[GHC] #11523: Infinite Loop when mixing UndecidableSuperClasses and the class/instance constraint synonym trick.

[GHC]

#11523: Infinite Loop when mixing UndecidableSuperClasses and the class/instance
constraint synonym trick.
-------------------------------------+-------------------------------------
        Reporter:  ekmett            |                Owner:  simonpj
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.0.1-rc1
  checker)                           |             Keywords:
      Resolution:                    |  UndecidableSuperClasses
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC rejects       |            Test Case:
  valid program                      |  polykinds/T11523
      Blocked By:                    |             Blocking:
 Related Tickets:  #11480            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 I guess so.  Can you offer an example?

 So far we we have precisely one example needing the magic... more examples
 would strengthen the case for making a change.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11523#comment:31>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler