print out the value of #<Book>

[Kim Shrier]

In my ongoing exploration of lilypond internals,  i am looking
at printing out the value of the argument being passed to
toplevel-book-handler, defined in ly/declarations-init.ly.

I have tried a few different functions such as

    (display-scheme-music book port)

or

    (pretty-print book port)

but all I get out is:

    #<Book>

My knowledge of Scheme and C++ is somewhat rusty as it has
been decades since I used either of these languages.  If I could
get a pointer to information on how to approach this, it would be
greatly appreciated.

Thanks,
Kim