Re: [Haskell-cafe] Re: Is Haskell a Good Choice for Web Applications? (ANN: Vocabulink)
Chris Forno (jekor) wrote: The idea is that I spent years studying different languages, generally with a textbook. The textbooks tend to focus on teaching rules and grammar, with a little bit of vocabulary and dialog each chapter. I think the focus should be reversed. I think it largely depends on the learner. Some people find vocabulary easier, or more interesting, others not. I have a hard time learning a lot of isolated facts (e.g. vocabulary), but I find it easier and more enjoyable to learn a rule that I can apply many times. But I know people who are the exact opposite. I wouldn't want to make an absolute rule. I generally like rules that will save me a lot of memorization. I hate rules that force me to memorize a lot. I am not good at memorization. I consider myself to be a highly logically-oriented (audio-digital?) learning type, as I expect many programmers are. However, I still don't remember most grammar lessons. The only way I successfully became fluent in a language (Esperanto) was through immersion, and that wouldn't have been possible without a decent vocabulary to start with. I totally understand, and I agree. And with only a few exceptions, I would say that vocabulary is more useful than grammar (even if I find the former harder to learn). That said, I cause Esperanto as a good example of a language with rules that make learning easier. In Esperanto, the ending of a word tells you if the word is a noun, a verb, an adjective, a subject, an object, etc. Knowing these rules makes it much easier for you to learn Esperanto. When I learn a language, I like learning rules that will make language learning easier. That being said, Esperanto, and even Japanese sentence structure perhaps is not as different as an agglutinative language like German. I'll need to study it more to find out. In the specific case of German, word order is a lot more important than any other language I know. You can get everything else about grammar wrong, but as long as you put the words in the right place people will probably understand you. But if you get everything else right, and put the words in the wrong place, you won't be understood. Absolutely. I'm not trying to claim that you only need 1,000 words to become fluent, like some courses claim. Ok. I probably misunderstood something. The idea is that once you can begin to read with a dictionary by your side you'll begin learning much faster because you can focus on reading what *you* are interested in rather than some contrived dialog from a textbook. In my case, the things I'm interested in are too technical :-( I've had a hard time finding things that are interesting and are simple enough for me to read in German. But I'll get better. So far I've been focusing on Japanese. I only have 15 or so stories currently. They take a bit of time to create ;) For now, the navigation is basically to click the Latest Links link in the header bar or in the Latest Links box. Ok. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is Haskell a Good Choice for Web Applications? (ANN: Vocabulink)
Hi Chris, Thanks. This should be interesting. I currently work as a web developer and I've been wondering how easy or hard it would be to develop web applications with Haskell. So I'll be interested in reading our article. On a separate topic, I also took a glance at vocabulink.com. I'm interested in languages (I am fluent in English and Spanish and speak advanced German). I will have to disagree a bit with your pedagogy: 1) You say that grammar doesn't matter. Well, for some languages it matters more than others. German, for example, has a very particular word order that takes some effort to learn, and if you get it wrong people really won't understand you. In German it's ok if you conjugate wrong, but it's not ok if you put words in the wrong place. Second, some people actually enjoy grammar better and find that grammar helps them understand the language. I am one of those people. Different people learn differently. I learn rules more easily than disconnected words. When I learn vocabulary I do better by learning word families, and so on. The Germanic languages rely heavily in word derivation (not so much English) so that can be important for learners like me. 2) Your analysis of word count is flawed. Sure, most of the words you read come from a very small vocabulary set, but most of the *meaning* in a sentence comes from the more obscure words. Imagine that you read this sentence: In the newspaper I read that the __ said that the problem is that the river has too much . In this sentence you can understand 90% of the words, but you have almost no idea of what's happening. What your word count test really shows is that human languages have a lot of redundancy. You could omit the word the from the above sentence and you would understand it almost as well. The word the is common and contains very little information. That said, do you have any stories in German? I can't figure out where to get the stories. Daniel. Chris Forno wrote: I decided to find out for myself. You can find the results at http://jekor.com/article/is-haskell-a-good-choice-for-web-applications Included is the source code for the web application powering http://www.vocabulink.com/ The source is roughly 2,000 lines of Haskell, along with some SQL and JavaScript. It's written in literate style and includes a 75-page PDF. It demonstrates and explains how to: * use FastCGI to communicate with a web server (nginx in this case) * move data to and from a PostgreSQL database (HDBC) * authenticate users with cookies * interact with users via asynchronous JavaScript and JSON (AJAJ) * collect data with HTML forms (formlets) * communicate with users via email * cache with memcached * implement a custom forums system (with threaded comments) I make no claims that the code is elegant or idiomatic. It is however real code that's running in the wild. And I hope it's useful to anyone else considering doing web development in Haskell. I welcome and encourage your feedback! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] When is it OK to create a new mailing list?
Duncan Coutts wrote: I wanted a mailing list for my project WxGeneric and I am wondering when it is OK to do so? How big must the potential audience be? Is there any kind of etiquette or guidelines? ... Yes, I would recommend for smaller project-specific mailing lists that you take advantage of the community server which is set up for this purpose. We provide code hosting, project webspace, shell access, trac instances and mailing lists. You can pick and choose, you don't need to use all of them. Would this not fit well in the wxHaskell mailing list? That list is not very high traffic and there is an obvious overlap in the target audience. Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell vs Clean (speed comparison)
Hi, I think the mail server may have been acting up earlier. I sent this to Haskell-beginners, but it more properly belongs here. I found something interesting. General wisdom is that Clean (or OCaml) is faster than Haskell. The claim is often followed by a link to the Debian shootout. But on closer inspection, I question this conclusion. The Debian shoot out actually has four sets of benchmarks: 1) Intel 32-bit one core. 2) Intel 32-bit quad-core. 3) Intel 64-bit one core. 4) Intel 64-bit quad-core. It turns out that Clean is only faster for (1). For the others, Haskell is faster. Here I compare Haskell, Clean, OCaml, Lisp SBCL, C# Mono and Fortran because they are all in the same ball mark: 32-bit sing core [1]: Lisp, Fortran, Clean, Haskell, C# Mono. 32-bit quad-core [2]: Haskell, C# Mono, Lisp, Clean, Fortran. 64-bit sing core [3]: Fortran, OCaml, Haskell, Clean, C# Mono, Lisp. 64-bit quad-core [4]: Haskell, OCaml, Lisp, C# Mono, Fortran, Clean. Notes: * The order is fast language first. * There are no results for OCaml for 32-bit. * Lisp is List SCBL whatever that is. Tentative conclusions: 1) Haskell makes very good use of multiple cores. It smokes Clean. 2) For single core, they are neck and neck. Whether Clean is faster depends non the architecture. What do you think? Daniel. P.S. [1]http://shootout.alioth.debian.org/u32/benchmark.php?test=alllang=alld=dataghc=onocaml=onsbcl=oncsharp=onifc=onclean=oncalc=calculatebox=1 [2]http://shootout.alioth.debian.org/u32q/benchmark.php?test=alllang=alld=dataghc=onocaml=onsbcl=oncsharp=onifc=onclean=oncalc=calculatebox=1 [3]http://shootout.alioth.debian.org/u64/benchmark.php?test=alllang=alld=dataghc=onocaml=onsbcl=oncsharp=onifc=onclean=oncalc=calculatebox=1 [4]http://shootout.alioth.debian.org/u64q/benchmark.php?test=alllang=alld=dataghc=onocaml=onsbcl=oncsharp=onifc=onclean=oncalc=calculatebox=1 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell vs Clean (speed comparison)
Gwern Branwen wrote: Perhaps it's just that no one has parallelized the Clean programs? Haskellers seem to care about the shootout programs much more than Cleaners do. I'm not sure about the second comment. I haven't seen the Haskell site mention the shootout, whereas web pages about Clean often do. Perhaps what happens is that Haskell has a larger community, so there's more chance that someone will submit an optimized program. Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell vs Clean (speed comparison)
Bulat Ziganshin wrote: 32-bit sing core [1]: Lisp, Fortran :) this test measures speed of some programs, not languages. I know. But since I know that you know that too, I opted for brevity. How can we benchmark a programming language? We can't - we benchmark programming language implementations. How can we benchmark language implementations? We can't - we measure particular programs. Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] data vs type
Hello all, I'm trying to figure out how 'data' and 'type'. I haven't read any documentation because I can't find any. Could someone point me to a document explaining these? I'm happy to RTFM, I just need to know where the FM is :) Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] data vs type
Ketil Malde wrote: I'm trying to figure out how 'data' and 'type'. How data and type...what? :-) oops... work :) Generally, 'type' introduces type synonyms, i.e. just gives a new name to an existing type, while 'data' defines new (algebraic) types. So you can use type Name = String Ah. Thanks. Did that help? Yes, a lot. :) Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] data vs type
Christian Maeder wrote: http://www.isi.edu/~hdaume/htut/tutorial.pdf 4.5 Data Types 47 8 Advanced Types 103 8.1 Type Synonyms Thanks! Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell vs Clean
Hi all, How would you compare Haskell and Clean? It looks like they are both pure functional languages with very similar syntax. It also appears that Clean is faster than Haskell, it appears to be fairly fast. I'm curious to learn about relative advantages and disadvantages of each. Thanks for the help! Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to print a string (lazily)
Hello, I've been studying more Haskell and I've improved a lot. But I just hit a small problem. I want to print all the elements of a linst (putStr). I'd like to write something like this: print_list [] = do putStr print_list (x:xs) = (do putStr x) print_list xs I know this is wrong, but I hope you can see what I'm trying to do. I know of other ways I could print a list. For example: print_list xs = do putStr(join xs) where join [] = join (x:xs) = (show x) ++ \n ++ join xs But the thing is, I want to write a lazy version of this function. It's not that I need such a function, I'm just trying to learn Haskell. Any suggestions? Question: What do you call a function that has side-effects? (like putStr) I know that function is the wrong term. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to print a string (lazily)
Sebastian Sylvan wrote: Others have already replied with a solution, but it looks to me like what you're missing is how to sequence commands, which is the whole purpose of the do notation. print_list [] = return () print_list (x:xs) = do putStr x print_list xs The do notation is used here to sequence to IO actions (which answers your second question), first it prints out the first character in the string, then it calls itself recursively to print the rest of the list. Thanks! And yes, I'm just learning how to sequence commands/actions, so I know I'm missing a lot. The empty list shouldn't print an empty string, it should do nothing (that is, just return IO () because that's the return type of print_list) Yeah... I just didn't know how to do nothing with Haskell. Thanks! Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to print a string (lazily)
Chris Kuklewicz wrote: What does lazy printing mean? I assume it means you evaluate the head of the list, print it, then recursively do this for the tail of the list. With an infinite list you will get inifinite output. I assume it does not mean you evaluate the whole list before printing anything. This would prevent infinite lists from producing output. Yes, that's exactly what I had in mind. I wanted to print [1..] (an infinite list) with each number on a different line. Thanks for the help. Yes, the function works now. main = do let hw = [Hello, ,World,!] mapM_ putStr hw mapM_ putStrLn hw putStr (unlines hw) -- see also: unwords, words, lines printList hw Cool. I didn't know about (un)words and unlines. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to print a string (lazily)
Neil Mitchell wrote: All Haskell functions are lazy, hence there is no need to write a lazy version of your print_list function. I think the function you probably want is: putStr (unlines xs) Hhmm... that does work, and I'm a bit surprised that it does. I guess I'm still stuck in the eager computation mindset. I would expect putStr to have to wait for the (unlines xs) to be finished before doing any printing, but it doesn't. Some day I'll get the hang of this lazy evaluation thing. :) The first one has fewer monads, so I prefer it, but take your pick :) Monads scare me, so I'll pick the first :) Thanks! Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell vs OCaml
Branimir Maksimovic wrote:
Well I want simple loop for(int i =0;i10;++i)doSomething(i);
in haskell that would be
for begin end f | begin /= end = do {f begin ; for (begin+1) end f}
| otherwise = return ()
How about:
result = [ doSomething(i) | i - [0..9] ]
I guess it depends on what doSomething() does.
Cheers,
Daniel.
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Re: [Haskell-cafe] Haskell vs OCaml
Tomasz Zielonka wrote: When it comes to Haskell, speed is mostly an implementation issue. Of course, there are many problems with making Haskell programs run fast, but on the other hand there are also many opportunities. For example recent developments of GHC promise that Haskell will be one of the best languages to use on SMP / multicore systems. So we can expect Haskell to get faster as GHC evolves and multicore systems becomre more common... There are many differences (Haskell on the left): - pure / impure Let's see if I understand this one. Haskell and OCaml both treat functions as first class objects, including the ability to pass functions as arguments or return functions. But OCaml allows you to change the value of a variable and that's what makes it impure. Yes? Does this mean that it's harder to prove an OCaml program correct? Or that you have to be careful to not accidentally change the value of variables? I've taken a glance at an OCaml tutorial, and the syntax looks a little more difficult than Haskell's (e.g. rec for recursive functions). - pretty / ugly :-) Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Speed
Hi all, I'm taking a look at the Computer Language Shootout Benchmarks. http://shootout.alioth.debian.org/ It looks like Haskell doesn't do very well. It seems to be near the bottom of the pile in most tests. Is this due to the inherent design of Haskell or is it merely the fact that GHC is young and hasn't had as much time to optimize as other compilers? For example, another very slow language is Ruby. In Ruby's case, there is a design factor that will always make it slow. I wonder if Haskell is in a smilar situation. Yes yes, I know that a high level language trades CPU time by programmer time. I'm still interested in the CPU time question though :) Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Tutorial uploaded
S Koray Can wrote: As a newbie... I agree that a newbie should be able to write this fairly early on: main = do x - getLine() putStrLn (The answer is ++ show(fib(read(x I'd agree for some definition of 'early'. I'll elaborate: [snip] The above code snippet contains typeclasses (show, read, monadic IO, lists), syntactic sugar (do, -). When you say a 'newbie' should be able to write that early on, I'd interpret that as 'a newbie should be able to regurgitate this early on' Well, I'm a newbie, and I wrote it. I have enough understanding to generate that code, even if I don't understand it all. This is what I know: * x is a string, fib wants an int, and read turns a string into a number. * The answer is is a string so you need ++. ++ expects a string, and show turns a number into a string. So, yes, I need *basic* knowledge of types (strings vs numbers) and the functions that convert from one to the other. But that's it. I don't need to know that do and - are syntactics sugar, or what a monad is (heck, I don't know those things). I think that the following is suitable for chapter 1: --//-- main = do putStrLn What is your name? name - getLine putStrLn(Hello ++ name) --//-- You don't need to learn about monads, or classes or lists for this. Yes, not even lists (Use ++ to catenate strings). All you need to know is strings, and that name - getLine gets a line from input and puts it in 'name'. I think that this is suitable for chapter 2: --//-- main = do putStrLn Please type a word: word - getLine putStrLn(This word has ++ (show( length word)) ++ letters) --//-- Here you learn about numbers, and converting numbers to strings (show). And this is for chapter 3: --//-- main = do putStrLn Please type a number: number - getLine putStrLn (number ++ ! = ++ (show (fac read(number))) --//-- Here you learn about converting a string to number. At some point between chapters 1 and 3 you'd learn how to write 'fac' (I guess chapter 1). Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Statements spanning multiple lines?
J. Garrett Morris wrote: Indent the second line: pythagoras n = [(a,b,c) | a -[1..n], b -[1..n], c -[1..n], a = b, b c, a*a + b*b == c*c] Thanks! Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Statements spanning multiple lines?
Greg Buchholz wrote: You might also like to try the slightly more efficient... pyth n = [(a,b,c) | a - [1..n], b - [a..n], c - [a+1..n], a*a + b*b == c*c ] Cool. I'm amazed that actually works. I've been writing filters upon filters in all my functions because I didn't realize you could write things like that. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Tutorial uploaded
Robin Green wrote: Whilst localising IO to a small part of the program is generally a good idea, beginners should not be scared off by the thought that IO in Haskell is so hard it has to be covered on page 94. This is not the case. It should be introduced on page 1. As a newbie... I'll agree with Robin. I /did/ think that IO in Haskell was probably very difficult because it's covered in page 94. I skimmed through YAHT and IO is covered wyyy deep into the document. I haven't read that section yet, but there is a lot of content and to me it looked like it must be something difficult. I guess/hope that when I get around to reading it I'll find out that it's not as scary as it looks. If people want Haskell to be treated as a practical language, not just something for doing academic teaching and research with, it should be taught as a practical language - which means that things like IO and space/time usage come to the forefront. Until recently I thought of Haskell as something you would use for Calculus and the like. It seemed like a tool for academia. You may be interested to know that one of the reasons I started looking at Haskell just now was to help a friend understand Calculus (the other reason is that Haskell looks very cool). Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Functions with side-effects?
Hi all, I'm a Haskell newbie and I don't really understand how Haskell deals with functions that really must have side-effects. Like a rand() function or getLine(). I know this has something to do with monads, but I don't really understand monads yet. Is there someone who might explain this in newbie terms? I don't need to understand the whole thing, I don't need a rand() function right this minute. I just want to understand how Haskell separates purely functional code from non-functional code (I understand that a rand() function is inevitably not functional code, right?) Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Tutorial uploaded
Udo Stenzel wrote: Strange, I always thought predictable, understandable and above all correct code would be the primary goal, with small and quick code coming later. Depends on what you mean by quick and small. Do you mean that the program should execute fast and have a small memmory foot-print? If so, I agree. If what you mean is that the programmer should be able to finish the project quickly and it shouldn't have too many lines of code, then I think those features are important. To write interactive Haskell code well, you have to understand higher order functions. That's scary, that you need advanced knowledge just to do IO. Unless you want to teach people to program as they would do in Basic, that is. I don't know what you mean by that. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Tutorial uploaded
Henning Thielemann wrote: IO is always complicated: I have never once thought it was complicated. All I've ever needed are print() and readLine() and those shouldn't be complicated IMO. And I wouldn't want to wait for page 120 to learn how to do that. My programs are not going to be useful if they can't get user input or produce output. I don't want to wait for page 120 to write my first useful program. So I prefer starting a tutorial without IO, interaction in GHCi and Hugs should be enough for the beginning. GHCi and Hugs are enough for the /beginning/ yes, but that doesn't mean that IO should go on chapter 7. How about putting it in chapter 2? Cheers, Daniel -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Functions with side-effects?
Thanks for all the help. I think things are much clearer now. And this bit: main = do putStrLn Hello, what is your name? name - getLine putStrLn (Hello, ++ name ++ !) Looks quite straight forward. I just wrote my very first IO program with Haskell: --//-- main = do x - getLine putStrLn( show(length x) ) --//-- That's not so scary. The next thing I need to figure out is how to act on the input data itself (not just its length). For example, if I wanted a program to output the nth element of the fibonacci sequence: --//-- $ ./fib 12 144 --//-- My first inclination would be to write it as: --//-- main = do x - getLine putStrLn( show(fib x) ) --//-- Of course that won't work because x is an IO String and 'fib' wants an Int. To it looks like I need to do a conversion IO a - b but from what Cale said, that's not possible because it would defeat the referential transparency of Haskell. Hmm... there must be a way to solve this problem though... In any event, thanks for the help. I'm learning :) Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Tutorial uploaded
Udo Stenzel wrote: Unless you want to teach people to program as they would do in Basic, that is. I don't know what you mean by that. You will soon. Once you get used to composing functions instead of sequencing actions, you'll appreciate the difference. Ah. Yes, I do think I understand the difference (my math background is stronger than my programming background). Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Tutorial uploaded
Daniel Fischer wrote: P.S.: In May, there was a 'Daniel Carrera' around, too. Isn't that a strange coincidence? That was myself, using a different email address. I didn't get too far with Haskell that time, but I remembered that I liked it, so I'm going back to it a bit now. But I'm still a newbie :) Notice that I was already familiar with a few, very basic concepts (what is functional programming?) Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Functions with side-effects?
Creighton Hogg wrote: x is a String, getLine has type IO String. That's what I was getting at in one of my last e-mails. Hmm... let's see if I understand: * getLine() has type IO String. * The - will convert an IO String to a plain String * So if I do x - getLine() then x has the type String. So, the - effectively ammounts to an IO a - a conversion. In another email John Hughes said that one could think of IO a as a set of instructins for obtaining a. I guess that means that IO is a sort of imperative layer that helps the purely functional code interact with the outside world. So I can have an IO bit (e.g. a do-block) that calls functions (which are purely functional code) but I can't have a function that executes any IO. For example, it is not possible to write a function my_read_file that could work like this: my_data = my_read_file(my_file.txt) Correct? Otherwise this would be a function that is not referentially transparent. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Tutorial uploaded
Sebastian Sylvan wrote: Well, I certainly disagree there. I'm not advocating going into a full-blown explanation of monads, just enough to actually be able to write a real stand-alone program after the first chapter. They only need to know that do-notation is for sequencing computations, and (-) is for binding a name to the result of a computation. That's it! As a newbie... I agree that a newbie should be able to write this fairly early on: main = do x - getLine() putStrLn (The answer is ++ show(fib(read(x Now, you just said do-notation is for sequencing computations. Would it be fair to say that do-blocks are imperative blocks in an otherwise functional program? You could spend the next ten chapters with coding examples that are not very IO-heavy, and lead with a good example of doing as much as possible in the pure world (as well as pointing out every now and then whenever a particularly good IO-separtion was achieved - to emphasize that it's good practice). When someone who has programmed before learns Haskell and gets the impression that IO is beeing left for later because it's hard they might think bah, what a rubbish language, IO in Visual Basic isn't hard at all!. I would agree with both paragraphs. Show basic IO and show that there's no need for complex IO because all the logic should be functional. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Tutorial uploaded
Sebastian Sylvan wrote: Beginners know that too. In fact, they often think that practical applications need far more IO than they really do! So to insinuate even slightly that Haskell is bad at IO by avoiding it for two thirds of a book, is really going to inforce the idea that Haskell isn't a practical language for practical applications. It's easily remedied by teaching them a little IO up front (to show them it's not scary), and then leaving it alone for a while, having a more thorugough treatment of it later on. You can show them this on the first page: main = do x - getLine() print my_program(x) And spend the next 200 pages showing them all the nifty things and purely functional things that my_program() could do and not mention monads until chapter 14. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Problems with square root...
Hey, The sqrt function is not doing what I want. This is what I want: round sqrt(2) The problem is that sqrt() returns a Floating value and round wants a ReacFrac: --//-- *Main round sqrt(2) interactive:1:0: No instances for (RealFrac (a - a), Integral (t - a1)) arising from use of `round' at interactive:1:0-4 Probable fix: add an instance declaration for (RealFrac (a - a), Integral (t - a1)) In the definition of `it': it = round sqrt (2) *Main --//-- I'm trying to figure out how to turn a Float into a RealFrac so I can pass it to 'round'. Any ideas? Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problems with square root...
Daniel Carrera wrote: Hey, The sqrt function is not doing what I want. This is what I want: round sqrt(2) Sigh... never fails. Spend an hour trying to solve a problem, and a minute after you write to the list you find the solution. I need brackets around sqrt. I'm surprised though. I don't understand why it dosn't work without brackets. Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problems with square root...
Radu Grigore wrote: I don't understand why it dosn't work without brackets. Function application is left associative in Haskell. Ah. I implicitly assumed right-association (it works in Perl ;) ) Thanks. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problems with square root...
Mark Goldman wrote:
nitpicky detail:
() - Parenthesis
{} - Braces
[] - Brackets
Sorry to be pedantic, but using the wrong terminology confuses me and
I'm sure others as well.
Being pedantic can be fun :)
The Macquarie Dictionary, which is the official dictionary in Australia,
says that () are brackets. It says that they are also called
parentheses or a round bracket, if you need to distinguish between
them and square brackets [], curly brackets {}, or angle brackets ,
and the definition for parenthesis is the upright brackets ().
Also, I believe, UK English (and International English) uses the term
brackets that way, but I'd have to check online to make sure; I don't
have a UK dictionary on me right this minute.
Cheers,
Daniel.
--
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/\/_/ http://opendocumentfellowship.org
/\/_/
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Re: [Haskell-cafe] First steps in Haskell
Simon Peyton-Jones wrote: I'm certain there are hurdles, but I think on the whole they are there by accident rather than design. Why certainly. I have never seen any on-line community that had hurdles by design. Hurdles are usually due to the fact that the people who design the website/community/whatever already know how everything works. As an example, I also participate in the OpenOffice.org community. The website is *impossible* to use. To be able to get anywhere you need to already have fairly in-depth knowledge of the structural organization of the project. Sure, the site makes perfect sense to those who designed it. That's because it's organized in a way that reflects the internal bureocracy, not the questions a visitor is likely to have in mind when he arrives. It turns out that there are a couple of introductory Wiki pages already: http://www.haskell.org/hawiki/HaskellNewbie http://www.haskell.org/hawiki/HaskellDemo Thanks! It'd be great if someone would like to improve them in the light of this thread. (Anyone can do this.) I'll take a look. I'm handy with documentation and usability (though not a trained expert in either). Cheers, Daniel -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal for a first tutorial.
Hal Daume III wrote: Daniel -- can you tell me what was missing from YAHT that wasn't sufficient for starting to use Haskell? It was really intended to solve these problems, at least partially, so if it's missing out, I'd like to fix it! I haven't read it. I refuse to give out personal information to read a tutorial. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal for a first tutorial.
Bayley, Alistair wrote: From this page http://haskell.org/hawiki/LearningHaskell there's a link to the tutorial http://www.isi.edu/~hdaume/htut/tutorial.pdf which seems to make no informational demands. I suggest updating this page: http://www.haskell.org/learning.html To point to that file. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Prime numbers
Hello all, Trying to learn Haskell here... In a Haskell tutorial I found a function deciding if a number is prime: --//-- prime n = not (factors 2 n) factors m n | m == n = False | m n = divides m n || factors (m+1) n divides a b = (mod a b == 0) --//-- Reference: http://www.cs.chalmers.se/Cs/Grundutb/Kurser/d1pt/d1pta/Function%20Definition%20by%20Cases%20and%20Recursion/sld038.htm This function seems to produce a wrong result on the number 38466629 (warning, slow computation). This number is prime but the function says that it's not. How do I know that 38466629 is prime? Beause: * http://www.rsok.com/~jrm/printprimes.html says that it is. * I wrote another prime function that says that it is. This is my function: --//-- prime 1 = False prime 2 = True prime n = filter (divides n) primes == [] where numbers = [x | x - [2..n-1], x*x = n] primes = filter prime numbers divides a b = (mod a b == 0) --//-- I can't figure out what's wrong with the first one. Can anyone spot the problem? (I'm just curious - trying to learn Haskell). Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Prime numbers
John Peterson wrote: Add a type signature: prime :: Integer - Bool It's defaulting to Int and you're getting overflows Thanks. Hmm... it's still not working. Btw, I mis-reported the problem. The offending number is 38466629, which is /not/ prime but the sample program reports as prime. 38466629 = 31 * 1240859 The offending program is: --//-- prime :: Integer - Bool prime n = not (factors 2 n) factors :: Integer - Integer - Bool factors m n | m == n = False | m n = divides m n || factors (m+1) n divides :: Integer - Integer - Bool divides a b = (mod a b == 0) --//-- The math behind the program seems correct... :( Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Prime numbers
Jens Fisseler wrote: What about this: 38466629 = 31 x 1240859 Yes, I wrote backwards. The offending program says that it's prime but it's not. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Prime numbers
Robert Dockins wrote: -divides a b = (mod a b == 0) +divides a b = (mod b a == 0) Oh, thanks. My program assumed one way to define 'divides' and the example assumed the other. When I wrote it I was thinking of (divides a) being a function that tells me if the input divides 'a'. Thanks! Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Prime numbers
Henning Thielemann wrote: factors :: Integer - Integer - Bool factors m n | m == n = False | m n = divides m n || factors (m+1) n Btw. I find the recursion harder to understand than the explicit definition: factors n = any (divides n) [2..(n-1)] For what it's worth, I also found this function un-intuitive. What I'd expect a function called factors to do is exactly what yours does, and not what the one in the example does. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: First steps in Haskell
Donn Cave wrote: I understand that interactive mode can be useful, I'm just wondering whether it belongs with Hello world in the scheme of things, or if at that first step it would be better to focus on the language. Let's compare sample instructions: Interactive mode: - 1. Write this on a file and save it as prog.hs fac 0 = 1 fac n | n 0 = n * fac(n-1) 2. Type ghci on a terminal. 3. Load the program with :load prog.hs 4. Type fac 12 Compiled mode: --- 1. Write this on a file and save it as prog.hs main = print fac 12 fac 0 = 1 fac n | n 0 = n * fac(n-1) 2. Type ghc prog.hs -o prog on a terminal. 3. Run the program with ./prog Comparison: ~~~ 1. The compiled mode instructions are only 1 step smaller, and that's because that step was moved into the program itself. You still need to explain that bit. 2. The compiled mode instructions also introduce main and print. Over-all, I think that the compiled mode instructions are *marginally* more complicated. Not enough to choose one over the other. I would choose the interactive mode because it is friendlier to experimentation. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Tutorial uploaded
Peter Simons wrote: In my humble opinion, it's unfortunate that many tutorials and introductionary texts leave the impression that monadic code would be something utterly different than normal Haskell code. I feel it intimidates the reader by making a monad appear like black magic, even though it's little more than syntactic sugar to describe implicit function arguments. I'm scared of monads :) I really don't know what a monad is. All I know is that you need it for IO because IO implies side-effects and I know that Monad is a very scary-looking word :) If we'd have an opaque World type instead of the IO monad, 'putStrLn' would be: putStrLn :: String - World - World That seems less scary. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Haskell-Cafe Digest, Vol 28, Issue 66
Scherrer, Chad wrote: Have you used Haskell's infix notation? It can help keep the order straight for operators like these. You can write a `mod` b -- instead of mod a b a `divides` b -- instead of divides a b. This can help with readability, too. No, I haven't. That's neat, very neat. Thanks for the tip. I just tried it, and all these are valid: (a `divides`) b (`divides` b) a That's neat because then you can make derived functions and compositions and all sorts of neat stuff. Cheers, Daniel -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] First steps in Haskell
Wolfgang Jeltsch wrote: In addition, Haskells requirement of a main variable is nothing new. Certainly nothing new. I just wish that the documentation I read had told me about it. `ghci fac.hs` doesn't give any errors. I don't understand why loading the file like that is ok but typing the entries is not. Because the interactive environments are about evaluating expressions based on declarations which were made in Haskell source files, not about creating new declarations. Expressions and declarations are just two different things. I think, Cale explained why it might be a bad idea to allow entering declarations at the command line. Ok. I think I understand. I'm sure this will make more sense later. This might be a problem for people exporing the language. Hmm, don't know. I think that usability is important. I'm a big fan of usability. You don't want to give artificial barriers to people who are just starting to explore the language. Those are the people most likely to turn away. Make the first step as simple as possible. The mini-tutorial I posted to the list would be enough. It's little more than a paragraph, and it gets the user past that first step. Best, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] First steps in Haskell
Wolfgang Jeltsch wrote: The problem is that the content of that page, and its links, didn't show me how to write a Haskell program (like you did). If you want to know how to feed, for example, Hugs with your Haskell program, you might have to have a look at some Hugs documentation. Remember that different Haskell implementations like Hugs, GHCi etc. may have different ways of reading Haskell programs. remember? This is the first time I hear this, and I'm bewildered. I expect two C compilers to be able to compile a correct C program. Certainly a hello world program. How is it possible that two Haskell implementations disagree on how to read a Haskell program? (unless it's an advanced program with very unique compiler features - which is bad). On the Learning Haskell page you can click, for example, on the Hugs link, then on Documentation and then on The Hugs 98 User's Guide or The Hugs 98 User Manual. I doubt a lot of people who didn't already know about Haskell would think to click on the manual for the *compiler* instead of the link that says Haskell Tutorial. Best, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] First steps in Haskell
Wolfgang Jeltsch wrote: The point is that the visitor should know that he/she might need a document about GHCi if he/she wants to use GHCi. A introductionary document about Haskell might not explain a specific Haskell system. If you read a book which is about C++ in general, it won't tell you how to use the GNU C++ compiler or Microsoft Visual C++. I just Googled for Introduction to C. The first link was: http://www.le.ac.uk/cc/tutorials/c/ It includes a brief section on both MS Visual C++ and the Unix CC. Maybe I've just been lucky in reading all the right tutorials until now :) but every time I learn a new language, the intro tutorial tells me how to get Hello World running. I have never looked for a compiler tutorial. I guess that Haskell is unique among interpreted languages in that there are two compilers and they work different. I wouldn't expect a huge and elaborate description of Hugs or GHCI on a tutorial. I'd expect a brief If you have Hugs do xyz and if you have GHC do abc. If you know that you need some GHC(i) documentation, it shouldn't be much of a problem to find it. But you see, I didn't. I thought I needed Haskell documentation, so that's what I looked for. At least, the site currently points to the GHC homepage. Yes. I thought it was for the purpose of installing it. Since I installed it with 'apt-get install ghc' I didn't think to click there. I find some usability problems in the documentation section. Which documentation section do you mean? The web page titled Learning Haskell. Maybe, some barriers could be lowered but I don't think that the barriers are currently very high. What do others think? To be fair, the barriers are not as high as they could be. For example, the Haskell community is friendly and helpful and that's a low barrier. It took no time between my posting a question and getting a good answer. So in the end it took me no more than a day to write Hello World. I do suggest that the Learning Haskell page could be improved with a brief (couple of paragraph) tutorial to get someone through Hello world. Or perhaps update the tutorials to say that. I wrote a suggestion on another post. * There's no way for a new user to figure out how to successfully run the simplest Haskell program. There is! The Hugs 98 User's Guide and The GHC User's Guide. Okay, I stand corrected. I rephrase the concern as The links that say Learn Haskell don't show you how to run a simple Haskell program. * The first tutorial listed requires the user to give up some personal information before getting the tutorial. That's bad, of course. These are very significant barriers. Concerning the latter one, I agree with you. :) But the barriers that exist are a problem because they hit the person who is trying to take the very very first step. If you can make that *fist* step easier, more people will take it. What do you mean with *fist* step? :-) :-) Heh... typing accuracy is over-rated. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] First steps in Haskell
Tomasz Zielonka wrote: I think what Wolfgang meant was that different Haskell implementations may have: - different executable names, so you have to invoke them differently - different options - different style of work etc... Of course, all of them should accept all Haskell 98 programs. Ah. Thanks. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Help with division
Hello all, Playing around with Haskell... I'm writing a 'choose' function: --//-- fac :: Int - Int fac 0 = 1 fac n = n*fac(n-1) choose :: Int - Int - Int choose n k = fac(n) / (fac(k) * fac(n-k)) --//-- I'm having problems with the last line. --//-- Prelude :l test.hs Compiling Main ( test.hs, interpreted ) test.hs:13:20: No instance for (Fractional Int) arising from use of `/' at test.hs:13:20 Probable fix: add an instance declaration for (Fractional Int) In the definition of `choose': choose n k = (fac (n)) / ((fac (k)) * (fac (n - k))) Failed, modules loaded: none. --//-- The problem is that it doesn't like the / sign. For example, if I replace the / by * the function is compiled just fine. Does anyone know what I'm missing? Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Help with division
Greg Buchholz wrote: Integral division is spelled div... Thanks, that worked. The course material on the website uses a /. See the second link from the top, English notes. On page 5, right at the bottom. This course material teaches Gofer which it claims is essentially a subset of Haskell. I guess that division must be one of the differences between Gofer and Haskell. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] First steps in Haskell
Hello all, I'm trying to write the simplest possible Haskell program, and I'm not getting anywhere. I have installed Hugs, GHC and GHCI. I want to run the following program: fac :: Integer - Integer fac 0 = 1 fac n | n 0 = n * fac (n-1) This is what I see: $ hugs Hugs.Base fac :: Integer - Integer ERROR - Undefined variable fac Hugs.Base fac 0 = 1 ERROR - Syntax error in input (unexpected `=') $ ghci Prelude fac :: Integer - Integer interactive:1:0: Not in scope: `fac' Prelude fac 0 = 1 interactive:1:6: parse error on input `=' $ # Write the program to fac.hs $ ghc fac.hs fac.hs:1:0: The main function `main' is not defined in module `Main' When checking the type of the main function `main' This is a real problem for Haskell. I expect that a lot of people try Haskell and give up because they can't even write the simplest function. It's hard not to be put off by this. I love the theory behind Haskell, but the practice of it seems to be a real problem. I hope someone will show me how to make this program work. Even better, I hope someone will fix the compilers and interpreters if they need fixing, or fix the documentation if that's what needs fixing. Best, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] First steps in Haskell
Lemmih wrote: GHC is a compiler. If you want to compile to a binary then you must define a function called 'main'. Otherwise just load the file in ghci (`ghci fac.hs`). I would expect GHC to be able to compile a program with a function that is not called 'main'. I wouldn't expect it to print anything when run, but I would expect it to compile. `ghci fac.hs` doesn't give any errors. I don't understand why loading the file like that is ok but typing the entries is not. This might be a problem for people exporing the language. Best, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] First steps in Haskell
Chris Kuklewicz wrote: Almost everything is explained under http://www.haskell.org/ghc/docs/6.4.1/html/users_guide/ghci.html Ok. How would a visitor to the Haskell site find this document? If this is the correct document for a beginner to start with Haskell, perhaps the site should be updated to point to it instead of the documents it currently points to. I find some usability problems in the documentation section. Think of usability in terms of barriers. If you have low barriers, a lot of people will have enough motivation to cross them and get started with Haskell. If the barriers are very high, only the most intent and motivated users will get started. Barriers are bad. Consider some barriers for a user who wants to learn Haskell: * There's no way for a new user to figure out how to successfully run the simplest Haskell program. * The first tutorial listed requires the user to give up some personal information before getting the tutorial. These are very significant barriers. Sure, it's not all bad. For example, Haskell has a friendly community (low barrier). But the barriers that exist are a problem because they hit the person who is trying to take the very very first step. If you can make that *fist* step easier, more people will take it. The main things is: The ghci prompt accepts either command, starting with a color such as :load filename or haskell IO code, since it is in a do-block. Thus let is required. I understand that the design of Haskell might force this behaviour (I don't know, but I guess it must). The best solution I can think of (from a usability POV) is to provide a very brief tutorial, just 1/2 page, just enough to get someone through hello world, and put it right at the top of the Learning Haskell section. I would remove the Intro section (it would fit better on the front page) and replace it with a 1/2 page tutorial. Something like this: -// Sugestion - 40-SECOND INTRO TO HASKELL (You must have linkHugs or GHC installed/link) 1. Open a text editor and type: fac :: Integer - Integer fac 0 = 1 fac n | n 0 = n * fac (n-1) 2. Save as fac.hs 3. On a terminal: $ ghci Prelude :load fac.hs Compiling Main ( fac.hs, interpreted ) Ok, modules loaded: Main. *Main fac 12 479001600 4. Press Ctrl+D to exit. For more information, look at the following tutorials: -// Sugestion - There. That's brief, and it's enough to get the user past the first step. It sends the message that Haskell is not so scary. More typically you would write your code in a file, as shown in: http://www.haskell.org/ghc/docs/6.4.1/html/users_guide/ch03s02.html Thanks. Best, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] First steps in Haskell
Joel Koerwer wrote: Then after you've played with you creation a bit, check out http://haskell.org/learning.html http://haskell.org/learning.html Thank you. I did find that page, and it was very easy to find. The problem is that the content of that page, and its links, didn't show me how to write a Haskell program (like you did). Best, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] About print and side-effects
Hi all, The recent responses to my first question (thanks guys!) included the following bit: main = print (fact 42) Now, print is a side-effect. Shouldn't it involve a do-block or a nomad or one of those scary things you hear about when learning about side effects in functional programs? How come 'print' is allowed to exist alone if it's a side-effect? Thanks for the help. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] About print and side-effects
Chris Kuklewicz wrote: By nomad you seemed to either be ridiculing or misspelling monad. Misspelling. It's a new word for me. I'm not really sure what it means. I expect it'll take me a while to figure it out. Thank you for the help. Best, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Int vs Integer
Hello all, I found a good Haskell tutorial (second link on the Tutorials column) (now that I know how to run the programs in it). I have a question. What's the difference between the types Int and Integer? Likewise, what's the difference between the types Float and Double? Are those just synonims? Thanks for the help. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Int vs Integer
Thanks for the info, and the link. I probably should have guessed the Double vs Float one. I did program in C a while ago... Cheers, Daniel. Jared Updike wrote: Int is for bounded values -2**32 to 2**32 (I think... maybe 2**-31 and 2**31 or less if it's boxed?) based on the underlying machine representation. Integer is unbounded (arbitrary precision, i.e. 7489571948579148758174534 is a valid Integer). Double is for floating point values corresponding to C doubles, in hardware (on 32 bit machines, 64 bit entities) and Floats are half that precision, i.e. 32 bits on 32 bit machines, corresponding to C floats. see http://www.haskell.org/onlinereport/basic.html#sect6.3 and http://www.haskell.org/onlinereport/basic.html#sect6.4 for more info. Jared. On 12/18/05, Daniel Carrera [EMAIL PROTECTED] wrote: Hello all, I found a good Haskell tutorial (second link on the Tutorials column) (now that I know how to run the programs in it). I have a question. What's the difference between the types Int and Integer? Likewise, what's the difference between the types Float and Double? Are those just synonims? Thanks for the help. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- [EMAIL PROTECTED] http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/I am not over-weight, I am under-tall. / ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Python?
Quinn Dunkan wrote: Python has first class functions and lexical scoping, and encourages higher-order functions, though to a much lesser degree than a real functional language. I was surprised to hear about first class functions and higher order functions. So I googled for a bit, and I found something neat: ---snip--- # Python implementation of Common Lisp's remove_if def remove_if(predicate, lst): return [elem for elem in lst if not predicate(elem)] print remove_if(lambda x:x % 2, [1,2,3,4,5,6,7,8]) ---snip--- This is so cool. So there we have a higher order function, passing a funtion as an argument, and even lambda notation. Neat. It is very natural to write in a somewhat functional style, especially in regards to sequence processing: higher order functions and listcomps provide the processing and its built in generators and iterator protocol provide some of the benefits of laziness. Hhhmmm.. I guess the above is also an example of that. [snip: lots of very interesting info I didn't know about] Thank you for all the information. I learned a lot today. I had no idea that Python had these features. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Python?
Erik de Castro Lopo wrote: Its good for small scripting tasks. Its good for string processing. I find the dynamic typing a pain. What's dynamic typing? I have a lady friend who wants to learn how to program. I just decided to teach her Python for practical reasons: Its a great first language for people who aren't interested in making a career of programming. But I do hesitate. I would like to teach her Haskell because I think it's a better language. Its a better language for people who either have a computer science background or intend to study computer science. I would not inflict a language like Haskell on someone who just wants to get the job done with as little fuss as possible. Thank you for the info, I really appreciate it. I feel better about Python now. Given my circunstances, do you think that's a reasonable approach for teaching her how to program? Teach her Python. If you try and teach her Haskell she will end up programming in visual basic :-). Heh. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] and what about AliceML?
fred wrote: As long as this group seems to tolerate What about Haskell and language X? As an aside... This group has been extremely tolerant of my newbie questions. I do want to say thank-you to everyone who has been explaining things to me. I've learned quite a bit about programming languages the last couple of weeks. Just as importantly, I understand better why Haskell rocks, and when it is appropriate to use. has anyone had any experience with AliceML? My initial impression is that it might be a nice tool for teaching fundamental concepts. I'd be interested to know too. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Python?
Hello, This might be a strange question to ask on a Haskell list, but I do want to hear your opinions. What do you think of Python? To explain where this question is comming from: I have a lady friend who wants to learn how to program. I just decided to teach her Python for practical reasons: 1) Python has a nice IDE-ish thing. It's called idle. It includes both a shell and an editor. The interface is simple and clear. 2) I can't get Helium to compile (since I can't get ghc to run) on Solaris. 3) Python has some nice introductory documentation. The Haskell documentation is more advanced. 4) She's interested in writing an OOo plugin some day. Python can do that. But I do hesitate. I would like to teach her Haskell because I think it's a better language. But I just don't seem to have the tools to teach it to a complete beginner (idle, documentation). So I'm thinking that perhaps I can use Python, but try to teach her functional principles, like not changing the value of a variable and not letting her functions have side-effects. Given my circunstances, do you think that's a reasonable approach for teaching her how to program? Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Can't compile GHC
Andrew Cheadle wrote: :-p ok,ok, lots of people (but will they really continue to - we dropped it from our labs long ago). Having said that, how many people don't have access to a Windoze or Linux I don't have access to Win or Linux. But that's besides the point. I think it's reasonable to expect to compile ghc on a standard unix system. While this might be true, having a compiler compile itself is massively important Having the compiler able to compile itself, yes. Making that the only way to compile it, that's another thing. Daniel. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Can't compile GHC
robert dockins wrote: Perhaps. Nonetheless it is common practice for compilers to be written in the target language and to be compiled via bootstrapping. Ever take a look at the GCC sources? You guessed it: C. Please don't confuse the compiler being written in the target language with the compiler requiring itself. It should be possible to compile it with a compiler for a /different/ language. You can compile gcc with Sun's CC. You should be able to compile ghc with nh98. If this is the binary you found, it is possible you have an incorrect version of GCC. No, that's not it. I have 2.95 $ gcc --version 2.95.3 Best, Daniel. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Can't compile GHC
Duncan Coutts wrote: This route is going to be your best bet. Find any binary version of ghc that works on your Solaris and then from there you've broken the GHC-GHC dep cycle. Okay. Is there a version that's more likely to work than others? Or should I try them sequentially from most recent, then go backwards? Best, Daniel. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] Re: Specify array or list size?
Max Vasin wrote: But why do you need that? Where do need to make an assumption about the size of the list? I'm implementing the RC4 algorithm, which requires a state array with 256 elements containing the bytes from 0 to 255. As the algorithm progresses, the elements of the array get shuffled around. This is what drives the pseudo-random number generator. But the size of the state array is always 256. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Specify array or list size?
Hamilton Richards wrote: Well, for starters, lists and arrays are two entirely different topics. I've noticed that Haskell newbies sometimes confuse them --possibly the use of [] in list types and enumerations triggers an unconscious association with [] used in conventional languages for array indexing. I think it's because there's no real reason for someone to think that the words list and array might not be synonims. I certainly don't seen a linguistic distinction. Either term refers to an ordered collection of items. Suppose that you learn a new computer language, and it happens to assign special meanings to the words collection and group. You don't know this. So you start talking about groups as you do in every day English and people tell you that you're mixing up concepts. I guess that a more likely example in programming would be a language that differentiates between functions, procedures and subroutines. As for Haskell arrays, I've been programming in Haskell since the early 1990's, and I've never really needed them. Most Haskell programmers find lists much more useful, and you'd probably be better off concentrating on lists until you encounter a problem in which arrays are really needed. Arrays have O(1) lookup, and Lists have O(n) lookup. For some purposes, arrays might be better. I'm thinking of reimplementing RC4 with arrays to see if it makes a differece. When you do, you'll discover that in Haskell as in most other languages, an array's size is not part of its type. Well... that's not quite what I was looking for. I just wanted to raise an error if the array ever has length other than 256. And I don't know how to do that on a language that doesn't have side-effects. It's nice to see you taking up Haskell with such enthusiasm. If you agree with many of us that Haskell's one of today's best programming programming languages, I hope you'll help spread the word. :-) A lot of concepts from Haskell match the way I think about problems. You see, my background is in math, not programming. For example, currying and higher order functions are essentially new names for things I've been doing for years. So after the concept was explained to me, it didn't take me that long to get it. My current impression is that Haskell is great for anyone with good mathematics education. But I don't know how it'd fare with other people. I have a lady friend who wants to learn how to program. She's a technical person, but has no math background to speak of. I can't decide whether to start with a clear-syntax imperative language (Ruby) or a functional language (Haskell). I confess I've been leaning towards Ruby. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Compiling with NHC98
Marcin 'Qrczak' Kowalczyk wrote: $ nhc98 prng.hs -o prng I/O error (user-defined), call to function `userError': In file ./RC4.hi: 1:1-1:6 Found _module_ but expected a interface GHC and NHC confuse each other with prng.hi files they produce and examine, in incompatible formats. You can delete them; they are needed to compile other modules which use that module. No look, I don't have /any/ .hi files. I don't know what a .hi file is. I don't have GHC either, I've never managed to make it compile. I just got my very first Haskell compiler (literally 10min ago). Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Specify array or list size?
Antti-Juhani Kaijanaho wrote: Your mistake is the start talking about groups as you do in every day English part. The point I'm trying to make is that you can't necessarily predict that a programming language will abscribe special meaning to standard known words like group or list. I can very well talk about a list without knowing that the members of this list (see?) might have a special meaning for that word that I'm not aware of. You can't possibly forsee that sort of thing. It is not a mistake to use the word group to mean what it means in English, I can't possibly know that an Algebraist has a particular definition of group that differs from every-day use. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Compiling with NHC98
David Menendez wrote: *.hi files are analogous to C's *.h files, except that the compiler generates them. Thanks, I learned something new today. You mentioned later that you don't have any *.hi files, so I'm guessing you didn't compile RC4.hs before you compiled prng.hs. Correct. I didn't know I had to :-) If I'm right, you need to do something like this first: $ nhc98 -c RC4.hs Okay, I did that and I see a .hi file now. Thanks! Once that step is done, you should be able to compile prng.hs. Interestingly, I get a different error now: $ nhc98 prng.hs -o prng Undefined first referenced symbol in file FN_RC4_46rand ./prng.o ld: fatal: Symbol referencing errors. No output written to prng collect2: ld returned 1 exit status Oh well, I'll figure this out later. For now I'll just have everything in one big file. At least that compiles cleanly. Incidentally, if you aren't already familiar with make or some other build system, I strongly recommend looking into one. Even for a project with only two files, having a build system keep track of compilation dependencies makes things a lot less tedious. Ok. I played with make once upon a time. Thanks for the advice. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Compiling with NHC98
Cale Gibbard wrote: Just out of curiosity, what platform are you on? There seem to be builds of GHC available for most common ones. Solaris :-( I hate Solaris. No, I didn't choose it; this is what the school provides. But if all goes well, I'll have my very own Ubuntu Linux box within a month or so. :-D Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Comparison with Clean?
Hi all, Anyone here familiar with the Clean programming language? http://www.cs.ru.nl/~clean/ It looks /very/ similar to Haskell, both in functionality and syntax. I would be grateful for any sort of comparison. I'm trying to decide which language I should try to learn. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Comparison with Clean?
Hi Jerzy, Thank you for your thorough response. I will archive it and come back to it as a reference. As I learn more about FP features (e.g. Monads) I'll be able to get more from your description. But just a quick note: 4. A general observation about the use of both languages by a beginner who wants to learn on examples: Haskell disposes of two decent interactive interpreters: Hugs and GHCI permitting to test directly small expression, to ask about their types, etc. which is often useful for debugging, and for grasping the essentials on small exercises. For me, right now, this makes a world of a difference. I'm experimenting with small exercises on Hugs right now. It must be admitted though that neither is really an *interactive* Yeah, I noticed... ;-) But I recently learned about a neat workaround: I have a file called Test.hs and load it with ':l Test'. Then I start exprimenting. I make a small change and type ':l Test' again. So it's almost interactive, and not excessively akward. I think I'll learn a bit more using Haskell, and then I'll be in a better position to decide where to continue (probably with Haskell at first). Now, for the people who asked those questions. Choose whatever you wish, if your philosophy is I have no time to learn two languages, only one, so tell me which one is better, then I have some VERY STRONG statements: * Whoever says to you H is *better* that C (or vice-versa) is LYING. :-) Well, I merely ask for general impressions and go from there. * If you want to learn FP, you should have a good view on the principal paradigms, not on particular syntactic constructs. Then, some knowledge of two different languages is more than helpful. Ok. Good to know. * Learning of languages is a big adventure and pleasure. That's why I'm here. :-) I have a strong preference for languages with clear, simple models. For example, I like C better than C++, and Ruby better than Python. Even if something might take fewer lines in C++ than in C, or be faster in Python than in Ruby, I like the feeling that I understand what I'm doing. And I see elegance in a simple model with few exceptions. * Here and elsewhere both H and C communities are helpful, people who know, answer all questions without pretensions nor suggestions that they are respectful gurus bothered by beginners (which happens too often on other language-oriented newgroups I visit from time to time...). Indeed. I've been pleasantly surprised by how friendly this group has been. I've learned a lot already, and now I have a lot of resources to continue my exploration of Haskell and FP. Incidentally, the Ruby community is friendly too. :-) Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Speed comparison?
John Hughes wrote: Benchmarks give a very one-sided view, ignoring the large effect that ease of programming can have on the final system's performance. Good point. Ease of programming helps you make /correct/ programs quicker, and some times allows you to use more advanced algorithms that you wouldn't dare try in C++. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Where do you use Haskell?
Tomasz Zielonka wrote: In my experience, the amount of IO code in an average Haskell program is from 1% to 20%, even in applications which have to do a fair amount of interaction with the outside world (networking, CGI, system utils). Ok, I can see that. Thanks. Haskell's IO is not just a mimicry of traditional imperative languages, it's an EDSL (embedded domain specific language) for doing IO. Because it's embedded it benefits from all the other features of Haskell, like first-class functions, higher-order functions, lexical closures, pattern matching, etc, etc. I guess this will make more sense to me as I learn more about the language. I'm quite new at this. If you mean that Haskell is rarely applicable, I disagree. Well... the purpose of asking here is so knowledgeable people can correct my errors. :-) Thank you for the info. I'm learning. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Where do you use Haskell?
Ben Lippmeier wrote: You might like to take a deep breath and start with: Tackling the awkward squad: monadic input/output, concurrency, exceptions, and foreign-language calls in Haskell - Simon Peyton Jones http://research.microsoft.com/Users/simonpj/papers/marktoberdorf/ Ok. And I'll get to learn what monadic IO is... :-) PS: Keep asking those questions. :-) I'm eager to learn. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Speed comparison?
Hi all, Thank you for all the information on my previous question. I learned a lot, and good pointers to more info. My next question is about speed. How fast would you consider Haskell? (say, for computational work). How would you compare it to C, Python and Ruby? I suggest C, Python and Ruby as a basis of comparison because: 1) C is what I'd use if I wanted something fast. 2) Python or Ruby is what I'd use if I wanted clean code. I know that Haskell can be compiled, thanks to ghc. Ruby is interpreted and I'm pretty sure Python is quasi-interpreted (it's compiled on the fly to Java-style bytecode and a VM runs the bytecode). Furthermore, the Haskell page says that ghc produces fast programs. So I would guess that Haskell is faster than Python, but not as fast as C. Would that be correct? For computational work (e.g. a simulation, factoring primes, whatever) does it approach C speed? I would be happy to hear a comparison with any other language you find interesting.:-) As well as any other information you'd like to share. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Speed comparison?
Greg Buchholz wrote: You might find the The Great Computer Language Shootout informative... http://shootout.alioth.debian.org/ Thanks! That's a great resource. At first glance, Haskell seems to do well over-all. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell vs OCaml
Hey, Marcin just mentioned OCaml as another functional programming language I should keep in mind. Can anyone offer an opinion on how Haskell and OCaml compare? Is OCaml as easy to learn as Haskell? Does it have much the same virtues? I'll go take a look at it. /daniel goes to Google. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell vs OCaml
Marcin, Are you sure that OCaml is similar to Haskell? At first glance, it doesn't even look functional. It looks like an imperative language. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Here's a curve ball for Haskell.
Alright, in Haskell there are no side-effects when you call a function twice on the same data you get the same result... I just decided I'll try to write a good pseudo random number generator in Haskell :-) I'm off to class now, but I'll try it tonight. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Array functions?
Hello, I hope these don't turn out to be RTFM questions, but I can't find them in my FM :-) 1) Is there a function to get the ith element from an array? 2) Is there a function to get the index of an entry in an array? I've implemented these two functions below: 1) find 0 (x:xs) = x find n (x:xs) = find (n-1) xs 2) index i (x:xs) = if i == x then 0 else 1 + index a xs This was a fun exercise, but I can't shack off the feeling that I just re-invented the wheel. I need these because I want to be able to swap any two elements from an array. This is my swap function: -- swap i j array = swaps the ith and jth elements of 'array'. -- swap i j arr = a_head ++ [item_j] ++ a_midd ++ [item_i] ++ a_tail where a_head = [a | a - arr, index a arr i] item_i = find i arr a_midd = [a | a - arr,(index a arr i) (index a arr j)] item_j = find j arr a_tail = [a | a - arr, index a arr j] I'm sure this was a poor way to accomplish this, but it was a learning experience. If anyone would like to show me a more elegant solution, I would be happy to see it. Cheers, Daniel. Haskell newbie. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Array functions?
Hi Ben, Take a look at this one: http://www.haskell.org/onlinelibrary/standard-prelude.html Thanks. What's the Prelude ? 1) Is there a function to get the ith element from an array? From your own implementations I gather you mean 'list', not 'array'. What's the difference? Now, if you happen to also want to know these functions for real arrays, not lists, I suppose you take a look at the standard library module Array. Thanks for all the info! Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Clarification on proof section of HS: The Craft of FP
Hi Echo, I'm totally new at Haskell btw. But I'll comment a bit. :-) My copy of HS: The Craft Of FP just arrived Is it good? Do you recommend it? Should I get a copy too? and I was reading section 8.5 about induction. On page 141, Simon Thompson gives a method of proving properties of functions on lists: 1) Prove that the property holds for the null list 2) Prove that the property holds for (x:xs) under the assumption that the property holds for xs. Cool. Mathematical induction. I can see how that would be a sueful skil for an FP programmer. In other words, how does proof of the property on empty lists and proof that the property holds on (x:xs) under the assumption that it holds on xs give proof that it holds on all lists? Isn't there a recursive dependency here? I'll offer two explanations. Hopefully one will make sense. :-) Explanation 1: Fact (*): You proved P(xs) = P(x:xs). step 0: prove for the empty list. step 1: given (*) and step 0, you get the result for a 1-item list. step 2: given (*) and step 1, you get the result for a 2-item list. ... step n: given (*) and step n-1, you get the result for a n-item list. Explanation 2: Start with any list xs, it can be written in the form (y:ys). So if you prove the property for ys you're done, right? Continue this recursively, removing one entry on each round. Eventually you'll hit an empty list. But you proved the property for the empty. So, recursively, you've proven it for all lists. Hope that helps. This is called mathematical iduction. It is one of the most popular methods of proving theorems in mathematics. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Clarification on proof section of HS: The Craft of FP
Henning Thielemann wrote: Well, I also omited the word countable. I figure it's understood since computers only deal with finite data. And given an infinite list, any finite head of it would meet the criteria, so the distinction is moot. Unless Haskell has some neat property I am not aware of :-) If you don't take care you may end up proving that e.g. repeat 1 ++ [0] == repeat 0 because for the first list you can prove that every reachable element is equal to its neighbour and the last element is 0. Note: I'm totally new at Haskell. What does ++ do? What does 'repeat' do? Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Where do you use Haskell?
Hi all, Again, I'm the new guy slowly learning this fuctional programming thing. :-) I've been reading, and I'm really liking the elgance of Haskell, and FP as a whole. But I wonder about the range of applicability. You see, one of the things about FP is that there are no side-effects and the same function on the same parameters always returns the same value. But any program that interacts with the real world cannot meet those properties. The function ask_user_name() will not return the same value each time. If write a chess program, the function get_user_move() will be different each time. And every time you update the screen, you're having a side-effect. So, I figure that to do these tasks you heed that do ... - work around. But that kills the whole point of using FP in the first place, right? So, I'm tempted to conclude that FP is only applicable to situations where user interaction is a small part of the program. For example, for simulations. Now, I'm sure I'm not the first person to have this train of thought. And I'm sure there is a good answer why I'm wrong. :-) I'm eager to hear what that might be. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Writing functions in Haskell.
Hello, I'm trying to get started with Haskell. I must say that as good as the language must be, the documentation was been a source of frustration. Only one document actually showed me how to get started (ie. run hugs or ghci), and I was asked to give out my email address before getting it. Sigh... Well, in any event, I did get that document in the end and I've been reading through it. I've compiled Hugs on my Solaris workstation. There were no errors at compilation. Yet, I think there's something seriously wrong with my installation. I can't seem to be able to defin functions: my/prompt $ hugs Hugs.Base fibs 1 = 1 ERROR - Syntax error in input (unexpected `=') And some functions seem to be missing. Hugs.Base Char.toUpper 'a' ERROR - Undefined qualified variable Char.toUpper I was hoping that someone could confirm or deny that my Hugs installation is broken. Thank you for your time. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Writing functions in Haskell.
Hello Cale, Thank you for your help. Cale Gibbard wrote: From the example you gave, it looks like you're using Yet Another Haskell Tutorial from http://www.isi.edu/~hdaume/htut/ which is actually my favourite tutorial. The tutorial itself is quite good, and I like it. I guess I've had a long day, and when I was asked for my name and email I didn't react well. Oh well, life goes on. When using hugs or ghci, you should note that what these do is to evaluate Haskell expressions and print (or execute) the results. To actually write programs, (define data types and functions and such) you'll need to fire up a text editor and enter your definitions into a .hs file, which you can then load with your interpreter by passing the filename on the commandline, or by using :load filename.hs at the hugs or ghci prompt. I think this handles your first problem. Alright, got it. In hinsight, I misunderstood the tutorial. It showed me the function but it didn't actually say to type it in. Thanks for the help, I can write functions now. :-) The second problem arises from hugs not doing the same thing as ghci [snip] You can tell hugs to also load the Char module on top of whatever code you have loaded by using the command :also Char, after which the prompt should look like Char and you can try toUpper 'a' Alright, yes that works. Thanks! There are a number of resources which you might be interested in for learning Haskell. You've already found the mailing lists, there is also an IRC channel: #haskell on irc.freenode.net, where there are plenty of people to help at any time. Oh, good. IRC is good. There's also a wiki at: http://www.haskell.org/hawiki/FrontPage The page http://www.haskell.org/hawiki/HaskellNewbie in particular might be useful, as it answers lots of common questions from new users. If you have additional questions, feel free to ask them there and someone will probably respond fairly quickly. Ok, thanks. I really appreciate the help. And thank you for the friendly response. I'm eager to keep learning Haskell. The language looks very impressive. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Writing functions in Haskell.
Alright, I have what I believe must be a simple question. As one of the exercises for the Haskell tutorial I got I have to implement an alternative to the 'map' function. This is what I have: - my/prompt $ cat Test.hs module Test where my_map p [] = [] my_map p (x:xs) = p x : my_map p xs my/prompt $ hugs [snip] Hugs.Base :l Test Test :also Char Char map toUpper Hello HELLO Char my_map toUpper Hello ERROR - Undefined variable my_map - I can define other functions now (e.g. Fibonacci, length of a list). So I'm not sure why I'm doing wrong here. Even if my syntax is wrong in some way, the function should be defined. I would be grateful if anyone could point out my error. Cheers, Daniel. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
