[2-3] What is the equivalent of EXPLODE and IMPLODE in Common Lisp?

Hopefully, the only reason you need to do this is as part of trying to port
some old MacLisp code to Common Lisp.  These functions predated the
inclusion of strings as a first-class data type in Lisp; symbols were used
as strings, and they ere EXPLODEd to allow the individual characters to be
manipulated in a list.

Probably the best approximations of these are:

   (defun explode (object)
     (loop for char across (prin1-to-string object)
           collect (intern (string char))))

   (defun implode (list)
     (read-from-string (coerce (mapcar #'character list) 'string)))

An alternate definition of EXPLODE which uses MAP instead of LOOP is:

   (defun explode (object)
     (map 'list #'(lambda (char) 
                    (intern (string char)))
          (prin1-to-string object)))

The creation of N conses of garbage to process a string of N
characters is a hideously inefficient way of doing the job.  Rewrite
EXPLODE code with PRIN1-TO-STRING, or better STRING if the arguments
are symbols without funny characters.  For IMPLODE, try to make its
caller use strings and try to make the result usable as a string to
avoid having to call INTERN or READ-FROM-STRING.