[GHC] #15590: Existentials in newtypes

[GHC]

#15590: Existentials in newtypes
-------------------------------------+-------------------------------------
           Reporter:  NioBium        |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Compiler       |           Version:  8.4.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Please allow existential quantification of phantom type arguments in
 newtypes.

 {{{
 type role A nominal representational phantom -- Or inferred roles.
 newtype B a b where
   B :: A a b c -> B a b
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15590>
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