1 files changed, 53 insertions, 0 deletions
diff --git a/src/order.sml b/src/order.sml
new file mode 100644
index 0000000..3f5bce6
--- /dev/null
+++ b/src/order.sml
@@ -0,0 +1,53 @@
+(* 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.
+ *)
+
+(* Utility code for implementing comparisons *)
+
+structure Order :> ORDER = struct
+
+fun join (o1, o2) =
+    case o1 of
+        EQUAL => o2 ()
+      | v => v
+             
+fun joinL f (os1, os2) =
+    case (os1, os2) of
+        (nil, nil) => EQUAL
+      | (nil, _) => LESS
+      | (h1 :: t1, h2 :: t2) =>
+        join (f (h1, h2), fn () => joinL f (t1, t2))
+      | (_ :: _, nil) => GREATER
+
+fun joinO f (v1, v2) =
+    case (v1, v2) of
+        (NONE, NONE) => EQUAL
+      | (NONE, _) => LESS
+      | (_, NONE) => GREATER
+
+      | (SOME v1, SOME v2) => f (v1, v2)
+
+end