[GHC] #7401: Can't derive instance for Eq when datatype has no constructor, while it is trivial do do so.

[GHC]

#7401: Can't derive instance for Eq when datatype has no constructor, while it is
trivial do do so.
-------------------------------------+-------------------------------------
        Reporter:  jpbernardy        |                   Owner:  osa1
            Type:  feature request   |                  Status:  new
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Compiler          |                 Version:  7.6.1
      Resolution:                    |                Keywords:  deriving,
Operating System:  Unknown/Multiple  |  newcomer
 Type of failure:  GHC rejects       |            Architecture:
  valid program                      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:  Phab:D978
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Comment (by rwbarton):

 Indeed. I for one think it should be changed to use an empty case. This
 ticket might not be the right place to discuss it though, since in any
 case standalone deriving and ordinary deriving should not produce two
 different instances. I only skimmed over the patch on Phab, but I assume
 the same code is used to actually generate the instances in those two
 cases, right?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7401#comment:36>
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