-fallow-overlapping-instances Request

[Ashley Yakeley]

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