More GND + role inference woes

[Edward Kmett]

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 <bgamari.foss at gmail.com> wrote:

> Richard Eisenberg <eir at cis.upenn.edu> 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
>
>
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