On 18/07/2011 19:14, Jerzy Karczmarczuk wrote:
> That's why I suggested how you might do that: for some datatypes, say
> the Emperors, you specify some special flying method (e.g. dummy or
> bombing), or you don't specify it at all. And the Emperors won't fly.
-- Here is my attempt
data Emperor = Emperor
data Robin = Robin
class Bird a where
fly :: a -> a -> a
walk :: a -> a -> a
instance Bird Robin where
fly x y = y
walk x y = x
instance Bird Emperor where
-- No fly method
walk x y = y
class (Bird a) => Penguin a where
-- I do not think that I can override the walk method in the sub-class
-- must be done in instance of Penguin
instance Penguin Emperor where
-- How can I override the walk method in the instance Penguin?
-- walk x y = x
Regards,
Pat
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