[GHC] #13135: Typechecker "panic! the 'impossible' happened"

[GHC]

#13135: Typechecker "panic! the 'impossible' happened"
-------------------------------------+-------------------------------------
        Reporter:  Saulzar           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.2
  checker)                           |
      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):

 OK this is a real bug, to do with the implementation of injective type
 families.  I'm struggling with time, but I at least understand the problem
 -- thank you!

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13135#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler