fre 2002-09-06 klockan 15.01 skrev MR K P SCHUPKE:

If I have a class:

class A m n where f :: m a -> n a

I can declare instances

instance A Maybe Maybe where f = id

instance A [] [] where f = id

but if I try and put a default method: f = id

I get a unification error (less polymorphic than expected).This seems a little odd - is there a work around for this?

Because that default method only works when m=n, which it's not in the general case. -- Martin Norbäck d95mback@dtek.chalmers.se Kapplandsgatan 40 +46 (0)708 26 33 60 S-414 78 GÖTEBORG http://www.dtek.chalmers.se/~d95mback/ SWEDEN OpenPGP ID: 3FA8580B