I have a function that can take a list in one of its arguments. I would like to be able to manipulate this list in the function but without having the elements of the list evaluated.

For example, if I have this:

external <- list("a" = mean, "foo" = sum)

foo <- function(x) {
  rlang::get_expr(x)
}

Then when I call foo(external), I’d like to have an object that I can manipulate inside foo() like:

$a
mean

$foo
sum

where mean and sum are symbols. So far, I have that:

foo(external)
#> $a
#> function (x, ...) 
#> UseMethod("mean")
#> <bytecode: 0x58773e2c7020>
#> <environment: namespace:base>
#> 
#> $foo
#> function (..., na.rm = FALSE)  .Primitive("sum")

but that isn’t what I’d like to have since the functions in the list are evaluated.

Is this possible? I’m ok with base or rlang solutions.