An Open-Ended Finite Domain Constraint Solver

We describe the design and implementation of a nite domain constraint solver embedded in a Prolog system using an extended uniication mechanism via attributed variables as a generic constraint interface. The solver is essentially a scheduler for indexicals, i.e. reactive functional rules encoding local consistency methods performing incre-mental constraint solving or entailment checking, and global constraints, i.e. general propagators which may use specialized algorithms to achieve a higher degree of consistency or better time and space complexity. The solver has an open-ended design: the user can introduce new constraints , either in terms of indexicals by writing rules in a functional notation, or as global constraints via a Prolog programming interface. Constraints deened in terms of indexicals can be linked to 0/1-variables modeling entailment; thus indexicals are used for constraint solving as well as for entailment testing. Constraints can be arbitrarily combined using the propositional connectives by automatic expansion to systems of reiied constraints.