reader exercise in c#

reader.cs

using System;
using NUnit.Framework;

namespace Workshop
{
    public static class ReaderExtensions
    {
        public static Func<T, B> Select<T, A, B>(this Func<T, A> reader, Func<A, B> f)
        {
            throw new NotImplementedException("TODO: pass example 1 and 2");
        }

        public static Func<T, B> SelectMany<T, A, B>(this Func<T, A> reader, Func<A, Func<T, B>> f)
        {
            throw new NotImplementedException("TODO: pass example 3");
        }

        public static Func<T, C> SelectMany<T, A, B, C>(this Func<T, A> reader, Func<A, Func<T, B>> f, Func<A,B,C> selector)
        {
            throw new NotImplementedException("TODO: pass example 4. (Last SelectMany can call this one)");
        }
    }

    public class Reader
    {
        Func<int, int> add1 = x => x + 1;
        Func<int, string> show = x => x.ToString();

        [Test]
        public void Example1()
        {
            var incAndShow = add1.Select(show);

            Assert.AreEqual("2", incAndShow(1));
        }
        
        [Test]
        public void Example2()
        {
            var incAndShow = from next in add1
                             select show(next);

            Assert.AreEqual("2", incAndShow(1));
        }
        
        [Test]
        public void Example3()
        {
            var incAndShow = add1.SelectMany<int,int,string>(a => t => show(a));

            Assert.AreEqual("2", incAndShow(1));
        }

        [Test]
        public void Example4()
        {
            var incPlusShow = from next in add1
                             from shown in show
                             select (next + " " + shown);

            Assert.AreEqual("2 1", incPlusShow(1));
        }        
    }
}