Concurrent Interactive Processes in a Pure Functional Language

Lecture Notes in Computer Science, 1996

1987

Abstract In this paper we present a model of interactive programs in a purely functional style. We exploit lazy evaluation in the modelling of streams as lazy lists. We show how programs may be constructed in an ad hoc way, and then present a small set of interactions and combinators which form the basis for a disciplined approach to writing such programs. One of the di culties of the ad hoc approach is that the way in which input and output are interleaved by the functions can be unpredictable.

ACM Transactions on Programming Languages and Systems, 1998

We propose a novel static type system for a process calculus, which ensures both partial deadlockfreedom and partial confluence. The key novel ideas are (1) introduction of the order of channel use as type information, and (2) classification of communication channels into reliable and unreliable channels based on their usage and a guarantee of the usage by the type system. We can ensure that communication on reliable channels never causes deadlock and also that certain reliable channels never introduce nondeterminism. After presenting the type system and formal proofs of its correctness, we show encodings of the λ-calculus and typical concurrent objects in the deadlockfree fragment of the calculus and demonstrate how type information can be used for reasoning about program behavior.

Journal of Systems Architecture, 1998

Many real-time systems make use of concurrent programming systems and are often designed using object oriented design methods. Concurrent Object Oriented Languages (COOLS) are a class of programming language that integrates the facilities of concurrent and object oriented programming in an integrated rather than orthogonal manner. With the increasing interest in the use of object oriented languages such as C++ for the programming of embedded and real-time systems COOLs seem to be a natural candidate for such tasks. Several COOLs have been described in the literature which address the requirements of concurrent programming, inter-process communication (IPC) and synchronisation in various dierent ways. This paper discusses one such language, ClassiC, and examines the approach to this problem taken in its design. In particular, it is shown that the features of ClassiC allow derivation of active classes from other active classes. It is shown how this property can be used to overcome some of the problems associated with synchronous IPC schemes while maintaining the advantages of them and how the use of the asynchronous IPC model allows ver-i®cation of synchronisation and deadlock properties based on the use of CSP methods.

Proceedings of the 4th Workshop on Scala - SCALA '13, 2013

The dataflow programming paradigm addresses how data flows inside programs. Program components, that are often concurrently active, send data to one another; this eases software composition. Mainstream programming languages do not support the paradigm well because of their deterministic and sequential nature. A language that focuses on concurrency is better suited to incorporate concepts from the dataflow paradigm. SubScript is an extension to the Scala programming language with constructs from the Algebra of Communicating Processes, targeted at event-driven and concurrent programming. Like ACP, SubScript focuses on program behavior; support for data was through local variables and parameters. However, the ACP background enabled SubScript to deal with the challenges of the dataflow paradigm. This is achieved through several new features. 1. A process may have a result value, like a method 2. A process result value may be passed on to another process that starts subsequently. This helps getting rid of variables, e.g., in GUI controller specifications. 3. Output actions from a process may be piped to a parallel process, yielding a similar expressiveness as pipes in Unix command shell language. 4. Actors written in Scala often need to keep track of a state, and their program text poorly expresses the conceptual control flow. When such actors are written in SubScript, incoming data may be treated as events that may appear anywhere in the specification, just like in SubScript GUI specifications.

1996

This paper presents an imperative and concurrent extension of the functional object-oriented calculus described in . It belongs to the family of so-called prototype-based object-oriented languages, in which objects are created from existing ones via the inheritance primitives of object extension and method override. Concurrency is introduced through the identification of objects and processes. To our knowledge, the resulting calculus is the first concurrent object calculus to be studied. We define an operational semantics for the calculus via a transition relation between configurations, which represent snapshots of the run-time system. Our static analysis includes a type inference system, which statically detects message.not.understood errors, and an effect system, which guarantees that synchronization code, specified via guards, is side-effect free. We present a subject reduction theorem, modified to account for imperative and concurrent features, and type and effect soundness theorems.

Proceedings of the 14th symposium on Principles and practice of declarative programming - PPDP '12, 2012

Task-Oriented Programming (TOP) is a novel programming paradigm for the construction of distributed systems where users work together on the internet. When multiple users collaborate, they need to interact with each other frequently. TOP supports the definition of tasks that react to the progress made by others. With TOP, complex multiuser interactions can be programmed in a declarative style just by defining the tasks that have to be accomplished, thus eliminating the need to worry about the implementation detail that commonly frustrates the development of applications for this domain. TOP builds on four core concepts: tasks that represent computations or work to do which have an observable value that may change over time, data sharing enabling tasks to observe each other while the work is in progress, generic type driven generation of user interaction, and special combinators for sequential and parallel task composition. The semantics of these core concepts is defined in this paper. As an example we present the iTask3 framework, which embeds TOP in the functional programming language Clean.

HAL (Le Centre pour la Communication Scientifique Directe), 2016

Choreographic Programming is an emerging paradigm for correct-by-construction concurrent programming. However, its applicability is limited by the current lack of support for reusable procedures. We propose Procedural Choreographies (PC), a choreographic language model with full procedural abstraction. PC includes unbounded process creation and name mobility, yielding a powerful framework for writing correct concurrent algorithms that can be compiled into a process calculus. This increased expressivity requires a typing discipline to ensure that processes are properly connected when enacting procedures.

Information and Computation, 2009

Deterministic behavior for parallel and distributed computation is rather difficult to ensure. To reach that goal, many formal calculi, languages, and techniques with well-defined semantics have been proposed in the past. But none of them focused on an imperative object calculus with asynchronous communications and futures. In this article, an object calculus, Asynchronous Sequential Processes (ASP), is defined, with its semantics. We prove also confluence properties for the ASP calculus. ASPs main characteristics are asynchronous communications with futures, and sequential execution within each process. This paper provides a very general and dynamic property ensuring confluence. Further, more specific and static properties are derived. Additionally, we present a formalization of distributed components based on ASP, and show how such components are used to statically ensure determinacy. This paper can also be seen as a formalization of the concept of futures in a distributed object setting.

1993

Abstract In a concurrent functional language processes are functions that are executed concurrently. Using special annotations based on lazy copying arbitrary dependencies between these functions can be used to specify arbitrary networks of processes. The communication and synchronization between the processes is realized using the lazy evaluation principle without any additional communication primitves. Communication takes place when a process demands a value that is being calculated by another process.