[pnathan]

I present to you print-object, a generic function in Common Lisp.

http://clhs.lisp.se/Body/f_pr_obj.htm

So say you have a object type FOO, you can do this:

    (defmethod print-object ((obj FOO) stream)
      ...)

Now, when you have a FOO on the repl, print-object will be called.

Obviously it doesn't provide a drilldown approach and any number of nifty and useful functions.