Example 1. The pick function.

(pick 1 2 3 4 5)
⇒ 3
(pick 1 2 3 4 5)
⇒ 2
(pick 1 1 1 0 2) ; poor man's weighted selection
⇒ 1

Example 2. Random selection using pick.

(define (play-pick len)
  (process repeat len
           for o = (pick 0 0 -24 24)
           for r = (pick .1 .2 .2 .2 .4)
           for k = (between 60 67)
           for a = (pick .25 .25 .24 .5 .5 .75)
           output (new midi :time (now)
                       :duration (* r (pick 1.5 .5))
                       :keynum (+ k o)
                       :amplitude a)
           wait r))

(events (play-pick 60) "test.mid")
⇒ "test.mid"