-"Add @code{fret-offset} to each fret indication in @code{diagram-definition}
-and return the resulting verbose fret-diagram-definition."
- (let ((verbose-definition
- (if (string? diagram-definition)
- (parse-terse-string diagram-definition)
- diagram-definition)))
- (map (lambda(item)
- (let ((code (car item)))
- (cond
- ((eq? code 'barre)
- (list-set! item 3
- (+ fret-offset (list-ref item 3)))
- item)
- ((eq? code 'capo)
- (list-set! item 1
- (+ fret-offset (list-ref item 1)))
- item)
- ((eq? code 'place-fret)
- (list-set! item 2
- (+ fret-offset (list-ref item 2)))
- item)
- (else item))))
- verbose-definition)))
-
+ "Add @var{fret-offset} to each fret indication in
+@var{diagram-definition} and return the resulting verbose
+@code{fret-diagram-definition}."
+ (let ((verbose-definition
+ (if (string? diagram-definition)
+ (parse-terse-string diagram-definition)
+ diagram-definition)))
+ (map (lambda (item)
+ (let* ((code (car item))
+ (nth (assq-ref '((barre . 3) (capo . 1) (place-fret . 2))
+ code)))
+ (if nth
+ ;; offset nth element of item by offset-fret
+ ;; without modifying the original list but
+ ;; sharing its tail
+ (let ((tail (list-tail item nth)))
+ (append! (list-head item nth)
+ (cons (+ (car tail) fret-offset)
+ (cdr tail))))
+ item)))
+ verbose-definition)))