WEBVTT

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Hello. This course is a bit unusual.

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I will present questions
to prepare exercises for next week.

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This session is the first session

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about the way we want you to think
about OOC.

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Do the exercises.
They're quite interesting.

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What are they? There are three of them.

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We'll ask you to implement not,
to implement or,

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and, most importantly,
to wonder why these exercises.

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Let's take a look at them.

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First, you have the Booleans
true and false.

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You have messages and objects.
How to implement not?

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It's quite easy.

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If you have false and send
the message not, it returns true.

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If you have true and send
the message not, it returns false.

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It's not so hard.
But how to implement this?

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The second question is about or.

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Or in Pharo is |. We took examples
from the Pharo implementation.

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Don't cheat. Do it without checking
how it's implemented.

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Once again, you have Booleans:
true and false.

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You have objects and messages.

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You have true | true returns true.

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true | false returns true.
true | anything returns true.

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It's the same with false.

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How to implement this?
That's the two questions.

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Take a piece of paper and try to answer.

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The third question:
"Why are you guys asking me this?"

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You must be thinking: "I'll never
implement Booleans in my life."

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You're right.

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Except if you have
to use three-valued logic:

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true, false, and unknown.

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How do you do this?

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You must wonder why we're wasting film
to ask you this question.

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It's the crucial question we ask
whenever we teach advanced programming.

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There must be a reason. We'll explain
next week what that reason is.

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Enjoy.