[GHC] #14247: Fails to coerce between newtypes directly

[GHC]

#14247: Fails to coerce between newtypes directly
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      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 goldfire):

 The `Coercible` solver is incomplete when recursive newtypes come into
 play. We admit this in the JFP paper. I don't know how to do better. And
 I'm pretty sure the problem is undecidable, anyway.

 Did this come up in the wild?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14247#comment:1>
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