Extract function parameters and default values from any function

Question

Is there a way to extract the parameters and their respective default values of any given function from outside the function?

For example, given:

myfunc <- function(a, b = 1) { print(c(a, b)) }

I'm looking for some function that will return:

list(a = NULL, b = 1) 

or some variation thereof.

Answer 1

You are looking for formals().

formals(myfunc)
# $a
#
#
# $b
# [1] 1

If you needed NULL for a, you could do some checking. a will be of the "name" class and empty.

lapply(formals(myfunc), function(x) if(is.name(x) & !nzchar(x)) NULL else x)
# $a
# NULL
#
# $b
# [1] 1