function Range(start, end, step) {
      if (!(this instanceof Range)) {
        return new Range(start, end, step);
      }
      invariant(step !== 0, 'Cannot step a Range by 0');
      start = start || 0;
      if (end === undefined) {
        end = Infinity;
      }
      step = step === undefined ? 1 : Math.abs(step);
      if (end < start) {
        step = -step;
      }
      this._start = start;
      this._end = end;
      this._step = step;
      this.size = Math.max(0, Math.ceil((end - start) / step - 1) + 1);
      if (this.size === 0) {
        if (EMPTY_RANGE) {
          return EMPTY_RANGE;
        }
        EMPTY_RANGE = this;
      }
    }
Returns a lazy seq of nums from start (inclusive) to end
(exclusive), by step, where start defaults to 0, step to 1, and end to
infinity. When start is equal to end, returns empty list.