here is a little "sketched" function STEP-TO-PITCH , perhaps OM could further develop the function...

 

;;; FUNCTION

(defun step-to-pitch (&key steps pitches start)
  (let ((pos (car (position-item start pitches))))
    (append (list (nth pos pitches))
            (loop for i in steps
              ;; setting pos by add the step to pos
              do (setf pos (+ pos i))
              ;; when pitch-range to small then reset to lowest pitch+step
              ;; could be a more intelligent solution
              when (> pos (length pitches))
              do (setf pos (+ 0 i))
              collect (nth pos pitches)))))



;;; EXAMPLES

(step-to-pitch :steps '(1 1 -1 2 2 -1)
               :pitches '(c4 d4 e4 f4 g4 a4)
               :start 'c4)

;; => (c4 d4 e4 d4 f4 a4 g4)


(step-to-pitch :steps '(1 1 -1 2 2 -1)
               :pitches (expand-tonality '(c4 chromatic))
               :start 'c4)

;; => (c4 cs4 d4 cs4 ds4 f4 e4)


(step-to-pitch :steps '(1 1 -1 2 2 -1 5)
               :pitches (expand-tonality '(c4 messiaen-mode6))
               :start 'c4)

;; => (c4 d4 e4 d4 f4 gs4 fs4 gs4)

 

This is how the new function TONALITY-STEP will work:

 

tonality-step (scale step &key start ambitus (sort t))

(tonality-step '(c4 d4 e4 g4 a4 f4) '(1 1 -1 2 2 -1))
=> (c4 d4 e4 d4 f4 a4 g4)

(tonality-step '(c4 d4 e4 g4 a4 f4) '(1 1 -1 2 2 -1 5 3 2 3 -2 -2 1 1))
=> (c4 d4 e4 d4 f4 a4 g4 f5 c6 e6 a6 f6 d6 e6 f6)

(tonality-step '(c4 chromatic) '(1 1 -1 2 2 -1))
 => (c4 cs4 d4 cs4 eb4 f4 e4)

(tonality-step '(c4 messiaen-mode6) '(1 1 -1 2 2 -1 5))
=> (c4 d4 e4 d4 f4 gs4 fs4 d5)

(tonality-step '(c4 messiaen-mode6) '(1 1 -1 2 2 -1 5 3 2 3 -2 -2 1 1))
=> (c4 d4 e4 d4 f4 gs4 fs4 d5 fs5 bb5 d6 b5 gs5 bb5 b5)

(tonality-step '(c4 messiaen-mode6) '(1 2 -1 2 2 -1 5 3 2 3 -2 -2 1 1) :ambitus 'scale)
=> (c4 d4 f4 e4 fs4 bb4 gs4 e4 gs4 b4 e4 c4 bb4 b4 c4)

(tonality-step '(c4 messiaen-mode6) '(1 2 -1 2 2 -1 5 3 2 3 -2 -2 1 1) :ambitus '(c3 a4))
=> (c4 d4 f4 e4 fs4 bb3 gs4 e4 gs4 b3 e4 c4 bb3 b3 c4)

(tonality-step '((c4d4e4g4a4f4) (c3 messiaen-mode6) (c4d4e4g4a4f4))
               '((1 1 -1 2 2 -1)
                 (5 3 2 3 -2 -2 1 1)
                 (2 -1 3 2 3 -2 -2 1 1)))
=> ((c4 d4 e4 d4 f4 a4 g4)
    (c3 gs3 c4 e4 gs4 f4 d4 e4 f4)
    (c4 e4 d4 g4 c5 f5 d5 a4 c5 d5))

 

great!!! 

Will be part of the next update. 

extended idea: would be nice to do it with chords => instead of a scale, a sequence with chords...

thanx a lot for such a quick developing/implementation!!

The scale can be anything even omn bar:

(tonality-step '(h fs5a5b3 e4b3) '(1 1 -1 2 2 -1))
=> (b3 b3 e4 b3 fs5 b4 a5)

(tonality-step '(h fs5a5b3 e4b3) '(1 1 -1 2 2 -1) :sort nil)
=> (fs5 a5 b3 a5 e4 fs6 b3)

 

Example with start:

(tonality-step '(c4d4e4f4g4a4) '(1 1 -1 2 2 -1) :start -2)
=> (g3 a3 c4 a3 d4 f4 e4)

 

Great !!

 

 

SB.

is it also possible to start at a specific pitch?

 

(tonality-step '(c4 d4 e4 g4 a4 f4) '(1 1 -1 2 2 -1) :start 'e4)

 

Just to let you know the TONALITY-MAP with :map 'shift is doing the same thing already 

 

(tonality-step '(c4 messiaen-mode6) '(1 1 -1 (2 2 -1) 5 3 (2 3 -2) -2 1 1))
=> (c4 d4 e4 d4 f4gs4fs4 d5 fs5 bb5d6b5 gs5 bb5 b5)

(tonality-map '(messiaen-mode6 :map shift)
               (interval-to-pitch '(1 1 -1 (2 2 -1) 5 3 (2 3 -2) -2 1 1)))
=> (c4 d4 e4 d4 f4gs4fs4 d5 fs5 bb5d6b5 gs5 bb5 b5)