weird closure error

(import '[java.io File])
(import '[javax.swing JFrame JButton SwingUtilities])
(import '[java.awt FlowLayout])
(import '[java.awt.event ActionListener])

(defn button [text listener]
  "Helper: makes a button with a text and an action listener"
  (doto (JButton. text)
    (.addActionListener listener)))

(defn listener [f]
  "Helper: turn a function (event) into a Proxy for ActionListener"
  (proxy [ActionListener] []
    (actionPerformed [e] (f e))))

(defn filenames [dir]
  "List filenames from a director :: string -> [string]"
  (->> dir File. .listFiles (map #(.getName %))))

(defn -main []
  "Makes a Frame with one button per file in /tmp"
  (let [frame (doto (JFrame. "opengl")
                (.setLayout (FlowLayout.))
                (.setSize 300 300)
                (.setVisible true))]
    (doseq [fn (filenames "/tmp")]
      (let [printer (fn [e] (println fn e))] ;; Syntax error compiling at (REPL:8:21). Unable to resolve symbol: x in this context
        (.add frame (button fn (listener printer)))))))

(defn main []
  (SwingUtilities/invokeLater -main))