[GHC] #3590: panic (the impossible happened) when compiling with -O2

[GHC]

#3590: panic (the impossible happened) when compiling with -O2
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    Reporter:  yairchu   |        Owner:         
        Type:  bug       |       Status:  new    
    Priority:  normal    |    Milestone:         
   Component:  Compiler  |      Version:  6.10.4 
    Severity:  normal    |   Resolution:         
    Keywords:            |   Difficulty:  Unknown
    Testcase:            |           Os:  MacOS X
Architecture:  x86       |  
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Comment (by yairchu):

 T3590.hs was lacking required instances for ListT. I added them and now it
 works. see attached standalone.hs

 re: elucidate. just learned a new word :)

 Yair

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3590#comment:2>
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