scale.clj

(import '(javax.sound.midi MidiSystem Synthesizer))

(defn play-note [synth channel note]
  (let [n (:note note 60)
	v (:velocity note 127)
	d (:duration note 1000)]
   (. channel noteOn n v)
   (Thread/sleep d)
   (. channel noteOff n)))

(defn play-notes
  [notes]
  (with-open [synth (doto (MidiSystem/getSynthesizer) .open)]
    (let [channel (aget (.getChannels #^Synthesizer synth) 0)]
      (loop [remaining notes]
	(when-not (empty? remaining)
	  (play-note synth channel (first remaining))
	  (recur (rest remaining)))))))

(defn play-c-major-scale []
  (let [c-major [0 2 4 5 7 9 11 12]]
    (play-notes (map #(hash-map :note (+ % 60) :duration 400)
		     (cycle (concat c-major (rest (reverse (rest c-major)))))))))

(play-c-major-scale)