[GHC] #1965: Allow unconstrained existential contexts in newtypes

[GHC]

#1965: Allow unconstrained existential contexts in newtypes
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        Reporter:  guest             |            Owner:
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:  7.6.2
       Component:  Compiler          |          Version:  6.8.1
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by heisenbug):

 Replying to [comment:13 pumpkin]:
 > To be clear about what I'm looking for:
 >

 Yes, I always wondered how existentially quantifying over a type
 constructor with non-* domain kinds can ever necessitate extra information
 at runtime. I fully support the reopen proposal because of `data Hidden ::
 k -> * where Hide :: t a -> Hidden t` wants to be a `newtype`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1965#comment:14>
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