On Tue, 2011-07-19 at 10:43 +0200, Yves Parès wrote: > > 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...
Note to self: don't respond to ml after 2am. I saw instance but read class. Regards
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