- Take the implementation of eval. from Paul Graham's "The Roots of Lisp" and add interesting extensions, like lexical environments, the different versions of nlambda, a macro facility, etc. See also "The Art of the Interpreter" by Guy Steele and Gerald Sussman at http://library.readscheme.org/page1.html for suggestions.

- A basic notion of 3-Lisp is that of a reflective tower. When macros and the CLOS MOP are different substrates of reflection, where are the reflective towers in those approaches?