Architecture The Alma Abstract Architecture (AAA) is the virtual architecture used during the intermediate code generation phase of the Alma-0 compiler. The AAA combines the features of the abstract machines for imperative languages and for logic programming languages. The compiler compiles the Alma-0 programs into AAA programs. In a second phase the AAA instructions are translated into C statements. As the Alma-0 language itself, the AAA aims to combine the best of both worlds; elements were taken from virtual machines used to compile imperative languages (in particular the RISC architecture described in Wirth [1996, pp. 55--59], and from the WAM machine used to compile a logical language (see Ait-Kaci [1991]). Still, the AAA resembles most the virtual machines used in the compilation of imperative languages. The additions made to provide for the extensions of the Alma-0 language are ---the failure handling instructions ONFAIL, FAIL, 40 \Delta Krzysztof R. Apt et al ---the log ...

First-order languages based on rewrite rules share many features with functional languages. But one difference is that matching and rewriting can be made much more expressive and powerful by incorporating some built-in equational theories. To provide reasonable programming environments, compilation techniques for such languages based on rewriting have to be designed. This is the topic addressed in this paper. The proposed techniques are independent from the rewriting language and may be useful to build a compiler for any system using rewriting modulo associative and commutative (AC) theories. An algorithm for many-to-one AC matching is presented, that works efficiently for a restricted class of patterns. Other patterns are transformed to fit into this class. A refined data structure, namely compact bipartite graph, allows encoding all matching problems relative to a set of rewrite rules. A few optimisations concerning the construction of the substitution and of the reduced term are described. We also address the problem of non-determinism related to AC rewriting and show how to handle it through the concept of strategies. We explain how an analysis of the determinism can be performed at compile time and we illustrate the benefits of this analysis for the performance of the compiled evaluation process. Then we briefly introduce the ELAN system and its compiler, in order to give some experimental results and comparisons with other languages or rewrite engines.

The syntax and semantics of the programming language Alma-0 have been specified in the ASF+SDF formalism. This report contains the interesting parts of the specification, embedded in text explaining its structure, various technical details and the choices that have been made during the specification process. The report also contains a short introduction to the language Alma-0, including some examples of meaningful Alma-0-programs.

In [ Apt et al., 1998 ] we introduced the imperative programming language Alma-0 that supports declarative programming. In this paper we illustrate the hybrid programming style of Alma-0 by means of various examples that complement those presented in [ Apt et al., 1998 ] . The presented Alma-0 programs illustrate the versatility of the language and show that "don't know" nondeterminism can be naturally combined with assignment.

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