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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.

Abstract. Many modern programs provide operating system-style services to extension modules. A Web server, for instance, behaves like a simple OS kernel. It invokes programs that dynamically generate Web pages and manages their resource consumption. Most Web servers, however, rely on conventional operating systems to provide these services. As a result, the solutions are inefficient, and impose a serious overhead on the programmer of dynamic extensions. In this paper, we show that a Web server implemented in a suitably extended high-level programming language overcomes all these problems. First, building a server in such a language is straightforward. Second, the server delivers static content at performance levels comparable to a conventional server. Third, the Web server delivers dynamic content at a much higher rate than a conventional server, which is important because a significant portion of Web content is now dynamically generated. Finally, the server provides programming mechanisms for the dynamic generation of Web content that are difficult to support in a conventional server architecture. Web Servers and High-Level Operating SystemsA Web server provides operating system-style services. Like an operating system, a server runs programs (e.g., CGI scripts). Like an operating system, a server protects these programs from each other. And, like an operating system, a server manages resources (e.g., network connections) for the programs it runs.Some existing Web servers rely on the underlying operating system to implement these services. Others fail to provide services due to shortcomings of the implementation languages. In this paper, we show that implementing a Web server in a suitably extended functional programming language is straightforward and satisfies three major properties. First, the server delivers static content at a performance level comparable to a conventional server. Second, the Web server delivers dynamic content at five times the rate of a conventional server. Considering the explosive growth of dynamically created Web pages [7], this performance improvement is important. Finally, our server provides programming mechanisms for the dynamic generation of Web content that are difficult to support in a conventional server architecture.

Programmers confront a minefield when they design interactive Web programs. Web interactions take place via Web browsers. With browsers, consumers can whimsically navigate among the various stages of a dialog and can thus confuse the most sophisticated corporate Web sites. In turn, Web services can fault in frustrating and inexplicable ways. The quickening transition from Web scripts to Web services lends these problems immediacy. To address this programming problem, we develop a foundational model of Web interactions and use it to formally describe two classes of errors. The model suggests techniques for detecting both classes of errors. For one class we present an incrementally checked record type system, which effectively eliminates these errors. For the other class, we introduce a dynamic safety check, which catches the mistakes relative to programmers' simple annotations.