Abstract. The PLT Scheme Web Server uses continuations to enable a natural, console-like program development style. We describe the implementation of the server and its use in the development of an application for managing conference paper reviews. In the process of developing this application, we encountered subtle forms of interaction not directly addressed by using continuations. We discuss these subtleties and offer solutions that have been successfully deployed in our application. Finally, we present some details on the server’s performance, which is comparable to that of the widely-used Apache Web server. 1. The Structure of Web Programs Consider the following sequence of Web interactions: 1. A user examines a list of books. 2. The user requests the page for book A. 3. The user presses the “buy now ” button on the page showing book A. As expected, the application registers a purchase for book A. This behavior, which corresponds to a traditional console application, seems entirely reasonable. Consider, however, the following sequence with the same implementation (the Wi name browser windows): 1. The user examines a list of books (W1). 2. The user requests the page for book A in a new browser window (W2). 3. The user switches to W1. 4. The user requests the page for book B in a new browser window (W3). 5. The user switches to W2 and presses the “buy now ” button on it. In some implementations, this sequence of interactions can result in a purchase of book B rather than of A. This is obviously not at all what the user intended.

Gregory Harold Cooper was born on New Year’s Day of 1978 in South County, Rhode Island. He has enjoyed mathematics and logic since he can remember and was addicted to computer programming by age 7. He was valedictorian of the class of 1996 at North Kingstown High School and a National Merit Scholar and Barry M. Goldwater Scholar at the University of Rhode Island. He also received an honorable mention in the National