Conditional include?

[Michael Scheer]

Hi Lilypond users,

I want to have a complete include conditional. I cannot do:

#(if (eq conditionvar #t) #{ \include "file.ily" #} )

...because errors. I think the include is replaced before the code is
interpreted.

So what I want to try then is, make the whole contents of the include file
conditional. But I fail, it complains it is not music. What I tried is this
(also tried "$(if"):

#(if (eq conditionvar #t)
#{
  % The original include code begin
  \header { instrument = "Klarinette 1" }
  SomeVar = "Yo Bro Whassup"
  ClarinetI = {
    \transposition h
    \key g \major \time 4/4
    c4 4 e e
  }
  % The original include code end
#}
)

Best regards
Michael