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 This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie