[GHC] #940: GADT + impredicative polymorphism => stack overflow

[GHC]

#940: GADT + impredicative polymorphism => stack overflow
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  Reporter:  guest                    |          Owner:         
      Type:  bug                      |         Status:  new    
  Priority:  normal                   |      Milestone:         
 Component:  Compiler (Type checker)  |        Version:  6.6    
  Severity:  normal                   |       Keywords:         
Difficulty:  Unknown                  |   Architecture:  Unknown
        Os:  Unknown                  |  
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The following makes the GHC 6.6 type checker loop/overflow:
 {{{
 {-# OPTIONS_GHC -fglasgow-exts #-}
 data Foo a b where F :: a -> Foo () a

 bar :: Foo () (forall a.a) -> ()
 bar (F _) = ()
 }}}
 ghc yields stack overflow, as does ghci. Reloading in GHCi leads to an
 infinite loop.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/940>
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