parse returns the parsed but unevaluated expressions in a
list.
parse(file = "", n = NULL, text = NULL, prompt = "?", keep.source = getOption("keep.source"), srcfile, encoding = "unknown")file is "" and text is missing or NULL
then input is taken from the console.n is NULL or negative or
NA the input is parsed in its entirety.NULL means to use R's prompt, getOption("prompt").TRUE, keep
source reference information.NULL, a character vector, or a
srcfile object. See the ‘Details’ section."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."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, a
"srcfile" attribute will be attached containing a copy of
srcfile, and a "wholeSrcref" attribute will be
attached containing a srcref record corresponding to
all of the parsed text. Detailed parse information will be stored in
the "srcfile" attribute, to be retrieved by
getParseData.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.
parse
signals an error. The partial parse data will be stored in the
srcfile argument if it is a srcfile object
and the text argument was used to supply the text. In other
cases it will be lost when the error is triggered. The partial parse data can be retrieved using
getParseData applied to the srcfile object.
Because parsing was incomplete, it will typically include references
to "parent" entries that are not present.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 EOF character is Ctrl-Z for the Windows front-ends.) The
line-length limit is 4095 bytes when reading from the console (which
may impose a lower limit: see ‘An Introduction to R’).
The default for srcfile is set as follows. If
keep.source is not TRUE, srcfile
defaults to a character string, either " or one
derived from file. When keep.source is
TRUE, 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.
When srcfile is a character string, error messages will
include the name, but source reference information will not be added
to the result. When srcfile is a srcfile
object, source reference information will be retained.
scan, source, eval,
deparse. The source reference information can be used for debugging (see e.g.
setBreakpoint) and profiling (see
Rprof). It can be examined by getSrcref
and related functions. More detailed information is available through
getParseData.
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")
# A partial parse with a syntax error
txt <- "
x <- 1
an error
"
sf <- srcfile("txt")
try(parse(text = txt, srcfile = sf))
getParseData(sf)
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