2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/30416We describe an approach to programming rule-based systems in Standard ML, with a focus on so-called overlapping rules, that is rules that can still be active when other rules are fired. Such rules are useful when implementing rule-based reactive systems, and to that effect we show a simple implementation of Loyall's Active Behavior Trees, used to control goal-directed agents in the Oz virtual environment. We discuss an implementation of our framework using a reactive library geared towards implementing those kind of systems.13 pages. Presented at RULE 2000, First International Workshop on Rule-Based Programming, Montreal, CanadaProgramming LanguagesD.3.3text