I always felt the decision to write flow in ocaml was ahead of its time. Flow compiler is much faster than TS.

Native bundlers like esbuild, swc etc. are mainstream now but they came much later.

But writing Typescript in Typescript allowed the language-designers to dogfood the developer-experience of being a Typescript-developer.

Just like MS eventually did with C# too. After the C#-compiler was reimplemented in C# (Roslyn), that’s when the language was truly allowed to develop. And it also made it much easier to make C# a truly cross-platform language.

When the language-designers don’t have to use their own language, they have objectively much less motivation to improve upon the language or it’s tooling than if they do.

The Flow-team didn’t use Flow to write Flow and that shows in its lack of development, its lack of tooling, its lack of contributors and ultimately in its lack of adoption.

I think the type system was easier to express in OCaml as you get some stuff for free.

I don’t know. I tried to understand the OCaml code and contribute to Flow, and in the end I nope-d my way out of there.