1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
|
% File src/library/base/man/formals.Rd
% Part of the R package, http://www.R-project.org
% Copyright 1995-2007 R Core Development Team
% Distributed under GPL 2 or later
\name{formals}
\alias{formals}
\alias{formals<-}
\title{Access to and Manipulation of the Formal Arguments}
\description{
Get or set the formal arguments of a function.
}
\usage{
formals(fun = sys.function(sys.parent()))
formals(fun, envir = environment(fun)) <- value
}
\arguments{
\item{fun}{a function object, or see \sQuote{Details}.}
\item{envir}{environment in which the function should be defined.}
\item{value}{a list (or pairlist) of \R expressions.}
}
\details{
For the first form, \code{fun} can also be a character string
naming the function to be manipulated, which is searched for from the
parent environment.
If it is not specified, the function calling \code{formals} is used.
Only \emph{closures} have formals, not primitive functions.
}
\value{
\code{formals} returns the formal argument list of the function
specified, as a \code{\link{pairlist}}, or \code{NULL} for a
non-function or primitive.
The replacement form sets the formals of a function to the
list/pairlist on the right hand side, and (potentially) resets the
environment of the function.
}
\seealso{
\code{\link{args}} for a human-readable version,
\code{\link{alist}},
\code{\link{body}},
\code{\link{function}}.
}
\examples{
require(stats); require(graphics)
length(formals(lm)) # the number of formal arguments
names(formals(boxplot)) # formal arguments names
f <- function(x) a+b
formals(f) <- alist(a=,b=3) # function(a,b=3)a+b
f(2) # result = 5
}
\keyword{programming}
|