(* 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" 
 
(* 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：yasai_list を買ったときの値段の合計を調べる *) 
(* total_price : string list -> (string * int) list -> int *) 
let total_price yasai_list yaoya_list = 
  (* 目的：yasai_list を買ったときの値段の合計を調べる *) 
  (* hojo : string list -> int option *) 
  let rec hojo yasai_list = match yasai_list with 
      [] -> Some (0) 
    | first :: rest -> 
        match price first yaoya_list with 
            None -> None 
          | Some (p) -> match hojo rest with 
                            None -> None 
                          | Some (q) -> Some (p + q) 
  in match hojo yasai_list with 
        None -> 0 
      | Some (p) -> p 
 
(* テスト *) 
let test1 = total_price ["たまねぎ"; "にんじん"] yaoya_list = 350 
let test2 = total_price ["たまねぎ"; "じゃがいも"; "にんじん"] yaoya_list = 0 
let test3 = total_price ["トマト"; "にんじん"] yaoya_list = 450 
 
(* 
(* 目的：item の値段を調べる *) 
(* price : string -> (string * int) list -> int *) 
let rec price item yaoya_list = match yaoya_list with 
    [] -> 0 
  | (yasai, nedan) :: rest -> 
      if item = yasai then nedan 
                      else price item rest 
 
(* 目的：yasai_list を買ったときの値段の合計を調べる *) 
(* total_price : string list -> (string * int) list -> int *) 
let rec total_price yasai_list yaoya_list = match yasai_list with 
    [] -> 0 
  | first :: rest -> 
      price first yaoya_list + total_price rest yaoya_list 
*)