anchor.diff:      (alexandria:appendf pattern-chain (list pattern))
       (unless (alexandria:length= 1 pattern-chain)
         (setf pattern (apply #'pchain pattern-chain)))
  -    ;; process :quant key. ;; FIX: should this be applied to the pdef, or the pattern itself?
  +    ;; process :quant key.
       (alexandria:when-let ((quant (getf pairs :quant)))
         (setf (quant pattern)
               (if (functionp quant)
  
positive.code:   (:report (lambda (condition stream)
               (format stream "The pstream has insufficient history to index to element ~d." (pstream-elt-index condition)))))
  
  (defun pstream-nth (n pstream)
    "Obsolete alias for `pstream-elt'."
    (warn "~s is deprecated; use ~s instead." 'pstream-nth 'pstream-elt)
    (pstream-elt pstream n))
  
  (defun pstream-elt (pstream n)
    "Return the Nth element from PSTREAM's history. Does not automatically advance PSTREAM if N is out of range.
  
  
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)))))
  
  