Fomus

(fomus
 :output '(:lilypond :view t)
 :verbose 1
 :ensemble-type :orchestra
 :parts
 (list
  (make-part
   :name "Piano"
   :instr :piano
   :events
   (loop repeat 3
     nconc (loop
        for off from 0 to 10 by 1/2
        collect (make-note :off off
                   :dur (if (< off 10) 1/2 1)
                   :note (+ 48 (random 25))
                   :voice '(1 2)))))))