However, one thing that does come to mind is that there’s a limited number of stack effects you need to support – maybe create higher order functions like one_two (for dup), two_two (for swap), etc, that would take a function as a parameter and return a function that takes in the env and ns parameters, pop the correct number of items, give them as args to the function received as a parameter, then push the return values?

Then you could do calls like:

let dup = one_two (fun a -> a, a);;