You might want to try and have a look at sbcl (steel bank common lisp) along with its documentation and various articles leading up to&#x2F;documenting its current design. It&#x27;s a real, and therefore complex, system - but I recall reading some rather approachable articles on it.<p>I don&#x27;t really know about that many other real, yet simple(ish) systems. Maybe Pharo Smalltalk, luajit, pypy, gnu guile (latest version)?