Extend ANTLR3 AST's

Question

With ANTLR2, you could define something like this in grammar definition file:

options
{
   language = \"CSharp\";
   namespace = \"Extended.Tokens\";
}

toke         


        

Answer 1

I know little C#, but there shouldn't be much difference with the Java target.

You can create - and let ANTLR use - a custom tree by setting the ASTLabelType in the options { ... } section (an XTree in this case):

T.g

grammar T;

options {
  output=AST;
  ASTLabelType=XTree;
}

tokens {
  ROOT;
}

@parser::header {
  package demo;
  import demo.*;
}

@lexer::header {
  package demo;
  import demo.*;
}

parse
  :  Any* EOF -> ^(ROOT Any*)
  ;

Any
  :  .
  ;

You then create a custom class which extends a CommonTree:

demo/XTree.java

package demo;

import org.antlr.runtime.*;
import org.antlr.runtime.tree.*;

public class XTree extends CommonTree {

  public XTree(Token t) {
    super(t);
  }

  public void x() {
    System.out.println("XTree.text=" + super.getText() + ", children=" + super.getChildCount());
  }
}

and when you create an instance of your TParser, you must create and set a custom TreeAdaptor which creates instances of your XTree:

demo/Main.java

package demo;

import org.antlr.runtime.*;
import org.antlr.runtime.tree.*;

public class Main {

  public static void main(String[] args) throws Exception {
    String source = "ABC";
    TLexer lexer = new TLexer(new ANTLRStringStream(source));
    TParser parser = new TParser(new CommonTokenStream(lexer));
    parser.setTreeAdaptor(new CommonTreeAdaptor(){
      @Override
      public Object create(Token t) {
        return new XTree(t);
      }
    }); 
    XTree root = (XTree)parser.parse().getTree();
    root.x();
  }
}

Running the demo:

java -cp antlr-3.2.jar org.antlr.Tool T.g -o demo/
javac -cp antlr-3.2.jar demo/*.java
java -cp .:antlr-3.2.jar demo.Main

will print:

XTree.text=ROOT, children=3

For more info, see: http://www.antlr.org/wiki/display/ANTLR3/Tree+construction