Catala

Catala is a domain-specific language for deriving faithful-by-construction algorithms from legislative texts.

Concepts

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.

Catala motivating example : French "allocations familiales"

In the example/allocations_familiales folder, you will find the allocations_familiales.catala file which contains the algorithm computing French family benefits. The algorithm consists of annotations to the legislative texts that define the family benetifs, using the literate programming paradigm. The Catala compiler can extract from the .catala file a lawyer-readable version of the annotated text.

Currently, this lawyer-readable version comes in the form of a LaTeX document. You will need to have a standard LaTeX distribution installed as well as the latexmk build tool in order to enjoy the automated document generation process.

To get that lawyer-readable version (which is a LaTeX-created) PDF, simply use

make allocations_familiales

from the repository root, once you have managed to install the compiler (see below). You can then open examples/allocations_familiales/allocations_familiales.pdf

Languages

The Catala language should be adapted to any legislative text that follows a general-to-specifics statutes order. Therefore, there exists multiple versions of the Catala surface syntax, adapted to the language of the lefislative text.

Currently, Catala supports English and French legislations via the --language=en or --language=fr option. Contact the authors if you are interested in adding support for another language.

Limitations and disclaimer

Early stage project

Catala is a research project from Inria, the French National Research Institute for Computer Science. The compiler is yet very unstable and lacks most of its features. Currently, it only parses the surface language to producde the lawyer-readable PDF, no interpreter or compiler backend is provided.

However, the language is bound to have a complete formal semantics in the near future. This semantics will guide the compiler implementation.

The Catala compiler

Requirements

The Catala compiler is written using OCaml. To install OCaml on your machine and if you're running Linux ou MacOS, open a terminal and enter :

./install_opam.sh

This will install opam, the OCaml dependency manager and the base OCaml compiler. If you're on Windows, the simplest solution would be to use Cygwin or the Windows Subsystem for Linux. Catala has been tested with OCaml version 4.09.1. You can switch to this version by typing :

opam switch create 4.09.1

or

opam switch 4.09.1

if this version of OCaml is already installed. Next, install all the build dependencies with

make install-dependencies

This should ensure everything is set up for developping on the Catala compiler !

Other features for generation of files and literate programming also require the following executables to be present

man2html virtualenv python3 rsync

please install them if they're not here. On a Debian distribution, this can be done with

sudo apt install python3-virtualenv man2html rsync

On ArchLinux :

sudo pacman -S python-virtualenv man2html rsync

Installation

The project is distributed as a Dune artifact. Use standard dune commands to build and install the library. Makefile aliases are here to help you: running

make build

builds the compiler from its OCaml sources.

Generating website assets

The Catala website features assets generated by the Catala compiler. They are needed to build the website. To produce them, simply run from this repository's root directory

./generate_website_assets.sh <path-to-catala-website>/assets

You will need the man2html executable to generate the HTML versions of the man pages, as well as the rsync executable to transfer files (preferred to cp) because it also works with a remote server.

Opam package

If you want to install the library as an opam package, use the following command at the root of the repository:

opam install ./

You can then can the compiler using the catala command.

Usage

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

Syntax highlighting

The Catala language also comes with syntax highlighting to ease program development. The syntax highlighting is done with the Iro compiler that allows writing the syntax only once, and then export it to formats understood by various IDE. Currently, two syntax highlighting plugins are under version control.

Atom

To get Catala syntax highlighting in Atom, simply enter from the root of the repository, depending on the language you want to use :

make atom_fr

or

make atom_en

You can now reload Atom and check that you have syntax highlighting on any .catala file.

Pygments

Pygments is a Python-based versatile lexer for various programming languages. To use a version of Pygments augmented with the Catala plugin, simply enter

make pygments

This will execute the script syntax_highlighting/fr/pygments/set_up_pygments.sh and syntax_highlighting/en/pygments/set_up_pygments.sh.

The scripts set up a virtual environement in syntax_highlighting/fr/pygments/pygments/env or syntax_highlighting/en/pygments/pygments/env, which will contain the modified version of Pygments that has Catala support. If you want to hack something, it is possible to use this virtual environnement directly with

source syntax_highlighting/fr/pygments/pygments/env/bin/activate

or

source syntax_highlighting/en/pygments/pygments/env/bin/activate

The pigmentize executable, used for instance by the minted LaTeX package, will now point to the Catala-enabled version inside the virtual environment. This source setup is not necessary if you use the rules in the Makefile.

Contributing

The project accepts pull requests. Please email the authors if you are interested, whether you are a law professional, a computer scientist or a developer. Please use this email address :

denis DOT merigoux AT inria DOT fr

Please note that the copyright of this code is owned by Inria; by contributing, you disclaim all copyright interests in favor of Inria.

License

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

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.