[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.
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        Reporter:  ekmett            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       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:                    |
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Comment (by simonpj):

 > I've yet to figure out why the shorter example passes, but the longer,
 which doesn't seem to change the part that spins forever fails.

 I explain precisely this in comment:14 above.  You (implicitly) claim that
 there is a finite number of superclasses. I claim the contrary.  We can't
 both be right :-).

 Maybe there's a bug in the example `Categories.h`?  That's my current
 belief.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11523#comment:23>
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