root/trunk/examples/complements/complements.lgt

% setup the object employee as a monitor for any message sent to itself:
:- initialization(define_events(before, employee, _, _, employee)).


:- object(employee).

    :- public([name/1, age/1, salary/1]).

    name(john).
    age(42).
    salary(23500).

:- end_object.


:- category(logging,
    implements(monitoring),     % built-in protocol for event handler methods
    complements(employee)).     % add the category predicates to the employee object

    % define a "before" event handler for the complemented object:
    before(This, Message, Sender) :-
        this(This),
        write('Received message '), writeq(Message), write(' from '), writeq(Sender), nl.

    % add a new method to the complemented object:
    :- public(predicates/1).

    predicates(Predicates) :-
        setof(Predicate, ::current_predicate(Predicate), Predicates). 

    % define an alias for a predicate of the complemented object:
    :- alias(employee, salary/1, income/1).

:- end_category.