[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            |   Component:  Compiler                         
     Version:  6.12.3            |    Keywords:  GADTs, warnings, pattern matching
          Os:  Unknown/Multiple  |    Testcase:                                   
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown                     
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 When using slightly complicated GADTs, GHC gives me erroneous non-
 exhaustive pattern match warnings.  I have attached an example.  I have
 observed this behavior in the four versions of ghc that I tried (6.10.4,
 and 6.12.{1,2,3}).

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