Conditional \book - possible?

Hi Lilypond users,

I want to have Lilypond print an additional book with a specific filename if a
variable is set. But the following logic does not print the book, it does
nothing. What am I not seeing?

Thx

%%% SNIPPET START %%%
publishMode = 1
[...]
#(if (= publishMode 1)
  #{
    \book {
      [...]
    }
  #}
)
%%% SNIPPET START %%%