[GHC] #12734: Missed use of solved dictionaries leads to context stack overflow

[GHC]

#12734: Missed use of solved dictionaries leads to context stack overflow
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        Reporter:  danilo2           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by danilo2):

 simonpj: thank you for a fast fix, I'm building head at the moment and
 I'll try it here!
 By the way, based on your description it reminded me about other bug I
 filled some time ago. Do you think it could be connected? It is not a high
 priority bug, but if it's connected maybe it's worth to mention it:
 https://ghc.haskell.org/trac/ghc/ticket/10778

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12734#comment:13>
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