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(Explained an incorrect solution,)
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</haskell>
 
</haskell>
   
Alternative grandparent:
+
This solution will not work. If the sheep has a father and only a maternal grandparent, this function will return Nothing:
 
<haskell>
 
<haskell>
 
grandparent :: Sheep -> Maybe Sheep
 
grandparent :: Sheep -> Maybe Sheep

Revision as of 17:49, 10 June 2013

parent :: Sheep -> Maybe Sheep
parent s = father s `mplus` mother s
 
grandparent :: Sheep -> Maybe Sheep
grandparent s = paternalGrandfather s `mplus` 
                paternalGrandmother s `mplus` 
                maternalGrandfather s `mplus` 
                maternalGrandmother s

This solution will not work. If the sheep has a father and only a maternal grandparent, this function will return Nothing:

grandparent :: Sheep -> Maybe Sheep
grandparent s = parent s >>= parent