[GHC] #13117: Derived functor instance for void types handles errors badly

[GHC]

#13117: Derived functor instance for void types handles errors badly
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        Reporter:  dfeuer            |                Owner:  dfeuer
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
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 dfeuer):

 My preference would be

 {{{#!hs
 fmap _ x = case x of
 }}}

 (effectively using `EmptyCase`).

 mpickering indicates there was some prior dispute about this, but I don't
 know where.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13117#comment:2>
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