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 = parent.frame()) <- value

### Arguments

`fun` | a function object, or see Details.
`envir` | environment in which the function should be defined.
`value` | a list of R expressions.

### Details

For the first form, `fun` can 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.

### Value

`formals` returns the formal argument list of the function specified.
The assignment form sets the formals of a function to the list on the right hand side.

### See Also

`args` for a “human-readable” version, `alist`, `body`, `function`.

### Examples

    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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