We provide a theoretical basis for studying termination of (general) logic programs with the Prolog selection rule. To this end we study the class of left terminating programs. These are logic programs that terminate with the Prolog selection rule for all ground goals. We offer a characterization of left terminating positive programs by means of the notion of an acceptable program that provides us with a practical method of proving termination. The method is illustrated by giving a simple proof of termination of the quicksort program for the desired class of goals. Then we extend this approach to the class of general logic programs by modifying the concept of acceptability. We prove that acceptable general programs are left terminating. The converse implication does not hold but we show that under the assumption of nonfloundering from ground goals every left terminating general program is acceptable. Finally, we prove that various ways of defining semantics coincide for acceptable gen...

Abstract: Mode and data dependency analyses find many applications in the generation of efficient exe-cutable code for logic programs. For example, mode information can be used to generate specialized unification instructions where permissible; to detect determinacy and functionality of programs; to gen-erate index structures more intelligently; to reduce the amount of runtime tests in systems that support goal suspension; and in the integration of logic and functional languages. Data dependency information can be used for various source-level optimizing transformations, to improve backtracking behavior, and to parallelize logic programs. This paper describes and proves correct an algorithm for the static infer-ence of modes and data dependencies in a program. The algorithm is shown to be quite efficient for pro-grams commonly encountered in practice.

We provide here a systematic comparative study of the relative strength and expressive power of a number of methods for program analysis of Prolog. Among others we show that these methods can be arranged in the following hierarchy: mode analysis ⇒ type analysis ⇒ monotonic properties ⇒ non-monotonic run-time properties. We also discuss a method allowing us to prove global run-time properties.

We provide simple conditions which allow us to conclude that in case of several well-known Prolog programs the unification algorithm can be replaced by iterated matching. The main tools used here are types and generic expressions for types. As already noticed by other researchers, such a replacement offers a possibility of improving the efficiency of program's execution.

In general, logic programs are undirected, i.e. there is no concept of "input" and "output" arguments to a procedure. An argument may be used either as an input or as an output argument, and programs may be executed either in a "forward" direction or in a "backward" direction. However, it is often the case that in a given program, a predicate is used with some of its arguments used consistently as input arguments and others as output arguments. Such mode information can be used by a compiler to effect various optimizations. This paper considers the problem of automatically inferring the modes of the predicates in a program. The dataflow analysis we use is more powerful than approaches relying on syntactic characteristics of programs, e.g. [18]. Our work differs from that of Mellish [14, 15] in that (i) we give a sound and efficient treatment of variable aliasing in mode inference; (ii) by propagating instantiation information using state transformations rather than through dependen...

This report surveys the major developments in sequential Prolog implementation during the period 1983--1993. In this decade, implementation technology has matured to such a degree that Prolog has left the university and become useful in industry. The survey is divided into four parts. The first part gives an overview of the important technical developments starting with the Warren Abstract Machine (WAM). The second part presents the history and the contributions of the major software and hardware systems. The third part charts the evolution of Prolog performance since Warren's DEC-10 compiler. The fourth part extrapolates current trends regarding the evolution of sequential logic languages, their implementation, and their role in the marketplace.

Interpretation Algorithms for Prolog: Two Optimization Techniques and their Experimental Evaluation* vincent englebert, baudouin le charlier and didier roland University of Namur, 21 rue Grandgagnage, B-5000 Namur, Belgium pascal van hentenryck+ Brown University, Box 1910, Providence, RI 02912, U.S.A.

This article reports some results on this correlation in the context of logic programs. A formal notion of the "precision" of an analysis algorithm is proposed, and this is used to characterize the worst-case computational complexity of a number of dataflow analyses with different degrees of precision. While this article considers the analysis of logic programs, the technique proposed, namely the use of "exactness sets" to study relationships between complexity and precision of analyses, is not specific to logic programming in any way, and is equally applicable to flow analyses of other language families.

. We consider how mode (such as input and output) and termination properties of typed higher-order constraint logic programming languages may be declared and checked effectively. The systems that we present have been validated through an implementation and numerous case studies. 1 Introduction Just like other paradigms logic programming benefits tremendously from types. Perhaps most importantly, types allow the early detection of errors when a program is checked against a type specification. With some notable exceptions most type systems proposed for logic programming languages to date (see [18]) are concerned with the declarative semantics of programs, for example, in terms of many-sorted, order-sorted, or higher-order logic. Operational properties of logic programs which are vital for their correctness can thus neither be expressed nor checked and errors will remain undetected. In this paper we consider how the declaration and checking of mode (such as input and output) and termina...

Abstract not found