Implicit forward declarations for Clojure

declare.clj

(defn def?
  [[a b]]
  (if (#{'defn 'def} a) b))

(defmacro progn
  [& sexps]
  (let [names (->> sexps (filter def?) (map def?))]
    `(do
       (declare ~@names)
       ~@sexps)))

(progn
  (defn x
    [n]
    (* (y n) n))

  (defn y
    [n]
    (* z n))

  (def z 3))

I wish the Clojure compiler did this automatically.