[GHC] #7384: Panic "ctEvTerm" when using functional dependencies and PolyKinds

[GHC]

#7384: Panic "ctEvTerm" when using functional dependencies and PolyKinds
------------------------------+---------------------------------------------
 Reporter:  goldfire          |          Owner:                                  
     Type:  bug               |         Status:  new                             
 Priority:  normal            |      Component:  Compiler                        
  Version:  7.7               |       Keywords:  FunctionalDependencies PolyKinds
       Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple                
  Failure:  None/Unknown      |       Testcase:                                  
Blockedby:                    |       Blocking:                                  
  Related:                    |  
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 The following code causes a panic:

 {{{
 {-# LANGUAGE FunctionalDependencies, PolyKinds #-}

 class Baz a b | a -> b where
   bar :: a -> ()

 instance Baz Bool Bool where
   bar _ = ()

 foo = bar False
 }}}

 The panic reads:

 {{{
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.7.20121031 for x86_64-apple-darwin):
         ctEvTerm: derived constraint cannot have id
 <<details unavailable>>
 }}}

 The panic does not happen without {{{-XPolyKinds}}}.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7384>
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