maxima debug feature? - or how to accomplish same

Hi,

Thanks for Maxima - it is a great tool!  :)

I am curious about how it operates; function call tree etc.  For example: 
identify the functions that are called when the user inputs '2+2;', or 
'collectterms(expand(sbs));'.   Unfortunately, maxima is written in lisp and I 
can't seem to debug it.   Tools with which I am familiar include gdb, the printf 
function, and the cpp macros __LINE__ etc. 


I do have the maxima-5.21.1 source code, and have managed to compile it.  

I have resolved to insert lines of code like 'at line __LINE__ in function 
__FUNC__' (or similar) into the functions in which I am interested, but cannot 
discover the syntax of lisp that would allow me to announce watchpoints like 
printf.

So in my desperation I thought to email this listserv to ask for help.

Is there a not-for-public-release 'debug' version of the source code with this 
type of code present?  


Thanks in advance,
Max