

                                                    propagate-alterability

    Declaration SPECIFIER
PROPAGATE-ALTERABILITY                              [Declaration specifier]

    Package
    series

    DESCRIPTION

The declaration specifier (PROPAGATE-ALTERABILITY INPUT OUTPUT) indicates
that attempts to alter an element of OUTPUT should be satisfied by altering
the corresponding element of INPUT.    (The corresponding element of INPUT
is the one most recently read at the moment when the output element is
written.)  This declaration can only appear in a call on PRODUCING.  INPUT
and OUTPUT must be an input and an output of the PRODUCING.  The example
below shows how the propagation of alterability could be supported in a
simplified version of UNTIL.

(DEFUN SIMPLE-UNTIL (BOOLS ITEMS) 
  (DECLARE (OPTIMIZABLE-SERIES-FUNCTION)) 
  (PRODUCING (Z) ((X BOOLS) (Y ITEMS) BOOL ITEM) 
    (DECLARE (PROPAGATE-ALTERABILITY Y Z)) 
    (LOOP 
      (TAGBODY 
        (SETQ BOOL (NEXT-IN X (TERMINATE-PRODUCING))) 
        (SETQ ITEM (NEXT-IN Y (TERMINATE-PRODUCING))) 
        (IF BOOL (TERMINATE-PRODUCING)) 
        (NEXT-OUT Z ITEM)))))


     SEE ALSO
     about-series
     about-generators
     producing

;Copyright 1989 by the Massachusetts Institute of Technology,
;Cambridge, Massachusetts.

;Permission to use, copy, modify, and distribute this software and its
;documentation for any purpose and without fee is hereby granted,
;provided that this copyright and permission notice appear in all
;copies and supporting documentation, and that the name of M.I.T. not
;be used in advertising or publicity pertaining to distribution of the
;software without specific, written prior permission. M.I.T. makes no
;representations about the suitability of this software for any
;purpose.  It is provided "as is" without express or implied warranty.

;    M.I.T. DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING
;    ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL
;    M.I.T. BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR
;    ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
;    WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
;    ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
;    SOFTWARE.



