Messing around with an IO type in C#

IOSample.cs

using System;

namespace Workshop.Terminal
{
    // Meh, close enough
    public sealed class Unit { }

    public sealed class IO<T>
    {
        private readonly Func<T> ioAction;
        public IO(Func<T> ioAction) { this.ioAction = ioAction; }

        public IO<TNext> Then<TNext>(IO<TNext> next)
        {
            return new IO<TNext>(() => {
                ioAction();
                return next.ioAction();
            });
        }

        public IO<TNext> Then<TNext>(Func<T, IO<TNext>> useValue)
        {
            return new IO<TNext>(() => {
               var value = ioAction();
               var nextIO = useValue(value);
               return nextIO.ioAction();
            });
        }

        public IO<TB> SelectMany<TA, TB>(Func<T, IO<TA>> useValue, Func<T, TA, TB> selector)
        {
            return new IO<TB>(() => {
               var value = ioAction();
               var nextIO = useValue(value);
               var nextValue = nextIO.ioAction();
               return selector(value, nextValue);
            });
        }

        public IO<TNext> Select<TNext>(Func<T, TNext> selector)
        {
            return new IO<TNext>(() => selector(ioAction()));
        }

        // DON'T CALL THIS!
        public T UnsafePerformIO() { return ioAction(); }
    }

    public static class IO
    {
        private static Random random = new Random();
        public static IO<Unit> WriteLine(string s)
        {
            return new IO<Unit>(() => { Console.WriteLine(s); return new Unit(); });
        }

        public static IO<string> ReadLine() { return new IO<string>(Console.ReadLine); }

        public static IO<int> Random(int min, int max)
        {
            return new IO<int>(() => random.Next(min, max));
        }
    }

    class Program
    {
        public static void SideEffecty()
        {
            Console.WriteLine("Hi, I'm C#. What's your name?");
            var name = Console.ReadLine();
            Console.WriteLine("Nice to meet you " + name);
        }

        public static Action NotSoSideEffecty()
        {
            return () =>
            {
                Console.WriteLine("Hi, I'm C#. What's your name?");
                var name = Console.ReadLine();
                Console.WriteLine("Nice to meet you " + name);
            };
        }

        public static IO<Unit> GuessNumber(int i)
        {
            return IO.ReadLine()
                      .Select(int.Parse) // should use Option type here for error handling
                      .Then(guess =>
                      {
                          if (guess > i)
                          {
                              return IO.WriteLine("Too high!").Then(GuessNumber(i));
                          }
                          else if (guess < i)
                          {
                              return IO.WriteLine("Too low!").Then(GuessNumber(i));
                          }
                          return IO.WriteLine("You got it!");
                      });
        }

        static void Main(string[] args)
        {
            var program =
                from a in IO.WriteLine("Hi, I'm C#. What's your name?")
                from name in IO.ReadLine()
                from b in IO.WriteLine("Nice to meet you " + name + 
                                       ". I'm thinking of a number between 1 and 10. Try and guess it!")
                from rand in IO.Random(1,10)
                from c in GuessNumber(rand)
                select new Unit();

            program.UnsafePerformIO();
            Console.ReadLine();
        }
    }
}

Accompanying post: http://davesquared.net/2013/04/side-effect-free-csharp.html