A Taste of Haskell

https://hookrace.net/blog/a-taste-of-haskell/

by def- • 10 years ago

157 116 10 years ago

androidfox• 10 years ago

Nice link. One related question : where have you used Haskell in real life. Do some top companies use Haskell to solve problems

wuschel• 10 years ago

I second this question and would like to add another one:

Where is it that Haskell shines?

sa15• 10 years ago

This State of the Haskell Ecosystem doc[1] is very informative. If you're looking at application domains, Haskell(and OCaml etc) is usually well suited for writing compilers, but its not bad for your usual server-side application either. The only domain its fundamentally unsuited for is systems/embedded programming.

[1] https://github.com/Gabriel439/post-rfc/blob/master/sotu.md

jfoutz2• 10 years ago

There are a bunch of fussy little problems that Haskell solves nicely. One example is looking up a value in a map

    map.get("foo") // returns null

is the value of the key null, or was there no key? Different languages have different approaches. Haskell let's you build up deep structures, a list of maps of list of maps ... and you'll have an indication of what path you took down the data structure to get a result. You can do this in any language, but it relies on programmer discipline, and everybody doing it the same way every time. In Haskell, it's the easy thing to do, and often the only way to do it. You'll wind up with something like

[Just ["foo"], Just ["bar"], Nothing]

The first two maps had once answer each, the final map had nothing.

Laziness means you have control of the order of evaluation. in practice you can make your own control structures without macros. bracket is a good example,

    bracket open_socket do_stuff close_socket

the socket always gets cleaned up, with an ordinary function. No try/catch.

One of the biggest hassles in programing is leaky abstractions. The type system means you can steal abstractions from mathematicians that just don't leak. There's some good stuff here [1] about the kinds of things you can say.

Purity means values can't change behind your back. there's no function to call that'll change the state of some object you're working with.

All together, it's nice for languages. You can build up parse trees any way you wish, and traverse those trees to execute the semantics. So if you can think of a dsl for your problem, you can whip up an interpreter pretty quick. If you change your mind, and want to turn it into a compiler, it's relatively painless.

It's a fun language.

[1] https://wiki.haskell.org/Typeclassopedia

harpocrates3• 10 years ago

For me, I think the answer to this is really that Haskell is pure and immutable.

Equational reasoning[1] is immensely useful when debugging. It isn't unusual to debug pieces of Java code that look like this.

    MyClass c = new MyClass(..);
    c.method1(..);
    c.method2(..);
    c.method3(..);
    assert(c.someField == ..) // fails!

To figure what went wrong, you have to read through all three methods and depending on whether you have dynamic dispatch coming into play, you might need to read through _multiple_ versions of all three methods.

[1] http://www.haskellforall.com/2013/12/equational-reasoning.ht...

marcosdumay• 10 years ago

Haskell shines at large codebases. It shines in a lot of other domains, but there's no mainstream competitor on dealing with messy, badly defined, big, changing problems.

Haskell shines on refactoring, API designing, and constrain setting (want to enforce safety? atomicity? thread ordering?). As a bonus, it'll also reduce your codebase an order of magnitude or two.

I mean, yes, if you never wrote a complex parser on Haskell, you should try. But that won't change your life too much.

imh• 10 years ago

Haskell is very strict in what the compiler allows you to do where. It's a really great alternative to just requiring developer discipline. It means that you can do some things (like refactoring) with much greater confidence because the compiler rules out some big classes of bugs. Same with using other people's libraries. You can only use them certain ways and they are explicit.

A side effect of being so strict (in the sense of picky) about what is allowed where is that it needs some really powerful abstractions to keep that from slowing you down. Its type system shines here. Often, these abstractions have a nice syntax in haskell and it makes for some really clean code, relative to a direct translation in other languages.

FullyFunctional• 10 years ago

I've loved Haskell for decades, but not yet had a chance to use it to pay bills. IMO, Haskell, more than any of the 1e3+ other PLs I know, shines in enabling 1) elegant and 2) robust ("better bugs") solutions.

Elegance comes from the non-strict functional part, enabling succent and modular implementations.

Robustness comes from the static typing which forces you to be explicit about the range and domain of functions.

What's unique about Haskell is that the type system is _very_ expressive, making this a practical approach. IMO, the type system is absolutely key to Haskell.

Where Haskell disappoints: Int. For reasons that I still cannot phantom, someone chose to infest a beautiful language that is almost free of pitfalls with the atrocity of a "C-like" Int type. Indeed, in Haskell, this isn't always true:

  a < a + 1 where a :: Int

which is a real shame IMO. It fails the largest value of Int (which BTW is implementation dependent). The correct answer would either to have (my preference) Int == Integer, that is arbitrary sized integers always, or at the _very_ least, have (+) fail on overflow, that is, return bottom like head [].

startling• 10 years ago

Writing parsers is really nice in Haskell: http://www.cs.nott.ac.uk/~pszgmh/pearl.pdf

Trifecta is a nice modern parsing library: https://hackage.haskell.org/package/trifecta

ianleeclark• 10 years ago

https://code.facebook.com/posts/745068642270222/fighting-spa...

This goes into detail about how Facebook uses haskell to fight spam. There's a talk that goes alongside it and the talk was one of the motivating factors for me to start learning Haskell.

samcal• 10 years ago

Yes, but only recently. The most notable example in a top company is Facebook's spam detection service, powered by their library called Haxl[0]. The language allows some very skilled programmers to build this library that makes it very easy to write spam rules. Lower-level engineers can then write very simple and elegant code that looks sequential but is automatically parallelized by the library.

The service is a big deal, because every action or request that anyone makes on Facebook touches this service.

[0] https://code.facebook.com/posts/302060973291128/open-sourcin...

dorfsmay3• 10 years ago

Facebook is the new FedEx. Name a technology, Facebook's probably using it!

ppcsf• 10 years ago

It's interesting that you said the Haskell allows programmers to build Haxl, with the implication being that other languages would disallow it.

I wrote a port of Haxl to C#[0]. At this point one might expect me to recite the whole Turing-completeness-means-all-languages-are-the-same banality, but my experience porting Haxl has actually led me to the opposite opinion.

Haxl probably wouldn't have been written in any other language other than Haskell. Because Haxl leans so heavily on concepts that other languages have no words for, I think it's inexpressible in C#, or most other mainstream languages. Obviously not literally inexpressible (there's an existence proof of a C# Haxl) but in an Orwellian, "these concepts are unthinkable in other languages" sort of way.

[0] https://github.com/joashc/HaxlSharp

sa15• 10 years ago

Standard Chartered has some 3 million lines of Haskell, but they don't use GHC, they have their own internal compiler.

tome5• 10 years ago

About one million of those lines are actually compiled with GHC and about two million with Mu (or at least that was roughly accurate last time I checked).

bbcbasic4• 10 years ago

Yes http://ambiata.com/

bertiewhykovich4• 10 years ago

This question gets asked regularly, and every time Facebook's spam detection service, Standard Chartered's (never-seen) codebase, and maybe one or two other firms that no one's ever heard of get invoked. These are seemingly the only examples.

spraak• 10 years ago

Facebook references all over this thread and literally the comment below yours is in regard to Standard Chartered :D

tome5• 10 years ago

Barclays Capital: http://neilmitchell.blogspot.co.uk/2016/09/full-time-haskell...

sa15• 10 years ago

Since when is visibility expected from corporate codebases?

tikhonj• 10 years ago

I'm currently using Haskell to do supply chain optimization at Target. It's pretty awesome! The language lets us express our models in ways that feel natural.

We're both solving some specific problems (ie inventory control, network/transport optimization) and building a pretty general framework for expressing, analyzing and solving large stochastic optimization problems. Haskell is a great fit because it's extremely expressive and lets us write and reason about our problems in a natural, expressive way. It helps that we have a very mathy team in a mathy field :).

Our team also has a bunch of people with programming language research backgrounds, and our long-term remit is to apply programming language ideas to operations research. Turns out that—for a whole class of PL problems and PL people—Haskell is the perfect language :).

I also know people use Haskell at Facebook (already mentioned), Google (Ganeti and some unnamed X project), a few banks (JP Morgan, Barclays and Standard Chartered) as well as a whole bunch of startups and small companies.

pea• 10 years ago

We're a startup in London (shameless plug: www.nstack.com) using Haskell to develop a containerised microservices platform, bringing in lots of low-level Linux coding along with high-level concepts such as typed DSLs.

So far it's working extremely well for us and has been a great decision - letting us build complex/reliable systems really quickly and effectively. It is also very good for attracting amazing people, and we have found a small Haskell team can deliver truly spectacular product. This does on how you architect a Haskell codebase: e.g. you could spend a ton of time focusing on the most pure approach vs. pragmatism, so it's a balancing act.

cx1000• 10 years ago

kittyhawk has an opening for a full time Haskell software engineer https://kittyhawk.aero/

eli_gottlieb• 10 years ago

Well, someone seems to show up to Boston Haskell every month having used it in industry, and I've used it for a paper on probabilistic modelling in my copious free time.

sa15• 10 years ago

That's not really the Sieve of Eratosthenes. The list data structure is not well suited for the algorithm. See [1] for a proper discussion. As someone who wants to write Haskell(and loves it) for code with mathematically well defined guarantees, the propagation of such examples, where the guarantees or behavior is not clear to the author, is not helpful.

[1] https://www.cs.hmc.edu/~oneill/papers/Sieve-JFP.pdf

harpocrates3• 10 years ago

Cannot agree more. I think the usual example of quicksort also falls under this category.

[1] http://stackoverflow.com/questions/7717691/why-is-the-minima...

pera• 10 years ago

It's the same example displayed in haskell.org though.

seagreen• 10 years ago

Totally fair point. haskell.org has a very . . . casual approach to presenting the language. It's been such an issue some people made an alternate homepage at haskell-lang.org.

kmill• 10 years ago

Or if Python's your thing: http://www.kylem.net/stuff/sieve_eratosthenes.html

kinkdr3• 10 years ago

Started learning Haskell just a couple of weeks ago. My only complaint with the language so far is that I cannot have the same name for a field in two records in the same module.

Other than that it is amazing the confidence it gives me; if it compiles it works (r).

sdegutis• 10 years ago

This may help you:

https://www.reddit.com/r/haskell/comments/2z248l/language_ex...

kinkdr3• 10 years ago

Thanks!

harpocrates3• 10 years ago

If you are using GHC, the newest version (8.0.1) actually supports duplicate record fields with the [DuplicateRecordFields](https://downloads.haskell.org/~ghc/latest/docs/html/users_gu...) extension. Check it out!

kinkdr3• 10 years ago

Ahh awesome! Thanks!

pyrale2• 10 years ago

Nice ! Does it work well with lenses ?

jjawssd• 10 years ago

How difficult is it in your experience for developers to learn Haskell while on the job?

chadaustin• 10 years ago

In my experience at IMVU, surprisingly not very difficult. It's easier to learn Haskell in a team environment than on your own because your peers can help you connect the dots and accomplish your task at hand.

It did seem like less experienced people picked it up faster, perhaps because they had less to unlearn. The hardest things were learning to parse GHC's error messages and learning all of the names of the functions to transform between various data types.

evincarofautumn2• 10 years ago

I basically learned Haskell at my first job (writing a compiler), and it was pretty easy to productively contribute starting on day 1, especially because there seems to be less risk of breakage than in many other languages. I also helped teach it at the next job, and developers found it pretty easy to pick up, just different from what they were used to.

Prior to this, I had some experience using it for hobby projects, but there was a lot more to learn for real-world use. My colleagues and I helped each other learn new concepts and write better code, as best we could, but we did end up making some questionable design decisions. I think you still need an experienced Haskeller to advise on good program architecture.

andrewchambers• 10 years ago

Compilers are a bit easier to start with because you can just deal with pure functions for the majority of the time

Dzugaru• 10 years ago

Don't know about Haskell, but what really got me (a long time CSharp programmer) into functional programming was this awesome site [1] (and a man behind it with his awesome talks) - which is focused on core aspects of FP (applicable in most languages nowadays) in real-world applications.

[1] https://fsharpforfunandprofit.com/

shados• 10 years ago

I love that site. The best part about it is that it gives you all of the common names for stuff like category theory concepts. Eg: the various ways map, flatMap, bind, etc are called across languages.

Because its a pain in the ass to learn those concepts from scratch when you're looking at code in one language but reading a tutorial in another...the concepts are language agnostic, the naming conventions however are not.

KennyCason6• 10 years ago

I love Haskell, but if you hate Java, but still want to leverage the nice Java ecosystem, (libs, IntelliJ, JVM, tooling, etc) try Kotlin! :) https://kotlinlang.org/

mahyarm5• 10 years ago

Does kotlin have the same compile time, binary size and IDE indexer choking issues as Swift? I've heard that it has similar problems. I would not use Kotlin for a large project if that is the case.

KennyCason6• 10 years ago

I used Kotlin for basically all of our machine learning/classifier code in a pretty large map/reduce + storm pipeline and have had no problems.

IntelliJ also does not seem to have any problem with it either. (The IntelliJ authors being the the creator of Kotlin) In terms of code size, Kotlin is definitely smaller and easier to maintain. In terms of raw/clean compile speed, I would expect it to be a bit slower, but there are ways to improve it. One of the bigger ways is via incremental builds. I.e. Only build changed chunks of code, which Kotlin supports, and is comparable to, and in some cases faster than Java: https://medium.com/keepsafe-engineering/kotlin-vs-java-compi...

In terms of executable size, I don't have good data, but will investigate, but I'd say likely not a major deterrent given all the other value adds. :)

whateveracct• 10 years ago

If you love Haskell I guarantee you will not love Kotlin in the same way. Your best overall bet for Haskell-like FP on the JVM is Scala+cats/scalaz and other Typelevel-endorsed libraries. Unlike Kotlin, it gets pretty close.

KennyCason6• 10 years ago

I mean, if you like Scala, you'll most likely like Kotlin, there are a LOT of similarities between the two.

KennyCason6• 10 years ago

Forgot to say, I agree with your statement. :) A pure Haskell fan, will likely not appreciate Kotlin the same way that a Java person appreciates Kotlin.

virtualwhys• 10 years ago

That would be an odd choice for a Haskell alternative. Lacking higher kinded types and type classes is a bit of a show stopper.

The obvious choice for Haskell on the JVM is Scala.

iLemming3• 10 years ago

Nope - the obvious choice for a functional language on JVM is not Scala and not Kotlin - it's Clojure.

KennyCason6• 10 years ago

In a standard conversation, I would totally agree with you. However, since the OP is comparing Java vs Haskell, I figured I would offer something that's, imo, better than Java, and perhaps good enough that a pragmatic Haskeller can accept.

Granted, Closure is probably a more pure alternative.

pyrale2• 10 years ago

The project is not super mature yet, but you could give Frege a try. Frege, as opposed to other solutions, is Haskell in a JVM.

https://github.com/Frege/frege

NotThe1Pct• 10 years ago

I tried haskell queues a while ago - under the advice of a friend and compared with a straightforward C++ queue - it was about 100x slower. Abandoned the idea.

bbcbasic4• 10 years ago

Let me guess ... you used [a]

sammoth• 10 years ago

What are you implying? What should they have used?

59nadir• 10 years ago

You should do a write-up on it and show your tests. As it stands, this post has almost no real value for anyone else and no one knows anything about what you used and how.

TheAceOfHearts• 10 years ago

I got started with Haskell recently, and I'm really regretting not having picked it up earlier. Most of what I knew about types came from C, C++, or Java; so it's a big leap.

I've been using Haskell for Mac IDE [0] while experimenting, and it's been great fun.

The thing that prompted me to give Haskell a a try was this video [1] of a guy using Haskell to generate Elm types, in order to maintain consistent types across the stack. This idea captivated my interests. I'm confident that GraphQL and Relay, or something along those lines, is gonna be the future.

My experience so far has been that Elixir feels more welcoming and beginner friendly. There's nothing wrong with the Haskell community (or my limited interactions with it so far), but so far it's just felt a bit drier.

[0] http://haskellformac.com/

[1] https://www.youtube.com/watch?v=sh4H8yzXnvw

Matachines• 10 years ago

Of course Elixir is more welcoming—the language is "practically" functional, easy, and made for building stuff. Haskell's purity and academic background is definitely a big impact on its culture.

not-much-io• 10 years ago

I wish there was a haskell-without-the-warts language with the same culture as Elixir - developer friendliness, practicality etc.

As it stands I can't help but feel discouraged when learning Haskell. Haskell feels like a research tool for furthering other programming languages...

I'm still going to learn Haskell, promised myself I would! But I do look to the Elixir folk with a bit of jealousy..

acchow3• 10 years ago

If you delve deep enough into C++ TMP, it's just as expressive (more expressive in some ways) as Haskell. You can actually do dependent types in C++.

yyhhsj05212• 10 years ago

You can, but would you?

deckiedan• 10 years ago

From what I understand, C++ can do anything! But sadly, it lets you do anything.

Haskell restricts what you can do hugely. But also lets you accomplish a whole lot within what it thinks of as safety.

I like Haskell - but think it's really just a playground for trying how far functional purity can be pushed, rather than being the actual best version of that paradigm.

Probably in 10-20 years time there will be a language around which takes all those concepts and comes together as a really pleasant unsurprising friendly developer experience. Maybe it'll come from slow evolution of Haskell... stack helps a lot, and a whole bunch of GHC extensions... but it's still got a lot of very impractical elements and hangovers from the past that really need to go.

mahyarm5• 10 years ago

I really want to warn people from using long-to-compile languages in big projects. And by long, I mean longer than C++. From what I heard Haskell has compile time issues.

You will regret it once your in that position and it is hard to get out of once your there.

dkubb• 10 years ago

It's a common misconception that Haskell is slow to compile but not really true, see for example: http://www.shimweasel.com/2016/10/24/fast-tests-and-static-l...

mahyarm5• 10 years ago

That feels like a limited optimization in the context of practical development.

Athas2• 10 years ago

I guess it depends on your expectations. I'm working on a ~38000 SLOC Haskell program (an optimising compiler: http://futhark-lang.org), and with GHC 8.0.1, a full build takes about 7 minutes. I can cut off a minute or two by passing `--fast` to Stack. However, even small incremental builds take a significant amount of time due to linking, which is what annoys me the most. It's still far from making me disavow Haskell, but it's definitely not among the fastest-compilable languages.

This program is also too big to load in GHCi, at least on my laptop with 8GiB of memory.

mbrock• 10 years ago

No, it's a very common issue brought up within the community that GHC takes a lot of time and memory.

That blog post just says that interpreting Haskell can be faster than compiling.

I worked with Haskell professionally on a pretty large codebase. It was split up into many separate libraries and binaries. There were a lot of coffee breaks when recompiling.

https://www.reddit.com/r/haskell/comments/45q90s/is_anything...

agentgt• 10 years ago

As for the Java bashing in the beginning I'm not saying Java is anywhere near the expressive power of Haskell but many people think different things based on Java because of features they either don't know about, outdated libraries used, or experiences with older versions and codebases.

For example most don't know that Java actually does have macro like capabilities through APT (annotation processor that will work automagically I might add). Some might say ewww its not macros but then again annotation processing might just be 80/20 good enough (aka what OCaml learned with ppx vs camlp) and that Java now sort of has traits and that its code swapping is actually fairly good (jrebel). There are even sadly people that don't know Java has lambdas, and even some (usually C++ dudes) that don't know it has generics. Most don't even know that you can combine interfaces with generic types as in: `<T extends Comparable & Serializable> void someFunc(T t)`.

Yes Java is not Rust, Haskell or even OCaml in expressiveness but it certainly is more powerful than Golang and definitely compiles fast (albeit starts up slow).

That being said OCaml is still my favorite. Compiles fast and easier for me to understand. Super mature and lots of companies use it.

iLemming3• 10 years ago

It's not Java what makes Java platform one of the most popular but rather JVM. That's why Clojure grows in popularity. Because it brings the expressiveness.

oweiler• 10 years ago

Please show me how Clojure is growing in popularity. Clojure has never been more than a niche language.

acchow3• 10 years ago

and lots of companies use it

Curious, who uses ocaml other than FB and Jane Street?

grault• 10 years ago

https://ocaml.org/learn/companies.html

xamuel3• 10 years ago

I taught myself Haskell because people say it improves you as a programmer. I didn't see that, but I have a math PhD so maybe I'm just too familiar with abstract types to gain new insight from Haskell.

As a language, it's sterile. You can tell it was designed by committee.

dorfsmay3• 10 years ago

Are you still using it? If not, what did you switch to for expressive, "fast" (faster than python) language?

xamuel3• 10 years ago

No not still using it. I use C or q (as in kdb+) when I want speed and expressiveness. Python if I want quick easy prototypes.

If you think Haskell is a weird language that challenges what you think about programming, it's nothing compared to q! :)

the_af2• 10 years ago

As a language, it's sterile. You can tell it was designed by committee.

This remark is puzzling. How do you tell if a language is sterile?

xamuel3• 10 years ago

Hard to put a finger on it but it lacks a certain "playfulness" which real-world languages have.

It's like the difference between Lojban/Esperanto (artificially constructed spoken languages) and English/Spanish. English/Spanish are "imperfect" but their warts are the results of thousands of years of culture (and may not be imperfections after all, they may be a case of some kind of coding theory emerging organically)

joobus• 10 years ago

I've spent quite a bit of time with Haskell, and all the beginner text like this link are easy to grok, but where I've constantly come up short is trying to write an app with, for example, a configuration and a database connection. Having multiple levels of Monad transformers just confuses me and I never get anywhere useful. Something like:

App MaybeT IO (StateT IO (EitherT IO Text SomeRecord))

Or something. I haven't figured this out.

spion2• 10 years ago

Use IO for everything at the beginning. Use wai/warp to run an app directly and setup handlers. Use postgresql-simple to send queries. Read the settings object once, then pass it everywhere.

You can slowly start writing generic types for your pure code after a while. For example, replace types such as `[t]` with `Functor f => f t` if the only list-related operation done in that function is `map` (fmap). Try to take advantage of the stuff here: https://wiki.haskell.org/Typeclassopedia

After a while of doing this, you can start looking into how you can write your code in a way to have more generic types, then specialise it for the concrete problems you're solving

Finally at this point transformers should become easier and more obvious. Perhaps the first one would be to replace passing the config everywhere with ReaderT. Implementing a few transformers by yourself should help. Start with MaybeT and continue with ReaderT. Tip: `liftIO` magically works but you don't have to always understand how. Maybe also try free monads if transformers seem too annoying!

spion2• 10 years ago

I almost forgot; use MVar [1] to keep mutable state around. Its seriously helpful.

https://hackage.haskell.org/package/base-4.9.0.0/docs/Contro...

joelthelion• 10 years ago

You shouldn't need this stuff if you don't want to use it. Just write a few IO functions for interaction with the real world, and pure functions for the rest. I made the same mistake in the past, and I was completely lost. I'm still nowhere near advanced, but sticking to simple stuff and learning slowly I am able to be quite productive now.

anentropic• 10 years ago

I hit the same problem... I had decided to start with a little toy 'dice rolling' program, but since it involved random numbers I unwittingly got hit with the monad problem up front.

It seemed I had two options: either I could pass a seed value around everywhere, or I could lift all my values into monads, necessitating the use of the 'monadic' version of all the operators etc everywhere.

I was unable to achieve what you suggest... I could not find a way to keep the 'inner' part of the code as pure functions just expressing simple operations.

I submitted here http://codereview.stackexchange.com/questions/114725/my-firs...

I had some useful feedback but no one addressed the "monad pollution" issue.

Apart from the different mindset of Haskell (which I found interesting) I struggled with having multiple ways to do everything, how to find the 'right' or monadic version of a particular function or operation, poor docs.

tome5• 10 years ago

App MaybeT IO (StateT IO (EitherT IO Text SomeRecord))

Ouch! I've written Haskell commercially for the last four years and I've never written (or had to read) anything like this!

lifeisstillgood• 10 years ago

How bad is it looking at the examples and thinking "I love that lambda symbol as a prompt. I want"

I have to revisit my base setup soon. The 1990s wants its bash_profile back

cies• 10 years ago

There are some book recommendations at the bottom of the article, which are missing the (IMHO) latest-and-greatest introductory resource to Haskell: the book Haskell from First Principles.

http://haskellbook.com

krautsourced• 10 years ago

This may sound (and probably is) quite superficial, but I am immediately put off by any language that uses syntax like this: foldr' (+) :: Num t1 => t1 -> [t1] -> t1 Why? Because of things like => and -> are just a pain to write all the time and make you chase all over the keyboard, even more so on non-english keyboards. Just my very personal preference of course, but still...

dancek• 10 years ago

It is quite superficial. Code being easy to read is much more important than code being easy to write. I'm not saying it's a bad idea to have both, but look at Java or C# that are a pain to write without a very smart IDE (just because of the amount of boilerplate). Even they have been saved by tooling.

Also, modern popular languages tend to use arrows (Java, C#, ES6). Not to say that popularity matters, but people are used to it nowadays.

A Taste of Haskell

Related Stories