:- module(attrmod, [domain/2]).

:- use_module(library(atts)).
:- use_module(library(clpz)).

:- attribute a/1.

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
?- attrmod:put_atts(X,a(test)).
   attrmod:put_atts(X,a(test)).

?- attrmod:put_atts(X, a(n(1))),
   attrmod:put_atts(Y, a(n(2))),
   X = Y.
   X = Y, attrmod:put_atts(Y,a(n(3))).

?- attrmod:put_atts(X, a(n(1))),
   X = a.
   caught: error(type_error(variable,a),get_atts/2)

?- attrmod:put_atts(X, a(n(1))), X = 1.
   X = 1.

?- attrmod:put_atts(X, a(n(1))), X = 3.
   false.

?- attrmod:put_atts(X, a(n(1))),
   attrmod:put_atts(Y, a(n(2))),
   X = Y,
   X = 3.
   X = 3, Y = 3.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

%verify_attributes(X, Y, _) :- throw(cannot_unify(X,Y)).
%verify_attributes(_, _, _) :- false.

% verify_attributes(Var, Value, []) :-
%         get_atts(Var, a(n(A))),
%         get_atts(Value, a(n(B))),    % step (1)
%         C #= A + B,                  % step (2)
%         put_atts(Value, a(n(C))).    % step (3)

% verify_attributes(Var, Value, []) :-
%         get_atts(Var, a(n(A))),
%         (   integer(Value) ->
%             Value =:= A
%         ;   get_atts(Value, a(n(B))),
%             C #= A + B,
%             put_atts(Var, -a(n(_))),
%             put_atts(Value, a(n(C)))
%         ).

:- use_module(library(ordsets)).
:- use_module(library(dif)).

:- attribute domain/1.

verify_attributes(Var, Other, []) :-
        (   get_atts(Var, domain(Dom1)) ->
            (   var(Other),
                get_atts(Other, domain(Dom2)) ->
                ord_intersection(Dom1, Dom2, Dom),
                dif(Dom, []),
                (   Dom = [Value] ->
                    Other = Value
                ;   put_atts(Other, domain(Dom))
                )
            ;   ord_memberchk(Other, Dom1)
            )
        ;   true
        ).

domain(X, List) :-
        list_to_ord_set(List, Dom),
        put_atts(X, domain(Dom)).