let ($) f x = f x
;;

let (<*>) f g x = f (g x)
;;

let flip f a b = f b a
;;

let fst (a, b) = a
;;

let snd (a, b) = b
;;

let rec pad v i l =
  match i with
    0 -> l
  | n -> v :: (pad v (i - 1) l)
;;

let char_list_of_string s =
  let str_length = String.length s in
  let rec aux s l buff =
    if l = str_length then
      buff
    else
      aux s (l + 1) ((String.get s l)::buff)
  in
    List.rev $ aux s 0 []