[il-antlr-interest: 22203] Re: [antlr-interest] Problem when parsing numerics

Mon, 02 Mar 2009 08:31:29 -0800

Thomas Woelfle wrote: 
Hi,

I've been running in an almost similar problem again.

The subject language that has to be parsed defines some keywords which 
begin with a '.'. Besides that there are specific names allowed and '.' 
is allowed to be a token too.

The reduced lexer grammar that produces the problem is:

DOT: '.';

ARG: ('.ARG')=> '.ARG';

ATT: ('.ATT')=> '.ATT';

NAME
  :
  ('A'..'Z')*;
This token allows a match of an empty string and is going to cause all sorts of problems. You want:

NAME : ('A'..'Z')+;

Then if you still have problems, either do:

DOT : '.';
ARG: 'ARG';
ATT : 'ATT';

ident : ID
        | DOT (ARG|ATT)
        ;

Or:

fragment ARG : ;  // Define token number and document
fragment ATT : ; // Define token number and document
DOT : '.'
           (  ('ARG')=>'ARG'  { $type = ARG; }
             | ('ATT')=>'ATT'    { $type = ATT; }
           )
    

Jim

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