(fn [ds]
  (let [is-map? (fn [ds] (:my-secret-key (conj ds [:my-secret-key true])))
        is-list? (fn [l] (= [:b :a] (take 2 (-> l (conj :a) (conj :b)))))
        is-vector? (fn [v] (= [:a :b] (take-last 2 (-> v (conj :a) (conj :b)))))
        is-set? (fn [s]
                  (= 1 (-> (group-by identity (-> s (conj :test) (conj :test)))
                           (get :test)
                           (count))))]
    (cond (is-map? ds)
          :map
          (is-set? ds)
          :set
          (is-list? ds)
          :list
          (is-vector? ds)
          :vector
          :default
          :unknown)))