All valid values of an argument of a function in R

Question

Suppose we have an R function whose arguments must be selected out of a finite set of elements. Like qplot(..., geom=\"\"). And geom can take only some

Answer 1

If the function of interest is defined like

f <- function(a = c("foo","bar")) {
    match.arg(a)
}

i.e. when the options are defined as a vector to be later checked with match.arg function, then you could use the formals function which would give you a list of arguments with the values like in the following example

> formals(f)
$a
c("foo", "bar")

Otherwise I don't think it is possible to get all valid argument values without RTFSing.