mapM package:pipes

mapM :: Monad m => (a -> m b) -> Pipe a b m r
pipes Pipes.Prelude
Apply a monadic function to all values flowing downstream 
mapM return = cat

mapM (f >=> g) = mapM f >-> mapM g
mapM_ :: Monad m => (a -> m ()) -> Consumer' a m r
pipes Pipes.Prelude
Consume all values using a monadic function
mapMaybe :: Functor m => (a -> Maybe b) -> Pipe a b m r
pipes Pipes.Prelude
(mapMaybe f) yields Just results of f. Basic laws: 
mapMaybe (f >=> g) = mapMaybe f >-> mapMaybe g

mapMaybe (pure @Maybe . f) = mapMaybe (Just . f) = map f

mapMaybe (const Nothing) = drain
As a result of the second law, 
mapMaybe return = mapMaybe Just = cat