EnumTest.cs

using System.Collections;

//Shouldn't we see the Debug.Log ("End printing") ? 
public class EnumTest : MonoBehaviour {
	
	static int a = 0;
	IEnumerator printRoutine = null;

	void Start() {
		StartCoroutine (main ());
		StartCoroutine (endPrinterAfter (4.0f));
	}

	IEnumerator endPrinterAfter(float seconds) {
		yield return new WaitForSeconds (seconds);
		StopCoroutine (printRoutine);
	}

	IEnumerator main() {
		Debug.Log ("Begin printing");
		printRoutine = printer ();
		yield return StartCoroutine (printRoutine);
		Debug.Log ("End printing");
	}

	IEnumerator printer() {
		while (true) {
			Debug.Log("Printing "+(a++)); 
			yield return new WaitForSeconds(0.5f);
		}
	}
}