Compiling Constraint Handling Rules

We introduce the most recent and advanced implementation of CHR which improves both on previous implementations (in terms of completeness, ex-ibility and eeciency) and on the principles that should guide such an implementation. The idea is to have three rather independent phases of the compiler that utilize templates to generate the code and macros to specialize it. Moreover, our new implementation of CHR emphasizes the need for and power of attributed variables. We compile constraints into clauses and store them in attributes of variables. This is the rst paper (besides from a lengthy technical report) that describes the implementation of CHR.