anchor.diff:  
   (declaim (ftype (function (rope) non-negative-fixnum) rope-height))
   (defun rope-height (rope)
  +  "Return height of rope"
     (etypecase rope
       ((or string symbol character) 0)
       (rope-node (rope-node-height rope))))
  
positive.code:                                  (funcall sep-fun (aref sequence j))))))
              (rope-array-cat tmp))))))
  
  (defun rope-parenthesize (a)
    (rope #\( a #\)))
  
negative.code: 
  (declaim (ftype (function (rope) rope-length-type) rope-length))
  (defun rope-length (rope)
    "Return the number of characters in rope"
    (etypecase rope
      (rope-node (rope-node-length rope))
      (simple-string (length rope))
  