package iterator.listone;
import java.util.NoSuchElementException;

/* public */
interface List {
	public Iterator newIterator();
}

/* public */
class ListF {
	private ListF() {}
	public static final List nil = new Nil(); /* Singleton */
	public static final List cons(int hd, List tl) /* Factory */ {
		return new Cons(hd, tl);
	}
}

/* public */
interface Iterator {
	public boolean hasNext();
	public int next();
}

/*
 *************************************************************************
 * List classes.
 *************************************************************************
 */
class Nil implements List {
	Nil() {}
	public String toString() { return "nil"; }
	public Iterator newIterator() { return new NullIterator(); }
}

class Cons implements List {
	final int hd;
	final List tl;
	Cons(int hd, List tl) { this.hd = hd; this.tl = tl; }
	public String toString() { return hd + "::" + tl.toString(); }
	public Iterator newIterator() { return new ListIterator(this); }
}

class NullIterator implements Iterator {
	NullIterator() { }
	public boolean hasNext() { return false; }
	public int next() { throw new NoSuchElementException(); }
}

class ListIterator implements Iterator {
	private List node;
	ListIterator(List node) { this.node = node; }
	public boolean hasNext() {
		return node != ListF.nil;
	}
	public int next() {
		if (! hasNext())
			throw new NoSuchElementException();
		int result = ((Cons)node).hd;
		node = ((Cons)node).tl;
		return result;
	}
}

/*
 *************************************************************************
 * A test case.
 *************************************************************************
 */
public class Main {
	public static void main(String[] args) {
		List test = ListF.cons(1, ListF.cons(2, ListF.cons(3, ListF.nil)));
		System.out.println(test);

		int sum=0;
		for (Iterator i = test.newIterator(); i.hasNext(); )
			sum += i.next();
		System.out.println(sum);

		List rev=ListF.nil;
		for (Iterator i = test.newIterator(); i.hasNext(); )
			rev = ListF.cons(i.next(),rev);
		System.out.println(rev);
	}
}