[antlr-interest] How to skip evaluating part of a rule?

[Marcin Rzeźnicki]

On Fri, May 14, 2010 at 6:25 PM, Charles Chan <chancharles at gmail.com> wrote:
> Hi, all. I have a parser optimization question for you guys. In my
> grammar (below), I have to evaluate an OR condition and an AND
> condition. We all know that "true OR true/false" is always true and
> "false AND true/false" is always false. So, technically, if I can skip
> evaluating RHS under those conditions.
>
> Is there a way for me to incorporate this kind of optimization in my
> grammar? Currently, I am retrieving the values from a Map so that
> performance is okay but I plan to retrieve them from DB, so any
> optimization to skip the retrieval process would be great.
>
> Any idea?
>

Sync to follow set if you have simple rules, where no element of
follow can possibly be present within the rule you're escaping from.
In your case you can freely sync to ';' so that should solve your
problems. In any case you can define special flag, like SKIPPING_STATE
= 10000; - set backtracking state to this value so you know that you
are escaping and continue with parsing, no actions will be taken so
you should be fine with this solution to. Just remember to unset
backtracking state on exit.


-- 
Pozdrawiam
Marcin Rzeźnicki