Re: [Haskell-cafe] Simple but interesting (for me) problem
Hallo, On 10/21/09, Tim Wawrzynczak inforichl...@gmail.com wrote: Here's an example in the IO monad: import Data.IORef import System.IO.Unsafe counter = unsafePerformIO $ newIORef 0 next = do modifyIORef counter (+1) readIORef counter Naturally, this uses unsafePerformIO, which as you know, is not kosher... This is different because counter is global. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Creating an alias for a function
Hallo, On Tue, Oct 6, 2009 at 11:01 PM, michael rice nowg...@yahoo.com wrote: How do I create an alias for a function, like giving CAR the same functionality as HEAD. I know I can do it by creating a definition (see below), but is there a better way, like Scheme's (define head car) car :: [a] - a car x = head x The reason for doing this is to more closely mirror legacy code. Just do: car = head -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell for Physicists
Hallo, On 9/30/09, ed...@ymonad.com ed...@ymonad.com wrote: Hi, I will give a seminar to physicists at USP (Universidade de São Paulo, Brazil) university and they asked me for a good title, something that can attract physicists. Anyone has some suggestions? (Will be a seminar about the use of Haskell to substitute C or Fortran in a lot of tasks, and how it can be used in some problems instead of Matlab, Mathematica, etc.) Haskell for physicists ? -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell programmers in São Carlo s - SP - Brazil?
Hallo, On 5/20/09, Diego Souza paravinic...@yahoo.com.br wrote: Not exactly São Carlos: São Paulo - SP. Me too, Sao Paulo - SP. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] compilation to C, not via-C
Hallo, On 4/24/09, Bulat Ziganshin bulat.zigans...@gmail.com wrote: so, if you just need haskell-C++ interaction, you may look into using FFI [1,2]. if you believe that you can compile some java/ruby/haskellwhatever code down to C++ and incorporate it into your function - sorry, they all have too different computing model Actually some Scheme compilers have a c-declare form that lets you create C functions, which can be called from C, Haskell, Java, Ruby etc. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[2]: [Haskell-cafe] compilation to C, not via-C
Hallo, On 4/24/09, Bulat Ziganshin bulat.zigans...@gmail.com wrote: and it supports lazy lists? :) all compiled languages has some FFI, the problem is that FFI limited to common subset of all those languages - i.e. primitive types and pointers I am not saying that Scheme is Haskell. I am just refuting your assertion that one cannot compile whatever code to C and incorporate it into your function. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] compilation to C, not via-C
Hallo, On 4/24/09, Donn Cave d...@avvanta.com wrote: Quoth Alex Queiroz asand...@gmail.com, Actually some Scheme compilers have a c-declare form that lets you create C functions, which can be called from C, Haskell, Java, Ruby etc. That would be like what you get with Haskell FFI export? When I do this with nhc98, I need a nhc98 main, and I would expect the same with GHC. Part of the deal would be smuggling in and initializing the Haskell runtime. Also figuring out storage, if returning any values from the exported Haskell function (as opposed to poking them into address parameters.) I can see how this would not be suitable for a library. Incurring the risk of being too much off-topic, I'll just say that I use the Gambit-C Scheme compiler to produce C code that I link with my C driver code. I need to write the driver (main and friends) in C because my software is compiled as a Windows service or POSIX daemon, which requires special care. But of course you must link in the Scheme runtime, with the garbage collector, Scheme data types etc. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Converting IO [XmlTree] to [XmlTree]
Hallo, On 4/14/09, rodrigo.bonifacio rodrigo.bonifa...@uol.com.br wrote: Dear Sirs, I guess this is a very simple question. How can I convert IO [XmlTree] to just a list of XmlTree? The short answer is: You cannot. The longer answer is: Only put things in the IO monad when you need to interact with the outside, i. e., reading, displaying etc. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Against cuteness
Hallo, On Fri, Mar 13, 2009 at 1:23 PM, Benjamin L. Russell dekudekup...@yahoo.com wrote: On Fri, 13 Mar 2009 12:29:25 +0100, Achim Schneider bars...@web.de Water overcomes stone: Shapeless, it requires no opening: The benefit of taking no action. Yet benefit without action, And experience without abstraction, Are practiced by very few. Nice poem. Did you write it yourself, or can you document the source? If I remember correctly, this is from the Daodejing. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] some ideas for Haskell', from Python
Hallo, On Wed, Jan 14, 2009 at 5:06 PM, Max Rabkin max.rab...@gmail.com wrote: On Wed, Jan 14, 2009 at 10:48 AM, Jonathan Cast jonathancc...@fastmail.fm wrote: Do you have an example of a macro that can't be replaced by higher-order functions and laziness? I believe I do: one macro I found useful when writing a web app in Lisp was something I called hash-bind, which binds variables to the values in a hashtable, with the variable names as keys. For example: I have one for binding GET/POST variables to regular variables transparently and with error checking, just inside the body of the macro. -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] some ideas for Haskell', from Python
Hallo, On Wed, Jan 14, 2009 at 5:16 PM, Max Rabkin max.rab...@gmail.com wrote: On Wed, Jan 14, 2009 at 11:11 AM, Alex Queiroz asand...@gmail.com wrote: I have one for binding GET/POST variables to regular variables transparently and with error checking, just inside the body of the macro. N! You reinvented PHP. What happens if a request variable shadows the name of another variable used in the body? I list the variables I want to bind in the form. I do not ask to automatically bind all of them. :) (query-let (id name job salary) (if ( salary 1000) ...)) -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] some ideas for Haskell', from Python
Hallo, On Wed, Jan 14, 2009 at 8:47 PM, Dougal Stanton ith...@gmail.com wrote: (defun avg (rest args) (/ (apply #'+ args) (length args))) Or as a macro like this: (defmacro avg (rest args) `(/ (+ ,@args) ,(length args))) The reason the macro is better is that the length of the list is known at compile time, so you don't need to traverse the list to calculate the length of the list. I'm trying to work out how awesome the (+) operator is that you can add the values together without needing to traverse the list ;-) Don't need to traverse the list at run time, not compile (actually macro-expansion) time. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: Salsa: A .NET Bridge for Haskell
Hallo, On Fri, Oct 10, 2008 at 5:48 PM, Andrew Coppin [EMAIL PROTECTED] wrote: Don Stewart wrote: This could be a game changer. In what way? As far as I'm aware, .NET never really caught on and has long since become obsolete. Or do you just mean the type system machinery that has been developed could be used for other projects? In what alternate universe? -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] New to Haskell
Hallo, On Dec 19, 2007 9:25 PM, John Meacham [EMAIL PROTECTED] wrote: Actually, it is a pretty fundamental feature of the lisp-derived languages that they can self modify their own source, and hence keep their own source representation all the way through runtime. This is not actually true. You may be thinking of macros, but macro expansion time is before compile time. After compilation, not many, if any, modern Lisps keep the source around. Of course the old Lisp machines were different. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Parsing R5RS Scheme with Parsec
Hallo, On 10/3/07, Pasqualino 'Titto' Assini [EMAIL PROTECTED] wrote: Hi Alex, I hope not to spoil your fun but have you had a look at this: Write Yourself a Scheme in 48 Hours http://halogen.note.amherst.edu/~jdtang/scheme_in_48/tutorial/overview.html Yes, I'm actually using it as a basis. But it doesn't parse the whole R5RS grammar. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Parsing R5RS Scheme with Parsec
Hallo,
For fun and learning I'm trying to parse R5RS Scheme with Parsec.
The code to parse lists follows:
--
-- Lists
--
parseLeftList :: Parser [SchDatum]
parseLeftList = do
char '('
many parseDatum = return . filter (/= SchAtmosphere)
parseDottedList :: [SchDatum] - Parser SchDatum
parseDottedList ls = do
char '.'
many1 parseAtmosphere
d - parseDatum
many parseAtmosphere
char ')'
return $ SchDottedList ls d
parseProperList :: [SchDatum] - Parser SchDatum
parseProperList ls = do
char ')'
return $ SchList ls
parseList :: Parser SchDatum
parseList = do
ls - parseLeftList
(parseDottedList ls) | (parseProperList ls)
I've factored out the common left sub-expression in
parseLeftList. The problem is that ... is a valid identifier so when
inside the left of the list the parser sees a single dot, it tries to
match it with ..., which fails. Can anybody give advice on how to
rewrite these list parsing functions?
Cheers,
--
-alex
http://www.ventonegro.org/
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Re: [Haskell-cafe] Parsing R5RS Scheme with Parsec
Hallo, On 10/2/07, Brandon S. Allbery KF8NH [EMAIL PROTECTED] wrote: On Oct 2, 2007, at 9:52 , Alex Queiroz wrote: (parseDottedList ls) | (parseProperList ls) I've factored out the common left sub-expression in parseLeftList. The problem is that ... is a valid identifier so when inside the left of the list the parser sees a single dot, it tries to match it with ..., which fails. Can anybody give advice on how to rewrite these list parsing functions? try (parseDottedList ls) | parseProperList ls Overuse of try is a bad idea because it's slow, but sometimes it's the only way to go; it insures backtracking in cases like this. This does not work. The parser chokes in parseLeftList, because it finds a single dot which is not the beginning of Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Parsing R5RS Scheme with Parsec
Hallo, On 10/2/07, Brandon S. Allbery KF8NH [EMAIL PROTECTED] wrote: Sorry, just woke up and still not quite tracking right, so I modified the wrong snippet of code. The trick is to wrap parseLeftList in a try, so the parser retries the next alternative when it fails. Since ... can only appear at the end of a list, I removed ... from the possible symbols and added a new function: parseThreeDottedList :: [SchDatum] - Parser SchDatum parseThreeDottedList ls = do string ... many parseAtmosphere char ')' return $ SchList $ ls ++ [SchSymbol ...] parseList :: Parser SchDatum parseList = do ls - parseLeftList try (parseThreeDottedList ls) | (parseDottedList ls) | (parseProperList ls) Thanks for the help. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Explaining monads
Hallo, On 8/14/07, Jeff Polakow [EMAIL PROTECTED] wrote: Hello, There is clearly a problem with the Haskell/monad tutorials out there... The tutorials seriously need to step back and start with something like, To enforce order of evaluation we evaluate closures* returning a defined type. The first closure will feed its result to the second which will in turn feed it's result to the third. Since the third closure can't be evaluated without having the results from the second and first (and thus they had to be evaluated earlier in time) we get a defined evaluation sequence. Here are some examples... The style of this description is nice; however the description itself is wrong. Monads DO NOT determine order of evaluation. Previous posts on this thread give several examples. And his point was completely missed. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Maintaining the community
Hallo, On 7/16/07, Malcolm Wallace [EMAIL PROTECTED] wrote: OK, so I'm not genuinely suggesting that you must possess or be studying for a PhD, to grok Haskell. But I find nothing alarming about the suggestion that one needs a fairly high level of intelligence, and some training, in order to be able to use Haskell effectively. If I say I'm not stupid, would you believe me? I'm not saying that Visual Basic-level programmers should be able to understand haskell without a lot more studying and practice. What I'm saying is that almost every topic in Haskell Café evolves into a very high level discussion that may frighten some beginners, as it seems that without a PhD in programming languages and category theory, the language is not for you. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Maintaining the community
Hallo, On 7/14/07, Michael T. Richter [EMAIL PROTECTED] wrote: While it is understandable, given the intense interest most grognards of any language have in playing with the language, for people to enjoy conversations that go into the ever-more-esoteric, it is decidedly not helpful to the newcomer striving to understand things. So yes: Answer politely. Explain your answer in detail suited to the perceived level of the asker. Clear common misunderstandings. But do not use this as a launchpad into the geek equivalent of language knowledge oneupmanship. It confuses far more than it helps. If you really need to enter into the game, branch out. Don't even reply to the thread but start a new thread with your reply. Leave the newcomer to the comprehensible side, even if it is perhaps somehow less than perfect by whatever standards you choose to measure perfection in. This is so much true. It has the effect of disguising Haskell as a PhD-only language. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type system madness
Hallo, On 7/11/07, Andrew Coppin [EMAIL PROTECTED] wrote: When I tell the editor to save UTF-8, it inserts some weird BOM character at the start of the file - and thus, any attempt at programatically processing that file instantly fails. :-( Are you sure it's not UTF-16? Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type system madness
Hallo, On 7/10/07, Andrew Coppin [EMAIL PROTECTED] wrote: Last time I looked, everything treats text as being 8 bits per character. (Or, more commonly, 7, and if the MSB isn't 0, weird things happen...) That's why (for example) HTML has lots of weird constructs such as hellip; in it, instead of just typing in the actual character you want. (And let's be clear here: SGML and all those decendents are all using and - the mathematical greater and less operations - when what they *really* mean are angle brackets, a quite distinct glyph.) Last time I checked, nobody was keen on using 64 bits per character... You must look out more. I use áéíóúç in web pages all the time. -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] In-place modification
Hallo, On 7/10/07, Sebastian Sylvan [EMAIL PROTECTED] wrote: I highly doubt that. For two reasons: 1. People can only cling to unproductive and clumsy tools for so long (we don't write much assembly any more...). Capitalism works to ensure this; people who are willing to switch to more efficient tools will put the rest out of business (if they really are more efficient). As I replied to Hugh, the Universe of computers is not restricted to PCs. We, embedded developers, will be using C for a lot of time still. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] In-place modification
Hallo, On 7/10/07, Sebastian Sylvan [EMAIL PROTECTED] wrote: That might eliminate the concurrency imperative (for a while!), but it doesn't adress the productivity point. My hypothesis is this: People don't like using unproductive tools, and if they don't have to, they won't. So you think we use C because we like it? :-) When this revolutionary tool of yours arrive that compiles Haskell to PIC devices, I'm gonna be the first to use it. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] In-place modification
Hallo, On 7/10/07, Sebastian Sylvan [EMAIL PROTECTED] wrote: The revolution (tm) won't come at the same time for all domains. C is probably used/supported in embedded devices mostly because it's popular for non-embedded devices (not because C is somehow uniquely suited for embedded devices). Wrong. Java and C# are far more popular languages, but C is just the right tool for the job. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Collections
Hallo, On 6/19/07, Andrew Coppin [EMAIL PROTECTED] wrote: However, Haskell only has 1 type of collection: linked lists. (And only single-linked at that.) While other normal programming languages spend huge amounts of effort trying to select exactly the right collection type for the task in hand, Haskell programs only ever use linked lists. Huh? -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] IDE?
Hallo, On 6/18/07, Michael T. Richter [EMAIL PROTECTED] wrote: Screenshots are worthless if they don't match my screen, aren't they? I guess I can open up exactly the same file that's in your screenshot and then use your screenshot as a background to my screen so I have the illusion of decent fonts, but that's not exactly a productive environment now, is it? So you'd rather use my image as background instead of compiling GTK Emacs for you? I've got another idea, why don't you use MS Word? It can save plain text files. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] yi or not to yi was: IDE?
Hallo, On 6/18/07, Andrew Coppin [EMAIL PROTECTED] wrote: OTOH... how the heck do you write an operating system in a language that doesn't even support I/O? :-S You can start from here: http://programatica.cs.pdx.edu/House/ Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Implementing Mathematica
Hallo, On 5/30/07, Andrew Coppin [EMAIL PROTECTED] wrote: OK, so you're saying that in 4 days you wrote something that out-performs Mathematica, a program that has existed for decades and has a vast, highly-funded RD effort behind it featuring some of the brightest minds in the field? I'm in a state of disbelief here. If you want some amusement, just search for Jon Harrop in comp.lang.lisp. -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Editor
Hallo, On 5/21/07, Michael T. Richter [EMAIL PROTECTED] wrote: Oh, and of course it wasn't just the config files I showed problems with, now, was it? I seem to remember something about modality and bad syntax highlighting. Maybe I was tripping. It happens. You may not like modality, it's entirely within your rights, but it is *not* a problem. Fortunately it's still there for the millions of us who like it. -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Poor first impression
Hallo, On 4/27/07, Fernando Cassia [EMAIL PROTECTED] wrote: Goodbye Haskell, I just wanted to compile a MP3 player, and perhaps if the compiler installed OK with no issues, I'd have taken a look at the language. But as of right now, I don't have time to waste with broken compiler installers. Byebye Haskell waves back, yelling 'good bye!' while the distance between them increases. As a last thought, feeling sorry for the poor boy, it raises a sign that reads: 'Newer Linux distributions come with libreadline.so.5 only (e.g. SuSE 9.2), so we have provided a readline4 compatiblity RPM for this case.' Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Multi Line String literals
Hallo, On 4/26/07, Neil Mitchell [EMAIL PROTECTED] wrote: Like the cpp will choke and die :) Multiline string literals were one of the motivations for cpphs. Does cpphs allow me to include a whole file into a Haskell source file, inserting automatically the string gaps? -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Multi Line String literals
Hallo, On 4/26/07, Neil Mitchell [EMAIL PROTECTED] wrote: No, but Hugs does with Here documents. Unfortunately I'm using GHC but thanks! Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
Hallo, On 4/12/07, kynn [EMAIL PROTECTED] wrote: Hi. I can't find that post. Could you point it to me please? It's in here: http://cgi.cse.unsw.edu.au/~dons/blog/2007/03/10#programmable-semicolons -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
Hallo, On 4/11/07, riccardo cagnasso [EMAIL PROTECTED] wrote: The post on dons' blog about the cpu scaler is a great example on how haskell can easily used in the day-to-day hacking! Just read it, it's a very nice post. I'm not afraid of math, but it's a relief to see some code I can relate with. :-) -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: A question about functional dependencies and existential
Hallo, On 3/29/07, Nicolas Frisby [EMAIL PROTECTED] wrote: A wee bit off topic... but bear with me. More off-topic... but bear with me. :-) I'm starting with Haskell. I'm writing a real application with Gtk2hs and HDBC for a small furniture shop. I have enjoyed it very much so far, and I like the productivity boost. But I do not understand GADTs or functional dependencies yet. When I read threads such as this I begin to think. Are these black magic type skills necessary for day-to-day work, or just for tasks not doable in other languages, or at least not doable without much effort? Are they for working around some problems of HM type systems or do they give Haskell super-language powers? I guess I could answer these questions if I understood what FD and GATDs are all about, but I'm not just there yet. :-) Cheers, -- -alex ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Newbie vs. laziness
Hallo list, I don't quite get how ($!) works. I have this function: dbCreateIndices con dtn dof = do let dummy = newDbItem let query = SELECT id FROM ++ (dtn dummy) ++ ORDER BY ++ (dof dummy) ids - liftM (map fromSql . concat ) $! quickQuery con query [] return $ IntMap.fromList $ zip ids [0..] quickQuery returns a lazy list of results, and I expected ($!) to make it strict. But my program crashes if I use it this way. But, if I add a print to the function: dbCreateIndices con dtn dof = do let dummy = newDbItem let query = SELECT id FROM ++ (dtn dummy) ++ ORDER BY ++ (dof dummy) ids - liftM (map fromSql . concat ) $! quickQuery con query [] print ids return $ IntMap.fromList $ zip ids [0..] print makes the ids list strict and all is well. How is the correct way to use ($!) ? Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Newbie vs. laziness
Hallo, On 3/20/07, Jules Bean [EMAIL PROTECTED] wrote: What $! does is force its arguments into WHNF before applying the function. WHNF means, roughly, either a lambda or a constructor at the top-level. I think I got it now. However that's a bit clumsy. What kind of error are you seeing when you say 'it crashes'? I must fetch all rows of the result, otherwise the database will be in an inconsistent state and all subsequent queries crash the application. Fetching all rows automatically finishes the previous statement, so I must evaluate the spine of the list. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Newbie vs. laziness
Hallo, On 3/20/07, Jules Bean [EMAIL PROTECTED] wrote: Personally I'd inclined to suggest use of the strict FetchRow which the library provides than struggle with explicit uses of seq to fight an over-lazy IO action. Sounds like a good suggestion. Thanks very much for the help! Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Read Instance for UArray won't port to linux
Hallo, On 3/14/07, Simon Peyton-Jones [EMAIL PROTECTED] wrote: Ah, a fine idea. I'll do that anyway; maybe others will have even better ideas, but that's a good start Ah! So now I knows what it means. I've also been beaten by this error message a couple of days ago. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: HDBC Windows binaries with SQLite 3 support
Hallo, On 3/6/07, John Goerzen [EMAIL PROTECTED] wrote: I should add, though, that you were pointing to the old HDBC site. Please download HDBC from http://software.complete.org/hdbc/downloads The Sqlite3 driver is at http://software.complete.org/hdbc-sqlite3/downloads The quux.org download site will go away. The links to the API docs from the wiki do not work. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] HDBC Windows binaries with SQLite 3 support
Hallo list, I guess the subject line says it all. Can anybody help me? -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: HDBC Windows binaries with SQLite 3 support
Hallo, On 3/5/07, ArtemGr [EMAIL PROTECTED] wrote: My instructions (i made it for myself! provided as is): Worked after some tweaks for my system. It was actually much easier than I thought. Thanks very much! -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] LGPL libraries
Hallo, Gtk2Hs and HDBC are both LGPL licensed, but aren't they always static linked? Is there a way to use them in closed-source programs? Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] LGPL libraries
Hallo, On 3/5/07, Duncan Coutts [EMAIL PROTECTED] wrote: If you're really worried (but I wouldn't be) then do recall that the static linking thing only requires that the end user be able to relink with a different version that preserves the same ABI. So you don't have to provide source for your closed source app, you'd just need to provide all the .o / .a files you need to link together to produce your final program. So it's a bit of a hassle but it does meet the requirements of the LGPL and allows a closed source app. Yeah, was pĺanning to send an object file with the application to allow relinking. I was just curious about the LGPL because GHC always links everything statically. Thanks for the thorough answer! Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] basic field questions
Hallo,
On 1/24/07, jamin1001 [EMAIL PROTECTED] wrote:
So then how should this be done? What if I want to do something like
data Chair = Chair {pos:: Int, color :: Int}
data Table = Table {pos:: Int, color :: Int}
data Chair = Chair { chairPos :: Int, chairColor :: Int }
Also, could someone tell me why this doesn't compile in GHC:
data Test = A {a::Int} | B {a::Int, b::Int}
data Test2 = C {c::A}
'A' is not a type, is a constructor for type 'Test'.
--
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Re: [Haskell-cafe] basic field questions
Hallo,
On 1/24/07, Ketil Malde [EMAIL PROTECTED] wrote:
jamin1001 wrote:
What if I want to do something like
data Chair = Chair {pos:: Int, color :: Int}
data Table = Table {pos:: Int, color :: Int}
data Properties = Props { pos, color :: Int }
data Chair = Chair Props
data Table = Table Props
Do you mean:
data Chair = Chair Properties
data Table = Table Properties
?
--
-alex
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Re: [Haskell-cafe] Beta Gtk2Hs Getting Started
Hallo, On 1/8/07, Hans van Thiel [EMAIL PROTECTED] wrote: Thanks, I didn't know that. What other widget libraries are supported at this time? Only GTK+. :-) -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Beta Gtk2Hs Getting Started
Hallo, On 1/8/07, Hans van Thiel [EMAIL PROTECTED] wrote: Hello All, The beta of the 'Gtk2Hs:Getting Started' short tutorial for beginners, Haskell GUI for Dummies, if you like :-) can be viewed at http://j-van-thiel.speedlinq.nl/gtk2hs/gtk2hsGetStart.html Nitpicking: Glade does not belong to GTK+, neither does libglade, which are independent projects. -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Building the community
Hallo, On 12/14/06, Paul Moore [EMAIL PROTECTED] wrote: But overall I'd agree, this is a very helpful community - it's just that you all seem so much cleverer than I, so I'm not sure I'll ever be smart enough to write Haskell programs :-) (50% joke...) I know the feeling. :-) -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Aim Of Haskell
Hallo, On 12/13/06, Claus Reinke [EMAIL PROTECTED] wrote: we have had lots of languages that were intended to be well-designed (good, beautiful, ..), but never much used in practice, and we have also had lots of languages that were intended to be pragmatic (practical, useful, ..), without much interest in theoretical beauty. but how many languages are there where the two aspects have converged, with both communities still actively interested in the result? Lua is a small scripting language created in academia, whose authors are academics, that has reached the industry embedded in several well-known products such as World of Warcraft or Adobe Lightroom (which is 40% Lua). Frequently people ask for bloat in the mailing list, and the usual answer is why?. The authors claim that when thinking about a new version of Lua they don't think of features to add, but what features they can remove. So I'd say it's perfectly possible to have an academia-backed language useful for the real world. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Large data structures
Hallo, On 12/11/06, Matthew Brecknell [EMAIL PROTECTED] wrote: Yes. Take a look at Data.Map. This data structure provides various operations which create a new map from an old one in O(log n) time, by splicing bits of the old map into the new one. Importantly, performing any of these operations does not destroy the old map if your code still references it. On the other hand, if your code drops references to the old map, then the garbage collector can reclaim any branches of the old map not used in the new one. You may also be interested in this paper: http://www.cs.cmu.edu/~rwh/theses/okasaki.pdf Thanks for the info and the link, looks interesting. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Large data structures
Hallo, On 12/12/06, Benjamin Franksen [EMAIL PROTECTED] wrote: Alex Queiroz wrote: On 12/11/06, Stefan O'Rear [EMAIL PROTECTED] wrote: No. Haskell's lists are linked lists, enlarge creates a single new link without modifying (and copying) the original. Thanks. Is there a way to mimic this behaviour with my own code? It is the default for any data structure you define. Data is by default represented internally as a pointer to the actual value. Otherwise recursive structures (see below for an example) would not be easily possible. And since no part of the data structure is 'mutable', different instances can share (memory-wise) as much of their structure as the implementation is able to find. Ok, I think I got it now. :-) PS: Please try to include exactly the relevant context in replies, no more, no less. Your original question (stripped down to the body of the text) would have been relevant, here, but neither 'Hello', nor 'Cheers' are worth quoting. Sorry, but I did not quote hello or cheers. -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Large data structures
Hi all, I'm considering the use of Haskell to manipulate large data structures for Computer Graphics (large geometric datasets). I'm wondering what's the best way to do it. As objects (not in the OO sense) in Haskell are immutable, how can I add a vertex to a large mesh without using obscene amounts of memory? Making an analogy: enlarge :: a - [a] - [a] enlarge c cs = c : cs enlarge 15 [1..10] Will this copy the whole list to make a new one with an element more? Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Large data structures
Hallo, On 12/11/06, Stefan O'Rear [EMAIL PROTECTED] wrote: No. Haskell's lists are linked lists, enlarge creates a single new link without modifying (and copying) the original. ___ Thanks. Is there a way to mimic this behaviour with my own code? Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: The Future of MissingH
Hallo, On 11/27/06, Max Vasin [EMAIL PROTECTED] wrote: A small addition: some GPLed libraries (libstdc++ AFAIK) allow linking with proprietary software by adding clause to lisence which relaxes GPL requirements. Nope, it's LGPL with an extra binary linking permission. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: best Linux for GHC?
Hallo, On 11/13/06, Mark T.B. Carroll [EMAIL PROTECTED] wrote: How up to date will Debian unstable's GHC be kept, though? It seems pretty good at the moment, but there have been times when we've had to install from source instead of via Debian earlier this year so that we had GHC features and bugfixes in place - the Debian version has got rather out of date at times with respect to stuff we needed. No OpenGL neither Gtk2hs in Debian Sid yet. :-( -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is Haskell a 5GL?
Hallo, On 9/25/06, Ch. A. Herrmann [EMAIL PROTECTED] wrote: Hi, Henning Thielemann wrote: assembly language (Assembler ist deutsch :-) for mysterious reasons it entered the English world. 'Assembly' is a language. 'Assembler' is a program. -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell web forum
Hallo, On 9/21/06, Bill Wood [EMAIL PROTECTED] wrote: I have only recently started accessing some web fora, but I've noticed that some of those powered by phpBB are vulnerable to spamming, whereas the news groups seem to be less so. For example, the python-forum has nearly lost it's General forum to spammers. Maybe the experts know better engines, better ways to set up a forum, or better ways to administer them after they're up, but it is a concern. I only hope this mailing list will continue. I can't stand the slowness/spams/avatar/size of web fora. -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] does the compiler optimize repeated calls?
Hallo, On 9/6/06, Tamas K Papp [EMAIL PROTECTED] wrote: PS: I realize that I am asking a lot of newbie questions, and I would like to thank everybody for their patience and elucidating replies. I am a newbie myself (second week of learning Haskell), but I'll give it a shot: Since functions have no side effects, the compiler executes the function only once. -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: does the compiler optimize repeated calls?
Hallo, On 9/6/06, Lennart Augustsson [EMAIL PROTECTED] wrote: Furthermore, doing that optimization (common subexpression elimination) can lead to space leaks. So you should not count on the compiler doing it. Besides, I often find it more readable and less error prone to name a common subexpression; only one place to change when you need to change the call. So there is no benefits from the functions have no side-effects property, performance-wise. Pity. -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
