ANTLRWorks :Can't get operators to work - antlr

Question

I've been trying to learn ANTLR for some time and finally got my hands on The Definitive ANTLR reference.
Well I tried the following in ANTLRWorks 1.4
grammar Test;
INT : '0'..'9'+
;
WS : ( ' '
| '\t'
| '\r'
| '\n'
) {$channel=HIDDEN;}
;
expression
: INT ('+'^ INT)*;
When I pass 2+4 and process expression, I don't get a tree with + as the root and 2 and 4 as the child nodes. Rather, I get expression as the root and 2, + and 4 as child nodes at the same level.
Can't figure out what I am doing wrong. Need help desparately.
BTW how can I get those graphic descriptions ?

Answer 1

Yes, you get the expression because it's an expression that your only rule expression is returning.
I have just added a virtual token PLUS to your example along with a rewrite expression that show the result your are expecting.
But it seems that you have already found the solution :o)
grammar Test;
options {
output=AST;
ASTLabelType = CommonTree;
}
tokens {PLUS;}
#members {
public static void main(String [] args) {
try {
TestLexer lexer =
new TestLexer(new ANTLRStringStream("2+2"));
CommonTokenStream tokens = new CommonTokenStream(lexer);
TestParser parser = new TestParser(tokens);
TestParser.expression_return p_result = parser.expression();
CommonTree ast = p_result.tree;
if( ast == null ) {
System.out.println("resultant tree: is NULL");
} else {
System.out.println("resultant tree: " + ast.toStringTree());
}
} catch(Exception e) {
e.printStackTrace();
}
}
}
expression
: INT ('+' INT)* -> ^(PLUS INT+);
INT : '0'..'9'+
;
WS : ( ' '
| '\t'
| '\r'
| '\n'
) {$channel=HIDDEN;}
;