Esterel is a synchronous concurrent programming language dedicated to reactive systems (controllers, protocols, man-machine interfaces, etc.). Esterel has an efficient standard software implementation based on well-defined mathematical semantics. We present a new hardware implementation of the pure synchronization subset of the language. Each program generates a specific circuit that responds to any input in one clock cycle. When the source program satisfies some statically checkable dynamic properties, the circuit is shown to be semantically equivalent to the source program. The hardware translation has been effectively implemented on the programmable active memory Perle0 developed by J. Vuillemin and his group at Digital Equipment.

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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.

Rockit is a system that identifies the possible graphical constraints between objects in a two-dimensional scene and allows the user to choose and apply the desired constraints quickly and easily. Rockit looks for intersections between the position of a designated object and the gravity fields of other objects to determine the possible constraints. These candidate constraints are passed to a rule system that encodes some simple knowledge about how graphical objects normally interact and can thus be constrained to one another. The rules are used to determine the most likely constraints to be applied between the designated object and the other objects in the scene. As the user manipulates the object, the object will gravitate towards the most likely constraint scenario. The inferred constraints are indicated by the creation of graphical and sonic feedback objects. Rockit makes it easy to try other likely scenarios by simply pressing a key, causing the system to cycle through the other p...

We introduce a constraint system called FT. This system offers a theoretical and practical alternative to the usual Herbrand system of constraints over constructor trees. Like Herbrand, FT provides a universal data structure based on trees. However, the trees of FT (called feature trees) are more general than the constructor trees of Herbrand, and the constraints of FT are of finer grain and of different expressiveness. The essential novelty of FT is provided by functional attributes called features which allow representing data as extensible records, a more flexible way than that offered by Herbrand's fixed arity constructors. The feature tree structure determines an algebraic semantics for FT. We establish a logical semantics thanks to three axiom schemes presenting the first-order theory FT. We propose using FT as a constraint system for logic programming. We provide a test for constraint unsatisfiability, and a test for constraint entailment. The former corresponds to unification ...

LIFE is an experimental programming language proposing to integrate logic programming, functional programming, and object-oriented programming. It replaces first-order terms with ψ-terms, data structures which allow computing with partial information. These are approximation structures denoting sets of values. LIFE further enriches the expressiveness of ψ-terms with functional dependency constraints. We must explain the meaning and use of functions in LIFE declaratively as solving partial information constraints. These constraints do not attempt to generate their solutions but behave as demons filtering out anything else.

A planar map is a figure formed by a set of intersecting lines and curves. Such an object captures both the geometrical and the topological information implicitly defined by the data. In the context of 2D drawing, it provides a new interaction paradigm, map sketching, for editing graphic shapes. To build a planar map, one must compute curve intersections and deduce from them the map they define. The computed topology must be consistent with the underlying geometry. Robustness of geometric computations is a key issue in this process. This report presents a robust solution to Bezier curve intersection that uses exact forward differencing and bounded rational arithmetic. Data structures and algorithms supporting incremental insertion of Bezier curves in a planar map are described. A prototype illustration tool using this method is also discussed. R esum e Considerons la figure plane formee par un ensemble de segments de droite et d'arcs de courbe intersectants. Une carte planaire est une ...

Much research has been devoted to path planning during the past decade, i.e. the geometrical problem of finding a collision-free path between two given postures (configurations) of an articulated body (robot) among obstacles. This problem has straightforward applications in robotic automation, computer aided design, and computer graphics animation. Current global techniques compute explicitly the non-colliding zones in configuration space. Thus, they require exponential space and time in the number of Degrees of Freedom (DOF) of the body. These methods are therefore untractable for more than 4 DOF. This report presents a new approach to path planning which does not require construction of an explicit description of the configuration space. The method consists of building and searching a graph connecting the local minima of a potential function defined over the configuration space. The graph is explored by means of a randomization technique that escapes the local minima by executing Bro...

The purpose of this paper is to give an exposition of material dealing with constructive logics, typed -calculi, and linear logic. The first part of this paper gives an exposition of background material (with the exception of the Girard-translation of classical logic into intuitionistic logic, which is new). This second part is devoted to linear logic and proof nets. Particular attention is given to the algebraic semantics (in Girard's terminology, phase semantics) of linear logic. We show how phase spaces arise as an instance of a Galois connection. We also give a direct proof of the correctness of the Danos-Regnier criterion for proof nets. This proof is based on a purely graph-theoretic decomposition lemma. As a corollary, we give an O(n 2 )-time algorithm for testing whether a proof net is correct. Although the existence of such an algorithm has been announced by Girard, our algorithm appears to be original. R esum e Le but de cet article est de donner une presentation d'elements...