Pyre, written in OCaml, is the closest thing that's stable. It has been discussed on HN a couple of times. Here is the 2021 discussion: https://news.ycombinator

Pyre, written in OCaml, is the closest thing that's stable. It has been discussed on HN a couple of times. Here is the 2021 discussion: https://news.ycombinator.com/item?id=27107647 https://news.ycombinator.com/item?id=27107647. Note that Pyre does not support Windows (https://github.com/facebook/pyre-check/issues/554 https://github.com/facebook/pyre-check/issues/554) and only provides wheels for x86_64 Linux and macOS (https://pypi.org/project/pyre-check/0.9.18/#files https://pypi.org/project/pyre-check/0.9.18/#files). While I don't use Windows, it makes me reluctant to adopt it. First, I want Windows users to be able to contribute to my projects that work on Windows. Mypy and (predictably) Pyright won't create an obstacle for Windows users. Second, the limited number of platforms makes Pyre seem a little internal-toolish. It may still be worth it. As of today, actually, one of my projects has a Pyre branch. I want to see what it is like developing with it.