+ (let* ((this-list (string-split test-string #\-))
+ (fret-number (string->number (car this-list))))
+ ;; If none of the above applies, `fret-number' needs to be a
+ ;; number. Throw an error, if not.
+ (if (not fret-number)
+ (ly:error
+ "Unhandled entry in fret-diagrams \"~a\" in \"~a\""
+ (car this-list)
+ test-string))