[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:  7.12.1
       Component:  Compiler          |                 Version:  6.8.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by oerjan):

 Replying to [comment:9 simonpj]:
 >  2. Only one field with nonzero width in that constructor (counting
 constraints as fields)

 I'd like to point out (as may already have been indented), that read
 literally, this should include things like

 {{{
 data Dict :: Constraint -> * where
   Dict :: a => Dict a
 }}}

 from the `constraints` package.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1965#comment:19>
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