http://davesquared.net/2013/04/side-effect-free-csharp.html Side-effect free programming in C#

SideEffect.cs

namespace SideEffect
{
    using System;

    class Program
    {
        static void Main(string[] args)
        {
            // SideEffecty();

            var prog1 = NotSoSideEffecty();
            var prog2 = NotSoSideEffecty();
            var prog3 = NotSoSideEffecty();

            prog3();

            // var program = IO.ReadLine().Then(name => IO.WriteLine("Nice to meet you " + name));

            Console.ReadKey();
        }

        static void SideEffecty()
        {
            Console.WriteLine("What's your name?");
            var name = Console.ReadLine();
            Console.WriteLine("Nice to meet you, " + name);
        }

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

    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>(Func<T, IO<TNext>> useVal)
        {
            return new IO<TNext>(
                () =>
                    {
                        var val = ioAction();
                        var next = useVal(val);
                        return next.ioAction();
                    });
        }
    }

    public static class IO
    {
        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);
        }
    }
}