[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:  7.8.3
             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:              |
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Comment (by simonpj):

 Whoa!  There appear to be two quite separate things going on here:
  * In [wiki:GhcAstAnnotations] the issue is attaching a `SrcSpan` to
 keywords
  * In comment:1 the issue appears to be about attaching an annotation of
 client-specified type to every node in the tree.

 These seem quite orthogonal to me.

 For the latter I would suggest looking at the `Located` type, instead of
 what you suggest in comment:1.  The `Located` type is wrapped around
 almost every node in the tree, and if you want to add some ubiquitous
 annotation type, it would be the place to do so.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9628#comment:3>
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