[GHC] #8516: Add (->) representation and the Invariant class to GHC.Generics

[GHC]

#8516: Add (->) representation and the Invariant class to GHC.Generics
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        Reporter:  nfrisby           |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler (Type    |              Version:  7.7
  checker)                           |
      Resolution:                    |             Keywords:  Generics
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 Replying to [comment:9 simonpj]:
 > But even in the more general form it would be quite do-able I think.
 So, if allowing quantified constraints will help, perhaps it's time we bit
 that bullet.

 I think this is do-able. (I'm not currently volunteering to do it, though.
 Perhaps in the future, as doing this looks fun.) See our conversation
 starting at comment:14:ticket:2256.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8516#comment:12>
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