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
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