evaluate(pulse) {
      const params = this.marshall(pulse.stamp),
        out = this.transform(params, pulse);
      params.clear();
      return out;
    }
Overrides {@link Operator.evaluate} for transform operators.
Marshalls parameter values and then invokes {@link transform}.
@param {Pulse} pulse - the current dataflow pulse.
@return {Pulse} The output pulse (or StopPropagation). A falsy return
         value (including undefined) will let the input pulse pass through.