[GHC] #9628: Add Annotations to the AST to simplify source to source conversions

[GHC]

#9628: Add Annotations to the AST to simplify source to source conversions
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              Reporter:  alanz       |            Owner:  alanz
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.9
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:  D297        |
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Comment (by NeilMitchell):

 Why does the user require consulting parser.y.pp? Things like the Let
 constructor obviously have a Let keyword and an In keyword. Things like
 instance declaration obviously have Instance and Where. They seem fairly
 predictable, and if you do want to comment it, that could be as short as
 "-- instance ... [where]". Or do you have in mind nodes which wouldn't be
 as clear, or places where the thing you are indexing isn't so obviously a
 keyword?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9628#comment:20>
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