annotate src/order.sml @ 1668:64c1e65c2365

Prevent horrifying loops in unification variable graph
author Adam Chlipala <adam@chlipala.net>
date Mon, 09 Jan 2012 16:20:10 -0500
parents ffa18975e661
children
rev   line source
adamc@193 1 (* Copyright (c) 2008, Adam Chlipala
adamc@193 2 * All rights reserved.
adamc@193 3 *
adamc@193 4 * Redistribution and use in source and binary forms, with or without
adamc@193 5 * modification, are permitted provided that the following conditions are met:
adamc@193 6 *
adamc@193 7 * - Redistributions of source code must retain the above copyright notice,
adamc@193 8 * this list of conditions and the following disclaimer.
adamc@193 9 * - Redistributions in binary form must reproduce the above copyright notice,
adamc@193 10 * this list of conditions and the following disclaimer in the documentation
adamc@193 11 * and/or other materials provided with the distribution.
adamc@193 12 * - The names of contributors may not be used to endorse or promote products
adamc@193 13 * derived from this software without specific prior written permission.
adamc@193 14 *
adamc@193 15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
adamc@193 16 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
adamc@193 17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
adamc@193 18 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
adamc@193 19 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
adamc@193 20 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
adamc@193 21 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
adamc@193 22 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
adamc@193 23 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
adamc@193 24 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
adamc@193 25 * POSSIBILITY OF SUCH DAMAGE.
adamc@193 26 *)
adamc@193 27
adamc@193 28 (* Utility code for implementing comparisons *)
adamc@193 29
adamc@193 30 structure Order :> ORDER = struct
adamc@193 31
adamc@193 32 fun join (o1, o2) =
adamc@193 33 case o1 of
adamc@193 34 EQUAL => o2 ()
adamc@193 35 | v => v
adamc@193 36
adamc@193 37 fun joinL f (os1, os2) =
adamc@193 38 case (os1, os2) of
adamc@193 39 (nil, nil) => EQUAL
adamc@193 40 | (nil, _) => LESS
adamc@193 41 | (h1 :: t1, h2 :: t2) =>
adamc@193 42 join (f (h1, h2), fn () => joinL f (t1, t2))
adamc@193 43 | (_ :: _, nil) => GREATER
adamc@193 44
adamc@479 45 fun joinO f (v1, v2) =
adamc@479 46 case (v1, v2) of
adamc@479 47 (NONE, NONE) => EQUAL
adamc@479 48 | (NONE, _) => LESS
adamc@479 49 | (_, NONE) => GREATER
adamc@479 50
adamc@479 51 | (SOME v1, SOME v2) => f (v1, v2)
adamc@479 52
adamc@193 53 end