anchor.diff:  
   (defmethod to-string((iter iterator))
     (with-slots (start end increment id quiet values cyclic) iter
  -    (format nil "start: ~A, end: ~A, quiet: ~A, inc: ~A, cyclic: ~A, values: ~{~A~^, ~}"
  +    (format T "start: ~A, end: ~A, quiet: ~A, inc: ~A, cyclic: ~A, values: ~A ~%"
               start end quiet increment cyclic values)))
  
positive.code:      collect (cons i j)))
  
  (defmacro make-iterator(&key (start 0) (end -1) (inc 1)
                            (id #'identity) (values ()) (cyclic Nil))
    `(let ((tmp (make-instance 'iterator :start ,start
                               :end (if (null ,values)
                                        ,end
                                        (1- (length ,values)))
                               :inc ,inc :id ,id :values ,values :cyclic ,cyclic)))
       (setf (slot-value tmp 'index) ,start)
       tmp))
           
  (defmacro with-iterator((name &key (start 0) (end -1) (increment 1)
  
negative.code:   ((init :initform (error "Stop iteration, iteration has exhausted."))))
  
  (defclass iterator()
    ((start :initform 0 :initarg :start)
     (index :initform 0)
     (end :initform -1 :initarg :end)
     (increment :initform 1 :initarg :inc)
     (id :initform #'identity :initarg :id)
     (quiet :initform T :initarg :quiet)
     (cyclic :initform nil :initarg :cyclic)
     (values :initform nil :initarg :values)
     (bound-check :initform #'<= :initarg :reverse)
     (comparer :initform #'(lambda(n values) (nth n values)))))
  
  (defmethod reset((iter iterator))
    (with-slots (start index) iter
      (setf index start)))
  
  (defmethod next((iter iterator))
    (with-slots (index end increment id quiet cyclic
                       comparer bound-check) iter
      (if (or (funcall bound-check index end) (eq end -1))
          (let ((current
                 (funcall id (if values
                                 (funcall comparer index values)
                                 index))))
            (incf index increment)
            current)
  