I'm with mpickering on this one. Each stage has a debug format that makes sense for the stage.  For parsing it is the exact ast

Alan

On 18 May 2016 12:43 PM, "GHC" <ghc-devs@haskell.org> wrote:
#11140: add command-line option to GHC to dump raw parse trees of Haskell programs
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        Reporter:  bollu             |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by mpickering):

 That is true but by them stages in the compilation pipeline you don't care
 about what the raw format looks like. When modifying the parser  you need
 to know the precise structure of the AST rather than some pretty printed
 version produced by `Outputtable`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11140#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler