(* The factorial function *)
let rec fac n = match n with
  | 0 -> 1
  | n -> n * fac (n - 1)


(* sumlist sums the elements of an int list *)
let rec sumlist ls = match ls with
  | [] -> 0
  | n::xs -> n + sumlist xs


(* a binary tree type *)
type 'a tree = Leaf of 'a
             | Node of 'a tree * 'a tree

(* a recursive function over binary trees *)
let rec leafproduct t = match t with
  | Leaf n -> n
  | Node (t1,t2) -> leafproduct t1 * leafproduct t2

(* an example tree *)
let mytree = Node (Leaf 42, Leaf 2)


(* a set of integers *)
module Intset =
  Set.Make (struct
              type t = int
              let compare n1 n2 =
                if n1 == n2 then 0 else
                  if n1 > n2 then 1 else -1
            end)

(* a set of set of integers *)
module Intsetset =
  Set.Make(struct
             type t = Intset.t
	     let compare = Intset.compare
           end)