[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):

 > The user's guide should contain an explanation sufficient for a user to
 understand what types will and will not work with deriving Functor.
 Ideally this should contain examples of both sorts.
 >
 > The wiki is intended for developer-facing documentation; users shouldn't
 have to consult the wiki to find out how to use a feature.

 OK, that makes sense. I definitely got a bit lazy by the time I got to the
 users' guide and more-or-less copypasted what was in the wiki—I'll try to
 address this when I get a chance.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10831#comment:6>
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