[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
-------------------------------------+-------------------------------------

Comment (by osa1):

 How should we proceed about this? Like @rwbarton mentioned in #10577, none
 of these is a part of the standard, so I think we can change behavior of
 standalone deriving to introduce an empty case, and then also change
 EmptyDataDecls deriving to make the behavior consistent. Should we move
 this discussion to the mailing list for feedbacks?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7401#comment:40>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler