anchor.diff:  
   , xclip ? null, xdotool ? null, dmenu ? null
   , x11Support ? !stdenv.isDarwin
  +, tomb
   }:
   
   with lib;
  
positive.code:     repo   = "pass-${p.name}";
      inherit (p) rev sha256;
    })) [
      { name = "import"; rev = "491935bd275f29ceac2b876b3a288011d1ce31e7"; sha256 = "02mbh05ab8h7kc30hz718d1d1vkjz43b96c7p0xnd92610d2q66q"; }
      { name = "update"; rev = "cf576c9036fd18efb9ed29e0e9f811207b556fde"; sha256 = "1hhbrg6a2walrvla6q4cd3pgrqbcrf9brzjkb748735shxfn52hd"; }
    ];
  
  in stdenv.mkDerivation rec {
  
negative.code:     tree
      which
      qrencode
      tomb
    ] ++ stdenv.lib.optional stdenv.isLinux procps
      ++ ifEnable x11Support [ dmenu xclip xdotool ]);
  
  