looking at lilypond data structures

[Kim Shrier]

Just to satisfy personal curiosity, I am looking at the lilypond source code
so I can get a better feel for what it is up to and how it accomplishes its
job.

My understanding is that the parser constructs a scheme data structure
which is subsequently processed by the iterators to turn it into a stream
(or several streams) of musical events.  Before I start looking at the
iterators, I would like to see what they are working with for input.

So, I have a few questions.

Is my understanding correct that the parser produces a single scheme
expression that is then processed for use in later stages?

If I wanted to print out this mythical data structure, is there an easy way
to do that?

Is it something that is appropriate to pass to displayMusic or
displayScheme?

How do I get a reference to this data structure?

What I would like to do is have lilypond parse some simple files that I
would create for the purposes of seeing the different things that the
parser generates.

If at all possible, I would like to avoid making special hacks in the
source for dumping out various data structures.  If I can do what I
want from scheme without touching the source, that would be ideal.
However, I can compile lilypond 2.19.81 so if I need to make changes,
that is an option.

Thanks,
Kim