[GHC] #7873: A poly-kinded newtype existential crisis

[GHC]

#7873: A poly-kinded newtype existential crisis
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Reporter:  ekmett                     |          Owner:                  
    Type:  bug                        |         Status:  new             
Priority:  normal                     |      Component:  Compiler        
 Version:  7.6.3                      |       Keywords:                  
      Os:  Unknown/Multiple           |   Architecture:  Unknown/Multiple
 Failure:  GHC rejects valid program  |      Blockedby:                  
Blocking:                             |        Related:                  
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Comment(by kosmikus):

 It works if you restrict `s` in `Magic` to be of a particular kind, for
 example `*`. I think it's indeed existential if not constrained.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7873#comment:3>
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