Optimized Execution of FreeCHR

Abstract

Constraint Handling Rules (CHR) is a rule-based programming language that rewrites collections of constraints. It is typically embedded into a general-purpose language. There exists a plethora of implementation for numerous host languages. However, the existing implementations often re-invent the method of embedding, which impedes maintenance and weakens assertions of correctness. To formalize and thereby standardize the embedding of a ground subset of CHR into arbitrary host languages, we introduced the framework FreeCHR and proved it to be a valid representation of classical CHR. For the sake of simplicity, abstract implementations of our framework did not yet include a concrete matching algorithm nor optimizations. In this paper, we introduce an improved execution and matching algorithm for FreeCHR. We also provide empirical evaluation of the algorithm.