/* *****************************************************************
*								   *
*	SB-Prolog						   *
*	Copyright SUNY at Stony Brook, 1986			   *
*								   *
****************************************************************** */

/*-----------------------------------------------------------------
SB-Prolog is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY.  No author or distributor
accepts responsibility to anyone for the consequences of using it
or for whether it serves any particular purpose or works at all,
unless he says so in writing.  Refer to the SB-Prolog General Public
License for full details.

Everyone is granted permission to copy, modify and redistribute
SB-Prolog, but only under the conditions described in the
SB-Prolog General Public License.   A copy of this license is
supposed to have been given to you along with SB-Prolog so you
can know your rights and responsibilities.  It should be in a
file named COPYING.  Among other things, the copyright notice
and this notice must be preserved on all copies. 
------------------------------------------------------------------ */


/* begin normvarocc1.P *********************************/

/* ********************************************************************** 
$normvarocc1_export([$normalize_var_occ/7]).

$normvarocc1_use($computil1,[_,_,_,_,_,$union_varsets/3,_,
		   $diff_sets/3,$intersect_sets/3,_,_,_,_,_,_,_,_,_,_,_]).
$normvarocc1_use($aux1,[_,_,_,_,_,_,_,_,$logical_or/3]).
$normvarocc1_use($blist,[_,_,$member1/2]).
$normvarocc1_use($listutil1,[_,_,_,_,_,_,_,$closetail/1]).
$normvarocc1_use($prococcbody1,[_,$list_pvars/2]).
********************************************************************** */

/*  "$normalize_var_occ" normalizes variable occurrences in disjunctive
     paths, so that every variable has a unique first/subsequent occurrence,
     irrespective of the disjunctive path considered. The algorithm is as
     follows:  If u0, u1, u2 and u3 be the variable occurring in goals at
     the points specified below, and V1 and V2 the set of variables that
     are added to normalize occurrences, then

		V1 = (u2 - u1) * (u3 - u0), and

		V2 = (u1 - u2) * (u3 - u0),  where  `*' = set intersection,
						    `-' = set difference.

			   +--------+ +--------+
		      -----+   u1   +-+   V1   +---- 
	+------+     /	   +--------+ +--------+     \       +------+
--------|  u0  |----<			   	      >------+  u3  +-->
	+------+     \     +--------+ +--------+     /       +------+
		      -----+   u2   +-+   V2   +----
			   +--------+ +--------+
									*/

$norm_newaddlist(L1,L2,L3,L) :-
	$diff_sets(L2,L1,D1), $intersect_sets(D1,L3,L).


$normalize_var_occ(nil,nil,[],[],[],[],0) :- !.
$normalize_var_occ(Body1,Body2,LinLeft,LinRight,Lout,Used,Chg) :-
	Body1 = and(A1,P,B1),
	!,
	$norm_pvars_seen(A1,PVars1), $union_varsets(LinLeft,PVars1,LinLeft1),
	$normalize_var_occ(B1,B2,LinLeft1,LinRight,L1,Used1,Chg1),
	$normalize_var_occ(A1,A2,LinLeft,L1,Lout,Used2,Chg2),
	$union_varsets(Used1,Used2,Used),
	$logical_or(Chg1,Chg2,Chg),
	((Chg =:= 0, Body2 = Body1) ;
	 (Chg =\= 0, Body2 = and(A2,P,B2))
	).
$normalize_var_occ(Body1,Body2,LinLeft,LinRight,Lout,Used,Chg) :-
	Body1 = if_then_else(T,P,A1,B1),
	!,
	$normalize_varocc_disj(A1,B1,LinLeft,LinRight,A2,B2,Used1,Used2,Chg),
	((Chg =:= 0, Body2 = Body1) ;
	 (Chg =\= 0, Body2 = if_then_else(T,P,A2,B2))
	),
	$union_varsets(Used1,Used2,Used0),
	$norm_pvars_seen(T,PvarsT), $union_varsets(PvarsT,Used0,Used),
	$union_varsets(Used,LinRight,Lout),
	$intersect_sets(Used1,Used2,PVars0),
	$union_varsets(PvarsT,PVars0,PVars),
	$member1(pvars(PVars),P),
	$closetail(P).
$normalize_var_occ(Body1,Body2,LinLeft,LinRight,Lout,Used,Chg) :-
	Body1 = or(A1,P,B1),
	!,
	$normalize_varocc_disj(A1,B1,LinLeft,LinRight,A2,B2,Used1,Used2,Chg),
	((Chg =:= 0, Body2 = Body1) ;
	 (Chg =\= 0, Body2 = or(A2,P,B2))
	),
	$union_varsets(Used1,Used2,Used),
	$union_varsets(Used,LinRight,Lout),
	$intersect_sets(Used1,Used2,PVars),
	$member1(pvars(PVars),P),
	$closetail(P).
$normalize_var_occ(not(A1,P),not(A2,P),LinLeft,LinRight,Lout,Lused,Chg) :-
	!,
	$normalize_var_occ(A1,A2,LinLeft,LinRight,Lout,Lused,Chg).
$normalize_var_occ('_call'(P,Args,X),'_call'(P,Args,X),_,LinRight,Lout,L,0) :-
	!,
	$list_pvars(Args,L),
	$union_varsets(L,LinRight,Lout),
	$member1(pvars(L),X).
$normalize_var_occ(C,C,_,L,L,[],0).

$normalize_varocc_disj(A1,B1,LinLeft,LinRight,A2,B2,Used1,Used2,Chg0) :-
	$normalize_var_occ(A1,A1a,LinLeft,LinRight,L1,Used1,Chg1),
	$normalize_var_occ(B1,B1a,LinLeft,LinRight,L2,Used2,Chg2),
	$logical_or(Chg1,Chg2,Chg3),
	$diff_sets(LinRight,LinLeft,LinNew),
	$norm_newaddlist(Used1,Used2,LinNew,NewAdd1),
	$norm_newaddlist(Used2,Used1,LinNew,NewAdd2), 
	((NewAdd1 = [], NewAdd2 = [], A2 = A1a, B2 = B1a, Chg4 = 0) ;
	 ($normalize1(A1a,NewAdd1,A2), $normalize1(B1a,NewAdd2,B2),
	  Body2 = if_then_else(T,P,A2,B2), Chg4 = 1
	 )
	),
	$logical_or(Chg3,Chg4,Chg0).

$norm_pvars_seen(and(C1,_,C2),L) :-
	$norm_pvars_seen(C1,L1),
	$norm_pvars_seen(C2,L2),
	$union_varsets(L1,L2,L).
$norm_pvars_seen(or(C1,_,C2),L) :-
	$norm_pvars_seen(C1,L1),
	$norm_pvars_seen(C2,L2),
	$union_varsets(L1,L2,L).
$norm_pvars_seen(if_then_else(T,_,G1,G2),L) :-
	$norm_pvars_seen(T,L1),
	$norm_pvars_seen(G1,L2),
	$norm_pvars_seen(G2,L3),
	$union_varsets(L2,L3,L4),
	$union_varsets(L1,L4,L).
$norm_pvars_seen(not(C,_),L) :- $norm_pvars_seen(C,L).
$norm_pvars_seen('_call'(_,Args,_),L) :- $list_pvars(Args,L).


$normalize1(A,[],A).
$normalize1(A1,[v(Vid,vrec(T,_,L,M))|VRest],A2) :-
   Prag1 = vrec(T,_,L,M), Prag2 = vrec(T,_,L,M),
   A3 = and(A1,_,'_call'('=',[v(Vid,Prag1),v(Vid,Prag2)],_)),
   $normalize1(A3,VRest,A2).

/* end normvarocc1.P *********************************/