Eden is a concurrent declarative language that aims at both the programming of reactive systems and parallel algorithms on distributed memory systems. In this paper, we explain the computation and coordination model of Eden. We show how lazy evaluation in the computation language is fruitfully combined with the coordination language that is specifically designed for multicomputers and that aims at maximum parallelism. The two-level structure of the programming language is reflected in its operational semantics, which is sketched shortly.

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We define a new language `EDEN' by extending a functional language by constructs for the explicit specification of dynamic process systems. Following Shapiro [Sha89] we distinguish transformational and reactive systems. Simple annotationlike notions for the explicit definition of processes are sufficient to describe the class of transformational systems. For the definition of reactive systems extra-functional constructs must be introduced. We show that a concept similar to the "incomplete message principle" from concurrent logic programming is a vital and powerful mechanism for the treatment of dynamically specified communication channels. Timedependencies are handled by special nondeterministic processes. 1 Introduction Most parallel programming languages used nowadays are based on the imperative programming paradigm. In such languages synchronization of and communication between processes must be handled by the programmer on a very low level of abstraction and the verification of pr...

This paper gives an overview of the main streams of research on concurrency in declarative languages and motivates the definition of the new concurrent functional language EDEN. Proceeding from the premise that parallelism should be expressed explicitly we have equipped the language with an explicit representation of processes and process abstractions. It is based on a lazy functional language and offers dynamic creation of processes and communication channels and a safe treatment of nondeterminism. 1. Introduction and Terminology Today the majority of parallel programs is written in imperative languages. This programming paradigm forces the programmer to use low-level constructs for synchronization and interprocess communication and it offers no support for the verification of programs. In contrast to imperative languages, declarative languages have the advantage that programs are able to retain parallelism inherent in the problem specification. Functional and logic programs can be ...