Ben wrote:
dear traversable geniuses --
i am looking for "better" implementations of
unzipMap :: M.Map a (b, c) -> (M.Map a b, M.Map a c) unzipMap m = (M.map fst m, M.map snd m)
I don't think you can give a more efficient implementation using the public interface of Data.Map. You need to have a sort of mapping function that allows you to thread them together, either via continuations or via a primitive: splitMap :: (a -> (b,c)) -> Map k a -> (Map k b, Map k c) This splitMap and the mapEither primitive could be combined: data Or a b = Fst a | Both a b | Snd b eitherOr (Left a) = Fst a eitherOr (Right b) = Snd a mapOr :: (a -> Or b c) -> Map k a -> (Map k b, Map k c) mapEither f = mapOr (eitherOr . f) splitMap f = mapOr (uncurry Both) And the type of John's primitive could be prettied up: unionWithJoin :: (Or a b -> c) -> Map k a -> Map k b -> Map k c -- Live well, ~wren