-fallow-overlapping-instances Request

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