Function getPulse

docs/app/js/sanddance-app.js:108585–108588

* Provide a correct pulse for evaluating an operator. If the operator has an * explicit source operator, we will try to pull the pulse(s) from it. * If there is an array of source operators, we build a multi-pulse. * Otherwise, we return a current pulse with correct source data. * If the pulse i

(op, encode)

 * @param {string} [encode] - An (optional) encoding set name with which to
 *   annotate the returned pulse. See {@link run} for more information.
 */ function getPulse(op, encode) {
    const s = op.source, stamp = this._clock;
    return s && (0, _vegaUtil.isArray)(s) ? new MultiPulse(this, stamp, s.map((_)=>_.pulse), encode) : this._input[op.id] || singlePulse(this._pulse, s && s.pulse);
}
function singlePulse(p, s) {
    if (s && s.stamp === p.stamp) return s;
    p = p.fork();