package scheme2.visitor;

import scheme2.AListFW;
import scheme2.IListAlgo;

/**
* Skips the first n elements and returns the remaining tail.
*/
public class SkipN implements IListAlgo
{
	int _n;

	public SkipN( int n )
	{
		_n = n;
	}
   
	/**
	 * @param host 
	 * @param input not used.
	 */
	public Object forEmpty(AListFW host, Object input)
	{
		if( _n == 0 )
			return host;
		throw new IllegalArgumentException ("Empty list has no data!");
	}

	/**
	 * @param host 
	 * @param input not used
	 */
	public Object forNonEmpty(AListFW host, Object input)
	{
		if( _n == 0 )
			return host;
		else
		{
			_n--;
			return host.getRest().execute (this, null);
		}
	}
}