Make polykinded on GHC 7.4

[phadej]

No description provided.

[RyanGlScott]

There exists a pretty nasty bug in GHC 7.4's implementation of -XPolyKinds that prevents interface files from being loaded (I can't find the exact Trac issue, but @ekmett might be able to), so I don't think this is a good idea.

[phadej]

I see. This is not critical; but I'd like to learn more about this.

Especially we could update https://ghc.haskell.org/trac/ghc/wiki/LanguagePragmaHistory with that knowledge, iff PolyKinds with 7.4 is discouraged.

[RyanGlScott]

Agreed, that'd be a useful addendum. (I think that -XConstraintKinds is also quite buggy on GHC 7.4, but again, I couldn't cite a particular Trac issue to back this up.)

[ekmett]

PolyKinds on 7.4 means that nobody can load the interface file.

[phadej]

@ekmett, is this https://ghc.haskell.org/trac/ghc/ticket/7022 the issue?

[ekmett]

Sounds right. I added a note to the LanguagePragmaHistory page warning people not to use it until 7.6