defining an \uppercase markup function

[Kieren MacMillan]

Hello all,

I'm trying to define an \uppercase markup function... so far, I've  
got [modelled on an existing snippet]

#(define-markup-command
  (uppercase paper props str)
  (string?)
    "Return the string characters in UPPERCASE. Syntax: \\uppercase # 
\"string\""
    (interpret-markup paper props
      (make-simple-markup
        (string-upcase str))))

The problem is, something like

  \markup \uppercase \fromproperty #'header:title

fails. In general, I'd rather have the syntax be

  \markup \uppercase { "test }

instead of

  \markup \uppercase #"test"

What do I have to do to my function to make this happen?

Thanks,
Kieren.