Functional Programming & Haskell - Computerphile 

One of the things that the Haskell language should really get kudos for is its community. I've learned many different languages, and participated in many different communities around them, but the Haskell community is on a whole other level. I often felt bad about how far the people in the Haskell community would go to make sure I understood things. I would ask a question and I would always find someone willing to work with me for HOURS if necessary, writing all kinds of example code to show me things, walking me through difficult concepts, etc. Many languages have helpful communities, but the Haskell community is simply the best I've ever seen. Top notch folks all.

6:35 John Hughes goes full code ninja mode. God help any computer that tries to modify his data.

My dad is an expert dragon slayer. "eeer but I don't see any dragons around... " You're welcome.

6:34 sudden rage-mode

Holy... that was very well explained. If you can get John back on camera that would be appreciated.

How wonderful to see my first, and very best, programming professor again! I took functional programming courses for prof Hughes in 2004. Very great memories from that time :-)

After three years' CS studies at Chalmers, I always name Functional Programming (the very first course we took, and in which John played a major role) as the most valuable course - the one I would pick if I could choose only one single course to have taken. Not only are functional languages absolutely fantastic to work with; one can also use many of the important concepts of FP in imperative languages like Java to write monumentally superior code.

Wow he must be an excellent teacher. You can tell he has a firm grasp on functional programming concepts because he can explain things in layman terms.

I wish they had some concrete examples. A lot of these summaries of programming paradigms fail to show what problem solving looks like and how it differs from other paradigms.

So proud! He was my teacher ^^

He was my professor in parallel functional programming, he's fantastic! Koen Claessen who also teaches Haskell at Chalmers is also incredible and was the reason why I got interested in functional programming.

I'm a javascript developer and I started programing funtionally and it makes so much sense I've never looked back

I was a core Object Oriented programmer but over the past few months have shifted to using Clojure which is another Functional Language very similar to Haskell and OMG does Functional Programming make so much more sense than OOP! Pure Functions means less bugs and the syntax of the language helps you write beautiful code that one can read so much more naturally. People who are getting into programming, give it a shot, you'll like it much more than OOP

I had subtitles on, so naturally I was suprised when it mentioned the airline programming language.

This really made my day! I like Computerphile, I like Haskell and functional programming and I like John Hughes! He was such a great lecturer to have on my first course on university, and he left a good enough impression that three years after the course it still makes me excited to see him in a video!

I find this dude's enthousiasm very communicative. I would love to attend one of his classes. His students are lucky.

I'd like to see a video on dependent types, and type systems in general, in the future. Types are extremely important to properly using languages like Haskell, and they have a rich history of interactions with the foundations of mathematics.

Having no side effects, now this is genius! I was so impressed with functional programming that I spent last 5 years of my life coming up with an algorithm that can tell if a function is going to halt or not in O(1) time even. I'd would like to share the code with you all but unfortunately that would be a side-effect so I can't.

Few clarifications: Functional programming in at of itself doesn't mean you don't have side-effects. Functions that doesn't mutate and always provides the same output with the same input are called pure functions, which are part of the functional programming paradigm. Side effects are inevitable if you work with I/O such as networking, threads/multiple processes. You can still use functional programming languages (like Haskell) to write functions that handles side-effect, but it's usually done by separating them out from other business logic. Scala is also not _really_ a functional programming language by itself. It is mix between functonal and object-oriented, similar to JavaScript.

YES. More of this! Love where this channel is going.

I was taught Miranda in my first year of university, 1989. Twenty years later into my career spent mostly with C and Java and I was surprised to find it making comeback! (in the form of Haskell, Scala, etc).

He wrote QuickCheck? I used it during a Functional Programming course in uni. Very useful to make sure you got a function right fast.

I have read some of Hughes' papers and listened to him on RU-vid and just wow... He is just so elaborate without confusing people.

Watching this in 2024, it's amazing to hear there was a time when there was no spam on facebook.

John Hughes is an incredibly nice man. Had the fortune to have met him twice so far.

I love the amount of passion this guy has about what he does. Very interesting stuff. Had no idea Haskell is used in so many ways. Good interview, and love the samurai remake =)

I was lucky enough to take multiple Haskell courses with Dr. Jon Peterson, a contributor to much of the Haskell98 documentation during his tenure @ Stanford, as well as a co-author of the Arrow ( -> ) Prelude extension class. He sadly passed near the end of my graduating semester - It was a privilege to learn from him.

I think one of the nicest parts about functional programming is the focus on composability. You can have functions that take functions and returns functions, which you can then run (btw, you can also do that in many mixed paradigm languages that are not pure functional).

So glad you put this out, I was just starting to teach myself Haskell

The most important thing is to pick the language and paradigm that works best for you and the project. It is nice to be able to use functional styles when the language and problem fits it. I tend to fluctuate between Functional and Imperative styles in the same project often. Sometimes that implicitly bound functional environment is nice to have other times a state modifying loop is handy. I tend to try and stay with what the language designers expect though. A lot of functional style recursion will blow the stack if implemented carelessly in many imperative languages. I tend to write in Common Lisp which allows for both but I can respect people who prefer one paradigm if it feels more "pure" to them.

Really like the way he explains the concepts at hand. Perhaps it is just suited to my learning style, but I understood everything he said and its implications, and I'm by no means an expert.

This was awesome! Very nicely explained. Computerphile needs to do a video on Lisp next- something on the history, or more modern dialects like Clojure. That would be really cool!

Functional is the future. I truly believe it. Haskell is my favourite functional language. Used Haskell at IMVU for many things.

Just did a module in a Java course that was about the functional programming implementation in Java. This is adds a neat perspective.

I love haskell! : D Thanks for covering it.

Yes! Thank you Computerphile, great great intro to some huge ideas!

Can we get more videos about Functional Programming / Lambda Calculus and how to solve simple problems with this way of programming?

very cool! had a module on Haskell last year which I really enjoyed; the teacher was super enthusiastic about it haha

Really enjoyable video, for a while I've been wondering what makes functional programming different. What I do find strange though, coming from a language which separates functions (return a value) and subroutines (no value return) is that it seems obvious to me that a function wouldn't do anything else than return a value - you could implement that paradigm just with a change of programming style

'I didn't think there was spam on facebook!' What...?

Would there be any possibility of actually covering the process of creating a language definition and writing a compiler and/or interpreter for it?

You should do a video on lambda calculus!

Fantastically explained, thank you very much sir!

I love using Haskell, thanks for the video!

Hughes! This brings back memories from my first fp course at Chalmers way back. :D

6:35 Those Karate lessons really are starting to pay off

I've never looked into functional programming that much. It's so very different from other types of programming that it pretty much requires going back to square one.

It should have been longer, very interesting theme and guy!

It's been years since I used Erlang. It was actually fun to build a prototype for my last project during my internship.

Now Mr Hughes is a professor I'd love to have at my faculty.

You really really need to do a video on monads. One of the functional programming topics that many of us have a lot of trouble getting our heads around.

Generally, whether you prefer OO or functional, your functions should be stateless and without side-effects unless they need to have state. Also unidirectional data flow is much easier to work with.

As a category theorist in training... I was waiting for the words like "Haskell enable composable side effects" which never came.

One thing he doesn't mention is the fact that functional programming languages are used only very, very rarely. Probably less than 1% of all produced code today is written in a purely functional language like Haskell. Almost all other languages are imperative with a few functional ideas mixed in, or (more rarely) hybrids of sort, like Scala. Even scientists, which are usually much more math-savvy than usual business programmers, rarely use Haskell. So why are functional languages so unpopular, despite all their advantages? My theory is that one problem is their inability to handle loops. As far as I understand, in functional languages you always have to use recursive functions instead of loops. Which has two problems: - Recursive functions are usually significantly harder to understand than loops, which makes writing and reading code more difficult, and increases the chance of making mistakes or not understanding someone's elses code. If programmers have the freedom to use either of them, they, in by far the most cases, use loops instead of recursive functions. - It is much easier to write inefficient code with recursive functions than with loops. E.g. if you write a loop inside a loop, you usually end up with a time complexity of about O(n^2), which can in most cases still be computed very quickly. However, if you write two recursive calls in your recursive function, you typically get something like O(2^n)! Computing this can get _extremely_ slow even for what you might consider medium sized inputs. (Also, if you want to make a recursive function really as efficient as a typical loop, you often have to make sure that your function is "tail-recursive", which is even harder to write and understand than usual recursion.)

I'd recommend watching some of Venkat Subramaniam's talks on functional programming for any developers watching this video

I learned haskell in my first semester programming course at uni. I absolutely hated it at first for its lack of global variables and pickyness with types, but once I understood the basics it was very nice to use and programming with it felt like a fun challenge.

6:36 It awakes the deepest part of my soul

For perfomance we theoretically could take the Rust's memory management model which allows us not to use Garbage Collector and at the compile time automatically create the instructions for freeing the unused memory.

Follow up please! Higher-order functions and type declarations :3

Rocky Horror and functional programming in one video? Great stuff.

This man represents perfectly the meaning of passion, easy to tell :)

Haskell and Erlang are both really nice languages to work in. I prefer it so so much over C/ C++.

6:36-6:38 startled me. :) Out of curiosity, does anyone know what laptop brand he's got there?

2:08 i like his „Oh“

Subtitles incorrectly say 'airline' instead of 'erlang' :-)

I love this guy's voice

Haskell has one awesome feature I've never seen anywhere else (but that's probably just my ignorance): partial application. If you define a function that takes three parameters, you can call it with just one parameter, and the result is a new function that takes the remaining two parameters, with the value you passed bound to the original first parameter. And this works for ANY function. When I write a function in Haskell, I tend to order the parameters according to how likely I am to want to bind each one like that.

At my work we were mixing and matching F# and C# for a while but ended up just ditching it in favour of using a single language (C#) for maintainability and performance, among other reasons, and using the ideas behind functional languages like immutability and avoiding side effects (e.g. using a [Pure] attribute and static code analysis) without the burden of the unintelligible syntax. I've yet to see anything in functional languages that you can't do in imperative languages, it's just a bit stricter.

What kind of programming language would you recommend for firing the missiles? Thanks

He make it sound like functional programming is something new. I thought it predated most "conventional" programming languages (like LISP from '58).

Do tasks like reading input and displaying output count as side effects? Is the idea for the program to have core functionality that is solely functional, called by a user interface written without the functional restrictions? Is functional programming better for particular kinds of programming tasks than others? If so, what kinds of projects does functional programming work best with and worst with?

Could be nice if you made a video on Kaspersky Lab's new secure operating system.

You were at Chalmers? If so, I hope you liked our university! I'm not a CS student, but I've heard about John through friends who are. Very interesting to hear from someone who helped pioneer the field.

6:09 Is it possible to run a whole functional program on a GPU? (because GPUs are usually better at multitasking) So as long as a function isn't depending on a previous function has to finish first you can push them all into the GPU (as long as there are available threads) and get the expected result each time?

I love the idea of func programming, but I constantly run into problems with efficiency. A lot of my code does large scale data processing. I end up doing a lot of caching/checkpointing on the filesystem. My code ends up being very confusing an error prone, but I just can’t do it any other way.

That was a better explanation than we ever got at university... That said, I find find the premise of it a bit odd. I *want* functions to be able to have side effects, encapsulation is one of the major foundations of object orientated programming... call a member function, have it update something, and (optionally) return another value... the same in C operating on global variables... I would argue it is more reliable to have well defined side effects than to go without them at all. A compiler could also easily tell you if a function referenced anything external to itself, as when compiled in isolation anything external would be unlinkable.

Please make a video, describing the general idea of functional programming

More of John Hughes please!

I have been studying Haskell for some years. I keep getting stuck on understanding monads. The term comes from Leibniz and I pretty well know what he meant with it. But what it has to do with Haskell I just can’t figure out. A video that explains what a monad is and how it is used would be very welcome.

Additionally, part of why local variables aren't side effects aside from how they are allocated on the stack is the same as the constant of integration.

Would be nice to have a little deeper discussion about functional programming. How to overcome its limitations for example. Not being able to easily use mutable variables is so foreign to a "normal" programmer that people get frustrated very fast when trying functional. I tried once and wasn't convinced that the benefits are worth the limitations. Later i met an earlier colleague and he was very enthusiastic about haskell. For a "normal" programmer functional programming is pretty hard at the beginning.

I love Scala; it was the subject of my 1-year independent study project.

Cool, seems I have chosen the right uni to learn functional programming!

Chalmers University and Functional programming? You better be getting ready to do an Agda and dependent (AKA Per Martin Lof) type theory video! Or perhaps a video on the Howard Curry Isomorphism or it's extension "computational trinitarianism"

6:35 When the java intro teacher sees students checking if 2 strings are the same with str1 == str2

I would LOVE to know more about "Quick check"

6:31 I have to say, I didn't see this coming. He surprised me.

I don't know the right words for talking about programming languages, but I have a question, so I'll just try my best… Regarding higher level programming languages, such as the one this video's about… Do the things that make it up, have a direct equivalent in a lower level language that's not machine code? Because one way I'm imagining how it works, is that someone decided on a list of things that it ought to be able to do, and then built those things with a lower level language, by going over them with a fine tooth comb to find bugs, spending a lot of time to make sure each one does what they mean it to. Then you use those things to build your program, like building a machine out of off the shelf assemblies of parts, like a motherboard is assembled from lots of little electronics, such as capacitors, resistors, chips, etc., and the parts can be equated to a low level language, and manufacturing process to make all of those individual parts is the equivalent of machine code.

If you don't specify all or correct requirements to the quickcheck there still will be gaps in the tests, so what does quickcheck solve? Is it trying to bring easier syntax (implementation) to describe a unit test?

One thing I don't catch is what he said at 6:20 - I mean you can have the same safe parallelism if you do a pass by value and spin-off two threads in a conventional program no?

Can you do a reactive functional programming? That would be cool, I can't find any video explaining the concept itself.

Does this mean we'll get Simon Peyton Jones too? (All these sorts of Haskell guys are awesome.)

The fact that closed captions have some [words] in '[ ]' ( funny-right?) erlang code is written as airline code every time.

Is there a java version of quick check as I'm not a fan of writing 100s of java JUnit tests for my code. It currently takes up 45% or more of my time per project.

not sure if you guys will read this, but the English subtitles seem auto-generated (even though they were seemingly manually uploaded), they're full of errors and strange notation with square brackets.

Would you do a section on Lisp languages?

I think of functional programming and side effects like this: A = B, where B is a function or operation. While we do this implicitly in math, we specify to computers the Boolean operators ==, and ===. Ultimately, A can be represented by whatever by is on the right so long as A == B is true. However A === B is false in a pure function. While A and B may have equal values, what happens to B is not directly happening to A. Take 7=4+3. 7 is 7, 4+3 is 4+3. In programming = would be an assignment, but in math it's a == in programming syntax. 7 can be represented by really any infinite combination of operations. In 7=4+3, 7 is never being directly changed or manipulated. A pure function's output is constant given the same inputs

4:08 omg that would be AWESOME i'm calling it Curry from now on

Quick check can't solve core issue with testing correctness of programs. Writing a test that checks that function does what it's supposed to? How do you know the results? By writing the function again in the test? And then test the test's test's tests.... It can only be used to check simple properties, like the length of the output. And to get any decent coverage you have to still write all these property-checks.. and on top of that you have to write a generator for valid inputs. Many functions have very complex scenarios where they don't throw an exception, so writing a generator that randoly manages to generate valid inputs is harder than writing the test itself. Nothing about this is automatically generated (and it can't ever be).

If i want to learn much of functional programming and related concepts which two should i choose out of haskell, clojure, racket, scala. can anyone give me a detailed explanation.