I've been thinking about what make a good language for configuration files, and the conclusion I've come to is that it ought to have:

- Local variables

- Pure functions with basic math and string manipulation capabilities

Possibly with an extended version that also has:

- Input variables (that must be provided by the code reading the file)

- Exportable functions that are callable by the host code

This extended version would be perfect for use cases like defining CI pipelines.

A language that did this but was otherwise simple and allowed no access to the host system, and had widely available library support across most common languages would be just awesome.