(* fn F5 *)

type intlist = NI | CI of int * intlist

let rec intlist_length l =
  match l with
    NI -> 0
  | CI(_, tl) -> 1 + intlist_length tl

type 'a mylist = Nil | C of 'a * 'a mylist

let rec mylist_length l =
  match l with
    Nil -> 0
  | C(_, tl) -> 1 + mylist_length tl

let rec make_list e k =
  if k = 0 then
    Nil
  else
    C(e, make_list e (pred k))
(* pred n === n + 1 *)

let rec concat l1 l2 =
  match l1 with
    Nil -> l2
  | C(e, tl) -> C(e, concat tl l2)

let rec fact_aux n p =
  if n = 0 then
    p
  else
    fact_aux (pred n) (n * p)

let fact n =
  fact_aux n 1

let fact n =
  let rec aux n p =
    if n = 0 then
      p
    else
      aux (pred n) (n * p) in
  aux n 1

let mylength l =   
  let rec aux l len =
    match l with
      Nil -> len
    | C(_, tl) -> aux tl (succ len) in
  aux l 0

                           (* succ n === n + 1 *)

let make_list e k =
  let rec aux k nl =
    if k = 0 then
      nl
    else
      aux (pred k) (C(e, nl)) in
  aux k Nil

let reverse l =
  let rec aux l rl =
    match l with
      Nil -> rl
    | C(e, tl) -> aux tl (C(e, rl)) in
  aux l Nil