On Fri, Jul 30, 2010 at 08:13:43PM -0700, 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)
unliftMap :: (Ord a) => M.Map a (b -> c) -> M.Map a b -> M.Map a c unliftMap mf ma = M.mapWithKey (\k v -> mf M.! k $ v) ma
the first is obviously inefficient as it traverses the map twice. the second just seems like it is some kind of fmap.
The second one assumes that every key in ma is also in mf. A generalization without that assumption is unliftMap = intersectionWith id As Wren said, it looks like a <*> operator, but in this case there's no corresponding pure function. To make the laws work, pure x would have to be a map that took every key to x.