(* あらかじめ sect18_1/price.ml を読み込んでおく必要あり *) 
#use "sect18_1/price.ml" (* price の定義 *) 
 
(* 八百屋においてある野菜と値段のリストの例 *) 
let yaoya_list = [("トマト", 300); ("たまねぎ", 200); 
		  ("にんじん", 150); ("ほうれん草", 200)] 
 
(* 目的：八百屋リストには入っていない野菜の数を返す *) 
(* count_urikire_yasai : string list -> (string * int) list -> int *) 
let rec count_urikire_yasai yasai_list yaoya_list = match yasai_list with 
    [] -> 0 
  | first :: rest -> 
      match price first yaoya_list with 
	  None -> 1 + count_urikire_yasai rest yaoya_list 
	| Some (p) -> count_urikire_yasai rest yaoya_list 
 
(* テスト *) 
let test1 = count_urikire_yasai ["たまねぎ"; "にんじん"] yaoya_list = 0 
let test2 = count_urikire_yasai ["たまねぎ"; "じゃがいも"; "にんじん"] yaoya_list = 1 
let test3 = count_urikire_yasai ["しいたけ"; "なす"; "にんじん"] yaoya_list = 2