I get why it reads like FP evangelism, but I don’t think it’s “ignoring decades of prior art.” I’m not claiming these ideas are exclusive to FP. I’m claiming FP ecosystems systematized a bundle of practices (ADT/state machines, exhaustiveness, immutability, explicit effects) that consistently reduce a specific failure mode: invalid state transitions and refactor breakage.

Rust is actually aligned with the point: it delivers major reliability wins via making invalid states harder to represent (enums, ownership/borrowing, pattern matching). That’s not “FP-first,” but it’s very compatible with functional style and the same invariants story.

If the TS example came off as “types instead of validation,” that’s on me to phrase better, the point wasn’t “types eliminate validation,” it’s “types make the shape explicit so validation becomes harder to forget and easier to review.”