[GHC] #10828: TH could do a better job of representing GADTs

[GHC]

#10828: TH could do a better job of representing GADTs
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        Reporter:  spinda            |                Owner:  jstolarek
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Template Haskell  |              Version:  7.10.2
      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 jstolarek):

 My proposal would be to add the following constructor to `Con` data type:

 {{{#!hs
    | GadtC Name [StrictType] [Type]
 }}}
 where the last field stores list of constructor indices.  Once we have
 this new constructor I would modify `DsMera` and `Convert` accordingly.
 Most importantly, GADT declarations would be now translated to use this
 new constructor instead of encoding that uses `ForallC` and `NormalC`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10828#comment:9>
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