Lazy evaluation in action with generators, and eager evaluation with lists (from Intro to RX)

LazyAndEager.cs

public static void HotIsEager_ColdIsLazy_InTheEnumerableObservableDuality()
{
  void ReadFirstValue(IEnumerable<int> list)
  {
    foreach (var i in list)
    {
      Console.WriteLine("Read out first value of {0}", i);
      break;
    }
  }
  IEnumerable<int> EagerEvaluation()
  {
    var result = new List<int>();
    Console.WriteLine("About to return 1 eagerly");
    result.Add(1);
    //The code below is executed but not used
    Console.WriteLine("About to return 2 eagerly");
    result.Add(2);
    return result;
  }
  IEnumerable<int> LazyEvaluation()
  {
    Console.WriteLine("About to return 1 lazily");
    yield return 1;
    //Execution stops here
    Console.WriteLine("About to return 2 lazily");
    yield return 2;
  }
  ReadFirstValue(EagerEvaluation());
  Console.ReadLine();
  ReadFirstValue(LazyEvaluation());
}