formals
Access to and Manipulation of the Formal Arguments
Get or set the formal arguments of a function.
- Keywords
- programming
Usage
formals(fun = sys.function(sys.parent()), envir = parent.frame())
formals(fun, envir = environment(fun)) <- valueArguments
- fun
a
function, or see ‘Details’.- envir
environmentin which the function should be defined (or found viaget()in the first case and whenfuna character string).- value
Details
For the first form, fun can also be a character string naming
the function to be manipulated, which is searched for in envir,
by default 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
formalArgs (from methods), a shortcut for names(formals(.)).
args for a human-readable version,
alist,
body,
function.
Examples
library(base)
# NOT RUN {
require(stats)
formals(lm)
## If you just want the names of the arguments, use formalArgs instead.
names(formals(lm))
methods:: formalArgs(lm) # same
## formals returns a pairlist. Arguments with no default have type symbol (aka name).
str(formals(lm))
## formals returns NULL for primitive functions. Use it in combination with
## args for this case.
is.primitive(`+`)
formals(`+`)
formals(args(`+`))
## You can overwrite the formal arguments of a function (though this is
## advanced, dangerous coding).
f <- function(x) a + b
formals(f) <- alist(a = , b = 3)
f # function(a, b = 3) a + b
f(2) # result = 5
# }