anchor.diff:  
     hub = pkgs.gitAndTools.hub;
   
  -  lab = pkgs-unstable.gitAndTools.lab;
  +  lab = pkgs-darwin.gitAndTools.lab;
   
     custom = rec {
       inherit (pkgs) callPackage;
  
positive.code:       sha256 = "0h2kzdfiw43rbiiffpqq9lkhvdv8mgzz2w29pzrxgv8d39x67vr9";
      }) {};
  
      vim = pkgs-unstable.callPackage ./vim {
        inherit metals yarn2nix;
        inherit (pkgs.vimUtils) buildVimPluginFrom2Nix;
      };
  
negative.code: # Based on https://github.com/nmattia/homies/blob/master/default.nix
  let
  
    pkgs = pkgs-darwin;
  
    pkgs-darwin = import (builtins.fetchTarball {
      # Descriptive name to make the store path easier to identify
      name = "nixpkgs-19.09-darwin";
      # rev obtained with `git ls-remote https://github.com/nixos/nixpkgs-channels nixpkgs-darwin`
      url = "https://github.com/nixos/nixpkgs/archive/bb7c495f2e74bf49c32b14051c74b3847e1e2be0.tar.gz";
      # hash obtained with `nix-prefetch-url --unpack <url from above>`
      sha256 = "0dm57i9cpyi55h519vc6bc9dlcmxr3aa4pf9pkff6lnkrywi30nm";
  