Another way to do this is to make a prototype and then modify it. For
example,
foo <- function(x, y, others) {
# the body can be anything, we won't touch it
}
args <- formals(foo)
# Make extra copies of the 3rd argument
args[3:(2 + length(argnms))] <- args[3]
# Set the names of the new ones (or use Iris's code to set all the
names, your choice)
names(args)[3:(2 + length(argnms))] <- argnms
formals(foo) <- args
Duncan Murdoch
On 2025-10-24 11:17 p.m., Rolf Turner wrote:
On Fri, 24 Oct 2025 22:31:53 -0400
Iris Simmons <[email protected]> wrote:
I would start by making a list of the desired length, where each
element is the missing argument:
f <- rep(list(quote(expr = )), 2 + length(argnms))
then add names to the list:
names(f) <- c("x", "y", argnms)
and then use formals<-
formals(foo) <- f
Wow! That was fast! And it seems to do exactly what I want.
What I was missing, I guess, was the quote(expr = ) structure. I have
never really understood quote(), nor expr() either. I'll just treat it
as a black box for now.
Although, I would ask if you're certain that this is actually what
you want to do. It's usually a bad idea to have variable names that
you don't know. I'd to think it'd be better to have the default
argument:
a = list()
and supply a list of `a` values instead of several `a` arguments.
Yes I understand that that would be the "sensible" approach but it
doesn't work in the context with which I am confronted.
I have more work to do before I get the approach that I've envisaged up
and running.
I may inflict more questions upon you later. (No good deed goes
unpunished! 🙂️)
cheers,
Rolf
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