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Solution3.html

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parent :: Sheep -> [Sheep]
parent s = (maybeToList (mother s)) ++ (maybeToList (father s))
 
grandparent :: Sheep -> [Sheep]
grandparent s = (maybeToList (paternalGrandfather s)) ++
                (maybeToList (paternalGrandmother s)) ++
                (maybeToList (maternalGrandfather s)) ++
                (maybeToList (maternalGrandmother s))

Alternate solution:

parent :: Sheep -> [Sheep]
parent s = (maybeToList $ mother s) `mplus` (maybeToList $ father s)
 
grandparent :: Sheep -> [Sheep]
grandparent s = parent s >>= parent