Why Study General PL Concepts?

[MUSIC] So now let's give some indication of why it's valuable to study general

programming language concepts outside the context of any particular detail or

programming language. This is the most abstract question in

terms of motivation so it will have the most abstract, probably least precise

answer. And I'd like to start basically with an

analogy. So, I get asked a lot of times what's my

favorite programming language. And my favorite answer is, well what's

your favorite kind of car? Or, what's your favorite pair of shoes? So go ahead

and take a second and imagine in your head the best kind of car.

What do you think the best car ever made anywhere in the world is? And, and think,

you know, that's the best car, it's better than all the other cars.

And whatever you think of is actually probably a really good car, and it's

probably better than a lot of other cars, but it can possibly be the best car for

all purposes. Right? You know, cars are used for a lot

of different things. I seriously doubt that whatever car you

picked is good at winning a race, you know, one of these things where people

drive around at 300 kilometers an hour, and good for taking a group of children

to go play soccer or football. Right? Cars just can't do both of those

really, really well and yet any car can participate in a race, and can take

people to where they need to go. So it's not that you can't do it with

these other cars, it's just that they focused on certain aspects of the design

at the expense of other aspects of the design.

Right? there's a bunch of other things you might do with a car.

You might want to go off of the highway onto dirt and rocky roads.

You might want to haul big items around like a mattress.

You might want to just have fun and roll down the top of a convertible car.

It might be raining, in which case that's a bad idea.

A lot of these things are in conflict with each other, even though the basic

idea of what a car can do and how a car can participate in these activities is

fairly universal. And of course it's the same with shoes.

A lot of people imagine i'ts their favorite shoes.

Something that they would wear with a very fancy dress or a suit or something

like this. Other people like to play sports.

I probably could play basketball with my fanciest pair of shoes on but it would be

painful. It would not be pleasant.

And I hope the analogy is clear here that programming languages in some sense are a

kind of shoe or a kind of car. And once you learn how to drive in

general it's not that hard to switch cars.

It get easier after you've done it a few times, but you still want to pick the

best thing for what you're trying to accomplish that day.

Let me push this analogy a little bit further one more slide on cars and then

we'll move on I promise. It's perfectly reasonable for a mechanic,

someone who fixes cars, to have a specialty.

They work on cars from a certain company or they are a certain age or what not,

and programmers can be better at certain languages.

But I think mechanics do have a general understanding of how cars work.

And they can participate and help even with cars that aren't right in their core

specialty. They also have a very good idea of what's

important and what's not. I've never gone to a mechanic and said my

engine, is making a funny noise, can you help me? And have the engine say, have

the mechanic say, well, your seats are blue and I only really

like cars where the seats are brown, right? And the analogy there is that sort

of unessential detail is syntax. Now syntax does matter to people.

people when they purchase cars really like certain colors, really like certain

mirrors, and things like this, but it's not essential to how the car actually

runs, and accomplishes its goals. Okay? So that's kind of from the

mechanic's perspective. What about someone actually designing

cars, whether it's a mechanical engineer, or someone else? Someone really trying to

make changes or understand what it is to be a car,

to be an automobile, really has to know how to get the most out of the different

design constraints. That if you try to make something better

over here it might be harder to make this other feature as good over there that

certain things are in conflict. And that's why I simply don't have a

favorite programming language, and I don't have a favorite kind of car either.

I find the question a little bit silly, it really does depend on what I'm trying

to do. Now, if you're trying to learn more about

cars, how they run, how to fix them, how to design better ones, one approach would

be to take a number of really good, really fancy, really expensive cars, and

study why they're so good and what they do and why people spend so much money to

buy them. But I would argue that that's often

counterproductive that those cars are very complicated and they're the result

of over 100 years of engineering and improvement and sometimes the best way to

learn is to go back to a simpler model. An older model.

Something like say the ML language, which is I would say over 25 years old.

Because it's simpler it doesn't deal with every modern feature and advance and

computer controlled gizmo. And it's much easier to understand an

older car. You can actually open the hood and see

the pieces. And then after you've learned those

basics, the modern state of the art, the more current things actually can be

easier to understand, and in some ways you can understand is actually less

elegant in some ways because things have become more complicated over time, due to

historical Improvements okay? Finally we also know that sometimes cars are very

popular even if they're not the best cars.

you know popularity is a very hard thing to understand why it happens or how it

happens. That doesn't mean that popular things are

bad, but we also know that popular things are not necessarily good.

You know popularity in and of itself is not evidence of being the the best.

So, in this course, we don't just study programming languages, we focus on two

key parts of them: the semantics, what do programming language concerts mean and

the idioms, what are ways to use those language constructs to perform common

tasks in elegant ways. The reason I focus on this,

it's really first of all the semantics. That, if you want to reason correctly

about what your program does, is the implementation of the language correct?

You wrote a library, someone's complaining that it's not working

properly. Are you wrong or are they wrong? You have

to understand language semantics. There's simply no room in software

development for well, I don't feel that's the way conditional expressions actually

work, or that's the way they should work. No, there's a way conditional expressions

work in a programming language, and either you're using them correctly or

they're not. This is not a matter of do you like curly

braces or parenthesis, or using the word and also versus the and character two

times in a row. This is really about what the concepts

mean. And so much of software development is

designing a precise interface and then using it.

And programming languages are probably the best example of this where the

definition has to be so precise that people all over the world can use the

language and agree on what's supposed to to happen.

So that's semantics. In terms of idioms, I just think they

make you a better programmer. That if you see something in multiple

settings, including languages where it's very convenient, then you can use it

anywhere. Then once you've seen data type bindings

and case expressions, it teaches you to think in terms of one-of types and all

the different possibilities, and even if your language does not provide direct

support for writing down your algorithm that way, it's still a great way to

think, and you find your code suddenly being much more nicely laid out and in

terms of exactly the cases you need to cover.

And that's why I often like to say that a lot of students taking this class have

seen Java in the past. We do almost no Java in this course and

yet I truly believe this course will make you a better Java programmer.

Okay, last one. as long as I'm really talking about the

beauty and generality of programming languages and why it's, useful to learn,

let me tell you about the play Hamlet by William Shakespeare.

The play Hamlet, if you've never seen it or watched it, I highly encourage it.

It is a beautiful work of art. It teaches deep eternal truths about the

human condition. It teaches about family relationships and

revenge and jealousy and murder and letting our emotions get the best of us.

It's also, even in modern day, the source of a number of expressions and sayings

that we actually use to understand life. if you've ever heard someone say, the

most important thing in life is to be true to yourself, in Hamlet, the line is

actually, This" above all, to thine own self be true" if I recall correctly.

And we study this stuff because it makes us a better person.

okay. Programming language concepts are like

that. There really are deep eternal truths

going on here. The fact that the booleans and

conditional expressions are nothing more than syntatic sugar for a data type

binding with two constructors called true and false.

Is a deep truth about logic and how things fit together and how we can

express there being two possibilities, yes and no, true and false.

And it's worth studying those things in sort of the purest settings that we can

and to see them in multiple settings. The same way the lessons of Hamlet Come

up in movies and plays and, and novels over and over and over again.

And we should learn these things even if the syntax is really annoying.

I don't particularly like reading Shakespeare because it's very hard to

understand and English is my first language.

But if I can get past the syntax and understand the deep truths that are going

on it makes me a better person. And I don't have to worry so much about

will learning this thing. This thing that will increase my

understanding. either the human condition for

Shakespeare or software for programming languages.

I don't need three weeks later to be able to apply for a new job.

That will come. I'll be able to pick up the skills later,

but in the meantime I can get the right foundation, the right perspective, of how

to look at the entire field.

Programming Languages, Part A

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