1
00:00:00,160 --> 00:00:02,960
Hello. This course is a bit unusual.

2
00:00:03,120 --> 00:00:06,680
I will present questions
to prepare exercises for next week.

3
00:00:06,840 --> 00:00:09,840
This session is the first session

4
00:00:10,000 --> 00:00:13,000
about the way we want you to think
about OOC.

5
00:00:13,160 --> 00:00:15,960
Do the exercises.
They're quite interesting.

6
00:00:16,120 --> 00:00:18,400
What are they? There are three of them.

7
00:00:19,120 --> 00:00:22,440
We'll ask you to implement not,
to implement or,

8
00:00:22,600 --> 00:00:26,480
and, most importantly,
to wonder why these exercises.

9
00:00:26,640 --> 00:00:28,480
Let's take a look at them.

10
00:00:28,640 --> 00:00:31,960
First, you have the Booleans
true and false.

11
00:00:32,120 --> 00:00:35,080
You have messages and objects.
How to implement not?

12
00:00:35,240 --> 00:00:36,680
It's quite easy.

13
00:00:36,840 --> 00:00:41,720
If you have false and send
the message not, it returns true.

14
00:00:41,880 --> 00:00:46,400
If you have true and send
the message not, it returns false.

15
00:00:46,560 --> 00:00:49,840
It's not so hard.
But how to implement this?

16
00:00:50,720 --> 00:00:52,960
The second question is about or.

17
00:00:53,120 --> 00:00:57,240
Or in Pharo is |. We took examples
from the Pharo implementation.

18
00:00:57,400 --> 00:01:00,840
Don't cheat. Do it without checking
how it's implemented.

19
00:01:01,000 --> 00:01:03,920
Once again, you have Booleans:
true and false.

20
00:01:04,080 --> 00:01:05,880
You have objects and messages.

21
00:01:06,040 --> 00:01:09,160
You have true | true returns true.

22
00:01:09,320 --> 00:01:12,480
true | false returns true.
true | anything returns true.

23
00:01:12,640 --> 00:01:14,920
It's the same with false.

24
00:01:15,080 --> 00:01:18,280
How to implement this?
That's the two questions.

25
00:01:18,440 --> 00:01:22,720
Take a piece of paper and try to answer.

26
00:01:23,840 --> 00:01:27,560
The third question:
"Why are you guys asking me this?"

27
00:01:27,720 --> 00:01:31,600
You must be thinking: "I'll never
implement Booleans in my life."

28
00:01:31,760 --> 00:01:33,760
You're right.

29
00:01:33,920 --> 00:01:36,640
Except if you have
to use three-valued logic:

30
00:01:36,800 --> 00:01:39,680
true, false, and unknown.

31
00:01:39,840 --> 00:01:41,200
How do you do this?

32
00:01:41,360 --> 00:01:46,160
You must wonder why we're wasting film
to ask you this question.

33
00:01:46,320 --> 00:01:50,520
It's the crucial question we ask
whenever we teach advanced programming.

34
00:01:50,680 --> 00:01:55,360
There must be a reason. We'll explain
next week what that reason is.

35
00:01:55,520 --> 00:01:56,720
Enjoy.