Durchlaufen von Syntaxbäumen

class Eval extends DepthFirstAdapter {
  public void outACompoundExpression 
        (ACompoundExpression node) {
    System.out.println (node);
    Integer l = 
       (Integer) getOut (node.getLeft());
    Integer r = 
       (Integer) getOut (node.getRight());
    setOut (node, l + r);
  }
  public void outAAtomicExpression 
        (AAtomicExpression node) { .. }
}