The presence of side effects in even a very simple language of expressions gives rise to a number of semantic questions. The issue of evaluation order becomes a crucial one and, unless a specific order is enforced, the language becomes non-deterministic. In this paper we study the denotational semantics of such a language under a variety of possible evaluation strategies, from simpler to more complex, concluding with unspecified evaluation order, unspecified order of side effects and the mechanism of sequence points that is particular to the ANSI C programming language. In doing so, we adopt a dialect of Haskell as a metalanguage, instead of mathematical notation, and use monads and monad transformers to improve modularity. In this way, only small modifications are required for each transition. The result is a better understanding of different evaluation strategies and a unified way of specifying their semantics. Furthermore, a significant step is achieved towards a complete and accurate semantics for ANSI C.

This paper uses the Fran system for functional reactive animation to give a simulation of a lift – or elevator – with many floors. The paper first introduces a two-floor version, and then indicates in detail how this is extended to give a simulation with an arbitrary number of floors and featuring more realistic animated graphics. The paper introduces those aspects of Fran relevant to the simulation, making it a self-contained tutorial on parts of Fran and how it is applied in practice. The full code for the system is available on the World Wide Web.

A simple implementation of an SML-like module system is presented as a module parameterized by a base language and its type-checker. This implementation is useful both as a detailed tutorial on the Harper–Lillibridge–Leroy module system and its implementation, and as a constructive demonstration of the applicability of that module system to a wide range of programming languages.

One well known algorithm is the Fast Fourier Transform (FFT). An efficient iterative version of the FFT algorithm performs as a first step a bit-reversal permutation of the input list. The bit-reversal permutation swaps elements whose indices have binary representations that are the reverse of each other. Using an amortized approach, this operation can be made to run in linear time on a random-access machine. An intriguing question is whether a linear-time implementation is also feasible on a pointer machine, that is, in a purely functional setting. We show that the answer to this question is in the affirmative. In deriving a solution, we employ several advanced programming language concepts such as nested datatypes, associated fold and unfold operators, rank-2 types and polymorphic recursion.

Since its inception in 1987, Haskell has provided a focal point for research in lazy functional programming. During this time the language has continually evolved, as a result of both theoretical advances and practical experience. Haskell has proved to be a powerful tool for many kinds of programming tasks, and applications in industry are beginning to emerge. The recent definition of Haskell 98 provides a long-awaited stable version of the language, but there are many exciting possibilities for future versions of Haskell.

The fourth Haskell Workshop will be held as part of the PLI 2000 colloquium on Principles, Logics, and Implementations of high-level programming languages in Montreal, 17th September 2000. Previous Haskell Workshops have been held in Paris (1999), Amsterdam (1997) and La Jolla (1995). Following on from these workshops, a special issue of the Journal of Functional Programming will be devoted to Haskell. Possible topics include, but are not limited to:

* Critiques of Haskell 98;

* New proposals for Haskell;

* Applications or case studies;

* Programming techniques;

* Reasoning about programs;

* Semantic issues;

* Pedagogical issues;

* Implementation.

Contributors to any of the Haskell workshops are invited to submit full papers to the special issue on Haskell, but submission is open to everyone. Submissions should be sent to guest editor (address below), with a copy to Nasreen Ahmad (nasreen@dcs.gla.ac.uk). Submitted articles should be sent in postscript format, preferably gzipped and uuencoded. In addition, please send, as plain text, title, abstract, and contact information. The submission deadline is 1st February 2001. For other submission details, please consult an issue of the Journal of Functional Programming or see the Journal's web pages.