1 Aug
2007
1 Aug
'07
1:41 p.m.
Am Mittwoch, 1. August 2007 14:41 schrieb apfelmus:
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The problem with the Functor/Cofunctor instances is that they are ambiguous as soon as a type constructor X is made an instance of both Functor and Cofunctor . Of course, such an X cannot exist in a mathematically useful way (really ?)
I think, it can: newtype Const a b = MkConst a instance Functor (Const a) where fmap fun (MkConst a) = MkConst a instance Cofunctor (Const a) where cofmap fun (MkConst a) = MkConst a
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Best wishes, Wolfgang