package lrs.visitor;

import lrs.*;
/**
*
* @author DXN
*/
class ReverseHelp implements IAlgo
{
   public static final ReverseHelp Singleton = new ReverseHelp ();

   private ReverseHelp ()
   {
   }

	/**
	 * @param host the remaining tail of the list to be reversed.
	 * @param top from top to host is the reversed list so far.
	 * @return null.
	 */
	public Object forEmpty(LRStruct remaining, Object top)
	{
		return null;
	}

	/**
	 * @param host the remaining tail of the list to be reversed.
	 * @param top from top to host is the reversed list so far.
	 * @return null.
	 */
	public Object forNonEmpty(LRStruct host, Object top)
	{
      Object hostFirst = host.removeFront(); // host has "advanced".
      ((LRStruct)top).insertFront (hostFirst);
      return host.execute(this, top);
	}
}