data Sheep = Sheep { name::String,
                     mom::Maybe Sheep,
                     dad::Maybe Sheep
                   }

instance Show Sheep where
  show s = show ( name s )

comb :: Maybe a -> (a -> Maybe b) -> Maybe b
comb Nothing  _ = Nothing
comb (Just x) f = f x

breedSheep :: Sheep
breedSheep = let adam    = Sheep "Adam" Nothing Nothing
                 eve     = Sheep "Eve" Nothing Nothing
                 thierry = Sheep "Thierry" (Just eve) (Just adam)
                 edith   = Sheep "Edith" (Just eve) (Just adam)
                 cecile  = Sheep "Cecile" (Just edith) (Just thierry)
             in Sheep "Dolly" (Just cecile) Nothing

maternalGrandfather :: Sheep -> Maybe Sheep
maternalGrandfather s = (Just s) `comb` mom `comb` dad

main :: IO ()
main = let dolly = breedSheep
       in do { print (mom dolly); print (dad dolly); print (maternalGrandfather dolly); }