Help to get started with the code of Maxima

Hi!

I'd like to start playing with Maxima's code. I suppose the maxima's
software is organized as follow:
1. the maxima prompt takes the input from the user
2. it is passed to a lisp function that translates it into some LISP sexpr
( something like "derivative (x^2,x);"  -> (some-function-for-derivative
'(^x 2) 'x) )
3. it is evaluated (i.e (* 2 x))
4. it is translated back into standard notation  (i.e "2*x") and passed
back to the prompt.

Please correct me if I am wrong. Now, what I'd like to do is to call the
maths functions directly from Common Lisp (i.e access directly to
"some-function-for-derivative" in my example). Is it possible to do so?

Many thanks,
Sam