What is Catala?

Catala is a programming language for law. Statutes and regulations are encoded in a syntax shaped like legislative drafting: definitions, exceptions, and layered conditions rather than general application code.

Statutes are written as general rules with exceptions scattered across articles. Catala uses default logic to mirror that structure in code, and can leave an outcome undefined or flag a conflict when the law does not force a single answer. Implementation is a specialist exercise: lawyers and programmers pair on annotated legislative text, validated with proofs, tests, and legal review. It is not a language the boardroom reads for sign-off.

Catala vs Lemma

Lemma requires every specification to be complete and unambiguous: every case resolved, every quantity defined, every effective date stated. That is what makes a Lemma spec something the boardroom can read, question, and verify against what runs in production.

Choose Catala when statute-shaped default logic, formal verification, or undefined/conflict outcomes must be part of the model. Choose Lemma when governance needs one portable language business and compliance can own, with temporal versioning and explainable evaluation built into the language itself.

A complete, more comprehensive comparison is coming soon. In the meantime, if you are weighing Catala against Lemma for a specific programme, schedule a call with our founder Ben Rogmans to discuss when Lemma is the superior solution.