[GHC] #11513: Work out when GADT parameters should be specified

[GHC]

#11513: Work out when GADT parameters should be specified
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        Reporter:  goldfire          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
                                     |  TypeApplications
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 goldfire):

 {{{
 data G a where
   MkG :: forall b a. b -> a -> G a
 }}}

 Currently, no wrapper is required here. Note that `G` is not a GADT. The
 worker has type `forall a b. b -> a -> G a`, with universals before
 existentials. Because we have no wrapper, the user sees the worker type.

 I'm proposing making a wrapper in this case.

 Does that clarify?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11513#comment:4>
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