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authorGravatar Adam Chlipala <adam@chlipala.net>2013-11-03 19:27:30 -0500
committerGravatar Adam Chlipala <adam@chlipala.net>2013-11-03 19:27:30 -0500
commitd2196dbd5c4379bdbc307d2035c8a07ef09b592d (patch)
tree03de0d970495a013a2e126010600137ebb5746dd /lib/ur/listPair.ur
parent65b818146effe2f74192a3b1d65b4ec792a8a350 (diff)
ListPair.map2, based on code by escalier@riseup.net
Diffstat (limited to 'lib/ur/listPair.ur')
-rw-r--r--lib/ur/listPair.ur11
1 files changed, 11 insertions, 0 deletions
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