pc:scale-from-pc   scheme

;; returns the type of scale given a pc or the pc itself
;; if no known scale is found
(define pc:scale-from-pc
   (lambda (pc)
      (let ((scale (let loop ((scale pc)
                              (ivls '()))
                      (if (null? (cdr scale))
                          (reverse ivls)
                          (loop (cdr scale) (cons (let ((v (- (cadr scale) (car scale))))
                                                     (if (< v 0)
                                                         (+ 12 v)
                                                         v)) ivls))))))
         (let check ((scales *pc:scales*))
            (if (null? scales)
                pc
                (if (equal? scale (cdar scales))
                    (caar scales)
                    (check (cdr scales))))))))