package list.visitor;
import list.*;

public class LastElement implements IListAlgo
{
    public final static LastElement Singleton = new LastElement();

    private LastElement()
    {
    }

     /**
     * Throws an IllegalArgumentException
     * @return does not return.
     */
    public Object forEmpty(AList host, Object input)
    {
	throw new IllegalArgumentException ("Empty List has no last element.");	
    }
    
    /**
     * Returns the last element of a list.
     */
    public Object forNonEmpty(AList host, Object input)
    {
	if (host.getRest() == ListFactory.Singleton.makeEmptyList())
	    return host.getFirst();
	else
	    return host.getRest().execute(this, null);
    }
}