OCaml function with variable number of arguments

Question

I'm exploring "advanced" uses of OCaml functions and I'm wondering how I can write a function with variable number of arguments.

For example, a function like:

let sum x1,x2,x3,.....,xn = x1+x2,+x3....+xn

Answer 1

With a bit of type hackery, sure:

let sum f = f 0
let arg x acc g = g (acc + x)
let z a = a

And the (ab)usage:

# sum z;;
- : int = 0
# sum (arg 1) z;;
- : int = 1
# sum (arg 1) (arg 2) (arg 3) z;;
- : int = 6

Neat, huh? But don't use this - it's a hack.

For an explanation, see this page (in terms of SML, but the idea is the same).