gistfile1.ml

type nat = Zero | Succ of nat

let rec int_of_nat x =
  match x with
    | Zero -> 0
    | Succ x' -> 1 + int_of_nat x'

let rec nat_of_int x =
  match x with
    | 0 -> Zero
    | _ -> Succ (nat_of_int (x-1))

let rec add x y =
  match y with
    | Zero -> x
    | Succ y' -> add (Succ x) y'

let rec eq x y =
  match (x, y) with
    | (Zero, Zero)       -> true
    | (Zero, _)          -> false
    | (_, Zero)          -> false
    | (Succ x', Succ y') -> eq x' y'

let rec even x =
  match x with
    | Zero -> true
    | Succ x' -> odd x'
and odd x =
  match x with
    | Zero -> false
    | Succ x' -> even x'

let rec range x y =
  if eq x y then
    []
  else
    x :: range (add x (Succ Zero)) y

let _ =
  let a = nat_of_int (int_of_string (Sys.argv.(1))) in
  let b = nat_of_int (int_of_string (Sys.argv.(2))) in
  let list = range a b in
  List.iter (fun x ->
    if even x then
      Printf.printf "%d " (int_of_nat x)
  ) list;
  print_newline ()