[GHC] #14961: QuantifiedConstraints: introducing classes through equality constraints fails

[GHC]

#14961: QuantifiedConstraints: introducing classes through equality constraints
fails
-------------------------------------+-------------------------------------
        Reporter:  mrkgnao           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.5
      Resolution:                    |             Keywords:
                                     |  QuantifiedConstraints wipT2893
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14860            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 It's fine; did not take long.  If the code above reflects something you
 want to do, I could just add it to our regression tests.  It seems to be a
 relatively sophisticated use of `QuantifiedConstraints`!

 I'm not following the details but I'm sure that you and Iceland Jack will
 tell us if any further infelicities show up.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14961#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler