Thanks a lot to all you that responded to me ( @andreiformiga @lexi.lambda @notjack @philip.mcgrath). So TR is a case of gradual and occurrence typing that seamlessly integrates with the rest of Racket’s ecosystem. TR occupies a different point in the design space than OCaml’s and Haskell’s. It is developed as a Racket macro library. Another type system approach is Turnstyle. This is very interesting, and thanks for the links.

Has anyone here ever used both TR and at least one of OCaml’s or Haskell’s type system in real world projects outside academia? Given these type system’s differences, what is your comparative experience with real-world use of these type systems? (e.g., produtivity, easiness, etc)