On 25/05/2011 2:05 PM, Peter Danenberg wrote:
> 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.
I suppose you can do a clunky workaround like this:
debug <- function(e1, e2, sentinel) {
e1 <- if(!missing(e1)) substitute(e1)
e2 <- if(!missing(e2)) substitute(e2)
if (!missing(sentinel)) stop("this function only handles 2
expressions")
print(e1)
print(e2)
}
(but use some finite limit that's more than 2).
Duncan Murdoch
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