Emacs lisp is handy for toying around with the editor, but it's a horrible Lisp.  It does not even have lexical scoping.  You are much better off in terms of entertainment (through learning interesting stuff) with e.g. PLT Scheme or perhaps Arc.<p>(My comment about pure languages above was meant to highlight the joys of Clean and Haskell.  Curry may also be worth a look.  And Prolog, if you dare.)