formals {base}

R Documentation

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

fun	a function object, or see ‘Details’.
envir	environment in which the function should be defined.
value	a list (or pairlist) of R expressions.

Details

For the first form, 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 formals is used.

Only closures have formals, not primitive functions.

Value

formals returns the formal argument list of the function specified, as a pairlist, or 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.

See Also

args for a human-readable version, alist, body, 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

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