The influence of browsers on evaluators or, continuations to program web servers

Abstract

While developing the software of a browser-operated educational CD-ROM, we had to face a number of problems. This paper presents these problems and the solutions we found. Amusingly, most of our solutions rely on continuations. Are browsers and multimedia the future of continuations?Through their "Back" button or "Clone window" menu item, browsers have powerful abilities that force servers to take care of multiply and simultaneously answered questions. A comprehensive tool to apprehend these problems as well as to solve them is to view these abilities as operators acting on the continuations of the computation performed by servers.Thematical trails are provided to walk through the CD-ROM but do not prevent students to wander elsewhere. A trail may contain choices or quizzes so the rest of the trail should adapt to the walked part. We consider the trail as a computation and the position of the student as a continuation within that computation.Moreover this paper advocates a computation-centric view of servers (in opposition to the usual page-centric view) where interactions with users suspend the computation into continuations that may be later resumed. This approach is superior because the continuation reifies, automatically and without errors, the whole state of the computation.