Name: 講義7A：メタサークル評価者、その1 (Lecture 7A: Metacircular Evaluator, Part 1)
Uploaded: 2021-01-14T10:26:54.000Z
Duration: 1 h 24 min 38 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

PROFESSOR: Well today we're going to learn about something

We're going to understand what we mean by a program a little

bit more profoundly than we have up till now.

Up till now, we've been thinking of programs as

So for example, looking at this still store, we see here

And what it is, is a character string description, if you

That this is a sort of compact notation which says, if n is

Well here comes n coming into this machine, and if it's 0,

then I control this switch in such a way that the switch

Otherwise, it's n times factorial of n minus one.

Well, I'm computing factorial of n minus one and multiplying

that by n, and, in the case that it's not 0, this switch

Of course, this is a machine with a potentially infinite

number of parts, because factorial occurs within

factorial, so we don't know how deep it has to be.

But that's basically what our notation for programs really

It's a character string description, if you will, of a

wiring diagram that could also be drawn some other way.

And, in fact, many people have proposed to me, programming

I'm not sure I believe there are many advantages.

The major disadvantage, of course, is that it takes up

more space on a page, and, therefore, it's harder to pack

But in any case, there's something very remarkable that

can happen in the competition world which is that you can

have something called a universal machine.

If we look at the second slide, what we see is a

There is a machine called eval, and I'm going to show it

What is remarkable is that it will fit on the blackboard.

However, eval is a machine which takes as input a

Having done so, it becomes a simulator for the factorial

machine such that, if you put a six in, out comes a 720.

That's a very remarkable sort of machine.

And the most amazing part of it is that it fits on a

By contrast, one could imagine in the analog electronics

world a very different machine, a machine which also

was, in some sense, universal, where you gave a circuit

diagram as one of the inputs, for example, of this little

low-pass filter, one-pole low-pass filter.

the scan lines are the signal that's describing what this

then the analog of that which is made out of electrical

circuits, should configure itself into a filter that has

That's a very hard machine to make, and, surely, there's no

chance that I could put it on a blackboard.

So we're going to see an amazing thing today.

And we'll see that among other things, it's extremely simple.

Now, we're getting very close to the real spirit in the

So I have to show a certain amount of reverence and

respect, so I'm going to wear a suit jacket for the only

time that you'll ever see me wear a suit jacket here.

And I think I'm also going to put on an appropriate hat for

Now, this is a lecturer which I have to warn you--

let's see, normally, people under 40 and who don't have

several children are advised to be careful.

If they're really worried, they should leave. Because

there's a certain amount of mysticism that will appear

Well in any case, let's see, I wish to write for you the

Now the evaluator isn't very complicated.

It's very much like all the programs we've seen already.

It's going to be-- and I'm going to write it right here--

And it's a procedure of two arguments in expression of an

But before I start on this, I want to tell you some things.

The program we're going to write on the blackboard is

ugly, dirty, disgusting, not the way I would write this is

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講義7A：メタサークル評価者、その1 (Lecture 7A: Metacircular Evaluator, Part 1)

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