For starters, SBCL's non-CL parts are separated into src/runtime directory, which makes it much easier to figure out what is just "support structure" and what i

For starters, SBCL's non-CL parts are separated into src/runtime directory, which makes it much easier to figure out what is just "support structure" and what is actual language. For learning more specifically on SBCL, you can look at following https://pvk.ca/Blog/2013/04/13/starting-to-hack-on-sbcl/ https://pvk.ca/Blog/2013/04/13/starting-to-hack-on-sbcl/ https://simonsafar.com/2020/sbcl/ https://simonsafar.com/2020/sbcl/ And of course SBCL code and comments. There are also some papers related to CMUCL (and before that, Spice Lisp) that talk about Python Compiler (the compiler used by CMU CL, SBCL, Scieneer CL)