(* count *)
(* val count: 'a  -> 'a list -> int *)
let rec count x xs =
  match xs with
  | a::xs when a == x -> 1 + count x xs
  | _::xs -> 0 + count x xs
  | [] -> 0

(* remove list duplicates *)
(* val nub : 'a list -> 'a list *)
let nub xs =
  let rec mem y ys =
    match ys with
    | a::bs when a == y -> true
    | a::bs -> mem y bs
    | _ -> false
  in

  let rec rem_dup res xs =
    match xs with
    | a::bs when (mem a res) -> rem_dup res bs
    | a::bs -> rem_dup (res@[a]) bs
    | [] -> res
  in

  rem_dup [] xs

let cheat_nub xs =
  List.sort_uniq compare xs
Sign up for free