code: func (w *Waveform) setSampleFunction(function SampleReduceFunc) error {
  	// Function cannot be nil
  	if function == nil {
  		return errSampleFunctionNil
  	}
  
  	w.sampleFn = function
  
  	return nil
  }
docs: // setSampleFunction directly sets the SampleReduceFunc member of the receiving
  // Waveform struct.