adamc@2: (* Copyright (c) 2008, Adam Chlipala
adamc@2:  * All rights reserved.
adamc@2:  *
adamc@2:  * Redistribution and use in source and binary forms, with or without
adamc@2:  * modification, are permitted provided that the following conditions are met:
adamc@2:  *
adamc@2:  * - Redistributions of source code must retain the above copyright notice,
adamc@2:  *   this list of conditions and the following disclaimer.
adamc@2:  * - Redistributions in binary form must reproduce the above copyright notice,
adamc@2:  *   this list of conditions and the following disclaimer in the documentation
adamc@2:  *   and/or other materials provided with the distribution.
adamc@2:  * - The names of contributors may not be used to endorse or promote products
adamc@2:  *   derived from this software without specific prior written permission.
adamc@2:  *
adamc@2:  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
adamc@2:  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
adamc@2:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
adamc@2:  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
adamc@2:  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
adamc@2:  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
adamc@2:  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
adamc@2:  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
adamc@2:  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
adamc@2:  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
adamc@2:  * POSSIBILITY OF SUCH DAMAGE.
adamc@2:  *)
adamc@2: 
adamc@2: structure Search :> SEARCH = struct
adamc@2: 
adamc@2: datatype ('state, 'abort) result =
adamc@2:          Return of 'abort
adamc@2:        | Continue of 'state
adamc@2: 
adamc@2: type ('data, 'state, 'abort) mapfold_arg =
adamc@2:      'data * 'state -> ('data * 'state, 'abort) result
adamc@2: 
adamc@2: type ('data, 'state, 'abort) mapfolder =
adamc@2:      'data -> 'state -> ('data * 'state, 'abort) result
adamc@2: 
adamc@2: fun return2 v acc = Continue (v, acc)
adamc@2: 
adamc@2: fun map (r, f) =
adamc@2:     case r of
adamc@2:         Continue acc => Continue (f acc)
adamc@2:       | Return x => Return x
adamc@2: 
adamc@2: fun map2 (r, f) acc =
adamc@2:     case r acc of
adamc@2:         Continue (x, acc) => Continue (f x, acc)
adamc@2:       | Return x => Return x
adamc@2: 
adamc@2: fun bind (r, f) =
adamc@2:     case r of
adamc@2:         Continue acc => f acc
adamc@2:       | Return x => Return x
adamc@2: 
adamc@2: fun bind2 (r, f) acc =
adamc@2:     case r acc of
adamc@2:         Continue (x, acc) => f x acc
adamc@2:       | Return x => Return x
adamc@2: 
adamc@2: fun bindP (r, f) =
adamc@2:     case r of
adamc@2:         Continue ((x, pos), acc) =>
adamc@2:         map (f (x, acc),
adamc@2:           fn (x', acc') =>
adamc@2:              ((x', pos), acc'))
adamc@2:       | Return x => Return x
adamc@2: 
adamc@2: end