The only need for the functor requirement is in the default definition of mapMaybe - so why not drop it? I would also suggest you add (modulo better names) partition :: (a -> Bool) -> f a -> (f a , f a) partitionWith :: (a -> Either b c) -> f a -> (f b, f c) catEithers :: f (Either b c) -> (f b, f c) lefts :: f (Either b c) -> f b rights :: f (Either b c) -> f c I think the class would still be equivalent to your current one, but more useful. On 2016-02-17 08:02, M Farkas-Dyck wrote:
I quietly posted this library to Hackage nearly a year ago, but lately learned that some seeking such a package had difficulty finding it, so i announce it now ☺
https://hackage.haskell.org/package/filtrable
class Functor f => Filtrable f where mapMaybe :: (a -> Maybe b) -> f a -> f b catMaybes :: f (Maybe a) -> f a filter :: (a -> Bool) -> f a -> f a
For laws, see docs on Hackage. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe