formals {base}R Documentation

Access to and Manipulation of the Formal Arguments


Get or set the formal arguments of a function.


formals(fun = sys.function(sys.parent()))
formals(fun, envir = environment(fun)) <- value



a function object, or see ‘Details’.


environment in which the function should be defined.


a list (or pairlist) of R expressions.


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.


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.


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 3.2.2 Index]