On Aug 3, 2015, at 11:02 AM, Zemyla <zemyla@gmail.com> wrote:

So:
1) Can this be implemented with GHC as it is now?

No.

2) Could this be implemented at all with any reasonable amount of work?

Depends on how reasonable you are. :)

The problem is that this would require all of the instance tables and lookup machinery to be available at runtime. Currently, that stuff is around only at compile time. So this would be a big change.

3) Should this be implemented? Would the benefits outweigh the costs?

I have a better idea of the costs than of the benefits here. The costs are non-trivial, to be sure. What are the benefits?