[GHC] #12526: regression in type inference with respect to type families

[GHC]

#12526: regression in type inference with respect to type families
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        Reporter:  Lemming           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.2
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      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 Lemming):

 It is pretty strange: If I compile synthesizer-llvm in one go then it can
 be compiled by ghc-8.0.1. Then I alter the problematic module (update of
 date is enough), re-compile, and now surprisingly also ghc-8.0.1 produces
 the same error message. That is, the error already existed in ghc-8.0.1
 but was not always triggered.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12526#comment:2>
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