I'm solving this exercise: http://www.haskell.org/haskellwiki/All_About_Monads#Exercise_4:_Using_the_Mo... I'm missing a function to transform a Maybe a into a MonadPlus m => m a. I did search on Hoogle with no luck. There is no standard definition for the "g" function I'm defining? My take on the exercise: data Sheep = Sheep { mother :: Maybe Sheep, father :: Maybe Sheep, name :: String } instance Show Sheep where -- for testing show = name g :: (MonadPlus m) => Maybe a -> m a g Nothing = mzero g (Just a) = return a mother' :: (MonadPlus m) => Sheep -> m Sheep mother' = g . mother father' :: (MonadPlus m) => Sheep -> m Sheep father' = g . father parent'' :: (MonadPlus m) => Sheep -> m Sheep parent'' s = mother' s `mplus` father' s grandparent'' :: (MonadPlus m) => Sheep -> m Sheep grandparent'' s = parent'' s >>= parent''