midi.clj

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

(defn play-note [synth channel note-map]
  (let [{:keys [note velocity duration]
         :or {note 60
              velocity 127
              duration 1000}} note-map]
    (. channel noteOn note velocity)
    (Thread/sleep duration)
    (. channel noteOff note)))

(defn play-notes
  [notes]
  (with-open [synth (doto (MidiSystem/getSynthesizer) .open)]
    (let [channel (aget (.getChannels synth) 0)]
      (doseq [note notes]
        (play-note synth channel note)))))

(defn play-c-major-scale []
  (let [c-major [0 2 4 5 7 9 11 12]
        c-major-notes (map #(hash-map :note (+ % 60) :duration 100) c-major)]
    (play-notes (cycle (concat c-major-notes
                         (rest (reverse c-major-notes)))))))

(play-c-major-scale)