public class SumAlgo implements IFunAlgo {
   private static SumAlgo _instance = new SumAlgo ();

   private SumAlgo () {
   }

   public static SumAlgo Singleton () {
      return _instance;
   }

   public Object forEmpty (EmptyFW list, Object input) {
      return new Integer (0);
   }

   public Object forCons (ConsFW list, Object input) {
      Integer carInt = list.car ();
      Integer tailSumInt = (Integer)list.cdr ().execute (this, null);
      return new Integer ( carInt.intValue () + tailSumInt.intValue ()); 
   }
}