Re: Recursive descent parsing and optimization, was Good practical language and OS agnostic text?

From	"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups	comp.compilers
Subject	Re: Recursive descent parsing and optimization, was Good practical language and OS agnostic text?
Date	2012-04-22 18:18 +0200
Organization	cbb software GmbH
Message-ID	<12-04-069@comp.compilers> (permalink)
References	<12-04-019@comp.compilers> <12-04-056@comp.compilers> <12-04-060@comp.compilers> <12-04-066@comp.compilers>

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On Sun, 22 Apr 2012 12:51:44 +0100, BartC wrote:

> "BGB" <cr88192@hotmail.com> wrote in message
>> On 4/21/2012 2:22 AM, Uli Kusterer wrote:
>
>> although I use recursive descent, the above sounds different from what I
>> usually do.
>
>> ReadStatement:
>>   checks for and handles vaious statement types
>>   calls ReadExpression
>>
>> ReadExpression:
>>   (actually, this is a tower of functions, one for each precedence
>> level, working from lowest to highest precedence)
>
> Sounds like it's influenced by the C grammar, which defines expressions
> using something like 13 or 17 layers of precedence.

Rather by an attempt to describe precedence using grammar means.

> Beyond about 3-4 levels, I found that unmanageable. For expression syntax, I
> don't use any precedence in the grammar at all; I have precedence as an
> attribute of an operator, and an expression can be parsed with a single
> function.

Yes, there is a very simple technique using two stacks, one for operands
another for operations.

> Or rather two: readfactor(priority), and readterm(). Readfactor() deals with
> the  binary operators linking successive terms, while readterm() does all
> the real work (since my syntax doesn't distinguish between expressions and
> statements, that's quite a big workload).

Actually operations have two priorities; left and right. When left < right
you have left to right association. When right > left, it becomes right to
left.

Some operators may have these priorities sufficiently different. For
example the assignment operator. If your unlucky languages allows it, then
A+B = C+D better be A+(B=(C+D)). That would require the following order of
partial priorities:

   LP("=") << LP( "+")  < RP("+")  << RP("=")

> Instead I read them as I go along, but with provision for a one-symbol
> look-ahead.

Same here. Except that I have one token look-ahead.

--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

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Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-17 21:28 +0000
  Re: Good practical language and OS agnostic text? Philip Herron <redbrain@gcc.gnu.org> - 2012-04-18 14:25 +0100
    Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-19 16:32 +0000
      Re: Good practical language and OS agnostic text? arnold@skeeve.com (Aharon Robbins) - 2012-04-20 03:58 +0000
        Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-22 10:10 +0000
      Re: Good practical language and OS agnostic text? "BartC" <bc@freeuk.com> - 2012-04-20 09:45 +0100
        Re: Good practical language and OS agnostic text? "Jonathan Thornburg" <jthorn@astro.indiana.edu> - 2012-04-21 15:04 +0000
  Re: Good practical language and OS agnostic text? BGB <cr88192@hotmail.com> - 2012-04-18 08:39 -0700
    Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-19 17:32 +0000
  Re: Good practical language and OS agnostic text? Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2012-04-18 18:24 +0200
    Re: Good practical language and OS agnostic text? Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2012-04-19 13:53 +0200
      Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-21 03:07 +0000
      Re: Good practical language and OS agnostic text? "BartC" <bc@freeuk.com> - 2012-04-21 12:01 +0100
        Re: code quality, was Good practical language and OS agnostic text? Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2012-04-22 12:41 +0200
    Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-19 11:31 +0000
      Re: Good practical language and OS agnostic text? "Jonathan Thornburg" <jthorn@astro.indiana.edu> - 2012-04-20 16:19 +0000
  Re: Good practical language and OS agnostic text? "Derek M. Jones" <derek@knosof.co.uk> - 2012-04-18 18:16 +0100
    Re: Good practical language and OS agnostic text? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-04-18 22:43 +0000
      Re: Good practical language and OS agnostic text? BGB <cr88192@hotmail.com> - 2012-04-19 00:05 -0700
      Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-19 11:31 +0000
    Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-19 16:32 +0000
  Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-18 19:30 +0000
    Re: Good practical language and OS agnostic text? "BartC" <bc@freeuk.com> - 2012-04-19 18:43 +0100
  Re: Good practical language and OS agnostic text? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-04-18 20:29 +0000
    Re: Good practical language and OS agnostic text? Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2012-04-19 14:20 +0200
    Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-19 19:05 +0000
      Re: Good practical language and OS agnostic text? Uli Kusterer <ulimakesacompiler@googlemail.com> - 2012-04-21 11:30 +0200
  Re: Good practical language and OS agnostic text? Roberto Waltman <usenet@rwaltman.com> - 2012-04-18 22:00 -0400
    Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-19 11:31 +0000
      Re: Good practical language and OS agnostic text? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-04-20 07:02 +0000
        Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-22 11:10 +0000
          Re: Good practical language and OS agnostic text? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-04-22 23:56 +0000
        Re: PL/360, was Good practical language and OS agnostic text? ArarghMail204@Arargh.com - 2012-04-24 19:13 -0500
  Re: Good practical language and OS agnostic text? Bakul Shah <usenet@bitblocks.com> - 2012-04-18 21:15 -0700
    Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-20 16:06 +0000
  Re: Good practical language and OS agnostic text? torbenm@diku.dk (Torben Ægidius Mogensen) - 2012-04-19 14:58 +0200
    Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-20 16:06 +0000
  Re: Good practical language and OS agnostic text? "Joe Schmo" <askmeforit@myisp.com> - 2012-04-21 02:53 -0600
    Re: Writing parsers, was Good practical language and OS agnostic text? Uli Kusterer <ulimakesacompiler@googlemail.com> - 2012-04-22 16:18 +0200
    Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-23 19:12 +0000
  Re: Good practical language and OS agnostic text? Uli Kusterer <ulimakesacompiler@googlemail.com> - 2012-04-21 11:22 +0200
    Re: Good practical language and OS agnostic text? BGB <cr88192@hotmail.com> - 2012-04-21 18:58 -0700
      Re: writing interpreters, was Good practical language and OS agnostic text? Uli Kusterer <ulimakesacompiler@googlemail.com> - 2012-04-22 12:53 +0200
        Re: writing interpreters, was Good practical language and OS agnostic text? BGB <cr88192@hotmail.com> - 2012-04-22 12:29 -0700
      Re: generating bytecode, was Good practical language and OS agnostic text? Uli Kusterer <ulimakesacompiler@googlemail.com> - 2012-04-22 13:12 +0200
      Re: Recursive descent parsing and optimization, was Good practical language and OS agnostic text? "BartC" <bc@freeuk.com> - 2012-04-22 12:51 +0100
        Re: Recursive descent parsing and optimization, was Good practical language and OS agnostic text? "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-04-22 18:18 +0200
          Re: Recursive descent parsing and optimization, was Good practical language and OS agnostic text? "Bartc" <bartc@freeuk.com> - 2012-04-23 10:59 +0100
        Re: Recursive descent parsing and optimization, was Good practical language and OS agnostic text? BGB <cr88192@hotmail.com> - 2012-04-22 13:45 -0700
    Re: Good practical language and OS agnostic text? compilers@is-not-my.name - 2012-04-22 22:11 +0000
      Re: Good practical language and OS agnostic text? "BartC" <bc@freeuk.com> - 2012-04-23 18:41 +0100
  Re: Good practical language and OS agnostic text? basile@starynkevitch.net - 2012-05-02 22:16 -0700
    Re: Good practical language and OS agnostic text? Johann 'Myrkraverk' Oskarsson <johann@2ndquadrant.com> - 2012-06-06 16:52 +0000

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