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Abstract.Clean is an experimental language for specifying functional computations in terms of graph rewriting. It is based on an extension of Term Rewriting Systems (TRS) in which the terms are replaced by graphs. Such a Graph Rewriting System (GRS) consists of a, possibly cyclic, directed graph, called the data graph and graph rewrite rules which specify how this data graph may be rewr~en. Clean is designed to provide a firm base for functional programming. In particular, Clean is suitable as an intermediate language between functional languages and (parallel) target machine architectures. A sequential implementation of Clean on a conventional machine is described and its performance is compared with other systems. The results show that Clean can be efficiently implemented.

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In this paper we p r esent a t ype system f o r g r aph rewrite systems: uniqueness typing. It employs u s a ge information to deduce whether an o b j e c t i s u n i q u e ' a t a certain moment, i.e. is only locally accessible. In a type of a function it can bespeci ed that the function requires a unique argument o b j e c t. The correctness of type assignment guarantees that no external a ccess on t h e o r iginal o bject will take place in the future. The presented t ype system is proven to be correct. We illustrate the power of the system by de ning an elegant q u i c ksort a l g orithm that performs the sorting in situ on the data structure.

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partially supported by the Dutch Parallel Reduction Machine Project. Abstract.Lean is an experimental language for specifying computations in terms of graph rewriting. It is based on an alternative to Term Rewriting Systems (TRS) in which the terms are replaced by graphs. Such a Graph Rewriting System (GRS) consists of a set of graph rewrite rules which specify how a graph may be rewritten. Besides supporting functional programming, Lean also describes imperative constructs and allows the manipulation of cyclic graphs. Programs may exhibit non-determinism as well as parallelism. In particular, Lean can serve as an intermediate language between declarative languages and machine architectures, both sequential and parallel.