anchor.diff:            ++ go-env
             ++ node-env
             ++ ocaml-env
  -          ++ python2-env
  -          ++ scala-env;
  +          ++ python2-env;
         };
       };
     }
  
positive.code: with pkgs;
  
  let
    is-osx = builtins.currentSystem == "x86_64-darwin";
    is-linux = builtins.currentSystem != "x86_64-darwin";
  
    pkg-set = {
      all ? [],
      osx ? [],
      linux ? []
    }: (
      all
      ++ (if is-osx then osx else [])
      ++ (if is-linux then linux else [])
    );
  
    nvim = pkgs.callPackage ./nvim {};
    eslint = pkgs.callPackage ./node/eslint.nix {};
    prettier = pkgs.callPackage ./node/prettier.nix {};
  
negative.code:     ++ network-tools
      ++ dev-tools;
  
    in rec {
      allowUnfree = true;
  
      firefox = {
  