[GHC] #3843: Merge plugins into HEAD

[GHC]

#3843: Merge plugins into HEAD
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    Reporter:  dreixel           |        Owner:  simonpj     
        Type:  task              |       Status:  new         
    Priority:  normal            |    Milestone:              
   Component:  Compiler          |      Version:  6.13        
    Keywords:                    |   Difficulty:              
          Os:  Unknown/Multiple  |     Testcase:              
Architecture:  Unknown/Multiple  |      Failure:  None/Unknown
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Changes (by pumpkin):

 * cc: pumpkingod@… (added)


Comment:

 I'd like to use plugins to help show the programmer what rewrite rules are
 firing and where. The current most verbose simplifier output doesn't
 provide enough information to allow an external program to figure out what
 was rewritten and where (it just says that a rule fired and gives the new
 version of the code). This would help to find performance bugs in fusion-
 heavy code for example.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3843#comment:3>
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