anchor.diff:  let
     cfg = config.networking.wireless;
     configFile = "/etc/wpa_supplicant.conf";
  -in
  -
  -{
  -
  -  ###### interface
  -
  +in {
     options = {
       networking.wireless = {
         enable = mkOption {
  
positive.code:     };
    };
  
  
    ###### implementation
  
    config = mkIf cfg.enable {
  
      environment.systemPackages =  [ pkgs.wpa_supplicant ];
  
      services.dbus.packages = [ pkgs.wpa_supplicant ];
  
      # FIXME: start a separate wpa_supplicant instance per interface.
      jobs.wpa_supplicant = let
        ifaces = cfg.interfaces;
      in { description = "WPA Supplicant";
  
          wantedBy = [ "network.target" ];
  
  
negative.code:           fi
          '';
  
          script = ''
            ${if ifaces == [] then ''
              for i in $(cd /sys/class/net && echo *); do
                DEVTYPE=
                source /sys/class/net/$i/uevent
                if [ "$DEVTYPE" = "wlan" -o -e /sys/class/net/$i/wireless ]; then
                  ifaces="$ifaces''${ifaces:+ -N} -i$i"
                fi
              done
            '' else ''
              ifaces="${concatStringsSep " -N " (map (i: "-i${i}") ifaces)}"
            ''}
            exec wpa_supplicant -s -u -D${cfg.driver} -c ${configFile} $ifaces
          '';
        };
  
        powerManagement.resumeCommands = ''
          ${config.systemd.package}/bin/systemctl try-restart wpa_supplicant
        '';
  
        # Restart wpa_supplicant when a wlan device appears or disappears.
        services.udev.extraRules = ''
          ACTION=="add|remove", SUBSYSTEM=="net", ENV{DEVTYPE}=="wlan", RUN+="${config.systemd.package}/bin/systemctl try-restart wpa_supplicant.service"
        '';
      })
      {
        meta.maintainers = with lib.maintainers; [ globin ];
      }
    ];
  }
  