Antlr 3.2 Rewrite Rules

Question

I've recently started learning Antlr and downloading AntlrWorks 1.4 which supposedly includes Antlr 3.2. Now, 3.2 is supposed to support the rewrite rules grammars like '->' but I've not been able to get even the simplest case I could construct to work either based on Lexer or Parser rules:

grammar TestRewrite;

ab  :   a b -> a;

a   :   A;
b   :   B;

A   :   'a';
B   :   'b';

When I try to compile this, I get the error:

[11:26:29] error(100): TestRewrite.g:3:13: syntax error: antlr: TestRewrite.g:3:13: unexpected token: a

Why is this. The construction seems simple enough: ab should generate a tree where only the a node is captured. Isn't that how you do it? I can't get it to work with rooting ('^') or ignoring ('!') either. I've very confused.

Answer 1

options {output=AST;}