anchor.diff:                                     new-state
                                      (ecase state
                                        (:conservative-search
  +                                      (setf conservative-place pme-or-place)
                                         (augment conservative-template))
                                        (:speculative-search
                                         conservative-template))
  
positive.code:                    (%continue :speculative-search) ; start speculative search
                     ;; :speculative-search
                     (%continue :speculative-search) ; continue speculative search
                     (return-from %expand
                       (%finish conservative-template pme-or-place env oldp))))))))))
      (recurse place-modification-expression :top-level #'identity #'identity)))
  
  (defmacro modify (&rest place-modification-expressions &environment env)
  
negative.code:                  (error "~S is not a valid place-modification-expression."
                          pme-or-place))
                 (when (eq operator :place)
                   (return-from recurse
                     (%finish speculative-template (second pme-or-place) env oldp)))
                 (when top-level-p
                   (setf state :conservative-search)))
  