20.1 An informal exception protocol

Our goal is to modify the method that adds a <time-offset> instance to a <time-of-day> instance. We redefine that method to detect overflow beyond the 24-hour period covered by a time of day, and to take special action in that case. In this section, we show a simple way to indicate and handle exceptions, without using the Dylan exception protocol. We then discuss the problems with this informal approach. In Section 20.2, we achieve the same goal using Dylan conditions, and discuss the advantages of that approach.