anchor.diff:  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 {};
  
positive.code:     ++ network-tools
      ++ dev-tools;
  
  in
    rec {
      allowUnfree = true;
  
      firefox = {
  
negative.code:     dep
    ];
  
    python2-env = with python27Packages; [
      (python27Full.withPackages (ps: [
        ps.setuptools
      ]))
      ipython
      flake8
      virtualenv
      Fabric
      pylint
    ];
  
    base-tools =
  