Why not f#? I would imagine it has good support for discrimated unions which are quite good for representing instruction sets. He wanted a more modern platform

Why not f#? I would imagine it has good support for discrimated unions which are quite good for representing instruction sets. He wanted a more modern platform than ocaml, or ml. He didn't want to go too deep down into the functional rabbit hole(haskell), and he didn't want to think about memory management at all(rust).