Message-ID: <4260D3FA.4030905@math.aau.dk>
Date: 2005-04-16T10:59:46Z
From: Duncan Murdoch
Subject: dealing with empty actual arguments matched by '...' formals
In-Reply-To: <425FDE7C.1080709@blackmesacapital.com>
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