code: func (c *IterateChain) EachValue(qs QuadStore, fnc func(quad.Value)) error {
  	if qs != nil {
  		c.qs = qs
  	}
  	if c.qs == nil {
  		return errNoQuadStore
  	}
  	// TODO(dennwc): batch NameOf?
  	return c.Each(func(v Value) {
  		if nv := c.qs.NameOf(v); nv != nil {
  			fnc(nv)
  		}
  	})
  }
docs: // EachValue is an analog of Each, but it will additionally call NameOf
  // for each graph.Value before passing it to a callback.