[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.
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    Reporter:  jpbernardy        |       Owner:                           
        Type:  feature request   |      Status:  infoneeded               
    Priority:  normal            |   Milestone:  7.8.1                    
   Component:  Compiler          |     Version:  7.6.1                    
    Keywords:  deriving          |          Os:  Unknown/Multiple         
Architecture:  Unknown/Multiple  |     Failure:  GHC rejects valid program
  Difficulty:  Unknown           |    Testcase:                           
   Blockedby:                    |    Blocking:                           
     Related:                    |  
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Comment(by monoidal):

 I can try to do on this, but let me ask:

 Allowing "data A deriving (Eq)" is not compatible with Haskell 98 nor 2010
 (point 6 at
 http://www.haskell.org/onlinereport/haskell2010/haskellch11.html#x18-18200011).
 Does this mean I should add an add a flag, say `-XEmptyDeriving`, or
 should GHC allow such declarations by default?

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7401#comment:7>
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