[GHC] #3822: pattern guards in arrow notation (Arrows extension) case statement cause compiler panic

[GHC]

#3822: pattern guards in arrow notation (Arrows extension) case statement cause
compiler panic
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    Reporter:  StephenBlackheath  |       Owner:                                  
        Type:  bug                |      Status:  new                             
    Priority:  normal             |   Component:  Compiler                        
     Version:  6.12.1             |    Keywords:  arrows pattern guards case panic
          Os:  Linux              |    Testcase:  patternGuard.hs                 
Architecture:  x86_64 (amd64)     |     Failure:  Compile-time crash              
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 The attached test case causes this panic message:

 -----
 ghc: panic! (the 'impossible' happened)
   (GHC version 6.12.1 for x86_64-unknown-linux):
         initC: srt_lbl

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 -----

 The offending line is the one with '| neg'.  It doesn't panic if you use
 the commented out line below it instead.

 This kind of case statement is specific to arrow notation (provided by the
 Arrows extension) - the compiler uses ArrowChoice to implement it.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3822>
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