Summing analog waveform bus

I'm trying to create function that accepts an analog waveform bus for example (4 current waveforms) called mywave<3:0>

point is to execute the same thing I can do with plus(mywave<3> mywave<2> mywave<1> mywave<0>) OR mywave<3>+mywave<2>+mywave<1>+mywave<0>

my function looks like this (but not working - what am I doing wrong):

procedure( mrAnalogBusSum( waveforms )

  (cond

  ;; Handle a single Waveform
  ((drIsWaveform waveforms)

    ;  Create Empty Wave
    sumWaveForm = drCreateEmptyWaveform()
    sumWaveForm = sumWaveForm + waveforms
    ;return waveform
    sumWaveForm

  ) ;drIsWaveform

  ;; Handle a family of waveforms
  ((famIsFamily waveforms)

    (famMap 'mrAnalogBusSum waveforms )

  ) ;famIsFamily

   ;; Default option - return error
   (t

    (error "mrAnalogBusSum - can't handle %L type of data\nExpecting a waveform OR waveform family\n" wave)

   );

 ) ;cond

) ;procedure

Thank you,

Matan.