anchor.diff:  ;; ;=> (1 2 4 8)
   
   See also: `pseries', `paccum'")
  -
  -(defmethod as-pstream ((pgeom pgeom))
  -  (with-slots (start grow length) pgeom
  -    (make-instance 'pgeom-pstream
  -                   :start (pattern-as-pstream start)
  -                   :grow (pattern-as-pstream grow)
  -                   :length (as-pstream length))))
   
   (defmethod next ((pgeom pgeom-pstream))
     (with-slots (start grow current-value) pgeom
  
positive.code:                                           0.125))
                              :length length))))
  
  (defmethod as-pstream ((pbrown pbrown))
    (with-slots (lo hi step length) pbrown
      (make-instance 'pbrown-pstream
                     :lo (pattern-as-pstream lo)
                     :hi (pattern-as-pstream hi)
                     :step (pattern-as-pstream step)
                     :length (as-pstream length))))
  
  (defmethod next ((pbrown pbrown-pstream))
    (unless (remaining-p pbrown 'length)
      (return-from next eop))
  
negative.code: 
  See also: `pxrand', `pwrand', `pwxrand'")
  
  (defmethod next ((prand prand-pstream))
    (unless (remaining-p prand 'length)
      (return-from next eop))
  