args Argument List of a Function

Description

Displays the argument names and corresponding default values of a function or primitive.

Usage

args(name)

Arguments

name	a function (a closure or a primitive). If name is a character string then the function with that name is found and used.

Details

This function is mainly used interactively to print the argument list of a function. For programming, consider using formals instead.

Value

For a closure, a closure with identical formal argument list but an empty (NULL) body.

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

NULL in case of a non-function.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

formals, help; 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`)