[GHC] #16148: Better type inference for Constraint vs Type

[GHC]

#16148: Better type inference for Constraint vs Type
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        Reporter:  simonpj           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.3
      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 simonpj):

 > (C) doesn't work

 Are you sure?  I was not expecting any quantification whatsoever over the
 T/C thing.  You say "don't worry about levity polymorphism", but the
 example you give is explicitly ruled out by our lev-poly story.  Can you
 give an example that would be allowed by lev-poly but would give rise to
 instantiation problems?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16148#comment:2>
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