anchor.diff:      stdenv.mkDerivation {
         name = "arx";
         buildCommand = ''
  -        ${haskellPackages.arx}/bin/arx tmpx ${archive} -o $out // ${startup}
  +        ${haskellPackages.arx}/bin/arx tmpx ${archive} -rm! -o $out // ${startup}
           chmod +x $out
         '';
       };
  
positive.code:   maketar = { targets }:
      stdenv.mkDerivation {
        name = "maketar";
        exportReferencesGraph = map (x: [("closure-" + baseNameOf x) x]) targets;
        buildCommand = ''
          storePaths=$(${perl}/bin/perl ${pathsFromGraph} ./closure-*)
  
          # printRegistration=1 ${perl}/bin/perl ${pathsFromGraph} ./closure-* > .reginfo
          tar cfj $out \
            --owner=0 --group=0 --mode=u+rw,uga+r \
            --hard-dereference \
  
negative.code:       '';
      };
  
    # TODO: eventually should this go in nixpkgs?
    nix-user-chroot = stdenv.mkDerivation {
      name = "nix-user-chroot-2b144e";
      src = fetchFromGitHub {
  