package schemeFW;

/**
 * Visitor representing an abstract algorithm to be executed by a host
 * <code>IList</code>.
 * Breaks up an algorithm into two separate cases:
 * <pre>
 * emptyCase() - to be called by an <code>IEmptyList</code> host;
 * nonEmptyCase() - to be called by an <code>INEList</code> host.
 * </pre>
 * @author Dung X. Nguyen
 * @author Stephen B. Wong
 * @Custom Copyright 2001 -All rights reserved
 * @dependency schemeFW.IEmptyList uses
 * @dependency schemeFW.INEList uses
 */
public interface IListAlgo {
    /**
     * The method called by <code>IEmptyList</code>, the empty list.
     * @param host The <code>IEmptyList</code> that is executing this algorithm.
     * @param inp generic input parameter that can be used for any purpose.
     * @return <code>Object</code> result from calling this method.
     */
    public abstract Object emptyCase(IEmptyList host, Object inp);

    /**
     * The method called by a <code>INEList</code>, a non-empty list.
     * @param host The <code>INEList<code> that is executing this algorithm
     * @param inp generic input parameter that can be used for any purpose.
     * @return <code>Object</code> result from calling this method.
     */
    public abstract Object nonEmptyCase(INEList host, Object inp);
}