dealing with empty actual arguments matched by '...' formals
Tony Plate wrote:
I'm trying to write some functions to deal with empty actual arguments that are picked up by '...' formals. Such actual arguments are common (and very useful) in calls to subsetting functions, e.g., x[1:2,]. It seems that R and S-PLUS treat these arguments differently: in S-PLUS list(...) will return a list containing just the non-empty arguments, whereas in R list(...) stops with an error:
> # In R: > f <- function(x, ...) list(...) > f(1,2)
[[1]] [1] 2
> f(1,2,)
Error in f(1, 2, ) : argument is missing, with no default
>
So it seems that quite different methods must be used in S-PLUS and R to detect and process the arguments of a function that can have empty arguments matched to '...'.
Can you give an example where it's useful to do this, i.e. to have a call like f(1,2,)? I've never used that construction as far as I can recall. Duncan Murdoch