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Logtalk - Object oriented extension to Prolog
Release 2.15.6

Copyright (c) 1998-2004 Paulo Moura.  All Rights Reserved.
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To load all objects in this example consult the viewpoints.loader utility
file (note that the *.loader files are Prolog files).

Example adopted from the paper "Classifying Prototype-Based Programming
Languages" by Christophe Dony, Jacques Malenfant and Daniel Bardou.

This prototype programming example ilustrates how we can do both property 
sharing and value sharing in Logtalk by calling the built-in predicate 
modification methods asserta/1, assertz/1 and retract/1 either in the 
context of "this" or in the context of "self".

In this example we have a prototype named joePerson, containing general 
data on joe like its age, name or address, and three descendants/viewpoints 
named joeSportsman, joeEmployee, joeChessPlayer, and joeFilmEnthusiast. Each 
descendant contains data related to a particular viewpoint about joe.