Re: Supporting multiple input syntaxes

From	Kaz Kylheku <793-849-0957@kylheku.com>
Newsgroups	comp.compilers
Subject	Re: Supporting multiple input syntaxes
Date	2020-08-13 00:43 +0000
Organization	Aioe.org NNTP Server
Message-ID	<20-08-003@comp.compilers> (permalink)
References	<20-08-002@comp.compilers>

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On 2020-08-12, luser droog <mijoryx@yahoo.com.dmarc.email.dmarc.email> wrote:
> I've got my project successfully parsing the circa-1975 C syntax
> from that old manual. I'd like to add parsers for K&R1 and c90
> syntaxes.
>
> How separate should these be? Should they be complete
> separate grammars, or more piecewise selection?
>
> My feeling is that separating them will be less headache, but maybe
> there's some advantage to changing out smaller pieces of the grammar
> in that it might be easier to make sure that they produce the same
> structure compatible with the backend.
>
> Any guidance in this area?
>
> https://github.com/luser-dr00g/pcomb/blob/master/pc9syn.c

I'd say that since you're not using a parser generator, but using code
statements to construct the grammar objects at initialization time, you
have the flexibility to merge the implementation, because you can check
the value of some dialect-selecting variable, and construct the parser
accordingly, and elsewhere check that same variable to do whatever else
needs to be done conditionally.

The trick is to find a way to embed the *semantics* of the older dialects
into the new so then everything after the parsing can be shared.

Similar remarks would apply to recursive descent.

If you were using something clunky like a Yacc, there are still ways
to combine everything into a single grammar. The input stream can be
primed with one of several "secret internal token" objects that has no
lexeme. (Primed, meaming that the first call to the lexer yields this
secret token instead of processing actual input.) Each token indicates
a dialect to parse. The top-level grammar production can then pick
one of several subordinate production rules corresponding to the entry
points for the respective dialects.  Those can then share common rules
as much as possible.

  translation_unit : C75_TOKEN c75_translation_unit /* orig flavor */
                   | C79_TOKEN c79_translation_unit /* "K&R" */
                   | C90_TOKEN c90_translation_unit /* ANSI/ISO */
                   ;

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Thread

Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-12 15:20 -0700
  Re: Supporting multiple input syntaxes Kaz Kylheku <793-849-0957@kylheku.com> - 2020-08-13 00:43 +0000
  Re: Supporting multiple input syntaxes Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2020-08-13 10:27 +0200
    Re: Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-13 21:36 -0700
    Re: Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-23 22:16 -0700
  Re: Supporting multiple input syntaxes minforth@arcor.de - 2020-08-13 14:15 -0700
    Re: Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-13 21:37 -0700
    RE: Supporting mulitple input syntaxes Christopher F Clark <christopher.f.clark@compiler-resources.com> - 2020-08-14 12:44 +0300
  Supporting multiple input syntaxes David Lovemore <davidlovemore@gmail.com> - 2020-08-15 06:42 -0700
    Re: Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-15 15:20 -0700
      Re: Supporting multiple input syntaxes David Lovemore <davidlovemore@gmail.com> - 2020-08-16 02:21 -0700
        Re: Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-20 14:45 -0700
          Re: Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-23 19:35 -0700
            Re: implementation languages, was Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-23 20:39 -0700
              Re: implementation languages, was Supporting multiple input syntaxes Thomas Koenig <tkoenig@netcologne.de> - 2020-08-24 17:01 +0000
                Re: implementation languages, was Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-28 10:56 -0700
              Re: stack languages, was Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-24 12:14 -0700
  Re: Supporting multiple input syntaxes gah4 <gah4@u.washington.edu> - 2020-08-23 14:26 -0700
  Re: Supporting multiple input syntaxes antispam@math.uni.wroc.pl - 2021-02-11 23:27 +0000
    Re: Supporting multiple input syntaxes Elijah Stone <elronnd@elronnd.net> - 2021-02-17 01:44 -0800
      Re: Supporting multiple input syntaxes antispam@math.uni.wroc.pl - 2021-02-23 23:28 +0000
        Re: Supporting multiple input syntaxes "ltc...@gmail.com" <ltcmelo@gmail.com> - 2021-03-14 21:08 -0400
  Re: Supporting multiple input syntaxes Rock Brentwood <rockbrentwood@gmail.com> - 2021-03-14 17:36 -0700

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