Linear algebra has this same kind of duality between data and function. A matrix is just a collection of data in most cases but when you multiply a matrix by some other matrix or a vector the matrix acts as a transform or a "function/code" on the data that passes through it. A change of basis is a transform matrix that acts as a function while at the same time could be further transformed by rotations and scaling matrices and act again as just data.

@Luredreier

5 жыл бұрын

Think of meta programming as inventing something new like multiplication or even pluss in math prior to those things being invented. Or any other new concept. For instance, there was a time when no one had invented zero. Math at the time had to be done with numbers with a value since there was no zero. In a programming language with metaprogramming you can invent such a new concept as zero, define it and use it instead of defining it every single time you need to use the concept.

@Evan490BC

4 жыл бұрын

Well, almost. A matrix is a *representation* of an operator relative to the given basis.

@pablo_brianese

3 жыл бұрын

Love this comment

@OverThinkKS

2 жыл бұрын

Please learn about geometry algebra

@ToveriJuri

Ай бұрын

@@OverThinkKS Linear algebra taught me to like math

Dude, please start a programmer's channel with a LOT more code. These videos are a tease.

@debjyotibiswas3793

6 жыл бұрын

Agreed. Show me some code.

@greenlight2k

6 жыл бұрын

If you want more code, check out "The Coding Train" channel ;-) Its... Javascript... but there you go...

@TheCandyDragon

6 жыл бұрын

aah, that channel is so fun

@debjyotibiswas3793

6 жыл бұрын

Yes Daniel Shiffman is very cool. But hate JS are there any other channels which are not JS.

@debjyotibiswas3793

6 жыл бұрын

Yes and JS is very easy to understand. The problem arises when JS is used interchangeably with node and starts doing weird things.

@2:52: *Reversed reverse Polish Notation* or as sane people would call it... polish notation ;-)

@SouravTechLabs

6 жыл бұрын

@science no it's at 2:50

@user-zz6fk8bc8u

6 жыл бұрын

@Sourav Goswami - Thanks. Fixed it.

@SteveHodge

6 жыл бұрын

Or as people who prefer descriptive rather than arbitrary names for things, "prefix notation".

@5:20 - I've been there, too. Writing the loop in assembly and forgetting to INC the counter. Those days the only cure was rebooting your pc.

"So could you give us an example?" "Oh sure, definitely. So lets say you wanted to draw an owl. First you just draw some circles. Right? Then you draw the rest of the owl, which I wont do here because its obvious."

@qwertyman1511

6 жыл бұрын

as i understand it: first, a function is a set of instructions. second, we can create data during runtime. third, we can interpret data as instructions. fourth, we can run interpreted data as a function. you created code at run time. the program wrote parts of itself.

@cj37373

6 жыл бұрын

Andrew McAuliffe you can base code on input from the user if you desire so

@ElagabalusRex

6 жыл бұрын

The way he described it, metaprogramming is the same as creating a library, which doesn't sound right.

@quadricode

6 жыл бұрын

ElagabalusRex you can create libraries of syntactic abstractions. That’s part of the point. :)

@quadricode

6 жыл бұрын

Kris2510 great, written out example!

This duality between data and code is much more common than most people think. One very simple example: most of us view a .c file as code. But to the compiler, it's data.

@Roxor128

6 жыл бұрын

Exactly. The very existence of compilers and interpreters relies on that duality.

@davidwuhrer6704

6 жыл бұрын

But can a C program evaluate, change, compile, and assemble it's own data at runtime?

I love listening to this guy talk, I don't know why

I don't know, all this meta & functional programming seem so powerful because you can allegedly write compact code. The problem I see is the same as with Perl: Can a third party actually decipher that code, or do we have to add 10 lines of comments for every line of code?

@LordShigi

6 жыл бұрын

Well, you don't really have to decipher it. At least not any average Joe has to. This technique lets you develop your own DSL (domain specific language) which will be really intuitive to its users. You can leave the writing of the actual interpreter to people that have the necessary skills to understand it.

@benjaminfacouchere2395

6 жыл бұрын

@Arkhitekton Idk. So if I let users extend my program by letting them write plugins in a DSL is this already seen as meta-programming? What's the boundary - compilation vs. interpretation? Or has it more to do with Harvard vs. von Neumann architecture? Can you give me a practical example?

@LordShigi

6 жыл бұрын

Ever used CSS or JavaScript? You had the opportunity to use a DSL there. When you write "nav > ul li.top:hover" you are abstracted away from all of the details of how the interpretation of that line works. It is interpreted for you by some interpreter in the browser, and yet you know exactly what that line does. This kind of support is quite hard to do in languages that do not support metaprogramming. It is not impossible in any way, but it does require you to spend more time on building up the scaffolding to make it work.

@malusmundus-9605

2 жыл бұрын

@@LordShigi yesss when I see ppl say "you can't do this in c/c++" I'm always like uhhhh yeah u can XD

I remember back in the early 1980s, when programmable calculators starting blurring the lines between computers and calculators, I read a quote (which I'm sorry I don't recall the author of) which said that the difference between calculators and computers is that the latter can operate on their own programs as if they were data and vice-versa, whereas the former cannot.

Really nice broad pass over metaprogramming 👍

Fun fact: ".. prefix notation is similar to postfix notation such as RPN." Beginning with the HP 48 calculator instead of using RPN the manual refers to RPL which is not defined. A search on the web gives the unofficial acronym of "Reverse Polish LISP" which it is. If i enter "{1 2 3 * +}" and press ENTER that program is placed on the stack. Pressing EVAL then evaluates the expression leaving "7" on the stack. Notice how the parens dissapear in RPN/RPL. There is no PROGRAM/RUN mode switch on this machine; everything is eval mode and is placed on the stack!

I want more from Robert Smith. This guy is good.

Am I correct to say that Lisp as he describes it is better off for math problems while C is better off for dealing with memory... cause that makes scenes why you would rather use Lisp over C for something like Quantum problems as stated in last video

@vyrsh0

4 ай бұрын

All abstract problems, while C is better for memory as you said

"reverse RPN" is not Reverse Reverse PN, it is just PN. Polish notation is like + 1 2 or add 1 and 2, RPN is 1 2 +. Polish notation was specifically prefix notation, which was considered more natural than 1+2 because you can write +1 * 2 3 to mean 1+(2*3), and indeed, this is a common notation used in compiler intermediate codes. However, RPN is considered even more natural than this because 2 3* 1+ exactly expresses operands and the operators that use them in proper order. Thus get 2, get 3, multiply, then get 1, and then add to the result of 2*3. It also is stack machine friendly. If there never were such a thing as polish notation, I'd agree that reverse RPN makes sense, but polish notation was a thing before RPN.

@Roxor128

6 жыл бұрын

Oh, dear. The comment-formatting system has gotten tripped up by your example and parsed the asterisks for multiplication as instructions to make the text bold.

@scottfranco1962

6 жыл бұрын

Thanks! Fixed it.

@Roxor128

6 жыл бұрын

I really wish they'd just use a subset of HTML or pseudo-HTML for the formatting. These errors would be so much less likely.

To me that for-loop example seems very similar to defining a function that takes other functions as its arguments, though perhaps with a nicer syntax. Would love some more in-depth examples.

@marios1861

5 жыл бұрын

the for loop takes a variable name, the starting value, the ending value, the increment and the body of code to be executed with each iteration. Can you make a function that you give as input a body of code? Can you bend the syntax of the language you use in any way you see fit?

@albertosimeoni7215

2 жыл бұрын

Is the standard C++ loop... The right example in C++ for metaprogramming are Virtual classes / methods

Duality: Tom Scott or John Green?

@jaymalby

6 жыл бұрын

RE now I can’t unsee it 😂

@AlterMacGyver

6 жыл бұрын

Trick question, Griffin McElroy

@taba1950

6 жыл бұрын

Arguably better than both

@mal2ksc

6 жыл бұрын

Tom Green.

@grivar

6 жыл бұрын

Or is is John Scott?

Would be interesting to see a clarification of how this topic compares to compilers in general -- because, of course, compilers are programs that write programs. I was waiting for the comparison and distinction to be made in this video, but it never happened.

Forth is another wonderful language that still stands the test of time. This vid mentions Postscript, which is very much a variant of Forth.

I'd love to see someone debug a metaprogram that contains thousands of lines of business logic :)

@albertosimeoni7215

2 жыл бұрын

During my job in a company i find a procedure that was modified costantly in 4 years ( a T-SQL store procedure) that has around 3000 rows with some part of code that write code that was executed... It takes about 1 week to under stand it...and about 1 time over 2 month it need to be modified...The source of this madness is called SAP

@Alsteraib985

5 ай бұрын

A lot better than the Java mess.

I'm getting all warm and fuzzy when I see the _LISP_ syntax. Brings back good memories from when I used it with AutoCAD.

4:23 That’s what a compiler for a high-level language does. The original name for this concept, from the 1950s, was “automatic programming”. At that time, the high-level language source was not considered the “program”: that name was reserved for the actual machine code that the computer could interpret.

I will remain indebted for sparking my interest in Lisp.

I did not really understand this, he seems to be skipping some important details in his explanation?

@maestbobo

3 жыл бұрын

I mean, it's obvious what he's saying. I don't understand what you're finding difficult about it.

I've yet to hear a convincing argument for LISP including this vid.

How different is that from ANY other interpreter? Or writing instructions directly to memory updating code on fly?

@TakanashiYuuji

6 жыл бұрын

It's not. Most languages have some kind of 'eval' feature.

@heller166

6 жыл бұрын

yeah i also don't understand what is so special about it.

@AMcAFaves

6 жыл бұрын

It is a more abstracted way to modify code. You are modifying the code at an Abstract Syntax Tree level. (And with abstraction can come more power.)

@cmckain13

6 жыл бұрын

TakanashiYuuji 0ⁿ

@nitowa

6 жыл бұрын

The special part is, that the program doesn't have to be recompiled by the programmer to introduce new features, formally this is called "at runtime". Simply speaking your program is conjuring itself while it's running, and doesn't come with all the necessary code (as defnined in the video) but instead it has the data necessary to create the code. A popular counterexample would be C, which requires you to compile it for the given architecture before executing it. C cannot add (for example) a function that was passed from the keyboard as C-code, despite being valid C code, and it cannot be executed at runtime. If you're looking for an "interpreted" language, you might find Java to be a suitable example (I know it's technically compiled, but it's also interpreted at the same time, so there's that). Although Java may modify the JVM runtime however it likes, changing the functionality of a method/function is prohibited, which severely limits its at-runtime capabilities (in practice it's possible but produces very patternized code and complex structures)

Could have introduced defmacro since that is often what is used at pre-compile time to turn the new syntax into something that the compiler will understand.

2:53 normally called Forward Polish Notation

More Robert! :D

Isn't RRPN just Polish Notation?

5:37 Assuming the increment of i lies at the bottom of that squiggle somewhere ... otherwise you’ve just written an endless loop.

I want to look at the video teased at the end, "fighting obsolescence", but can't find it anywhere. Anyone got a link?

How is the for loop example (and how it is an example of metaprogramming if a for loop didnt originally exist in the syntax) different from inline functions or #define

This is a rather confusing example of the usage of Metaprogramming

@quadricode

6 жыл бұрын

Unusual Activities you didn’t have for loops before, now you do. Is it confusing because everybody already has them? Maybe a better example would be: Imagine you wanted to specify logical constraints a la prolog. You can use metaprogramming to add such a facility to your program. But that means you’d have to explain what prolog is...

@webgpu

6 жыл бұрын

that's what you get when you assign that "confusing" guy to present this video..

@defense200x

6 жыл бұрын

I mean, I get it, actually I would to turn data into code for a project I'm currently working on but the language im working in (C++) won't let me :p

@zacharymetz9975

6 жыл бұрын

you could implement a scripting language then you could execute instruction that were created

Great video! I enjoyed the explanations and written examples. Thanks Mr. Robert Smith. 😊

Hmmm... can i think about this similar to Lambda-Expression in C# or Java? Which, like... IS program code at compile time and BECOMES data at runtime? Or, is that too far fetched? ^^

@jakejakeboom

6 жыл бұрын

A lambda expression is a functional concept so yes, that's somewhat similar.

@kwanarchive

6 жыл бұрын

The comparison breaks down when you try to pick apart the lambda-expression - which you can't do in C# or Java. You can create a lambda, but you can't pull it apart and pick bits and pieces out of it. With metaprogramming, you would be able to compose functions together, and then later on, pick them apart and, say, recompose the functions in a different way based on some conditions for optimization. C# and Java have no way to do this.

@shanehebert396

6 жыл бұрын

Currying using lambdas is an example of how to achieve some of what the video talks about.

@Luredreier

5 жыл бұрын

You can then get data that becomes code at runtime too...

Interesting to learn a bit about lisp

Where's the rest?

It's strange as a comparability theorist, I consider data and code to be the same thing. Though we explicitly use numbers for both.

i personally, since the moment I learned about variables that can store functions, see this distinction of "code vs. data" as wholly arbitrary. code is data describing how to transform data. it's all just data, the difference is in how you interpret it.

@malusmundus-9605

2 жыл бұрын

Every abstraction in programming has meaning in the correct context... otherwise we're just talking about 1's and 0's

*_...but tight code is used repeatedly-on scads of data; (Amer. scads, Brit. jillions)..._* *_...on the other hand, the similarity shows in loop parameters, i++, list descriptors,..._* *_...((in the control/addressing variables-but not, in the data itself/results per se))..._*

wouldnt reversed reverse polish notation just be polish notation?

@davidwuhrer6704

6 жыл бұрын

Yes.

It doesn't seem like Robert Smith understands what he is saying. There wasn't much of an explanation here.

Could you do a video on how to group logic gates to acomplish complex actions, such as multiplication, division, and converting binary to different two exponent bases

@davidwuhrer6704

6 жыл бұрын

I think they already did, using domino bricks.

@rafeu2288

2 жыл бұрын

I would recommend you check the video game "Turing Complete" on steam, it goes there and beyond, allowing you to learn how to implement a full 8-bit Harvard Style computer.

So... functional programming then?

@Luredreier

5 жыл бұрын

Not quite. It's a programming paradigm. You *can* do this with a functional programming language (well some of them). But this and functional programming isn't the same exact thing.

Von Neumann understood this perfectly well. The only ones who have forgotten tend to use languages like Java or C#. Oh, and PHP.

@GreyDeathVaccine

Жыл бұрын

Don't be a hater. Use the best tool to solve problem at hand.

@chpsilva

11 ай бұрын

​@@GreyDeathVaccine couldn't have said better

What a joy it must be to debug a Lisp program.

@rommelmartinez5599

6 жыл бұрын

You bet.

@ciscoserrano

5 ай бұрын

Just don't write any bugs. :p

How is that different from other languages and interpreters? I'm pretty sure you could do the same thing in C++ or Java or Haskell without any "duality". Also I thought computer scientists had largely abandoned meta programming.

Hmmm still not getting it, I hope there are more of these.

@CaptainJeoy

4 жыл бұрын

It's just a method of abstracting useful functions as an evaluable data

Are macros the same thing as Metaprogramming?

@charleslambert246

5 жыл бұрын

Haritha Wickremasinghe They are a form of meta-programming.

Is it possible to get similar meta programming capabilities in languages other than lisp? IE are there other programming languages that can do similar meta programming?

@rafeu2288

2 жыл бұрын

Rust lang is another language with a somewhat powerful macro system. But it seems Homoiconicity is one of the qualities that make meta-programming easier to implement.

@glowingone1774

Жыл бұрын

Nim, im not sure about "rust" but people have built whole DSL's with it in nim.

I want to see a non-contrived example

@jaymalby

6 жыл бұрын

The trouble with metaprogramming is that all it does is give the user the same power as a programming language designer. What that means is if your programming language doesn’t have something, you can add it. The problem for explaining metaprogramming is the non-contrived examples have all either been implemented in other languages by language designers (so they seem silly nowadays), are really trivial (but nice) conveniences, or take a lot more time than they had here (like adding a new programming paradigm as a library).

@quadricode

6 жыл бұрын

Elijah Malaby this is a really great explanation!

@webgpu

6 жыл бұрын

quadricode being hyper sarcastic :)

@badsyntax173

6 жыл бұрын

Meta programming is just another layer of abstraction. You have assembly code to make processors do what you want, you have languages to make assembly code do what you want. This is a language to make a language to do what people want. A really powerful tool especially in academia and research. Simple examples will make not convey the power of the concept and always feel contrived. Non simple examples are non contrived but hard to explain

@jeffreyjdesir

5 жыл бұрын

@@badsyntax173 The power in 'code as data' is thanks to macros. there's no real equivalent of a macro in languages like Java or Python. While Java's added a 'reflect' library that keeps a table of functions created in namespace, it still doesn't treat them equally 'first class citizens'. There's no way for example to define '+' (plus) as '-' (minus)...or multiply or any function you want really. There's no constraint or workaround in having predictable code adjusting itself.

"write a programm that writes programms", many of us do that already. for example a few days ago i wrote a simple python script to dynamically to my needs created LaTeX source code. also, automatically generating config files (config files may be considered as code sometimes) follows this scheme. more interesting: if the program and the generated program both are in the same language.

5:37 this is what you had to write to iterate ten times, yes but in assembly you could: times 10 instr instr (some instruction you want to do 10 times)

Not impressed at all with the last two videos on this. There's just no substantial concrete content, it's all "Lisp can do this" but doesn't show how

@timh.6872

6 жыл бұрын

Unfortunately, the concept of metaprogramming is just like recursion/induction when trying to explain it to someone that hasn't tried it: you can't. "To understand recursion you must first understand recursion" is actually true in my experience. That means no matter how I try to explain it to someone that's never written a recursive function (or inductive proof), they won't get it, until suddenly their mental process steps back, sees the loop, and 'gets it'. The same thing for metaprogramming. You can see in the video that the speaker is having difficulty expressing the idea of writing code that writes code, because there's a similar (if not identical) nugget of self-reference at the center of the idea. I think this channel is trying to cater to people that are not familiar with programming concepts, and that really ties the hands of the presenters, because they can't use the vocabulary necessary to express this idea, because it's all abstract nonsense until you have an actual problem to solve.

@quadricode

6 жыл бұрын

It’s very difficult to pack all of that in sub-10 minute videos with paper and pencil. Maybe Computerphile should use a computer in more videos? :)

I'm assuming that in Lispland eval isn't evil?

@surabax

6 жыл бұрын

You don't use eval directly in Lispland, you define macros instead.

I had a guy demo lisp for me yesterday for the first time, now it is everywhere.

Is this the latest "Programmers are also human" video?

so how can we do this in ruby? metaprogramming in ruby was a selling point but the only thing we hear today is rails. the language bent to the framework how can we do metaprogramming in ruby?

@DonVittorio

6 жыл бұрын

Quite easy actually, due to the fact that everything is an object, you can construct many different things (classes, methods for specific objects, ...) with ease. Ruby's syntax also allows to create quite clean DSL's!

@dandan7884

6 жыл бұрын

can you show me an example (external url)? im not a ruby dev so id like to see that working people use metaprogramming in rails too?

@DonVittorio

6 жыл бұрын

Well, rails is already a full blown framework, I'm not sure if you ever really need to do metaprogramming there. However, a simple example would be the attr_accessor function, which creates getters and setters for a field of a class. class Person attr_accessor :name end Is a functions which basically gets converted to class Person def name @name end def name=(value) @name = value end end This isn't exactly like the metaprogramming shown in the video, but you're still creating new "keywords" to make life easier. You can't do the same thing in Java for example (at least not when I used to write Java)

@f1r3w4rr10r

6 жыл бұрын

I think one of the best examples for metaprogramming are how ORMs (Object-Relational Mappers) create the Ruby classes for database tables. In Ruby you do not have to define methods to get and set the value for every single column. Most of the time, all you need to write down is your class name and point the ORM at the right table. The ORM will then for example use MySQL queries to get the column definitions of the table and define the methods for you, at run time. This defining of code on the fly and adding it to classes and objects is the metaprogramming. All this happens in memory. In contrast, Java for example would have the ORM literally write source code files for you, where it defines all those methods before compiling. You should then never touch those, because the next time you generate them, your changes are lost. With Ruby then, you have the advantage that you don't have to change anything in case of a change to a part of a table, that your code does not touch. Some keywords you can look up in ruby: "include", "extend" (both when called in a class definition and when called on an instance object), "send", "method_missing", "define_method" and of course the 'dreaded' "eval".

i feel bad for the computer scientists who worked on programs writing programs like this. because their way was the much more elegant, much more beautiful and pragmatic approach to programs that write programs. but instead we just went with this huge mess we call GPT-3 and language models. now nobody cares about this stuff even though it’s some of the coolest programming science out there.

Please try to get the interviewees to explain their subjects more concretely (i.e. with code samples)

hey phile can you explain exactly about symbolic data from the book structure and interpration of computer program

That "assembly" for the for-loop is not actually that correct. The evaluation of the repeat condition is actually made before you enter the loop in a standard for-loop. What he wrote down is more akin to a do-while loop, which runs trough the loop once unconditionally, and then repeats if the condition evaluates to true. Actually, it's a bit of a hybrid, because he set the iteration-variable at the top, and is still using an iteration variable.

nim-lang.org can do that and its procedural.

@AMcAFaves

6 жыл бұрын

capoiosct If that is the case, then nim wouldn't just be procedural, it would be multi-paradigm, because then you could just write macros to add OOP, functional or any other paradigm functionality to the language. :-)

To iterate is imperative and to recuse is functional?

Very well explained.

I'm not sure where he is going with this. So, you're not happy with the tools a language give you such as for loops. So, do you want to be able to make your code flow in whatever fashion you want? Use labels on C. Yes, it will be considered spaghetti code, because it is. Also a c source file IS data, although stored less efficiently. So is Java code, and so is Java bytecode and assembly. A smart enough program could write programs in any of these languages. The difference is that some are readable, and some aren't. Judge for yourself which are.

@Luredreier

5 жыл бұрын

It's not about not being happy about for loopes. It's about being able to *implement* for loops on the fly in a language where it doesn't exist already. Or any other feature for that matter. If you can come up with a new consept you can implement it and use user input as a part of the implementation if desired. You can change the code itself based on user input. And sure, you can write a program that can write code for its own code. However what about writing a program that can write the code used to run itself during the runtime? Regarding the spagetti code argument. Yes, partially. But it doesn't have to be.

I would just like to suggest to anyone that is interested in this, check out terra lang :) It's basically a scriptable compiler and deserves more love

He forgot to increment i in the pseudocode

@CrushaKRool

6 жыл бұрын

al Khwarismi And to have the initial check of the loop, which usually means an unconditional jump to its end, right after initializing i.

@quadricode

6 жыл бұрын

The pseudo code is definitely inaccurate!

At the end credit there's a snippet on the 'current state of quantum computing'. Where's that vid? I can't find it.

Please make a video about how code generation works. E.g. LLVM

I really like this guy

Haskell doesn't have for-loops though :P It uses recursion, it being functional and all.

KZread just showed me a 24-minute ad--that’s over *three times* longer than the video I wanted to watch. Never mind--I just let it play with the tab muted, while I did something else. That way you still get the ad revenue, right?

@Computerphile can we have a video about the Julia programming language?

is all of this related to code? like Metaprogramming and/or Software defined Networking? Where can i learn these things? Are they being taught in Computer Science?

>Is there a simple example of that?

@esobrev

7 ай бұрын

he literally gave an example

Isn't it true most programming languages have an eval function where you could pass data (string, var, number, etc) to be evaluated and executed?

@notnullnotvoid

6 жыл бұрын

Only some scripting languages have this, and compiled languages generally can't. Eval also usually operates on program text, rather than directly on a generated AST.

Love this man!

Actually, everything is data (even machine code is made of "data").

Hmm, since code is written exactly the same as data, I wonder if I could write a program that reads a different program and then tells me if that program would eventually stop?

reverse reverse polish notation = polish notation

What do you think about using Marvin Minsky frames as the base for metaprogramming language? I took his idea, only one element type: Frame object can hold scalar value, associative array (names slots points to other frames) and array holds pointers to other frames _in order_. In results, I can construct networks of directed interconnected objects, looks very very close to the attribute grammar structure. The key is some subset of data must have active nature: they must be executable, or more precise evaluatable in some execution context.

@dmitryponyatov2158

5 жыл бұрын

I played with this concept a lot, using some sort of FORTH script language to construct and manipulate such a structure type. Results look attractable. To represent say program-like structures I can inherit base Frame class to set of classes close to any generic script language -- functions, loops.

@dmitryponyatov2158

5 жыл бұрын

But what stops me going further this way: complexity rises too fast when I try to rewrite system in itself (metacircular implementation). Maybe I should not try to generate Python code too earlier, and I first should describe the system only at a very high level, I don't know.

Whats the difference between lisp and a langue where i can run the eval() from javascript?

A very powerful tool which I lost control over on day 2🤣🤣🤣now i kinda see where the elixir quote comes from...

data is to code what information is to knowledge

Aren't compilers in general an implementation of metaprogramming?

Code is just data to a lower-level processor. What is the lowest-level processor? Is it the laws of physics?

so its like the eval function in javascript and php which have been around for ages... and are generally considered as "dangerous", especially if you use it with user input.

@malusmundus-9605

2 жыл бұрын

Anytime you handle data from an unknown source it's dangerous... you have to predict what might come and handle it.

@m.h.6470

2 жыл бұрын

@@malusmundus-9605 and therein lies the hubris... unless you restrict the data, you can't possibly predict everything and handle it - especially with user input. A hacker can use these weak points to execute code without your knowledge and gain access to systems or data.

so... in other words..... HUH ?!?!? where is the example again !?? i must have missed it.

@qwertyman1511

6 жыл бұрын

as i understand it: first, a function is a set of instructions. second, we can create data during runtime. third, we can interpret data as instructions. fourth, we can run interpreted data as a function. you created code at run time. the program wrote parts of itself.

@jkoh93

6 жыл бұрын

QWERTY man but writing a program to write parts of itself is just adding another layer of complexity. how is it any better than just writing the end program yourself? we are not using assembly anymore

@qwertyman1511

6 жыл бұрын

Joel Koh an artificial intelligence might want to write an algorithm which solves a problem.

@jkoh93

6 жыл бұрын

QWERTY man that kind of makes sense but i dont think AI is at that stage yet. if an AI does write its own code, it would be its initial program telling it to write that code if it encounters that specific case, which is no different from writing that end code yourself. i dont think the AI is smart enough to write code that noone programmed it to write in the first place. its definitely not how neural networks work. maybe long in the future, AI will be smart enough to write completely new code, although by that time, completely new programming languages would have been invented to suit that need

@qwertyman1511

6 жыл бұрын

Joel Koh give it a year.

You can also directly obfuscate your code for exemple, turning it into base64 data and create "eval" function that decode and read it. So powerful !

code = evaluated data

Eval is a common misspelling of evil

Shout out Julia

I think it's meaningless to say that before high level languages For... did not exist. The only way that makes sense is to say that literally it didn't exist. Which is also meaningless really because conceptually it doesn't matter which language you use to implement the idea it is conceptually the same thing.

"For loops exist in every language"... ever used Haskell? No loops.

@GeorgeTsiros

6 жыл бұрын

Skylar he probably meant "the concept of iteration/repetition"

@quadricode

6 жыл бұрын

Tail recursion or a fold/reduction give more or less the same thing as a for-loop.

@itsacorporatething

5 жыл бұрын

Skylar, there is the forM function which is like a for loop for sequencing nomadic actions. Eg forM [1..10] $ \i -> print i

I remember programming in QBasic with subs and things like be for learning java and functions :p

How is this any different from C's #define?

@gracicot42

6 жыл бұрын

Final Spartan you cannot have instructions that write defines and you cannot then generate code that are using those defines. Macros are expanded before even compilation starts. Templates in C++ are a bit closer to what is shown in this video, since you can manipulate types and their structure as data and output new types. For example, I have a function that takes a lambda as parameter (a lambda is simultaneously a type and it's instance) and that function returns a new lambda with slightly different parameters.

@HrHaakon

6 жыл бұрын

#DEFINE gives you text substitutions. defmacro let you tell the compiler what you want done with something. You can tell it how JSON works and from then onwards, you can give your compiler JSON and it will give you an object back out.

@marceloconceicao2587

6 жыл бұрын

#define is VERY limited on what it can do. You cannot, for instance, change/create a #define based on user input because #defines are preprocessors (They are evaluated at compile time (even before that, actually)) And even regular programming is very hard to do with defines. Try to pass a macro as a parameter to another macro . Spoliers: You can't. The preprocessor definitions are evaluated only once

@MidnightSt

6 жыл бұрын

how is this different from #define ? ...completely. define is basically a shortcut/automation of string search and replace. what he's talking about in the video is basically programmaticaly building expression trees (code as data), which you can then execute by traversing them.

@PetrSojnek

6 жыл бұрын

The better example would be function like printf. You fill in parameters that will tell you what you do with other parameters. Essentially the "format string" is data that defines procedure to be applied on the rest of data.

Can't you also create assembler code in a C program and then execute it? Isn't that the same?

@kwanarchive

6 жыл бұрын

You can't take the generated code and make it into data again within the language. You'd have to disassemble the generated code, recreate the C from it (which is hard due to optimizations) and somehow make it recompilable. The other way is for your C program to create a miniature VM to interpret byte code your program creates, but that, again, takes you out of the language.

So Macros are also a type of MetaProgramming?? right!

this is somewhat similar to templates in c++ no?

@jaymalby

6 жыл бұрын

guild man similar- C++ templates generate code for you, but in very rigid and structured ways and you write the templates in a special templating language instead of using C++ code to manipulate other C++ code directly as a data-structure.