5345523da3
git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@561 b08c6af1-5177-4d33-ba66-4b1c6b8b522a
110 lines
1.9 KiB
Plaintext
110 lines
1.9 KiB
Plaintext
=================================================================
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Logtalk - Object oriented extension to Prolog
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Release 2.14.1
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Copyright (c) 1998-2002 Paulo Moura. All Rights Reserved.
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=================================================================
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% we can start by asking joe its age:
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| ?- joePerson::age(Age).
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Age = 30
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yes
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% the same question could be made via any of its viewpoints:
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| ?- joeSportsman::age(Age).
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Age = 30
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yes
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% now let's tell joe to grow old:
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| ?- joePerson::growOld.
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yes
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% we can verify the effect of the above message from any of the viewpoints:
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| ?- joeFilmEnthusiast::age(Age).
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Age = 31
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yes
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% because the growOld/0 and the age/1 predicates are implemented using
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% property sharing, we can send the growOld message to any viewpoint:
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| ?- joeEmployee::growOld.
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yes
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% we can check this by asking joe its age:
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| ?- joePerson::age(Age).
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Age = 32
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yes
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% as you can see, although the modification message have been sent to a
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% descendant, its the predicate age/1 in the parent that got updated
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% to illustrate value sharing we use a couple of predicates, counter/1 and
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% incCounter/0, defined in joePerson:
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| ?- joePerson::counter(Counter).
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Counter = 0
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yes
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% initially, counter/1 is only defined for joePerson, so every descendant
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% or viewpoint will share its value/definition:
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| ?- joeSportsman::counter(Counter).
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Counter = 0
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yes
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% but if we decide to increment the counter by sending the incCounter/0
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% message to a descendant:
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| ?- joeFilmEnthusiast::incCounter.
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yes
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| ?- joeFilmEnthusiast::counter(Counter).
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Counter = 1
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yes
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% then the descendant will now have a local definition for counter/1,
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% independent of the definition in its parent, joePerson:
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| ?- joePerson::counter(Counter).
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Counter = 0
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yes
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% the other descendants/viewpoints will continue to share the definition
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% in joePerson:
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| ?- joeSportsman::counter(Counter).
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Counter = 0
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yes
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