[GHC] #15628: Higher-rank kinds

[GHC]

#15628: Higher-rank kinds
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.6.1-beta1
      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 Iceland_jack):

 I should have known. I can close it or label it with imprediativity,

 I still find it mysterious that

 {{{#!hs
 -- works
 newtype Bar = Bar (forall (f :: FOO). ())
 }}}

 adding a `Proxy` induces an existential variable `x` seemingly without
 introducing quantification, but this is maybe a problem with my intuition?
 Or at least something rings odd about this (then again higher-rank kinds
 are odd and interesting)

 {{{#!hs
 -- oops, you are actually writing
 --   Proxy @(x -> Type) (f @x)
 newtype Bar = Bar (forall (f :: FOO). Proxy f -> ())
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15628#comment:2>
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