Parser error with self-defined predicate symbol-or-markup? in markup function

[Reinhold Kainhofer]

I'm defining my own predicate symbol-or-markup? for the argument of a markup 
function. 

    #(define-public (symbol-or-markup? x)
      (or (symbol? x) (markup? x)))

    #(define-markup-command (mytest layout props label arg)
      (symbol-or-markup? markup?)
      (let* ((s (if (symbol? label) (symbol->string label) (label))))
        (interpret-markup layout props 
                          (markup #:concat ("Label: " s " arg: " arg)))))

If I pass a symbol, then everything works fine
    \markup \mytest #'test \bold "f"

but, as soon as I try to pass a markup, the parser complains that it expects 
an SCM_IDENTIFIER or SCM_TOKEN:

    \markup \mytest "test" \bold "f"
    \markup \mytest \bold "test" \bold "f"
    \markup \mytest \markup { "test" } \bold "f"

markup-or-symbol.ly:15:21: Fehler: syntax error, unexpected STRING, expecting 
SCM_IDENTIFIER or SCM_TOKEN
\markup \mytest "test
                     " \bold "f"
markup-or-symbol.ly:16:16: Fehler: syntax error, unexpected MARKUP_FUNCTION, 
expecting SCM_IDENTIFIER or SCM_TOKEN
\markup \mytest 
                \bold "test" \bold "f"
markup-or-symbol.ly:17:16: Fehler: syntax error, unexpected \markup, expecting 
SCM_IDENTIFIER or SCM_TOKEN
\markup \mytest 
                \markup { "test" } \bold "f"


Simple test case attached. Any idea what might be wrong?

Thanks,
Reinhold
-- 
------------------------------------------------------------------
Reinhold Kainhofer, address@hidden, http://reinhold.kainhofer.com/
 * Financial & Actuarial Math., Vienna Univ. of Technology, Austria
 * http://www.fam.tuwien.ac.at/, DVR: 0005886
 * LilyPond, Music typesetting, http://www.lilypond.org

markup-or-symbol.ly
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