catala VS mlang

Programming and law can go together tho https://github.com/CatalaLang/catala

Law is a mess, in part because its authors take shortcuts. For example, from the first example on CatalaLang's README.md:

> If the property was acquired by gift [and various conditions apply], then for the purpose of determining loss the basis shall be such fair market value. [emphasis added]

I think (and I'm not a lawyer or a tax expert) that this means that the basis of an asset can have a different value for the purpose of determining gain or determining loss. Wow, basis isn't just a number, although one might not notice this if one didn't read the six emphasized words.

But the Catala code seems to completely ignore this. Oops. I filed an issue:

https://github.com/CatalaLang/catala/issues/514

In a real use case, I imagine that substantial refactoring of the parts that consume basis might be needed when one notices that the basis is not a number.

Catals is a language trying to exactly this.

There's even a programming language for that: https://catala-lang.org/

french tax code has a semi-official DSL syntax

https://github.com/MLanguage/mlang

France has an open source implementation of their tax code [0]. The paper [1] gives an overview of the implementation language, mlang.

[0] https://github.com/MLanguage/mlang

The french initiative started in 2013 is still alive (last commit a few days ago), and passes the gov test suite (they keep in touch with our version of the IRS): https://github.com/openfisca/openfisca-france

The way we got this is interestingly twisted.

French citizens requested the software used by the administration, and they managed to get it!

But, it's was written in Mlang is a proprietary language created by the french administration in the 90: https://github.com/MLanguage/mlang.

Someone then decided to create an OCaml compiler that takes mlang and emits python: https://arxiv.org/abs/2011.07966

As a result, we got we got open fisca. I know believe there are other techs in the mix...

A slide of the story: https://www.slideshare.net/Etalab/opening-up-the-french-tax-...

They have open sourced the algorithm they use to compute taxes here: https://gitlab.adullact.net/dgfip/ir-calcul which used a purpose made programming language https://github.com/MLanguage/mlang

It's important to note that this isn't universal across the entire legal system. Some subsets like France's tax system are defined in code, and there's some efforts to create more general systems as computational law advances as a field.

--> https://github.com/MLanguage/mlang

*"Compiler for the M language, used to compute the income tax of French taxpayers"*