[GHC] #4370: Bring back monad comprehensions

[GHC]

#4370: Bring back monad comprehensions
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    Reporter:  simonpj           |        Owner:  nsch        
        Type:  feature request   |       Status:  new         
    Priority:  normal            |    Milestone:  7.2.1       
   Component:  Compiler          |      Version:  6.12.3      
    Keywords:                    |     Testcase:              
   Blockedby:                    |   Difficulty:              
          Os:  Unknown/Multiple  |     Blocking:              
Architecture:  Unknown/Multiple  |      Failure:  None/Unknown
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Comment(by igloo):

 Does it happen in batch mode even without `-O`?

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4370#comment:39>
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