maydwell at gmail.com
Fri Nov 6 07:43:47 UTC 2015
Well, this might not be the most efficient, but:
mapKeysMaybe f = Data.Map.mapMaybeWithKey (const . f)
What do you reckon?
On Fri, Nov 6, 2015 at 6:29 PM, Dennis Raddle <dennis.raddle at gmail.com>
> Can someone give me a clever way to implement mapKeysMaybe, defined as
> Ord k => (k -> Maybe k) -> Map k a -> Map k a
> where the transformed keys that evaluate to Just are the only ones kept?
> I am thinking this will probably help me understand a new type, like
> traversable or something.
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> Beginners at haskell.org
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