Re: More GND + role inference woes

Correct. With 7.8 we'll need to hand-implement those instances rather than derive them. On Sat, Dec 14, 2013 at 7:59 PM, Ben Gamari wrote:

Richard Eisenberg writes:

...

Yes, I believe that's right. As far as I can figure out, these classes really *are* problematic, in that if we allowed GeneralizedNewtypeDeriving for them, there would be a way to subvert the type system. To make these derivable, we would need to be able to restrict various type parameters from taking on values that take a nominal argument. Without the ability to restrict the values in this way, there could be trouble.

I suppose it's unlikely that the roles mechanism will be extended to allow for such restriction?

Cheers,

- Ben