I want to spend a month going deep on a programming language that I'm not very familiar with.
What language would you recommend and why?
(Not eligible: JS, TS, Python, Rust, C, C++, Java, Smalltalk)
Conversation
The language itself is simple. The ideas behind the system it lives in (the Nix package manager), and its main application (the beast called nixpkgs) are worth understanding.

