RDBG: a Reactive Programs Extensible Debugger

Abstract

Debugging reactive programs requires to provide a lot of inputs -- at each reaction step. Moreover, because a reactive system reacts to an environment it tries to control, providing realistic inputs can be hard. The same considerations apply for automatic testing. This work take advantage on previous work on automated testing of reactive programs that close this feedback loop. This article demonstrates how to implement opportunistically such a debugging commands interpreter by taking advantage of an existing (ocaml) toplevel Read-Eval-Print Loop (REPL). Then it shows how a small kernel is enough to build a full-featured debugger with little effort. The given examples provide a tutorial for end-users that wish to write their own debugging primitives, fitting to their needs, or to tune existing ones. An orthogonal contribution of this article is to present an efficient way to implement the debugger coroutining using continuations. The Reactive programs DeBuGger (RDBG) prototype aims at being versatile and general enough to be able to deal with any reactive languages. We have experimented it on 2 synchronous programming: Lustre and Lutin.