I was thrilled to see this in the change log:
> match.call() gains an envir argument for specifying the environment from
> which to retrieve the ... in the call, if any; this environment was wrong (or
> at least undesirable) when the definition argument was a function.
This was an issue I ran into a few years ago. I ended up writing my own
version that allows specification of the environment, but being able to rely on
the built in R version seems much better. That said, one issue remains as far
as I can tell: if the `...` values are expressions they are substituted by
`..1`, `..2`, etc. For example:
> fun0 <- function(...) {
> fun_gpar <- function(b, ...) {
> fun_par <- function(a)
> match.call(fun_gpar, sys.call(sys.parent()), envir=parent.frame(2L))
> fun_par()
> }
> fun_gpar(...)
> }
> fun0(999, 2 + 2, 3 * pi(), 4)
Returns:
> fun_gpar(b = 999, ..2, ..3, 4)
Instead of:
> fun_gpar(b = 999, 2 + 2, 3 * pi(), 4)
This is better than what used to happen before we had access to the `envir`
parameter:
> fun_gpar(b = ..1, ..2, 4)
The dot substitution happens in `subDots` in `main/src/unique.c@1228` (in 3.2.2
sources available as of today in CRAN). Here is a snippet from that function:
> for(a = dots, b = rval, i = 1; i <= len; a = CDR(a), b = CDR(b), i++) {
> SET_TAG(b, TAG(a));
> t = CAR(a);
> while (TYPEOF(t) == PROMSXP)
> t = PREXPR(t);
> if( isSymbol(t) || isLanguage(t) )
> SETCAR(b, installDDVAL(i)); // <-- HERE
> else
> SETCAR(b, t);
> }
The `installDDVAL(i)` generates the `..X` symbols. I'm sure there is a very
good reason why this is done, but then it does lead to the issues above.
Am I just doing something wrong?
My workaround (https://github.com/brodieG/matchcall) addresses both the `..X`
issue as well as the environment issue, but I'd prefer to deprecate it in favor
of a base R solution if possible.
B.
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