How constant are defconstants?

[Rob MacLachlan <RAM@CMU-CS-C.ARPA>]

    Although defconstants are second-rate constants as compared to
literal constants inline in code, I think that previous decisions
forbidding modification of constants would apply here.  In any case,
you can obtain the desired effect by specifying the contents at the
time the array is created:
(defconstant the-data (make-array n :initial-contents
  (list <long-computation> ...)))

  Rob