Programming with rules and everything else, seamlessly

Abstract: Logic rules are powerful for expressing complex reasoning and analysis problems. At the same time, they are inconvenient or impossible to use for many other aspects of applications. Integrating rules in a language with sets and functions, and furthermore with updates to objects, has been a subject of significant study. What's lacking is a language that integrates all constructs seamlessly. This paper presents a language, Alda, that supports all of rules, sets, functions, updates, and objects as seamlessly integrated built-ins, including concurrent and distributed processes. The key idea is to support predicates as set-valued variables that can be used and updated in any scope, and support queries and inference with both explicit and automatic calls to an inference function. We develop a complete formal semantics for Alda. We design a compilation framework that ensures the declarative semantics of rules, while also being able to exploit available optimizations. We describe a prototype implementation that builds on a powerful extension of Python and employs an efficient logic rule engine. We develop a range of benchmarks and present results of experiments to demonstrate Alda's power for programming and generally good performance.