reflow(fork) {
      if (fork) return this.fork(ALL).reflow();
      const len = this.add.length,
        src = this.source && this.source.length;
      if (src && src !== len) {
        this.mod = this.source;
        if (len) this.filter(MOD$1, filter$1(this, ADD));
      }
      return this;
    }
Forces a "reflow" of tuple values, such that all tuples in the backing
source are added to the MOD set, unless already present in the ADD set.
@param {boolean} [fork=false] - If true, returns a forked copy of this
  pulse, and invokes reflow on that derived pulse.
@return {Pulse} - The reflowed pulse instance.