[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 simonpj):

 This ticket has a long thread, which is discouraging for anyone
 approaching it for the first time.

 My suggestion: write a wiki page proposing a particular design.  Advertise
 it on the Haskell and libraries mailing list (this is practically a core-
 libraries committee issue).  Drive the discussion to a consensus.
 Implement it.

 It's very much a corner case so what we really need is a well documented
 decision rather than a long debate.  It just that it's hard to see the
 wood for the trees now.

 Thanks!

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7401#comment:41>
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