[GHC] #11028: Refactor ConDecl

[GHC]

#11028: Refactor ConDecl
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        Reporter:  simonpj           |                Owner:  alanz
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              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 simonpj):

 Replying to [comment:22 alanz]:
 > Ok, the problem is in `rnConDecl` in the `ConDeclGADT` case, which in
 this branch simply calls `rnHsSigType`.
 >
 > Instead it should perform as per the original, which splits the result
 type,leaving it as `MaybeO ex t` in this case.

 Wait!  Why?  What would the difference be in the result of `rnConDecl`?
 I'm suspicious; I'd like to understand better.  An example perhaps?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11028#comment:23>
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