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 frame. 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

[Package base version 2.15.1 Index]