[GHC] #14859: Allow explicit impredicativity

[GHC]

#14859: Allow explicit impredicativity
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        Reporter:  simonpj           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:
                                     |  ImpredicativeTypes
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):

 Should we allow visible application of polytypes //carte blanche//? What
 happens when visible kind application rolls in and we can write this?

 {{{#!hs
 hm :: forall (f :: forall a. a -> a).
       Proxy @(forall a. a -> a) f
 hm = Proxy
 }}}

 The type `Proxy @(forall a. a -> a) f` seems to have a strongly
 impredicative flavor, but this is only a hunch. What do others think?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14859#comment:4>
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