1(*
2 * Copyright (c) 1997-1999 Massachusetts Institute of Technology
3 * Copyright (c) 2003, 2007-14 Matteo Frigo
4 * Copyright (c) 2003, 2007-14 Massachusetts Institute of Technology
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
19 *
20 *)
21
22(*************************************************************
23 *    Functional associative table
24 *************************************************************)
25
26(*
27 * this module implements a functional associative table.
28 * The table is parametrized by an equality predicate and
29 * a hash function, with the restriction that (equal a b) ==>
30 * hash a == hash b.
31 * The table is purely functional and implemented using a binary
32 * search tree (not balanced for now)
33 *)
34
35type ('a, 'b) elem =
36    Leaf
37  | Node of int * ('a, 'b) elem * ('a, 'b) elem * ('a * 'b) list
38
39let empty = Leaf
40
41let lookup hash equal key table =
42  let h = hash key in
43  let rec look = function
44      Leaf -> None
45    | Node (hash_key, left, right, this_list) ->
46        if (hash_key < h) then look left
47        else if (hash_key > h) then look right
48        else let rec loop = function
49            [] -> None
50          | (a, b) :: rest -> if (equal key a) then Some b else loop rest
51        in loop this_list
52  in look table
53
54let insert hash key value table =
55  let h = hash key in
56  let rec ins = function
57      Leaf -> Node (h, Leaf, Leaf, [(key, value)])
58    | Node (hash_key, left, right, this_list) ->
59        if (hash_key < h) then
60          Node (hash_key, ins left, right, this_list)
61        else if (hash_key > h) then
62          Node (hash_key, left, ins right, this_list)
63        else
64          Node (hash_key, left, right, (key, value) :: this_list)
65  in ins table
66