An important difference between grandparent and parent comments is that the former mentioned a post about Haskell where the type system is based on category the

An important difference between grandparent and parent comments is that the former mentioned a post about Haskell where the type system is based on category theory, and type refinements don't apply much (if at all). On the other hand, the latter talks about Typescript, which has a type system is based on set theory and type refinements apply very well. Anothet example similar to Typescript is Ruby's Sorbet type checker, which is also based on set theory and does a great usage of type refinements as well.