The Common Gateway Interface (CGI) for generating dynamic documents on web servers imposes much accidental complexity on the programmer. The Haskell/CGI library documented in this paper hides all this unpleasantness by using the common sense ‘design pattern’ of separating model and presentation. Low-level query string requests are represented by association lists, and primitive HTTP responses are easily constructed using a set of HTML generating combinators. The CGI programmer only needs to write a worker function that maps an abstract request into an abstract response. A (higher-order) wrapper function then transmutes the worker into a real low-level CGI script that deals with the exact format of concrete requests and responses as required by the CGI standard.

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.

In this work we put forward an algorithm for the mechanical verification of an extension of Martin-Löf's theory of types with dependent record types and subtyping. We first give a concise description of that theory and motivate its use for the formalization of algebraic constructions. Then we concentrate on the informal explanation and specification of a proof checker that we have implemented. The logical heart of this proof checker is a type checking algorithm for the forms of judgement of a particular formulation of the extended theory which incorporates a notion of parameter. The algorithm has been proven sound with respect to the latter calculus. We include a discussion on that proof in the present work.

Kamareddine, F., & Ríos (1997) conjecture that the λse-calculus preserves the strong normalisation of the λ-calculus. We prove here that this conjecture is false.

Pure type systems make use of domain-full λ-abstractions λx:D.M. We present a variant of pure type systems, which we call domain-free pure type systems, with domain-free λ-abstractions λx.M. Domain-free pure type systems have a number of advantages over both pure type systems and so-called type assignment systems (they also have some disadvantages), and have been used in theoretical developments as well as in implementations of proof-assistants. We study the basic properties of domain-free pure type systems, establish their formal relationship with pure type systems and type assignment systems, and give a number of applications of these correspondences.

In this paper we present two type inference systems for detecting useless-code in higher-order typed functional programs. Type inference can be performed in an efficient and complete way, by reducing it to the solution of a system of constraints. We also give a useless-code elimination algorithm which is based on a combined use of these type inference systems. The main application of the technique is the optimization of programs extracted from proofs in logical frameworks, but it could be used as well in the elimination of useless-code determined by program transformations.

Indeterminism is typical for concurrent computation. If several concurrent actors compete for the same resource then at most one of them may succeed, whereby the choice of the successful actor is indeterministic. As a consequence, the execution of a concurrent program may be nonconfluent. Even worse, most observables (termination, computational result, and time complexity) typically depend on the scheduling of actors created during program execution. This property contrast concurrent programs from purely functional programs. A functional program is uniformly confluent in the sense that all its possible executions coincide modulo reordering of execution steps. In this paper, we investigate concurrent programs that are uniformly confluent and their relation to eager and lazy functional programs. We study uniform confluence in concurrent computation within the applicative core of the π-calculus which is widely used in different models of concurrent programming (with interleaving semantics). In particular, the applicative core of the π-calculus serves as a kernel in foundations of concurrent constraint programming with first-class procedures (as provided by the programming language Oz). We model eager functional programming in the λ-calculus with weak call-by-value reduction and lazy functional programming in the call-by-need λ-calculus with standard reduction. As a measure of time complexity, we count application steps. We encode the λ-calculus with both above reduction strategies into the applicative core of the π-calculus and show that time complexity is preserved. Our correctness proofs employs a new technique based on uniform confluence and simulations. The strength of our technique is illustrated by proving a folk theorem, namely that the call-by-need complexity of a functional program is smaller than its call-by-value complexity.

We propose a parallel specialized language that ensures portable and cost-predictable implementations on parallel computers. The language is basically a first-order, recursion-less, strict functional language equipped with a collection of higher-order functions or skeletons. These skeletons apply on (nested) vectors and can be grouped into four classes: computation, reorganization, communication and mask skeletons. The compilation process is described as a series of transformations and analyses leading to SPMD-like functional programs which can be directly translated into real parallel code. The language restrictions enforce a programming discipline whose benefit is to allow a static, symbolic and accurate cost analysis. The parallel cost takes into account both load balancing and communications, and can be statically evaluated even when the actual size of vectors or the number of processors are unknown. It is used to automatically select the best data distribution among a set of standard distributions. Interestingly, this work can be seen as a cross-fertilization between techniques developed within the FORTRAN parallelization, skeleton and functional programming communities.

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 trie is a search tree scheme that employs the structure of search keys to organize information. Tries were originally devised as a means to represent a collection of records indexed by strings over a fixed alphabet. Based on work by C. P. Wadsworth and others, R. H. Connelly and F. L. Morris generalized the concept to permit indexing by elements built according to an arbitrary signature. Here we go one step further, and define tries and operations on tries generically for arbitrary datatypes of first-order kind, including parameterized and nested datatypes. The derivation employs techniques recently developed in the context of polytypic programming and can be regarded as a comprehensive case study in this new programming paradigm. It is well known that for the implementation of generalized tries, nested datatypes and polymorphic recursion are needed. Implementing tries for first-order kinded datatypes places even greater demands on the type system: it requires rank-2 type signatures and second-order nested datatypes. Despite these requirements, the definition of tries is surprisingly simple, which is mostly due to the framework of polytypic programming.

Kleisli is a modern data integration system that has made a significant impact on bioinformatics data integration. This paper contains a brief introduction to the Kleisli system and an example to illustrate its uses in the bioinformatics arena. The primary query language provided by Kleisli is called CPL, which is a functional query language whose surface syntax is based on the comprehension syntax. Kleisli is itself implemented using the functional language SML. So this paper also describes the influence of functional programming research that benefits the Kleisli system, especially the less obvious ones at the implementation level.

Availability. Kleisli has been commercialized under the name “KRIS”. It is available from Kris Technology Inc., 713 Santa Cruz Ave, #2, Menlo Park, CA 94025, USA. Direct email to [email protected] and web browser to http://www.kris-inc.com.

Researchers have recently proposed that for certain applications it is advantageous to use functional languages whose type systems are based upon linear logic: so-called linear functional languages. In this paper we develop reasoning techniques for programs in a linear functional language, linPCF, based on their operational behaviour. The principal theorem of this paper is to show that contextual equivalence of linPCF programs can be characterised coinductively. This characterisation provides a tractable method for reasoning about contextual equivalence, and is used in three ways:

[bull ] A number of useful contextual equivalences between linPCF programs is given.

[bull ] A notion of type isomorphism with respect to contextual equivalence, called operational isomorphism, is given. In particular the types !ϕ[otimes ]!ψ and !(ϕ&ψ) are proved to be operationally isomorphic.

[bull ] A translation of non-strict PCF into linPCF is shown to be adequate, but not fully abstract, with respect to contextual equivalence.

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.

A program derivation is said to be polytypic if some of its parameters are data types. Often these data types are container types, whose elements store data. Polytypic program derivations necessitate a general, non-inductive definition of ‘container (data) type’. Here we propose such a definition: a container type is a relator that has membership. It is shown how this definition implies various other properties that are shared by all container types. In particular, all container types have a unique strength, and all natural transformations between container types are strong.

The Bee is an integrated development environment for the Scheme programming language. It provides the user with a connection between Scheme and the C programming language, a symbolic debugger, a profiler, an interpreter, an optimizing compiler that delivers stand alone executables, a source file browser, a project manager, user libraries and online documentation. This article details the facilities of the Bee, its user interface, and presents an overview of the implementation of its main components.

This paper introduces a sequence of λ-expressions modeling the binary expansion of integers. We derive expressions computing the test for zero, the successor function, and the predecessor function, thereby showing the sequence to be an adequate numeral system, i.e. one in which all recursive functions are lambda-definable. These functions can be computed efficiently; To this end, we introduce a notion of complexity that is independent of the order of evaluation.

The understanding of polymorphic typechecking and type errors is poorly supported by contemporary functional language implementations. Here, a novel visualisation of functions and their types is presented based on the generation of function specific icons with graphical type representations which change dynamically as functions are applied. This visualisation has been implemented for a Standard ML subset within a graphical environment in which function combinations are constrained by type matching.

Program generation has the prospect of being an integral part of a wide range of software development processes. Recent studies investigate different aspects of program generation systems, including their semantics, their applications, and their implementation. Existing theories and systems address both high-level (source) language and low-level (machine) language generation. A number of programming languages now support program generation and manipulation, with different goals, implementation techniques, and targeted at different applications. In this context, a PLI workshop dedicated to this theme (SAIG'00) was held in Montreal in September 2000. Following on from this workshop, a special issue of the Journal of Functional Programming will be devoted to the same theme.

Full-length, archival-quality submissions are solicited on topics including both theoretical and practical models and tools for building program generation systems, Examples include:

[bull ] Semantics, type systems, and implementations for multi-stage languages.

[bull ] Run-time specialization systems, e.g. compilers, operating systems.

[bull ] High-level program generation (applications, foundations, environments).

[bull ] Symbolic computation, linking and explicit substitution, in-lining and macros.

Reports on applications of these techniques to real-world problems are especially encouraged, as are submissions that relate ideas and concepts from several of these topics, or bridge the gap between theory and practice.

Contributors to SAIG'00 are encouraged to submit, but submission is open to everyone. Papers will be reviewed as regular JFP submissions, and acceptance in the special issue will be based on relevance to the theme. The special issue also welcomes high-quality survey and position papers that would benefit a wide audience. Accepted papers exceeding the space restrictions will be published as regular JFP papers.

Submissions should be sent to the guest editor (address below), with a copy to Nasreen Ahmad ([email protected]). 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 page at http://www.dcs.gla.ac.uk/jfp/.