#7536: Panic with TypeFamilies and FlexibleInstances
Reporter:  snowleopard         |          Owner:                  
    Type:  bug                 |         Status:  new             
Priority:  normal              |      Component:  Compiler        
 Version:  7.6.1               |       Keywords:                  
      Os:  Unknown/Multiple    |   Architecture:  Unknown/Multiple
 Failure:  Compile-time crash  |      Blockedby:                  
Blocking:                      |        Related:                  
 The code below brings GHC to panic.

 {-# LANGUAGE TypeFamilies, FlexibleInstances #-}

 module Bug where

 type Node v = Int

 class Predicate a where
    type Var a
    variable :: Var a -> a

 instance Predicate (Node v) where
    type Var (Node v) = v
    variable = undefined

 Panic details:

 ghc: panic! (the 'impossible' happened)
   (GHC version 7.4.2 for i386-unknown-mingw32):
     ( v{tv aa3} [tv] :: ghc-prim:GHC.Prim.*{(w) tc 34d} )

 Can be reproduced on GHC versions 7.4.2 and 7.6.1.

 Possibly, a duplicate of
 [http://hackage.haskell.org/trac/ghc/ticket/7458], but difficult to tell
 without additional info on the latter.

Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7536>
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