Scheme question

[Arle Lommel]

I am a total neophyte to Scheme, but not to coding. I’ve written a simple function, but it does not work (I’ve reduced it to just the problematic lines. Can anyone tell me how to write the line indicated below?

shifter =

#(define-music-function

  (parser location padding)

  (number?)

  #{

    \once \override Accidental.extra-offset = #(cons padding . 0) %<- THIS LINE

  #}

)

The relevant errors it throws when invoked are:

error: GUILE signaled an error for the _expression_ beginning here

warning: type check for `extra-offset' failed; value `#<unspecified>' must be of type `pair of numbers’

The closest thing I can find to explaining how this works is here: http://lilypond.org/doc/v2.18/Documentation/extending/scheme-function-definitions

But I’m apparently missing something very obvious.

-Arle