Specification of a reactive computation model for OpenMusic
Résumé
OpenMusic is a domain-specific visual programming language designed for computer-aided music composition. This language based on Common Lisp allows composers to develop functional processes generating or transforming musical data, and to execute them locally by demand-driven evaluations. This transformational declarative paradigm is hard to conciliate with reactive data-flow, an evaluation scheme more adequate to develop interactive systems that can be used during musical performances. In this article we propose to link these two evaluation paradigms in a same and consistent visual programming framework. In this report we establish a denotational semantics of the visual language, which gives account for its demand-driven evaluation mechanism and the incremental construction of programs. We then extend this semantics to enable reactive computations in the functional graphs. The resulting evaluation model merges data-driven executions with the exist- ing demand-driven mechanism. A conservative implementation is proposed. We show that the incremental construction of programs and their data-driven and demand-driven evaluations can be smoothly integrated in the visual programming workflow. This integration allows for the propagation of changes in the programs, and the evaluation of graphically-designed functional expressions as a response to external events, a first step in bridging the gap between computer-assisted composition environments and real-time musical systems. This work has been partially funded by ANR project INEDIT (ANR-12-CORD-0009). The core content of this report will be published in the Journal of Visual Languages and Computing, although we give some additional precisions here that do not appear in the article. The journal version will include a more detailed presentations of the problematic.
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