mlang VS openfisca-france

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"*

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-...

That line in the summary is a bit misleading. The authors didn't find a "bug" in any law - instead they found a corner case that wasn't included in an online tool hosted by the French government to estimate family benefits under French law:

> After close inspection of the OpenFisca code, a discrepancy was located with the Catala implementation. Indeed, according to article L755-12 of the Social Security Code, the income cap for the family benefits does not apply in overseas territories with single-child families. This subtlety was not taken into account by OpenFisca, and was fixed after its disclosure by the authors.

Here's the pull request for their fix to the benefits simulator: https://github.com/openfisca/openfisca-france/issues/1426