[GHC] #10075: Muddling Constraint and * means that Core is inconsistent

[GHC]

#10075: Muddling Constraint and * means that Core is inconsistent
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        Reporter:  goldfire          |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.8.4
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by goldfire):

 If running `coreView` -- the function that unwraps type synonyms before
 inspecting a type -- also returned `Just *` when given `Constraint`, I
 think the problem would be solved. This essentially treats `Constraint` as
 a type synonym for `*` in `coreView`, but not in `tcView`.

 On the other hand, if we implemented this `coreView` idea, then my example
 code wouldn't compile, as the type instances would overlap. From a Haskell
 (as opposed to Core) point of view, the overlap here would be strange, as
 `Constraint` and `*` ''are'' distinct in Haskell.

 Perhaps we really do need kind equalities to sort this one out... :)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10075#comment:2>
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