[GHC] #9804: Layering: Suspicious dependency from Parser to TcEvidence

[GHC]

#9804: Layering: Suspicious dependency from Parser to TcEvidence
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              Reporter:  rodlogic    |            Owner:
                  Type:  bug         |           Status:  closed
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
            Resolution:  invalid     |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Changes (by simonpj):

 * status:  new => closed
 * resolution:   => invalid


Comment:

 Fair point, but there is a good reason for this.  The same `HsSyn` syntax
 tree is used for
  * The output of the parser
  * The output of the renamer
  * The output of the typechecker

 The latter, in particular, decorates the tree with information generated
 by the typechecker; the data types for much of that information is in
 `TcEvidence`.

 There are alternatives, of course.  Eg have three data types not one; or
 use more aggressive parameterisation. But the cure seems worse than the
 disease.

 By all means suggest improvements, but I'll close this for now as "by
 design".

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9804#comment:2>
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