Garbage Collection questions

[Sam Tregar]

Hey guys.  I've got some questions about garbage collection.  I'm working
on Perl bindings for Guile and getting their GC mechanisms to play nice is
starting to look like a real pain.  Perl uses an explicit refcounting GC
which is very easy to manipulate.  So far I can't see any easy ways to
examine/manipulate Guile's GC...  Anwyay, the questions:

1) Is it possible to examine/walk the GC mark tree from C code?  That
would be a huge help in debugging and might also help me in other ways too
perverse to get into here.

2) Under what circumstances do I need to protect an SCM?  Say, for
instance I write:

  result = scm_cons(a, b);

Do I need to do something with result to keep it from getting GC'd at some
arbitrary point in the future?

Thanks!
-sam