[antlr-interest] Understanding priorities in lexing (newbie) [Suggestion]

[Terence Parr]

On Jul 13, 2007, at 10:18 AM, Susan Jolly wrote:

> I really appreciate people who take the time to write the simplest  
> possible
> grammar that illustrates the problem they are having rather than  
> embedding
> huge grammars in their posts.

Hi Susan!  Agreed.

> Here is one way to get v3 to generate the code so the lexer looks  
> ahead for
> the original example.  Is there any reason not to do this?
>
> fragment KEYWORD : 'a' 'b' 'c' ;
> fragment OTHER : 'a' | 'b' | 'c';
> DUMMY : (  (KEYWORD) => KEYWORD {$type = KEYWORD;}
>         |  OTHER  {$type = OTHER;}
>         );

That is a correct grammar.  Note that the following is not really  
going to work:

DUMMY
options {backtrack=true;}
	: (KEYWORD {$type = KEYWORD;}  | OTHER{$type = OTHER;})
	;

it will not execute the backtracking in this case as it thinks it  
knows what it's doing. :(

Ter