Standard ML is one of a number of new programming languages developed in the 1980s that are seen as suitable vehicles for serious systems and applications programming. It offers an excellent ratio of expressiveness to language complexity, and provides competitive efficiency. Because of its type and module system, Standard ML manages to combine safety, security, and robustness with much of the flexibility of dynamically typed languages like Lisp. It is also has the most well-developed scientific foundation of any major language. Here I review the strengths and weaknesses of Standard ML and describe some of what we have learned through the design, implementation, and use of the language.

Polyphonic C# is an extension of the C# language with new asynchronous concurrency constructs, based on the join calculus. We describe the design and implementation of the language and give examples of its use in addressing a range of concurrent programming problems.

We investigate whether the π-calculus is able to serve as a good foundation for the design and implementation of a strongly-typed concurrent programming language. The first half of the dissertation examines whether the π-calculus supports a simple type system which is flexible enough to provide a suitable foundation for the type system of a concurrent programming language. The second half of the dissertation considers how to implement the π-calculus efficiently, starting with an abstract machine for π-calculus and finally presenting a compilation of π-calculus to C. We start the dissertation by presenting a simple, structural type system for π-calculus, and then, after proving the soundness of our type system, show how to infer principal types for π-terms. This simple type system can be extended to include useful type-theoretic constructions such as recursive types and higherorder polymorphism. Higher-order polymorphism is important, since it gives us the ability to implement abstract datatypes in a type-safe manner, thereby providing a greater degree of modularity for π-calculus programs. The functional computational paradigm plays an important part in many programming languages. It is well-known that the π-calculus can encode functional computation. We go further and show that the type structure of λ-terms is preserved by such encodings, in the sense that we can relate the type of a λ-term to the type of its encoding in the π-calculus. This means that a π-calculus programming language can genuinely support typed functional programming as a special case. An efficient implementation of π-calculus is necessary if we wish to consider π-calculus as an operational foundation for concurrent programming. We first give a simple abstract machine for π-calculus and prove it correct. We then show how this abstract machine inspires a simple, but efficient, compilation of π-calculus to C (which now forms the basis of the Pict programming language implementation).

We adapt the Damas-Milner typing discipline to the join-calculus. The main result is a new generalization criterion that extends the polymorphism of ML to join-definitions. We prove the correctness of our typing rules with regard to a chemical semantics. We also relate typed extensions of the core join-calculus to functional languages. 1 Introduction The distributed implementation of concurrent calculi with message passing raises the problem of implementing communication channels, which finally reduces to the specification of channel managers. In order to reflect this need in the language itself, a new formalism has been recently introduced : the join-calculus [2]. This calculus is similar to Milner's asynchronous ß-calculus, except that the operations of restriction, reception and replication are all combined into a single receptor definition. Such a combination yields better control over communication. In [2, 3], we relied on this locality property to model realistic distributed sys...

Abstract. In these lecture notes, we give an overview of concurrent, distributed, and mobile programming using JoCaml. JoCaml is an extension of the Objective Caml language. It extends OCaml with support for concurrency and synchronization, the distributed execution of programs, and the dynamic relocation of active program fragments during execution. The programming model of JoCaml is based on the join calculus. This model is characterized by an explicit notion of locality, a strict adherence to local synchronization, and a natural embedding of functional programming à la ML. Local synchronization means that messages always travel to a set destination, and can interact only after they reach that destination; this is required for an efficient asynchronous implementation. Specifically, the join calculus uses ML’s function bindings and pattern-matching on messages to express local synchronizations. The lectures and lab sessions illustrate how to use JoCaml to program

We present a methodology for the systematic realisation of control flow analyses and illustrate it for Concurrent ML. We start with an abstract specification of the analysis that is next proved semantically sound with respect to a traditional small-step operational semantics; this result holds for terminating as well as non-terminating programs. The analysis is defined coinductively and it is shown that all programs have a least analysis result (that is indeed the best one). To realise the analysis we massage the specification in three stages: (i) to explicitly record reachability of subexpressions, (ii) to be defined in a syntax-directed manner, and (iii) to generate a set of constraints that subsequently can be solved by standard techniques. We prove equivalence results between the different versions of the analysis; in particular it follows that the least solution to the constraints generated will be the least analysis result also to the initial specification. 1 Introduction Many c...

A general approach for defining behavioural preorders over process terms as the maximal pre--congruences induced by basic observables is examined. Three different observables, that provide information about the initial communication capabilities of processes and about the possibility that processes get engaged in divergent computations, will be considered. We show that the pre--congruences induced by our basic observables coincide with intuitive and/or widely studied behavioural preorders. In particular, we retrieve in our setting the must preorder of De Nicola and Hennessy and the fair/should preorder introduced by Cleaveland and Natarajan and by Brinksma, Rensink and Vogler. A new form of testing preorder, which we call safe--must, also emerges. The alternative characterizations we offer shed light on the differences between these preorders, and on the role played in their definition by tests for divergence. 1 Introduction In the classical theory of functional programming, the point...

We present an extension to Haskell which supports reactive, concurrent programming with objects, sans the problematic blocking input. We give a semantics together with a number of programming examples, and show an implementation based on a preprocessor and a library implementing seven monadic constants. 1 Introduction With the advent of Haskell 1.3 the monadic I/O model has become well established [PH96]. At the top level, a Haskell program is now a sequence of imperative commands that transforms a state consisting of the real world and/or some program state into a final configuration. In a pure state transformational approach, carrying a monolithic program state around is likely to complicate modular design; however, this problem can to a large extent be circumvented by introducing first-class references in the monadic framework [LJ94]. Taken together, these additions make the resulting Haskell programs --- on the top level at least --- more and more reminiscent of programs written i...

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We describe a case study where novel program analysis technology has been used to pinpoint a subtle bug in a formally developed control program for an embedded system. The main technology amounts to first defining a process algebra (called behaviours) suited to the programming language used (in our case CML) and secondly to devise an annotated type and effect system for extracting behaviours from programs in a such a manner that an automatic inference algorithm can be developed. The case study is a control program developed for the "Karlsruhe Production Cell" and our analysis of the behaviours shows that one of the safety conditions fails to hold.