Section: Scientific Foundations
Synchronous Programming
Participants : Cédric Auger, Nicolas Bertaux, Léonard Gérard, Louis Mandel, Florence Plateau, Marc Pouzet.
The goal is to propose high-level languages for the development of critical embedded systems with both high temporal requirements and safety [51] , [88] , [52] , [59] . Our research activities concern the extension of synchronous languages with richer abstraction mechanisms (e.g., higher-order, functionality, dedicated type systems such as the clock calculus), the ability to describe heterogeneous systems (e.g., data-flow and control-flow, discrete and continous) or to account for resources through dedicated type-systems.
These research activities are experimented inside two programming languages, Lucid Synchrone and ReactiveML.
Lucid Synchrone is a data-flow language based on a Lustre semantics and is dedicated to real-time embedded software. It extends Lustre with features usually found in ML-languages such as typing and higher-order functions. It provides original features such as the arbitrary mix of data-flow and hierarchical automata [2] [68] , various type-based static analysis [69] , [70] and modular compilation into sequential code [60] , [55] [54] .
ReactiveML is an extension of Objective Caml with synchronous concurrency (based on synchronous parallel composition and broadcast of signals). The goal is to provide a general model of deterministic concurrency inside a general purpose functional language to program reactive systems (e.g., graphical interfaces, simulation systems). The research activity concerns the development of compilation techniques, dedicated type systems to ensure various safety properties (e.g., determinism, reactivity, boundedness) or the mix of both synchronous and asynchronous concurrency.
In collaboration with Albert Cohen and Christine Eisenbeis (INRIA Alchemy), Marc Duranton (Philips Natlabs, Eindhoven), we have introduced in 2005 a new programming model for the design of video intensive applications. This model, called the N -synchronous model, is based on an extension of the synchronous model allowing to combine non strictly synchronous streams provided that they can be synchronized through the use of bounded buffers. This is obtained by introducing particular clocks as infinite binary periodic words [111] . Thanks to the periodic nature of these clocks, we are able to verify properties like the absence of buffer overflows and deadlocks during the execution. Clock verification is expressed as a type-inference problem with a sub-typing rule. The core of the model has been settled in [65] and [66] . Florence Plateau works since that time on this subject. We introduced a notion of abstractions for these clocks in 2008 as a mean to reason about sets of (non necessarily periodic) clocks [67] .
