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Re: Maintaining scope while parsing C with a YACC grammar

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eliben <eliben@gmail.com> writes:

> On Apr 26, 7:22 pm, Robert A Duff <bobd...@shell01.TheWorld.com>
> wrote:
>> I strongly recommend the "build a tree" solution.  It might seem like
>> a lot of trouble at first, but it will simplify things in the long
>> run.
>>
>> Do all the interesting work during a subsequent walk of the tree.  Or
>> multiple walks.
>
> Since it's parsing of C I'm talking about, this approach will have to
> somehow handle ambiguity of this kind:
>
> T * x;

Right, that's what I meant by:

    ...except that C requires some sort of kludgery to
    deal with typedefs.

in my earlier post.

> This can be either a declaration or a multiplication, depending on
> earlier symbol table information (whether T is a type or not).
>
> So are you proposing to build an ambiguous AST that contains *both*
> parses and resolve between them in later passes?

I have never seen a C parser that does that.  I've seen Ada parsers
that do that (Ada has an ambiguous grammar, too).  The idea is that
you create a single tree node that represents "this or that", and
during semantic analysis, you transform it into a "this" or a "that"
tree.  It works well for Ada.  I don't know how well it would work for
C.

The typical approach for C is to do as you say -- put typedefs in the
symbol table, and have them affect the parse (or really, the lexer).

In any case, I stand by my statement, 'I strongly recommend the "build a
tree" solution.' even for C.  Defer as much as possible of semantic
analysis until after parsing, where "as much as possible" is not
necessarily "all of it".

>... Or just pick one and maybe modify it later?

That's possible, but kind of kludgy.

>...Do you have references (papers, books, etc.)
> explaining this technique?

No, sorry.  I'd be interested to hear if anybody built a C parser that
didn't use any feedback into the parser from a symbol table to deal
with the typedef issue.

- Bob

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Thread

Maintaining scope while parsing C with a YACC grammar eliben <eliben@gmail.com> - 2011-04-25 05:14 -0700
  Re: Maintaining scope while parsing C with a YACC grammar Robert A Duff <bobduff@shell01.TheWorld.com> - 2011-04-26 12:22 -0400
    Re: Maintaining scope while parsing C with a YACC grammar Robert A Duff <bobduff@shell01.TheWorld.com> - 2011-04-26 14:08 -0400
    Re: Maintaining scope while parsing C with a YACC grammar eliben <eliben@gmail.com> - 2011-04-28 23:20 -0700
      Re: Maintaining scope while parsing C with a YACC grammar Robert A Duff <bobduff@shell01.TheWorld.com> - 2011-05-02 20:19 -0400
        Re: Maintaining scope while parsing C with a YACC grammar "Ira Baxter" <idbaxter@semdesigns.com> - 2011-05-13 17:46 -0500
        Maintaining scope while parsing C with a Yacc grammar Chris F Clark <cfc@shell01.TheWorld.com> - 2011-06-12 20:43 -0400
      Re: Maintaining scope while parsing C with a YACC grammar torbenm@diku.dk (Torben Ægidius Mogensen) - 2011-05-03 09:51 +0200
  Re: Maintaining scope while parsing C with a YACC grammar Paul B Mann <paul@paulbmann.com> - 2011-05-06 10:43 -0700

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