[antlr-interest] Invalid parser generation

[mark4 at voila.fr]

Hi Stefan,

I wanted to revert to your post. You recommended to put the most specific lexer rules first. But how can I do if 2 rules are close, or even identical?

For instance:
DIMENSION : ID;
ITEM : ID;

They automatically generate an error in ANTLR. Of course, this situation seems useless, but in the future, I may modify these rules and make them different. That's the reason why I'd like to distinguish them in the grammar file.

Thanks in advance,
Mark

> Message du 04/09/12 à 15h40
> De : "Stefan Mätje"
> A : antlr-interest at antlr.org
> Copie à : "mark4 at voila.fr"
> Objet : Re: [antlr-interest] Invalid parser generation
>
> Am 04.09.2012 14:35, schrieb mark4 at voila.fr:> Hi Stefan,
> >
> > Thanks for your reply. I didn't understand the difference between
> > lexer rules and parser rules because,
> > in fine, a parser rule will always resolve in a series of lexer
> > rules...
>
> Please don't mix the lexer and the parser phase in your mind. The lexer
> deals with single characters and groups them into tokens.
>
> The parser doesn't know anything about single characters and deals only
> with tokens.
>
> > Anyway, I applied the modification but I now get an error:
> >
> > COMPTE : ('0'..'9')+;
> >
> > ID : ('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'0'..'9'|'_')* ;
> >
> > The following token definitions can never be matched because prior
> > tokens match the same input: COMPTE,ID
>
> You have rules in your grammar before COMPTE and ID that define a
> superset of the character sequences that COMPTE and ID can match.
>
> > Well, I have several entities in my grammar that have different
> > encoding forms, so how can I specify them one after the other?
>
> If at the end one type of token should be produced all needed
> regular expressions have to go into one rule.
>
> > Thanks,
> > Mark
> >
>
> As rule of thumb write the most specific lexer rules first and then
> follow them with the less specific rules. The lexer will give the
> rules first written a higher precedence.
>
> So put your keywords first (which are fixed strings). Then follow them
> with something like operators (also fixed strings). At the lower level
> rules that can match different strings like ID and COMPTE follow.
>
> See what Antlrworks tells you about multiple matches and which rules are
> involved.
>
> Don't know if this may help but the rule that matches both COMPTE and ID
> would be most interesting.
>
> Best regards,
> Stefan
>
> PS.: Please reply also to the list.
>
>

___________________________________________________________
10 conseils pour un ventre plat sur Voila.fr http://actu.voila.fr/evenementiel/beaute-minceur/conseils-ventre-plat/