adamc@193: (* Copyright (c) 2008, Adam Chlipala
adamc@193:  * All rights reserved.
adamc@193:  *
adamc@193:  * Redistribution and use in source and binary forms, with or without
adamc@193:  * modification, are permitted provided that the following conditions are met:
adamc@193:  *
adamc@193:  * - Redistributions of source code must retain the above copyright notice,
adamc@193:  *   this list of conditions and the following disclaimer.
adamc@193:  * - Redistributions in binary form must reproduce the above copyright notice,
adamc@193:  *   this list of conditions and the following disclaimer in the documentation
adamc@193:  *   and/or other materials provided with the distribution.
adamc@193:  * - The names of contributors may not be used to endorse or promote products
adamc@193:  *   derived from this software without specific prior written permission.
adamc@193:  *
adamc@193:  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
adamc@193:  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
adamc@193:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
adamc@193:  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
adamc@193:  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
adamc@193:  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
adamc@193:  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
adamc@193:  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
adamc@193:  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
adamc@193:  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
adamc@193:  * POSSIBILITY OF SUCH DAMAGE.
adamc@193:  *)
adamc@193: 
adamc@193: (* Utility code for implementing comparisons *)
adamc@193: 
adamc@193: structure Order :> ORDER = struct
adamc@193: 
adamc@193: fun join (o1, o2) =
adamc@193:     case o1 of
adamc@193:         EQUAL => o2 ()
adamc@193:       | v => v
adamc@193:              
adamc@193: fun joinL f (os1, os2) =
adamc@193:     case (os1, os2) of
adamc@193:         (nil, nil) => EQUAL
adamc@193:       | (nil, _) => LESS
adamc@193:       | (h1 :: t1, h2 :: t2) =>
adamc@193:         join (f (h1, h2), fn () => joinL f (t1, t2))
adamc@193:       | (_ :: _, nil) => GREATER
adamc@193: 
adamc@479: fun joinO f (v1, v2) =
adamc@479:     case (v1, v2) of
adamc@479:         (NONE, NONE) => EQUAL
adamc@479:       | (NONE, _) => LESS
adamc@479:       | (_, NONE) => GREATER
adamc@479: 
adamc@479:       | (SOME v1, SOME v2) => f (v1, v2)
adamc@479: 
adamc@193: end