anchor.diff:  
       binaryTarball = pkgs.lib.genAttrs systems (system:
   
  -      # FIXME: temporarily use a different branch for the Darwin build.
         with import nixpkgs { inherit system; };
   
         let
  
positive.code: { nix ? builtins.fetchGit ./.
  , nixpkgs ? fetchTarball channel:nixos-17.09
  , officialRelease ? false
  , systems ? [ "x86_64-linux" "i686-linux" "x86_64-darwin" "aarch64-linux" ]
  }:
  
negative.code:             --subst-var-by nix ${toplevel} \
              --subst-var-by cacert ${cacert}
  
            if type -p shellcheck; then
              shellcheck -e SC1090 $TMPDIR/install
              shellcheck -e SC1091,SC2002 $TMPDIR/install-darwin-multi-user
            fi
  
            chmod +x $TMPDIR/install
            chmod +x $TMPDIR/install-darwin-multi-user
  