The article is using immutable records and sum types as “more like Rust” and I am just sitting in the corner, wondering whether everyone has forgotten that these things came from FP in the first place. In my mind, a language isn’t “Rust-like” because it uses concepts we learned in FP.

We have languages like Haskell and, before it, ML. And I know ML didn’t invent it. We also have Scala, and for Scala, we don’t even have to leave the JVM. There’s also F#, which is a kind of cousin-of-a-cousin to Java.

Rust has sum types and immutability because tons of people thought these features were important, and lots of languages adopted them in parallel with the appearance of Rust.