Skip subtree in Listener ANTLR4

Question

Is there any Way to skip the parsing of specific block while using Listener in ANTLR4 using enter or exit method. I have read link here but unable to make it work. Thank You!

Answer 1

By the time you're using the Listener pattern with your own Listener class, the input is already correctly lexed and parsed. Therefore, the answer to your question is no. When you're using the listener you're typically just walking the tree post-parse.

Does that mean all is lost though? Of course not. All you have to do is simply not code the Enter or Exit events for those constructs you want to "ignore." It's that easy.

As to if-else statements, I've always implemented them using the visitor pattern like this:

As to how to program an if statement, I'll give you a peek at they way I implement them:

    public override MuValue VisitIfstmt(LISBASICParser.IfstmtContext context)
    {
        LISBASICParser.Condition_blockContext[] conditions = context.condition_block();
        bool evaluatedBlock = false;
        foreach (LISBASICParser.Condition_blockContext condition in conditions)
        {
            MuValue evaluated = Visit(condition.expr());
            if (evaluated.AsBoolean())
            {
                evaluatedBlock = true;
                Visit(condition.stmt_block());
                break;
            }
        }
        if (!evaluatedBlock && context.stmt_block() != null)
        {
            Visit(context.stmt_block());
        }
        return MuValue.Void;
    }

Granted, this probably doesn't make much sense out of context, but rest assured it works. To see this in its full context, please visit Bart Kiers for an excellent example of grammar and implementation .