anchor.diff:    # use a pinned version of nixpkgs for reproducability
     pkgs = import (builtins.fetchTarball {
       # Descriptive name to make the store path easier to identify
  -    name = "nixpkgs-18.09-2019-05-14";
  -    # rev obtained with `git ls-remote https://github.com/nixos/nixpkgs-channels nixpkgs-18.09-darwin`
  -    url = "https://github.com/nixos/nixpkgs/archive/1e9e709953e315ab004951248b186ac8e2306451.tar.gz";
  +    name = "nixpkgs-19.03-2019-05-17";
  +    # rev obtained with `git ls-remote https://github.com/nixos/nixpkgs-channels nixpkgs-19.03-darwin`
  +    url = "https://github.com/nixos/nixpkgs/archive/c86f09d2d939f0f6993447117f841f19242500c2.tar.gz";
       # hash obtained with `nix-prefetch-url --unpack <url from above>`
  -    sha256 = "0vimw4pqiqiz23hnpbcir413n4mbmz8bpq430w7d234mpzws48w7";
  -  }) {};
  -
  -  unstable-pkgs = import (builtins.fetchTarball {
  -    # Descriptive name to make the store path easier to identify
  -    name = "nixpkgs-unstable-2019-05-14";
  -    # rev obtained with `git ls-remote https://github.com/nixos/nixpkgs-channels nixpkgs-unstable`
  -    url = "https://github.com/nixos/nixpkgs/archive/9ebc6ad944c9e53f58536ef50c64b6f057e5fa4c.tar.gz";
  -    # hash obtained with `nix-prefetch-url --unpack <url from above>`
  -    sha256 = "1hv53kw8nwg9k3kim19ykbmn3yksgmlw1gjbd6d5midhmjjc6mhv";
  +    sha256 = "0fvxn8w368wg8d0lgbmrkr3ws1i1484hjrzsr65y4wldz0w9chrq";
     }) {};
   
     hub = pkgs.gitAndTools.hub;
  
positive.code:     };
    };
  
    allPlatforms = with custom;
      [
        # Customized packages
  
negative.code:   custom = rec {
      inherit (pkgs) callPackage;
  
      ddgr = pkgs.ddgr;
  
      # Git with config baked in
      git = callPackage ./git {};
  
      pijul = callPackage ./pijul {
        pijul = pkgs.pijul;
      };
  
      pure-prompt = callPackage ./zsh/pure-prompt.nix {};
  