MonadSheep

Sheep.hs

data Sheep = SheepCreator String (Sheep, Sheep) | NONE
         deriving Show

father:: Sheep -> Maybe Sheep
father (SheepCreator name (NONE, _)) = Nothing
father (SheepCreator name (f, _)) = Just f

mother:: Sheep -> Maybe Sheep
mother (SheepCreator name (_, NONE)) = Nothing
mother (SheepCreator name (_, m)) = Just m

maternalGrandfather :: Sheep -> Maybe Sheep
maternalGrandfather s = (return s) >>= mother >>= father

maternalGrandfatherDo :: Sheep -> Maybe Sheep
maternalGrandfatherDo s = do m <- mother s
                             mf <- father m
                             return mf

fathersMaternalGrandmother :: Sheep -> Maybe Sheep
fathersMaternalGrandmother s = (return s) >>= father >>= mother >>= mother

fathersMaternalGrandmotherDo :: Sheep -> Maybe Sheep
fathersMaternalGrandmotherDo s = do f <- father s
                                    mf <- mother f
                                    mmf <- mother mf
                                    return mmf