[giraffe_lady]

Algorithm W is 40 years old and HM has vastly better ergonomics than TS's types.

Why certain approaches didn't catch on until recently, or ever, is an interesting thing to think about but "we didn't know how" is not the story here.

[cubefox]

The "or" (and "and") types in TypeScript are set theoretic rather than algebraic, so they don't require wrapping and unwrapping. It seems to me that they are the ones with better ergonomics.

[giraffe_lady]

It sounds neat when you phrase it that way but my decade of professional experience in typescript has not shown it to be the case in practice. ymmv I guess.