[GHC] #2110: Rules to eliminate casted id's

[GHC]

#2110: Rules to eliminate casted id's
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    Reporter:  igloo             |       Owner:                  
        Type:  feature request   |      Status:  new             
    Priority:  lowest            |   Milestone:  7.6.2           
   Component:  Compiler          |     Version:  6.8.2           
    Keywords:                    |          Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown    
  Difficulty:  Unknown           |    Testcase:                  
   Blockedby:                    |    Blocking:                  
     Related:                    |  
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Comment(by nomeata):

 Today after the Haskell Symposium, I again shocked someone by telling him
 that "map unT" or "map T, where T is a newtype constructor, is not
 optimized away, so I was reminded of this bug. There really ought to
 happen something here.

 If the rule is representable internall, but not easily written in user
 code, how about a compiler pass that detects map-like functions and then
 automatically adds appropriate rules to the source?

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2110#comment:18>
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