CHR Compilers: http://www.probp.com/chr/

CHR (Constraint Handling Rules) is a popular high-level rule-based language. It was originally designed for implementing constraint solvers but it has found its way into applications far beyond constraint solving. Two compilers for CHR run on B-Prolog: the Leuven compiler and a compiler, called chr2ar, which translates CHR into action rules. The former has been around for some time; and the later compiler is a preliminary one. Some results have obtained showing that action rules can serve as an efficient alternative intermediate language for compiling CHR.