anchor.diff:  
   (defun test ()
     "
  -do:     test the ascii package; signal an error if something is wrong.
  -return: :success
  +DO:     test the ascii package; signal an error if something is wrong.
  +RETURN: :success
   "
     (loop
        :for ch :across *ascii-characters*
  
positive.code:      :for code :from (ascii-code #\0) :to (ascii-code #\9)
       :for n :from 0
       :do (assert (eql n (code-ascii-digit-p code))))
    (string= (ascii-string #(65 66 67 68)) "abcd")
    (bytes=  #(65 66 67 68)  (ascii-bytes "abcd"))
    (let ((*readtable* (copy-readtable nil)))
      (set-dispatch-macro-character #\# #\Y (function ascii-dispatch-macro)
                                    *readtable*)
  
negative.code:          :code code
           :coding-system :us-ascii
           :message (cond
                      ((or (< code sp) (= code del))
                       "ASCII control codes cannot be converted to characters.")
                      ((< del code)
                       "Codes greater than 127 are not ASCII codes.")
                      (t
                       "[SHOULD NOT OCCUR]"))))
  