parse {base}

R Documentation

Parse Expressions

Description

parse returns the parsed but unevaluated expressions in a list.

Usage

parse(file = "", n = NULL, text = NULL, prompt = "?", srcfile,
      encoding = "unknown")

Arguments

file	a connection, or a character string giving the name of a file or a URL to read the expressions from. If file is "" and text is missing or NULL then input is taken from the console.
n	integer (or coerced to integer). The maximum number of expressions to parse. If n is NULL or negative or NA the input is parsed in its entirety.
text	character vector. The text to parse. Elements are treated as if they were lines of a file. Other R objects will be coerced to character (without method dispatch) if possible.
prompt	the prompt to print when parsing from the keyboard. NULL means to use R's prompt, getOption("prompt").
srcfile	NULL, or a srcfile object. See the ‘Details’ section.
encoding	encoding to be assumed for input strings. If the value is "latin1" or "UTF-8" it is used to mark character strings as known to be in Latin-1 or UTF-8: it is not used to re-encode the input. To do the latter, specify the encoding as part of the connection con or via options(encoding=): see the example under file.

Details

If text has length greater than zero (after coercion) it is used in preference to file.

All versions of R accept input from a connection with end of line marked by LF (as used on Unix), CRLF (as used on DOS/Windows) or CR (as used on classic Mac OS). The final line can be incomplete, that is missing the final EOL marker.

See source for the limits on the size of functions that can be parsed (by default).

When input is taken from the console, n = NULL is equivalent to n = 1, and n < 0 will read until an EOF character is read.

The default for srcfile is set as follows. If options("keep.source") is FALSE, srcfile defaults to NULL. Otherwise, if text is used, srcfile will be set to a srcfilecopy containing the text. If a character string is used for file, a srcfile object referring to that file will be used.

Value

An object of type "expression", with up to n elements if specified as a non-negative integer.

When srcfile is non-NULL, a "srcref" attribute will be attached to the result containing a list of srcref records corresponding to each element, and a "srcfile" attribute will be attached containing a copy of srcfile.

A syntax error (including an incomplete expression) will throw an error.

Character strings in the result will have a declared encoding if encoding is "latin1" or "UTF-8", or if text is supplied with every element of known encoding in a Latin-1 or UTF-8 locale.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

scan, source, eval, deparse.

Examples

cat("x <- c(1,4)\n  x ^ 3 -10 ; outer(1:7,5:9)\n", file="xyz.Rdmped")
# parse 3 statements from the file "xyz.Rdmped"
parse(file = "xyz.Rdmped", n = 3)
unlink("xyz.Rdmped")

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