// Empty stacks.
// 
// For purpose statements and algebraic specification, see Stack.java.

class EmptyStack<E> extends StackBase<E> {

    EmptyStack () { }

    public Stack<E> push (E x) {
        return new Push<E> (this, x);
    }

    public boolean  isEmpty () {
        return true;
    }

    public E top () {
        String msg1
            = "attempted to compute the top of an empty StackInt";
        throw new RuntimeException (msg1);
    }

    public Stack<E> pop () {
        return this;                   // FIXME: this is evil
    }

    public int size () {
        return 0;
    }
}