On Fri, Jul 30, 2010 at 08:13:43PM -0700, Ben wrote:
> 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
I always thought a useful map primitive would be
unionWithJoin
:: (a -> b -> c) -- combine values that appear in both maps
-> (b -> c) -- value appears in second map but not the first
-> (a -> c) -- value appears in first map but not second
-> Map k a -> Map k b -> Map k c
along with the 'WithKey' and 'Maybe' variants.
John
--
John Meacham - ⑆repetae.net⑆john⑈ - http://notanumber.net/
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