I think the author values immutability and/or managed mutation quite highly, as well as functional programming. Since their last startup was CircleCI where they picked Clojure[Script] and later for Dark they picked OCaml, and said they were considering F#, Haskell and Rust. So I'm guessing that disqualified non functional mutation heavy alternatives like Go.
Yeah, Go isn’t a very pleasant language for writing parsers, interpreters, compilers, etc albeit in my opinion this has more to do with sum types and less to do with immutability (you can emulate sum types in Go via interfaces but the ergonomics are quite a lot worse than in an ML-inspired language). This has been my experience anyway, as an avid Go enthusiast.
Yeah, that's sorta right. I didn't want to evaluate every language under the sun. Rust I assumed had similar semantics to what I had been using before, which is why it was so heavily considered.
