5 Mar
2008
5 Mar
'08
8:27 p.m.
Just something I have been wondering. I would like to implement somehting like: type family F a :: * -> * ... class C a b where ... instance (F a ~ F b) => C a b where ... But apparently type equality coercions can not be used as a single context. If I enable -fallow-undecidable-instances, whenever the equality does not hold, the instance returns a compile error, what does make sense. Is there any way I could overcome this? Thanks, hugo