Daniel Cabeza Gras

A New Module System for Prolog

It is now widely accepted that separating programs into modules is useful in program development and maintenance. While many Prolog implementations include useful module systems, we argue that these systems can be improved in a number of ways, such as, for example, being more amenable to effective global analysis and transformation and allowing separate compilation or sensible creation of standalone executables. We discuss a number of issues related to the design of such an improved module system for Prolog and propose some novel solutions. Based on this, we present the choices made in the Ciao module system, which has been designed to meet a number of objectives: allowing separate compilation, extensibility in features and in syntax, amenability to modular global analysis and transformation, enhanced error detection, support for meta-programming and higher-order, compatibility to the extent possible with official and de-facto standards, etc.

Global Analysis of Standard Prolog Programs

Abstract interpretation-based data-flow analysis of logic programs is, at this point, relatively well understood from the point of view of general frameworks and abstract domains. On the other hand, comparatively little attention has been given to the problems which arise when analysis of a full, practical dialect of the Prolog language is attempted, and only few solutions to these problems have been proposed to date. Existing proposals generally restrict in one way or another the classes of programs which can be analyzed. This paper attempts to fill this gap by considering a full dialect of Prolog, essentially the recent ISO standard, pointing out the problems that may arise in the analysis of such a dialect, and proposing a combination of known and novel solutions that together allow the correct analysis of arbitrary programs which use the full power of the language.

Extracting non-strict independent and-parallelism using sharing and freeness information

Logic programming systems which exploit and-parallelism among non-deterministic goals rely on notions of independence among those goals in order to ensure certain efficiency properties. “Non-strict” independence (NSI) is a more relaxed notion than the traditional notion of “strict” independence (SI) which still ensures the relevant efficiency properties and can allow considerable more parallelism than SI. However, all compilation technology developed to date has been based on SI, because of the intrinsic complexity of exploiting NSI. This paper fills this gap by developing a technique for compile-time detection of NSI. It also proposes algorithms for combined compile-time/run-time detection, presenting novel run-time checks for this type of parallelism. The approach is based on the knowledge of certain properties regarding the run-time instantiations of program variables —sharing and freeness— for which compile-time technology is available, with new approaches being currently proposed.