[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 alanz):

 Replying to [comment:20 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?

 Some of the structures are nested quite deeply, an/or reused in multiple
 roles. But I think anyone working at the detail level of the annotations
 is going to be looking closely at the relationship between the source, the
 parse tree and the annotations anyway, so it should not be a problem.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9628#comment:22>
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