anchor.diff:  
   (defun peek (in)
     (with-slots (src pos) (the code-stream in)
  -    (char-code (char src pos))))
  +    (aref *map* (char-code (char src pos)))))
   
   (defun eat (in)
     (with-slots (pos) (the code-stream in)
  
positive.code: (defun read (in)
    (prog1 (peek in)
      (eat in)))
  
negative.code:            eos?
             peek
             eat
             read
  
             init-code-mapping
             save-code-mapping))
  (in-package :code-stream)
  
  (declaim (inline make-code-stream make eos? peek eat read))
  
  (defvar *map*)
  
  (defstruct code-stream
    (src 0 :type simple-string)
  