# formals

0th

Percentile

Get or set the formal arguments of a function.

Keywords
programming
##### 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.

args for a human-readable version, alist, body, function.
library(base) 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