I haven't followed the thread carefully but why does the bird have to be a penguin?
A bird doesn't have to be a penguin : *instance* (Penguin b) => Bird b where fly = -- fly method for penguins Says that every Penguin is a Bird. But thinking back about it, there is a problem when trying to define the method walk, because: class Penguin p where walkPenguin :: .... instance (Penguin b) => Bird b where fly = ..... walk = walkPenguin is kind of awful, because walk has to be duplicated. So, not the best way to go... 2011/7/19 Maciej Marcin Piechotka <uzytkownik2@gmail.com>
On Tue, 2011-07-19 at 01:13 +0200, Yves Parès wrote:
Oh, I got it: You want to have:
class Bird b where
class Penguin p where
instance (Penguin b) => Bird b where fly = -- fly method for penguins
I haven't followed the thread carefully but why does the bird have to be a penguin?
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As a side note - I agree with Christopher Done that the answer is that you shouldn't require for bird to fly.
Regards
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