async/await behavior without the keywords

AsyncMonad.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Scratch
{
    class Program
    {
        public static void Main(string[] args)
        {
            var sum = from a in Task.Run(() => 3)    // 3
                      from b in AddAsync(a, 2)       // 5
                      from result in AddAsync(a, b)  // 8
                      select a + b + result;         // 16

            Console.WriteLine(sum.Result);
            Console.ReadKey();
        }

        /// <summary>
        /// A sample async method for testing
        /// </summary>
        public static Task<int> AddAsync(int x, int y)
        {
            return Task.Run(() => x + y);
        }
    }

    public static class AsyncExtensions
    {
        public static Task<TResult> SelectMany<TSource, TSelector, TResult>
            (this Task<TSource> source,
             Func<TSource, Task<TSelector>> selector,
             Func<TSource, TSelector, TResult> resultSelector)
        {
            return source
                .ContinueWith(result => selector(result.Result)
                .ContinueWith(result2 => resultSelector(result.Result, result2.Result)))
                .Unwrap();
        }
    }
}