Scheme function problems

[Kieren Richard MacMillan]

Hello, all --

Can anyone tell me why the code

\version "2.8.1"
barpadding = #(define-music-function (parser location padding music)  
(number? ly:music?)
        #{
		\once \override Score.BarLine #'space-alist = #'((first-note extra- 
space . $padding))
                $music
        #}
)
{ c'1 \barpadding #32.0 { c' c' } c' }

returns

ERROR: Wrong type (expecting real number): lilyvartmpa

Thanks!
Kieren.