[trollerator23]

They do?? Sauce?

[stefanos82]

https://github.com/facebook/pyre-check

https://github.com/facebook/flow

https://github.com/facebook/infer

https://github.com/facebook/hhvm/tree/master/hphp/hack

[ysleepy]

I remember reading years ago that the hack compiler was built in ocaml. compilers and such are often built using languages with nice ADTs afaik.

[itishappy]

The Rust compiler was bootstrapped from OCaml as well!