package schemeFW;

/**
 * Concrete IListFactory to manufacture IList as composites.
 * EmptyList and NEList are static nestes classes and hidden from all external
 * client code.
 * @author D.X. Nguyen
 */
public class CompositeListFactory implements IListFactory {

    private static class EmptyList implements IEmptyList {
        public final static EmptyList Singleton = new EmptyList ();

        private EmptyList() {
        }

        public Object execute(IListAlgo algo, Object inp) {
            return algo.emptyCase(this, inp);
        }
    }

    public class NEList implements INEList {
        private Object _first;
        private IList _rest;

        public NEList(Object dat, IList tail) {
            _first = dat;
            _rest = tail;
        }

        public Object getFirst() {
            return _first;
        }

        public IList getRest() {
            return _rest;
        }

        public Object execute(IListAlgo algo, Object inp) {
            return algo.nonEmptyCase(this, inp);
        }
    }

    public static final CompositeListFactory Singleton =
                                                    new CompositeListFactory();
    private CompositeListFactory() {
    }

    public IEmptyList makeEmptyList() {
        return EmptyList.Singleton;
    }

    public INEList makeNEList(Object first, IList tail) {
        return new NEList(first, tail);
    }
}