Lean is a currently-niche programming language / proof-assistant.
A proof assistant is basically a tool to construct mathematical proofs, which verifies that the proofs are correct like how a compiler verifies types in your programs.
IIUC a regular programming language with a certain set of restrictions already duals as a proof-assistant as discovered by Curry & Howard. By restrictions, I mean something like how Rust forces you to follow certain rules compared to Java.
Way before @noamraph put it up on in pypi it was internally available in our company. To my knowledge he didn't yet make it 30 years ago, but if he did then probably at least not for Python!
IIUC a regular programming language with a certain set of restrictions already duals as a proof-assistant as discovered by Curry & Howard. By restrictions, I mean something like how Rust forces you to follow certain rules compared to Java.