anchor.diff:                          :accessor hipsterish-tendency
                           :documentation "How likely would this individual be nonconformist at any given time."))
     (:documentation "An inhabitant in a hipster town."))
  -          
   
   (defclass town-snapshot ()
     ((ticks :initform 0
  
positive.code:                      (if (true-with-probability stickiness)
                           (styles i)
                           (aref town-styles (random (length town-styles)))))))))
  (defgeneric tick! (town)
    (:documentation "Destructively modifies a snapshot to become the next iteration of the simulation.")
    (:method ((town town-snapshot))
  
negative.code:     (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)
    "Builds a new town with a population of population, seeding with the two types of clothes."
    (make-instance 'town-snapshot
  