ANTLR, heterogeneous AST problem - antlr

Question

I examine heterogeneous trees in ANTLR (using ANTLRWorks 1.4.2).
Here is the example of what I have already done in ANTLR.
grammar test;
options {
language = java;
output = AST;
}
tokens {
PROGRAM;
VAR;
}
#members {
class Program extends CommonTree {
public Program(int ttype) {
token = new CommonToken(ttype, "<start>");
}
}
}
start
: program var function
// Works fine:
//-> ^(PROGRAM program var function)
// Does not work (described below):
-> ^(PROGRAM<Program> program var function)
;
program
: 'program'! ID ';'!
;
var
: TYPE^ ID ';'!
;
function
: ID '('! ')'! ';'!
;
TYPE
: 'int'
| 'string'
;
ID
: ('a'..'z' | 'A'..'Z')+
;
WHITESPACE
: (' ' | '\t' '\n'| '\r' | '\f')+ {$channel = HIDDEN;}
;
Sample input:
program foobar;
int foo;
bar();
When I use rewrite rule ^(PROGRAM<Program> program var function), ANTLR stumbles over and I get AST like this:
Whereas when I use this rewrite rule ^(PROGRAM program var function) it works:
Could anyone explain where am I wrong, please? Frankly, I do not really get the idea of heterogeneous trees and how do I use <…> syntax in ANTLR.
What do r0 and r1 mean (first picture)?

Answer 1

I have no idea what these r0 and r1 mean: I don't use ANTLRWorks for debugging, so can't comment on that.
Also, language = java; causes ANTLR 3.2 to produce the error:
error(10): internal error: no such group file java.stg
error(20): cannot find code generation templates java.stg
error(10): internal error: no such group file java.stg
error(20): cannot find code generation templates java.stg
ANTLR 3.2 expects it to be language = Java; (capital "J"). But, by default the target is Java, so, mind as well remove the language = ... entirely.
Now, as to you problem: I cannot reproduce it. As I mentioned, I tested it with ANTLR 3.2, and removed the language = java; part from your grammar, after which everything went as (I) expected.
Enabling the rewrite rule -> ^(PROGRAM<Program> program var function) produces the following ATS:
and when enabling the rewrite rule -> ^(PROGRAM program var function) instead, the following AST is created:
I tested both rewrite rules this with the following class:
import org.antlr.runtime.*;
import org.antlr.runtime.tree.*;
import org.antlr.stringtemplate.*;
public class Main {
public static void main(String[] args) throws Exception {
ANTLRStringStream in = new ANTLRStringStream("program foobar; int foo; bar();");
testLexer lexer = new testLexer(in);
CommonTokenStream tokens = new CommonTokenStream(lexer);
testParser parser = new testParser(tokens);
testParser.start_return returnValue = parser.start();
CommonTree tree = (CommonTree)returnValue.getTree();
DOTTreeGenerator gen = new DOTTreeGenerator();
StringTemplate st = gen.toDOT(tree);
System.out.println(st);
}
}
And the images are produced using graph.gafol.net (and the output of the Main class, of course).