Obtain the number of notes and rests from "ly:music?" parameter passed to a function

[Paolo Prete]

Hello,

in the snippet below how can I replace "4" (in the denominator of "\times") with the number of notes+rests (including "s") in $notes ?

Thanks

%%%%%%%%

createTuplet = #(define-music-function (parser location notes) (ly:music?)

#{

  \times 2/4 $notes

#})

{

  \createTuplet {c' e' r g'}

}