a21cefd6ca
git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@494 b08c6af1-5177-4d33-ba66-4b1c6b8b522a
110 lines
1.9 KiB
Plaintext
110 lines
1.9 KiB
Plaintext
=================================================================
|
|
Logtalk - Object oriented extension to Prolog
|
|
Release 2.12.0
|
|
|
|
Copyright (c) 1998-2002 Paulo Moura. All Rights Reserved.
|
|
=================================================================
|
|
|
|
|
|
|
|
% we can start by asking joe its age:
|
|
|
|
| ?- joePerson::age(Age).
|
|
|
|
Age = 30
|
|
yes
|
|
|
|
|
|
% the same question could be made via any of its viewpoints:
|
|
|
|
| ?- joeSportsman::age(Age).
|
|
|
|
Age = 30
|
|
yes
|
|
|
|
|
|
% now let's tell joe to grow old:
|
|
|
|
| ?- joePerson::growOld.
|
|
|
|
yes
|
|
|
|
|
|
% we can verify the effect of the above message from any of the viewpoints:
|
|
|
|
| ?- joeFilmEnthusiast::age(Age).
|
|
|
|
Age = 31
|
|
yes
|
|
|
|
|
|
% because the growOld/0 and the age/1 predicates are implemented using
|
|
% property sharing, we can send the growOld message to any viewpoint:
|
|
|
|
| ?- joeEmployee::growOld.
|
|
|
|
yes
|
|
|
|
|
|
% we can check this by asking joe its age:
|
|
|
|
|
|
| ?- joePerson::age(Age).
|
|
|
|
Age = 32
|
|
yes
|
|
|
|
|
|
% as you can see, although the modification message have been sent to a
|
|
% descendant, its the predicate age/1 in the parent that got updated
|
|
|
|
|
|
% to illustrate value sharing we use a couple of predicates, counter/1 and
|
|
% incCounter/0, defined in joePerson:
|
|
|
|
|
|
| ?- joePerson::counter(Counter).
|
|
|
|
Counter = 0
|
|
yes
|
|
|
|
|
|
% initially, counter/1 is only defined for joePerson, so every descendant
|
|
% or viewpoint will share its value/definition:
|
|
|
|
| ?- joeSportsman::counter(Counter).
|
|
|
|
Counter = 0
|
|
yes
|
|
|
|
|
|
% but if we decide to increment the counter by sending the incCounter/0
|
|
% message to a descendant:
|
|
|
|
| ?- joeFilmEnthusiast::incCounter.
|
|
|
|
yes
|
|
|
|
| ?- joeFilmEnthusiast::counter(Counter).
|
|
|
|
Counter = 1
|
|
yes
|
|
|
|
|
|
% then the descendant will now have a local definition for counter/1,
|
|
% independent of the definition in its parent, joePerson:
|
|
|
|
| ?- joePerson::counter(Counter).
|
|
|
|
Counter = 0
|
|
yes
|
|
|
|
|
|
% the other descendants/viewpoints will continue to share the definition
|
|
% in joePerson:
|
|
|
|
| ?- joeSportsman::counter(Counter).
|
|
|
|
Counter = 0
|
|
yes
|