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