display-scheme-music not working inside markup-command-definition?

[Thomas Morley]

Hi,

exploring chordnaming further, I thought it might be nice, if a
formating procedures for ChordNames could be used in a markup-command
outputting equal designed chord-names.

Though, looks like I have a problem:

#(display-scheme-music #{ \chordmode { c:m } #})
works ofcourse.

But for

#(define-markup-command (foo parser location)()
  (display-scheme-music #{ \chordmode { c:m } #})
  (interpret-markup parser location "xy"))

\markup \foo

I get this:

Preprocessing graphical
objects.../home/harm/lilypond-git/build/out/share/lilypond/current/scm/parser-ly-from-scheme.scm:70:21:
In procedure ly:parser-clone in expression (ly:parser-clone parser
closures ...):
/home/harm/lilypond-git/build/out/share/lilypond/current/scm/parser-ly-from-scheme.scm:70:21:
Wrong type argument in position 1 (expecting Lily_parser): #<
Output_def>

I've not a real clue what's wrong and how to fix/proceed.

Any hint?

Cheers,
  Harm