package scheme2;

/**
 * Manufactures AListFW objects.
 * Implemented as a singleton.
 * 
 * @author Dung X. Nguyen
 * @version 1.0
 * @since 09/17/00
 * @Custom Copyright 2000 -All rights reserved
 */
public class ListFWFactory
{
	public final static ListFWFactory Singleton = new ListFWFactory ();

	private ListFWFactory()
	{
	}

	public AListFW makeEmptyList()
	{
      return EmptyListFW.Singleton;
	}

	/**
	 * Creates a non-empty list with a given non-null first element and a non-nul tail.
	 * Throws an IllegalArgumentException if any of the parameters is null.
	 * 
	 * @param dat != null, the fist data element of the non-empty list.
	 * @param tail !- null, the tail of this non-empty list.
	 */
	public AListFW makeNEList(Object dat, AListFW tail)
	{
      if (null == dat || null == tail)
      {
         throw new IllegalArgumentException ("dat and tail must be non-null.");
      }
      return new NEListFW (dat, tail);
	}
}