Name: Lecture 1B: Procedures and Processes; Substitution Model
Uploaded: 2020-03-29T16:07:31.000Z
Duration: 58 min 22 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

To-infinitive

You've seen that the job of a programmer is to design

processes that accomplish particular goals, such as

finding the square roots of numbers or other sorts of

Of course, the way in which a programmer does this is by

constructing spells, which are constructed out of procedures

And that these spells are somehow direct a process to

accomplish the goal that was intended by the programmer.

In order for the programmer to do this effectively, he has to

understand the relationship between the particular things

that he writes, these particular spells, and the

behavior of the process that he's attempting to control.

So what we're doing this lecture is attempt to

establish that connection in as clear a way as possible.

What we will particularly do is understand how particular

patterns of procedures and expressions cause particular

I'm going to start with a very simple program.

This is a program to compute the sum of the

And we'll define the sum of the squares of x and y to be

and the square of y where the square of x is the

Now, supposing I were to say something to this, like, to

the system after having defined these things, of the

form, the sum of the squares of three and four, I am hoping

Because the square of three is nine, and the square of four

If we're going to understand processes and how we control

them, then we have to have a mapping from the mechanisms of

this procedure into the way in which these processes behave.

What we're going to have is a formal, or semi-formal,

mechanical model whereby you understand how a machine

Whether or not the actual machine really does what I'm

In fact, this is an engineering model in the same

way that, electrical resistor, we write down a model v equals

If I put up current through the resistor it goes boom.

So the voltage is not always proportional to the current,

but for some purposes the model is appropriate.

In particular, the model we're going to describe right now,

which I call the substitution model, is the simplest model

that we have for understanding how procedures work and how

And that substitution model will be accurate for most of

the things we'll be dealing with in the next few days.

But eventually, it will become impossible to sustain the

illusion that that's the way the machine works, and we'll

go to other more specific and particular models that will

OK, well, the first thing, of course, is we say, what are

And these cryptic symbols are made out of pieces.

And we have-- and so far I see things like numbers.

We have seen things before like lambda expressions, but

Lambda expressions, we'll worry about them later.

There are particular rules for each of these.

I'm going to tell you, however, the rules for doing a

Because, in fact, over here, all I really have are

combinations and some symbols and numbers.

And the simple things like a number, well, it

They won't be there at the time when you need them, when

So the only thing I really have to explain to you is, how

Subtitles ListPlay Video

Lecture 1B: Procedures and Processes; Substitution Model

sort

eventually

process

alternative