[GHC] #10831: Document conditions on deriving Functor

[GHC]

#10831: Document conditions on deriving Functor
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        Reporter:  htebalaka         |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  low               |               Milestone:
       Component:  Compiler (Type    |                 Version:  7.10.2
  checker)                           |
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Documentation     |  Unknown/Multiple
  bug                                |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by RyanGlScott):

 Replying to [comment:3 simonpj]:
 > But I think we still lack a user-oriented specification, and such a
 thing would be tremendously welcome.

 What exactly would we want from a "user-oriented specification"? Do we
 want to see the compile-time error messages improved? Or do we want to see
 particular portions of the Commentary page and/or users' guide fleshed
 out?

 I'll admit that I didn't do a thorough job of how to follow along with
 `DeriveFunctor`'s many nuances as a newcomer to GHC in the Commentary page
 (I had the privilege of understanding it before I wrote it), so please
 point out specific parts that need work.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10831#comment:4>
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