string_identifier into string? Was: Creating arbitrary lines (or other postscript things)

[Andrew C. Smith]

> 
> Thanks for this I have sent this example to LilyPond Snippet Repository (LSR) 
> as I think this is a nice simple and clear way of how to do this for us 
> lesser mortals.
> 

Thanks, I'll probably be searching for it in a year or two...

I'm having yet more trouble, this time creating a music function. This function:

follower = 
#(define-music-function (parser location switch) (string?)
#{
        \once \override VoiceFollower #'style = #'dashed-line
        \change Staff = $switch
#})

...

\follower "sTwo" g1 

throws the error 

<string>:3:24: error: syntax error, unexpected STRING_IDENTIFIER, expecting 
STRING
        \change Staff = 
                        \lilyvartmpb
/Users/acsmith/Documents/Creativity/LilyPond/Topology.ly:59:8: error: errors 
found, ignoring music expression
        
        \new StaffGroup {

---

As far as I can see, this is just a normal text-replacement function. I googled 
around though, and can't find much related to string_identifier aside from a 
printout of the entire bison grammar specification for Lilypond, which wasn't 
too helpful. How do I turn a string_identifier into a string?