\version "2.9.17"

#(define output (open-output-file "graph.dot"))
#(define node-num 0)
#(define last-grob-action '())

#(define sym-blacklist
  '(cause font))

#(define sym-whitelist
  '(left-neighbors right-neighbors left-items right-items))

#(define file-line-blacklist
  '())

#(define file-line-whitelist
  '())

% an event is relevant if
% (it is on some whitelist or all whitelists are empty)
% and
% (it isn't on any blacklist)

#(define (relevant? grob file line prop)
  (let ((file-line `(,file . ,line)))
   (and
    (or
     (= 0 (length file-line-whitelist) (length sym-whitelist))
     (memq prop sym-whitelist)
     (member file-line file-line-whitelist))
    (and
     (not (memq prop sym-blacklist))
     (not (member file-line file-line-blacklist))))))

#(display "digraph G {\nrankdir=\"LR\"\nnode [shape=rectangle]\n" output)

#(define (grob-mod grob file line prop val)
  (let* ((prev (assv grob last-grob-action))
	 (val-str0 (format "~a" val))
	 (val-str (string-take val-str0 (min 50 (string-length val-str0)))))
   (if (relevant? grob file line prop)
    (begin
     (display (format "~a [label=\"~a\\n~a:~a\\n~a <- ~a\"]\n" node-num grob file line prop val-str) output)
     (display (format "subgraph cluster_~a {\nlabel = \"~a\"\ncolor=blue\n~a\n}\n"
	       (string-filter file char-alphabetic?) file node-num) output)
     (if (pair? prev)
      (display (format "~a -> ~a\n" (cdr prev) node-num) output))
     (set! last-grob-action (assv-set! last-grob-action grob node-num))
     (set! node-num (1+ node-num))))))

#(define (grob-create grob file line)
  (display (format "~a [label=\"~a\\n~a:~a\",color=green]\n" node-num grob file line) output)
  (display (format "subgraph cluster_~a {\nlabel = \"~a\"\ncolor=blue\n~a\n}\n"
	       (string-filter file char-alphabetic?) file node-num) output)
  (set! last-grob-action (assv-set! last-grob-action grob node-num))
  (set! node-num (1+ node-num)))

#(ly:set-grob-modification-callback grob-mod)
#(ly:set-grob-creation-callback grob-create)
{
a b c d a b c d
}