This is Info file elisp, produced by Makeinfo-1.63 from the input file elisp.texi. This version is the edition 2.4b of the GNU Emacs Lisp Reference Manual. It corresponds to Emacs Version 19.34. Published by the Free Software Foundation 59 Temple Place, Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996 Free Software Foundation, Inc. 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 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 this permission notice may be stated in a translation approved by the Foundation. 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.  File: elisp, Node: Daylight Savings, Next: Diary Customizing, Prev: Time Display Format, Up: Calendar 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.  File: elisp, Node: Diary Customizing, Next: Hebrew/Islamic Entries, Prev: Daylight Savings, Up: Calendar 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 (*note Regular Expressions::.) 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.  File: elisp, Node: Hebrew/Islamic Entries, Next: Fancy Diary Display, Prev: Diary Customizing, Up: Calendar 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.  File: elisp, Node: Fancy Diary Display, Next: Sexp Diary Entries, Prev: Hebrew/Islamic Entries, Up: Calendar Fancy Diary Display =================== Diary display works by preparing the diary buffer and then running the hook `diary-display-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.  File: elisp, Node: Sexp Diary Entries, Next: Appt Customizing, Prev: Fancy Diary Display, Up: Calendar 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.)  File: elisp, Node: Appt Customizing, Prev: Sexp Diary Entries, Up: Calendar 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.  File: elisp, Node: Tips, Next: GNU Emacs Internals, Prev: Calendar, Up: Top 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. * Menu: * Style Tips:: Writing clean and robust programs. * Compilation Tips:: Making compiled code run fast. * Documentation Tips:: Writing readable documentation strings. * Comment Tips:: Conventions for writing comments. * Library Headers:: Standard headers for library packages.  File: elisp, Node: Style Tips, Next: Compilation Tips, Up: Tips 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. *Note Compiling Macros::. 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. *Note Hooks::. * 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 ESC except following another ESC. (That is, it is ok to bind a sequence ending in `ESC ESC'.) The reason for this rule is that a non-prefix binding for 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 (*note Autoload::.). 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. *Note Text Lines::. * 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. *Note The Mark::. 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'. *Note The Echo Area::. * When you encounter an error condition, call the function `error' (or `signal'). The function `error' does not return. *Note Signaling Errors::. 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. *Note Recursive Editing::. * 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.  File: elisp, Node: Compilation Tips, Next: Documentation Tips, Prev: Style Tips, Up: Tips 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 (*note Array Functions::.) while `elt' is not (*note Sequence Functions::.): (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. *Note Inline Functions::.  File: elisp, Node: Documentation Tips, Next: Comment Tips, Prev: Compilation Tips, Up: Tips 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 `*'. *Note Defining Variables::. * 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. (In this manual, we normally do use single-quotes for those symbols.) * 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 `\\[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.) *Note Keys in Documentation::. * 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.  File: elisp, Node: Comment Tips, Next: Library Headers, Prev: Documentation Tips, Up: Tips 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 TAB (`lisp-indent-line') automatically indent comments according to these conventions, depending on the number of semicolons. *Note Manipulating Comments: (emacs)Comments.  File: elisp, Node: Library Headers, Prev: Comment Tips, Up: Tips 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 ;; Maintainer: Eric S. Raymond ;; 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 ;; Dave Sill ;; Dave Brennan ;; Eric Raymond `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.  File: elisp, Node: GNU Emacs Internals, Next: Standard Errors, Prev: Tips, Up: Top 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. * Menu: * Building Emacs:: How to preload Lisp libraries into Emacs. * Pure Storage:: A kludge to make preloaded Lisp functions sharable. * Garbage Collection:: Reclaiming space for Lisp objects no longer used. * Writing Emacs Primitives:: Writing C code for Emacs. * Object Internals:: Data formats of buffers, windows, processes.