public void traverse(ASTVisitor visitor) throws Exception {
   if (visitor.visit(this)) {
     for (UsePart part : parts) {
       part.traverse(visitor);
     }
     visitor.endvisit(this);
   }
 }
 @Override
 public void traverse(ASTVisitor visitor) throws Exception {
   if (visitor.visit(this)) {
     visitor.endvisit(this);
   }
 }