/** Scheme-like pairs that can be used to form a list of 
 *  integers. */
public class IntList {
    public int head;
    public IntList tail;

    /** A List with head and tail. */
    public IntList (int head, IntList tail) {
        this.head = head; this.tail = tail;
    }

    /** A List with null tail, and head = 0. */
    public IntList () { this (0, null); }
    // NOTE: public IntList () { }  would also work.

    /** A new IntList containing the ints in ARGS. */
    public static IntList list (Integer ... args) {
        IntList result, p;

        if (args.length > 0)
            result = new IntList (args[0], null);
        else 
            return null;

        int k;
        for (k = 1, p = result; k < args.length; k += 1, p = p.tail)
            p.tail = new IntList (args[k], null);
        return result;
    }

    /** True iff X is an IntList containing the same sequence of ints
     *  as THIS. */
    public boolean equals (Object x) {
        if (! (x instanceof IntList))
            return false;
        IntList L = (IntList) x;
        IntList p;
        for (p = this; p != null && L != null; p = p.tail, L = L.tail) {
            if (p.head != L.head)
                return false;
        }
        if (p != null || L != null)
            return false;
        return true;
    }

}