public class Sum implements FLVisitor_I {
  public static Sum only = new Sum();

  private Sum() {
  }

  public Object forEmpty(Empty list) {
    return new Integer(0);
  }

  public Object forCons (Cons list) {
    Integer firstInt = list.first();
    Integer restSumInt = (Integer)list.rest().execute(this);
    return new Integer(firstInt.intValue() + restSumInt.intValue());
  }
}