[GHC] #12593: ghci spins forever

[GHC]

#12593: ghci spins forever
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 To make it easier to read the ticket, the code is very short.
 {{{
 {-# LANGUAGE GADTs, ConstraintKinds, PolyKinds, TypeInType,
 KindSignatures, RankNTypes #-}

 module T12593 where

 import Data.Kind

 newtype Free k p a b where
   Free :: (forall q. k q => (forall c d. p c d -> q c d) -> q a b)
        -> Free k p a b

 run :: k2 q => Free k k1 k2 p a b
             -> (forall (c :: k) (d :: k1). p c d -> q c d)
             -> q a b
 run (Free cat) = cat
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12593#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler