Options for Expression Deparsing

Description

Process the deparsing options for deparse, dput and dump.

Usage

.deparseOpts(control)

Arguments

Details

This is called by deparse, dput and dump to process their control argument.

The control argument is a vector containing zero or more of the following strings. Partial string matching is used.

keepInteger

Either surround integer vectors by as.integer() or use suffix L, so they are not converted to type double when parsed. This includes making sure that integer NAs are preserved (via NA_integer_ if there are no non-NA values in the vector, unless "S_compatible" is set).

quoteExpressions

Surround expressions with quote(), so they are not evaluated when re-parsed.

showAttributes

If the object has attributes (other than a source attribute), use structure() to display them as well as the object value. This is the default for deparse and dput.

useSource

If the object has a source attribute, display that instead of deparsing the object. Currently only applies to function definitions.

warnIncomplete

Some exotic objects such as environments, external pointers, etc. can not be deparsed properly. This option causes a warning to be issued if the deparser recognizes one of these situations.

Also, the parser in R < 2.7.0 would only accept strings of up to 8192 bytes, and this option gives a warning for longer strings.

keepNA

Integer, real and character NAs are surrounded by coercion functions where necessary to ensure that they are parsed to the same type. Since e.g. NA_real_ can be output in R, this is mainly used in connection with S_compatible.

all

An abbreviated way to specify all of the options listed above. This is the default for dump, and the options used by edit (which are fixed).

delayPromises

Deparse promises in the form <promise: expression> rather than evaluating them. The value and the environment of the promise will not be shown and the deparsed code cannot be sourced.

S_compatible

Make deparsing as far as possible compatible with S and R < 2.5.0. For compatibility with S, integer values of double vectors are deparsed with a trailing decimal point. Backticks are not used.

hexNumeric

Real and finite complex numbers are output in "%a" format as binary fractions (coded as hexadecimal: see sprintf) with maximal opportunity to be recorded exactly to full precision. Complex numbers with one or both non-finite components are output as if this option were not set.

(This relies on that format being correctly supported: known problems on Windows are worked around as from R 3.1.2.)

digits17

Real and finite complex numbers are output using format "%.17g" which may give more precision than the default (but the output will depend on the platform and there may be loss of precision when read back). Complex numbers with one or both non-finite components are output as if this option were not set.

For the most readable (but perhaps incomplete) display, use control = NULL. This displays the object's value, but not its attributes. The default in deparse is to display the attributes as well, but not to use any of the other options to make the result parseable. (dput and dump do use more default options, and printing of functions without sources uses c("keepInteger", "keepNA").)

Using control = c("all", "hexNumeric") comes closest to making deparse() an inverse of parse(). However, not all objects are deparse-able even with this option. A warning will be issued if the function recognizes that it is being asked to do the impossible. Also, representing double and complex numbers as decimals may well not be exact.

Only one of "hexNumeric" and "digits17" can be specified.

Value

A numerical value corresponding to the options selected.