Recursion is nowadays taught to students since their first programming days in order to embed it deeply in their brains. However, students' first impact on Prolog programs execution sometimes weakens their faith in recursive programming thus invalidating our initial efforts. The selection and computation rules implemented by all Prolog systems, although clearly explained in textbooks, are hard to be interiorized by students also due to the poor system debugging primitives. Problems increase in Constraint Logic Programming when unification is replaced by constraint simplification in a suitable constraint domain. In this paper, we extend PrettyProlog, a light-weight Prolog interpreter written in Java capable of system primitives for SLD tree visualization, to deal with Constraint Logic Programming over Finite Domains. The user, in particular, can select the propagation strategies (e.g. arc consistency vs bound consistency) and can view the (usually hidden) details of the constraint propagation stage.
