Experiments in IO monad (C#)

IOMonad.cs

using System;
using System.Runtime.InteropServices;

// ReSharper disable CheckNamespace
// ReSharper disable InconsistentNaming
// ReSharper disable PartialTypeWithSinglePart

sealed partial class IO<T>
{
    readonly Func<T> _func;

    public IO(Func<T> func) { _func = func; }
    public T Run() => _func();
}

static partial class IO
{
    public static IO<T> Create<T>(Func<T> func) =>
        new IO<T>(func);

    public static IO<U> Bind<T, U>(this IO<T> io, Func<T, IO<U>> f) =>
        Create(() => f(io.Run()).Run());

    public static IO<U> Select<T, U>(this IO<T> io, Func<T, U> selector) =>
        io.Bind(x => Create(() => selector(x)));

    public static IO<V> SelectMany<T, U, V>(this IO<T> first, Func<T, IO<U>> secondSelector, Func<T, U, V> resultSelector) =>
        first.Bind(x => secondSelector(x).Bind(y => Create(() => resultSelector(x, y))));

    public static IO<string> ReadLine() =>
        Create(() => Console.ReadLine());

    public static IO<Unit> WriteLine(string s) =>
        Create(() => { Console.WriteLine(s); return new Unit(); });
}

static class Program
{
    static void Main() =>
        Wain().Run();

    static IO<Unit> Wain() =>
        from _1 in IO.WriteLine("Enter X: ")
        from xx in IO.ReadLine()
        from _2 in IO.WriteLine($"X is {xx}. Now enter Y: ")
        from yy in IO.ReadLine()
        from _3 in IO.WriteLine($"{xx} + {yy} = {int.Parse(xx) + int.Parse(yy)}")
        select new Unit();
}

/// <summary>
/// A type that indicates the absence of a specific value. It has only a
/// single value, which acts as a placeholder when no other value exists or
/// is needed.
/// </summary>

[Serializable]
[StructLayout(LayoutKind.Sequential, Size = 1)]
public struct Unit : IEquatable<Unit>
{
    public static bool operator ==(Unit a, Unit b) => true;
    public static bool operator !=(Unit a, Unit b) => false;
    public bool Equals(Unit other) => true;
    public override bool Equals(object obj) => obj is Unit;
    public override int GetHashCode() => 0;
}