[GHC] #5462: Deriving clause for arbitrary classes

[GHC]

#5462: Deriving clause for arbitrary classes
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    Reporter:  simonpj           |        Owner:              
        Type:  feature request   |       Status:  new         
    Priority:  normal            |    Milestone:              
   Component:  Compiler          |      Version:  7.2.1       
    Keywords:                    |     Testcase:              
   Blockedby:                    |   Difficulty:              
          Os:  Unknown/Multiple  |     Blocking:              
Architecture:  Unknown/Multiple  |      Failure:  None/Unknown
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Comment(by hvr):

 Replying to [comment:14 guest]:
 > I'd think getting a boring instance of default methods is precisely what
 s/he would expect if deriving from a class w/o any default method
 signatures. So why not let him/her have it? Apart from probable
 uselessness, is there a price to be payed by such a choice?

 How would this interact with the GeneralizedNewtypeDeriving extension?
 Could there be cases where the code compiles fine with and without
 GeneralizedNewtypeDeriving, but in the first case the wrapped types'
 instance methods are "inherited", and in the second case the default
 methods of the typeclass would be used. Would this be a bad thing if
 switching on language extensions changes the semantics of the program (w/o
 any visible compile warning)?

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5462#comment:15>
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