It appears that this is a simple matter of the PolyKinds extension not being enabled in libraries/base/GHC/Generics.hs and presumably the reason is the same for the Data instance.

It doesn't seem particularly controversial generalize those instances.

On Fri, Jul 17, 2015 at 3:06 PM Carl Howells <chowells79@gmail.com> wrote:
At the moment, the following two instances are listed in the haddocks
for Data.Proxy.Proxy:

    Data t => Data (Proxy * t)
    Generic (Proxy * t)

Do those instances need to be that restrictive?  Would it be possible
to generalize those instances to these?

    Data (Proxy k t)
    Generic (Proxy k t)

I'm not 100% comfortable with either of those classes, so I'm not sure
if those instances work right, but it seems like they should in a
hand-wavy way.

--
Carl Howells
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