A substantial part of the french social and tax system is being coded as free software. One of the teams writes the source code in YAML.

It's not a programming language, but rather a specification for calculable parts of the law. A JS programm then generates Typeform-like simulators, a node library, and an online interactive documentation (it is now compulsory for french administrations to explain their algorithms).

I'm not sure YAML is the good long-term design choice, but as we can't afford to write our own language, it's bootstrapped the project successfully.

Here is the main file : https://github.com/betagouv/syso/blob/master/source/règles/b... Don't be afraid by the number of lines, it's just a collection of variables.