(* This code extends 'mini_prelude'. *)

type ('a) queue = 
    Queue of ('a) list * ('a) list ;;

let empty = (Queue (Nil, Nil)) ;;

let is_empty = 
  (fun v5 -> 
    (match v5 with 
        (Queue (v4, v3)) -> 
          (match v4 with 
              Nil -> true 
            | (Cons (v2, v1)) -> false))) ;;

let checkf = 
  (fun v5 -> 
    (match v5 with 
        (Queue (v4, v3)) -> 
          (match v4 with 
              Nil -> (Queue ((REVERSE v3), Nil)) 
            | (Cons (v2, v1)) -> (Queue ((Cons (v2, v1)), v3))))) ;;

let snoc = 
  (fun v3 -> 
    (fun v4 -> 
      (match v3 with 
          (Queue (v2, v1)) -> (checkf (Queue (v2, (Cons (v4, v1)))))))) ;;

let head = 
  (fun x -> 
    (match x with 
        (Queue (v4, v3)) -> 
          (match v4 with 
              Nil -> (raise (Match_failure (string_of_bool true, 0, 0))) 
            | (Cons (v2, v1)) -> v2))) ;;

let tail = 
  (fun x -> 
    (match x with 
        (Queue (v4, v3)) -> 
          (match v4 with 
              Nil -> (raise (Match_failure (string_of_bool true, 0, 0))) 
            | (Cons (v2, v1)) -> (checkf (Queue (v1, v3)))))) ;;