[GHC] #4139: Spurious non-exhaustive pattern match warnings are given using GADTs

[GHC]

#4139: Spurious non-exhaustive pattern match warnings are given using GADTs
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  Reporter:  blarsen                            |          Owner:                                   
      Type:  bug                                |         Status:  new                              
  Priority:  normal                             |      Milestone:  7.0.1                            
 Component:  Compiler                           |        Version:  7.4.1                            
Resolution:                                     |       Keywords:  GADTs, warnings, pattern matching
        Os:  Unknown/Multiple                   |   Architecture:  Unknown/Multiple                 
   Failure:  Incorrect warning at compile-time  |     Difficulty:  Unknown                          
  Testcase:                                     |      Blockedby:                                   
  Blocking:                                     |        Related:                                   
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Changes (by simonpj):

  * difficulty:  => Unknown


Comment:

 Good example.  It has the same cause as #3927. Sorry no imminent cure.
 Needs someone to pay proper attention to it.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4139#comment:5>
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