package catala

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Low-level language for tax code specification


Dune Dependency






The Catala language is designed to be a low-level target for higher-level specification languages for fiscal legislation.

Published: 22 Dec 2020


Catala logo


Catala is a domain-specific language for deriving faithful-by-construction algorithms from legislative texts. To learn quickly about the language and its features, you can jump right to the official Catala tutorial.


Catala is a programming language adapted for socio-fiscal legislative literate programming. By annotating each line of the legislative text with its meaning in terms of code, one can derive an implementation of complex socio-fiscal mechanisms that enjoys a high level of assurance regarding the code-law faithfulness.

Concretely, you have to first gather all the laws, executive orders, previous cases, etc. that contain information about the socio-fiscal mechanism that you want to implement. Then, you can proceed to annotate the text article by article, in your favorite text editor :


Once your code is complete and tested, you can use the Catala compiler to produce a lawyer-readable PDF version of your implementation. The Catala language has been specially designed in collaboration with law professionals to ensure that the code can be reviewed and certified correct by the domain experts, which are in this case lawyers and not programmers.


The Catala language is special because its logical structure mimics the logical structure of the law. Indeed, the core concept of "definition-under-conditions" that builds on default logic has been formalized by Professor of Law Sarah Lawsky in her article A Logic for Statutes. The Catala language is the only programming language to our knowledge that embeds default logic as a first-class feature, which is why it is the only language perfectly adapted to literate legislative programming.

Building and installation

See the dedicated readme.


Use catala --help to get more information about the command line options available.


See the dedicated readme.


See the dedicated readme.

Test suite

See the dedicated readme.


Formal semantics

See the dedicated readme.

Compiler documentation

The compiler documentation is auto-generated from its source code using dune and odoc. Use

make doc

to generate the documentation, then open the doc/odoc.html file in any browser.


The library is released under the Apache license (version 2).

Limitations and disclaimer

Catala is a research project from Inria, the French National Research Institute for Computer Science. The compiler is yet unstable and lacks some of its features.

Pierre Catala

The language is named after Pierre Catala, a professor of law who pionneered the French legaltech by creating a computer database of law cases, Juris-Data. The research group that he led in the late 1960s, the Centre d’études et de traitement de l’information juridique (CETIJ), has also influenced the creation by state conselor Lucien Mehl of the Centre de recherches et développement en informatique juridique (CENIJ), which eventually transformed into the entity managing the LegiFrance website, acting as the public service of legislative documentation.

Dependencies (14)

  1. odate >= "0.6"
  2. ocamlgraph >= "1.8.8"
  3. dune >= "2.2"
  4. zarith >= "1.10"
  5. re >= "1.9.0"
  6. cmdliner >= "1.0.4" & < "1.1.0"
  7. dune-build-info >= "2.0.1"
  8. bindlib = "5.0.1"
  9. unionFind >= "20200320"
  10. menhirLib >= "20200211"
  11. menhir >= "20200211" & < "20211215"
  12. sedlex >= "2.1"
  13. ANSITerminal >= "0.8.2"
  14. ocaml >= "4.08.0"

Dev Dependencies


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