cljs.spec.impl.gen/dynaload

(defmacro dynaload [[quote s]]
  (let [xs     (string/split (namespace s) #"\.")
        cnt    (count xs)
        checks (map
                 (fn [n xs]
                   `(c/exists? ~(symbol (string/join "." (take n xs)))))
                 (range 2 cnt)
                 (repeat xs))]
    `(cljs.spec.impl.gen/LazyVar.
       (fn []
         (if (and ~@checks (c/exists? ~s))
           ~(vary-meta s assoc :cljs.analyzer/no-resolve true)
           (throw
             (js/Error.
               (str "Var " '~s " does not exist, "
                    (namespace '~s) " never required")))))
       nil)))