/**
* Assigns the input list to the host.  host thus "becomes" the input list.
* Both host and the input list share the same head node.
* @author Dung X. Nguyen
*/
public class Becomes implements IAlgo
{
	public final static Becomes Singleton = new Becomes ();

	private Becomes()
	{
	}

	/**
	 * @param host 
	 * @param input 
	 * @return 
	 */
	public Object nullCase(QFList host, Object input)
	{
      return assign (host, (QFList)input);
	}

	/**
	 * @param host 
	 * @param input 
	 * @return 
	 */
	public Object nonNullCase(QFList host, Object input)
	{
      return assign (host, (QFList)input);
	}

   private Object assign (QFList lhs, QFList rhs)
   {
      lhs.insertFront (null);
      lhs.setRest (rhs);
      lhs.removeFront();
		return null;
   }
}