anchor.diff:  
   let
   
  +  cfg = config.networking.wireless;
     configFile = "/etc/wpa_supplicant.conf";
   
     ifaces =
  -    config.networking.wireless.interfaces ++
  +    cfg.interfaces ++
       optional (config.networking.WLANInterface != "") config.networking.WLANInterface;
   
   in
  
positive.code: 
    options = {
    
      networking.wireless.enable = mkOption {
        default = false;
        description = ''
          Whether to start <command>wpa_supplicant</command> to scan for
          and associate with wireless networks.  Note: NixOS currently
          does not generate <command>wpa_supplicant</command>'s
          configuration file, <filename>${configFile}</filename>.  You
          should edit this file yourself to define wireless networks,
          WPA keys and so on (see
          <citerefentry><refentrytitle>wpa_supplicant.conf</refentrytitle>
          <manvolnum>5</manvolnum></citerefentry>).
        '';
      };
  
      networking.WLANInterface = mkOption {
        default = "";
        description = "Obsolete. Use <option>networking.wireless.interfaces</option> instead.";
      };
  
      networking.wireless.interfaces = mkOption {
        default = [];
        example = [ "wlan0" "wlan1" ];
        description = ''
          The interfaces <command>wpa_supplicant</command> will use.  If empty, it will
          automatically use all wireless interfaces.
        '';
      };
  
    };
  
  
    ###### implementation
    
    config = mkIf config.networking.wireless.enable {
  
      environment.systemPackages =  [ pkgs.wpa_supplicant ];
  
  
negative.code:             '' else ''
                ifaces="${concatStringsSep " -N " (map (i: "-i${i}") ifaces)}"
              ''}
              exec wpa_supplicant -s -u ${optionalString (cfg.driver != "") "-D${cfg.driver}"} -c ${configFile} $ifaces
            '';
        };
    
  