[GHC] #5677: Allow the definition of extra functions in typeclass instances

[GHC]

#5677: Allow the definition of extra functions in typeclass instances
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    Reporter:  FUZxxl                        |        Owner:                           
        Type:  feature request               |       Status:  new                      
    Priority:  normal                        |    Milestone:                           
   Component:  Compiler                      |      Version:  7.2.1                    
    Keywords:  instance typeclass extension  |     Testcase:                           
   Blockedby:                                |   Difficulty:                           
          Os:  Unknown/Multiple              |     Blocking:                           
Architecture:  Unknown/Multiple              |      Failure:  GHC rejects valid program
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Comment(by simonpj):

 Your suggestion makes perfect sense, but for me it falls just on the side
 of not-quite-worth-it.  Let's see if there's a lot of other support.

 Simon

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5677#comment:1>
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