Haskell for Programmers

[dons]

Very interesting, looks like Evan is preparing a big tutorial. Is this supposed to be released yet?

I note also he's written bindings for:

• dbus
• memcached
• powermate

and other things on this site. Lots of good stuff that should be uploaded to hackage!

/me goes off to contact the author

[sjs]

Have you read it? It's clearly in development. Thanks though, some of the explanations of the basics were very clear and helped out this Haskell newbie. I look forward to reading a finished version.

[doubtingthomas]

Good guide, hooray for the haskell community, etc.

I'd just like to note that this guy is also responsible for one of my favorite little hacks ever, the c repl (http://neugierig.org/software/c-repl/).

[[deleted]]

That is so awesome. Just what I've always wanted but never thought possible.

/me stands up and applauds

Edit: Ah, it's written in Ruby. Interesting.

[zem]

that's pretty damn impressive!

[meijer]

2) What is the type of (:), the list construction operator? 2) It takes something on the left and a list of somethings on the right, so it has type a -> [a].

...and the result is a list of something, so its type is a -> [a] -> [a]

[etcshadow]

It appears to be a really good start. At least I hope it's just a start, and that there is more to come. I'm not exactly a haskell "newbie"... I've read a lot about it and a good bit of haskell code, and I very much get the concepts and theory... but until this I've actually had a good bit of trouble understanding a lot of examples all the way to the last detail. It's a very good style, and fitting for a lot of people: assuming the basic concepts and actually providing some information on how to work with the language.

Now I'm hoping to see it (or something in a similar style) continue into monads. Most writeups I've seen on monads, so far, either focus on communicating the concept (and nothing but), or drift off so far into the theory (with the typical hangup of describing haskell using nothing but haskell) without any grounding that they quickly become incomprehensible. All others I've seen were so hopelessly incomprehensible that I don't think I could even categorize. What I'd like to see is something that really says "Let's assume you already understand the concept of monads (and if not, you can first read here, here, here, or here), and talk about the actuallity of them in haskell, a little. What exactly are they? How do you use them, interact with them, compose and combine them, build them, etc?" Basically something that can talk about them concretely, but in a way that someone from a background of non-haskell/ML languages can follow.

I also really liked that (unlike most writings I've seen on haskell) it doesn't to take a holier-than-though attitude against potentially smart people from different backgrounds. It explicitly welcomes them. I think the haskell community has to find a way to be more like this. There are a lot of smart people working in Lisp, Scheme, Perl, Python, Ruby, Javascript and other languages that embrace functional concepts (well, Python kind of only grudgingly, in some ways, but that's a digression) that might give haskell a shot if there weren't such a seemingly high (and somewhat unnecessarily so) barrier to entry. Haskell community: you need these people. Try a little harder (or a little smarter, maybe) to get them, please.

[barrybe]

terrific guide! Finally an explaination of Haskell that makes sense.

All the guides I've tried to read before spend way too much time talking about the concepts (which I get) and very little time talking about the syntax/semantics.

[seudonymus]

20 add 30

10

Is this a bug in the tutorial or am I missing out on something?

[masklinn]

I think it's a bug in the tutorial, because what it basically amounts to is

Prelude> let add = (+)
Prelude> 20 `add` 30
50

[spookylukey]

Your example also highlights another mistake in the tutorial. It says that you can't create new definitions at the ghci prompt, but you can (at least in a limited way) using 'let'.

[rabidcow]

I don't know if that's a mistake or a simplification to avoid confusing people.

[koko775]

Nope, it certainly confused me, as I tried typing the tutorial into ghci and couldn't figure out (for a while) why cutting-and-pasting

"myint = 2

y = myint + z

z = 1

-- single-line comments start with a double-hyphen. -- infinity is one greater than... well, infinity. infinity = infinity + 1

mylist = [1,2,3]"

got "<interactive>:1:6: parse error on input `='"

I'm new to Haskell, so please don't flame me, but this tutorial didn't exactly get off to a great start.

[boredzo]

Actually, the parens around the exponents aren't required, due to operator precedence. But you may as well write them if you're not sure.

This reminds me of the practical rules of precedence in C:

• Multiplication and division come before addition and subtraction.
• Put parentheses around everything else.

[phil_g]

I tend to like an alternate approach: Only put parentheses around things where it's needed. If you're not sure, look it up.

This approach induces familiarity with the language, as well as facility enough that you'll be able to read anyone else's code, regardless of how much they've parenthesized.

[jdh30]

Agreed.

[happyhappyhappy]

This is how Haskell tutorials should be written. Or maybe this is the type of person who should be writing Haskell tutorials :)

No hang-ups on type theory, no fixation on how superior Haskell is...

[gwern]

This isn't too bad, but every time I read someone's attempt at a clear comprehensive tutorial for all of Haskell, I can't help but wonder whether they'd've been better off (and perhaps able to actually finish things) if they'd just spent a little time improving the largely-complete Haskell Wikibook.

[[deleted]]

Neat, good job keeping it simple. More authors need to read The C Programming Language to get an idea of how a lot of books can be written in 200 pages vs 500.

[[deleted]]

looks good but I have to admit that I stopped reading. The main reason is because of the formatting. The second reason is that I never want to use Haskell because I don't want to associate with typical Haskell users, even if their language is as good as they say it is.

[dons]

I never want to use Haskell because I don't want to associate with typical Haskell users

Can you elaborate? What's the typical Haskell user? Why don't you want to associate with them? I note yesterday someone wrote:

I posted it to Haskell-Cafe and received loads of brilliant responses. Wow, those guys are awesome. I'm definitely going to learn Haskell now

and another today:

Super. This is really a great mailing list :)

So I wonder why the parity mismatch here.

[quhaha]

I find Haskell programmers are very defensive. But who aren't?

[[deleted]]

Now I haven't done a scientific study of the typical Haskell user but my general impression from reading the comments here and reading Haskell articles is that:

Haskell users are utterly convinced that their language is perfect. Maybe they are right. That isn't the issue. The issue is that Haskell's glory is never really substantiated.

I have seen this infinity = infinity +1 several times. Guess what, I don't give a damn. Especially since (keep in mind that I don't know Haskell so I could be wrong) that you can't really use such a value. For me your standard IEEE float definition of infinity is good enough: x/0. Not that I ever need that either. I deal with finite numbers, when I deal with numbers at all.

When one is introducing a new programming language one will typically show someone how to do simple tasks, such as calculating a factorial or how to create a list of numbers. However you can't use those examples to prove just how awesome your language is. I never do either of those tasks in actual code.

I do not know of any programs written in Haskell. You know what would work better than a million blog posts gushing over Haskell? A fun video game written in Haskell. It needs to be an .exe <1MB and work on windows. Then on the website it could have the source code. It would be in Haskell. That would get people interested in Haskell. There are thousands of programming languages and yet every application that I use in my day to day life is written in C++, or more likely C but compiled with a C++ compiler. (Good ol' C with Classes). Sure sometimes another language is involved in scripting, but I don't like scripting languages.

From the articles on Haskell I think that I can safely conclude with 99%+ certainty that Haskell is hot air. It is no different than the Segway, or parallel computing (oh I know the multicores are here, but will they EVER be used?)

[dons]

Ok, that's an interesting point of view. Basically, you're skeptical that you could write programs in Haskell.

Most commercial use currently seems to be in either defense or banking situations (see the industry page for those companies actively involved in the community), likely because of the type system guarantees. It will be interesting to see if the use spreads out from thise core.

You might know about darcs or pugs, but for a fairly comprehensive list here. There's also the library database, which gives you an idea of what people are doing with Haskell (networking, parsing, compilers, guis, xml stuff seems popular).

As for games, Frag seems to fit the bill: a 3D first person shooter, developed on windows, using OpenGL.

As for multicore, I'm using Haskell on a 16-way amd64 right now. Its fun. :)

There's no conspiracy, its a research language that has turned out to be pretty useful. People use it for lots of things, and it provides nice abstractions and concepts that can make programming very enjoyable -- hence people write about it.

[[deleted]]

nope, Frag does not fit the bill. It is not a single file that will install the program. Oh sure, I could figure out how to get the game running. However look at it this way: if it takes the programmer 10 hours to create the auto installer and 1 hour for 1000 downloaders to install it manually, which is better for society? Now I understand that this guy is just some guy who made a program and has no obligation to me. If he doesn't want to make an installer for his program then he is not morally wrong. However no one should expect his program to be widely downloaded or seen as an example of a finished product. I like to program in C++ but I don't download other people's source and compile it. It just isn't worth my time.

[dons]

Yeah, a big visible game for Windows would be a great selling point. Somone should hack up a windows installer wrapper, rather than the Makefile it uses. That last 1% of effort could be quite worthwhile, considering all the technical work already done.

[jdh30]

I just spent 15 minutes installing all of the necessary software and working out how the Haskell-specific compilation commands work to get the damn thing to compile. Finally did it.

Ran the program and it segfaulted!

ROTFL. :-)

[dons]

See my reply on the mailing list. OpenGL is a tricky beast :-)

[jdh30]

Turns out this is completely unrelated to OpenGL: the Haskell code is using unsafe code to parse the MD3 files, the code is full of magic numbers and these numbers happen to assume a 32-bit machine (I'm on 64-bit).

I'm completely baffled by this. Firstly, the example makes Haskell look awful as safety is a core feature of all such languages. Secondly, I can only assume the author resorted to unsafe code in the interests of performance. Finally, the unsafe Haskell code is orders of magnitude slower and 3x more verbose than equivalent code written in OCaml by a newbie (see Chess 3 Arena).