[GHC] #13895: "Illegal constraint in a type" error - is it fixable?

[GHC]

#13895: "Illegal constraint in a type" error - is it fixable?
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
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):

 Interesting. Simon once [https://mail.haskell.org/pipermail/ghc-
 devs/2016-September/012824.html commented] that using `TypeApplications`
 to call a polymorphic function at a polymorphic type fell under a safe
 subset of `ImpredicativeTypes` (that ought not require bringing in the
 other baggage that `ImpredicativeTypes` implies). If we had this
 capability, would `Typeable @(forall k. k -> Type) t` be a thought GHC
 could think? (I realize that we don't yet have visible kind applications,
 but you get the idea.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13895#comment:2>
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