[GHC] #8809: Prettier error messages?

[GHC]

#8809: Prettier error messages?
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        Reporter:  joelteon          |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.9
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
  #8809,#10073,#10179                |
       Wiki Page:                    |
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Comment (by thomie):

 Replying to [comment:19 niteria]:
 > Does anyone know if they diverged in functionality/semantics? If not,
 would it be a useful step to migrate GHC's `Doc` to annotated version?

 In #10735, I made GHC's copy of `pretty` pretty much the same as
 pretty-1.2.0, except GHC's copy uses `FastString` instead of `String`.

 pretty-1.2.1 has 2 more commits, but I didn't apply them because of
 performance worries (`compiler/utils/Pretty.hs` is incredibly performance
 sensitive!), see ticket:10735#comment:23.

 Right after pretty-1.2.1, those annotations were added.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8809#comment:20>
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