public static class Option
    {
        public static Option<T> Some<T>(T item)
            => new Option<T>(item);
        public static Option<T> None<T>()
            => new Option<T>();
    }
    public struct Option<T>
    {
        private readonly T value;

        public Option(T value)
        {
            this.value = value;
            IsSuccessful = value != null;
        }
        public bool IsSuccessful { get; }

        public Option<T> Or(Option<T> other)
            => IsSuccessful ? this : other;
        public T Or(T value)
            => IsSuccessful ? this.value : value;
        public Option<T> Or(Func<Option<T>> other)
            => IsSuccessful ? this : other();
        public T Or(Func<T> other)
            => IsSuccessful ? value : other();
        public Option<U> Select<U>(Func<T, U> f)
            => IsSuccessful ? Option.Some(f(value)) : Option.None<U>();
        public Option<V> SelectMany<U, V>(Func<T, Option<U>> f, Func<T, U, V> g)
        {
            if (!IsSuccessful)
                return Option.None<V>();
            var u = f(value);
            if (u.IsSuccessful)
                return Option.Some(g(value, u.value));
            else
                return Option.None<V>();
        }
        public Option<U> SelectMany<U>(Func<T, Option<U>> f)
            => IsSuccessful ? f(value) : Option.None<U>();
        public Option<T> Where(Func<T, bool> f)
            => IsSuccessful && f(value) ? this : Option.None<T>();

        public R Switch<R>(Func<T, R> some, Func<R> none)
            => IsSuccessful ? some(value) : none();
        public R Switch<R>(Func<T, R> some, R none)
            => IsSuccessful ? some(value) : none;
        public void Switch(Action<T> some, Action none)
        {
            if (IsSuccessful)
                some(value);
            else
                none();
        }
    }