[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 niteria):

 > It seems that this might be related to the work that Bartosz has done in
 making GHC more deterministic.

 > That is, the error already existed in ghc-8.0.1 but was not always
 triggered.

 Most of the determinism patches were merged *after* ghc-8.0.1, so it
 sounds unlikely. My best bet would be that some exposed thing isn't
 recorded in the interface file.

 Lemming: Can you provide step by step repro?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12526#comment:4>
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