/*
 * Created on Oct 10, 2003
 */
package listFW.visitor;

import listFW.*;
/**
 * Computes the length of a list using anonymous inner class.
 *
 * @author root
 */
public class Average implements IListAlgo
{

 private static int _accLen;
 private static int _accSum;

 public static final Average Singleton = new Average();
 private Average() {
 }

 /**
  * Returns 0 because the empty list has no elements.
  * @param host an empty list.
  * @param nu not used.
  * @return Integer
  */
 public Object emptyCase(IEmptyList host, Object nu) {
  return new Integer(0);
 }


 /**
  * @param host a non-empty list.
  * @param nu not used.
  * @return Integer
  */
 public Object nonEmptyCase(INEList host, Object nu) {
  _accLen = 1;
  _accSum = ((Integer)host.getFirst ()).intValue ();
  // call helper as an anonymous inner class:
  return host.getRest().execute(new IListAlgo() {

   public Object emptyCase(IEmptyList h, Object nu) {
    return new Integer (_accSum/_accLen);
   }

   public Object nonEmptyCase(INEList h, Object nu) {
    _accLen += 1;
    _accSum += ((Integer)h.getFirst ()).intValue ();
    return h.getRest ().execute (this, null);
   }
  },  // end of anonymous inner class.
  null); 
 }
}