anchor.diff:    (when (numberp styles)
       (setf styles (subseq *style-character-list* 0 styles)))
     (make-instance 'town-snapshot
  -                 :population (generate-random-town population styles volatile)
  -                 :styles styles
  -                 :hipsterish-tendency hipsterish-tendency))
  +                 :population (generate-random-town population styles volatile hipsterish-tendency)
  +                 :styles styles))
   
   (defun make-delayed-town (population period &key (hipsterish-tendency 2/3) (styles #(#\# #\.)) volatile)
     (when (numberp styles)
       (setf styles (subseq *style-character-list* 0 styles)))
     (make-instance 'delayed-town
  -                 :population (generate-random-town population styles volatile)
  +                 :population (generate-random-town population styles volatile hipsterish-tendency)
                    :period period
                    :history (make-array (list period population) :adjustable volatile :initial-element nil)
  -                 :hipsterish-tendency hipsterish-tendency
                    :styles styles))
   
   (defmethod initialize-instance :after ((instance delayed-town) &key)
  
positive.code: 
  ;;; Class constructors
  
  (defun generate-random-town (population styles volatile)
    "Generates a random town of n people with the given vector of styles."
    (let ((out (make-array (list population) :adjustable volatile)))
      (dotimes (i population)
        (setf (aref out i) (make-instance 'inhabitant :style (aref styles (random (length styles))))))
      out))
  
  (defun make-town (population &key (hipsterish-tendency 2/3) (styles #(#\# #\.)) volatile)
  
negative.code:     (make-instance
       'foggy-town
       :visibility          (visibility town)
       :styles              (copy-seq (styles town))
       :population          (map 'vector #'copy (population town))
       :time                (ticks town)))
  