[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:  highest           |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  8.0.1-rc1
  checker)                           |             Keywords:
      Resolution:                    |  UndecidableSuperClasses
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11480            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"8871737db588b1cb8f7d33d60c5af80b85b2422d/ghc" 8871737/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="8871737db588b1cb8f7d33d60c5af80b85b2422d"
 Document and improve superclass expansion

 When investigating Trac #11523 I found that superclass
 expansion was a little over-aggressive; we were sort of
 unrolling each loop twice.

 This patch corrects that, and adds explanatory comments.
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11523#comment:4>
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