I spent far too much time debugging an issue with metacadr (see the
cons-list commits for details), but this now successfully recurses
and all of its code paths are exercised by the factorial/fibonacci
exercises. This is a Coffeescript implementation of the language
described at the end of chapter 1 of Lisp In Small Pieces.
Also, added a syntax-aware pretty printer. It's very primitive, but
it's good enough for some debugging.