anchor.diff:  (defgeneric next (pattern)
     (:documentation "Get the next value of a pstream, function, or other object, advancing the pstream forward in the process.
   
  -See also: `peek', `next-n', `next-upto-n'")
  +See also: `next-n', `next-upto-n', `peek'")
     (:method-combination pattern))
   
   (defmethod next ((pattern t))
  
positive.code:     (if (>= n (length history))
          (error 'pstream-out-of-range :index n)
          (elt-wrap history n))))
  
  (defun pstream-nth-future (n pstream)
    "Obsolete alias for `pstream-elt-future'."
    (warn "~s is deprecated; use ~s instead." 'pstream-nth-future 'pstream-elt-future)
    (pstream-elt-future pstream n))
  
  (defun pstream-elt-future (pstream n)
    "Return the Nth element from PSTREAM's history, automatically advancing PSTREAM as necessary if the Nth element has not yet occurred.
  
negative.code:   (:documentation "Abstract pattern superclass."))
  
  (defun all-patterns ()
    "Get a list of all defined patterns.
  
  See also: `all-pdefs'"
    (remove-if (lambda (s) (eql s 'pstream))
               (mapcar #'class-name (closer-mop:class-direct-subclasses (find-class 'pattern)))))
  
  