Running a Startup on Haskell | Hacker News Reader

Running a Startup on Haskell

infoq.com

121 pointspuredanger37 comments

For anyone who'd prefer a direct video link rather than the infoq flash player: http://d1snlc0orfrhj.cloudfront.net/presentations/11-sep-run...

(Retrieved by setting my User-Agent to that of an iPad, which causes infoq to serve up a <video> tag.)

Thanks for the link, and for the hack. That's quite handy.

Haskell web frameworks are maturing rapidly and the language is a joy to work in, once you learn how to approach problems in it. Haskell has probably not reached the peak of it's popularity yet (and frankly it's overdue for some mainstream love).

I think Haskell (and functional languages in general) will become increasingly popular as it is (they are) a powerful way to deal with concurrency and can easily take advantage of multiple processors. Languages are tools in a developers toolbox, and Haskell turns out to be a powerful one for several growing problems.

It's not just that. Haskell has exceptionally strong typing and containment of mutable computations, making it much easier to write correct programs. When a module compiles, it's usually pretty bug-free.

Space leaks, stack overflows (foldl vs. foldl'), failed pattern matches (head []), etc. There are tons of bugs lurking in well-formed Haskell programs.

Tons being a vast overstatement. I mean, you could exploit these things to cause bugs, but really do you encounter them on a day to day basis? I know I rarely if ever have.

How does the strong typing compare with Java/C#? Thanks.

Several things jump out immediately:

  - Haskell has exceptionally thorough type inference (almost all type declarations are optional).
  - anything impure (e.g. involving an I/O) is typed as such
  - the types are easier to read and tend to give a good idea of what the function in question is doing
  - much more complicated types are readable
  - idioms like Monads lead to a lot of code that is much more abstract and generic than anything I've seen in Java. There are tons of library functions that can work on lists, or IO things, or parsers, or random values...

Some things that I found particularly cool in Haskell: - functions (and even constants!) can be polymorphic on their return type. The function read, for example, always takes in a String but returns whatever type you happen to need. - You can easily express things like a "list of list": [[a]]. I don't even know how to begin writing a function like join in Java. (On lists, join takes a list of lists of something and flattens it.)

Overall, I've found Haskell's type system to be much more useful, and much less of a burden, than Java's.

That said, I'm just a college student with limited experience with either language. I've used Java more than Haskell but I've been using the latter more recently; I've never used C#.

Maybe it's better with more experience or when you're reading your own code, but I find that reading a Haskell program is often like reading a math paper - you can't skim it; you have to slow way down and study it, one line at a time, and look up the definition of each term as you go and think about what it means, and try out simple examples. And sometimes you don't have the background to understand the underlying concepts, so you have to study a prerequisite first.

So I think to like Haskell, you have to truly believe that more abstraction is better. It's very much a mathematician's language.

The thing is, when writing code, I don't want to write a math paper. When I'm done, I want it to be as smooth and easy to read and as obvious as an article in the New Yorker.

"When I'm done, I want it to be as smooth and easy to read and as obvious as an article in the New Yorker."

Your metaphor is apt; if your code is going to be that smooth, you need to learn Haskell to the same extent you know English for the New Yorker. The Internet suggests that the New Yorker is written for a "10th grade reading level", but of course the average American has between an 8th or 9th grade level.

It does get easier with practice to read the language, and what's left after that is whatever core difficult the code being expressed has regardless of the target language, the essential difficulty. Haskell can hardly be blamed for bringing that to the foreground where other languages stuff it in the background.

If I learn Haskell well and start writing code that's idiomatic for that audience, I'm limiting my audience to the few people who also know Haskell (and the particular Haskell idioms I'm using). It's like writing in Esperanto instead of English. My ideal is more along the lines of the Python examples that Peter Norvig writes, which can be understood by pretty much any programmer, even if they're not all that fluent in Python.

It has nothing to do with being a mathematician. There are common patterns as any language. Those patterns often end up as higher order functions. But at some point, it becomes very natural to read.

The higher order monadic join concept cannot be implemented in java but a simpler function in terms of flattening a list of list is easy enough. In a functional language a simple way would be to fold over (++) append.

so in java a simple way would be to initialize an l = arrayList and then do a foreach on each list in the list of the lists and foreach element in each list add it to the arrayList l. Not as elegant, much more how instead of what but 4 noisy lines max.

C# has list.selectMany( _ => _ ) for that.

> In a functional language a simple way would be to fold over (++) append.

Though you probably wouldn't want to do use that approach for performance reasons.

Does Haskell offer any tangible, practical advantages or benefits over other languages in the context of a web framework, aside from just "if you prefer a functional style of programming and you're working on a web project, here's a way to do it"?

I'd love for somebody to convince me why a Haskell approach to web frameworks is superior to Python/PHP/Ruby/JS beyond the usual "it's a matter of taste" argument.

Haskell's advantages (and disadvantages) as a Web Framework are generally the same as in any other application domain: performance, concurrency, and correctness.

While I agree regarding correctness and concurrency, I wouldn't emphasize performance, even for Java and .NET, whose GCs are more developed, tuned and tested in the production environment than Haskell's one.

Edit: And for Haskell, achieving needed performance can be quite tricky with regard to its laziness.

Edit: And for Haskell, achieving needed performance can be quite tricky with regard to its laziness.

But Snap is driven by enumerators/iteratees (via the enumerator package), which make it much easier to do fast near-constant space IO.

I have built a web application that uses Snap to query large (parse) treebanks, and it was easy to make it performant.

There was some discussion on HN about the Snap Web framework benchmarks relative to some other frameworks: http://news.ycombinator.com/item?id=1380405

No .Net in there, though.

For one, GHC gives you M:N threads with the runtime handling the async IO under the hood, making it possible to write code in a simple blocking style while still getting use of all your cores and having fast IO. This is also true for Erlang, Go, and a few others, though, and it's not terribly relevant for lots of simple web code, but it is a practical advantage.

"Does Haskell offer any tangible, practical advantages or benefits over other languages in the context of a web framework, aside from just "if you prefer a functional style of programming and you're working on a web project, here's a way to do it"?"

At the moment, my answer is "Not yet, but ask again in a year." There are tons of interesting things happening in the area of letting you have "performance, correctness, rapid development and prototyping, pick three", but they're still in the early phases yet.

I only read the slides, but at one point the author mentions that they've built an hybrid app using (Haskell + C#).

Next, the author mentions about several limitations that C# has and that Haskell has a much better approach.

So, why use C#? Why not only use Haskell?

Our app consists of two parts: there's a client component that integrates into Outlook, and a server part that does all the actual heavy lifting.

The client-side code is written in C# because the .net APIs for Office are the easiest to deal with.

He mentions that later on during the Q&A session

Could you please repeat it here so we don't have to search? Thanks.

Their application is an extension of Outlook, which only has a dot.net API.

I wonder why they didn't use F#.

He answered that too: language maturity. He was unfamiliar with the .NET ecosystem in general, and the availability of help/expertise/examples etc was much greater for C# than F#.

Brian just didn't wanted to have another risk, because F# is less mainstream than C#.

Ok, thanks.

So no-one has built a QuickCheck for Ruby or Python?

I'd like to use this "property-based testing" he stressed.

There are plenty of implementations linked from http://en.wikipedia.org/wiki/QuickCheck. (I'm not sure in what state they are though.)

anyone watch this yet? worth the 50 minutes? is there a transcript?

If you're interested in Haskell then yes it is a good presentation. In my opinion, Bryan is one of the more thoughtful speakers around.

Slides are here: http://bos.github.com/strange-loop-2011/talk/talk.html#%281%...

Navigation uses keyboard arrows.

He had a similar/same talk about a month prior and here is the video on Vimeo if you're not a fan of InfoQ's format:

http://vimeo.com/27192476 (Bryan O'Sullivan - Building Solid Distributed Applications with Haskell and Riak)

Absolutely!

Terrific video! Thank you very much for posting! UP!

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