[GHC] #4170: Invalid "duplicate instance" error

[GHC]

#4170: Invalid "duplicate instance" error
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    Reporter:  verdelyi          |        Owner:              
        Type:  bug               |       Status:  new         
    Priority:  normal            |    Milestone:              
   Component:  Compiler          |      Version:  6.12.3      
    Keywords:                    |   Difficulty:              
          Os:  Unknown/Multiple  |     Testcase:              
Architecture:  Unknown/Multiple  |      Failure:  None/Unknown
---------------------------------+------------------------------------------

Comment(by simonpj):

 See #4230 for a more global discussion

 Simon

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4170#comment:2>
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