The R Project SVN R

% File src/library/base/man/args.Rd
% Part of the R package, https://www.R-project.org
% Copyright 1995-2022 R Core Team
% Distributed under GPL 2 or later

\name{args}
\alias{args}
\title{Argument List of a Function}
\description{
  Displays the argument names and corresponding default values of a
  (non-primitive or primitive) function.
}
\usage{
args(name)
}
\arguments{
  \item{name}{a function (a primitive or a closure, i.e.,
    \dQuote{non-primitive}).
    If \code{name} is a character string then the function with that
    name is found and used.}
}
\value{
  For a closure, a closure with identical formal argument list but an
  empty (\code{NULL}) body.

  For a primitive (function), a closure with the documented usage and \code{NULL}
  body.  Note that some primitives do not make use of named arguments
  and match by position rather than name.

  \code{NULL} in case of a non-function.
}
\details{
  This function is mainly used interactively to print the argument list
  of a function.  For programming, consider using \code{\link{formals}}
  instead.
}
\references{
  Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
  \emph{The New S Language}.
  Wadsworth & Brooks/Cole.
}
\seealso{
  \code{\link{formals}}, \code{\link{help}};
  \code{\link{str}} also prints the argument list of a function.
}
\examples{
## "regular" (non-primitive) functions "print their arguments"
## (by returning another function with NULL body which you also see):
args(ls)
args(graphics::plot.default)
utils::str(ls) # (just "prints": does not show a NULL)

## You can also pass a string naming a function.
args("scan")
## ...but :: package specification doesn't work in this case.
tryCatch(args("graphics::plot.default"), error = print)

## As explained above, args() gives a function with empty body:
list(is.f = is.function(args(scan)), body = body(args(scan)))

## Primitive functions mostly behave like non-primitive functions.
args(c)
args(`+`)
## primitive functions without well-defined argument list return NULL:
args(`if`)
}
\keyword{documentation}