public class PostOrder implements ExpressionVisitor {

  public void visit(IntExp e) {

    System.out.print( " " + e.getValue() );

  }

  public void visitBefore(AddExp e) {
      // nothing here
  }

  public void visit(AddExp e) {
      // nothing here
  }

  public void visitAfter(AddExp e) {
      System.out.print( " +" );
  }

}