#| -*-Scheme-*-

$Id$

Copyright 2006 Massachusetts Institute of Technology

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at
your option) any later version.

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301,
USA.

|#

;;;; Boolean constraint types

(declare (usual-integrations))

(define cp:B=A
  (cp:make-constraint-type '(b a)
    (lambda (constraint)
      (let ((b (cp:get-connector constraint 'b))
	    (a (cp:get-connector constraint 'a)))
	(cond ((cp:has-value? a)
	       (cp:set-value b (cp:value-of a) (list a) constraint))
	      ((cp:has-value? b)
	       (cp:set-value a (cp:value-of b) (list b) constraint)))))))

(define cp:B=-A
  (cp:make-constraint-type '(b a)
    (lambda (constraint)
      (let ((b (cp:get-connector constraint 'b))
	    (a (cp:get-connector constraint 'a)))
	(cond ((cp:has-value? a)
	       (cp:set-value b
			     (not (cp:value-of a))
			     (list a)
			     constraint))
	      ((cp:has-value? b)
	       (cp:set-value a
			     (not (cp:value-of b))
			     (list b)
			     constraint)))))))

(define cp:C=A^B
  (cp:make-constraint-type '(c b a)
    (lambda (constraint)
      (let ((c (cp:get-connector constraint 'c))
	    (b (cp:get-connector constraint 'b))
	    (a (cp:get-connector constraint 'a)))
	(cond ((and (cp:has-value? a)
		    (cp:has-value? b))
	       (cp:set-value c
			     (and (cp:value-of a) (cp:value-of b))
			     (list a b)
			     constraint))
	      ((not (cp:has-value? c))
	       (cond ((cp:value-is? a #f)
		      (cp:set-value c #f (list a) constraint))
		     ((cp:value-is? b #f)
		      (cp:set-value c #f (list b) constraint))))
	      ((cp:value-is? c #f)
	       (cond ((cp:value-is? a #t)
		      (cp:set-value b #f (list a c) constraint))
		     ((cp:value-is? b #t)
		      (cp:set-value a #f (list b c) constraint))))
	      (else
	       (cp:set-value a #t (list c) constraint)
	       (cp:set-value b #t (list c) constraint)))))))

(define cp:C=AvB
  (cp:make-constraint-type '(c b a)
    (lambda (constraint)
      (let ((c (cp:get-connector constraint 'c))
	    (b (cp:get-connector constraint 'b))
	    (a (cp:get-connector constraint 'a)))
	(cond ((and (cp:has-value? a)
		    (cp:has-value? b))
	       (cp:set-value c
			     (or (cp:value-of a) (cp:value-of b))
			     (list a b)
			     constraint))
	      ((not (cp:has-value? c))
	       (cond ((cp:value-is? a #t)
		      (cp:set-value c #t (list a) constraint))
		     ((cp:value-is? b #t)
		      (cp:set-value c #t (list b) constraint))))
	      ((cp:value-is? c #t)
	       (cond ((cp:value-is? a #f)
		      (cp:set-value b #t (list a c) constraint))
		     ((cp:value-is? b #f)
		      (cp:set-value a #t (list b c) constraint))))
	      (else
	       (cp:set-value a #f (list c) constraint)
	       (cp:set-value b #f (list c) constraint)))))))

#|

(let ((cn (cp:make-network 'test)))
  (let ((j1 (cp:make-connector 'j1 cn))
	(j2 (cp:make-connector 'j2 cn))
	(p1 (cp:make-connector 'p1 cn))
	(p2 (cp:make-connector 'p2 cn))
	(t (cp:make-connector 't cn)))
    (cp:assume-value t #t)
    (cp:make-constraint cp:B=-A #f cn j1 p1)
    (cp:make-constraint cp:B=-A #f cn j2 p2)
    (cp:make-constraint cp:C=AvB #f cn t j1 j2)
    (cp:make-constraint cp:C=AvB #f cn t p1 p2)
    (cp:assume-value j2 #t)
    (write-line (cp:value-of j1))
    (write-line (cp:value-of j2))
    (write-line (cp:value-of p1))
    (write-line (cp:value-of p2))
    ))
#f
#t
#t
#f
;Unspecified return value

(let ((cn (cp:make-network 'test)))
  (let ((j1 (cp:make-connector 'j1 cn))
	(j2 (cp:make-connector 'j2 cn))
	(p1 (cp:make-connector 'p1 cn))
	(p2 (cp:make-connector 'p2 cn))
	(t (cp:make-connector 't cn)))
    (cp:assume-value t #t)
    (cp:make-constraint cp:B=-A #f cn j1 p1)
    (cp:make-constraint cp:B=-A #f cn j2 p2)
    (cp:make-constraint cp:C=AvB #f cn t j1 j2)
    (cp:make-constraint cp:C=AvB #f cn t p1 p2)
    (cp:assume-value j1 #t)
    (write-line (cp:value-of j1))
    (write-line (cp:value-of j2))
    (write-line (cp:value-of p1))
    (write-line (cp:value-of p2))
    ))
#t
#f
#f
#t
;Unspecified return value

|#