(* あらかじめ sect17_5/search.ml を読み込んでおく必要あり *) 
#use "sect17_5/search.ml" (* 'a tree_t の定義 *) 
 
(* 木の例 *) 
let tree1 = Empty 
let tree2 = Leaf (3) 
let tree3 = Node (tree1, 4, tree2) 
let tree4 = Node (tree2, 5, tree3) 
 
(* 目的：tree に含まれる整数をすべて加える *) 
(* sum_tree : int tree_t -> int *) 
let rec sum_tree tree = match tree with 
    Empty -> 0 
  | Leaf (n) -> n 
  | Node (t1, n, t2) -> sum_tree t1 + n + sum_tree t2 
 
(* 0 と + を使っているため tree の型は 'a tree ではなく int tree となる *) 
 
(* テスト *) 
let test1 = sum_tree tree1 = 0 
let test2 = sum_tree tree2 = 3 
let test3 = sum_tree tree3 = 7 
let test4 = sum_tree tree4 = 15