anchor.diff:    (iterate-elements
      (data data-set)
      (lambda (datum)
  -     (format out "~{~A ~}~C" datum #\Linefeed)))
  +     (format out "~{~S ~}~C" datum #\Linefeed))) ; gnuplot wants strings/labels/... quoted
     (format out "e~C" #\Linefeed))
   
   (defmethod make-plot ((plot-kind symbol) data 
  
positive.code: 
  (defmethod make-data-point ((point-kind (eql :box)) datum
                              &key (x-coord 'first) (y-coord 'second) (width 0.5)
                              (offset nil)
                              &allow-other-keys)
    (append 
  
negative.code:               (if offset offset 0)))
       nil)
     (if y-coord (list (funcall y-coord datum)) nil)
     (list (determine-width width))
     (if label (list (funcall label datum)) nil)
     ))
  
  (defmethod determine-width ((width number))
    (values width))
  