Example 1. Generating random rhythms followed by their retrograde.

(define (non-retro pat)
  (new thunk :of (lambda ()
                   (let ((per (next pat #t)))
                     (append per (reverse per))))))

(define messiaen
  (non-retro (new heap :of '(s e e. q q+s e.)
                  :for (new weighting :of '(3 4 5 )))))

(next messiaen #t)
⇒ (q+s e s e. e. s e q+s)
(next messiaen #t)
⇒ (e. q e e. e. e q e.)
(next messiaen #t)
⇒ (s q+s q q q+s s)

Example 2. Generating P I R and RI of a row.

(let ((alban '(0 3 7 11 14 17 21 25 28 30 32 34)))
  (define albans
    (new heap
         :of (list (new thunk :of (lambda () alban))
                   (new thunk :of (lambda () (invert alban)))
                   (new thunk :of (lambda () (reverse alban)))
                   (new thunk :of (lambda () (reverse (invert alban))))))))

(define transp (new thunk :of (lambda () (between 55 68))))

(define (play-rows reps rows keys rate)
  (process with key
           for i below reps
           when (= (mod i 12) 0)
           set key = (next keys)
           output (new midi :time (now) 
                       :keynum (transpose (next rows) key)
                       :duration (* rate 1.5))
           wait rate))

(events (play-rows 120 albans transp .1) "test.mid")
⇒ "test.mid"