anchor.diff:  rec {
   
     
  -  nixpkgsRel = "nixpkgs-0.12pre9486";
  +  nixpkgsRel = "nixpkgs-0.12pre10056";
   
   
     configuration = {
  
positive.code:   # Get a recent copy of Nixpkgs.
    nixpkgsTarball = pkgs.fetchurl {
      url = configuration.installer.nixpkgsURL + "/" + nixpkgsRel + ".tar.bz2";
      md5 = "22deefec0696d2fb263864b97e2238d3";
    };
  
  
  
negative.code:     environment = {
        extraPackages = pkgs: [
          pkgs.vim
          pkgs.subversion # for nixos-checkout
        ];
      };
     
  