CHR for XSB

XSB is a highly declarative programming system consisting of Prolog extended with tabled resolution. It is useful for many tasks, some of which require constraint solving. Thus flexible and high level support for constraint systems is required. Constraint Handling Rules is exactly such a high level language embedded in Prolog for writing application tailored constraint solvers. In this paper we present the integration of a CHR system in the XSB system and especially our findings on how to integrate CHR with tabled resolution, such as how to deal with issues as call abstraction of constraints, constraint store merging, answer store projection and constraint store representations for tabling. We illustrate the power of the XSB-CHR combination with two examples in the field of model checking. It is indeed possible to quickly write application specific constraint solvers, experiment with them and achieve a reasonable performance and high readability. The combination of XSB’s goal-driven fixpoint execution model with CHR’s committed choice bottom-up approach has proven not only feasible, but considerably useful as well.