/**
 * Represents an abstract Scheme-like list, an  immutable linear recursive
 * structure of data. Has abstract methods to provide its internal data and
 * structure to the client. Since an AList has an internal structure that is
 * isomorphic to itself, it's best to implement it using the composite pattern.
 * @author Dung X. Nguyen
 * @version 1.1
 * @since 01/25/02
 * @Custom Copyright 2002 -All rights reserved
 */
public abstract class AList {
    /**
     * Returns the first element in this AList, if any.
     * The behavior for the empty list is undefined.
     * @return behavior relegated to concrete subclasses.
     */
    public abstract Object getFirst();

    /**
     * Returns the tail ("rest") of this AList, if any.
     * The behavior for the empty list is undefined.
     * @return behavior relegated to concrete subclasses.
     */
    public abstract AList getRest();

    /**
     * Computes and returns the number of elements in this AList.
     * @return int >= 0.
     */
    public abstract int getLength();

    /**
     * Computes and returns the minimum of this AList, assuming it contains
     * Integer objects.
     * @return behavior relegated to concrete subclasses.
     */
     public abstract int getMinimum();

    /**
     * Computes the length of this AList.  Uses helpGetLen.
     * @return int >= 0.
     */
    public abstract int getLen();

    /**
     * Uses the accumulated length of the original list to help compute the
     * length of the original list.
     * @param acc the accumlated length of the original list.
     * @return behavior relegated to concrete subclasses.
     */
    protected abstract int helpGetLen(int acc);

    /**
     * Computes the minimum of this AList, assuming it contains Integer objects.
     * Uses helpGetMin.
     * @return behavior relegated to concrete subclasses.
     */
    public abstract int getMin();

    /**
    * Computes the minimum of the preceding list and this AList using the
    * accumlated minimum.
    * @param accMin the smallest int containing in the list preceding this AList.
    * @return behavior relegated to concrete subclasses.
    */
    protected abstract int helpGetMin(int accMin);
}