[GHC] #8560: undeducable Typeable error with data kinds when deriving Data for GADT in GHC version 7.7.20131122

[GHC]

#8560: undeducable Typeable error with data kinds when deriving Data for GADT in
GHC version 7.7.20131122
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        Reporter:  carter            |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.7
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by simonpj):

 I have not even begun to think what `deriving( Data )` might do for GADTs.

 At Lennart's request, we did make "standalone deriving" simply generate
 code, and if it doesn't typecheck it's your problem.  See
 [http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html
 #stand-alone-deriving the manual] (fourth bullet).  See #3102, and #3702
 for someone who liked it.

 I'm not sure that was a good decision, especially for jolly complicated
 classes like `Data`.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8560#comment:4>
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