From d2196dbd5c4379bdbc307d2035c8a07ef09b592d Mon Sep 17 00:00:00 2001
From: Adam Chlipala <adam@chlipala.net>
Date: Sun, 3 Nov 2013 19:27:30 -0500
Subject: ListPair.map2, based on code by escalier@riseup.net

---
 lib/ur/listPair.ur | 11 +++++++++++
 1 file changed, 11 insertions(+)

(limited to 'lib/ur/listPair.ur')

diff --git a/lib/ur/listPair.ur b/lib/ur/listPair.ur
index 0182af19..d69993f9 100644
--- a/lib/ur/listPair.ur
+++ b/lib/ur/listPair.ur
@@ -33,3 +33,14 @@ fun all [a] [b] f =
     in
         all'
     end
+
+fun map2 [a] [b] [c] (f : a -> b -> c) =
+    let
+        fun map2' ls1 ls2 =
+            case (ls1, ls2) of
+                ([], []) => []
+              | (x1 :: ls1, x2 :: ls2) => f x1 x2 :: map2' ls1 ls2
+              | _ => error <xml>ListPair.map2: Unequal list lengths</xml>
+    in
+        map2'
+    end
-- 
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