\version "2.13.19"

#(define (NoteEvent? music)
   (equal? (ly:music-property music 'name) 'NoteEvent))

#(define (EventChord? music)
   (equal? (ly:music-property music 'name) 'EventChord))

#(define (get-notename NoteEvent)
   (ly:pitch-notename (ly:music-property NoteEvent 'pitch)))

#(define (make-textscript dir txt)
   (make-music 'TextScriptEvent
               'direction dir
               'text txt))

#(define (make-tab-number NoteEvent)
   (make-textscript
     UP
     (number->string (get-notename NoteEvent))))

#(define (make-tab-numbers EventChord)
   (let ((elts (ly:music-property EventChord 'elements)))
     (map make-tab-number (filter NoteEvent? elts))))

#(define (add-tab-numbers music)
   (if (EventChord? music)
       (set! (ly:music-property music 'elements)
             (append (ly:music-property music 'elements)
                     (make-tab-numbers music))))
    music)

harmonicaTab =
#(define-music-function
  (parser location music)
  (ly:music?)
  (music-map add-tab-numbers music))

\relative c' \harmonicaTab {
  c d <c e> <d f>
}