[GHC] #9858: Typeable instances should be kind-aware

[GHC]

#9858: Typeable instances should be kind-aware
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        Reporter:  dreixel           |                   Owner:  dreixel
            Type:  bug               |                  Status:  new
        Priority:  highest           |               Milestone:  7.10.1
       Component:  Compiler          |                 Version:  7.9
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by dreixel):

 Replying to [comment:24 simonpj]:
 > One drastic remedy: do not derive `Typeable` for polykinded type
 constructors.  That would be easy to implement, and would certainly fix
 it.  But it's a bit drastic.

 Isn't that very drastic? So a data constructor that is declared with
 `PolyKinds` on, but can be used without it (such as `Proxy`), won't be
 allowed to have a `Typeable` instance at all? Or would we allow a (orphan)
 `Typeable` instance to be derived in a module that does not have
 `PolyKinds` on? Even if so, I'm afraid this might have important
 ramifications, also given that SYB requires `Typeable`...

 How about just marking `Typeable` instances for polykinded type
 constructors as Unsafe (if that's possible)?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9858#comment:25>
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