Task-oriented programming in a pure functional language

Lecture Notes in Computer Science, 1996

Lecture Notes in Computer Science, 2008

In these lecture notes we present the iTask system: a set of combinators to specify work flows in a pure functional language at a very high level of abstraction. Work flow systems are automated systems in which tasks are coordinated that have to be executed by either humans or computers. The combinators that we propose support work flow patterns commonly found in commercial work flow systems. In addition, we introduce novel work flow patterns that capture real world requirements, but that can not be dealt with by current systems. Compared with most of these commercial systems, the iTask system offers several further advantages: tasks are statically typed, tasks can be higher order, the combinators are fully compositional, dynamic and recursive work flows can be specified, and last but not least, the specification is used to generate an executable web-based multi-user work flow application. With the iTask system, useful work flows can be defined which cannot be expressed in other systems: a work can be interrupted and subsequently directed to other workers for further processing. The iTask system has been constructed in the programming language Clean, making use of its generic programming facilities, and its iData toolkit with which interactive, thin-client, form-based web applications can be created. In all, iTasks are an excellent case of the expressive power of functional and generic programming.

2018

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Proceedings of IEEE International Symposium on Parallel Algorithms Architecture Synthesis, 1997

Programming massively-parallel machine is a daunting task for any human programmer and parallelization may even be impossible for any compiler. Instead, the functional programming paradigm may prove to be an ideal solution by providing an implicitly parallel interface to the programmer. We describe here the Sisal project (Stream and Iteration in a Single Assignment Language) and its goal to provide a general-purpose user interface for a wide range of parallel processing platforms.

Lecture Notes in Computer Science, 1989

FACILE is a language which symmetrically integrates concurrent and functional programming. It is a typed and statically scoped language. The language supports both function and process abstractions.

2011

Workflow languages are a form of high-level programming language designed for coordinating tasks implemented by different pieces of software, often executed across multiple computers using technologies such as web services. Advantages of workflow languages include automatic parallelisation, built-in support for accessing services, and simple programming models that abstract away many of the complexities associated with distributed and parallel programming. In this thesis, we focus on data-oriented workflow languages, in which all computation is free of side effects. Despite their advantages, existing workflow languages sacrifice support for internal computation and data manipulation, in an attempt to provide programming models that are simple to understand and contain implicit parallelism. These limitations inconvenience users, who are forced to define additional components in separate scripting languages whenever they need to implement programming logic that cannot be expressed in the workflow language itself. In this thesis, we propose the use of functional programming as a model for data-oriented workflow languages. Functional programming languages are both highly expressive and amenable to automatic parallelisation. Our approach combines the coordination facilities of workflow languages with the computation facilities of functional programming languages, allowing both aspects of a workflow to be expressed in the one language. We have designed and implemented a small functional language called ELC, which extends lambda calculus with a minimal set of features necessary for practical implementation of workflows. ELC can either be used directly, or as a compilation target for other workflow languages. Using this approach, we developed a compiler for XQuery, extended with support for web services. XQuery's native support for XML processing makes it well-suited for manipulating the XML data produced and consumed by web services. Both languages make it easy to develop complex workflows involving arbitrary computation and data manipulation. Our workflow engine, NReduce, uses parallel graph reduction to execute workflows. It supports both orchestration, where a central node coordinates all service invocation, and choreography, where coordination, scheduling, and data transfer are carried out in a decentralised manner across multiple nodes. The details of orchestration and choreography are abstracted away from the programmer by the workflow engine. In both cases, parallel invocation of services is managed in a completely automatic manner, without any explicit direction from the programmer. Our study includes an in-depth analysis of performance issues of relevance to our approach. This includes a discussion of performance problems encountered during our implementation work, and an explanation of the solutions we have devised to these. Such issues are likely to be of relevance to others developing workflow engines based on a similar model. We also benchmark our system using a range of workflows, demonstrating high levels of performance and scalability.

arXiv (Cornell University), 2022

The Internet of Things (IoT) is growing fast. In 2018, there was approximately one connected device per person on earth and the number has been growing ever since. The devices interact with the environment via different modalities at the same time using sensors and actuators making the programs parallel. Yet, writing this type of programs is difficult because the devices have little computation power and memory, the platforms are heterogeneous and the languages are low level. Task Oriented Programming (TOP) is a declarative programming language paradigm that is used to express coordination of work, collaboration of users and systems, the distribution of shared data and the human-computer interaction. The mTask language is a specialized, yet full-fledged, multi-backend TOP language for IoT devices. With the bytecode interpretation backend and the integration with iTask, tasks can be executed on the device dynamically. This means that-according to the current state of affairs-tasks can be tailor-made at run time, compiled to device-agnostic bytecode and shipped to the device for interpretation. Tasks sent to the device are fully integrated in iTask to allow every form of interaction with the tasks such as observation of the task value and interaction with Shared Data Sources (SDSs). The entire IoT application-both server and devices-are programmed in a single language, albeit using two embedded Domain Specific Languages (EDSLs).

1996

Introduction This PhD Thesis is the result of a four-year research project conducted at the Department of Functional Programming, the Faculty of Mathematics and Informatics, at the University of Nijmegen as 'Assistent-in-Opleiding' under supervision of Professor M.J. Plasmeijer. In this chapter we give a survey of the research project and its theses. 1.1 Functional programming and the Clean project 3 we will encounter some of these cases which show up because of the complexity of the I/O system. The functional programming language we consider in this PhD.Thesis is pure and lazy. Due to strong normalisation lazy functional languages are preferable over their eager relatives. However, lazyness complicates their implementation. In general lazy languages are less time and space efficient than eager languages, or imperative languages. A lot of research has been conducted in this area in the last decades, and is still continuing. One specific approach to investigate and provide solutions to the problems of efficient implementations of functional languages is the (Concurrent) Clean project. Clean is a sequential lazy, purely functional programming language (

In these lecture notes we present the iTask system: a set of combinators to specify workflows in a pure functional language at a very high level of abstraction. Workflow systems are automated systems in which tasks are coordinated that have to be executed by either humans or computers. The combinators that we propose support workflow patterns commonly found in commercial workflow systems. In addition, we introduce novel workflow patterns that capture real world requirements, but that can not be dealt with by current systems. Compared with most of these commercial systems, the iTask system offers several further advantages: tasks are statically typed, tasks can be higher order, the combinators are fully compositional, dynamic and recursive workflows can be specified, and last but not least, the specification is used to generate an executable web-based multi-user workflow application. With the iTask system, useful workflows can be defined which cannot be expressed in other systems: a work can be interrupted and subsequently directed to other workers for further processing. The iTask system has been constructed in the programming language Clean, making use of its generic programming facilities, and its iData toolkit with which interactive, thin-client, form-based web applications can be created. In all, iTasks are an excellent case of the expressive power of functional and generic programming.

This paper gives an overview of the concurrent functional programming language and its development, dissemination, and use. Erlang was developed at Ericsson and is used for several large and important telecom systems. It is also available externally, both supported and through open source. Erlang provides a highly relevant case-study of technology diffusion since its development touches upon many relevant topics such as applied research in the industrial environment and spread of technology through open source.

2003

Abstract: We describe a programming language for distributed computations that supports mobile resources and is based on a process calculus. The syntax, semantics and implementation of the language are presented with a focus on the novel model of computation. Key Words: Process-Calculus, Distributed Computing, Mobile Resources Category: D. 1.3, D. 3.2

Nederlands Tijdschrift Voor Geneeskunde, 2007

In this paper we introduce the iTask system: a set of combinators to specify work flows in a pure functional language at a very high level of abstraction. Work flow systems are automated systems in which tasks are coordinated that have to be executed by humans and computers. The combinators that we propose support work flow patterns commonly found in commercial work flow systems. Compared with most of these commercial systems, the iTask system offers several advantages: tasks are statically typed, tasks can be higher order, the combinators are fully compositional, dynamic and recursive work flows can be specified, and last but not least, the specification is used to generate an executable web-based multi-user work flow application. With the iTask system, useful work flows can be defined which cannot be expressed in other systems: work can be interrupted and subsequently directed to other workers for further processing.

2007

Our aim is to define the kernel of a simple and uniform programming model—the reactor model—suitable for building and evolving internet-scale programs. A reactor consists of two principal components: mutable state, in the form of a fixed collection of relations, and code, in the form of a fixed collection of rules in the style of datalog. A reactor’s code is executed in response to an external stimulus, which takes the form of an attempted update to the reactor’s state. As in classical process calculi, the reactor model accommodates collections of distributed, concurrently executing processes. However, unlike classical process calculi, our observable behaviors are sequences of states, rather than sequences of messages. Similarly, the interface to a reactor is simply its state, rather than a collection of message channels, ports, or methods. One novel feature of our model is the ability to compose behaviors both synchronously and asynchronously. Also, our use of datalog-style rules allows aspect-like composition of separately-specified functional concerns in a natural way

Proceedings of the Tenth Workshop on Language Descriptions, Tools and Applications - LDTA '10, 2010

Workflow management systems guide and monitor tasks performed by humans and computers. The workflow specifications are usually expressed in special purpose (graphical) formalisms. These formalisms impose severe restrictions on what can be expressed. Modern workflow management systems should handle intricate data dependencies, offer a web-based interface, and should adapt to dynamically changing situations, all based on a sound formalism. To address these challenges, we have developed the iTask system, which is a novel workflow management system. We entirely embed the iTask specification language in a modern general purpose functional language, and generate a complete workflow application. In this paper we report our experiences in developing the iTask system. It not only inherits state-of-the-art programming language concepts such as generic programming and a hybrid static/dynamic type system from the host language Clean, but also offers a number of novel concepts to generate complex, real-world, multi-user, web based workflow applications.

Proceedings of the 31st Symposium on Implementation and Application of Functional Languages

Small Microcontroller Units (MCUs) drive the omnipresent Internet of Things (IoT). These devices are small, cheap, and energy efficient. However, they are not very powerful and lack an Operating System. Hence it is difficult to apply high level abstractions and write software that stays close to the design. Task Oriented Programming (TOP) is a paradigm for creating multiuser collaborative systems. A program consists of tasksdescriptions of what needs to be done. The tasks represent the actual work and a task value is observable during execution. Furthermore, tasks can be combined and transformed using combinators. mTask is an embedded Domain Specific Language (eDSL) to program MCUs following the TOP paradigm. Previous work has described the mTask language, a static C code generator, and how to integrate mTask with TOP servers. This paper shows that for dynamic IOT applications, tasks must be sent at runtime to the devices for interpretation. It describes in detail how to compile specialized IOT TOP tasks to bytecode and how to interpret them on devices with very little memory. These additions allow the creation of complete, dynamic IOT applications arising from a single source using a mix of iTasks and mTask tasks. Details such as serialization and communication are captured in simple abstractions. CCS CONCEPTS • Computer systems organization → Distributed architectures; • Software and its engineering → Client-server architectures; Functional languages; Domain specific languages.