1 files changed, 12 insertions, 0 deletions
diff --git a/src/pair_key_fn.sml b/src/pair_key_fn.sml
new file mode 100644
index 00000000..cd33950d
--- /dev/null
+++ b/src/pair_key_fn.sml
@@ -0,0 +1,12 @@
+functor PairKeyFn (structure I : ORD_KEY
+                     structure J : ORD_KEY)
+        : ORD_KEY where type ord_key = I.ord_key * J.ord_key = struct
+
+type ord_key = I.ord_key * J.ord_key
+
+fun compare ((i1, j1), (i2, j2)) =
+    case I.compare (i1, i2) of
+        EQUAL => J.compare (j1, j2)
+      | ord => ord
+
+end