R devel - May 2005 - Getting ... without evaluating it?

I'd like a function to get an unevaluated copy of its argument list, 
including ... .  That is, I'd like

f <- function(...) {
   args <- <what goes here??>
   args
}

when called as

f(a = 1+1, b = foo)

to return something like list(a = quote(1+1), b = quote(foo)).  If I use 
args <- list(...) then it tries to evaluate the arguments and dies 
(because foo doesn't exist).  If I use args <- substitute(...) then it 
gives just 1+1, it doesn't keep the names or give the whole list.

Is this possible?

Duncan Murdoch

On Thu, 19 May 2005, Duncan Murdoch wrote:
> I'd like a function to get an unevaluated copy of its argument list, 
> including ... .  That is, I'd like
>
> f <- function(...) {
>  args <- <what goes here??>
>  args
> }
>
> when called as
>
> f(a = 1+1, b = foo)
>
> to return something like list(a = quote(1+1), b = quote(foo)).  If I use
args
> <- list(...) then it tries to evaluate the arguments and dies (because
foo
> doesn't exist).  If I use args <- substitute(...) then it gives just
1+1, it
> doesn't keep the names or give the whole list.
> f <- function(...) as.list(match.call())[-1]
> f(a = 1+1, b = foo)
$a
1 + 1

$b
foo

(which is what list(a = quote(1+1), b = quote(foo)) prints as).


-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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