anchor.diff:  
   ;;;# Dereferencing
   
  -(defun convert-foreign-type (type-keyword &optional (context :normal))
  +(defun convert-foreign-type (type-keyword)
     "Convert a CFFI type keyword to an Allegro type."
     (ecase type-keyword
       (:char             :char)
  
positive.code:                  t  ; callback
                   :c ; convention
                   ;; return type '(:c-type lisp-type)
                   ',(allegro-type-pair (convert-foreign-type rettype :funcall))
                   ;; arg types '({(:c-type lisp-type)}*)
                   '(,@(loop for type in types
                             collect (allegro-type-pair
                                      (convert-foreign-type type :funcall))))
                   nil ; arg-checking
                   ff::ep-flag-never-release))))
  
  
negative.code:     (:unsigned-long    :unsigned-long)
      (:float            :float)
      (:double           :double)
      (:pointer          :unsigned-nat)
      (:void             :void)))
  
  (defun %mem-ref (ptr type &optional (offset 0))
  