[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:                           
        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 kosmikus):

 It's useful for example when you're using such a type as an argument to
 another datatype, which happens to place an Eq constraint on its argument.

 However, it seems that this works when standalone deriving is used. That
 might be a viable workaround if it's somehow difficult to fix.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7401#comment:5>
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