[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 guest):

 I would argue that it is worth the extra compactness, in that I want
 to be able to teach this to first years.  I don't want to teach them
 to use

  ... deriving Show

 to get unpretty printing, but then they have to use the more long-winded

  instance (Pretty a, Pretty b) => Pretty (Tree a b)

 to get pretty printing.  If it's good for the goose (your built-in
 derived types) it's good for the gander (my custom derived types).

 -- Philip Wadler (logged in as guest because the registration function is
 buggy)

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5462#comment:2>
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