Section: New Results

Reactive Programming

Participants : Guillaume Baudart, Louis Mandel, Cédric Pasteur, Marc Pouzet.

ReactiveML is an extension of OCaml 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. It is particularly suited to program discrete simulations, for instance of sensor networks.

One of the current focus of the research is being able to simulate huge systems, composed of millions of agents, by extending the current purely sequential implementation in order to be able to take advantage of multi-core and distributed architectures. This goal has led to the introduction of a new programming construct, reactive domain, which allows to define local time scales. These domains help for the distribution of the code but also increase the expressiveness of the language. In particular, it allows to do time refinement. A paper on this new construct and the related static analysis has been published [20] . An extended version is under submission.

We continued the work on a new reactivity analysis which ensures that a process can not prevent the other ones to from executing. This analysis has published in [19] . An English version is under submission.

The runtime of ReactiveML has been cleanup and a multi-threaded implementation has been developed. A paper describing this new implementation will be published in [27] .

All these novelties has been described precisely in the PhD thesis of Cédric Pasteur [1] .

During the year, ReactiveML has also bee applied to mixed music. Mixed music is about live musicians interacting with electronic parts which are controlled by a computer during the performance. It allows composers to use and combine traditional instruments with complex synthesized sounds and other electronic devices. There are several languages dedicated to the writing of mixed music scores. Among them, the Antescofo language coupled with an advanced score follower allows a composer to manage the reactive aspects of musical performances: how electronic parts interact with a musician. However these domain specific languages do not offer the expressiveness of functional programming.

We defined a synchronous semantics for the core language of Antescofo and an alternative implementation based on an embedding inside ReactiveML [9] . The semantics reduces to a few rules, is mathematically precise and leads to an interpretor of only a few hundred lines. The efficiency of this interpretor compares well with that of the actual implementation: on all musical pieces we have tested, response times have been less than the reaction time of the human ear. Moreover, this approach offers to the composer recursion, higher order, inductive types, as well as a simple way to program complex reactive behaviors thanks to the synchronous model of concurrency on which ReactiveML is built [10] .