Yep that's why as Hickey says people are excited about union types. But in the context of a refactor or a change to an API where you care about breaking existin

Yep that's why as Hickey says people are excited about union types. But in the context of a refactor or a change to an API where you care about breaking existing users, there's a perfectly valid way forward. Basically I don't think Option types are as unwieldy as Hickey is making them about to be. Indeed Dotty (one of the examples in the talk) will be keeping Option even in the presence of union types (mainly because union types fall down with nested Options and with polymorphism). That being said Haskell (and Scala) is annoying when it comes to trying to combine different kinds of errors together, if you want an error type more expressive than Option. OCaml here (and Purescript) have a much better story with polymorphic variants.