[GHC] #14323: Occurs check regressions in GHC 8.2.1 (and HEAD)

[GHC]

#14323: Occurs check regressions in GHC 8.2.1 (and HEAD)
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.2.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 I'm quite confused. Why should an occurs check ever fire in the first
 place for `b ~R# f b`? This is a perfectly legitimate constraint that can
 be witnessed, for instance, by letting `f` be `Identity` (since `b` is
 representationally equal to `Identity b`). Thus, I'd argue that `hm2` and
 `hm3` are //not// wrong programs.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14323#comment:4>
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