[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 simonpj):

 In the ''worker'', I'm sure we should put the universals first.  We always
 have, and I see no reason to change.  Moreover in a pattern we drop the
 universals, so it must be easy to find them.

 In the ''wrapper'' can't we just do whatever we do for normal type
 signatures. Eg
 {{{
 data T a b where
   T1 :: T [x] [x]
   T2 :: T [x] y
 }}}
 Here we just get `T1 :: forall x. T [x] [x]` and `T2 :: forall x y. T [x]
 y`.  If those were ordinary functions we'd be done. So why aren't we done?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11513#comment:1>
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