measurePosition within a music function?

[Marc Hohl]

Hello,

I have a music function which simply outputs the durations of every note:

\version "2.13.13"

#(define (test-apply m)
   (if (eq? 'NoteEvent (ly:music-property Voice 'name))
       (let ((dur (ly:music-property m 'duration)))
             (display "\nduration: ")(display dur)(display "\n--\n"))
    )
  m)

test-func=#(define-music-function (parser location music) (ly:music?)
     (music-map test-apply music))

melody={ c4. d8 e8*2 f2 }

\test-func { \melody }

This works fine, but I wanted to evaluate the position of the current note
within the current bar. I found the measurePosition property, but to use

ly:context-property context 'measurePosition

in my function, I need the appropriate context. How can I achieve that?

(I think it must be something very simple, but digging in the sources and
the manuals, I didn't get a hint. the lsr provides a solution with
\applyOutput, but this doesn't work here).

Thanks,

Marc