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Re: Supporting multiple input syntaxes

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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
>
> [Really, it's up to you.  My inclination would be to make them
> separate but use some sort of macro setup so you can insert
> common pieces into each of the grammars. -John]

Gnu Pascal supports several Pascal dialects.  Gnu Pascal uses
unified parser for all dialects.  Some ideas used:
- flags in scanner decide if dialect specific tokens are
  recognized
- superset parsing: several constructs are generalized so
  that single construct represents things that othewise
  would lead to conflits.  Later semantic stage looks at
  dialects flags, prunes things not allowed in given
  dialect.  Example of superset contruction is rule
  'call_or_cast', it handles several syntactically similar
  constructs that are usually given by separate syntax
  rules.  Semantic rules beside dialect flags use types to
  decide of meaning.
- even after usin two tricks above grammar still have
  LALR conflicts, they are resolved using GLR option
  of Bison.  All conflicts are resolvable using lookahead,
  and AFAICS some are only resolvable with lookahead.
  Parser lookahead means that traditional trick of
  passing semantic info back to scanner does not work
  (parser actions are delayed, so scanner may be forced
  to produce token before semantic info is available).
  Still, it seems that GLR leads to cleaner parser.

My impression is that variation in Pascal dialects is larger
than in C dialects, so case for unified parser in C IMHO
is much stronger.  OTOH Gnu Pascal is full compiler with
semantic actions invoked from grammar rules.  Semantic code
embedded in the parser changed much more than grammar rules,
so maintaining separate parsers probably would be a
nightmare.

--
                              Waldek Hebisch

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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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