Constraint Handling Rules (CHR) is both a versatile theoretical formalism based on logic and an efficient practical high-level programming language based on rules and constraints.
…one of the most powerful multiset rewriting languages. Professor Kazunori Ueda, Waseda University, Japan, and Norio Kato in »Programming Logical Links«
…a powerful, highly optimized, lazy rule engine […] consistently outperforms Rete-based systems. Peter Van Weert, K.U. Leuven, Belgium, in »Efficient Lazy Evaluation of Rule-Based Programs«
… [Concurrent CHR in Haskell] exhibits significant speed up in most problems when executed on multi-core systems. Members of the National University of Singapore at the Concurrent Constraint Handling Rules Home Page
Since CHR seems to subsume most of the other formalisms that have been related to it, it has the potential to become a lingua franca, a hub which collects and dispenses research efforts from and to the various related fields. Jon Sneyers, K.U. Leuven, Belgium, in »Optimizing Compilation and Complexity of CHR«