An Evaluation Algorithm for Datalog with Equality

We describe an evaluation algorithm for relational Horn logic (RHL). RHL extends Datalog with quantification over sorts, existential quantification in conclusions and, crucially, the ability to infer equalities. These capabilities allow RHL evaluation to subsume and expand applications of Datalog and congruence closure algorithms. We explain how aspects of a fast congruence closure algorithm can be incorporated into Datalog evaluation to obtain an efficient RHL evaluation algorithm. We then sketch how Steensgaard's points-to analysis and type inference can be implemented using RHL evaluation. RHL and the evaluation algorithm described here are the foundation of the Eqlog Datalog engine.