(defstruct (test (:print-function my-print-test))
  x)

(defun my-print-test (atest stream depth)
  (print "ok" stream))

...oo-browser says "invalid feature entry, `[structure],-(test,
(defstruct (test'

Neither CLISP nor CMUCL has any problem with it [except that picky ol'
CMUCL complains if you don't have a (declare (ignorable atest depth))]:

        > (defstruct (test (:print-function my-print-test))
            x)
        TEST
        > (defun my-print-test (atest stream depth)
            (declare (ignorable atest depth))
            (print "ok" stream))
        MY-PRINT-TEST
        > (make-test :x 37)
        "ok"
        >

-Rob

  I don't use OO-Browser, but it shouldn't be too hard to find the
  place where it picks out the name of the struct, unless it uses
  regexps to do it, of course, and test for a list and if so, use its
  first element, instead of the whole thing.  From the error message,
  it looks like it uses regexps, which would provide yet another good
  example of why using regexps is the wrong solution in the general
  case and real parsing is not replaceable with regexps hacks.  If it
  does use regexps, all hope is probably lost, and you have rewrite a
  lot of hairy code to get a simple thing like this fixed.