We extend the rule-based, multiset rewriting language CHR with multiset comprehension patterns. Multiset comprehension provides the programmer with the ability to write multiset rewriting rules that can match a variable number of entities in the state. This enables implementing algorithms that coordinate large amounts of data or require aggregate operations in a declarative way, and results in code that is more concise and readable than with pure CHR. We call this extension CHR^cp. In this paper, we formalize the operational semantics of CHR^cp and define a low-level optimizing compilation scheme based on join ordering for the efficient execution of programs. We provide preliminary empirical results that demonstrate the scalability and effectiveness of this approach.

44 pages

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