I probably need to write a blog post about this, but "full-blown programming languages" have 2 features that config files generally don't. And people often con

I probably need to write a blog post about this, but "full-blown programming languages" have 2 features that config files generally don't. And people often conflate them: 1. arbitrary I/O -- can I read a file from disk, open a socket, make a DNS query, etc. 2. arbitrary computation -- can I do arithmetic, can I capitalize strings, can I write a (pure) Lisp interpreter, etc. I claim that the first IS a problem but the second ISN'T. Arbitrary I/O is a problem because it means the configuration isn't reproducible / deterministic, so it's not debuggable. Your deployed system could be in a state that depends on the developer's laptop, and then nobody else can debug it. The second is NOT a problem. As long as the state of the deployed system is a FUNCTION of what you have versioned/configured, then it's no problem. Functions are useful. Pure functions can also be expressed in an imperative style (another design issue that's commonly confused). Related thread: https://lobste.rs/s/gcfdnn/why_dhall_advertises_absence_turing https://lobste.rs/s/gcfdnn/why_dhall_advertises_absence_turi... and my other comment in this thread: https://news.ycombinator.com/item?id=26277812 https://news.ycombinator.com/item?id=26277812