conditionals in scheme?

[Marc Hohl]

I'm working on some extensions of the tablature facilities of lilypond.
Now I have defined modern TAB clefs for 4, 5, 6 and 7 string 
instruments, for example

tabClefIV = \markup {
 \raise #0.7 {
   \override #'(font-family . sans)
   \bold\fontsize #-1.0
   \override #'(baseline-skip . 1.5  )
   \column { "T" "A" "B" }
 }
}

The other clefs simply use other values for raise, fontsize and 
baseline-skip,
so my idea is to use conditionals to get these values on the right place,
depending on the number of strings, which in turn can be evaluated using
the list of pitches in TabStaff.stringTunings. I would be glad if someone
points me in the right direction, and as I want to learn scheme, any 
links to
good tutorials, books etc. are appreciated.

Thanks in advance

Marc