CLEAN: a programming environment based on term graph rewriting

The main features of the lazy functional language Concurrent Clean and of its semantics based on Term Graph Rewriting are presented. 1 History The pure, lazy functional language Concurrent Clean (version 1.0) is a major upgrade of the previous release (0.84b) of Clean ((3,10,11]). Clean was originally designed as an experimental intermediate language and deliberately kept syntactically as poor as possible to be able to focus on the essential language and implementation issues. This strategy enabled us to study new concepts (such as term graph rewriting 1], lazy copying 4], abstract reduction 8], uniqueness typing 2]) without too much implementation eeort. The ideas were tested in the Clean compiler which could be used on small machines and produced state-of-the-art code 13]. The consequence was that people started to use Clean to construct large applications even though Clean was actually not intended as a programming language. So, it became necessary to turn the experimental intermediate language into a proper practical applicable general purpose functional programming language suited for the development of real world applications. 1.1 What is special about Concurrent Clean 1.0? Compared with the previous version of Clean a lot of new features are added based on our own experience with writing complex applications (such as the new Clean I/O system). Many of the added language constructs are similar to those commonly found in other modern lazy functional languages (such as Miranda 15], SML 5], Haskell 7]. People familiar with these languages will have no diiculty to program in Clean and we hope that they enjoy the compilation speed and quality of the produced code. In addition Clean ooers a couple of very special features. Of particular importance for practical use is Cleans' uniqueness typing enabling the incorporation of destructive updates c 1995 Elsevier Science B. V.