input/regression/scheme-engraver-instance.ly

   1 \header {
   2
   3   texidoc = "Scheme engravers may be instantiated, with
   4   instance-scoped slots, by defining a 1 argument procedure which
   5   shall return the engraver definition as an alist, with the private
   6   slots defined in a closure.  The argument procedure argument is the
   7   context where the engraver is instantiated."
   8
   9 }
  10
  11 \version "2.13.15"
  12
  13 \layout {
  14   \context {
  15     \Voice
  16     \consists
  17     #(let ((instance-counter 0))
  18        (lambda (context)
  19          (set! instance-counter (1+ instance-counter))
  20          (let ((instance-id instance-counter)
  21                (private-note-counter 0))
  22            `((listeners
  23               (note-event
  24                . ,(lambda (engraver event)
  25                     (set! private-note-counter (1+ private-note-counter))
  26                     (let ((text (ly:engraver-make-grob engraver 'TextScript event)))
  27                       (ly:grob-set-property! text 'text
  28                                              (format "~a.~a" instance-id
  29                                                      private-note-counter))))))))))
  30   }
  31 }
  32
  33 <<
  34   \relative c'' { c4 d e f }
  35   \\ \relative c' { c4 d e f }
  36 >>