zip3 function in OCaml.

zip3.ml

(* Define the unfold function that takes 3 inputs.*)
let rec unfold p g b1 b2 b3 =
  if p b1 b2 b3 then [] else
    (match g b1 b2 b3 with (a, (b1prime, b2prime, b3prime)) ->
       a :: unfold p g b1prime b2prime b3prime)
;;

(* Define the zip3 function.*)
let zip3 = unfold
  (* Define p.*)
  (fun x y z -> ((List.length x = 0) || (List.length y = 0) || (List.length z = 
0) ))
  (* Define g.*)
  (fun x y z -> ( (List.hd x, List.hd y, List.hd z), (List.tl x, List.tl y, List
.tl z)))
;;

See my blog post.