From: Robert Feldt <feldt@...>
Date: 2001-10-30T20:28:54+09:00
Subject: [ruby-talk:23833] Re: GUI for Ruby

On Tue, 30 Oct 2001, hipster wrote:

> JFYI: ANTLR should be able to handle any type 0-3 grammar using
> semantic and syntactic predicates, multiple parsers/lexers, AST
> transformations, &c. Still extra work, but no need to rewrite the
> grammar.
> 
Maybe we are misunderstanding each other but I would consider this extra
work a rewrite of the grammar since when I have a grammar in my head there
is no need for syntactic predicates, multiple lexers etc. If you need it
to describe the grammar then the tool adds unnecessary things. I'm not
saying its evil (since you would typically get better performance by
describing things in more detail) just that it adds things so its no
simpler.

The only situation were you *HAVE* to add things to your grammar
is if it is ambigous and you want the parser to return only one tree. All
other situations are tool-specifics.

The big drawback with GLR and Early parsing is that the algorithmic
complexity is higher for *some* grammars, ie. parsing can take *long*
time. However, in practice these grammars are rare. Another drawback is
that we have less experience with these algorithms so there are still
implementation issues etc. You might want to check out the article "Why
Bison is becoming extinct" at
http://www.acm.org/crossroads/xrds7-5/bison.html for some info
relating to this. However, he doesn't mention ANTLR. If you want to check
out mature GLR and Early parser gens you might take a look at Accent and
ASF+SDF. Sorry if this is already familiar to you.

I'm unfamiliar with the term "type 0-3" grammar. How does it relate to
Context-freeness an LL(k), LALR(k) etc?

Oh, and ANTLR seems to be a really powerful tool. And its a plus you get
parser that can be read by a human (compared to table-based ones). I
especially like the rewrite stuff in there and how you can use the same
formalism both for lexing and parsing. Cool stuff.

Regards,

Robert