ensure-node.clj

(defmacro ensure-node [nodes parent-selector tag transform-fn]
  `(ensure-node* nodes (selector ~parent-selector) (selector [:> ~tag]) tag transform-fn))

(defn ensure-node* [nodes parent-selector child-selector tag transform-fn]
  (transform nodes parent-selector
    (fn [elt] (let [content (:content elt)
                      content* (transform content child-selector transform-fn)]
                 (if (= content content*) ;; hmm no it would be better to use zip-select