[antlr-interest] Re: lexical nondeterminism

[howardk at fatdog.com]

Matthew, that's brilliant. Thanks. It's obvious when you see it!

Howard

--- "Matthew Ford" <Matthew.Ford at f...> wrote:
> I think it is
> > QName: (NCName COLON)? NCName;
> Antlr does not know which NCName to choose
> 
> try
>  QName: NCName (COLON NCName)?;
> 
> now COLON tell antlr to continue looking
> 
> matthew

> ----- Original Message -----
> From: <howardk at f...>
> 
> > Sigh, I hate to bother people with this one. I thought I'd gotten
> > reasonably ok at working out nondeterminism problems, but I can't 
see
> > why the following (slightly simplified) lexical grammar isn't
> > working. antlr is complaining about the production QName. 
Lookahead
> > is k=2.
> >
> > QName: (NCName COLON)? NCName;
> >
> > protected
> > NCName: ( Letter | '_' ) (NCNameChar)*;
> >
> > protected
> > NCNameChar: Letter | Digit | DOT | '-' | '_';
> >
> > protected
> > Letter: 'A' .. 'Z';
> >
> > Here's the message I get:
> >
> > warning: lexical nondeterminism upon
> > k==1: 'A' .. 'Z', '_'
> > k==2: '-','.','0'..'9','A'..'Z','_'
> > between alts 1 and 2 of block
> >
> > I know this isn't hard, but I'm going blind (and I'm not even 
doing
> > THAT!) Any help much appreciated,
> >
> > Howard
> >
> >
> >
> >
> >
> > Your use of Yahoo! Groups is subject to 
http://docs.yahoo.com/info/terms/
> >
> >


 

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