What I Wish I Knew When Learning Haskell

http://dev.stephendiehl.com/hask/

by Cieplak • 6 years ago

286 143 6 years ago

dev.stephendiehl.com

dcl• 6 years ago

Great timing. I was just pondering what functional programming language I should attempt to learn in all my new downtime.

Apollidore• 6 years ago

Haskell is fun, but bear in mind that it's followes a purely functional programming paradigm, meaning you either do things the Haskell or you don't do them :). But it's a fun language to learn, and there are lots of free quality ressources on the internet

marceloabsousa3• 6 years ago

What do you mean by "either do things the Haskell (way) or you don't do them"? Isn't that the same with every language? I still don't understand why people put all sorts of unfair labels on Haskell. By labelling Haskell with "fun", we almost make it sound like it can't be used in production.

masklinn• 6 years ago

it's followes a purely functional programming paradigm

I'd say that it's one take on that paradigm, the Way of Monads is not the only way to do purely functional, Clean uses uniqueness typing instead. Though it otherwise has rather similar properties to Haskell.

fulafel• 6 years ago

Though The Haskell Way includes the io monad, which is imperative code in practice :)

Random_ernest• 6 years ago

I tried to learn FP multiple times by learning haskell. Never clicked, tried clojure and I was productive after roughly 2 days.

lonelappde10• 6 years ago

For the 99%, Haskell's purpose is to teach you what to hate about your working language, not to be a working language.

https://blog.plover.com/prog/haskell/what-goes-wrong-2.html

rkangel• 6 years ago

Haskell is very much the deep end of learning functional programming - it's at an extreme end of the spectrum in purity and type system.

The language I recommend as a first step to most people is Elixir (or Erlang). It's fairly pure, data is immutable, relies on recursion at the lowest level etc. Good code in Elixir is structure in a similar to good code in a lot of other functional languages (and so teaches good habits), but being dynamically typed is avoids that immediate pain of learning about how to keep the compiler happy.

dan-robertson• 6 years ago

As a counterpoint, I picked up (some) haskell pretty quickly.

I read a lot of code and didn’t get bogged down reading explanations of what a monad is. I also avoided trying to understand too well what the evaluation semantics of the language were.

When I read code, I focused on looking at the type signatures and understanding what they meant, then I would stare at the code and try to work out in my head why those definitions would get those types.

I did this at a time when there were lots of “I wrote a program in Haskell. Let me explain how it works” blog posts on this site.

I defined some data structures and solved a bunch of project euler problems as practice

BoiledCabbage• 6 years ago

If you want to learn a functional language absolutely do not learn Haskell.

If you're interested in static functional programming, learn Elm and then F#/OCaml.

If you're interested in dynamically typed then learn Clojure or possibly Racket.

That's it. Spending time learning Haskell as your first (or even second) fp language is a terrible idea and has done more to slow FP adoption than anything.

You can learn Elm literally in a weekend it's so small and well organized (go to their site and follow the tutorial). The concepts you pick up will double the speed you learn any other static FP.

F# on .net core is cross platform and can run via a vs code plugin. Plus you have a batteries included full class library of practical needs via dot net.

Clojure is very productive, great concepts as well. A bit worse tooling / debuggingqgen you have to drop down to deal with java, but also had batteries included java libs.

Racket is probably the most isolated of the above. A scheme dialect and a bit closer to historical scheme and Lisp.

Don't learn Haskell it's a horrible use of time as a first language. You get 80% of the value in the above languages in somewhere between 1/10 to 1/4th the effort (depending on which lang you choose), and have learned a more practical language, and will actually learn that lang plus Haskell faster than if you had started in Haskell.

hvs• 6 years ago

Agreed. Haskell is masters class in functional programming that is generally more interested in pushing theory forward (not necessarily a bad thing). If you are a .NET developer, F# is a wonderful language (based on OCaml) that allows you to ease in to FP since it supports functional, oop, and procedural programming. Plus, you have the whole .NET ecosystem as well. You can become very productive, very quickly.

outlace• 6 years ago

I’ve tried learning Haskell once or twice and it didn’t really click. However, I’m know knee deep in learning Lean, which is a dependently typed functional language that is also a theorem prover and it’s been a much easier ride. It’s not any less complex than Haskell but learning FP by essentially doing mathematics has made it a lot easier for some reason.

StreamBright• 6 years ago

I like to think that ML languages, in general, are good to start to learn FP with.

SML by Dan Grossman is a great resource because it explains the concepts very well. Anything that you learn after will be easier, does not matter if you go for Haskell or F# later.

https://www.youtube.com/watch?v=a1fkhDjCHB8&list=PL-eVNDa9MN...

jlevers• 6 years ago

I see a lot of people below saying to chose a functional language other than Haskell. As someone who's currently learning Haskell, I'm finding it _incredibly_ interesting...but I've heard that many of the free online resources don't lay the necessary foundation for learning the more advanced concepts.

I'm 6 chapters into Haskell Programming from First Principles [0], and I highly recommend it.

[0] https://haskellbook.com/

Iceland_jack2• 6 years ago

Haskell is definitely interesting, there is so much to explore and the community is eager

Iceland_jack2• 6 years ago

Just learn Haskell

CJefferson2• 6 years ago

I feel this might have grown beyond its title.

Picking the point where I gave up, giving me a list of 7 vscode plugins, without any guidance as to which are more mature, doesnt feel like a thing anyone would wish to know before they start.

quchen• 6 years ago

I'm pretty sure this (evolving) article has been around well before VSCode's initial release.

CJefferson2• 6 years ago

I'm sure you are right. That is just picking at one thing I will admit, but I do use vscode, so when I saw a section about how to best use haskell in vscode i was interested. I'm not interested enough, or as a beginner qualified, to evaluate 7 options.

ninkendo• 6 years ago

Is there maybe an article somebody can actually stand a chance of reading end to end? I think GP is right, there’s not a chance somebody who’s actually new to Haskell would find this useful as a true “things I wish I knew” article. It’s more of a complete reference to the entire language.

To me at least, “things I wish I knew” implies it’s some sort of companion to a real language guide/tutorial/book, not a replacement for one.

lmm• 6 years ago

I have to agree. A more opinionated guide would be more useful than one full of so many long lists of alternatives; a learner is in no position to make those choices.

lonelappde10• 6 years ago

No one said it's what they would wish to know before they start.

Take it from someone who spent 10 years on and off learning Haskell: It's a guide to navigating the boobytrapped minefield of the Haskell ecosystem, from the difficulties of installing it for the first time, to the confusing type theory.

Those aren't 7 plugins to choose from. Those are 7 plugins you should use all 7 of because there is no unified coherent Haskell IDE or plugin, but there are a dozen other broken ones that look good in the catalog.

Much the same with libraries. You need a guide to tell you which ones are usable and which are abandoned experiments, since both live side by side in the main repos.

gstipi2• 6 years ago

Please take a closer look at the first plugin listed for VS Code, haskell-ide-engine, https://github.com/haskell/haskell-ide-engine

It is under active development and is the closest you can get to a "unified coherent Haskell plugin" - it comes with all the features you would get from installing the 7 plugins individually.

mFixman• 6 years ago

What's the point of using 7 VSCode plugins for a language you don't even know? Just pick up any terminal, any text editor, and the freshest stable copy of GHC.

gstipi2• 6 years ago

The VS Code plugin listed (haskell-ide-engine, https://github.com/haskell/haskell-ide-engine - to be more precise, it's a language server supporting many editors) is probably the one which sees the most development at the moment and comes with many of the other plugins listed or equivalent functionality (syntax highlighting, tab completion, linting via hlint, code formatting, refactoring) included. It certainly is the tool I would recommend to VS Code users.

gavinray• 6 years ago

I would go one further and suggest people use the VS Code Devcontainer made pre-bundled with Haskell + Haskell IDE Engine installed and configured.

Properly setting up HIE was a bit of a mission:

https://github.com/hmemcpy/haskell-hie-devcontainer

This should be the #1 recommendation to anyone looking to get started IMO, it cleanly sets everything up for you and extracts it into an isolated development container.

eska• 6 years ago

Not what I expected. Seems to be more of a primer/tutorial.

kmorgh• 6 years ago

I like this reference style of documentation, it tries to give a full overview of everything there is. Which is usually what I'm looking for. The sections are also concise.

TazeTSchnitzel3• 6 years ago

What's up with the formatting on this page? In Firefox for iOS (same rendering engine as mobile Safari), all lines but the first one in code listings have 4-character indents, and lines use a larger-than-normal font size seemingly at random.

The_rationalist• 6 years ago

It might have to do with the fact that webkit is mostly a deprecated browser?

recursive2• 6 years ago

1. Firefox doesn't use webkit. 2. Webkit isn't deprecated. 3. Webkit isn't a browser.

lonelappde10• 6 years ago

That's what mobile Firefox does to most of the web.

TazeTSchnitzel3• 6 years ago

Not in my experience.

hopia7• 6 years ago

I find myself coming back to this for various stuff all the time. It's a great reference that touches basically everything important for writing real apps with Haskell.

merricksb• 6 years ago

Earlier discussions:

https://news.ycombinator.com/item?id=5546679 (2013)

https://news.ycombinator.com/item?id=6868303 (2013)

https://news.ycombinator.com/item?id=7637278 (2014)

https://news.ycombinator.com/item?id=10209249 (2015)

dang• 6 years ago

https://news.ycombinator.com/item?id=14226310 (2017)

https://news.ycombinator.com/item?id=7904987 (2014)

eklavya• 6 years ago

Really just learn it.

It's a pity I don't use Haskell at work and yet learning Haskell was the single most bang for buck exercise I have ever done. "Parallel and Concurrent Programming in Haskell" is the best resource I have ever read on parallel and concurrent programming concepts.

Every programmer should learn this language even if they never plan/get to use it.

efnx• 6 years ago

Agreed. The concepts are very useful and applicable elsewhere.

mikorym• 6 years ago

If I am not mistaken, Dijkstra advocated for Haskell to be used as a language of instruction at universities. There is an essay somewhere online about it. What I could find is this: [1].

Edit: Indeed, the PDF that is linked to in [1] looks like a scan of the original. [2]

[1] https://chrisdone.com/posts/dijkstra-haskell-java/

[2] http://www.cs.utexas.edu/users/EWD/OtherDocs/To%20the%20Budg...

m4lvin• 6 years ago

Thank you for mentioning, finding and linking to this!

lonelappde10• 6 years ago

Note that Dijkstra recommendes Haskell over Java because Haskell is arcane and mathematical, which is good for learning computer science, not because it's good for writing software.

goto11• 6 years ago

Colleagues from outside the state (still!) often wonder how I can survive in a place like Austin, Texas, automatically assuming that Texas’s solid conservatism guarantees equally solid mediocrity. My usual answer is something like “Don’t worry. The CS Department is quite an enlightened place...

Very Dijkstra to start by insulting the intended audience. Wonder if it had the intended effect?

DavidWoof2• 6 years ago

I agree with this, learning Haskell was transformative for me. It changed the way I approached problems in every other language. I treat learning it as one of the 2 or 3 things that has most influenced my development skills.

But the truth is that I still don't feel comfortable writing anything more than toy apps in Haskell. I'm not really sure how to unit test things when I'm passing complex monad transformers around. I feel like I'm just guessing at best practices for arranging, say, a website of moderate complexity.

There's tons of resources for learning the language itself, but very few on actually applying it successfully to anything other than a single purpose command line app.

agumonkey• 6 years ago

I'm probably a lot lower than you but I feel I hit a similar wall. I naturally end up writing a function soup which feels super dirty.. as much as I dislike the term (uml-overload) there's a need for architecture that I don't know how to address in FP.

zetalemur2• 6 years ago

I treat learning it as one of the 2 or 3 things that has most influenced my development skills.

If you don't mind, what were the other 1 or 2 things?

pwm• 6 years ago

From my experience the key to becoming comfortable writing "real" apps in Haskell, or any language for that matter, is to just do it and keep at it. The easiest path, and the one I chose, is to do it full time as your day job. When you write Haskell all day every day you'll get comfortable with it surprisingly quickly. You also realise that it's not a panacea, it's just a language but a damn fine one at that. You can (and should!) write super simple, unceremonial Haskell the vast majority of the time if you are writing "real" apps as opposed to pushing theoretical boundaries.

Re code architecture and arranging code - It's not that different from what you'd do in any other language and it's more of a domain question (a webapp?, a game?) then a language one. If and when you change your mind though to move things around/re-architecture your code that is when Haskell really shines. Compiler assisted refactoring is one of the superpowers. It's like having google maps in a foreign city, it guides you to whatever your destination is.

mlthoughts20185• 6 years ago

I learned Haskell and used it (and heavily functional Scala) professionally for about 6 years.

I feel learning Haskell was worthless. It did not teach me anything about decomposing problems into function units, compositional sequences, pure functions / immutable data structures, lazy evaluation or asynchronous programming that I have found useful in modeling solutions to software problems.

Guarantees from the compiler and use of the type system itself for type designs like phantom types and type class patterns did not help reduce behavioral bugs and the slower development cycle of waiting for compilation (instead of just using occasional unit test runs to check simple safety conditions in lighter weight dynamically typed languages) was a very significant cost.

It was no easier, and often much harder, to enable extensibility into systems designed in Haskell because the constraints of the extensible needs of the system were only ever learned from changing business circumstances after the fact and could not be reflected in anticipated up-front design, which is perhaps the number one need of business software yet is an area where functional languages are uniquely poorly suited even with veteran, highly experienced engineers on the team like we had.

In the end, following simple patterns of composition and function purity while avoiding cookie-cutter design patterns and avoiding use of object / class constructs is all you need. This is easy to achieve in many imperative languages while leaving much greater flexibility to choose mutation, treat safety as a resource to be traded off instead of enforced in all cases, etc.

“Module oriented programming” in Python or C, letting lightweight unit tests replace heavy reliance on type system patterns, just using simple structs / namedtuples / dataclasses that posses zero function logic, and creating imperative APIs around functional-inspired core implementations is strictly better.

Really, strong adherence to statically typed functional languages with lazy evaluation is a religious trap. Learning that it’s not all it’s cracked up to be early in your career is critical for success.

jmeister• 6 years ago

Thank you. This is an important point that deserves to be discussed more.

Would you mind sharing what business domain you were working in? I’ve seen static FP being used/popular in finance but not much elsewhere.

Also, do you have a favourite language now?

stavros• 6 years ago

Why is this downvoted? It's pretty extensive and well thought-out, which should be upvoted.

If you disagree, post a rebuttal.

koala_man2• 6 years ago

I feel learning Haskell was worthless. It did not teach me anything [..]

Did you already know most of it from Scala?

sdegutis• 6 years ago

This is my same experience except with Clojure. It’s pretty much equivalent to well written JavaScript. Actually no, the latter is usually cleaner and clearer.

hopia7• 6 years ago

yet is an area where functional languages are uniquely poorly suited

Can you clarify if you mean that the type system gets in the way here, or the same would apply to even dynamically typed functional languages?

I'm trying to understand if you think a static type system is the hindrance here, or the language being functional in paradigm.

frankmcsherry• 6 years ago

Haskell.

JonCox• 6 years ago

http://learnyouahaskell.com/chapters

philzook• 6 years ago

It's true.

w3mmpp• 6 years ago

Ah, Haskell, the language I wish used s-expressions...

lonelappde10• 6 years ago

https://www.reddit.com/r/haskell/comments/2u5gac/haskell_wit...

anaphor2• 6 years ago

In the section on "Boolean Blindness", I find the example a bit confusing.

I would expect `isNotJust (Just foo)` to equal `False`, not `True`, and vice versa `isNotJust Nothing` to equal `True`.

The point has some validity (that you should try to encode data into the types if you can), but the example makes no sense in my opinion.

http://dev.stephendiehl.com/hask/#boolean-blindness

runaway• 6 years ago

I thought that was the point of the section- that you may be able to tell something is wrong with the example, but the compiler can't. Thus by programming in that fashion you're not taking advantage of the power of the compiler.

The improved way below where the Just a is unwrapped with a case allows the compiler to see whether or not x is valid.

anaphor2• 6 years ago

Ah ok, that wasn't really clear to me, but that makes way more sense. Clearly I hadn't had any coffee when I read it earlier.

shahbaby2• 6 years ago

A few years ago I accidentally deleted my entire Haskell assignment about 1 day before it was due.

Within a few hours I rebuilt it from scratch.

That's when I realized the power of functional programming. There's no way I have been able to recover that quickly if I had used an imperative programming language.

Since that experience I've tried to follow a functional programming style whenever I can. I've realized that every variable is another state which adds to the complexity of the code.

UncleMeat• 6 years ago

But it was a programming assignment. Building a thing fast is, outside of very few situations, not a thing to optimize for. Building something to be maintained and evolved over time by non rockstars is far far more important, IMO. Perl is great for ripping through some script quickly but it has problems for long term maintenance.

yakshaving_jgt5• 6 years ago

Building a thing fast is absolutely something to optimise for in business.

Time is money.

shahbaby2• 6 years ago

Actually outside of a programming assignment, I think maintenance rather than speed is precisely why a company would want a functional code base.

How much time is wasted on debugging? Functional programming forces you to deal with your bugs at a much earlier point of development.

It also forces you to avoid some bad practices just to meet a deadline.

And since you're re-using so many component, you spend much less time with boiler plate code.

sullyj34• 6 years ago

It's definitely possible to write "boring Haskell". getting fancy is more of a cultural tendency than a necessity when building things with Haskell.

https://www.snoyman.com/blog/2019/11/boring-haskell-manifest...

WorldMaker• 6 years ago

Though the interesting point here was that it made it easy to write the program fast the second time. While it should be very rare you need to write exactly the same program a second time, and can be a useful thing (albeit a hard thing) to optimize a language for if in writing a program a first time in that language you wind up with such a clarity on the problems you encountered that "solving" them again a second time feels trivial.

harry82• 6 years ago

If you're thinking of learning Haskell you should consider the software written in haskell as an indicator of, well, something.

List all the programs useful for something other than programming a computer written in haskell:

Xmonad window manager Git annexe Pandoc

What else, let's get the full list. Exclude anything that we can't directly see or use.

I say, yes! Learn Haskell! Just don't expect to write any useful programs because they're pretty rare for people to have written when they've doesn't time learning Haskell.

It is great fun. Do it!

Ericson2314• 6 years ago

And how many programmers are paid to write anything anyone has heard of? And how many new well-known not-de elopement-related tools have been written in the last few years?

yakshaving_jgt5• 6 years ago

Look at all these hundreds of companies who use Haskell to write apparently useless software.

https://haskellcosm.com/

harry82• 6 years ago

Look at the thousands of people who learned Haskell and then also felt inspired to write a monad tutorial and publish it on the internet. Your search engine will help to see just how many there are.

Contrast with the number of useful applications you can actually install and run that are for some purpose that is not programming.

In fact there are more Haskell textbooks you can read than haskell programs you can install (excluding programs for programming - because that's some pyramid scheme vibe there).

This tells us something, I didn't even suggest what it tells us. What it suggests to you is what you thought of.

And fwiw imho pandoc is extremely useful! And Haskell is great fun and worth your time to learn!

What have you written in haskell that we can use?

privethedge• 6 years ago

For those who really want to blow their mind, I suggest learning Coq instead https://softwarefoundations.cis.upenn.edu/

spopejoy• 6 years ago

It's really aggravating that HN goes against it's own culture so thoroughly when it comes to Haskell. We're supposed to comment on what TFA says, not lick our wounds about how Haskell wasn't what we wanted it to be. f you can't contribute to the thrust of TFA how about creating space to listen to people who actually know what they're talking about?

Every single piece of hackneyed received wisdom and FUD in here can be easily countered if you talk to somebody with actual production Haskell experience. Speaking for myself:

- I run a startup that has production applications making money for 4 years now written entirely in Haskell with 6 devs doing nothing but Haskell (as well as engineers working in JS and our own language, Pact, yes, written in Haskell).

- When we need more bandwidth, we work with an all-Haskell consultancy that itself has no trouble finding work and is very successful in their own right.

- Before that, I built a group at a major bank writing Haskell code and getting it out in production, and outperforming Java apps.

- The tired "eww static types aren't for real business" is opinions masquerading as "facts". If you are a half-decent engineer in ANY language you can make your code refactorable for changing requirements. Whining that types makes that harder just shows your own limitations. Any decent programmer working in a strongly-typed system leverages types to make code _more_ refactorable in _less_ time with _fewer_ bugs. But hey these are just our anecdata too. Here's what I'm not doing: spreading FUD about Python or Clojure or JS, I'm too busy loving what I do.

- From a hiring perspective, Haskell programmers as a group offer an immense strategic advantage, and it's mainly _because_ they had to learn Haskell on the weekend and it wasn't handed to them. That shows passion and grit. I've built two teams from scratch now in totally different circumstances and it is simply breezy to find a wide variety of experience levels to craft a team from; they are by far the best teams I have ever worked with, with zero duds. The community is strong and excellent and helps each other out as far as job hunting goes.

Don't blame Haskell if it didn't stick, don't hate on Haskell if you find it intimidating or pointless. If anything, you should be grateful that there is a language that is actually different enough to attract a different kind of programmer, lord knows it's why I'm here: after having jobs in Java, C++, Perl, Ruby, JS, Visual Basic, Hypercard, you name it, it was nice to see that there's a different way to do things. It's really fun, there's always more to learn (not true of every language btw), and finally, it kicks serious ass on the performance side (as GC/runtime languages go).

What I Wish I Knew When Learning Haskell

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