Currently -fallow-overlapping-instances only allows overlapping instances
if one is a strict subset of the other. This is good (determinate), but
sometimes you really need two instances that partially overlap. It would
be nice if this could be disambiguated simply with another instance
declaration. For instance:
class C a b;
instance C a ();
instance C () a;
instance C () ();
As you can see, the first two instances partially overlap, but the third
one disambiguates. I think it would be nice if GHC
-fallow-overlapping-instances allowed this.
This would take some of the pain out of overlapping instance resolution...
--
Ashley Yakeley, Seattle WA
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