R: Argument List of a Function

args {base} | R Documentation

## 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`)

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