[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:
       Component:  Compiler          |              Version:  6.8.1
      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 simonpj):

 But the `Some` at the link is this:
 {{{
 data Some tag :: (k -> *) -> * where
   This :: !(tag t) -> Some k tag
 }}}
 There's no reason why this can't be a `newtype` today, is there?

 So it doesn't look relevant to this ticket.  (Except I suppose that if
 comment:9 was implemented, it'd be efficient already.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1965#comment:24>
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