How to pass a fraction as a parameter for a Scheme function

[Paolo Prete]

Hello,

I don't understand how to use a fraction as a parameter for a scheme function. More specifically, this gives me an error:

%%%%%%%%%%%%

proportionalNotationDur = #(define-music-function (parser location frac) (scheme?)                          #{ \set Score.proportionalNotationDuration = #(ly:make-moment frac) #})

{

  \proportionalNotationDur 1/16 

  c' c' c' c'

}

%%%%%%%%%%%%

How can I fix it? 

Thanks!