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 <[email protected]> wrote: > Richard Eisenberg <[email protected]> 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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