Nix / NixOS

Yeah the way you need to maintain two codebases: one for types and one for actual logic is annoying.

Also nix is purely functional (which is necessary, for more information read the Nix Pills), Typescript is not, so unless it's only a purely functional subset or severely limits Nix (in the form of abstractions, after skimming over it, I think this is the case), it will run into issues...