Aggregates for Constraint Handling Rules

Abstract. We extend the Constraint Handling Rules language with ag-gregates such as sum, count, findall, and min. The proposed exten-sion features nested aggregate expressions over guarded conjunctions of constraints, a series of predefined aggregates, and application-tailored user-defined aggregates. We formally define the operational semantics of aggregates, and show how incremental aggregate computation facilitates efficient implementations. Case studies demonstrate that language sup-port for aggregates significantly reduces program size, thus improving readability and maintainability considerably.