Start of elaboration

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