27 Nov
2016
27 Nov
'16
12:08 p.m.
On 07:10 Sun 27 Nov , Baldur Blöndal wrote:
catMaybes :: (Foldable f) => f (Maybe a) -> [a] catMaybes :: (Foldable f, Foldable g) => f (g a) -> [a] catMaybes = foldMap toList
mapMaybes :: (a -> Maybe b) -> (forall f. Foldable f => f a -> [b]) mapMaybes :: Foldable m => (a -> m b) -> (forall f. Foldable f => f a -> [b]) mapMaybes f = foldMap (toList . f)
These two as well as 'filter' are generalized in witherable[1]. [1]: https://hackage.haskell.org/package/witherable/