Fomus

(fomus
 :output '(:lilypond :view t)
 :parts
 (list
  (make-part
   :name "Piano"
   :instr :piano
   :events
   (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)))))))