[GHC] #5934: ghc: panic! (the 'impossible' happened)

[GHC]

#5934: ghc: panic! (the 'impossible' happened)
-------------------------------+--------------------------------------------
    Reporter:  guest           |       Owner:                    
        Type:  bug             |      Status:  new               
    Priority:  normal          |   Milestone:                    
   Component:  Compiler        |     Version:  7.4.1             
    Keywords:                  |          Os:  Linux             
Architecture:  x86_64 (amd64)  |     Failure:  Compile-time crash
  Difficulty:  Unknown         |    Testcase:                    
   Blockedby:                  |    Blocking:                    
     Related:                  |  
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Changes (by simonpj):

 * cc: dimitris@… (added)
  * difficulty:  => Unknown


Comment:

 Thanks.  I know what is going on here.  Will fix as part of the
 refactoring Dimitrios is doing on the constraint solver.

 Simon

 Her's a standalone test case
 {{{
 {-# LANGUAGE RankNTypes, TypeFamilies, KindSignatures #-}

 module T5934 where
 import Control.Monad.ST

 data Gen s
 type GenST s = Gen (PrimState (ST s))

 run :: (forall s . GenST s) -> Int
 run = 0

 type family PrimState (m :: * -> *)
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5934#comment:1>
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