pc:make-chord   scheme

Defined in:  https://github.com/digego/extempore/tree/v0.8.9/libs/core/pc_ivl.xtm


;; pc:make-chord
;; creates a list of "number" pitches between "lower" and "upper"
;; bounds from the given "pc".  a division of the bounds
;; by the number of elements requested breaks down the selection into
;; equal ranges from which each pitch is selected.
;; make-chord attempts to select pitches of all degrees of the pc.
;; it is possible for elements of the returned chord to be -1 if no
;; possible pc is available for the given range.
;; non-deterministic (i.e. result can vary each time)
;; arg1: lower bound (inclusive)
;; arg2: upper bound (exclusive)
;; arg3: number of pitches in chord
;; arg4: pitch class
;; example: c7
;; (pc:make-chord 60 85 4 '(0 4 7 10)) => (60 70 76 79)
(define pc:make-chord
   (lambda (lower upper number pc)
      (let ((chord '()))
         (let loop ((l (round lower))
                    (u (round upper))
                    (n number)
                    (p pc))
            (if (< n 1)
                (map (lambda (x)
                       (real->integer x))
                     (cl:sort (cl:remove -1 chord) <)) ; lowest pitch to highest pitch remove -1s
                (let* ((range (- u l))
                       (gap (round (/ range n)))
                       (pitch (pc:random l (+ l gap) p)))
                   (if (not pitch) ; if new pitch is #f, try from whole range
                       (set! chord (cons (pc:random lower upper p) chord))
                       (set! chord (cons pitch chord)))
                   (loop (+ l gap)
                         (- n 1)
                         (if (> (length p) 1)
                             (cl:remove (modulo (car chord) 12) p)

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