A zip function in OCaml that stops zipping when any of the input lists' first element is zero, or when any of the input list is empty.

zip_no_zero.ml

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

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

See my blog post.