[GHC] #8020: Closed type families break substitution

[GHC]

#8020: Closed type families break substitution
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Reporter:  goldfire          |          Owner:  goldfire        
    Type:  bug               |         Status:  new             
Priority:  normal            |      Component:  Compiler        
 Version:  7.7               |       Keywords:                  
      Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
 Failure:  None/Unknown      |      Blockedby:                  
Blocking:                    |        Related:                  
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 This code causes a Core Lint error:

 {{{
 {-# LANGUAGE TypeFamilies #-}

 type family F a b where
   F (Maybe a) [a] = Int
   F b c           = Bool

 data Proxy a = P

 type family G

 foo :: Proxy d -> F d d -> Bool
 foo _ = not

 bar :: Bool -> Bool
 bar = foo (P :: Proxy G)
 }}}

 The solution needs to freshen variables before doing apartness checking. I
 will fix in due course.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/8020>
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