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The Keyword Super

To be able to send or delegate messages to the super-objects in a convenient way while following the inheritance protocol, the keyword super is provided. The calls:

        super :: method, or
        super <: method

mean: send or delegate (respectively) method to the super-objects according to the inheritance protocol. A simple example illustrates this concept: assume that john in the above example has three id-cards, one stored in his sportsman prototype identifying the club he is member of, one stored in his professor prototype identifying the university he works in, and finally one stored locally identifying his social-security number. Given the following methods in the object john:

m1(X) :-
        super <: id_card(X) &
m2(X) :-
        super(S), S <: id_card(X) &

one may ask the following:

| ?- john :: m1(X).
     % will follow the default inheritance and returns:
X = johns_club ;

| ?- john :: m2(X).
     % will backtrack through the possible supers returning:
X = johns_club ;
X = johns_university ;