function that inserts a toplevel expression

[Urs Liska]

Hi list,

I'm sorry that I once more have a basic Scheme question.

[
Any suggestion for a reading to find my way into Scheme?
I think I have some programming experience (although without any formal 
IT tuition), mainly from object pascal, but also a little bit with other 
languages.
But when it comes to Scheme I'm absolutely lost. I don't seem to be able 
to find out even such things as to pass a color to a function ... All 
these brackets and ticks and #s are so confusing, that it also isn't 
possible getting somewhere through trial and error.
I have read much of LilyPond's Scheme introduction, but it doesn't seem 
to help me much. So maybe I'd rather read something elsewhere and come 
back trying to get that together with LilyPond when I'm a little bit 
familiar with Scheme.
]

So now the question:
How can I write a function that produces a toplevel expression?

I want to be able to write:

\debugCurvesOn

or

#(debug-curves-on)

(or something similar) which should then expand to

\layout {
  \context {
    \Score
    \override Slur #'stencil = #(display-control-points)
    \override PhrasingSlur #'stencil = #(display-control-points) 
    \override Tie #'stencil = #(display-control-points) 
  }
}

(you see where this is going? ;-) )

So far I have realized this with an include file.
This works without problems, but calling a function seems
- more elegant and
- you don't need to remember the path (the function would be included 
through the general library anyway)

Furthermore I will later want to write functions for the \score block, 
and I will want to pass some parameters in there - which doesn't work 
with include files.

Any help is appreciated
Best
Urs