Optimized Compilation of Multiset Rewriting with Comprehensions

We extend the rule-based, multiset rewriting language CHR with multiset comprehension patterns. Multiset compre-hension provides the programmer with the ability to write multiset rewriting rules that can match a variable number ofentities in the state. This enables implementing algorithms that coordinate large amounts of data or require aggregateoperations in a declarative way, and results in code that is more concise and readable than with pure CHR. We call thisextension CHR . In this paper, we formalize the operational semantics of CHR and define a low-level optimizingcompilation scheme based on join ordering for the efficient execution of programs. We provide preliminary empiricalresults that demonstrate the scalability and effectiveness of this approach. ∗ This paper was made possible by grant NPRP 09-667-1-100, Effective Programming for Large Distributed Ensembles, fromthe Qatar National Research Fund (a member of the Qatar Foundation). The statements made herein are solely the responsibility ofthe authors.