catmaybes -package:yesod-paginator -package:vector-stream package:streamly-core

catMaybes :: Monad m => Fold m a b -> Fold m (Maybe a) b
streamly-core Streamly.Data.Fold Streamly.Internal.Data.Fold Streamly.Internal.Data.Fold.Type
Modify a fold to receive a Maybe input, the Just values are unwrapped and sent to the original fold, Nothing values are discarded. 
>>> catMaybes = Fold.mapMaybe id

>>> catMaybes = Fold.filter isJust . Fold.lmap fromJust
catMaybes :: Monad m => Stream m (Maybe a) -> Stream m a
streamly-core Streamly.Data.Stream Streamly.Internal.Data.Stream.StreamD.Transform
In a stream of Maybes, discard Nothings and unwrap Justs. 
>>> catMaybes = Stream.mapMaybe id

>>> catMaybes = fmap fromJust . Stream.filter isJust
Pre-release