Ellipsis collection into a variable

[dgkf]

In R, ellipsis are often collected into a list of values using function(...) { list(...) }, but if we are to add #47, then we don't really have a good way of collecting "the rest". Instead, we should have some way of collecting ellipsis contents into a variable.

f <- function(a, b, ..rest) {
}

This would assign a new variable rest which contains the contents of list(...).

Together with #47, this would mean that we could also do something like:

list(head, ..tail) <- list(1, 2, 3, 4, 5, 6, 7)