append.ml

(* Write a function append : int list -> int list -> int list such that
append l1 l2 is the concatenation of l1 and l2. *)

let rec append l1 l2 =
  let rec rev acc = function
    | [] -> acc
    | x::xs -> rev (x::acc) xs
  in
  let rec aux l = function
      [] -> l
    | x::xs -> aux (x::l) xs
  in
  aux l2 (rev [] l1) ;;