On the Implementation of GNU Prolog

GNU Prolog is a general-purpose implementation of the Prolog language, which distinguishes itself from most other systems by being, above all else, a native-code compiler which produces standalone executables which don't rely on any byte-code emulator or meta-interpreter. Other aspects which stand out include the explicit organization of the Prolog system as a multipass compiler, where intermediate representations are materialized, in Unix compiler tradition. GNU Prolog also includes an extensible and high-performance finite domain constraint solver, integrated with the Prolog language but implemented using independent lower-level mechanisms. This article discusses the main issues involved in designing and implementing GNU Prolog: requirements, system organization, performance and portability issues as well as its position with respect to other Prolog system implementations and the ISO standardization initiative.Comment: 30 pages, 3 figures, To appear in Theory and Practice of Logic Programming (TPLP); Keywords: Prolog, logic programming system, GNU, ISO, WAM, native code compilation, Finite Domain constraint

Some considerations on the compile-time analysis of constraint logic programs

This paper discusses some issues which arise in the dataflow analysis of constraint logic programming (CLP) languages. The basic technique applied is that of abstract interpretation. First, some types of optimizations possible in a number of CLP systems (including efficient parallelization) are presented and the information that has to be obtained at compile-time in order to be able to implement such optimizations is considered. Two approaches are then proposed and discussed for obtaining this information for a CLP program: one based on an analysis of a CLP metainterpreter using standard Prolog analysis tools, and a second one based on direct analysis of the CLP program. For the second approach an abstract domain which approximates groundness (also referred to as "definiteness") information (i.e. constraint to a single valué) and the related abstraction functions are presented

A Framework for Efficient Execution of Logic Programs.

The focus of this dissertation is to develop an efficient framework for sequential execution of logic programs. Within this framework the logic programs are executed by pruning the goal-search tree whenever applicable. Three new concepts for pruning of computation during execution of logic programs are introduced. (1) Failure-binding. A Failure-binding for a literal is a binding which when applied to the literal fails the goal obtained from the literal. Failure-bindings for a literal are identified by analyzing the goal-tree of a goal which is obtained from the literal. The failure-bindings for a literal are used for intelligent backtracking based on the generator-consumer approach. Intelligent backtracking based on failure-bindings prune the computation of search space which lead to late detection of failure. (2) Failure-solution. A Failure-solution of a goal is unacceptable to some other subgoal in the forward execution. Failure-solutions of a goal are identified by analyzing the history of computation, during execution. Failure-solutions of the goals are used for intelligent forward execution. Intelligent forward execution prunes the computation of search space which leads to repeated failure resulting from repeated successes of a goal. (3) Forward jumping. Forward jumping is a method to avoid reexecution of some subgoals after backtracking (instead of naive forward execution after backtracking). Forward jumping is based on the dynamic subgoal dependencies in a rule. Such jumping prunes the computation of the search spaces which leads to the same sequences of successes of subgoals after backtracking. To facilitate the implementation of these concepts a new data structure, called segmented-stack, is defined. The space complexity of a segmented stack is linear in the number of nodes in the stack. Depth-first search as well as breadth-first search are very easily implemented on a segmented-stack during execution of logic programs. Execution of logic programs on a segmented-stack allows association of the search space, as well as the solutions, of a goal with the frame of the goal. This enables implementation of intelligent backtracking, intelligent forward execution and forward jumping. The search based on each of these paradigms is proved to be sound and complete. It is also shown that the implementation of these paradigms preserves the order of results obtained by Prolog. The effects of the non-logical operators, in Prolog, on the paradigms are studied. The search based on the these paradigms is compared individually, and collectively, with the standard search by Prolog

SICStus MT - A Multithreaded Execution Environment for SICStus Prolog

The development of intelligent software agents and other complex applications which continuously interact with their environments has been one of the reasons why explicit concurrency has become a necessity in a modern Prolog system today. Such applications need to perform several tasks which may be very different with respect to how they are implemented in Prolog. Performing these tasks simultaneously is very tedious without language support. This paper describes the design, implementation and evaluation of a prototype multithreaded execution environment for SICStus Prolog. The threads are dynamically managed using a small and compact set of Prolog primitives implemented in a portable way, requiring almost no support from the underlying operating system

Programming Languages for Distributed Computing Systems

When distributed systems first appeared, they were programmed in traditional sequential languages, usually with the addition of a few library procedures for sending and receiving messages. As distributed applications became more commonplace and more sophisticated, this ad hoc approach became less satisfactory. Researchers all over the world began designing new programming languages specifically for implementing distributed applications. These languages and their history, their underlying principles, their design, and their use are the subject of this paper. We begin by giving our view of what a distributed system is, illustrating with examples to avoid confusion on this important and controversial point. We then describe the three main characteristics that distinguish distributed programming languages from traditional sequential languages, namely, how they deal with parallelism, communication, and partial failures. Finally, we discuss 15 representative distributed languages to give the flavor of each. These examples include languages based on message passing, rendezvous, remote procedure call, objects, and atomic transactions, as well as functional languages, logic languages, and distributed data structure languages. The paper concludes with a comprehensive bibliography listing over 200 papers on nearly 100 distributed programming languages

1957-2007: 50 Years of Higher Order Programming Languages

Fifty years ago one of the greatest breakthroughs in computer programming and in the history of computers happened – the appearance of FORTRAN, the first higher-order programming language. From that time until now hundreds of programming languages were invented, different programming paradigms were defined, all with the main goal to make computer programming easier and closer to as many people as possible. Many battles were fought among scientists as well as among developers around concepts of programming, programming languages and paradigms. It can be said that programming paradigms and programming languages were very often a trigger for many changes and improvements in computer science as well as in computer industry. Definitely, computer programming is one of the cornerstones of computer science. Today there are many tools that give a help in the process of programming, but there is still a programming tasks that can be solved only manually. Therefore, programming is still one of the most creative parts of interaction with computers. Programmers should chose programming language in accordance to task they have to solve, but very often, they chose it in accordance to their personal preferences, their beliefs and many other subjective reasons. Nevertheless, the market of programming languages can be merciless to languages as history was merciless to some people, even whole nations. Programming languages and developers get born, live and die leaving more or less tracks and successors, and not always the best survives. The history of programming languages is closely connected to the history of computers and computer science itself. Every single thing from one of them has its reflexions onto the other. This paper gives a short overview of last fifty years of computer programming and computer programming languages, but also gives many ideas that influenced other aspects of computer science. Particularly, programming paradigms are described, their intentions and goals, as well as the most of the significant languages of all paradigms