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yap-6.3/Logtalk/examples/viewpoints/viewpoints.lgt

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% general information about Joe:
:- object(joePerson).
:- public(getOlder/0).
:- public(address/1).
:- public(age/1).
:- dynamic(age/1).
:- public(name/1).
:- public(phone/1).
:- public(score/1).
:- dynamic(score/1).
:- public(setScore/1).
getOlder :- % this predicate uses property sharing, i.e.
retract(age(Old)), % the property and its value are shared by all
New is Old + 1, % descendant prototypes/viewpoints; changes
asserta(age(New)). % are shared no matter which viewpoint receives
% the getOlder/1 message
address('8 Octave Street').
age(30).
name('John').
phone(11-11-11-11).
score(0). % default value for the score/1 property,
% shared by all descendant prototypes/viewpoints;
setScore(Score) :- % changing the default value results in
::retractall(score(_)), % in a local value stored in the descendant
::asserta(score(Score)). % prototype that received the setScore/1 message
:- end_object.
% information on Joe as an employee:
:- object(joeEmployee,
extends(joePerson)).
:- public(worksFor/1).
:- public(salary/1).
:- dynamic(salary/1).
:- public(giveRaise/1).
worksFor('ToonTown').
salary(1500).
giveRaise(Raise) :- % another example of property sharing
retract(salary(Old)),
New is Old + Raise,
asserta(salary(New)).
:- end_object.
% information on Joe as an chess player:
:- object(joeChessPlayer,
extends(joePerson)).
:- public(category/1).
category('National Master').
:- end_object.
% information on Joe as a movies fan:
:- object(joeFilmEnthusiast,
extends(joePerson)).
:- public(favActor/1).
:- public(favFilm/1).
:- public(favDirector/1).
favActor('Fred Filistone').
favFilm('The Wizard of Oz').
favDirector('Krzystof Kieslowski').
:- end_object.
% information on Joe as a sportsman:
:- object(joeSportsman,
extends(joePerson)).
:- public(sport/1).
:- public(stamina/1).
:- public(weight/1).
sport(snowboard).
stamina(30).
weight(111).
:- end_object.