Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
> -----Original Message-----
> From: William Dunlap
> Sent: Wednesday, May 25, 2011 11:20 AM
> To: 'Peter Danenberg'
> Cc: r-devel@r-project.org
> Subject: RE: [Rd] External special functions (SPECIALSXP)
>
> > f <- function(...) {
> + dotArgList <- substitute(list(...))
> + dotArgList
> + }
> > f(cat("foo\n"), stop("Oops"), warning("Hmm"))
> list(cat("foo\n"), stop("Oops"), warning("Hmm"))
> > # i.e., no argument was evaluated
Or, if you'd prefer a pairlist over a call to list:
> fp <- function(...) {
+ dotArgList <- substitute(...())
+ dotArgList
+ }
> fp(message=cat("foo\n"), error=stop("Oops"),
possibleProblem=warning("Hmm"))
$message
cat("foo\n")
$error
stop("Oops")
$possibleProblem
warning("Hmm")
> class(.Last.value)
[1] "pairlist"
I would not have thought of this syntax myself but have
seen it in other folks' code.
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
>
> > -----Original Message-----
> > From: r-devel-boun...@r-project.org
> > [mailto:r-devel-boun...@r-project.org] On Behalf Of Peter Danenberg
> > Sent: Wednesday, May 25, 2011 11:06 AM
> > To: Duncan Murdoch
> > Cc: r-devel@r-project.org
> > Subject: Re: [Rd] External special functions (SPECIALSXP)
> >
> > > However, if you don't want to evaluate the arguments, just pass
> > > substitute(arg) to your function instead of arg.
> >
> > Thanks, Duncan; the problem is, I'm trying to substitute on
> `...' and
> > I don't think I can access `...' without inadvertently
> evaluating it.
> >
> > I'm trying to write a debugging function which, given any number of
> > expressions, prints the expression next to its evaluation.
> >
> > This is trivial to do in the single arity case:
> >
> > debug <- function(expression) {
> > cat(substitute(expression), expression, "\n")
> > }
> >
> > a <- 2
> > debug(a)
> >
> > a 2
> >
> > but I'm not sure how to make it work with variable arity without
> > resorting to SPECIALSXP.
> >
> > ______________________________________________
> > R-devel@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
> >
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