Catala: a programming language for the law

Law at large underpins modern society, codifying and governing many aspects of citizens' daily lives. Oftentimes, law is subject to interpretation, debate challenges throughout various courts jurisdictions. But in some other areas, leaves little room for essentially aims rigorously describe a computation, decision procedure or, simply said, an algorithm. Unfortunately, prose remains woefully inadequate tool the job. The lack formalism ambiguities; structure legal statutes, with paragraphs sub-sections spread across multiple pages, makes it hard compute intended outcome algorithm underlying given text; and, as any piece poorly-specified critical software, use informal, natural language corner cases unaddressed. We introduce Catala, new programming that we specifically designed allow straightforward systematic translation statutory into executable implementation. Notably, Catala easy express general case / exceptions logic permeates law. bring together lawyers programmers through shared medium, which they can understand, edit evolve, bridging gap too often results dramatically incorrect implementations have implemented compiler proven correctness its core compilation steps using F* proof assistant. evaluate on several texts are algorithms disguise, notably section 121 US federal income tax byzantine French family benefits; doing so, uncover bug official implementation benefits. observe consequence formalization process enables rich interactions between programmers, leading greater understanding original legislative intent, while producing correct-by-construction specification reusable by software ecosystem. Doing increases trust institutions, mitigates risk societal damage due