[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:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by bgamari):

 I should note that adding an index and `Monad` instance to `Doc` isn't
 entirely trivial. I believe it is possible (and have a patch with much of
 the work) but I haven't yet proven to myself that it will preserve the
 invariants that the Hughes pretty-printer expects.

 There are a few implementations of annotated pretty-printers of various
 flavors on Hackage, but they either provide only `Functor` (e.g.
 [[http://hackage.haskell.org/package/pretty-1.1.3.2/docs/Text-PrettyPrint-
 Annotated.html|pretty]], [[http://hackage.haskell.org/package/annotated-
 wl-pprint-0.6.0/docs/Text-PrettyPrint-Annotated-Leijen.html|annotated-wl-
 pprint]]), or are of the Wadler-Leijan variety (e.g.
 [[http://hackage.haskell.org/package/wl-pprint-extras-3.5.0.5/docs/Text-
 PrettyPrint-Free-Internal.html|wl-pprint-extras]]).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8809#comment:11>
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