[antlr-interest] Re: Determinig the real ambiguities

[Terence Parr]

On Jul 15, 2004, at 3:46 PM, thrutchy wrote:

> --- In antlr-interest at yahoogroups.com, Terence Parr <parrt at c...> wrote:
>> It is. ;)  However, the new ANTLR 3.0 prototype handles this situation
>> trivially.  It tries more and more lookahead until it realizes it 
>> needs
>> arbitrary lookahead and then it builds a tight little DFA that walks
>> out until it sees the C or D and then it knows which production will
>> succeed using real parsing.
>
> Very nice.  I think this will help out quite a bit.  I assume you will
> still be able to have it let you know when it is resorting to this so
> that the grammar can be refactored to not do the DFA thing and be
> faster.   Or better yet, have ANTLR do the refactoring for at least
> simple cases...

ANTLR will be able to profile your grammar and even be able to tell you 
if it's fixed k or arbitrary lookahead for each decision point.  
Refactoring is something that Loring Craymer is all hot-n-bothered 
about. :)

> How do yo see ANTLR 3.0 comparing to Perl 5.6+ regular expressions?

ANTLR will always have less bells and whistles than PERL.  I like 
simplicity.  Plus, perl has to overcome lack of a real parser (though I 
hear they are making one) with complicated regular expressions.  
Lookback / ahead in perl are primarily used I'm sure to make up for the 
fact that you don't have a real grammar giving you context information.

> Do you see the parser and lexer in ANTLR becoming one in the same at
> some point?

Yes, a unified parser/lexer is planned.

>   One could choose what the input (character or token
> stream, etc) and output (token stream or AST) would be.
>
> Do you have a feature list of ANTLR 3.0 around somewhere?

Not really ;)  You can look at the cabal notes and other stuff on the 
blog

http://www.antlr.org/blog/index.tml

> Thanks for the tool, Terrance!

At your service,

Terence
--
CS Professor & Grad Director, University of San Francisco
Creator, ANTLR Parser Generator, http://www.antlr.org
Cofounder, http://www.jguru.com
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