[GHC] #5581: ConstraintKinds lets you put the typechecker into a loop

[GHC]

#5581: ConstraintKinds lets you put the typechecker into a loop
---------------------------------+------------------------------------------
    Reporter:  pumpkin           |       Owner:                         
        Type:  bug               |      Status:  new                    
    Priority:  normal            |   Component:  Compiler (Type checker)
     Version:  7.3               |    Keywords:  ConstraintKinds        
    Testcase:                    |   Blockedby:                         
          Os:  Unknown/Multiple  |    Blocking:                         
Architecture:  Unknown/Multiple  |     Failure:  Compile-time crash     
---------------------------------+------------------------------------------
 Ed Kmett was playing with them the other day and Dan Doel and I reduced
 the issue to this:

 {{{
 {-# LANGUAGE ConstraintKinds, FlexibleContexts, FlexibleInstances,
 KindSignatures #-}

 class C (p :: Constraint)
 class D (p :: Constraint)

 instance C (D p) => C (D (D p))

 {-
 -- This works
 data E a = E
 class F a
 instance F (E a) => F (E (E a))
 -}
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5581>
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