cljs.reader/maybe-read-tagged-type

(defn maybe-read-tagged-type
  [rdr initch]
  (let [tag (read-symbol rdr initch)
        pfn (get @*tag-table* (str tag))
        dfn @*default-data-reader-fn*]
    (cond
     pfn (pfn (read rdr true nil false))
     dfn (dfn tag (read rdr true nil false))
     :else (reader-error rdr
                         "Could not find tag parser for " (str tag)
                         " in " (pr-str (keys @*tag-table*))))))