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 ‘\w’ in regexp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496 ‘\W’ in regexp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496

<

< . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 <= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

1

1- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 1+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

A

abbrev . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519 abbrev table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519 abbrev tables in modes . . . . . . . . . . . . . . . . . . . . . . . 300 abbrev-all-caps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522 abbrev-expansion. . . . . . . . . . . . . . . . . . . . . . . . . . . . 521 abbrev-file-name. . . . . . . . . . . . . . . . . . . . . . . . . . . . 521 abbrev-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519 abbrev-prefix-mark . . . . . . . . . . . . . . . . . . . . . . . . . 522 abbrev-start-location . . . . . . . . . . . . . . . . . . . . . . 522

abbrev-start-location-buffer . . . . . . . . . . . . . . 522

abbrev-symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521 abbrev-table-name-list. . . . . . . . . . . . . . . . . . . . . 520 abbreviate-file-name . . . . . . . . . . . . . . . . . . . . . . . 347 abbrevs-changed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521 abort-recursive-edit . . . . . . . . . . . . . . . . . . . . . . . 273 aborting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 abs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 absolute file name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347 accept-process-output . . . . . . . . . . . . . . . . . . . . . . 538 accessibility of a file . . . . . . . . . . . . . . . . . . . . . . . . . . 337 accessible portion (of a buffer) . . . . . . . . . . . . . . . . 438 accessible-keymaps . . . . . . . . . . . . . . . . . . . . . . . . . 292 acos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 activate-mark-hook . . . . . . . . . . . . . . . . . . . . . . . . . 447 active display table . . . . . . . . . . . . . . . . . . . . . . . . . . . 584 active keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281

active-minibuffer-window . . . . . . . . . . . . . . . . . . 241

add-abbrev . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520 add-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 add-name-to-file. . . . . . . . . . . . . . . . . . . . . . . . . . . . 342 add-text-properties . . . . . . . . . . . . . . . . . . . . . . . . 479 add-to-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 address field of register . . . . . . . . . . . . . . . . . . . . . . . . 20 after-change-function . . . . . . . . . . . . . . . . . . . . . . 490 after-change-functions. . . . . . . . . . . . . . . . . . . . . 489 after-find-file. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 after-init-hook. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545

after-insert-file-functions . . . . . . . . . . . . . . . 485

after-load-alist. . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 after-make-frame-hook . . . . . . . . . . . . . . . . . . . . . . 409 after-revert-hook . . . . . . . . . . . . . . . . . . . . . . . . . . 367 after-save-hook. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333 after-string (overlay property) . . . . . . . . . . . . . 576 alist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

all-christian-calendar-holidays . . . . . . . . . . 588

all-completions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

all-hebrew-calendar-holidays . . . . . . . . . . . . . . 588
all-islamic-calendar-holidays. . . . . . . . . . . . . 588

alt characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 and . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 anonymous function . . . . . . . . . . . . . . . . . . . . . . . . . . 148 anonymous lambda expressions (Edebug) . . . . . 192 apostrophe for quoting . . . . . . . . . . . . . . . . . . . . . . . 103 append . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 append-to-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 apply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 apply, and debugging . . . . . . . . . . . . . . . . . . . . . . . . 188 appt-audible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597

appt-delete-window-function . . . . . . . . . . . . . . . 597
appt-disp-window-function . . . . . . . . . . . . . . . . . 597

appt-display-duration . . . . . . . . . . . . . . . . . . . . . . 597 appt-display-mode-line. . . . . . . . . . . . . . . . . . . . . 597

appt-message-warning-time . . . . . . . . . . . . . . . . . 597

appt-msg-window. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597 appt-visible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597 apropos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324 aref . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 argument binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 argument descriptors . . . . . . . . . . . . . . . . . . . . . . . . . 244 argument evaluation form . . . . . . . . . . . . . . . . . . . . 244 argument prompt. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 arguments, reading . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 arith-error example . . . . . . . . . . . . . . . . . . . . . . . . 116 arith-error in division . . . . . . . . . . . . . . . . . . . . . . . 40 arithmetic shift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 array elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 arrayp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 ASCII character codes . . . . . . . . . . . . . . . . . . . . . . . . 17 aset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 ash. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 asin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 ask-user-about-lock . . . . . . . . . . . . . . . . . . . . . . . . 336

ask-user-about-supersession-threat . . . . . . . 375

asking the user questions . . . . . . . . . . . . . . . . . . . . . 237 assoc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 association list. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 assq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 asynchronous subprocess. . . . . . . . . . . . . . . . . . . . . . 529 atan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 atom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 atom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 atoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 attributes of text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478 Auto Fill mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467 auto-fill-function . . . . . . . . . . . . . . . . . . . . . . . . . 467 auto-mode-alist. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 auto-save-default . . . . . . . . . . . . . . . . . . . . . . . . . . 365 auto-save-file-format . . . . . . . . . . . . . . . . . . . . . . 356 auto-save-file-name-p . . . . . . . . . . . . . . . . . . . . . . 364 auto-save-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365 auto-save-interval . . . . . . . . . . . . . . . . . . . . . . . . . 365

auto-save-list-file-name . . . . . . . . . . . . . . . . . . 366

auto-save-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363 auto-save-timeout . . . . . . . . . . . . . . . . . . . . . . . . . . 365

                                                auto-save-visited-file-name . . . . . . . . . . . . . . . 364

auto-saving. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363 autoload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 autoload errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 automatically buffer-local . . . . . . . . . . . . . . . . . . . . . 134

B

back-to-indentation . . . . . . . . . . . . . . . . . . . . . . . . 476 backquote (list substitution) . . . . . . . . . . . . . . . . . . 155 backslash in character constant . . . . . . . . . . . . . . . . 19 backslash in strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 backslash in symbols. . . . . . . . . . . . . . . . . . . . . . . . . . . 19 backspace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 backtrace. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 backtrace-debug. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 backtrace-frame. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 backtracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 backup file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 backup files, how to make them . . . . . . . . . . . . . . . 360 backup-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 backup-by-copying . . . . . . . . . . . . . . . . . . . . . . . . . . 360

                                                backup-by-copying-when-linked. . . . . . . . . . . . . 361
                                                backup-by-copying-when-mismatch . . . . . . . . . . 361
                                                backup-enable-predicate . . . . . . . . . . . . . . . . . . . 360

backup-file-name-p . . . . . . . . . . . . . . . . . . . . . . . . . 362 backup-inhibited. . . . . . . . . . . . . . . . . . . . . . . . . . . . 360 backward-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430

                                                backward-delete-char-untabify. . . . . . . . . . . . . 455

backward-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435 backward-prefix-chars . . . . . . . . . . . . . . . . . . . . . . 515 backward-sexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436

                                                backward-to-indentation . . . . . . . . . . . . . . . . . . . 476

backward-word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431 balancing parentheses . . . . . . . . . . . . . . . . . . . . . . . . 581

                                                barf-if-buffer-read-only . . . . . . . . . . . . . . . . . . 376

base buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380 basic code (of input character) . . . . . . . . . . . . . . . . 252 batch mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565 batch-byte-compile . . . . . . . . . . . . . . . . . . . . . . . . . 173 baud-rate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563 beep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586 beeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586 before point, insertion . . . . . . . . . . . . . . . . . . . . . . . . 452 before-change-function. . . . . . . . . . . . . . . . . . . . . 490

                                                before-change-functions . . . . . . . . . . . . . . . . . . . 489

before-init-hook. . . . . . . . . . . . . . . . . . . . . . . . . . . . 545 before-make-frame-hook. . . . . . . . . . . . . . . . . . . . . 409 before-revert-hook . . . . . . . . . . . . . . . . . . . . . . . . . 367 before-string (overlay property) . . . . . . . . . . . . 576 beginning of line. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433 beginning of line in regexp . . . . . . . . . . . . . . . . . . . . 494 beginning-of-buffer . . . . . . . . . . . . . . . . . . . . . . . . 431 beginning-of-defun . . . . . . . . . . . . . . . . . . . . . . . . . 436 beginning-of-line . . . . . . . . . . . . . . . . . . . . . . . . . . 432 bell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586 bell character. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 binary files and text files. . . . . . . . . . . . . . . . . . . . . . 356 binary-process-input . . . . . . . . . . . . . . . . . . . . . . . 529 binary-process-output . . . . . . . . . . . . . . . . . . . . . . 529 binding arguments. . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 binding local variables . . . . . . . . . . . . . . . . . . . . . . . . 122 binding of a key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 bitwise and . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 bitwise exclusive or . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 bitwise not . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 bitwise or . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 blink-matching-open . . . . . . . . . . . . . . . . . . . . . . . . 581 blink-matching-paren . . . . . . . . . . . . . . . . . . . . . . . 581

blink-matching-paren-delay . . . . . . . . . . . . . . . . 581
blink-matching-paren-distance. . . . . . . . . . . . . 581

blink-paren-function . . . . . . . . . . . . . . . . . . . . . . . 581 blink-paren-hook. . . . . . . . . . . . . . . . . . . . . . . . . . . . 581 blinking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581 bobp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 body of function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 bold (face name) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 578 bold-italic (face name) . . . . . . . . . . . . . . . . . . . . . 578 bolp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 boolean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 boundp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 box diagrams, for lists . . . . . . . . . . . . . . . . . . . . . . . . . 21 box representation for lists. . . . . . . . . . . . . . . . . . . . . 61 break . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 bucket (in obarray) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 buffer contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449 buffer file name. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372 buffer input stream . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 buffer internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618 buffer list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377 buffer modification . . . . . . . . . . . . . . . . . . . . . . . . . . . 374 buffer names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 buffer output stream . . . . . . . . . . . . . . . . . . . . . . . . . 216 buffer text notation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 buffer, read-only. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376

buffer-access-fontified-property . . . . . . . . . 486
buffer-access-fontify-functions . . . . . . . . . . 486

                                                buffer-auto-save-file-name . . . . . . . . . . . . . . . . 363

buffer-backed-up. . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 buffer-base-buffer . . . . . . . . . . . . . . . . . . . . . . . . . 381 buffer-disable-undo . . . . . . . . . . . . . . . . . . . . . . . . 463 buffer-display-table . . . . . . . . . . . . . . . . . . . . . . . 584 buffer-enable-undo . . . . . . . . . . . . . . . . . . . . . . . . . 463 buffer-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430 buffer-file-format . . . . . . . . . . . . . . . . . . . . . . . . . 355 buffer-file-name . . . . . . . . . . . . . . . . . . . . . . . 372, 373 buffer-file-number . . . . . . . . . . . . . . . . . . . . . . . . . 373 buffer-file-truename . . . . . . . . . . . . . . . . . . . . . . . 373 buffer-file-type. . . . . . . . . . . . . . . . . . . . . . . . . . . . 356 buffer-flush-undo . . . . . . . . . . . . . . . . . . . . . . . . . . 463

                                                buffer-invisibility-spec . . . . . . . . . . . . . . . . . . 570

buffer-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377 buffer-local variables. . . . . . . . . . . . . . . . . . . . . . . . . . 134 buffer-local variables in modes . . . . . . . . . . . . . . . . 301 buffer-local-variables. . . . . . . . . . . . . . . . . . . . . 136 Buffer-menu-mode-map . . . . . . . . . . . . . . . . . . . . . . . 631 buffer-modified-p . . . . . . . . . . . . . . . . . . . . . . . . . . 374 buffer-modified-tick . . . . . . . . . . . . . . . . . . . . . . . 374 buffer-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 buffer-offer-save. . . . . . . . . . . . . . . . . . . . . . 332, 380 buffer-read-only. . . . . . . . . . . . . . . . . . . . . . . . . . . . 376 buffer-saved-size . . . . . . . . . . . . . . . . . . . . . . . . . . 366 buffer-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430 buffer-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451 buffer-substring. . . . . . . . . . . . . . . . . . . . . . . . . . . . 450

                                                buffer-substring-no-properties . . . . . . . . . . . 451

buffer-undo-list. . . . . . . . . . . . . . . . . . . . . . . . . . . . 461 bufferp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 buffers, controlled in windows. . . . . . . . . . . . . . . . . 390 buffers, creating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378 buffers, killing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379 building Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609 building lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 built-in function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 bury-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378 button-down event . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 byte-code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 byte-code. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 byte-code function. . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 byte-code interpreter . . . . . . . . . . . . . . . . . . . . . . . . . 173 byte-code-function-p . . . . . . . . . . . . . . . . . . . . . . . 140 byte-compile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 byte-compile-dynamic . . . . . . . . . . . . . . . . . . . . . . . 175

                                                byte-compile-dynamic-docstrings . . . . . . . . . . 174

byte-compile-file . . . . . . . . . . . . . . . . . . . . . . . . . . 173 byte-compiling macros . . . . . . . . . . . . . . . . . . . . . . . . 154 byte-compiling require. . . . . . . . . . . . . . . . . . . . . . . 167

byte-recompile-directory . . . . . . . . . . . . . . . . . . 173

bytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

C

C-c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 C-g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 C-h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 C-M-x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 c-mode-abbrev-table . . . . . . . . . . . . . . . . . . . . . . . . 523 c-mode-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631 c-mode-syntax-table . . . . . . . . . . . . . . . . . . . . . . . . 517 C-q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564 C-s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564 C-x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 C-x 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 C-x 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 C-x a. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 C-x n. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 C-x r. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 cache-long-line-scans . . . . . . . . . . . . . . . . . . . . . . 569

calendar-date-display-form . . . . . . . . . . . . . . . . 590
calendar-daylight-savings-ends . . . . . . . . . . . 591
calendar-daylight-savings-ends-time . . . . . . 591
calendar-daylight-savings-starts . . . . . . . . . 591
calendar-daylight-savings-starts-time . . . 591
calendar-daylight-time-offset. . . . . . . . . . . . . 591
calendar-holiday-marker . . . . . . . . . . . . . . . . . . . 587

calendar-holidays . . . . . . . . . . . . . . . . . . . . . . . . . . 588 calendar-load-hook . . . . . . . . . . . . . . . . . . . . . . . . . 587 calendar-mark-today . . . . . . . . . . . . . . . . . . . . . . . . 587 calendar-star-date . . . . . . . . . . . . . . . . . . . . . . . . . 587

calendar-time-display-form . . . . . . . . . . . . . . . . 590

calendar-today-marker . . . . . . . . . . . . . . . . . . . . . . 588 call stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 call-interactively . . . . . . . . . . . . . . . . . . . . . . . . . 248 call-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526 call-process-region . . . . . . . . . . . . . . . . . . . . . . . . 528 calling a function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 cancel-debug-on-entry . . . . . . . . . . . . . . . . . . . . . . 183 cancel-timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558 candle lighting times . . . . . . . . . . . . . . . . . . . . . . . . . 596 capitalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 capitalize. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 capitalize-region . . . . . . . . . . . . . . . . . . . . . . . . . . 476 capitalize-word. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477 car. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 car-safe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 case changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476 case in replacements . . . . . . . . . . . . . . . . . . . . . . . . . . 503 case-fold-search. . . . . . . . . . . . . . . . . . . . . . . . . . . . 506 case-replace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506 case-table-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 catch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 category (overlay property) . . . . . . . . . . . . . . . . . . 575 category (text property) . . . . . . . . . . . . . . . . . . . . . 482 category of text character. . . . . . . . . . . . . . . . . . . . . 482 cbreak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565 cdr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 cdr-safe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 ceiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 centering point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399 change hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489 change hooks for a character . . . . . . . . . . . . . . . . . . 483 change-major-mode-hook. . . . . . . . . . . . . . . . . . . . . 301 changing key bindings . . . . . . . . . . . . . . . . . . . . . . . . 288 changing to another buffer . . . . . . . . . . . . . . . . . . . . 369 changing window size . . . . . . . . . . . . . . . . . . . . . . . . . 404 char-after . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449 char-equal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 char-or-string-p. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 char-syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514 char-to-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 character arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 character case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 character insertion. . . . . . . . . . . . . . . . . . . . . . . . . . . . 453 character printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 character quote . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511 character set (in regexp) . . . . . . . . . . . . . . . . . . . . . . 494 character to string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 characters for interactive codes . . . . . . . . . . . . . . . 245 child process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525 christian-holidays . . . . . . . . . . . . . . . . . . . . . . . . . 588 CL note—allocate more storage. . . . . . . . . . . . . . . 612 CL note—case of letters . . . . . . . . . . . . . . . . . . . . . . . 19 CL note—default optional arg . . . . . . . . . . . . . . . . 142 CL note—integers vrs eq . . . . . . . . . . . . . . . . . . . . . . 37 CL note—lack union, intersection . . . . . . . . . . . 73 CL note—no continuable errors . . . . . . . . . . . . . . . 114 CL note—only throw in Emacs . . . . . . . . . . . . . . . 111 CL note—rplaca vrs setcar. . . . . . . . . . . . . . . . . . . 67 CL note—set local . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 CL note—special forms compared. . . . . . . . . . . . . 102 CL note—special variables . . . . . . . . . . . . . . . . . . . . 131 CL note—symbol in obarrays . . . . . . . . . . . . . . . . . . 90 cl-specs.el . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 cl.el (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 cleanup forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 clear-abbrev-table . . . . . . . . . . . . . . . . . . . . . . . . . 519

clear-visited-file-modtime . . . . . . . . . . . . . . . . 375

click event. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 close parenthesis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581

close parenthesis character. . . . . . . . . . . . . . . . 511

closures not available . . . . . . . . . . . . . . . . . . . . . . . . . 132 codes, interactive, description of . . . . . . . . . . . . . . 245 coding standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 599 columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 command descriptions . . . . . . . . . . . . . . . . . . . . . . . . . 12 command history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 command in keymap . . . . . . . . . . . . . . . . . . . . . . . . . 285 command line arguments . . . . . . . . . . . . . . . . . . . . . 546 command line options . . . . . . . . . . . . . . . . . . . . . . . . 546 command loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 command loop, recursive . . . . . . . . . . . . . . . . . . . . . 271 command-debug-status . . . . . . . . . . . . . . . . . . . . . . . 188 command-execute. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 command-history. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 command-history-map . . . . . . . . . . . . . . . . . . . . . . . . 631 command-line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546 command-line-args . . . . . . . . . . . . . . . . . . . . . . . . . . 547 command-line-functions. . . . . . . . . . . . . . . . . . . . . 547 command-line-processed. . . . . . . . . . . . . . . . . . . . . 546 command-switch-alist . . . . . . . . . . . . . . . . . . . . . . . 546 commandp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 commandp example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 commands, defining . . . . . . . . . . . . . . . . . . . . . . . . . . 244 comment ender . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512 comment starter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512 comment syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512 comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Common Lisp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Common Lisp (Edebug) . . . . . . . . . . . . . . . . . . . . . . 192

compare-buffer-substrings . . . . . . . . . . . . . . . . . 451

comparing buffer text. . . . . . . . . . . . . . . . . . . . . . . . . 451 comparison of modification time . . . . . . . . . . . . . . 375 compilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 compilation functions . . . . . . . . . . . . . . . . . . . . . . . . . 172 compile-defun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 compiled function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 complete key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 completing-read. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 completion, file name . . . . . . . . . . . . . . . . . . . . . . . . . 349 completion-auto-help . . . . . . . . . . . . . . . . . . . . . . . 233 completion-ignore-case. . . . . . . . . . . . . . . . . . . . . 230

completion-ignored-extensions. . . . . . . . . . . . . 350

complex arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 complex command. . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 compute-motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434 concat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 concatenating lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 concatenating strings . . . . . . . . . . . . . . . . . . . . . . . . . . 51 cond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 condition name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 condition-case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 conditional evaluation . . . . . . . . . . . . . . . . . . . . . . . . 106 cons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 cons cell as box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 cons cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 consing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 consp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 continuation lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568 continue-process. . . . . . . . . . . . . . . . . . . . . . . . . . . . 535 control character key constants . . . . . . . . . . . . . . . 288 control character printing . . . . . . . . . . . . . . . . . . . . . 323 control characters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 control characters in display . . . . . . . . . . . . . . . . . . 583 control characters, reading . . . . . . . . . . . . . . . . . . . . 265 control structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Control-X-prefix. . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 conventions for writing minor modes . . . . . . . . . . 309 conversion of strings . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

                                                convert-standard-filename . . . . . . . . . . . . . . . . . 350
                                                coordinates-in-window-p . . . . . . . . . . . . . . . . . . . 405

copy-alist. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 copy-face. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579 copy-file. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343 copy-keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 copy-marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443 copy-region-as-kill . . . . . . . . . . . . . . . . . . . . . . . . 458 copy-sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 copy-syntax-table . . . . . . . . . . . . . . . . . . . . . . . . . . 513 copying alists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 copying files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342 copying lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 copying sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 copying strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 copying vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 cos. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 count-lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433 count-loop. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 counting columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 coverage testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 create-file-buffer . . . . . . . . . . . . . . . . . . . . . . . . . 331 creating buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378 creating keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 ctl-arrow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583 ctl-x-4-map. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281, 631 ctl-x-5-map. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281, 631 ctl-x-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281, 631 current binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 current buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 current buffer excursion . . . . . . . . . . . . . . . . . . . . . . 437 current buffer mark. . . . . . . . . . . . . . . . . . . . . . . . . . . 445 current buffer point and mark (Edebug) . . . . . . 203 current buffer position . . . . . . . . . . . . . . . . . . . . . . . . 429 current command. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 current stack frame . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 current-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 current-case-table . . . . . . . . . . . . . . . . . . . . . . . . . . 59 current-column . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 current-fill-column . . . . . . . . . . . . . . . . . . . . . . . . 467

current-frame-configuration . . . . . . . . . . . . . . . 421

current-global-map . . . . . . . . . . . . . . . . . . . . . . . . . 282 current-indentation . . . . . . . . . . . . . . . . . . . . . . . . 472 current-input-mode . . . . . . . . . . . . . . . . . . . . . . . . . 559 current-justification . . . . . . . . . . . . . . . . . . . . . . 465 current-kill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459 current-left-margin . . . . . . . . . . . . . . . . . . . . . . . . 467 current-local-map . . . . . . . . . . . . . . . . . . . . . . . . . . 283

current-minor-mode-maps . . . . . . . . . . . . . . . . . . . 283

current-prefix-arg . . . . . . . . . . . . . . . . . . . . . . . . . 271 current-time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553 current-time-string . . . . . . . . . . . . . . . . . . . . . . . . 553 current-time-zone . . . . . . . . . . . . . . . . . . . . . . . . . . 553

current-window-configuration . . . . . . . . . . . . . . 406

cursor-in-echo-area . . . . . . . . . . . . . . . . . . . . . . . . 570 cust-print . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 cut buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425 cyclic ordering of windows . . . . . . . . . . . . . . . . . . . . 388

D

data type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 data-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326 daylight savings time . . . . . . . . . . . . . . . . . . . . . . . . . 591 deactivate-mark. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447 deactivate-mark-hook . . . . . . . . . . . . . . . . . . . . . . . 447 debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 debug-ignored-errors . . . . . . . . . . . . . . . . . . . . . . . 182 debug-on-entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 debug-on-error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 debug-on-error use . . . . . . . . . . . . . . . . . . . . . . . . . . 114 debug-on-next-call . . . . . . . . . . . . . . . . . . . . . . . . . 188 debug-on-quit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 debugger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 debugger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 debugger command list . . . . . . . . . . . . . . . . . . . . . . . 185 debugger-mode-map . . . . . . . . . . . . . . . . . . . . . . . . . . 631 debugging errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 debugging specific functions . . . . . . . . . . . . . . . . . . 182 decode-time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555 decoding file formats . . . . . . . . . . . . . . . . . . . . . . . . . 354 decrement field of register. . . . . . . . . . . . . . . . . . . . . . 20 dedicated window . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395 deep binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 def-edebug-spec. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 defalias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 default (face name). . . . . . . . . . . . . . . . . . . . . . . . . . 578 default argument string. . . . . . . . . . . . . . . . . . . . . . . 245 default init file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544 default key binding . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 default value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 default-abbrev-mode . . . . . . . . . . . . . . . . . . . . . . . . 519 default-boundp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

default-buffer-file-type . . . . . . . . . . . . . . . . . . 357
default-case-fold-search . . . . . . . . . . . . . . . . . . 506

default-ctl-arrow . . . . . . . . . . . . . . . . . . . . . . . . . . 583 default-directory . . . . . . . . . . . . . . . . . . . . . . . . . . 348 default-file-modes . . . . . . . . . . . . . . . . . . . . . . . . . 344 default-fill-column . . . . . . . . . . . . . . . . . . . . . . . . 466 default-frame-alist . . . . . . . . . . . . . . . . . . . . . . . . 411 default-justification . . . . . . . . . . . . . . . . . . . . . . 465 default-major-mode . . . . . . . . . . . . . . . . . . . . . . . . . 306

default-minibuffer-frame . . . . . . . . . . . . . . . . . . 419
default-mode-line-format . . . . . . . . . . . . . . . . . . 314
default-text-properties . . . . . . . . . . . . . . . . . . . 479

default-truncate-lines. . . . . . . . . . . . . . . . . . . . . 568 default-value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 ‘default.el’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543 defconst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 define-abbrev . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520 define-abbrev-table . . . . . . . . . . . . . . . . . . . . . . . . 520 define-derived-mode . . . . . . . . . . . . . . . . . . . . . . . . 308 define-key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 define-key-after. . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 define-logical-name . . . . . . . . . . . . . . . . . . . . . . . . 343 define-prefix-command . . . . . . . . . . . . . . . . . . . . . . 281 defining a function . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 defining commands . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 defining menus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 defining-kbd-macro . . . . . . . . . . . . . . . . . . . . . . . . . 275 definition of a symbol. . . . . . . . . . . . . . . . . . . . . . . . . . 88 defmacro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 defsubst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 defun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 defun-prompt-regexp . . . . . . . . . . . . . . . . . . . . . . . . 436 defvar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 delete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 delete previous char . . . . . . . . . . . . . . . . . . . . . . . . . . 455

delete-auto-save-file-if-necessary . . . . . . . 365

delete-auto-save-files. . . . . . . . . . . . . . . . . . . . . 366 delete-backward-char . . . . . . . . . . . . . . . . . . . . . . . 455 delete-blank-lines . . . . . . . . . . . . . . . . . . . . . . . . . 457 delete-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455 delete-directory. . . . . . . . . . . . . . . . . . . . . . . . . . . . 352

delete-exited-processes . . . . . . . . . . . . . . . . . . . 531

delete-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343 delete-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 delete-frame event . . . . . . . . . . . . . . . . . . . . . . . . . . 258

delete-horizontal-space . . . . . . . . . . . . . . . . . . . 455

delete-indentation . . . . . . . . . . . . . . . . . . . . . . . . . 456 delete-other-windows . . . . . . . . . . . . . . . . . . . . . . . 387 delete-overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577 delete-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531 delete-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454 delete-to-left-margin . . . . . . . . . . . . . . . . . . . . . . 467 delete-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387 delete-windows-on . . . . . . . . . . . . . . . . . . . . . . . . . . 387 deleting files. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342 deleting processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 530 deleting whitespace . . . . . . . . . . . . . . . . . . . . . . . . . . . 455 deleting windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386 deletion of elements. . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 deletion of frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 deletion vs killing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454 delq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 describe-bindings . . . . . . . . . . . . . . . . . . . . . . . . . . 293

describe-buffer-case-table . . . . . . . . . . . . . . . . . 59

describe-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

describe-prefix-bindings . . . . . . . . . . . . . . . . . . 326

description for interactive codes. . . . . . . . . . . . . . . 245 description format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 diagrams, boxed, for lists . . . . . . . . . . . . . . . . . . . . . . 21 dialog boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424 diary buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594 diary-anniversary . . . . . . . . . . . . . . . . . . . . . . . . . . 595 diary-astro-day-number. . . . . . . . . . . . . . . . . . . . . 596 diary-cyclic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595 diary-date-forms. . . . . . . . . . . . . . . . . . . . . . . . . . . . 592 diary-day-of-year . . . . . . . . . . . . . . . . . . . . . . . . . . 596 diary-display-hook . . . . . . . . . . . . . . . . . . . . . . . . . 594 diary-entry-marker . . . . . . . . . . . . . . . . . . . . . . . . . 587 diary-french-date . . . . . . . . . . . . . . . . . . . . . . . . . . 596 diary-hebrew-date . . . . . . . . . . . . . . . . . . . . . . . . . . 596 diary-islamic-date . . . . . . . . . . . . . . . . . . . . . . . . . 596 diary-iso-date . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596 diary-julian-date . . . . . . . . . . . . . . . . . . . . . . . . . . 596

diary-list-include-blanks . . . . . . . . . . . . . . . . . 594

diary-mayan-date. . . . . . . . . . . . . . . . . . . . . . . . . . . . 596 diary-omer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596 diary-parasha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596 diary-phases-of-moon . . . . . . . . . . . . . . . . . . . . . . . 596 diary-rosh-hodesh . . . . . . . . . . . . . . . . . . . . . . . . . . 596 diary-sabbath-candles . . . . . . . . . . . . . . . . . . . . . . 596 diary-sunrise-sunset . . . . . . . . . . . . . . . . . . . . . . . 596 diary-yahrzeit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596 digit-argument . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 ding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586 directory name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345 directory name abbreviation . . . . . . . . . . . . . . . . . . 346 directory part (of file name) . . . . . . . . . . . . . . . . . . 344 directory-abbrev-alist. . . . . . . . . . . . . . . . . . . . . 346 directory-file-name . . . . . . . . . . . . . . . . . . . . . . . . 346 directory-files. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351 directory-oriented functions . . . . . . . . . . . . . . . . . . . 351 dired-kept-versions . . . . . . . . . . . . . . . . . . . . . . . . 362 dired-mode-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631 disable undo. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463 disable-command. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 disabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 disabled command. . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 disabled-command-hook . . . . . . . . . . . . . . . . . . . . . . 274 disassemble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 disassembled byte-code . . . . . . . . . . . . . . . . . . . . . . . 177 discard input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 discard-input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 display columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567 display lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567 display table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583 display-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393

                                                display-buffer-function . . . . . . . . . . . . . . . . . . . 395
                                                display-completion-list . . . . . . . . . . . . . . . . . . . 233

displaying a buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391 displays, multiple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 do-auto-save . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365 ‘DOC’ (documentation) file . . . . . . . . . . . . . . . . . . . . 319 doc-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322 documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320 documentation conventions . . . . . . . . . . . . . . . . . . . 319 documentation for major mode . . . . . . . . . . . . . . . 307 documentation notation . . . . . . . . . . . . . . . . . . . . . . . 11 documentation of function . . . . . . . . . . . . . . . . . . . . 143 documentation strings . . . . . . . . . . . . . . . . . . . . . . . . 319 documentation, keys in . . . . . . . . . . . . . . . . . . . . . . . 322 documentation-property. . . . . . . . . . . . . . . . . . . . . 320 dotted lists (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . . 206 dotted pair notation . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 double-click events . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 double-click-time . . . . . . . . . . . . . . . . . . . . . . . . . . 257 double-quote in strings . . . . . . . . . . . . . . . . . . . . . . . . 23 down-list. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436 downcase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 downcase-region. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477 downcase-word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477 downcasing in lookup-key . . . . . . . . . . . . . . . . . . . . 264 drag event. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 dribble file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562 dump-emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 610 dynamic loading of documentation . . . . . . . . . . . . 174 dynamic loading of functions . . . . . . . . . . . . . . . . . 174 dynamic scoping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

E

echo area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569 echo-keystrokes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570 edebug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Edebug. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 Edebug execution modes. . . . . . . . . . . . . . . . . . . . . . 193 Edebug mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 Edebug specification list . . . . . . . . . . . . . . . . . . . . . . 204 edebug-all-defs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 edebug-all-forms . . . . . . . . . . . . . . . . . . . . . . . 192, 209

edebug-continue-kbd-macro . . . . . . . . . . . . . . . . . 210
edebug-display-freq-count . . . . . . . . . . . . . . . . . 201
edebug-eval-top-level-form . . . . . . . . . . . . . . . . 192
edebug-global-break-condition . . . . . . . . 196, 211

edebug-initial-mode . . . . . . . . . . . . . . . . . . . . . . . . 209 edebug-on-error. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210 edebug-on-quit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210 edebug-print-circle . . . . . . . . . . . . . . . . . . . . . . . . 210 edebug-print-length . . . . . . . . . . . . . . . . . . . 200, 210 edebug-print-level . . . . . . . . . . . . . . . . . . . . 200, 210

edebug-print-trace-after. . . . . . . . . . . . . . 201, 210
edebug-print-trace-before . . . . . . . . . . . . 201, 210
edebug-save-displayed-buffer-points . . . . . . 209

edebug-save-windows . . . . . . . . . . . . . . . . . . . . . . . . 209

edebug-set-global-break-condition . . . . . . . . 196

edebug-setup-hook . . . . . . . . . . . . . . . . . . . . . . . . . . 209 edebug-test-coverage . . . . . . . . . . . . . . . . . . . . . . . 210 edebug-trace . . . . . . . . . . . . . . . . . . . . . . . . . . . 201, 210 edebug-tracing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 edebug-unwrap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 edit-abbrevs-map. . . . . . . . . . . . . . . . . . . . . . . . . . . . 631 edit-and-eval-command . . . . . . . . . . . . . . . . . . . . . . 226 edit-tab-stops-map . . . . . . . . . . . . . . . . . . . . . . . . . 631 editing types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 editor command loop . . . . . . . . . . . . . . . . . . . . . . . . . 243

electric-buffer-menu-mode-map. . . . . . . . . . . . . 631

electric-future-map . . . . . . . . . . . . . . . . . . . . . . . . . 14 electric-history-map . . . . . . . . . . . . . . . . . . . . . . . 631 element (of list) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 elements of sequences . . . . . . . . . . . . . . . . . . . . . . . . . . 80 elt. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Emacs event standard notation . . . . . . . . . . . . . . . 323 emacs-build-time. . . . . . . . . . . . . . . . . . . . . . . . . . . . 610 emacs-lisp-mode-map . . . . . . . . . . . . . . . . . . . . . . . . 631

emacs-lisp-mode-syntax-table . . . . . . . . . . . . . . 517

emacs-major-version . . . . . . . . . . . . . . . . . . . . . . . . 610 emacs-minor-version . . . . . . . . . . . . . . . . . . . . . . . . 610 emacs-pid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552 emacs-version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 610 ‘emacs/etc/DOC-version’. . . . . . . . . . . . . . . . . . . . . . 319 EMACSLOADPATH environment variable. . . . . . . . . . 162 empty list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 enable-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 enable-flow-control . . . . . . . . . . . . . . . . . . . . . . . . 564 enable-flow-control-on. . . . . . . . . . . . . . . . . . . . . 565 enable-local-eval . . . . . . . . . . . . . . . . . . . . . . . . . . 306 enable-local-variables. . . . . . . . . . . . . . . . . . . . . 305

enable-recursive-minibuffers . . . . . . . . . . . . . . 242

encode-time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 556 encoding file formats . . . . . . . . . . . . . . . . . . . . . . . . . 354 end of buffer marker . . . . . . . . . . . . . . . . . . . . . . . . . . 443 end-of-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432 end-of-defun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436 end-of-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 end-of-line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432 enlarge-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404

enlarge-window-horizontally . . . . . . . . . . . . . . . 404

environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 environment variable access. . . . . . . . . . . . . . . . . . . 551 environment variables, subprocesses. . . . . . . . . . . 526 eobp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 eolp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 eq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 equal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 equality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 erase-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454 error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 error cleanup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 error debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 error description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 error display. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569 error handler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 error in debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 error message notation. . . . . . . . . . . . . . . . . . . . . . . . . 12 error name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 error symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 error-conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 error-message-string . . . . . . . . . . . . . . . . . . . . . . . 116 errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 ⟨\underline{\overline{ESC}}⟩ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 esc-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 ESC-prefix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 escape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 escape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511 escape characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 escape characters in printing. . . . . . . . . . . . . . . . . . 218 escape sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 ‘etc/DOC-version’. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319 eval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 eval, and debugging. . . . . . . . . . . . . . . . . . . . . . . . . . 188 eval-after-load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 eval-and-compile. . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 eval-current-buffer . . . . . . . . . . . . . . . . . . . . . . . . . 96

eval-current-buffer (Edebug) . . . . . . . . . . . . . . 192

eval-defun (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . 192

eval-expression (Edebug) . . . . . . . . . . . . . . . . . . . 193

eval-minibuffer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 eval-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 eval-region (Edebug) . . . . . . . . . . . . . . . . . . . . . . . 192 eval-when-compile . . . . . . . . . . . . . . . . . . . . . . . . . . 175 evaluated expression argument . . . . . . . . . . . . . . . . 247 evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 evaluation error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 evaluation list group . . . . . . . . . . . . . . . . . . . . . . . . . . 199 evaluation notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 evaluation of buffer contents . . . . . . . . . . . . . . . . . . . 96 evaporate (overlay property) . . . . . . . . . . . . . . . . . 576 event printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 event type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 event-basic-type. . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 event-click-count . . . . . . . . . . . . . . . . . . . . . . . . . . 257 event-convert-list . . . . . . . . . . . . . . . . . . . . . . . . . 261 event-end. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 event-modifiers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 event-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 eventp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252 events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252 examining windows . . . . . . . . . . . . . . . . . . . . . . . . . . . 390 examples of using interactive . . . . . . . . . . . . . . . 247 excursion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437 exec-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526 exec-path. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526 execute program. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525 execute with prefix argument . . . . . . . . . . . . . . . . . 249

execute-extended-command . . . . . . . . . . . . . . . . . . 249

execute-kbd-macro . . . . . . . . . . . . . . . . . . . . . . . . . . 275 executing-macro. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 execution speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602 exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 exit recursive editing . . . . . . . . . . . . . . . . . . . . . . . . . 272 exit-minibuffer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 exit-recursive-edit . . . . . . . . . . . . . . . . . . . . . . . . 273 exiting Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547 exp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 expand-abbrev . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522 expand-file-name. . . . . . . . . . . . . . . . . . . . . . . . . . . . 347 expansion of file names . . . . . . . . . . . . . . . . . . . . . . . 347 expansion of macros . . . . . . . . . . . . . . . . . . . . . . . . . . 153 expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 expression prefix . . . . . . . . . . . . . . . . . . . . . . . . . . . 512 expt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

                                                extended-command-history . . . . . . . . . . . . . . . . . . 227

extent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

                                                extra-keyboard-modifiers . . . . . . . . . . . . . . . . . . 559

F

face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 578 face (overlay property). . . . . . . . . . . . . . . . . . . . . . . 575 face (text property). . . . . . . . . . . . . . . . . . . . . . . . . . 482 face codes of text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482 face id . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 578 face-background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580

                                                face-differs-from-default-p . . . . . . . . . . . . . . . 581

face-equal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581 face-font. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580 face-foreground. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580 face-id . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581 face-list. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579 face-stipple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580 face-underline-p. . . . . . . . . . . . . . . . . . . . . . . . . . . . 580

                                                facemenu-background-menu . . . . . . . . . . . . . . . . . . 631

facemenu-face-menu . . . . . . . . . . . . . . . . . . . . . . . . . 632

                                                facemenu-foreground-menu . . . . . . . . . . . . . . . . . . 632
                                                facemenu-indentation-menu . . . . . . . . . . . . . . . . . 632
                                                facemenu-justification-menu . . . . . . . . . . . . . . . 632

facemenu-menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631 facemenu-special-menu . . . . . . . . . . . . . . . . . . . . . . 632 facep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 578 false . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 fancy-diary-display . . . . . . . . . . . . . . . . . . . . . . . . 594 fboundp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 fceiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 featurep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 fetch-bytecode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 ffloor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 field width. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 file accessibility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337 file age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338 file attributes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340 file format conversion . . . . . . . . . . . . . . . . . . . . . . . . . 354 file hard link . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342 file locks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 file mode specification error. . . . . . . . . . . . . . . . . . . 305 file modes and MS-DOS . . . . . . . . . . . . . . . . . . . . . . 344 file modification time . . . . . . . . . . . . . . . . . . . . . . . . . 338 file name completion subroutines. . . . . . . . . . . . . . 349 file name of buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372 file name of directory . . . . . . . . . . . . . . . . . . . . . . . . . 345 file names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344 file names in directory . . . . . . . . . . . . . . . . . . . . . . . . 351 file open error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 file symbolic links . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 file types on MS-DOS . . . . . . . . . . . . . . . . . . . . . . . . 356 file with multiple names . . . . . . . . . . . . . . . . . . . . . . 342

file-accessible-directory-p . . . . . . . . . . . . . . . 338

file-already-exists . . . . . . . . . . . . . . . . . . . . . . . . 343 file-attributes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341 file-directory-p. . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 file-error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 file-executable-p . . . . . . . . . . . . . . . . . . . . . . . . . . 337 file-exists-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337 file-local-copy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354 file-locked . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337 file-locked-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 file-modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340 file-name-absolute-p . . . . . . . . . . . . . . . . . . . . . . . 347

file-name-all-completions . . . . . . . . . . . . . . . . . 349

file-name-all-versions. . . . . . . . . . . . . . . . . . . . . 351 file-name-as-directory. . . . . . . . . . . . . . . . . . . . . 346

file-name-buffer-file-type-alist . . . . . . . . . 356

file-name-completion . . . . . . . . . . . . . . . . . . . . . . . 350 file-name-directory . . . . . . . . . . . . . . . . . . . . . . . . 345 file-name-history . . . . . . . . . . . . . . . . . . . . . . . . . . 227 file-name-nondirectory. . . . . . . . . . . . . . . . . . . . . 345

file-name-sans-extension . . . . . . . . . . . . . . . . . . 345
file-name-sans-versions . . . . . . . . . . . . . . . . . . . 345

file-newer-than-file-p. . . . . . . . . . . . . . . . . . . . . 338 file-newest-backup . . . . . . . . . . . . . . . . . . . . . . . . . 363 file-nlinks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340

file-ownership-preserved-p . . . . . . . . . . . . . . . . 338

file-precious-flag . . . . . . . . . . . . . . . . . . . . . . . . . 333 file-readable-p. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337 file-regular-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 file-relative-name . . . . . . . . . . . . . . . . . . . . . . . . . 348 file-supersession . . . . . . . . . . . . . . . . . . . . . . . . . . 375 file-symlink-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 file-truename . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340 file-writable-p. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338 fill-column . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466

                                                fill-individual-paragraphs . . . . . . . . . . . . . . . . 464
                                                fill-individual-varying-indent . . . . . . . . . . . 465

fill-paragraph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464

                                                fill-paragraph-function . . . . . . . . . . . . . . . . . . . 465

fill-prefix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466 fill-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464

                                                fill-region-as-paragraph . . . . . . . . . . . . . . . . . . 465

fillarray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 filling a paragraph . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464 filling, automatic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467 filling, explicit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464 filter function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536 find-backup-file-name . . . . . . . . . . . . . . . . . . . . . . 363 find-buffer-file-type . . . . . . . . . . . . . . . . . . . . . . 356 find-file. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 find-file-binary. . . . . . . . . . . . . . . . . . . . . . . . . . . . 357 find-file-hooks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 find-file-name-handler. . . . . . . . . . . . . . . . . . . . . 354 find-file-noselect . . . . . . . . . . . . . . . . . . . . . . . . . 330

                                                find-file-not-found-hooks . . . . . . . . . . . . . . . . . 331

find-file-other-window. . . . . . . . . . . . . . . . . . . . . 330 find-file-read-only . . . . . . . . . . . . . . . . . . . . . . . . 330 find-file-text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357 finding files. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 finding windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388 first-change-hook . . . . . . . . . . . . . . . . . . . . . . . . . . 490 fixup-whitespace. . . . . . . . . . . . . . . . . . . . . . . . . . . . 456 float . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 floatp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 floor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 flow control characters . . . . . . . . . . . . . . . . . . . . . . . . 564 flow control example. . . . . . . . . . . . . . . . . . . . . . . . . . 560 flush input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 fmakunbound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 focus event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 following-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449 font-lock-defaults . . . . . . . . . . . . . . . . . . . . . . . . . 300 fonts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 foo. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 for . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 force-mode-line-update. . . . . . . . . . . . . . . . . . . . . 311 forcing redisplay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 format definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354 format of keymaps. . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 format specification. . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 format-alist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354 format-find-file. . . . . . . . . . . . . . . . . . . . . . . . . . . . 356 format-insert-file . . . . . . . . . . . . . . . . . . . . . . . . . 356 format-time-string . . . . . . . . . . . . . . . . . . . . . . . . . 554 format-write-file . . . . . . . . . . . . . . . . . . . . . . . . . . 355 formatting strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 formfeed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 forms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 forward-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430 forward-comment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517 forward-line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433 forward-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435 forward-sexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436 forward-to-indentation. . . . . . . . . . . . . . . . . . . . . 476 forward-word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431 frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 frame configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 frame visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 frame-char-height . . . . . . . . . . . . . . . . . . . . . . . . . . 415 frame-char-width. . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 frame-height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 frame-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 frame-live-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 frame-parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . 411 frame-pixel-height . . . . . . . . . . . . . . . . . . . . . . . . . 415 frame-pixel-width . . . . . . . . . . . . . . . . . . . . . . . . . . 415 frame-selected-window . . . . . . . . . . . . . . . . . . . . . . 418 frame-title-format . . . . . . . . . . . . . . . . . . . . . . . . . 416 frame-top-window. . . . . . . . . . . . . . . . . . . . . . . . . . . . 418 frame-visible-p. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 frame-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 framep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 free list. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 612 frequency counts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 fround . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 fset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 ftp-login. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 ftruncate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 full keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 funcall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 funcall, and debugging . . . . . . . . . . . . . . . . . . . . . . 188 function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 function call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 function call debugging . . . . . . . . . . . . . . . . . . . . . . . 182 function cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 function cell in autoload . . . . . . . . . . . . . . . . . . . . . . 164 function definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 function descriptions. . . . . . . . . . . . . . . . . . . . . . . . . . . 12 function form evaluation . . . . . . . . . . . . . . . . . . . . . . 100 function input stream . . . . . . . . . . . . . . . . . . . . . . . . 214 function invocation . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 function keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 function name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 function output stream . . . . . . . . . . . . . . . . . . . . . . . 217 function quoting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 function-key-map . . . . . . . . . . . . . . . . . . . . . . . 560, 632 functionals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 functions in modes . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 functions, making them interactive. . . . . . . . . . . . 244 Fundamental mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 fundamental-mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . 305

                                                fundamental-mode-abbrev-table. . . . . . . . . . . . . 523

fundamental-mode-map . . . . . . . . . . . . . . . . . . . . . . . 632

G

garbage collection protection. . . . . . . . . . . . . . . . . . 614 garbage collector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611 garbage-collect. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 612

                                                garbage-collection-messages . . . . . . . . . . . . . . . 613

gc-cons-threshold . . . . . . . . . . . . . . . . . . . . . . . . . . 613 general-holidays. . . . . . . . . . . . . . . . . . . . . . . . . . . . 588 generate-new-buffer . . . . . . . . . . . . . . . . . . . . . . . . 378

                                                generate-new-buffer-name . . . . . . . . . . . . . . . . . . 372

geometry specification . . . . . . . . . . . . . . . . . . . . . . . . 415 get. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 get-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372 get-buffer-create . . . . . . . . . . . . . . . . . . . . . . . . . . 378 get-buffer-process . . . . . . . . . . . . . . . . . . . . . . . . . 536 get-buffer-window . . . . . . . . . . . . . . . . . . . . . . . . . . 390 get-buffer-window-list. . . . . . . . . . . . . . . . . . . . . 391 get-char-property . . . . . . . . . . . . . . . . . . . . . . . . . . 478 get-file-buffer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373 get-file-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 get-largest-window . . . . . . . . . . . . . . . . . . . . . . . . . 388 get-lru-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388 get-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531 get-register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488 get-text-property . . . . . . . . . . . . . . . . . . . . . . . . . . 478 getenv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551 global binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 global break condition . . . . . . . . . . . . . . . . . . . . . . . . 196 global keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 global variable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 global-abbrev-table . . . . . . . . . . . . . . . . . . . . . . . . 523 global-key-binding . . . . . . . . . . . . . . . . . . . . . . . . . 287 global-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 global-mode-string . . . . . . . . . . . . . . . . . . . . . . . . . 313 global-set-key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 global-unset-key. . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 glyph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585 glyph table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585 glyph-table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585 goto-char. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430 goto-line. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432

H

hack-local-variables . . . . . . . . . . . . . . . . . . . . . . . 307 handle-switch-frame . . . . . . . . . . . . . . . . . . . . . . . . 419 handling errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 hash notation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 hashing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 header comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605 hebrew-holidays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588 help for major mode . . . . . . . . . . . . . . . . . . . . . . . . . . 307 help-char. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 help-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 help-form. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326 help-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325

Helper-describe-bindings . . . . . . . . . . . . . . . . . . 326

Helper-help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326 Helper-help-map. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632 highlight (face name) . . . . . . . . . . . . . . . . . . . . . . . 578 highlighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582 history list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 history of commands . . . . . . . . . . . . . . . . . . . . . . . . . 274 holiday forms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588

holidays-in-diary-buffer . . . . . . . . . . . . . . . . . . 592

HOME environment variable . . . . . . . . . . . . . . . . . . . . 525 hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316 hooks for changing a character . . . . . . . . . . . . . . . . 483 hooks for loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 hooks for motion of point . . . . . . . . . . . . . . . . . . . . . 483 hooks for text changes . . . . . . . . . . . . . . . . . . . . . . . . 489 horizontal position. . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 horizontal scrolling . . . . . . . . . . . . . . . . . . . . . . . . . . . 401 hyper characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

I

icon-title-format . . . . . . . . . . . . . . . . . . . . . . . . . . 416 iconified frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 iconify-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 iconify-frame event . . . . . . . . . . . . . . . . . . . . . . . . . 258 identity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 idleness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558 IEEE floating point. . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 if. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 ignore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

ignored-local-variables . . . . . . . . . . . . . . . . . . . 305
imenu-create-index-function . . . . . . . . . . . . . . . 301

imenu-generic-expression . . . . . . . . . . . . . . . . . . 301

implicit progn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 inc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

include-other-diary-files . . . . . . . . . . . . . . . . . 595
indent-according-to-mode . . . . . . . . . . . . . . . . . . 473

indent-code-rigidly . . . . . . . . . . . . . . . . . . . . . . . . 474 indent-for-tab-command. . . . . . . . . . . . . . . . . . . . . 473 indent-line-function . . . . . . . . . . . . . . . . . . . . . . . 473 indent-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474 indent-region-function. . . . . . . . . . . . . . . . . . . . . 474 indent-relative. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475 indent-relative-maybe . . . . . . . . . . . . . . . . . . . . . . 475 indent-rigidly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474 indent-tabs-mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . 473 indent-to. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472 indent-to-left-margin . . . . . . . . . . . . . . . . . . . . . . 467 indentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472 indenting with parentheses. . . . . . . . . . . . . . . . . . . . 516 indirect buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380 indirect specifications . . . . . . . . . . . . . . . . . . . . . . . . . 206 indirect-function . . . . . . . . . . . . . . . . . . . . . . . . . . 100 indirection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 infinite loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 infinite recursion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 infinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Info-edit-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632 Info-mode-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632 inherit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512 inheritance of text properties . . . . . . . . . . . . . . . . . 484 inheriting a keymap’s bindings . . . . . . . . . . . . . . . . 280 inhibit-default-init . . . . . . . . . . . . . . . . . . . . . . . 545

inhibit-file-name-handlers . . . . . . . . . . . . . . . . 354
inhibit-file-name-operation . . . . . . . . . . . . . . . 354
inhibit-point-motion-hooks . . . . . . . . . . . . . . . . 483

inhibit-quit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 inhibit-read-only . . . . . . . . . . . . . . . . . . . . . . . . . . 376

inhibit-startup-echo-area-message . . . . . . . . 544
inhibit-startup-message . . . . . . . . . . . . . . . . . . . 544

init file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544

initial-calendar-window-hook . . . . . . . . . . . . . . 587

initial-frame-alist . . . . . . . . . . . . . . . . . . . . . . . . 411 initial-major-mode . . . . . . . . . . . . . . . . . . . . . . . . . 306 initialization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543 inline functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 innermost containing parentheses . . . . . . . . . . . . . 516 input events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252 input focus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419 input modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558 input stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 input-pending-p. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 insert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452

insert-abbrev-table-description . . . . . . . . . . 520

insert-and-inherit . . . . . . . . . . . . . . . . . . . . . . . . . 485 insert-before-markers . . . . . . . . . . . . . . . . . . . . . . 452

insert-before-markers-and-inherit . . . . . . . . 485

insert-behind-hooks (overlay property) . . . . . 576 insert-behind-hooks (text property) . . . . . . . . 483 insert-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453

insert-buffer-substring . . . . . . . . . . . . . . . . . . . 453

insert-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452

insert-default-directory . . . . . . . . . . . . . . . . . . 235

insert-directory. . . . . . . . . . . . . . . . . . . . . . . . . . . . 352

insert-directory-program . . . . . . . . . . . . . . . . . . 352

insert-file-contents . . . . . . . . . . . . . . . . . . . . . . . 334

insert-hebrew-diary-entry . . . . . . . . . . . . . . . . . 594

insert-in-front-hooks (overlay property) … 576 insert-in-front-hooks (text property) . . . . . . 483

insert-islamic-diary-entry . . . . . . . . . . . . . . . . 594
insert-monthly-hebrew-diary-entry . . . . . . . . 594
insert-monthly-islamic-diary-entry . . . . . . . 594

insert-register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489

insert-yearly-hebrew-diary-entry . . . . . . . . . 594
insert-yearly-islamic-diary-entry . . . . . . . . 594

inserting killed text. . . . . . . . . . . . . . . . . . . . . . . . . . . 459 insertion before point . . . . . . . . . . . . . . . . . . . . . . . . . 452 insertion of text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452 inside comment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516 inside string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516 installation-directory. . . . . . . . . . . . . . . . . . . . . 551 int-to-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 intangible (text property) . . . . . . . . . . . . . . . . . . . 482 integer to decimal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 integer to hexadecimal . . . . . . . . . . . . . . . . . . . . . . . . . 56 integer to octal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 integer to string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 integer-or-marker-p . . . . . . . . . . . . . . . . . . . . . . . . 442 integerp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 integers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 interactive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 interactive call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 interactive code description . . . . . . . . . . . . . . . . . . . 245 interactive commands (Edebug). . . . . . . . . . . . . . . 192 interactive completion . . . . . . . . . . . . . . . . . . . . . . . . 245 interactive function . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 interactive, examples of using. . . . . . . . . . . . . . . 247 interactive-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 intern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 intern-soft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 internals, of buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618 internals, of process . . . . . . . . . . . . . . . . . . . . . . . . . . 621 internals, of window . . . . . . . . . . . . . . . . . . . . . . . . . . 619 interning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 interpreter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 interpreter-mode-alist. . . . . . . . . . . . . . . . . . . . . 307

                                                interprogram-cut-function . . . . . . . . . . . . . . . . . 460
                                                interprogram-paste-function . . . . . . . . . . . . . . . 460

interrupt-process . . . . . . . . . . . . . . . . . . . . . . . . . . 534 intervals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 486 invalid function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 invalid prefix key error. . . . . . . . . . . . . . . . . . . . . . . . 289 invalid-function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 invalid-read-syntax . . . . . . . . . . . . . . . . . . . . . . . . . 15 invalid-regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496 Inverse Video. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582 inverse-video . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582 invert-face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580 invisible (overlay property) . . . . . . . . . . . . . . . . . 576 invisible (text property) . . . . . . . . . . . . . . . . . . . . 482 invisible frame. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 invisible text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570 invocation-directory . . . . . . . . . . . . . . . . . . . . . . . 551 invocation-name. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551 isearch-mode-map. . . . . . . . . . . . . . . . . . . . . . . . . . . . 632 islamic-holidays. . . . . . . . . . . . . . . . . . . . . . . . . . . . 588 ISO Latin 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 ISO Latin-1 characters (input) . . . . . . . . . . . . . . . . 562 iso-syntax. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 iso-transl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562 italic (face name) . . . . . . . . . . . . . . . . . . . . . . . . . . . 578 iteration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

J

joining lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 just-one-space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457 justify-current-line . . . . . . . . . . . . . . . . . . . . . . . 465

K

kept-new-versions . . . . . . . . . . . . . . . . . . . . . . . . . . 361 kept-old-versions . . . . . . . . . . . . . . . . . . . . . . . . . . 361 key. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 key binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 key lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 key sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 key sequence error . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 key sequence input . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 key translation function . . . . . . . . . . . . . . . . . . . . . . 561 key-binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 key-description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 key-translation-map . . . . . . . . . . . . . . . . . . . 561, 632 keyboard macro execution . . . . . . . . . . . . . . . . . . . . 249 keyboard macro termination . . . . . . . . . . . . . . . . . . 586 keyboard macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 keyboard macros (Edebug) . . . . . . . . . . . . . . . . . . . 194 keyboard-quit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 keyboard-translate . . . . . . . . . . . . . . . . . . . . . . . . . 560

keyboard-translate-table . . . . . . . . . . . . . . . . . . 559

keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 keymap entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 keymap format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 keymap in keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 keymap inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 keymap of character . . . . . . . . . . . . . . . . . . . . . 482, 576 keymap prompt string . . . . . . . . . . . . . . . . . . . . . . . . 278 keymap-parent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 keymapp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 keymaps in modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 keys in documentation strings . . . . . . . . . . . . . . . . 322 keystroke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 keystroke command . . . . . . . . . . . . . . . . . . . . . . . . . . 140 kill command repetition . . . . . . . . . . . . . . . . . . . . . . 250 kill ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457

kill-all-local-variables . . . . . . . . . . . . . . . . . . 137

kill-append . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460 kill-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379 kill-buffer-hook. . . . . . . . . . . . . . . . . . . . . . . . . . . . 380

kill-buffer-query-functions . . . . . . . . . . . . . . . 380

kill-emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547 kill-emacs-hook. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548

kill-emacs-query-functions . . . . . . . . . . . . . . . . 548

kill-local-variable . . . . . . . . . . . . . . . . . . . . . . . . 136 kill-new . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460 kill-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 535 kill-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458 kill-ring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461 kill-ring-max . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461 kill-ring-yank-pointer. . . . . . . . . . . . . . . . . . . . . 461 killing buffers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379 killing Emacs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547

L

lambda expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 lambda expression in hook . . . . . . . . . . . . . . . . . . . . 316 lambda in debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 lambda in keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 lambda list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 lambda-list (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . . 207 last-abbrev . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522 last-abbrev-location . . . . . . . . . . . . . . . . . . . . . . . 522 last-abbrev-text. . . . . . . . . . . . . . . . . . . . . . . . . . . . 522 last-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 last-command-char . . . . . . . . . . . . . . . . . . . . . . . . . . 251 last-command-event . . . . . . . . . . . . . . . . . . . . . . . . . 251 last-event-frame. . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 last-input-char. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 last-input-event. . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 last-kbd-macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 last-nonmenu-event . . . . . . . . . . . . . . . . . . . . . . . . . 251 Latin-1 character set (input). . . . . . . . . . . . . . . . . . 562 lazy loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 left-margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467 length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 let . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 let* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 lexical binding (Edebug) . . . . . . . . . . . . . . . . . . . . . . 198 lexical comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 library compilation . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 library header comments. . . . . . . . . . . . . . . . . . . . . . 605 line wrapping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568

line-move-ignore-invisible . . . . . . . . . . . . . . . . 571

lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432 lines in region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433 linking files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342 Lisp debugger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 Lisp expression motion . . . . . . . . . . . . . . . . . . . . . . . 435 Lisp history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Lisp library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 Lisp nesting error. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 Lisp object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Lisp printer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 Lisp reader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213

lisp-interaction-mode-map . . . . . . . . . . . . . . . . . 632

lisp-mode-abbrev-table. . . . . . . . . . . . . . . . . . . . . 523 lisp-mode-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632 ‘lisp-mode.el’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 LISP_FLOAT_TYPE configuration macro . . . . . . . . . 36 list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 list elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 list form evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 list in keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 list length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 list motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435 list structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 list-buffers-directory. . . . . . . . . . . . . . . . . . . . . 374

list-diary-entries-hook . . . . . . . . . . . . . . . . . . . 595
list-hebrew-diary-entries . . . . . . . . . . . . . . . . . 593
list-islamic-diary-entries . . . . . . . . . . . . . . . . 593

list-processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531 listify-key-sequence . . . . . . . . . . . . . . . . . . . . . . . 263 listp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 lists and cons cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 lists as sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 lists represented as boxes . . . . . . . . . . . . . . . . . . . . . . 61 literal evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 ln. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343 load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 load error with require. . . . . . . . . . . . . . . . . . . . . . . . 167 load errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 load-average . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552 load-history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 load-in-progress. . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 load-path. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 load-read-function . . . . . . . . . . . . . . . . . . . . . . . . . 163 loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 loading hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 ‘loadup.el’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609 local binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 local keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 local variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 local-abbrev-table . . . . . . . . . . . . . . . . . . . . . . . . . 523 local-holidays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588 local-key-binding . . . . . . . . . . . . . . . . . . . . . . . . . . 287 local-map (text property) . . . . . . . . . . . . . . . 482, 576 local-set-key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 local-unset-key. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 local-variable-p. . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 local-write-file-hooks. . . . . . . . . . . . . . . . . . . . . 333 lock-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 log. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 log10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 logand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 logb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 logical and . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 logical exclusive or. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 logical inclusive or . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 logical not . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 logical shift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 logior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 lognot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 logxor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 looking-at . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 499 lookup-key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 loops, infinite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 lower case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 lower-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 lowering a frame. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 lsh. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

M

M-x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 Maclisp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 macro argument evaluation . . . . . . . . . . . . . . . . . . . 157 macro call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 macro call evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 100 macro compilation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 macro descriptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 macro expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 macroexpand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 magic file names. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352 mail-host-address . . . . . . . . . . . . . . . . . . . . . . . . . . 550 major mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 major mode hook. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 major mode keymap . . . . . . . . . . . . . . . . . . . . . . . . . . 282 major-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 make-abbrev-table . . . . . . . . . . . . . . . . . . . . . . . . . . 519

make-auto-save-file-name . . . . . . . . . . . . . . . . . . 364

make-backup-file-name . . . . . . . . . . . . . . . . . . . . . . 362 make-backup-files . . . . . . . . . . . . . . . . . . . . . . . . . . 359 make-byte-code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 make-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352 make-display-table . . . . . . . . . . . . . . . . . . . . . . . . . 583 make-face. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579 make-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 make-frame-invisible . . . . . . . . . . . . . . . . . . . . . . . 420 make-frame-on-display . . . . . . . . . . . . . . . . . . . . . . 410 make-frame-visible . . . . . . . . . . . . . . . . . . . . . . . . . 420 make-frame-visible event . . . . . . . . . . . . . . . . . . . 258 make-help-screen. . . . . . . . . . . . . . . . . . . . . . . . . . . . 326 make-indirect-buffer . . . . . . . . . . . . . . . . . . . . . . . 380 make-keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 make-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 make-local-hook. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 make-local-variable . . . . . . . . . . . . . . . . . . . . . . . . 135 make-marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442 make-overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577 make-sparse-keymap . . . . . . . . . . . . . . . . . . . . . . . . . 279 make-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 make-symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 make-symbolic-link . . . . . . . . . . . . . . . . . . . . . . . . . 343 make-syntax-table . . . . . . . . . . . . . . . . . . . . . . . . . . 513 make-temp-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349

make-variable-buffer-local . . . . . . . . . . . . . . . . 136

make-vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 makunbound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 map-y-or-n-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 mapatoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 mapcar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 mapconcat. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 mapping functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 mark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445 mark excursion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437 mark ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445 mark, the . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445 mark-active . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447

mark-diary-entries-hook . . . . . . . . . . . . . . . . . . . 595
mark-diary-entries-in-calendar . . . . . . . . . . . 587
mark-hebrew-diary-entries . . . . . . . . . . . . . . . . . 593
mark-holidays-in-calendar . . . . . . . . . . . . . . . . . 587
mark-included-diary-files . . . . . . . . . . . . . . . . . 595
mark-islamic-diary-entries . . . . . . . . . . . . . . . . 593

mark-marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446 mark-ring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447 mark-ring-max . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447 marker argument . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 marker garbage collection. . . . . . . . . . . . . . . . . . . . . 441 marker input stream. . . . . . . . . . . . . . . . . . . . . . . . . . 213 marker output stream . . . . . . . . . . . . . . . . . . . . . . . . 217 marker relocation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441 marker-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444 marker-position. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444 markerp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442 markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441 markers as numbers . . . . . . . . . . . . . . . . . . . . . . . . . . 441 match data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501 match-beginning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502 match-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504 match-end. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502 match-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502 mathematical functions . . . . . . . . . . . . . . . . . . . . . . . . 46 max. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 max-lisp-eval-depth . . . . . . . . . . . . . . . . . . . . . . . . . 97 max-specpdl-size. . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 membership in a list . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 memory allocation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 611 memory-limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614 memq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 menu bar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 menu keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 menu prompt string . . . . . . . . . . . . . . . . . . . . . . . . . . 294 menu-bar-edit-menu . . . . . . . . . . . . . . . . . . . . . . . . . 632 menu-bar-files-menu . . . . . . . . . . . . . . . . . . . . . . . . 632 menu-bar-final-items . . . . . . . . . . . . . . . . . . . . . . . 298 menu-bar-help-menu . . . . . . . . . . . . . . . . . . . . . . . . . 633 menu-bar-search-menu . . . . . . . . . . . . . . . . . . . . . . . 633 menu-bar-tools-menu . . . . . . . . . . . . . . . . . . . . . . . . 633 menu-bar-update-hook . . . . . . . . . . . . . . . . . . . . . . . 298 menu-prompt-more-char . . . . . . . . . . . . . . . . . . . . . . 296 message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569 message-log-max. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570 meta character key constants . . . . . . . . . . . . . . . . . 288 meta character printing. . . . . . . . . . . . . . . . . . . . . . . 323 meta characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 meta characters lookup . . . . . . . . . . . . . . . . . . . . . . . 278 meta-prefix-char. . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 min. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 minibuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 minibuffer history . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 minibuffer input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 minibuffer window. . . . . . . . . . . . . . . . . . . . . . . . . . . . 389 minibuffer-auto-raise . . . . . . . . . . . . . . . . . . . . . . 421 minibuffer-complete . . . . . . . . . . . . . . . . . . . . . . . . 232

                                                minibuffer-complete-and-exit . . . . . . . . . . . . . . 232
                                                minibuffer-complete-word . . . . . . . . . . . . . . . . . . 232
                                                minibuffer-completion-confirm. . . . . . . . . . . . . 232
                                                minibuffer-completion-help . . . . . . . . . . . . . . . . 232
                                                minibuffer-completion-predicate . . . . . . . . . . 232
                                                minibuffer-completion-table . . . . . . . . . . . . . . . 232

minibuffer-depth. . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 minibuffer-exit-hook . . . . . . . . . . . . . . . . . . . . . . . 241 minibuffer-frame-alist. . . . . . . . . . . . . . . . . . . . . 411 minibuffer-help-form . . . . . . . . . . . . . . . . . . . . . . . 241 minibuffer-history . . . . . . . . . . . . . . . . . . . . . . . . . 227

                                                minibuffer-local-completion-map . . . . . . . . . . 231

minibuffer-local-map . . . . . . . . . . . . . . . . . . . . . . . 225

                                                minibuffer-local-must-match-map . . . . . . . . . . 231
                                                minibuffer-local-ns-map . . . . . . . . . . . . . . . . . . . 225

minibuffer-prompt . . . . . . . . . . . . . . . . . . . . . . . . . . 240

                                                minibuffer-prompt-width . . . . . . . . . . . . . . . . . . . 241
                                                minibuffer-scroll-window . . . . . . . . . . . . . . . . . . 241

minibuffer-setup-hook . . . . . . . . . . . . . . . . . . . . . . 241 minibuffer-window . . . . . . . . . . . . . . . . . . . . . . . . . . 241

                                                minibuffer-window-active-p . . . . . . . . . . . . . . . . 241

minimum window size . . . . . . . . . . . . . . . . . . . . . . . . 405 minor mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 minor mode conventions . . . . . . . . . . . . . . . . . . . . . . 309 minor-mode-alist. . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 minor-mode-key-binding. . . . . . . . . . . . . . . . . . . . . 287 minor-mode-map-alist . . . . . . . . . . . . . . . . . . . . . . . 283 mod. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 mode help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 mode hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 mode line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 mode line construct . . . . . . . . . . . . . . . . . . . . . . . . . . 311 mode loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 mode variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 mode-class property . . . . . . . . . . . . . . . . . . . . . . . . . 301

mode-line-buffer-identification . . . . . . . . . . 313

mode-line-format. . . . . . . . . . . . . . . . . . . . . . . . . . . . 311

mode-line-inverse-video . . . . . . . . . . . . . . . . . . . 582

mode-line-modified . . . . . . . . . . . . . . . . . . . . . . . . . 313 mode-line-process . . . . . . . . . . . . . . . . . . . . . . . . . . 314 mode-name. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 mode-specific-map. . . . . . . . . . . . . . . . . . . . . . 281, 633 modeline (face name) . . . . . . . . . . . . . . . . . . . . . . . . 578 modification flag (of buffer) . . . . . . . . . . . . . . . . . . . 374 modification of lists. . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 modification time, comparison of. . . . . . . . . . . . . . 375 modification-hooks (overlay property). . . . . . . 576 modification-hooks (text property). . . . . . . . . . 483 modifier bits (of input character) . . . . . . . . . . . . . 252

modify-frame-parameters . . . . . . . . . . . . . . . . . . . 411

modify-syntax-entry . . . . . . . . . . . . . . . . . . . . . . . . 514 modulus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

momentary-string-display . . . . . . . . . . . . . . . . . . 574

motion event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 mouse click event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 mouse drag event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 mouse motion events . . . . . . . . . . . . . . . . . . . . . . . . . 257 mouse pointer shape . . . . . . . . . . . . . . . . . . . . . . . . . . 424 mouse position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 mouse tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 mouse-face (overlay property) . . . . . . . . . . . . . . . . 575 mouse-face (text property) . . . . . . . . . . . . . . . . . . . 482 mouse-movement-p. . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 mouse-pixel-position . . . . . . . . . . . . . . . . . . . . . . . 422 mouse-position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 move-marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445 move-overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577 move-to-column . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 move-to-left-margin . . . . . . . . . . . . . . . . . . . . . . . . 467 move-to-window-line . . . . . . . . . . . . . . . . . . . . . . . . 434 MS-DOS and file modes . . . . . . . . . . . . . . . . . . . . . . 344 MS-DOS file types. . . . . . . . . . . . . . . . . . . . . . . . . . . . 356 multiple displays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 multiple windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383 multiple X terminals. . . . . . . . . . . . . . . . . . . . . . . . . . 409 multiple-frames. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417

N

named function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 NaN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 narrow-to-page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439 narrow-to-region. . . . . . . . . . . . . . . . . . . . . . . . . . . . 438 narrowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438 natnump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 natural numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 nconc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 negative infinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 negative-argument . . . . . . . . . . . . . . . . . . . . . . . . . . 271 network connection . . . . . . . . . . . . . . . . . . . . . . . . . . . 541 new file message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 newline. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 newline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454 newline and Auto Fill mode . . . . . . . . . . . . . . . . . . 454 newline in print . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 newline in strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 newline-and-indent . . . . . . . . . . . . . . . . . . . . . . . . . 473 next input. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 next-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 next-history-element . . . . . . . . . . . . . . . . . . . . . . . 240

next-matching-history-element. . . . . . . . . . . . . 240

next-overlay-change . . . . . . . . . . . . . . . . . . . . . . . . 578 next-property-change . . . . . . . . . . . . . . . . . . . . . . . 480

next-screen-context-lines . . . . . . . . . . . . . . . . . 399
next-single-property-change . . . . . . . . . . . . . . . 481

next-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389 nil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 nil and lists. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 nil in keymap. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 nil in lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 nil input stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 nil output stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 nil, uses of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 nlistp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 no-catch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 no-redraw-on-reenter . . . . . . . . . . . . . . . . . . . . . . . 567 nondirectory part (of file name). . . . . . . . . . . . . . . 344

nongregorian-diary-listing-hook . . . . . . . . . . 593
nongregorian-diary-marking-hook . . . . . . . . . . 593

noninteractive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565 noninteractive use . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565 nonlocal exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 nonprinting characters, reading . . . . . . . . . . . . . . . 265

normal-auto-fill-function . . . . . . . . . . . . . . . . . 468

normal-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 not . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 not-modified . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374 nreverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 nth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 nthcdr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 null . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 num-input-keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264 number equality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

number-of-diary-entries . . . . . . . . . . . . . . . . . . . 592

number-or-marker-p . . . . . . . . . . . . . . . . . . . . . . . . . 442 number-to-string. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 numberp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 numeric prefix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 numeric prefix argument . . . . . . . . . . . . . . . . . . . . . . 270 numeric prefix argument usage. . . . . . . . . . . . . . . . 247

O

obarray. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 obarray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 obarray in completion . . . . . . . . . . . . . . . . . . . . . . . . 228 object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 object internals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617 object to string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 obsolete buffer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375 occur-mode-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633 octal character code . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 octal character input . . . . . . . . . . . . . . . . . . . . . . . . . 265 omer count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596 one-window-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386 only-global-abbrevs . . . . . . . . . . . . . . . . . . . . . . . . 520

open parenthesis character . . . . . . . . . . . . . . . . . 510

open-dribble-file . . . . . . . . . . . . . . . . . . . . . . . . . . 562 open-network-stream . . . . . . . . . . . . . . . . . . . . . . . . 541 open-termscript. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563 operating system environment . . . . . . . . . . . . . . . . 549 option descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 optional arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 options on command line . . . . . . . . . . . . . . . . . . . . . 546 or. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 ordering of windows, cyclic . . . . . . . . . . . . . . . . . . . 388 other-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377 other-holidays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588 other-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390

other-window-scroll-buffer . . . . . . . . . . . . . . . . 399

Outline mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487 output from processes . . . . . . . . . . . . . . . . . . . . . . . . 535 output stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 overall prompt string . . . . . . . . . . . . . . . . . . . . . . . . . 278 overflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 overlay arrow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573 overlay-arrow-position. . . . . . . . . . . . . . . . . . . . . 573 overlay-arrow-string . . . . . . . . . . . . . . . . . . . . . . . 573 overlay-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577 overlay-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577 overlay-get . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577 overlay-put . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577 overlay-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577 overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575 overlays-at . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577 overriding-local-map . . . . . . . . . . . . . . . . . . . . . . . 284

                                                overriding-local-map-menu-flag . . . . . . . . . . . 284
                                                overriding-terminal-local-map. . . . . . . . . . . . . 284

overwrite-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454

P

padding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 page-delimiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506 paired delimiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512 paragraph-separate . . . . . . . . . . . . . . . . . . . . . . . . . 506 paragraph-start. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506 parasha, weekly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596 parent process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525 parenthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 parenthesis depth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516 parenthesis matching . . . . . . . . . . . . . . . . . . . . . . . . . 581 parenthesis syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511 parse state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516 parse-partial-sexp . . . . . . . . . . . . . . . . . . . . . . . . . 515

                                                parse-sexp-ignore-comments . . . . . . . . . . . . . . . . 517

parsing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509 PATH environment variable . . . . . . . . . . . . . . . . . . . . 525 path-separator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551 pausing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 peculiar error. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 peeking at input. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 percent symbol in mode line . . . . . . . . . . . . . . . . . . 311 perform-replace. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 performance analysis . . . . . . . . . . . . . . . . . . . . . . . . . 201 permanent local variable. . . . . . . . . . . . . . . . . . . . . . 137 permission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340 pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 530 plist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 plist-get . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 plist-put . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 point excursion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437 point in window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395 point with narrowing . . . . . . . . . . . . . . . . . . . . . . . . . 429 point-entered (text property) . . . . . . . . . . . . . . . 483 point-left (text property) . . . . . . . . . . . . . . . . . . . 483 point-marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442 point-max. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 point-max-marker. . . . . . . . . . . . . . . . . . . . . . . . . . . . 443 point-min. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 point-min-marker. . . . . . . . . . . . . . . . . . . . . . . . . . . . 443 pointer shape. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424 pop-mark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446 pop-to-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392 pop-up-frame-alist . . . . . . . . . . . . . . . . . . . . . . . . . 394 pop-up-frame-function . . . . . . . . . . . . . . . . . . . . . . 393 pop-up-frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393 pop-up-windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393

pos-visible-in-window-p . . . . . . . . . . . . . . . . . . . 397

position (in buffer) . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 position argument . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 position in window . . . . . . . . . . . . . . . . . . . . . . . . . . . 395 position of mouse. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 positive infinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 posix-looking-at. . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 posix-search-backward . . . . . . . . . . . . . . . . . . . . . . 500 posix-search-forward . . . . . . . . . . . . . . . . . . . . . . . 500 posix-string-match . . . . . . . . . . . . . . . . . . . . . . . . . 500 posn-col-row . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 posn-point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 posn-timestamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 posn-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 posn-x-y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 post-command-hook . . . . . . . . . . . . . . . . . . . . . . . . . . 243 pre-abbrev-expand-hook. . . . . . . . . . . . . . . . . . . . . 522 pre-command-hook. . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 preceding-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 predicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 prefix argument . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 prefix argument unreading . . . . . . . . . . . . . . . . . . . . 266 prefix command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 prefix key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 prefix-arg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 prefix-help-command . . . . . . . . . . . . . . . . . . . . . . . . 326 prefix-numeric-value . . . . . . . . . . . . . . . . . . . . . . . 271 preventing backtracking . . . . . . . . . . . . . . . . . . . . . . 206 preventing prefix key . . . . . . . . . . . . . . . . . . . . . . . . . 285 previous complete subexpression . . . . . . . . . . . . . . 516 previous-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418

previous-history-element . . . . . . . . . . . . . . . . . . 240
previous-matching-history-element . . . . . . . . 240
previous-overlay-change . . . . . . . . . . . . . . . . . . . 578
previous-property-change . . . . . . . . . . . . . . . . . . 481
previous-single-property-change . . . . . . . . . . 481

previous-window. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389 primitive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 primitive function internals . . . . . . . . . . . . . . . . . . . 614 primitive type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 primitive-undo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463 prin1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 prin1-to-string. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 princ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 print . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 print example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 print name cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 print-diary-entries . . . . . . . . . . . . . . . . . . . . . . . . 592

                                                print-diary-entries-hook . . . . . . . . . . . . . . . . . . 592

print-escape-newlines . . . . . . . . . . . . . . . . . . . . . . 220

                                                print-help-return-message . . . . . . . . . . . . . . . . . 325

print-length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 print-level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 printed representation . . . . . . . . . . . . . . . . . . . . . . . . . 15 printed representation for characters . . . . . . . . . . . 17 printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 printing (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 printing circular structures . . . . . . . . . . . . . . . . . . . 200 printing limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 printing notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 priority (overlay property) . . . . . . . . . . . . . . . . . . 575 process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525 process filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536 process input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533 process internals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621 process output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 535 process sentinel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 539 process signals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534 process-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 535 process-command. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532

                                                process-connection-type . . . . . . . . . . . . . . . . . . . 530

process-environment . . . . . . . . . . . . . . . . . . . . . . . . 551 process-exit-status . . . . . . . . . . . . . . . . . . . . . . . . 533 process-filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538 process-id . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532

                                                process-kill-without-query . . . . . . . . . . . . . . . . 531

process-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531 process-mark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536 process-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 process-send-eof. . . . . . . . . . . . . . . . . . . . . . . . . . . . 533 process-send-region . . . . . . . . . . . . . . . . . . . . . . . . 533 process-send-string . . . . . . . . . . . . . . . . . . . . . . . . 533 process-sentinel. . . . . . . . . . . . . . . . . . . . . . . . . . . . 540 process-status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 process-tty-name. . . . . . . . . . . . . . . . . . . . . . . . . . . . 533 processp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525 ‘profile.el’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602 profiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602 prog1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 prog2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 progn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 program arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . 525 program directories . . . . . . . . . . . . . . . . . . . . . . . . . . . 526 programmed completion . . . . . . . . . . . . . . . . . . . . . . 236 programming types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 prompt string (of menu) . . . . . . . . . . . . . . . . . . . . . . 294 prompt string of keymap . . . . . . . . . . . . . . . . . . . . . 278 properties of text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478 property list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 property list cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 property lists vs association lists . . . . . . . . . . . . . . . 92 protected forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 provide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 providing features . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 ptys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 530 punctuation character . . . . . . . . . . . . . . . . . . . . . . 510 pure storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611 pure-bytes-used. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611 purecopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611 purify-flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611 push-mark. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446 put. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 put-text-property . . . . . . . . . . . . . . . . . . . . . . . . . . 479

Q

query-replace-history . . . . . . . . . . . . . . . . . . . . . . 227 query-replace-map. . . . . . . . . . . . . . . . . . . . . . 500, 633 querying the user . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 question mark in character constant. . . . . . . . . . . . 19

quietly-read-abbrev-file . . . . . . . . . . . . . . . . . . 521

quit-flag. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 quit-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 535 quitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 quitting from infinite loop . . . . . . . . . . . . . . . . . . . . 182 quote . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 quote character. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516 quoted character input . . . . . . . . . . . . . . . . . . . . . . . 265 quoted-insert suppression . . . . . . . . . . . . . . . . . . . 290 quoting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 quoting characters in printing. . . . . . . . . . . . . . . . . 218 quoting using apostrophe . . . . . . . . . . . . . . . . . . . . . 103

R

raise-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 raising a frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 random . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 random numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 rassoc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 rassq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 raw prefix argument . . . . . . . . . . . . . . . . . . . . . . . . . . 270 raw prefix argument usage . . . . . . . . . . . . . . . . . . . . 247 re-search-backward . . . . . . . . . . . . . . . . . . . . . . . . . 498 re-search-forward . . . . . . . . . . . . . . . . . . . . . . . . . . 497 read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 read command name . . . . . . . . . . . . . . . . . . . . . . . . . 249 read syntax. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 read syntax for characters . . . . . . . . . . . . . . . . . . . . . 17 read-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 read-char. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265 read-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 read-event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265

read-expression-history . . . . . . . . . . . . . . . . . . . 228

read-file-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235 read-from-minibuffer . . . . . . . . . . . . . . . . . . . . . . . 224 read-from-string. . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 read-key-sequence . . . . . . . . . . . . . . . . . . . . . . . . . . 263 read-minibuffer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 read-no-blanks-input . . . . . . . . . . . . . . . . . . . . . . . 225 read-only (text property) . . . . . . . . . . . . . . . . . . . . 482 read-only buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376 read-only buffers in interactive . . . . . . . . . . . . . . . . 245 read-only character . . . . . . . . . . . . . . . . . . . . . . . . . . . 482 read-quoted-char. . . . . . . . . . . . . . . . . . . . . . . . . . . . 265 read-quoted-char quitting . . . . . . . . . . . . . . . . . . . 269 read-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 read-variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 reading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 reading interactive arguments. . . . . . . . . . . . . . . . . 246 reading symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 rearrangement of lists. . . . . . . . . . . . . . . . . . . . . . . . . . 70 rebinding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 recent-auto-save-p . . . . . . . . . . . . . . . . . . . . . . . . . 365 recent-keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562 recenter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399 record command history . . . . . . . . . . . . . . . . . . . . . . 249 recursion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 recursion-depth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 recursive command loop . . . . . . . . . . . . . . . . . . . . . . 271 recursive editing level. . . . . . . . . . . . . . . . . . . . . . . . . 271 recursive evaluation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 recursive-edit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 redirect-frame-focus . . . . . . . . . . . . . . . . . . . . . . . 420 redo. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461 redraw-display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567 redraw-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567 regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492 regexp alternative . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495 regexp grouping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495 regexp searching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497 regexp-history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 regexp-quote . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496 regexps used standardly in editing . . . . . . . . . . . . 506 region (face name) . . . . . . . . . . . . . . . . . . . . . . . . . . . 578 region argument . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 region, the . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447 region-beginning. . . . . . . . . . . . . . . . . . . . . . . . . . . . 447 region-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448 region-face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581 register-alist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488 registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488 regular expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492 regular expression searching . . . . . . . . . . . . . . . . . . 497

reindent-then-newline-and-indent . . . . . . . . . 473

relative file name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347 remainder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 remove-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 remove-text-properties. . . . . . . . . . . . . . . . . . . . . 479 rename-auto-save-file . . . . . . . . . . . . . . . . . . . . . . 366 rename-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372 rename-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343 renaming files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342 repeat events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 repeated loading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 replace bindings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 replace characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487

replace-buffer-in-windows . . . . . . . . . . . . . . . . . 392

replace-match . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503 replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 require . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 require-final-newline . . . . . . . . . . . . . . . . . . . . . . 334 requiring features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 resize redisplay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567 rest arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 restriction (in a buffer) . . . . . . . . . . . . . . . . . . . . . . . 438 resume (cf. no-redraw-on-reenter) . . . . . . . . . . 567 return . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 reversing a list. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 revert-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366 revert-buffer-function. . . . . . . . . . . . . . . . . . . . . 367

revert-buffer-insert-file-contents-function

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367 rm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343 rosh hodesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596 round . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 rounding in conversions . . . . . . . . . . . . . . . . . . . . . . . . 38 rounding without conversion . . . . . . . . . . . . . . . . . . . 42 rplaca . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 rplacd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 run time stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 run-at-time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 556 run-hooks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 run-with-idle-timer . . . . . . . . . . . . . . . . . . . . . . . . 557

S

same-window-buffer-names . . . . . . . . . . . . . . . . . . 394

same-window-regexps . . . . . . . . . . . . . . . . . . . . . . . . 395 save-abbrevs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521 save-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332 save-excursion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437 save-match-data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505 save-restriction. . . . . . . . . . . . . . . . . . . . . . . . . . . . 439 save-selected-window . . . . . . . . . . . . . . . . . . . . . . . 388 save-some-buffers . . . . . . . . . . . . . . . . . . . . . . . . . . 332 save-window-excursion . . . . . . . . . . . . . . . . . . . . . . 406 saving text properties. . . . . . . . . . . . . . . . . . . . . . . . . 485 saving window information . . . . . . . . . . . . . . . . . . . 406 scan-lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516 scan-sexps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516 scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 screen layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 screen of terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383 screen size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567 screen-height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567 screen-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567 scroll-bar-event-ratio. . . . . . . . . . . . . . . . . . . . . 262 scroll-bar-scale. . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 scroll-down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 scroll-left . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401 scroll-other-window . . . . . . . . . . . . . . . . . . . . . . . . 399 scroll-right . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401 scroll-step . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399 scroll-up. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 scrolling vertically . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 search-backward. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492 search-failed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491 search-forward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491 searching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491 searching and case . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505 searching for regexp . . . . . . . . . . . . . . . . . . . . . . . . . . 497 secondary-selection (face name) . . . . . . . . . . . . 578 select-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419 select-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387 selected frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419 selected window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383 selected-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419 selected-window. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387 selecting a buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 selecting windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387 selection (for X windows) . . . . . . . . . . . . . . . . . . . . . 425 selective display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571 selective-display . . . . . . . . . . . . . . . . . . . . . . . . . . 571

selective-display-ellipses . . . . . . . . . . . . . . . . 572

self-evaluating form . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 self-insert-and-exit . . . . . . . . . . . . . . . . . . . . . . . 240 self-insert-command . . . . . . . . . . . . . . . . . . . . . . . . 453 self-insert-command override. . . . . . . . . . . . . . . . 290 self-insert-command, minor modes . . . . . . . . . . 310 self-insertion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453

send-string-to-terminal . . . . . . . . . . . . . . . . . . . 563

sending signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534 sentence-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506 sentinel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 539 sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 sequence length. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 sequencep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 set-auto-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 set-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 set-buffer-auto-saved . . . . . . . . . . . . . . . . . . . . . . 365 set-buffer-major-mode . . . . . . . . . . . . . . . . . . . . . . 306 set-buffer-modified-p . . . . . . . . . . . . . . . . . . . . . . 374 set-case-syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 set-case-syntax-delims . . . . . . . . . . . . . . . . . . . . . . 59 set-case-syntax-pair . . . . . . . . . . . . . . . . . . . . . . . . 59 set-case-table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 set-default . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 set-default-file-modes. . . . . . . . . . . . . . . . . . . . . 344 set-face-background . . . . . . . . . . . . . . . . . . . . . . . . 580 set-face-font . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580 set-face-foreground . . . . . . . . . . . . . . . . . . . . . . . . 580 set-face-stipple. . . . . . . . . . . . . . . . . . . . . . . . . . . . 580 set-face-underline-p . . . . . . . . . . . . . . . . . . . . . . . 580 set-file-modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

set-frame-configuration . . . . . . . . . . . . . . . . . . . 421

set-frame-position . . . . . . . . . . . . . . . . . . . . . . . . . 415 set-frame-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 set-input-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558 set-keymap-parent . . . . . . . . . . . . . . . . . . . . . . . . . . 280 set-left-margin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466 set-mark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446 set-marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444 set-match-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504

set-mouse-pixel-position . . . . . . . . . . . . . . . . . . 422

set-mouse-position . . . . . . . . . . . . . . . . . . . . . . . . . 422 set-process-buffer . . . . . . . . . . . . . . . . . . . . . . . . . 536 set-process-filter . . . . . . . . . . . . . . . . . . . . . . . . . 538 set-process-sentinel . . . . . . . . . . . . . . . . . . . . . . . 539 set-register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488 set-right-margin. . . . . . . . . . . . . . . . . . . . . . . . . . . . 466 set-screen-height . . . . . . . . . . . . . . . . . . . . . . . . . . 568 set-screen-width. . . . . . . . . . . . . . . . . . . . . . . . . . . . 568

set-standard-case-table. . . . . . . . . . . . . . . . . . . . . 59

set-syntax-table. . . . . . . . . . . . . . . . . . . . . . . . . . . . 515 set-text-properties . . . . . . . . . . . . . . . . . . . . . . . . 480

set-visited-file-modtime . . . . . . . . . . . . . . . . . . 375

set-visited-file-name . . . . . . . . . . . . . . . . . 334, 373 set-window-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . 390

                                                set-window-configuration . . . . . . . . . . . . . . . . . . 406

set-window-dedicated-p. . . . . . . . . . . . . . . . . . . . . 395

                                                set-window-display-table . . . . . . . . . . . . . . . . . . 584

set-window-hscroll . . . . . . . . . . . . . . . . . . . . . . . . . 402 set-window-point. . . . . . . . . . . . . . . . . . . . . . . . . . . . 396 set-window-start. . . . . . . . . . . . . . . . . . . . . . . . . . . . 397 setcar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 setcdr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 setenv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551 setplist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 setprv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552 setq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 setq-default . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 setting modes of files . . . . . . . . . . . . . . . . . . . . . . . . . 342 setting-constant. . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 sexp diary entries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595 sexp motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435 shadowing of variables . . . . . . . . . . . . . . . . . . . . . . . . 122 shallow binding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Shell mode mode-line-format . . . . . . . . . . . . . . . . 312 shell-command-history . . . . . . . . . . . . . . . . . . . . . . 228 shrink-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404

                                                shrink-window-horizontally . . . . . . . . . . . . . . . . 404

side effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 signal-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 535 signaling errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534 simple-diary-display . . . . . . . . . . . . . . . . . . . . . . . 594 sin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 single-key-description. . . . . . . . . . . . . . . . . . . . . 323 sit-for . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 ‘site-init.el’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609 ‘site-load.el’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609 site-run-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544 ‘site-start.el’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543 size of screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567 size of window. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402 skip-chars-backward . . . . . . . . . . . . . . . . . . . . . . . . 437 skip-chars-forward . . . . . . . . . . . . . . . . . . . . . . . . . 436 skip-syntax-backward . . . . . . . . . . . . . . . . . . . . . . . 515 skip-syntax-forward . . . . . . . . . . . . . . . . . . . . . . . . 515 skipping characters . . . . . . . . . . . . . . . . . . . . . . . . . . . 436 skipping comments . . . . . . . . . . . . . . . . . . . . . . . . . . . 517 sleep-for. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 Snarf-documentation . . . . . . . . . . . . . . . . . . . . . . . . 322 sort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 sort-columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 sort-diary-entries . . . . . . . . . . . . . . . . . . . . . . . . . 594 sort-fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470 sort-lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470 sort-numeric-fields . . . . . . . . . . . . . . . . . . . . . . . . 471 sort-pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470 sort-paragraphs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470 sort-regexp-fields . . . . . . . . . . . . . . . . . . . . . . . . . 469 sort-subr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468 sorting diary entries . . . . . . . . . . . . . . . . . . . . . . . . . . 594 sorting lists. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 sorting text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468 source breakpoints. . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 sparse keymap. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 ⟨\underline{\overline{SPC}}⟩ in minibuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 special . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 special form descriptions . . . . . . . . . . . . . . . . . . . . . . . 12 special form evaluation . . . . . . . . . . . . . . . . . . . . . . . 101 special forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 special forms (Edebug) . . . . . . . . . . . . . . . . . . . . . . . 192 special forms for control structures. . . . . . . . . . . . 105

special-display-buffer-names . . . . . . . . . . . . . . 394
special-display-frame-alist . . . . . . . . . . . . . . . 394
special-display-function . . . . . . . . . . . . . . . . . . 394
special-display-popup-frame . . . . . . . . . . . . . . . 394
special-display-regexps . . . . . . . . . . . . . . . . . . . 394

speedups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602 splicing (with backquote) . . . . . . . . . . . . . . . . . . . . . 155 split-height-threshold. . . . . . . . . . . . . . . . . . . . . 393 split-line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454 split-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384

split-window-horizontally . . . . . . . . . . . . . . . . . 386
split-window-vertically . . . . . . . . . . . . . . . . . . . 385

splitting windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384 sqrt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 stable sort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 standard regexps used in editing . . . . . . . . . . . . . . 506 standard-case-table . . . . . . . . . . . . . . . . . . . . . . . . . 59 standard-display-table. . . . . . . . . . . . . . . . . . . . . 584 standard-input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 standard-output. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 standard-syntax-table . . . . . . . . . . . . . . . . . . . . . . 517 standards of coding style . . . . . . . . . . . . . . . . . . . . . 599 start up of Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543 start-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529

start-process-shell-command . . . . . . . . . . . . . . . 530

‘startup.el’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543 sticky text properties . . . . . . . . . . . . . . . . . . . . . . . . . 484 stop points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 stop-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 535 stopping an infinite loop . . . . . . . . . . . . . . . . . . . . . . 182 stopping on events. . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 store-match-data. . . . . . . . . . . . . . . . . . . . . . . . . . . . 505 stream (for printing). . . . . . . . . . . . . . . . . . . . . . . . . . 216 stream (for reading) . . . . . . . . . . . . . . . . . . . . . . . . . . 213 string equality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 string in keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 string input stream . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 string length. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 string quote. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511 string search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491 string to character . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 string to number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 string to object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 string, writing a doc string . . . . . . . . . . . . . . . . . . . 319 string-equal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 string-lessp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 string-match . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498 string-to-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 string-to-int . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 string-to-number. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 string= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 string< . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 stringp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 strings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 strings, formatting them . . . . . . . . . . . . . . . . . . . . . . . 55 subprocess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525 subr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 subrp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 subst-char-in-region . . . . . . . . . . . . . . . . . . . . . . . 487

                                                substitute-command-keys . . . . . . . . . . . . . . . . . . . 323
                                                substitute-in-file-name . . . . . . . . . . . . . . . . . . . 348
                                                substitute-key-definition . . . . . . . . . . . . . . . . . 289

substituting keys in documentation . . . . . . . . . . . 322 substring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 super characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 super-apropos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 suppress-keymap. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 suspend (cf. no-redraw-on-reenter) . . . . . . . . . 567 suspend evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 suspend-emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548 suspend-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549 suspend-resume-hook . . . . . . . . . . . . . . . . . . . . . . . . 549 suspending Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548 switch-to-buffer. . . . . . . . . . . . . . . . . . . . . . . . . . . . 391

                                                switch-to-buffer-other-window. . . . . . . . . . . . . 392

switches on command line . . . . . . . . . . . . . . . . . . . . 546 switching to a buffer. . . . . . . . . . . . . . . . . . . . . . . . . . 391 symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 symbol components . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 symbol constituent. . . . . . . . . . . . . . . . . . . . . . . . . . 510 symbol equality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 symbol evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 symbol function indirection . . . . . . . . . . . . . . . . . . . . 99 symbol in keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 symbol name hashing . . . . . . . . . . . . . . . . . . . . . . . . . . 89 symbol-function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 symbol-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 symbol-plist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 symbol-value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 symbolp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 synchronous subprocess. . . . . . . . . . . . . . . . . . . . . . . 526 syntax classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509 syntax descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510 syntax error (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . 207 syntax flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512 syntax for characters . . . . . . . . . . . . . . . . . . . . . . . . . . 17 syntax table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509 syntax table example . . . . . . . . . . . . . . . . . . . . . . . . . 302 syntax table internals. . . . . . . . . . . . . . . . . . . . . . . . . 518 syntax tables in modes . . . . . . . . . . . . . . . . . . . . . . . 300 syntax-table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515 syntax-table-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509 system-configuration . . . . . . . . . . . . . . . . . . . . . . . 550 system-key-alist. . . . . . . . . . . . . . . . . . . . . . . . . . . . 564 system-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550 system-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549

T

t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 t and truth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 t input stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 t output stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 tab deletion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455 ⟨\underline{\overline{TAB}}⟩ in minibuffer. . . . . . . . . . . . . . . . . . . . . . . . . . . 225 tab-stop-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476 tab-to-tab-stop. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476 tab-width. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583 tabs stops for indentation. . . . . . . . . . . . . . . . . . . . . 475 tag on run time stack. . . . . . . . . . . . . . . . . . . . . . . . . 111 tan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 TCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541 temacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609

temp-buffer-show-function . . . . . . . . . . . . . . . . . 574

TERM environment variable . . . . . . . . . . . . . . . . . . . . 545 term-file-prefix. . . . . . . . . . . . . . . . . . . . . . . . . . . . 545 term-setup-hook. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546 Termcap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545 terminal frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 terminal input. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558 terminal input modes . . . . . . . . . . . . . . . . . . . . . . . . . 558 terminal output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562 terminal screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383 terminal-specific initialization . . . . . . . . . . . . . . . . . 545 terminate keyboard macro . . . . . . . . . . . . . . . . . . . . 267 termscript file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563 terpri . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 testing types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449 text files and binary files. . . . . . . . . . . . . . . . . . . . . . 356 text insertion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452 text parsing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509 text properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478 text properties in files . . . . . . . . . . . . . . . . . . . . . . . . 485 text-char-description . . . . . . . . . . . . . . . . . . . . . . 324 text-mode-abbrev-table. . . . . . . . . . . . . . . . . . . . . 523 text-mode-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633 text-mode-syntax-table. . . . . . . . . . . . . . . . . . . . . 517 text-properties-at . . . . . . . . . . . . . . . . . . . . . . . . . 478 text-property-any . . . . . . . . . . . . . . . . . . . . . . . . . . 481 text-property-not-all . . . . . . . . . . . . . . . . . . . . . . 481 this-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 this-command-keys . . . . . . . . . . . . . . . . . . . . . . . . . . 251 three-step-help. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 throw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 throw example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 tiled windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383 timer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 556 timing programs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602 tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 599

today-invisible-calendar-hook. . . . . . . . . . . . . 588
today-visible-calendar-hook . . . . . . . . . . . . . . . 587

toggle-read-only. . . . . . . . . . . . . . . . . . . . . . . . . . . . 376 top-level. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 top-level form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 tq-close . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540 tq-create. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540 tq-enqueue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540 trace buffer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 track-mouse. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258, 422 tracking the mouse . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 transaction queue . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540 transcendental functions . . . . . . . . . . . . . . . . . . . . . . . 46 Transient Mark mode. . . . . . . . . . . . . . . . . . . . . . . . . 447 transient-mark-mode . . . . . . . . . . . . . . . . . . . . . . . . 447 translate-region. . . . . . . . . . . . . . . . . . . . . . . . . . . . 488 translating input events . . . . . . . . . . . . . . . . . . . . . . 559 transpose-regions . . . . . . . . . . . . . . . . . . . . . . . . . . 489

trim-versions-without-asking . . . . . . . . . . . . . . 362

triple-click events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 true . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 truename (of file) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 truncate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 truncate-lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568

truncate-partial-width-windows . . . . . . . . . . . 568

truth value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 try-completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 two’s complement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 type checking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 type checking internals . . . . . . . . . . . . . . . . . . . . . . . 618 type predicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 type-of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

U

unbinding keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 undefined. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 undefined in keymap. . . . . . . . . . . . . . . . . . . . . . . . . 285 undefined key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 underline (face name) . . . . . . . . . . . . . . . . . . . . . . . 578 undo avoidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487 undo-boundary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462 undo-limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464 undo-strong-limit . . . . . . . . . . . . . . . . . . . . . . . . . . 464 unexec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 610

unhandled-file-name-directory. . . . . . . . . . . . . 354

unintern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 uninterned symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 universal-argument . . . . . . . . . . . . . . . . . . . . . . . . . 271 unload-feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 unloading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 unlock-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 unread-command-char . . . . . . . . . . . . . . . . . . . . . . . . 266 unread-command-events . . . . . . . . . . . . . . . . . . . . . . 266 unreading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 unwind-protect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 unwinding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 up-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435 upcase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 upcase-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477 upcase-word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477

update-directory-autoloads . . . . . . . . . . . . . . . . 165

update-file-autoloads . . . . . . . . . . . . . . . . . . . . . . 165 upper case. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 upper case key sequence . . . . . . . . . . . . . . . . . . . . . . 264 use-global-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 use-hard-newlines . . . . . . . . . . . . . . . . . . . . . . . . . . 466 use-local-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 user option . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 user-defined error. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 user-full-name . . . . . . . . . . . . . . . . . . . . . . . . . 552, 553 user-login-name . . . . . . . . . . . . . . . . . . . . . . . . 552, 553 user-mail-address . . . . . . . . . . . . . . . . . . . . . . . . . . 552 user-real-login-name . . . . . . . . . . . . . . . . . . 552, 553 user-real-uid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553 user-uid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553 user-variable-p. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 user-variable-p example . . . . . . . . . . . . . . . . . . . . 234

V

value cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 value of expression. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 variable definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 variable descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 variable limit error . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 variable-documentation. . . . . . . . . . . . . . . . . . . . . 319 variable-interactive . . . . . . . . . . . . . . . . . . . . . . . 127 variables, buffer-local . . . . . . . . . . . . . . . . . . . . . . . . . 134 vc-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 vconcat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 vector evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 vector length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 vectorp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

                                                verify-visited-file-modtime . . . . . . . . . . . . . . . 375

version number (in file name) . . . . . . . . . . . . . . . . . 344 version-control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361 vertical scrolling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 vertical tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 vertical-motion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434

                                                view-calendar-holidays-initially . . . . . . . . . 587
                                                view-diary-entries-initially . . . . . . . . . . . . . . 587

view-file. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330 view-mode-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633 view-register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488 visible frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 visible-bell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586 visible-frame-list . . . . . . . . . . . . . . . . . . . . . . . . . 417 visited file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372 visited file mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 visited-file-modtime . . . . . . . . . . . . . . . . . . . . . . . 375 visiting files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 void function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 void function cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 void variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 void-function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 void-variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

W

waiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 waiting for command key input . . . . . . . . . . . . . . . 266

waiting-for-user-input-p . . . . . . . . . . . . . . . . . . 540

wakeup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526 walk-windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390 where-is-internal . . . . . . . . . . . . . . . . . . . . . . . . . . 293 while . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 whitespace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 whitespace character . . . . . . . . . . . . . . . . . . . . . . . 510 wholenump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 widen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439 widening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439 window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383 window (overlay property) . . . . . . . . . . . . . . . . . . . . 575 window configuration (Edebug) . . . . . . . . . . . . . . . 203 window configurations . . . . . . . . . . . . . . . . . . . . . . . . 406 window excursions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 438 window internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 619 window ordering, cyclic . . . . . . . . . . . . . . . . . . . . . . . 388 window point. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395 window point internals . . . . . . . . . . . . . . . . . . . . . . . 620 window position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395 window resizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404 window size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402 window size, changing . . . . . . . . . . . . . . . . . . . . . . . . 404 window splitting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384 window top line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396 window-at. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 window-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390 window-configuration-p. . . . . . . . . . . . . . . . . . . . . 407 window-dedicated-p . . . . . . . . . . . . . . . . . . . . . . . . . 395 window-display-table . . . . . . . . . . . . . . . . . . . . . . . 584 window-edges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403 window-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396 window-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418 window-height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402 window-hscroll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401 window-live-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386 window-min-height . . . . . . . . . . . . . . . . . . . . . . . . . . 405 window-min-width. . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 window-minibuffer-p . . . . . . . . . . . . . . . . . . . . . . . . 241 window-point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396

window-scroll-functions . . . . . . . . . . . . . . . . . . . 400

window-setup-hook . . . . . . . . . . . . . . . . . . . . . . . . . . 586

window-size-change-functions . . . . . . . . . . . . . . 400

window-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396 window-system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586 window-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402 windowp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384 Windows file types . . . . . . . . . . . . . . . . . . . . . . . . . . . 356 windows, controlling precisely. . . . . . . . . . . . . . . . . 390

                                                with-output-to-temp-buffer . . . . . . . . . . . . . . . . 573

with-timeout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 557 word constituent . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510 word search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492 word-search-backward . . . . . . . . . . . . . . . . . . . . . . . 492 word-search-forward . . . . . . . . . . . . . . . . . . . . . . . . 492 words-include-escapes . . . . . . . . . . . . . . . . . . . . . . 431 write-abbrev-file . . . . . . . . . . . . . . . . . . . . . . . . . . 521 write-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 write-contents-hooks . . . . . . . . . . . . . . . . . . . . . . . 333 write-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332 write-file-hooks. . . . . . . . . . . . . . . . . . . . . . . . . . . . 333 write-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335

                                                write-region-annotate-functions . . . . . . . . . . 485

writing a documentation string . . . . . . . . . . . . . . . 319

                                                wrong-number-of-arguments . . . . . . . . . . . . . . . . . 141

wrong-type-argument . . . . . . . . . . . . . . . . . . . . . . . . . 29

X

X window frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 X Window System. . . . . . . . . . . . . . . . . . . . . . . . . . . . 586 x-close-connection . . . . . . . . . . . . . . . . . . . . . . . . . 410 x-color-defined-p . . . . . . . . . . . . . . . . . . . . . . . . . . 425 x-color-values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426

                                                x-display-backing-store . . . . . . . . . . . . . . . . . . . 427

x-display-color-cells . . . . . . . . . . . . . . . . . . . . . . 427 x-display-color-p . . . . . . . . . . . . . . . . . . . . . . . . . . 427 x-display-grayscale-p . . . . . . . . . . . . . . . . . . . . . . 427 x-display-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410 x-display-mm-height . . . . . . . . . . . . . . . . . . . . . . . . 427 x-display-mm-width . . . . . . . . . . . . . . . . . . . . . . . . . 427 x-display-pixel-height. . . . . . . . . . . . . . . . . . . . . 427 x-display-pixel-width . . . . . . . . . . . . . . . . . . . . . . 427 x-display-planes. . . . . . . . . . . . . . . . . . . . . . . . . . . . 427 x-display-save-under . . . . . . . . . . . . . . . . . . . . . . . 427 x-display-screens . . . . . . . . . . . . . . . . . . . . . . . . . . 427 x-display-visual-class. . . . . . . . . . . . . . . . . . . . . 427 x-get-cut-buffer. . . . . . . . . . . . . . . . . . . . . . . . . . . . 425 x-get-resource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426 x-get-selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425 x-open-connection . . . . . . . . . . . . . . . . . . . . . . . . . . 410 x-parse-geometry. . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 x-pointer-shape. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424 x-popup-dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424 x-popup-menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423

                                                x-sensitive-text-pointer-shape . . . . . . . . . . . 424

x-server-vendor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427 x-server-version. . . . . . . . . . . . . . . . . . . . . . . . . . . . 427 x-set-cut-buffer. . . . . . . . . . . . . . . . . . . . . . . . . . . . 425 x-set-selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425

Y

y-or-n-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 y-or-n-p-with-timeout . . . . . . . . . . . . . . . . . . . . . . 238 yahrzeits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596 yank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459 yank suppression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 yank-pop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459 yes-or-no questions . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 yes-or-no-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

Z

zerop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Short Contents

GNU GENERAL PUBLIC LICENSE . . . . . . . . . . . . . . . . . . . . 1 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2 Lisp Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3 Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 4 Strings and Characters . . . . . . . . . . . . . . . . . . . . . . . . . . 49 5 Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 6 Sequences, Arrays, and Vectors . . . . . . . . . . . . . . . . . . . . . 79 7 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 8 Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 9 Control Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 10 Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 11 Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 12 Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 13 Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 14 Byte Compilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 15 Debugging Lisp Programs. . . . . . . . . . . . . . . . . . . . . . . . 181 16 Reading and Printing Lisp Objects . . . . . . . . . . . . . . . . . 213 17 Minibuffers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 18 Command Loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 19 Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 20 Major and Minor Modes. . . . . . . . . . . . . . . . . . . . . . . . . 299 21 Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319 22 Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 23 Backups and Auto-Saving. . . . . . . . . . . . . . . . . . . . . . . . 359 24 Buffers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 25 Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383 26 Frames. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 27 Positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 28 Markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441 29 Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449 30 Searching and Matching . . . . . . . . . . . . . . . . . . . . . . . . . 491 31 Syntax Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509 32 Abbrevs And Abbrev Expansion . . . . . . . . . . . . . . . . . . . 519 33 Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525

ii GNU Emacs Lisp Reference Manual

34 Operating System Interface. . . . . . . . . . . . . . . . . . . . . . . 543 35 Emacs Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567 36 Customizing the Calendar and Diary . . . . . . . . . . . . . . . . 587 Appendix A Tips and Standards . . . . . . . . . . . . . . . . . . . . . 599 Appendix B GNU Emacs Internals . . . . . . . . . . . . . . . . . . . . 609 Appendix C Standard Errors . . . . . . . . . . . . . . . . . . . . . . . . 623 Appendix D Buffer-Local Variables. . . . . . . . . . . . . . . . . . . . 627 Appendix E Standard Keymaps . . . . . . . . . . . . . . . . . . . . . . 631 Appendix F Standard Hooks . . . . . . . . . . . . . . . . . . . . . . . . 635 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 639

Table of Contents

GNU GENERAL PUBLIC LICENSE . . . . . . . . . . 1

Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION

AND MODIFICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 How to Apply These Terms to Your New Programs . . . . . . . . . . . . . 6

1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.1 Caveats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.2 Lisp History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.3 Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

1.3.1 Some Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.3.2 nil and t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.3.3 Evaluation Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.3.4 Printing Notation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.3.5 Error Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.3.6 Buffer Text Notation. . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.3.7 Format of Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . 12

1.3.7.1 A Sample Function Description . . . . . . . . 12 1.3.7.2 A Sample Variable Description . . . . . . . . . 14

1.4 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2 Lisp Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.1 Printed Representation and Read Syntax. . . . . . . . . . . . . . . . . 15 2.2 Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.3 Programming Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.3.1 Integer Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.3.2 Floating Point Type . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.3.3 Character Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.3.4 Symbol Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.3.5 Sequence Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.3.6 Cons Cell and List Types . . . . . . . . . . . . . . . . . . . . . . 20

2.3.6.1 Dotted Pair Notation. . . . . . . . . . . . . . . . . . 22 2.3.6.2 Association List Type . . . . . . . . . . . . . . . . . 22

2.3.7 Array Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.3.8 String Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.3.9 Vector Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.3.10 Function Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.3.11 Macro Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.3.12 Primitive Function Type . . . . . . . . . . . . . . . . . . . . . . 25 2.3.13 Byte-Code Function Type . . . . . . . . . . . . . . . . . . . . . 25 2.3.14 Autoload Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2.4 Editing Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.4.1 Buffer Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.4.2 Marker Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.4.3 Window Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.4.4 Frame Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.4.5 Window Configuration Type. . . . . . . . . . . . . . . . . . . . 28 2.4.6 Process Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.4.7 Stream Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.4.8 Keymap Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.4.9 Syntax Table Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.4.10 Display Table Type . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.4.11 Overlay Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2.5 Type Predicates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.6 Equality Predicates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3 Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

3.1 Integer Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 3.2 Floating Point Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 3.3 Type Predicates for Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 3.4 Comparison of Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.5 Numeric Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.6 Arithmetic Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 3.7 Rounding Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3.8 Bitwise Operations on Integers . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3.9 Standard Mathematical Functions . . . . . . . . . . . . . . . . . . . . . . . 46 3.10 Random Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4 Strings and Characters . . . . . . . . . . . . . . . . . . . . 49

4.1 String and Character Basics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 4.2 The Predicates for Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 4.3 Creating Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 4.4 Comparison of Characters and Strings . . . . . . . . . . . . . . . . . . . 52 4.5 Conversion of Characters and Strings . . . . . . . . . . . . . . . . . . . . 53 4.6 Formatting Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 4.7 Character Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 4.8 The Case Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

5 Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

5.1 Lists and Cons Cells. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 5.2 Lists as Linked Pairs of Boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 5.3 Predicates on Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 5.4 Accessing Elements of Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 5.5 Building Cons Cells and Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 5.6 Modifying Existing List Structure . . . . . . . . . . . . . . . . . . . . . . . 67

5.6.1 Altering List Elements with setcar . . . . . . . . . . . . . 67 5.6.2 Altering the CDR of a List . . . . . . . . . . . . . . . . . . . . . 69 5.6.3 Functions that Rearrange Lists . . . . . . . . . . . . . . . . . 70

5.7 Using Lists as Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 5.8 Association Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

6 Sequences, Arrays, and Vectors . . . . . . . . . . . . 79

6.1 Sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 6.2 Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 6.3 Functions that Operate on Arrays . . . . . . . . . . . . . . . . . . . . . . . 82 6.4 Vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 6.5 Functions That Operate on Vectors . . . . . . . . . . . . . . . . . . . . . . 83

7 Symbols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

7.1 Symbol Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 7.2 Defining Symbols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 7.3 Creating and Interning Symbols . . . . . . . . . . . . . . . . . . . . . . . . . 89 7.4 Property Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

7.4.1 Property Lists and Association Lists . . . . . . . . . . . . 92 7.4.2 Property List Functions for Symbols . . . . . . . . . . . . 92 7.4.3 Property Lists Outside Symbols . . . . . . . . . . . . . . . . 93

8 Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

8.1 Eval. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 8.2 Kinds of Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

8.2.1 Self-Evaluating Forms. . . . . . . . . . . . . . . . . . . . . . . . . . 98 8.2.2 Symbol Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 8.2.3 Classification of List Forms . . . . . . . . . . . . . . . . . . . . . 99 8.2.4 Symbol Function Indirection. . . . . . . . . . . . . . . . . . . . 99 8.2.5 Evaluation of Function Forms . . . . . . . . . . . . . . . . . 100 8.2.6 Lisp Macro Evaluation . . . . . . . . . . . . . . . . . . . . . . . . 100 8.2.7 Special Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 8.2.8 Autoloading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

8.3 Quoting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

9 Control Structures. . . . . . . . . . . . . . . . . . . . . . . 105

9.1 Sequencing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 9.2 Conditionals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 9.3 Constructs for Combining Conditions . . . . . . . . . . . . . . . . . . . 108 9.4 Iteration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 9.5 Nonlocal Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

9.5.1 Explicit Nonlocal Exits: catch and throw . . . . . . 110 9.5.2 Examples of catch and throw . . . . . . . . . . . . . . . . . 111 9.5.3 Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

9.5.3.1 How to Signal an Error . . . . . . . . . . . . . . . 113 9.5.3.2 How Emacs Processes Errors. . . . . . . . . . 114 9.5.3.3 Writing Code to Handle Errors. . . . . . . . 114 9.5.3.4 Error Symbols and Condition Names . . 117

9.5.4 Cleaning Up from Nonlocal Exits . . . . . . . . . . . . . . 118

10 Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

10.1 Global Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 10.2 Variables That Never Change . . . . . . . . . . . . . . . . . . . . . . . . . 121 10.3 Local Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 10.4 When a Variable is “Void” . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 10.5 Defining Global Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 10.6 Tips for Defining Variables Robustly. . . . . . . . . . . . . . . . . . . 127 10.7 Accessing Variable Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 10.8 How to Alter a Variable Value . . . . . . . . . . . . . . . . . . . . . . . . 129 10.9 Scoping Rules for Variable Bindings . . . . . . . . . . . . . . . . . . . 131

10.9.1 Scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 10.9.2 Extent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 10.9.3 Implementation of Dynamic Scoping . . . . . . . . . . 133 10.9.4 Proper Use of Dynamic Scoping . . . . . . . . . . . . . . 133

10.10 Buffer-Local Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 10.10.1 Introduction to Buffer-Local Variables . . . . . . . 134 10.10.2 Creating and Deleting Buffer-Local Bindings. . 135 10.10.3 The Default Value of a Buffer-Local Variable. . 137

11 Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

11.1 What Is a Function? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 11.2 Lambda Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

11.2.1 Components of a Lambda Expression . . . . . . . . . 140 11.2.2 A Simple Lambda-Expression Example . . . . . . . . 141 11.2.3 Advanced Features of Argument Lists . . . . . . . . . 141 11.2.4 Documentation Strings of Functions. . . . . . . . . . . 143

11.3 Naming a Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 11.4 Defining Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 11.5 Calling Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 11.6 Mapping Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 11.7 Anonymous Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 11.8 Accessing Function Cell Contents. . . . . . . . . . . . . . . . . . . . . . 149 11.9 Inline Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 11.10 Other Topics Related to Functions . . . . . . . . . . . . . . . . . . . 152

12 Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

12.1 A Simple Example of a Macro. . . . . . . . . . . . . . . . . . . . . . . . . 153 12.2 Expansion of a Macro Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 12.3 Macros and Byte Compilation. . . . . . . . . . . . . . . . . . . . . . . . . 154 12.4 Defining Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 12.5 Backquote . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 12.6 Common Problems Using Macros. . . . . . . . . . . . . . . . . . . . . . 156

12.6.1 Evaluating Macro Arguments Repeatedly. . . . . . 156 12.6.2 Local Variables in Macro Expansions. . . . . . . . . . 158 12.6.3 Evaluating Macro Arguments in Expansion …. 158 12.6.4 How Many Times is the Macro Expanded? …. 159

13 Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

13.1 How Programs Do Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 13.2 Autoload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 13.3 Repeated Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 13.4 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 13.5 Unloading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 13.6 Hooks for Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

14 Byte Compilation. . . . . . . . . . . . . . . . . . . . . . . 171

14.1 Performance of Byte-Compiled Code. . . . . . . . . . . . . . . . . . . 171 14.2 The Compilation Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 14.3 Documentation Strings and Compilation . . . . . . . . . . . . . . . 174 14.4 Dynamic Loading of Individual Functions . . . . . . . . . . . . . . 174 14.5 Evaluation During Compilation . . . . . . . . . . . . . . . . . . . . . . . 175 14.6 Byte-Code Function Objects . . . . . . . . . . . . . . . . . . . . . . . . . . 176 14.7 Disassembled Byte-Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

15 Debugging Lisp Programs . . . . . . . . . . . . . . . 181

15.1 The Lisp Debugger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 15.1.1 Entering the Debugger on an Error . . . . . . . . . . . 181 15.1.2 Debugging Infinite Loops. . . . . . . . . . . . . . . . . . . . . 182 15.1.3 Entering the Debugger on a Function Call . . . . . 182 15.1.4 Explicit Entry to the Debugger . . . . . . . . . . . . . . . 184 15.1.5 Using the Debugger. . . . . . . . . . . . . . . . . . . . . . . . . . 184 15.1.6 Debugger Commands . . . . . . . . . . . . . . . . . . . . . . . . 185 15.1.7 Invoking the Debugger . . . . . . . . . . . . . . . . . . . . . . . 186 15.1.8 Internals of the Debugger . . . . . . . . . . . . . . . . . . . . 187

15.2 Debugging Invalid Lisp Syntax . . . . . . . . . . . . . . . . . . . . . . . . 189 15.2.1 Excess Open Parentheses. . . . . . . . . . . . . . . . . . . . . 189 15.2.2 Excess Close Parentheses. . . . . . . . . . . . . . . . . . . . . 190

15.3 Debugging Problems in Compilation . . . . . . . . . . . . . . . . . . . 190 15.4 Edebug. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

15.4.1 Using Edebug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 15.4.2 Instrumenting for Edebug . . . . . . . . . . . . . . . . . . . . 192 15.4.3 Edebug Execution Modes . . . . . . . . . . . . . . . . . . . . 193 15.4.4 Jumping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 15.4.5 Miscellaneous Edebug Commands. . . . . . . . . . . . . 195 15.4.6 Breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

15.4.6.1 Global Break Condition . . . . . . . . . . . . . 196 15.4.6.2 Source Breakpoints . . . . . . . . . . . . . . . . . 197

15.4.7 Trapping Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 15.4.8 Edebug Views . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 15.4.9 Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 15.4.10 Evaluation List Buffer . . . . . . . . . . . . . . . . . . . . . . 199 15.4.11 Printing in Edebug . . . . . . . . . . . . . . . . . . . . . . . . . 200 15.4.12 Trace Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 15.4.13 Coverage Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 15.4.14 The Outside Context . . . . . . . . . . . . . . . . . . . . . . . 202

15.4.14.1 Checking Whether to Stop. . . . . . . . . . 202 15.4.14.2 Edebug Display Update . . . . . . . . . . . . 202 15.4.14.3 Edebug Recursive Edit . . . . . . . . . . . . . 203

15.4.15 Instrumenting Macro Calls . . . . . . . . . . . . . . . . . . 204 15.4.15.1 Specification List . . . . . . . . . . . . . . . . . . 204 15.4.15.2 Backtracking . . . . . . . . . . . . . . . . . . . . . . 207 15.4.15.3 Specification Examples . . . . . . . . . . . . . 208

15.4.16 Edebug Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

16 Reading and Printing Lisp Objects . . . . . . 213

16.1 Introduction to Reading and Printing . . . . . . . . . . . . . . . . . . 213 16.2 Input Streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 16.3 Input Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 16.4 Output Streams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 16.5 Output Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 16.6 Variables Affecting Output. . . . . . . . . . . . . . . . . . . . . . . . . . . . 220

17 Minibuffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

17.1 Introduction to Minibuffers . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 17.2 Reading Text Strings with the Minibuffer . . . . . . . . . . . . . . 224 17.3 Reading Lisp Objects with the Minibuffer . . . . . . . . . . . . . . 225 17.4 Minibuffer History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 17.5 Completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228

17.5.1 Basic Completion Functions . . . . . . . . . . . . . . . . . . 228 17.5.2 Completion and the Minibuffer . . . . . . . . . . . . . . . 230 17.5.3 Minibuffer Commands That Do Completion … 231 17.5.4 High-Level Completion Functions . . . . . . . . . . . . . 233 17.5.5 Reading File Names . . . . . . . . . . . . . . . . . . . . . . . . . 235 17.5.6 Programmed Completion. . . . . . . . . . . . . . . . . . . . . 236

17.6 Yes-or-No Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 17.7 Asking Multiple Y-or-N Questions . . . . . . . . . . . . . . . . . . . . . 239 17.8 Minibuffer Miscellany. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240

18 Command Loop . . . . . . . . . . . . . . . . . . . . . . . . 243

18.1 Command Loop Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 18.2 Defining Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

18.2.1 Using interactive . . . . . . . . . . . . . . . . . . . . . . . . . . 244 18.2.2 Code Characters for interactive . . . . . . . . . . . . 245 18.2.3 Examples of Using interactive . . . . . . . . . . . . . . 247

18.3 Interactive Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 18.4 Information from the Command Loop . . . . . . . . . . . . . . . . . 250 18.5 Input Events. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252

18.5.1 Keyboard Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252 18.5.2 Function Keys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 18.5.3 Mouse Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 18.5.4 Click Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 18.5.5 Drag Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 18.5.6 Button-Down Events . . . . . . . . . . . . . . . . . . . . . . . . 256 18.5.7 Repeat Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 18.5.8 Motion Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 18.5.9 Focus Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 18.5.10 Miscellaneous Window System Events. . . . . . . . 258 18.5.11 Event Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 18.5.12 Classifying Events . . . . . . . . . . . . . . . . . . . . . . . . . . 259 18.5.13 Accessing Events . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 18.5.14 Putting Keyboard Events in Strings. . . . . . . . . . 262

18.6 Reading Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 18.6.1 Key Sequence Input . . . . . . . . . . . . . . . . . . . . . . . . . 263 18.6.2 Reading One Event . . . . . . . . . . . . . . . . . . . . . . . . . . 264 18.6.3 Quoted Character Input . . . . . . . . . . . . . . . . . . . . . 265 18.6.4 Miscellaneous Event Input Features . . . . . . . . . . . 266

18.7 Waiting for Elapsed Time or Input . . . . . . . . . . . . . . . . . . . . 267 18.8 Quitting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 18.9 Prefix Command Arguments . . . . . . . . . . . . . . . . . . . . . . . . . . 270 18.10 Recursive Editing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 18.11 Disabling Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 18.12 Command History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 18.13 Keyboard Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275

19 Keymaps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277

19.1 Keymap Terminology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 19.2 Format of Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 19.3 Creating Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 19.4 Inheritance and Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 19.5 Prefix Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 19.6 Active Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 19.7 Key Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 19.8 Functions for Key Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 19.9 Changing Key Bindings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 19.10 Commands for Binding Keys . . . . . . . . . . . . . . . . . . . . . . . . . 291 19.11 Scanning Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 19.12 Menu Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

19.12.1 Defining Menus . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 19.12.2 Menus and the Mouse . . . . . . . . . . . . . . . . . . . . . . 295 19.12.3 Menus and the Keyboard . . . . . . . . . . . . . . . . . . . 296 19.12.4 Menu Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296 19.12.5 The Menu Bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 19.12.6 Modifying Menus . . . . . . . . . . . . . . . . . . . . . . . . . . . 298

20 Major and Minor Modes . . . . . . . . . . . . . . . . 299

20.1 Major Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 20.1.1 Major Mode Conventions . . . . . . . . . . . . . . . . . . . . 300 20.1.2 Major Mode Examples . . . . . . . . . . . . . . . . . . . . . . . 302 20.1.3 How Emacs Chooses a Major Mode . . . . . . . . . . . 305 20.1.4 Getting Help about a Major Mode . . . . . . . . . . . . 307 20.1.5 Defining Derived Modes. . . . . . . . . . . . . . . . . . . . . . 308

20.2 Minor Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 20.2.1 Conventions for Writing Minor Modes. . . . . . . . . 309 20.2.2 Keymaps and Minor Modes . . . . . . . . . . . . . . . . . . 310

20.3 Mode Line Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 20.3.1 The Data Structure of the Mode Line . . . . . . . . . 311 20.3.2 Variables Used in the Mode Line. . . . . . . . . . . . . . 312 20.3.3 %-Constructs in the Mode Line . . . . . . . . . . . . . . . 314

20.4 Hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

21 Documentation . . . . . . . . . . . . . . . . . . . . . . . . . 319

21.1 Documentation Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319 21.2 Access to Documentation Strings . . . . . . . . . . . . . . . . . . . . . . 320 21.3 Substituting Key Bindings in Documentation. . . . . . . . . . . 322 21.4 Describing Characters for Help Messages . . . . . . . . . . . . . . . 323 21.5 Help Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324

22 Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329

22.1 Visiting Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 22.1.1 Functions for Visiting Files . . . . . . . . . . . . . . . . . . . 329 22.1.2 Subroutines of Visiting. . . . . . . . . . . . . . . . . . . . . . . 331

22.2 Saving Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332 22.3 Reading from Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334 22.4 Writing to Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 22.5 File Locks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 22.6 Information about Files. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337

22.6.1 Testing Accessibility . . . . . . . . . . . . . . . . . . . . . . . . . 337 22.6.2 Distinguishing Kinds of Files . . . . . . . . . . . . . . . . . 339 22.6.3 Truenames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 22.6.4 Other Information about Files . . . . . . . . . . . . . . . . 340

22.7 Changing File Names and Attributes . . . . . . . . . . . . . . . . . . 342 22.8 File Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

22.8.1 File Name Components . . . . . . . . . . . . . . . . . . . . . . 344 22.8.2 Directory Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345 22.8.3 Absolute and Relative File Names . . . . . . . . . . . . 347 22.8.4 Functions that Expand Filenames. . . . . . . . . . . . . 347 22.8.5 Generating Unique File Names . . . . . . . . . . . . . . . 349 22.8.6 File Name Completion . . . . . . . . . . . . . . . . . . . . . . . 349 22.8.7 Standard File Names . . . . . . . . . . . . . . . . . . . . . . . . 350

22.9 Contents of Directories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351 22.10 Creating and Deleting Directories . . . . . . . . . . . . . . . . . . . . 352 22.11 Making Certain File Names “Magic” . . . . . . . . . . . . . . . . . 352 22.12 File Format Conversion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354 22.13 Files and MS-DOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356

23 Backups and Auto-Saving . . . . . . . . . . . . . . . 359

23.1 Backup Files. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 23.1.1 Making Backup Files . . . . . . . . . . . . . . . . . . . . . . . . 359 23.1.2 Backup by Renaming or by Copying? . . . . . . . . . 360 23.1.3 Making and Deleting Numbered Backup Files. . 361 23.1.4 Naming Backup Files . . . . . . . . . . . . . . . . . . . . . . . . 362

23.2 Auto-Saving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363 23.3 Reverting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366

24 Buffers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369

24.1 Buffer Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 24.2 The Current Buffer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 24.3 Buffer Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 24.4 Buffer File Name. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372 24.5 Buffer Modification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374 24.6 Comparison of Modification Time . . . . . . . . . . . . . . . . . . . . . 375 24.7 Read-Only Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376 24.8 The Buffer List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377 24.9 Creating Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378 24.10 Killing Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379 24.11 Indirect Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380

25 Windows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383

25.1 Basic Concepts of Emacs Windows . . . . . . . . . . . . . . . . . . . . 383 25.2 Splitting Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384 25.3 Deleting Windows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386 25.4 Selecting Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387 25.5 Cyclic Ordering of Windows . . . . . . . . . . . . . . . . . . . . . . . . . . 388 25.6 Buffers and Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390 25.7 Displaying Buffers in Windows . . . . . . . . . . . . . . . . . . . . . . . . 391 25.8 Choosing a Window for Display . . . . . . . . . . . . . . . . . . . . . . . 393 25.9 Windows and Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395 25.10 The Window Start Position . . . . . . . . . . . . . . . . . . . . . . . . . . 396 25.11 Vertical Scrolling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 25.12 Hooks for Vertical Scrolling . . . . . . . . . . . . . . . . . . . . . . . . . . 400 25.13 Horizontal Scrolling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401 25.14 The Size of a Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402 25.15 Changing the Size of a Window . . . . . . . . . . . . . . . . . . . . . . 404 25.16 Coordinates and Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 25.17 Window Configurations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406

26 Frames. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409

26.1 Creating Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 26.2 Multiple Displays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 26.3 Frame Parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410

26.3.1 Access to Frame Parameters. . . . . . . . . . . . . . . . . . 410 26.3.2 Initial Frame Parameters . . . . . . . . . . . . . . . . . . . . . 411 26.3.3 X Window Frame Parameters . . . . . . . . . . . . . . . . 412 26.3.4 Frame Size And Position . . . . . . . . . . . . . . . . . . . . . 415

26.4 Frame Titles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416 26.5 Deleting Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 26.6 Finding All Frames. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 26.7 Frames and Windows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418 26.8 Minibuffers and Frames. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418 26.9 Input Focus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419 26.10 Visibility of Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 26.11 Raising and Lowering Frames . . . . . . . . . . . . . . . . . . . . . . . . 421 26.12 Frame Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 26.13 Mouse Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 26.14 Mouse Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 26.15 Pop-Up Menus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423 26.16 Dialog Boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424 26.17 Pointer Shapes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424 26.18 X Selections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425 26.19 Color Names. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425 26.20 X Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426 26.21 Data about the X Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427

27 Positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429

27.1 Point. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 27.2 Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430

27.2.1 Motion by Characters. . . . . . . . . . . . . . . . . . . . . . . . 430 27.2.2 Motion by Words . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431 27.2.3 Motion to an End of the Buffer . . . . . . . . . . . . . . . 431 27.2.4 Motion by Text Lines . . . . . . . . . . . . . . . . . . . . . . . . 432 27.2.5 Motion by Screen Lines . . . . . . . . . . . . . . . . . . . . . . 433 27.2.6 Moving over Balanced Expressions . . . . . . . . . . . . 435 27.2.7 Skipping Characters . . . . . . . . . . . . . . . . . . . . . . . . . 436

27.3 Excursions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437 27.4 Narrowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438

28 Markers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441

28.1 Overview of Markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441 28.2 Predicates on Markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442 28.3 Functions That Create Markers . . . . . . . . . . . . . . . . . . . . . . . 442 28.4 Information from Markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444 28.5 Changing Marker Positions . . . . . . . . . . . . . . . . . . . . . . . . . . . 444 28.6 The Mark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445 28.7 The Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447

29 Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449

29.1 Examining Text Near Point . . . . . . . . . . . . . . . . . . . . . . . . . . . 449 29.2 Examining Buffer Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 29.3 Comparing Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451 29.4 Inserting Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452 29.5 User-Level Insertion Commands . . . . . . . . . . . . . . . . . . . . . . . 453 29.6 Deleting Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454 29.7 User-Level Deletion Commands . . . . . . . . . . . . . . . . . . . . . . . 455 29.8 The Kill Ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457

29.8.1 Kill Ring Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . 458 29.8.2 Functions for Killing . . . . . . . . . . . . . . . . . . . . . . . . . 458 29.8.3 Functions for Yanking . . . . . . . . . . . . . . . . . . . . . . . 459 29.8.4 Low-Level Kill Ring . . . . . . . . . . . . . . . . . . . . . . . . . 459 29.8.5 Internals of the Kill Ring. . . . . . . . . . . . . . . . . . . . . 460

29.9 Undo. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461 29.10 Maintaining Undo Lists. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463 29.11 Filling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464 29.12 Margins for Filling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466 29.13 Auto Filling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467 29.14 Sorting Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468 29.15 Counting Columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 29.16 Indentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472

29.16.1 Indentation Primitives . . . . . . . . . . . . . . . . . . . . . . 472 29.16.2 Indentation Controlled by Major Mode. . . . . . . 473 29.16.3 Indenting an Entire Region. . . . . . . . . . . . . . . . . . 474 29.16.4 Indentation Relative to Previous Lines . . . . . . . 475 29.16.5 Adjustable “Tab Stops” . . . . . . . . . . . . . . . . . . . . . 475 29.16.6 Indentation-Based Motion Commands. . . . . . . . 476

29.17 Case Changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476 29.18 Text Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478

29.18.1 Examining Text Properties . . . . . . . . . . . . . . . . . . 478 29.18.2 Changing Text Properties . . . . . . . . . . . . . . . . . . . 479 29.18.3 Property Search Functions . . . . . . . . . . . . . . . . . . 480 29.18.4 Properties with Special Meanings . . . . . . . . . . . . 482 29.18.5 Formatted Text Properties . . . . . . . . . . . . . . . . . . 483 29.18.6 Stickiness of Text Properties . . . . . . . . . . . . . . . . 484 29.18.7 Saving Text Properties in Files . . . . . . . . . . . . . . 485 29.18.8 Lazy Computation of Text Properties . . . . . . . . 486 29.18.9 Why Text Properties are not Intervals . . . . . . . 486

29.19 Substituting for a Character Code . . . . . . . . . . . . . . . . . . . . 487 29.20 Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488 29.21 Transposition of Text. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489 29.22 Change Hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489

30 Searching and Matching . . . . . . . . . . . . . . . . 491

30.1 Searching for Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491 30.2 Regular Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492

30.2.1 Syntax of Regular Expressions . . . . . . . . . . . . . . . . 493 30.2.2 Complex Regexp Example. . . . . . . . . . . . . . . . . . . . 497

30.3 Regular Expression Searching . . . . . . . . . . . . . . . . . . . . . . . . . 497 30.4 POSIX Regular Expression Searching . . . . . . . . . . . . . . . . . . 499 30.5 Search and Replace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 30.6 The Match Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501

30.6.1 Simple Match Data Access . . . . . . . . . . . . . . . . . . . 501 30.6.2 Replacing the Text That Matched . . . . . . . . . . . . 503 30.6.3 Accessing the Entire Match Data . . . . . . . . . . . . . 504 30.6.4 Saving and Restoring the Match Data . . . . . . . . . 505

30.7 Searching and Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505 30.8 Standard Regular Expressions Used in Editing . . . . . . . . . 506

31 Syntax Tables . . . . . . . . . . . . . . . . . . . . . . . . . . 509

31.1 Syntax Table Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509 31.2 Syntax Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509

31.2.1 Table of Syntax Classes . . . . . . . . . . . . . . . . . . . . . . 510 31.2.2 Syntax Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512

31.3 Syntax Table Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513 31.4 Motion and Syntax. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515 31.5 Parsing Balanced Expressions . . . . . . . . . . . . . . . . . . . . . . . . . 515 31.6 Some Standard Syntax Tables. . . . . . . . . . . . . . . . . . . . . . . . . 517 31.7 Syntax Table Internals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 518

32 Abbrevs And Abbrev Expansion. . . . . . . . . 519

32.1 Setting Up Abbrev Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519 32.2 Abbrev Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519 32.3 Defining Abbrevs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520 32.4 Saving Abbrevs in Files. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521 32.5 Looking Up and Expanding Abbreviations . . . . . . . . . . . . . 521 32.6 Standard Abbrev Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523

33 Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525

33.1 Functions that Create Subprocesses. . . . . . . . . . . . . . . . . . . . 525 33.2 Creating a Synchronous Process . . . . . . . . . . . . . . . . . . . . . . . 526 33.3 MS-DOS Subprocesses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529 33.4 Creating an Asynchronous Process . . . . . . . . . . . . . . . . . . . . 529 33.5 Deleting Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 530 33.6 Process Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531 33.7 Sending Input to Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . 533 33.8 Sending Signals to Processes . . . . . . . . . . . . . . . . . . . . . . . . . . 534 33.9 Receiving Output from Processes . . . . . . . . . . . . . . . . . . . . . . 535

33.9.1 Process Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 535 33.9.2 Process Filter Functions. . . . . . . . . . . . . . . . . . . . . . 536

33.9.3 Accepting Output from Processes . . . . . . . . . . . . . 538 33.10 Sentinels: Detecting Process Status Changes . . . . . . . . . . 539 33.11 Transaction Queues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540 33.12 Network Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541

34 Operating System Interface . . . . . . . . . . . . . 543

34.1 Starting Up Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543 34.1.1 Summary: Sequence of Actions at Start Up. … 543 34.1.2 The Init File: ‘.emacs’ . . . . . . . . . . . . . . . . . . . . . . . 544 34.1.3 Terminal-Specific Initialization . . . . . . . . . . . . . . . 545 34.1.4 Command Line Arguments . . . . . . . . . . . . . . . . . . . 546

34.2 Getting Out of Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547 34.2.1 Killing Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547 34.2.2 Suspending Emacs. . . . . . . . . . . . . . . . . . . . . . . . . . . 548

34.3 Operating System Environment . . . . . . . . . . . . . . . . . . . . . . . 549 34.4 User Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552 34.5 Time of Day . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553 34.6 Time Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554 34.7 Timers for Delayed Execution . . . . . . . . . . . . . . . . . . . . . . . . . 556 34.8 Terminal Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558

34.8.1 Input Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558 34.8.2 Translating Input Events . . . . . . . . . . . . . . . . . . . . . 559 34.8.3 Recording Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562

34.9 Terminal Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562 34.10 System-Specific X11 Keysyms . . . . . . . . . . . . . . . . . . . . . . . . 563 34.11 Flow Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564 34.12 Batch Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565

35 Emacs Display . . . . . . . . . . . . . . . . . . . . . . . . . 567

35.1 Refreshing the Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567 35.2 Screen Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567 35.3 Truncation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568 35.4 The Echo Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569 35.5 Invisible Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570 35.6 Selective Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571 35.7 The Overlay Arrow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573 35.8 Temporary Displays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573 35.9 Overlays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575

35.9.1 Overlay Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . 575 35.9.2 Managing Overlays . . . . . . . . . . . . . . . . . . . . . . . . . . 577

35.10 Faces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 578 35.10.1 Standard Faces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 578 35.10.2 Merging Faces for Display . . . . . . . . . . . . . . . . . . . 579 35.10.3 Functions for Working with Faces. . . . . . . . . . . . 579

35.11 Blinking Parentheses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581 35.12 Inverse Video . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582 35.13 Usual Display Conventions. . . . . . . . . . . . . . . . . . . . . . . . . . . 582 35.14 Display Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583 35.14.1 Display Table Format . . . . . . . . . . . . . . . . . . . . . . . 583 35.14.2 Active Display Table. . . . . . . . . . . . . . . . . . . . . . . . 584 35.14.3 Glyphs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585 35.14.4 ISO Latin 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585

35.15 Beeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586 35.16 Window Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586

36 Customizing the Calendar and Diary …. 587

36.1 Customizing the Calendar . . . . . . . . . . . . . . . . . . . . . . . . . . . . 587 36.2 Customizing the Holidays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588 36.3 Date Display Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 590 36.4 Time Display Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 590 36.5 Daylight Savings Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 591 36.6 Customizing the Diary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592 36.7 Hebrew- and Islamic-Date Diary Entries . . . . . . . . . . . . . . . 593 36.8 Fancy Diary Display. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594 36.9 Sexp Entries and the Fancy Diary Display . . . . . . . . . . . . . 595 36.10 Customizing Appointment Reminders. . . . . . . . . . . . . . . . . 597

Appendix A Tips and Standards . . . . . . . . . . . 599

A.1 Writing Clean Lisp Programs . . . . . . . . . . . . . . . . . . . . . . . . . . 599 A.2 Tips for Making Compiled Code Fast . . . . . . . . . . . . . . . . . . 602 A.3 Tips for Documentation Strings. . . . . . . . . . . . . . . . . . . . . . . . 603 A.4 Tips on Writing Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604 A.5 Conventional Headers for Emacs Libraries . . . . . . . . . . . . . . 605

Appendix B GNU Emacs Internals . . . . . . . . . 609

B.1 Building Emacs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609 B.2 Pure Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611 B.3 Garbage Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611 B.4 Writing Emacs Primitives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614 B.5 Object Internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617

B.5.1 Buffer Internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618 B.5.2 Window Internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 619 B.5.3 Process Internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621

Appendix C Standard Errors . . . . . . . . . . . . . . . 623

Appendix D Buffer-Local Variables . . . . . . . . . 627

Appendix E Standard Keymaps . . . . . . . . . . . . 631

Appendix F Standard Hooks . . . . . . . . . . . . . . . 635

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 639