calculation in scheme

[Stefan Thomas]

Dear community,
I would like to define a variable with sheme and I want to substract the number one from this variable.
I tried it with:

> % the following defines a Slur, lasting a certain number of eigth-notes
> xaS = #(define-music-function (parser location x) (number?) 
>   #{ % in der folgenden Zeile Lilypondcode eingeben 
>     s1*0 (  \repeat unfold  #(- $x 1)  {s8 } s8) 
> #})

Unfortunately without succes!