anchor.diff:    };
   
     nixUnstable = lib.lowPrio (common rec {
  -    name = "nix-1.12pre4523_3b81b26";
  -    src = fetchurl {
  -      url = "http://hydra.nixos.org/build/33598573/download/4/${name}.tar.xz";
  -      sha256 = "0469zv09m85824w4vqj2ag0nciq51xvrvsys7bd5v4nrxihk9991";
  +    name = "nix-1.12${suffix}";
  +    suffix = "pre4911_b30d1e7";
  +    src = fetchFromGitHub {
  +      owner = "NixOS";
  +      repo = "nix";
  +      rev = "b30d1e7ada0a8fbaacc25e24e5e788d18bfe8d3c";
  +      sha256 = "04j6aw2bi3k7m5jyqwn1vrf78br5kdfpjsj15b5r5lvxdqhlknvm";
       };
  +    fromGit = true;
     });
   
   }
  
positive.code: { lib, stdenv, fetchurl, perl, curl, bzip2, sqlite, openssl ? null, xz
  , pkgconfig, boehmgc, perlPackages, libsodium
  , storeDir ? "/nix/store"
  , stateDir ? "/nix/var"
  }:
  
  let
  
    common = { name, src }: stdenv.mkDerivation rec {
      inherit name src;
  
      outputs = [ "out" "dev" "man" "doc" ];
  
      nativeBuildInputs = [ perl pkgconfig ];
  
      buildInputs = [ curl openssl sqlite xz ]
        ++ lib.optional (stdenv.isLinux || stdenv.isDarwin) libsodium;
  
      propagatedBuildInputs = [ boehmgc ];
  
  
negative.code:       '';
  
      configureFlags =
        [ "--with-store-dir=${storeDir}"
          "--localstatedir=${stateDir}"
          "--sysconfdir=/etc"
          "--with-dbi=${perlPackages.DBI}/${perl.libPrefix}"
          "--with-dbd-sqlite=${perlPackages.DBDSQLite}/${perl.libPrefix}"
          "--disable-init-state"
          "--enable-gc"
        ]
        ++ lib.optional (!lib.versionAtLeast version "1.12pre") [
          "--with-www-curl=${perlPackages.WWWCurl}/${perl.libPrefix}"
        ];
  
      makeFlags = "profiledir=$(out)/etc/profile.d";
  
  