code: function lazyVisitChildren(len, children, i, f, k) {
      while (i < len) {
          var child = children[i++];
          if (child && !isEmptyNode(child)) return lazyVisit(child, f, [len, children, i, f, k]);
      }
      return appk(k);
  }
docs: Recursively visit all values stored in an array of nodes lazily.