[GHC] #2439: Missed optimisation with dictionaries and loops

[GHC]

#2439: Missed optimisation with dictionaries and loops
---------------------------------+------------------------------------------
    Reporter:  rl                |       Owner:  simonpj                
        Type:  bug               |      Status:  new                    
    Priority:  lowest            |   Milestone:  7.6.2                  
   Component:  Compiler          |     Version:  6.9                    
    Keywords:                    |          Os:  Unknown/Multiple       
Architecture:  Unknown/Multiple  |     Failure:  Runtime performance bug
  Difficulty:  Unknown           |    Testcase:                         
   Blockedby:                    |    Blocking:                         
     Related:                    |  
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Comment(by simonpj):

 Can you explain eaxtly how making single-method classes be a data type
 would break edward's library?

 And example where forcing a single method would be bad:
 {{{
 class C a where
   foo :: a

 instance C Int where
   foo = undefined

 bar :: C a => Int -> Int
 bar x = x

 main = print (bar (3 :: Int))
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2439#comment:19>
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