package lrs.visitor;

import lrs.LRStruct;
import lrs.IAlgo;

/**
* Computes the length of a LRStruct host.  The length of an empty LRStruct is 0.
* @author Dung X. Nguyen
*/
public class Length implements IAlgo
{
   /**
   * Singleton pattern.
   */
	public final static Length Singleton = new Length ();
   /**
   * Hidden from all external client to implement the Singleton pattern.
   */
   private Length ()
   {
   }

	/**
    * Returns Integer (0).
	 * @param host the LRStruct whose length is to be computed.
	 * @param input not needed.
	 * @return Integer (0).
	 */
	public Object forEmpty (LRStruct host, Object input)
	{
		return new Integer (0);
	}

	/**
    * Recurs on the tail of this LRStruct and add one to the result.
	 * @param host the LRStruct whose length is to be computed.
	 * @param input not needed.
	 * @return an Integer representing 1 + the length of the tail of this LRStruct.
	 */
	public Object forNonEmpty (LRStruct host, Object input)
	{
      Integer tLen = (Integer)host.getRest().execute(this, null);
		return new Integer (1 + tLen.intValue());
	}
}