package listFW.visitor;

import listFW.*;

/**
 * Computes the number of elements in a list, using a helper.
 * @author D. X. Nguyen
 * @since Copyright 2002 - DXN All rights reserved
 */
public class GetLen implements IListAlgo {

    public static final GetLen Singleton = new GetLen();

    private GetLen() {
    }

    /**
     * Returns 0 because the empty list has no elements.
     * @param host an empty list.
     * @param nu not used.
     * @return Integer(0)
     */
    public Object emptyCase(IEmptyList host, Object nu) {
        return new Integer(0);
    }


    /**
     * Passes the accumulated length (1) to the rest and
     * asks for help to compute the length.
     * @param host a non-empty list.
     * @param nu not used.
     * @return Integer
     */
    public Object nonEmptyCase(INEList host, Object nu) {
        return host.getRest().execute(GetLenHelp.Singleton,
                                      new Integer(1));
    }
}