(*************************************************************************)

(*                                                                       *)

(*                         OCaml LablTk library                          *)

(*                                                                       *)

(*            Jacques Garrigue, Kyoto University RIMS                    *)

(*                                                                       *)

(*   Copyright 1999 Institut National de Recherche en Informatique et    *)

(*   en Automatique and Kyoto University.  All rights reserved.          *)

(*   This file is distributed under the terms of the GNU Library         *)

(*   General Public License, with the special exception on linking       *)

(*   described in file ../../../LICENSE.                                 *)

(*                                                                       *)

(*************************************************************************)

(* $Id$ *)

type ('a, 'b) assoc_list =

    Nil

  | Cons of 'a * 'b * ('a, 'b) assoc_list

let rec assq key = function

    Nil -> raise Not_found

  | Cons (a, b, l) ->

      if key == a then b else assq key l

let fast ~f =

  let memo = ref Nil in

  fun key ->

    try assq key !memo

    with Not_found ->

      let data = f key in

      memo := Cons(key, data, !memo);

      data