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
.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.
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.\ifelse{latex}{\out{~}}{ } 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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