/*
A slow logical implementation of logical association feature.
}Value{ = '}{'(Cache,[Value|_])
*/
:-op(700,xfy, '<=').
:-op(700,xfy, '<+').
:-op(700,yf, '<+').
:-op(700,xfy, '=>').

:-public init_element/1,init_element/2,poke_element/2,peek_element/2.
:-public commit_element/1,commit_element/2.
:-public (<=)/2, (<+)/2, (<+)/1, (=>)/2.
init_element(Elem):-Elem='}{'(_,_).
init_element(Elem,Init):-
	Tail=[Init|_],
	Elem='}{'(Tail,Tail).

Elem<=Value :- poke_element(Elem,Value).
poke_element(Elem,Value):-
	arg(2,Elem,Body),
	findtail(Body,[_|Tail]),
	Tail = [Value|_].	% _ makes the new Tail

Elem=>Value :- peek_element(Elem,Value).
peek_element(Elem,Value):-
	arg(2,Elem,Body),
	nonvar(Body),
	findtail(Body,Tail),	
	arg(1,Tail,Value).

Elem<+ :-
	commit_element(Elem).
commit_element(Elem):-
	peek_element(Elem,Value),
	commit_element(Elem,Value).
Elem<+Value:-
	commit_element(Elem,Value).
commit_element(Elem,Value):-
	poke_element(Elem,Value).

findtail([X|Y],Tail):-
	nonvar(Y),!,
	findtail(Y,Tail).
findtail(Tail,Tail).	% We found the Tail value