- Haskell-Cafe - Haskell.org

Chicago Haskell User Group?
by Tom Tobin 13 Aug '09

13 Aug '09

There isn't a Chicago-area Haskell group, is there? If not, would anyone be interested in forming one? I used to run Chicago's Django (a Python web framework) group, but lost interest (and since I lived in the suburbs back then, got sick of the commute). Unlike Python, I'm still very much a beginner with Haskell, so I feel I'd be able to benefit quite a bit from picking the brains of more skilled users and cooperating with other beginners. My particular interests are web development (as that's my professional field) and multimedia organization (I'm working on a Haskell audio tagging library to help teach myself the language), but I'm open to learning just about anything. :-)

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Re: [Haskell-cafe] Chicago Haskell User Group?
by Louis Wasserman 12 Aug '09

12 Aug '09

Count me in. I'm a student at UChicago. Louis Wasserman wasserman.louis(a)gmail.com

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Database written in Haskell?
by Günther Schmidt 12 Aug '09

12 Aug '09

Hi, is there an SQL database written in Haskell like HSQLDB which is written in Java? Günther

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Examples
by Andrew Coppin 12 Aug '09

12 Aug '09

As some of you may remember, I recently released a couple of packages on Hackage. I'd like to also release some example programs using these packages, but I'm not sure of the best way to do this. Do I make the example programs part of the package itself? Do I release a seperate package which just contains the example code? Something else entirely? What's the recommendation here?

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Next BostonHaskell meeting: August 18th at MIT
by Ravi Nanavati 12 Aug '09

12 Aug '09

I'm pleased to announce the August meeting of the Boston Area Haskell Users' Group. Based on the feedback from the July meeting and the constraints of our speakers, the August meeting has been scheduled for Tuesday, August 18th from 6:30pm - 8:30pm. Like the past two meetings, it will be held in the MIT CSAIL Reading Room (32-G882, i.e. a room on the 8th floor of the Gates Tower of the MIT's Stata Center at 32 Vassar St in Cambridge, MA). We're making a slight departure from our meeting format this month. Our featured speaker will be Edward Kmett, who will be sharing a two-part presentation focusing on monoids and parsing. The first part of Edward's presentation is titled "Introduction to Monoids". After the first part of Edward's presentation, Shae Erisson will be presenting short overview of Haskell and emacs integration. Following Shae, Paul Chiusano will be talking briefly about functional programming opportunities at ClariFI (the job advertisement he recently posted to the BostonHaskell list). Paul is planning to be available to talk to anyone interested during our customary break. As you might guess, there isn't really room for Lightning Talks or other advertisements in August, but please feel free to contact me if you have something you'd like to talk about at a future meeting (since we're still very hungry for content for future meetings). After the break, Edward will be picking up with the second part of his presentation: "A Parallel Parsing Trifecta: Iteratees, Parsec, and Monoids". We're trying a new attendance poll this month: http://doodle.com/participation.html?pollId=x8rbbbprtezdtaan As before, responding to this poll will help with two things: 1. Getting an idea of what fraction of the Boston-area Haskell community can and can't attend this meeting (to help with future scheduling). 2. Giving me an estimated count of attendees, since I have talked my wife into baking some more goodies and bringing drinks again. Sponsorship of or other assistance with refreshments is still being eagerly solicited. I'm also still having trouble embedding this poll in a page on our Google Group, so if anyone has any ideas about that, please feel free to try (any group member can edit pages) and/or offer other assistance or suggestions. If you have any questions about the meeting please send them to the BostonHaskell mailing list: bostonhaskell(a)googlegroups.com or contact me directly. I look forward to seeing many Boston-area Haskellers at the August meeting! Thank you, - Ravi Nanavati

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Finalizers on FunPtrs
by Maurício CA 12 Aug '09

12 Aug '09

I see in Foreign.Ptr documentation that it is good practice to call freeHaskellFunPtr when a pointer to a Haskell function (obtained using 'dynamic' stubs) is not going to be used anymore. Is it possible to do that in a way that is similar to ForeignPtr behavior, where pointers are finalized when GC knows they're not going to be used anymore? See this attempt: In an IO monad: a <- giveMeFunPtr b <- castFunPtrToPtr a :: IO (Ptr something) foreignFunPtr <- newForeignPtr funPtrFinalizer b :: IO (ForeignPtr something) With funPtrFinalizer a FunPtr to: baseFunPtrFinalizer p = freeHaskellFunPtr . castPtrToFunPtr p Is something like that expected to work, i.e., would I get a ForeignPtr that I could cast and give to foreign functions, and still expect that my function pointer would be freed when not needed anymore? Thanks, Maurício

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Re: [Haskell-cafe] Haskell's type system compared to CLOS
by Matthias-Christian Ott 11 Aug '09

11 Aug '09

On Tue, Aug 11, 2009 at 11:20:02PM +0100, Philippa Cowderoy wrote: > Matthias-Christian Ott wrote: >> What has Haskell to provide what Common Lisp and Dylan haven't? > Static typing (with inference). Very large difference, that. That's true. This is a big advantage when compiling programmes. But as far as I know type inference is not always decidable in Haskell. Am I right? Dylan does type inference too and Hannes Mehnert is currently working on better type inference for the dylan compiler [1]. Regards, Matthias-Christian [1] https://berlin.ccc.de/wiki/Dem_Compiler_beim_Optimieren_zuschauen

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ANNOUNCE: HacPDX, A Hackathon in Portland
by Thomas DuBuisson 11 Aug '09

11 Aug '09

HacPDX is an opportunity for Portland Haskell hackers to join together in building and improving libraries and tools. If you've never been, hackathons are typically not only a good opportunity for experienced devs to work together but also a great way for newcomers to get involved in the community. WHEN Friday Sept 25 3:30PM to 6:00 PM Saturday Sept 26 10:00AM to 6:00 PM Sunday Sept 27 10:00AM to 6:00 PM We can work however late, but tentatively let's plan on eating and sleeping. The Friday times give an opportunity to meet and test your network connectivity, should you so desire. Afterwards we can head out to grab a pint! WHERE We will be in rooom 86-01 (downstairs) of the fourth avenue building (1900 SW 4th Ave), which is part of Portland State University. As the building is locked during the weekends, I'll be letting attendees in via the Harrison Street entrance. EQUIPMENT You should bring a laptop with wireless (802.11). The room has whiteboards and a projector for any discussions or should anyone wish to give a talk. Further Information is available on the wiki [1]. Suggestions, wiki edits, organization and coordination help are all welcome. Thomas DuBuisson [1] http://haskell.org/haskellwiki/HacPDX

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Haskell's type system compared to CLOS
by Matthias-Christian Ott 11 Aug '09

11 Aug '09

Hi, usually I'm sceptical of programming languages which are not based on the von Neumann architecture, but recently I got interested in functional programming languages. The arrogance of lots of Haskell users, who made me feel that using a programming language other than Haskell is a waste of time, combined with vanguard mathematical notation has been very attractive to me and I have decided to get at least an idea of Haskell and its concepts. Some weeks ago I learned programming in Dylan and was impressed by its object system which is basically a stripped version of CLOS. Multiple dispatch together with a well-thought-out object system is quite powerful, because it removes the burden of including methods in the class definition. At the moment I'm reading the "Functional Programming using Standard ML" and I'm in the chapter on data types. This afternoon it occurred to me that classes and data types are symmetric. In a class hierarchy you start an abstract super class (the most abstract is the class object in some languages) and further specialise them via inheritance; with data types you can start with specialized versions and abstract them via constructors (I'm not sure how message sending to a superclass looks like in this analogy). Anyhow, I also came across an interesting presentation. Andreas Löh and Ralf Hinze state in their presentation "Open data types and open functions" [1]: * OO languages support extension of data, but not of functionality. * FP languages support extension of functionality, but not of data. Their first point refers to the fact that in most object-oriented languages don't allow the separate definition of classes and their respective methods. So to add new functions, you have edit the class definitions. However, in functional programming languages you can easily add new functionality via pattern matching, but have to either introduce new types or new constructors, which again means to modify existing code. In Dylan (and in Common Lisp) you define methods separate from classes and have pattern matching based on types. This solves all mentioned problems. So my question is, how are algebraic data types in Haskell superior to CLOS (despite the fact that CLOS is impure)? How do both compare? What has Haskell to provide what Common Lisp and Dylan haven't? Thanks! Regards, Matthias-Christian [1] http://people.cs.uu.nl/andres/open-japan.pdf

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Galois is Hiring
by Don Stewart 11 Aug '09

11 Aug '09

Galois is continuing to hire. We will also be at ICFP and related events, so come and see Lee Pike or me. We have multiple positions for talented functional programmers (with both junior and senior positions). A strong functional programming ability is an advantage (you will be programming in Haskell), and a good computer science background is required. Experience with compilers, operating systems, networking, security, and formal methods is of particular interest. Galois is based in Portland, Oregon. Our engineers work with functional languages, designing and developing advanced technologies for safety and security-critical systems, networks, and applications. Galois technical staff members play a pivotal role in developing advanced software technology. Enginners work in small team settings, and must successfully interact with clients, partners, and other employees in a highly cooperative, collaborative, and intellectually challenging environment. Technical staff may be called upon to write proposals, gather requirements, and work in all stages of the software development process, from requirements gathering to testing and validation. Additional duties may include project management, technology research and development, and technical infrastructure development. We’re looking for people who can invent, learn, think, and inspire. We reward creativity and thrive on collaboration. We offer great benefits and perks, including a 401K plan, stock options, paid vacation, family health plan, flexible work schedule, a casual work environment, snacks, espresso and foosball. A Masters or Ph.D. degree in Computer Science is desirable. Additionally, a strong programming background and experience with Haskell or other functional programming languages is preferred. You must work well with customers, including building rapport, identifying needs, and communicating with strong written, verbal and presentation skills. Must be highly motivated and able to self-manage to deadlines and quality goals. To learn more about us, visit http://www.galois.com and http://www.galois.com/company/careers The types of technology we use are covered in our blog: http://www.galois.com/blog/ We’d like to hear from you! Send your cover letter and resume to us at jobs2009 at galois.com.

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GTK2HS OpenGL demo doesn't work on Vista when compiled?
by Peter Verswyvelen 11 Aug '09

11 Aug '09

GTK2HS 0.10.1 comes with an OpenGL demo (share/demo/opengl/RotatingCube.hs) On my machine (Vista 32-bit) it runs fine under GHCi, but not when compiling using GHC (no rendering happens, unless I resize the window, then rendering happens from time to time) I'm using GHC 6.10.3 (installed Haskell Platform 2009.2.0.1). Do other people using Windows experience this problem? Cheers, Peter Verswyvelen

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Re: Any comments about Clojure language?
by Mark Volkmann 11 Aug '09

11 Aug '09

> On Mon, 10 Aug 2009 09:35:48 -0700, Don Stewart <dons at galois.com> > wrote: > > Another possible disadvantage of Clojure is the lack of high-quality > free online tutorials. I wrote an extensive intro. to Clojure at http://ociweb.com/mark/clojure/article.html. -- R. Mark Volkmann Object Computing, Inc.

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Re: Re[2]: [Haskell-cafe] unsafeDestructiveAssign?
by Job Vranish 11 Aug '09

11 Aug '09

Opps, didn't "reply to all" I hate it when that happens... On Tue, Aug 11, 2009 at 1:00 PM, Job Vranish <jvranish(a)gmail.com> wrote: > haha, yeah. > > What I'm actually trying to do is make a way to manipulate arbitrary > recursive algebraic data structures as if they were graphs (not for > performance reasons but because it makes manipulating them much easier) > > It's similar to the data-reify package, but I need it to work on any > algebraic datatype. > > I'm not planning on using it for actually production code. I'm mostly just > experimenting with as a potentially interesting language feature. > > - Job > > > On Tue, Aug 11, 2009 at 12:50 PM, Bulat Ziganshin < > bulat.ziganshin(a)gmail.com> wrote: > >> Hello Job, >> >> Tuesday, August 11, 2009, 8:45:29 PM, you wrote: >> > What I am trying to do is hyper unusual and I really do need an >> unsafeHorribleThings to do it. >> >> yes, assigning 5 to 8 is really unusual in math :) >> >> >> -- >> Best regards, >> Bulat mailto:Bulat.Ziganshin@gmail.com >> >> >

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Re: Examples
by John Lato 11 Aug '09

11 Aug '09

Hello, Looking at just examples, there are a few separate issues here. 1. Installation of example source for review 2. Building/installation of example programs For the second issue, the buildExamples flag suggested by Henning works well to actually build the examples with cabal, but the install location is still a problem. Most users wouldn't want example executables to go into their bin directory, especially not in the case of global installs. To the best of my knowledge, Cabal currently doesn't support separate installation locations for multiple executables, nor does it support building but not installing executables. With the first issue, the problem is simpler. There's no location for source code to be installed to. Users can download the package and unpack it themselves, or the developer can include demo source as a "data file" and install it to the datadir (IMO a poor choice). One option is to add support for different installation locations for each executable. Perhaps the --installdir flag could be extended to support a syntax like the following: --installdir=executableName:/path/to/install where if executableName matches one of the executables known to cabal, it will install just that executable to the specified location. This puts a larger burden on users, however, since they would need to know the name(s) of all the demo executables. It also doesn't address the issue of source location. Another way is to add a special type of executable for tests and demo programs to cabal. A user would specify a directory in the .cabal file (or command-line) to which tests would be installed. Cabal would then build the identified tests/demos for the package and put them into that specific directory, as well as the source code. This also answers the question of where to put executables that are Buildable but not Installable. Thoughts? Cheers, John Lato > Date: Sun, 9 Aug 2009 21:07:53 -0400 > From: "John D. Ramsdell" <ramsdell0(a)gmail.com> > Subject: Re: [Haskell-cafe] Examples > To: Haskell Cafe <haskell-cafe(a)haskell.org> > Message-ID: > <7687290b0908091807y1d4a5329w6b452c6a3af5e044(a)mail.gmail.com> > Content-Type: text/plain; charset=UTF-8 > > Maybe in addition to having a buildable boolean in a library or > executable section, there should be an installable boolean. It would > default to true, but when false, the library or executable section is > ignored during package installation. > > John >

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Haskell2Xml
by Dmitry Olshansky 11 Aug '09

11 Aug '09

Hello all, I need a convenient tool to generate Haskell types from XML W3C Schema Definition (xsd) and vice versa - generate instances for Haskell ADT's to make corresponding XML. It is just the same that HaXml do with DTD. I need - using XSD - support for unicode - using xml-attributes as far as elements are very desirable - by my opinion TemplateHaskell for generate instances is prefferable than using DrIFT (which used in HaXml) - both possibilities is great of course - generation of xsd by Haskell type is a good feature also and so on... Does this tool exist? Do some articles / thoughts / standards / recomendations about correspondence between XML and Haskell ADT's exist? Best wishes, Dmitry

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C2HS issues on Hackage
by Michael Snoyman 11 Aug '09

11 Aug '09

Hi all, I've written a Yaml library built on top of libyaml (the same C library at the core of Python's yaml library). All is well on my local system and my server; I'm currently using it in production. However, the build is failing on Hackage with the following build log: http://hackage.haskell.org/packages/archive/yaml/0.0.1/logs/failure/ghc-6.10 . It seems that whichever version of C2HS is installed on the server does not allow "type" (or perhaps other keywords?) to be used as C identifiers. Unfortunately, "type" is the name of a field in a C struct I need to integrate with. It's obviously not vital that I get it to compile on hackage, but 1) I'm worried this is a sign of a bigger problem, and 2) it's always nice to have the API documentation available online. Any suggestions? Thanks, Michael

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Any comments about Clojure language?
by Sukit Tretriluxana 11 Aug '09

11 Aug '09

Hi all, I start reading about Closure language (http://clojure.org) and it seems an interesting language. I don't know much about this language especially in comparison to Haskell feature by feature. Could it perhaps be what Haskell on JVM would have been with the dressing of Lisp syntax? Any one would like to chime in your comments about the language, in comparison to Haskell? Thanks, Ed

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Re: Announce: EnumMap-0.0.1
by Louis Wasserman 10 Aug '09

10 Aug '09

Pardon my asking, but are fromEnum and toEnum guaranteed to preserve order on types like Double? I'd like to see a Double-backed Patricia tree map, but are we certain that EnumMap as presented will behave properly on such types? Louis Wasserman wasserman.louis(a)gmail.com

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[ANNOUNCE] hgettext 0.1.10 - last major release
by Vasyl Pasternak 10 Aug '09

10 Aug '09

Hello, I've uploaded last (and latest) significant version on hgettext module. Currently it works fine, and has bindings to all gettext functions (from libintl.h). Next versions will be only bug fixes of this version. GNU GetText allows you only to create simple, standalone desktop applications for Linux, to make something complex you should use different trick, fortunately Haskell could do these tricks much easier than other languages (if you want to see, how to build Gtk application, which supports run time language switching, and shows information on two languages simultaneously you could download example from http://hgettext.googlecode.com/files/gtk-hello-0.0.2.tar.gz , or read about it from http://progandprog.blogspot.com/2009/04/multilingual-ui-and-dynamic-languag…) I don't see any strong reasons to write any combinators over this basic bindings. Haskell needs more powerful internationalization library, and I am plan to design it, but it will be completely different from gettext principles, so this library will be released with another name. CHANGELOG: * Added '--version' command line parameter to hgettext tool * Added support for literate haskell files to hgettext tool * Changed all functions to throw IOError when they fails instead of return Nothing * Added bindings for: ngettext, dgettext, dngettext, dcgettext and dcngettext functions -- Best regards, Vasyl Pasternak

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[Haskell Cafe] Parsec: using two different parser for the same string
by Paul Sujkov 10 Aug '09

10 Aug '09

Hi everybody, suppose I have two different parsers: one just reads the string, and another one parses some values from it. E.g.: parseIntList :: Parser [Integer] parseIntList = do char '(' res <- liftM (map read) (sepBy1 (many1 digit) (char ';')) char ')' return res parseIntString :: Parser String parseIntString = manyTill anyChar eof so for some input like this - "(1;2;3;4)" - I will have two different result: *Parlog> parseTest parseIntList "(1;2;3;4)" [1,2,3,4] *Parlog> parseTest parseIntString "(1;2;3;4)" "(1;2;3;4)" but the thing that I actually want is something like Parser ([Integer], String) - results from both parsers at a time, no matter whether one of them fails or not: *Parlog> parseTest parseIntListAndString "(1;2;3;4)" ([1,2,3,4], "(1;2;3;4)") it is impossible at first sight, because first parser to use will consume all the input, and there will be nothing to parse for the second one Parsec contains "choice" function, but it is implemented via <|> and that is mplus - so it tries second alternative only if the first one fails. Is it possible to use two parsers for the same string (with try-like backtracking, no input actually consumed till the second parser finishes)? I can assume only dirty hacks with the GenParser internals - manual position storing and backtracking - but that is obviously not good however, my first attempt to solve the problem was kind a like that: to parse string to String, and then to use it as an input for the next level parse call: parseIntListAndString :: Parser ([Integer], String) parseIntListAndString = do str <- parseIntString return (res str, str) where res str = case (parse parseIntList "" str) of Left err -> [] Right val -> val but the problems with such a method began when I switched from Parser to GenParser with user state: function parseIntList have to update the state, but it can't have the same state as the parseIntListAndString any more: it has it's own. I can explicitly pass the state from parseIntListAndString to parseIntList, but I see no suitable way for the parseIntList to update it. I can return the updated state value from the parseIntList function, and call setState on a result - but it seems rather ugly to mee. However, if nothing else will do, that is an alternative it is of course possible to use two different parsers sequentially, but it is also very ineffective: I need to use such multiple parsing on a relatively small substring of the actual input, so little backtracking would be a much nicier approach. Any suggestions? -- Regards, Paul Sujkov

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haskell embedded
by Kevin Smith 10 Aug '09

10 Aug '09

Hello, Could someone point me in the the direction of any references for using Haskell as an embedded language in an application. Xmonad seems to come to mind because the configuration files are written using Haskell. Any other information ? Thanks in advance.

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Request for Changelogs
by Joachim Breitner 09 Aug '09

09 Aug '09

Hi, (this is mostly a rant, but hopefully a constructive one) the Haskell/cabal/hackage eco system is pretty great, as we all know. But there is one huge gaping omission there: Changelogs! I’m involved in packaging Haskell stuff for Debian. Now, the Debian tools we have for that tell me „Hlint has a new version, 1.6.5, which is newer than the one you packages, 1.6.4. Huh, nice. What has changed? Is it relevant for Debian? Is it worth a new upload? There is no easy way to find out: http://hackage.haskell.org/package/hlint lists no changes http://community.haskell.org/~ndm/hlint/ lists no changes (and not every package has a homepage) http://community.haskell.org/~ndm/darcs/hlint/ contains on Changes file (and not every package has a (linked) darcs repository) http://community.haskell.org/~ndm/darcs/hlint/ also has no web frontend. Which leaves me with the option of getting the darcs repo and looking through "darcs changes". If I know of a repository for the package. So please, package authors, put Changes files in your packages and keep the current for now. And cabal/hackage guys: Llease introduce a standard Changes format for cabal packages so that http://hackage.haskell.org/package/hlint readily lists (or links to) changes. Thanks, Joachim -- Joachim "nomeata" Breitner Debian Developer nomeata(a)debian.org | ICQ# 74513189 | GPG-Keyid: 4743206C JID: nomeata(a)joachim-breitner.de | http://people.debian.org/~nomeata

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ANNOUNCE: cabal-query 0.1
by Max Desyatov 09 Aug '09

09 Aug '09

This package was written to assist you at finding a set of packages, which satisfy your needs. At the moment it doesn't have a standalone executable, but you can do the queries from your Haskell code. It uses Data.Generics.PlateData, so * when Cabal package format changes, we don't have to rewrite anything * all queries are statically typed * as a disadvantage, we may suffer some performance loss when doing very complex queries, anyway most of processing goes while we read package descriptions, not querying them Example of enduser querying code: > module Main where > import qualified Data.ByteString.Lazy as B > import System.Environment > import Distribution.Query > import Distribution.Compiler > import Distribution.License > import Distribution.ModuleName hiding (main) > import Distribution.Package > import Distribution.PackageDescription > import Distribution.Version > import Distribution.Text > import Language.Haskell.Extension > main = (head `fmap` getArgs) >>= > B.readFile >>= > mapM_ (putStrLn . show . (x -> (display $ package x, display $ license x))) . > queryIndex (Not (Id (== GPL)) :& Not (Id (== BSD3))) This queries an index file, which is commonly located at ~/.cabal/packages/hackage.haskell.org/00-index.tar in POSIX systems. You can query any field of PackageDescription no matter how deep it is. You don't need to provide any type signature for comparison functions, which are wrapped in Id, as long as you use data constructors for which type can be inferred. In the future versions I want to add some query expressions parser, for invoking cabal-query from command-line. I suppose this will look like: cabal-query -q 'license == BSD3 & stability == stable & testedWith == GHC & repoType == (git | darcs)' <path_to_cabal-files_or_index-file>

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Complex numbers and (**)
by Paul Sargent 09 Aug '09

09 Aug '09

Hi, First post to the cafe, so "Hello everybody!". Hope this is reasonable subject matter and not too long. I've been working on some algorithms that involved taking the n-th root of complex numbers. In my code I've implemented this as raising the complex number ('z') to 1/n using the (**) operator. Obviously, there are n roots, but I only need one of them so this is fine. Q1) Have I missed a method that's a little less general than 'raising to a Complex'? We have integer powers, but not integer roots? All seems to work fine, except I have a little wrapper function to prefer real roots of real numbers, until I started seeing NaNs appearing. This happened when I tried to take the root of 0+0i. In fact raising 0+0i to any power with (**) causes NaNs to appear. (^) and (^^) have no problem, assuming the calculation is one that can be represented with those operators. Neither is there a problem when the values being raised are not in complex form. Prelude Data.Complex> let xs = [0.0 :+ 0.0, 1.0 :+ 0.0, 2.0 :+ 0.0, 3.0 :+ 0.0] Prelude Data.Complex> [x ^ 2 | x <- xs] [0.0 :+ 0.0,1.0 :+ 0.0,4.0 :+ 0.0,9.0 :+ 0.0] Prelude Data.Complex> [x ^^ 2 | x <- xs] [0.0 :+ 0.0,1.0 :+ 0.0,4.0 :+ 0.0,9.0 :+ 0.0] Prelude Data.Complex> [x ** 2 | x <- xs] [NaN :+ NaN,1.0 :+ 0.0,4.0 :+ 0.0,9.000000000000002 :+ 0.0] Prelude Data.Complex> let xs = [0.0,1.0,2.0,3.0] Prelude Data.Complex> [x ** 2 | x <- xs] [0.0,1.0,4.0,9.0] Digging deeper I've discovered this is because Complex inherits it's definition of (**) as "x ** y = exp (log x * y)". Well... the log of 0+0i is -Inf+0i. Multiply this by a real number in complex form and you end up with -Infinity * 0.0 as one of the terms. According to the IEEE floating point spec, this is NaN. That NaN propagates through exp, and you end up with NaN :+ NaN as the result. Q2) Do people agree this is a bug in the definition of Data.Complex? Seems like the thing to do to fix this is have an instance of (**) for Data.Complex that special cases (0 :+ 0) ** _ to always return (0 :+ 0). An alternative would be to use the underlying non-complex (**) operator for arguments with no imaginary parts. One downside is that this would change the output of Complex (**) so that raising a real argument to a real power always produced a real result (which is actually what I want, but may not be what others expect / have got used to) Q3) Do people agree with these options? Any opinions? How would I submit a patch? I did send a mail to the glasgow-haskell-bugs list, but it doesn't appear to shown up in the archives, so I assume it didn't make it. It also didn't seem quite the right place as this is in the libraries. Apologies if anybody reading this is getting deja-vu. Paul

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Using -Nx Option with GHC
by Mark Wassell 08 Aug '09

08 Aug '09

Hi, I am trying to compile and run my program so that it utilises more than one core on my machine. I have looked at http://haskell.org/haskellwiki/Shootout/Parallel/BinaryTrees and am using parMap at a point in my code. I compile with ghc --make -O2 -threaded and run with the options +RTS -N5 The runtime complains that it doesn't understand the N option. I am running 6.10.4 on Windows XP. Cheers Mark

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Hugs faster and more reliable than GHC for large list monad 'do' block
by Henning Thielemann 08 Aug '09

08 Aug '09

Today a student has shown me a program that consists of a large 'do' block for the list monad. The program looks like do x1 <- [0..3] x2 <- [0..2] ... x600 <- [0..5] guard (x1+x2+2*x3 >= 0) ... return (x1,x2,....,x600) It was actually generated by another program. The results were: GHC-6.4 was not able to compile that program at all, because it stopped because of memory exhaustion. GHC-6.8.2 finished compilation after two minutes but the program aborted quickly because of a corrupt thunk identifier. GHC-6.10 not yet tested. Hugs-2006 executed the program without complaining and showed the first result after a few seconds: (0,0,0,0,0,...,0). Eventually the program must run on a Linux cluster with a not up-to-date Linux kernel, that is, I suspect newer GHC versions cannot be used due to the 'timer_create' problem. (At least, the 'cabal' executable that I generated with a GHC-6.8.2 had this problem when running on the cluster which reminded me on the problems with GHC-6.8 itself running on older Linux kernels.) Since the list monad sorts the variable values in lexicographic order which is inappropriate for the considered problem, I recommended the use of control-monad-omega. Luke, I hope this monad can cope with 600 variables. :-)

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Haskell Weekly News: Issue 127 - August 8, 2009
by Brent Yorgey 08 Aug '09

08 Aug '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090808 Issue 127 - August 08, 2009 --------------------------------------------------------------------------- Welcome to issue 127 of HWN, a newsletter covering developments in the [1]Haskell community. Apologies for the long hiatus, mostly due to organizing Hac phi (which was a [2]great success!). And I'm now going on vacation for a couple weeks and may have limited Internet access, so don't hold your breath for an issue of the HWN next week either... anyway, a ton of interesting stuff has happened over the past three weeks (of course), including a bunch of [3]discussion on the Haskell-prime mailing list, a number of package releases, Haskell Platform discussion, and more. Announcements bindings-posix 0.0.2. Mauricio [4]announced [5]bindings-posix, a low level binding to Posix. It makes use of facilities and design from the [6]bindings-common package to map the [7]standard Posix library. bindings-common 0.2.1. Mauricio [8]announced a new release of [9]bindings-common, which offers basic code that provides a common design standard and common utilities for writing modules providing low-level foreign library bindings. The major new feature of this release is the availability of hsc2hs custom macros, and a corresponding reduction in code size. Dyre - Dynamic Program Recompilation (Xmonad-style configuration). Will Donnelly [10]announced the release of [11]dyre, a library for xmonad-style program recompilation. It is based in spirit after the HConf library written by the Yi project, but with a focus on simple integration, state persistence as an optional feature, and Windows support. nntp 0.0.2. Maciej Piechotka [12]announced the release of [13]nntp, a library to connect to nntp (i.e. mainly USENET) servers. This version represents a complete rewrite from version 0.0.1, including a new NntpT monad and basic support for XHDR. GLUT 2.2.0.0. Sven Panne [14]announced a new version of the [15]GLUT package, which depends on the new OpenGL, StateVar and Tensor packages, but is otherwise unchanged except for a new demo. OpenGL 2.3.0.0. Sven Panne [16]announced a new version of the [17]OpenGL package, which is now only a convenience layer upon the [18]OpenGLRaw and [19]GLURaw packages, written in in pure Haskell without the FFI. The latter two packages load the native libraries dynamically and do not rely on any C headers, making it possible to build all OpenGL-related packages even on machines without any installed native OpenGL support. yices 0.0.0.1. Ki Yung Ahn [20]announced [21]yices, a Haskell interface to the [22]Yices SMT solver. ALUT 2.2.0.0. Sven Panne [23]announced a new version of the ALUT package, which now depends on the highly portable [24]StateVar package instead of [25]OpenGL. OpenAL 1.4.0.0. Sven Panne [26]announced a new version of the [27]OpenAL package, which now depends on the highly portable [28]StateVar, [29]ObjectName and [30]Tensor packages, instead of [31]OpenGL. Tensor 1.0.0.1. Sven Panne [32]announced the [33]Tensor package, yet another spin-off of the OpenGL package, containing a few tensor data types and their instances for some basic type classes. darcs 2.3.0. Petr Rockai [34]announced a new stable release of [35]darcs, version 2.3.0. This version includes a number of improvements and bugfixes over the previous stable release, 2.2. Moreover, work has been done to improve performance of "darcs whatsnew" for large repositories. uacpid-0.0.4. Dino Morelli [36]announced the release of [37]uacpid, a daemon designed to be run in userspace that will monitor the local system's acpid socket for hardware events. These events can then be acted upon by handlers with access to the user's environment. Korean translation of "Programming in Haskell". Ki Yung Ahn [38]announced a new [39]non-English book on Haskell, published on July 24. TABI 0.1: a typeful tagged cross-language calling convention. Bulat Ziganshin [40]announced a preliminary release of [41]TABI, a library providing a typeful, tagged cross-language calling convention. Typeful/Text/HTMLs (for AngloHaskell/for scrap?). Jon Fairbairn [42]announced an [43]HTML library which guarantees standards compliance via types, even down to the nesting restrictions. yst 0.2.1. John MacFarlane [44]announced the release of [45]yst, which generates static websites from YAML or CSV data files and StringTemplates. This approach combines the speed, security, and ease of deployment of a static website with the flexibility and maintainability of a dynamic site that separates presentation and data. The Haskell Platform 2009.2.0.2. Don Stewart [46]announced the third release (2009.2.0.2) of the [47]Haskell Platform, a single, standard Haskell distribution for everyone. atom 0.1.0. Tom Hawkins [48]announced the 0.1.0 release of [49]Atom, a Haskell DSL for hard realtime applications. This release includes support for assertions and functional coverage to aid simulation and testing. tkhs-0.1.* Presentation Utility. Yusaku Hashimoto [50]announced the release of [51]tkhs-0.1.*, a simple presentation utility. If you are thinking PowerPoint is overkill for your presentation, Tkhs may fit the purpose. RFC: Unicode support in Alex. Jean-Philippe Bernardy [52]requested feedback on his modifications to the [53]Alex lexer generator to support Unicode. The prototype is [54]available on github. The Monad.Reader - Issue 14. Wouter Swierstra [55]announced Issue 14 of [56]The Monad.Reader. This issue contains three articles "Fun with Morse Code" by Heinrich Apfelmus, "Hieroglyph 2: Purely Functional Information Graphics Revisited" by Jefferson Heard, and "Lloyd Allison's Corecursive Queues: Why Continuations Matter" by Leon P Smith. TBC: Testing By Convention. Peter Gammie [57]announced the release of [58]TBC, a test harness which has features complementary to existing harnesses: it attempts to compile and run all tests, even if some do not compile or run; and tests following conventions require a lot less boilerplate. Elerea version 1.x.x. Patai Gergely [59]announced an update of his FRP library, [60]Elerea, along with some updates to the accompanying [61]example programs. The interface was changed into a monadic-applicative hybrid that distinguishes stateful and stateless combinators for safety reasons: most importantly, the latcher was removed due to various practical issues, and it is replaced by much better behaved stateless higher-order constructs. The library is now capable of handling arbitrary higher-order signals. haskell-src-exts-1.1.0. Niklas Broberg [62]announced the release of [63]haskell-src-exts-1.1.0, bringing you tuple sections, comments, and a few bug fixes. graphviz-2999.1.0.2. Ivan Lazar Miljenovic [64]announced a bug fix release of the [65]graphviz package, which fixes a bug spotted by Srihari Ramanathan where the Dot representation of Color values were double-quoted when they shouldn't have been. Leksah 0.6. Hamish Mackenzie [66]announced the 0.6 release of [67]Leksah, a Haskell IDE. New features include integrated GHCi based debugging, multi-window support, improved layout control, regular expression find and replace, ability to grep files in the current package, and improved Mac OS X integration. Semantic Web. Vasili I. Galchin [68]announced the [69]cabalisation of [70]Swish-0.2.1 (Semantic Web Inference uSing Haskell), a semantic web toolkit designed and implemented by Graham Klyne. The package now builds on GHC 6.8.2, with more improvements planned. graphviz-2999.1.0.1. Ivan Lazar Miljenovic [71]announced a bug-fix release to fix the problems with Either-based Attributes in the previous release (2999.0.0.0), spotted mainly by Zsolt Dollenstein. cautious-file 0.1.1: Ways to write a file cautiously, to avoid data loss. Robin Green [72]announced the first public release of [73]cautious-file, which provides a writeFile function that has several advantages over Prelude.writeFile: it uses the recommended way of writing a file on POSIX, so as not to expose the user to the risk of data loss after a crash or power failure; and it uses a temporary, randomly-named file for writing and only overwrites an existing file once the write is complete. Google Summer of Code Progress updates from participants in the 2008 [74]Google Summer of Code. Haddock improvements! Isaac Dupree has [75]cleaned up most of the loose edges on cross-package documentation, and has [76]begun moving comment parsing from GHC to Haddock. EclipseFP. Thomas Ten Cate is [77]finally happy with his refactorings of the Scion client, and has done [78]quite a bit of cleanup of compilation warnings and unit tests. Improving the Haskell space profiling experience. Gergely Patai posted about [79]segfaults with gtk2hs, and using Cairo instead of OpenGL for rendering, and has some [80]nice screenshots of the profiling client. haskell-src-exts -> haskell-src. Niklas Broberg has [81]started working on comment support. Fast darcs. Petr Rockai has made [82]much [83]progress, released [84]darcs 2.3.0, and posted a [85]discussion on patch formats. Discussion Adding binary to the Haskell Platform. Don Stewart began a [86]discussion thread on the possibility of adding the [87]binary package to the [88]Haskell Platform. Thinking about what's missing in our library coverage. Don Stewart [89]asked how to identify packages that ought to be added to the [90]Haskell Platform, and areas of functionality that are missing. Proposal: TypeDirectedNameResolution. Johannes Waldmann began a [91]discussion on a proposed language extension, [92]type-directed name resolution. Implicit concatenation in list comprehensions. Max Bolingbroke started a [93]discussion on a proposed syntax extension to allow multiple expressions on the left-hand side of a list comprehension, resulting in implicit concatenation. Jobs Postdoc and Ph.D. position on 3gERP-project at DIKU. Fritz Henglein [94]announced the availability of a postdoc position and a Ph.D. scholarship at the Department of Computer Science, University of Copenhagen (DIKU) within 3d generation enterprise resource planning systems (3gERP), a collaborative strategic research project with partners at DIKU (computer science), Copenhagen Business School (CBS, information systems) and Microsoft Development Center Copenhagen (MDCC, enterprise systems). Blog noise [95]Haskell news from the [96]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * >>> Joel Ray King: [97]Starting out with Haskell. * JP Moresmau: [98]Yoohoo: mazes of monad is kind of popular!. * Don Stewart (dons): [99]Haskell Package Popularity Rankings : August 2009. * David Amos: [100]Where we've been, and where we're going. * >>> Michael Feathers: [101]Functional Refactoring and "You Can't Get There From Here". * Magnus Therning: [102]Updating GHC on Arch. * Tom Schrijvers: [103]Monadic Constraint Programming with Gecode. * Luke Plant: [104]Haskell string support. * Don Stewart (dons): [105]The Haskell Platform 2009.2.0.2. * Gergely Patai: [106]More profiling goodies. * Don Stewart (dons): [107]Heuristics for Blessing Software Packages. * David Amos: [108]How to count the number of positions of Rubik's cube. * Edward Kmett: [109]Slides from Hac Phi: "All About Monoids". * Brent Yorgey: [110]Primitive species and species operations, part II. * Magnus Therning: [111]Making a choice from a list in Haskell, Vty (part 4). * Brent Yorgey: [112]Primitive species and species operations. * Thomas ten Cate: [113]The Green Bar. * Petr Rockai: [114]soc progress 10. * Brent Yorgey: [115]Hac phi roundup. * Brent Yorgey: [116]More from Hac phi. * Roman Cheplyaka: [117]CCC #5: Trial. * Eric Kow: [118]some ideas for practical QuickCheck. * Nathan Sanders: [119]Profiling in Haskell, part 2. * >>> Björn Winckler: [120]Inverse functions in Haskell. * >>> Alex Handy: [121]Everyone's talking about Haskell. * Niklas Broberg: [122]Starting on the comment support . * Gergely Patai: [123]Pango font rendering on an OpenGL canvas . * Brent Yorgey: [124]Hac phi day 2. * Petr Rockai: [125]Patch Formats. * Brent Yorgey: [126]Introducing Math.Combinatorics.Species!. * Magnus Therning: [127]Making a choice from a list in Haskell, Vty (part 3). * Michael Snoyman: [128]Embedding files in a binary. * Darcs: [129]darcs 2.3.0 is released!. * Petr Rockai: [130]Darcs 2.3.0. * >>> Ionuţ: [131]Haskell's prefix and infix notations. * >>> Ionuţ: [132]The minus operator in Haskell. * >>> Ken Jenkins: [133]Learning Haskell (Part 2). * James Iry: [134]Void vs Unit. * Justin Grant: [135]Generating pi in Haskell. * Petr Rockai: [136]soc progress 9. * >>> Ken Jenkins: [137]Learning Haskell (Part 1). * Isaac Dupree: [138]Next Project, Move doc-parsing to from GHC to Haddock. * Roman Cheplyaka: [139]SchrÃ¶dinger's cat. * Magnus Therning: [140]Ping server in Haskell (not that kind of ping, and rather silly). * >>> hydo: [141]Haskell and Hack fanboyism.. * Chris Smith: [142]Calculating Multiplicative Inverses in Modular Arithmetic. * David Amos: [143]Faster graph symmetries using distance partitions. * Isaac Dupree: [144]more cross-package docs details. * Nick Cameron: [145]ECOOP Day 3 - Day 1 of the main conference . * Ryan Lothian: [146]Haskell Graph Plotter - Part 1. * >>> Matias Giovannini: [147]Monadic Golf. * >>> Stephan Mann: [148]Cool Haskell Function. * >>> n0ne: [149]How do you use Haskell at work?. * Adam Blinkinsop: [150]Mastermind Solver in Haskell. * Ivan Uemlianin: [151]decorate-sort-undecorate in Haskell -- Advanced!. * Don Stewart: [152]Interview for SDTimes: "Everyone's talking about Haskell". * Don Stewart: [153]Haskell Platform Progress Report. * David Amos: [154]Strong generating sets for graph symmetries. * Chris Smith: [155]The Magic of Type Classes. * Twan van Laarhoven: [156]CPS based functional references . * Thomas ten Cate: [157]More robust Scion client code. * Paul Butler: [158]N-Queens in a Tweet. Quotes of the Week * dons: i heard there were webservers written in languages other than haskell * yrlnry2: #haskell is the most functional channel I've ever seen. * JonFairbairn: And one of the tests failed because Bolivia is now the Plurinational State of Bolivia, so I've add a patch for that. I've seen politics get in the way of programming, but I've never had a bug caused by /international/ politics before. * Adamant: ah, monads. the pons asinorum of Haskell. * QP: i drink i'm two thunk for this... i'm seeing (Double, Double) * benmachine: wait why am I giving advice I don't know anything * jfredett: <shapr> @yow ! <jfredett> YOW! I seem to SEE a SHAPR asking for FUNNY ZIPPY QUOTES, TOO bad I left them in my OTHER PANTS * Berengal: Anyone doubting the immutable value philosophy needs to try vacuum * badsheepy: [in response to a spammer] my word, i feel immediately compelled to medicate myself. * monochrom: Haskell has solved programming. All that can be said programming is already said in tutorials and the haskell wiki. That is why we drift to meta topics. * kalven: <yottis> i thought there were like 10 haskell jobs in the world, all in the "let's replace excel sheets with something else" industry <kalven> there are at least 20. * BMeph: okmij.net, conal.net, comonad.reader, and sigfpe.blogspot.com; the four horsemen of the Haskell Apocalypse. * jaredj: [on parsec] i thought i got it but i need to 'try' again * gwern: *ponders Haskell nerdcore: 'I'm all about exact math, yo; I eat CReal for breakfast'* * Baughn: remember that comments take up space in compiled Haskell programs, and furthermore they take up processing time if execution passes through them. For these reasons, keep comments to a minimum, and never put comments inside of optimized Haskell code. Ideally all of your comments will lie outside of the path of execution. * gbacon: okay, I just tried to type Monday, but it came out Monady. Assimilation complete. * BenLippmeier: Are Haskell and OCaml destined to be The Velvet Underground of programming languages, where hardly anyone has heard them, but everyone who does forms a band? About the Haskell Weekly News New editions are posted to [159]the Haskell mailing list as well as to [160]the Haskell Sequence and [161]Planet Haskell. [162]RSS is also available, and headlines appear on [163]haskell.org. To help create new editions of this newsletter, please see the information on [164]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [165]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://byorgey.wordpress.com/2009/07/29/hac-phi-roundup/ 3. http://news.gmane.org/gmane.comp.lang.haskell.prime 4. http://article.gmane.org/gmane.comp.lang.haskell.libraries/11611 5. http://hackage.haskell.org/package/bindings-posix 6. http://hackage.haskell.org/package/bindings%2Dcommon 7. http://hackage.haskell.org/package/bindings%2Dcommon 8. http://article.gmane.org/gmane.comp.lang.haskell.libraries/11610 9. http://hackage.haskell.org/package/bindings%2Dcommon 10. http://article.gmane.org/gmane.comp.lang.haskell.general/17425 11. http://hackage.haskell.org/package/dyre 12. http://article.gmane.org/gmane.comp.lang.haskell.general/17407 13. http://hackage.haskell.org/package/nntp 14. http://article.gmane.org/gmane.comp.lang.haskell.general/17406 15. http://hackage.haskell.org/package/GLUT 16. http://article.gmane.org/gmane.comp.lang.haskell.general/17405 17. http://hackage.haskell.org/package/OpenGL 18. http://hackage.haskell.org/package/OpenGLRaw 19. http://hackage.haskell.org/package/GLURaw 20. http://article.gmane.org/gmane.comp.lang.haskell.general/17397 21. http://hackage.haskell.org/package/yices 22. http://yices.csl.sri.com/ 23. http://article.gmane.org/gmane.comp.lang.haskell.general/17395 24. http://hackage.haskell.org/package/StateVar 25. http://hackage.haskell.org/package/OpenGL 26. http://article.gmane.org/gmane.comp.lang.haskell.general/17394 27. http://hackage.haskell.org/package/OpenAL 28. http://hackage.haskell.org/package/StateVar 29. http://hackage.haskell.org/package/ObjectName 30. http://hackage.haskell.org/package/Tensor 31. http://hackage.haskell.org/package/OpenGL 32. http://article.gmane.org/gmane.comp.lang.haskell.general/17393 33. http://hackage.haskell.org/package/Tensor 34. http://article.gmane.org/gmane.comp.lang.haskell.general/17391 35. http://darcs.net/ 36. http://article.gmane.org/gmane.comp.lang.haskell.general/17388 37. http://hackage.haskell.org/package/uacpid 38. http://article.gmane.org/gmane.comp.lang.haskell.general/17386 39. http://hackage.haskell.org/package/uacpid 40. http://article.gmane.org/gmane.comp.lang.haskell.general/17384 41. http://tabi.googlecode.com/ 42. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61980 43. http://homepage.ntlworld.com/jon.fairbairn/Typeful/Text/HTMLs/ 44. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61915 45. http://hackage.haskell.org/package/yst 46. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61874 47. http://hackage.haskell.org/platform/ 48. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61849 49. http://hackage.haskell.org/package/atom 50. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61845 51. http://hackage.haskell.org/package/tkhs 52. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61809 53. http://hackage.haskell.org/package/alex 54. git://github.com/jyp/Alex.git 55. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61800 56. http://themonadreader.wordpress.com/ 57. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61707 58. http://hackage.haskell.org/package/TBC 59. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61706 60. http://hackage.haskell.org/package/elerea 61. http://hackage.haskell.org/package/elerea-examples 62. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61703 63. http://hackage.haskell.org/package/haskell%2Dsrc%2Dexts 64. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61690 65. http://hackage.haskell.org/package/graphviz 66. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61663 67. http://leksah.org/ 68. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61613 69. http://hackage.haskell.org/package/swish 70. http://www.ninebynine.org/Software/swish-0.2.1.html 71. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61545 72. http://article.gmane.org/gmane.comp.lang.haskell.cafe/61523 73. http://hackage.haskell.org/package/cautious-file 74. http://hackage.haskell.org/trac/summer-of-code/wiki/SoC2008 75. http://haddock2009.wordpress.com/2009/07/20/more-cross-package-docs-details/ 76. http://haddock2009.wordpress.com/2009/07/21/next-project-move-doc-parsing-t… 77. http://eclipsefp.wordpress.com/2009/07/19/more-robust-scion-client-code/ 78. http://eclipsefp.wordpress.com/2009/07/30/the-green-bar/ 79. http://just-bottom.blogspot.com/2009/07/using-pango-fonts-on-opengl-canvas.… 80. http://just-bottom.blogspot.com/2009/08/more-profiling-goodies.html 81. http://nibrofun.blogspot.com/2009/07/starting-on-comment-support.html 82. http://web.mornfall.net/blog/soc_progress_9.html 83. http://web.mornfall.net/blog/soc_progress_10.html 84. http://web.mornfall.net/blog/darcs_2.3.0.html 85. http://web.mornfall.net/blog/patch_formats.html 86. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/11658 87. http://hackage.haskell.org/package/binary 88. http://www.haskell.org/haskellwiki/Haskell_Platform 89. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/11625 90. http://www.haskell.org/haskellwiki/Haskell_Platform 91. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/61723 92. http://hackage.haskell.org/trac/haskell-prime/wiki/TypeDirectedNameResoluti… 93. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/61514 94. http://article.gmane.org/gmane.comp.lang.haskell.general/17431 95. http://planet.haskell.org/ 96. http://haskell.org/haskellwiki/Blog_articles 97. http://joelrayking.wordpress.com/2009/08/08/starting-out-with-haskell/ 98. http://jpmoresmau.blogspot.com/2009/08/yoohoo-mazes-of-monad-is-kind-of.html 99. http://donsbot.wordpress.com/2009/08/06/haskell-package-popularity-rankings… 100. http://haskellformaths.blogspot.com/2009/08/where-weve-been-and-where-were-… 101. http://blog.objectmentor.com/articles/2009/08/05/functional-refactoring-and… 102. http://therning.org/magnus/archives/713 103. http://tomschrijvers.blogspot.com/2009/08/monadic-constraint-programming-wi… 104. http://lukeplant.me.uk/blog.php?id=1107301701 105. http://donsbot.wordpress.com/2009/08/03/the-haskell-platform-2009-2-0-2/ 106. http://just-bottom.blogspot.com/2009/08/more-profiling-goodies.html 107. http://donsbot.wordpress.com/2009/08/01/heuristics-for-blessing-software-pa… 108. http://haskellformaths.blogspot.com/2009/08/how-to-count-number-of-position… 109. http://comonad.com/reader/2009/hac-phi-slides/ 110. http://byorgey.wordpress.com/2009/07/31/primitive-species-and-species-opera… 111. http://therning.org/magnus/archives/710 112. http://byorgey.wordpress.com/2009/07/30/primitive-species-and-species-opera… 113. http://eclipsefp.wordpress.com/2009/07/30/the-green-bar/ 114. http://web.mornfall.net/blog/soc_progress_10.html 115. http://byorgey.wordpress.com/2009/07/29/hac-phi-roundup/ 116. http://byorgey.wordpress.com/2009/07/25/more-from-hac-%cf%86/ 117. http://ro-che.blogspot.com/2009/07/ccc-5.html 118. http://koweycode.blogspot.com/2009/07/some-ideas-for-practical-quickcheck.h… 119. http://sandersn.com/blog/index.php?title=profiling_in_haskell_part_2 120. http://b4winckler.wordpress.com/2009/07/28/inverse-functions-in-haskell/ 121. http://www.sdtimes.com/blog/post/2009/07/27/Everyonee28099s-talking-about-H… 122. http://nibrofun.blogspot.com/2009/07/starting-on-comment-support.html 123. http://just-bottom.blogspot.com/2009/07/using-pango-fonts-on-opengl-canvas.… 124. http://byorgey.wordpress.com/2009/07/25/hac-%cf%86-day-2/ 125. http://web.mornfall.net/blog/patch_formats.html 126. http://byorgey.wordpress.com/2009/07/24/introducing-math-combinatorics-spec… 127. http://therning.org/magnus/archives/702 128. http://blog.snoyman.com/2009/07/23/embedding-files-in-a-binary/ 129. http://blog.darcs.net/2009/07/darcs-230-is-released.html 130. http://web.mornfall.net/blog/darcs_2.3.0.html 131. http://learninghaskell.wordpress.com/2009/07/23/haskell-prefix-and-infix-no… 132. http://learninghaskell.wordpress.com/2009/07/23/the-minus-operator-in-haske… 133. http://webscript.princeton.edu/~kjenkins/wordpress/2009/07/learning-haskell… 134. http://james-iry.blogspot.com/2009/07/void-vs-unit.html 135. http://jng.imagine27.com/articles/2009-07-23-094212_generating_pi_in_haskel… 136. http://web.mornfall.net/blog/soc_progress_9.html 137. http://webscript.princeton.edu/~kjenkins/wordpress/2009/07/learning-haskell/ 138. http://haddock2009.wordpress.com/2009/07/21/next-project-move-doc-parsing-t… 139. http://ro-che.blogspot.com/2009/07/schrodingers-cat.html 140. http://therning.org/magnus/archives/698 141. http://www.l2mlogistics.com/2009/07/haskell-and-hack-fanboyism.html 142. http://cdsmith.wordpress.com/2009/07/20/calculating-multiplicative-inverses… 143. http://haskellformaths.blogspot.com/2009/07/faster-graph-symmetries-using-d… 144. http://haddock2009.wordpress.com/2009/07/20/more-cross-package-docs-details/ 145. http://featherweightmusings.blogspot.com/2009/07/ecoop-day-3-day-1-of-main-… 146. http://www.ryanlothian.com/articles/haskell-graphplotter 147. http://alaska-kamtchatka.blogspot.com/2009/07/monadic-golf.html 148. http://stephenmann.net/2009/07/17/cool-haskell-function/ 149. http://actuarialprog.wordpress.com/2009/07/13/how-do-you-use-haskell-at-wor… 150. http://adam.blinkinblogs.net/mastermind-solver-in-haskell 151. http://llaisdy.wordpress.com/2009/07/11/decorate-sort-undecorate-in-haskell… 152. http://donsbot.wordpress.com/2009/07/27/interview-for-sdtimes-everyone%e2%8… 153. http://donsbot.wordpress.com/2009/07/26/haskell-platform-progress-report/ 154. http://haskellformaths.blogspot.com/2009/07/strong-generating-sets-for-grap… 155. http://cdsmith.wordpress.com/2009/07/23/the-magic-of-type-classes/ 156. http://twan.home.fmf.nl/blog/haskell/cps-functional-references.details 157. http://eclipsefp.wordpress.com/2009/07/19/more-robust-scion-client-code/ 158. http://paulbutler.org/archives/n-queens-in-a-tweet/ 159. http://www.haskell.org/mailman/listinfo/haskell 160. http://sequence.complete.org/ 161. http://planet.haskell.org/ 162. http://sequence.complete.org/node/feed 163. http://haskell.org/ 164. http://haskell.org/haskellwiki/HWN 165. http://code.haskell.org/~byorgey/code/hwn/

1 0

What would be required to make a LLVM backend for GHC
by Alex Mason 08 Aug '09

08 Aug '09

Hi all, I've been talking to one of the LLVM developers, who's working on an operating system called AuroraUX, which, among other things, is trying to use LLVM as much as possible in the system (using clang as the default compiler, compiler-rt [libgcc replacement from the LLVM team], etc.). He would like to know exactly what would need to be implemented in LLVM to allow ghc to be ported to LLVM, and he would do his best to get these features implemented. I know the LLVM guys are quite open to suggestions, and want to get people using it as much as possible, so if we can let them know what we need, hopefully they can help make life easier for us. Thanks, Alex Mason

3 2

Re: [Haskell-cafe] Re: SQL Database in Haskell?
by Max Desyatov 08 Aug '09

08 Aug '09

As I can say from my experience of usage of hdbc-sqlite3 and happstack-state, the latter covers everything you ever wanted from sqlite3 and more. It you aren't too concerned about performance, you can free yourself from many tedious routines that are imminent when you work with relational database. Elaborated data model design coupled with some generics technique (uniplate with derive, e.g.) gives you a possibility to write down your domain problem directly to haskell. CK Kashyap <ck_kashyap(a)yahoo.com> writes: > I'd be very interested to see a rdbms implementation in Haskell ... > perhaps a port of sqlite > > Regards, > Kashyap

2 1

Linking failing due to Control.Monad.State.Strict?
by phil＠beadling.co.uk 07 Aug '09

07 Aug '09

Hi, I'm getting a linker error when generating makefile dependencies on the below library for a program I'm using. It links fine under 'ghc -- make'. I'm using (more or less) the makefile from the haskell docs. I am using the Strict State Monad in the object files it is complaining about, the compile is fine, just the linker which is blowing up. Any ideas what is causing this? I'm using GHC 6.10.4 on PPC Mac OS X 10.5. I've included the makefile below the error. Cheers! Phil. ghc -o OptionCalculator -O2 -Wall ./FrameworkInterface.o ./Maths/ Prime.o ./Misc/Debug.o ./MonteCarlo/DataStructures.o ./MonteCarlo/ European.o ./MonteCarlo/Framework.o ./MonteCarlo/Interface.o ./ MonteCarlo/Lookback.o ./Normal/Acklam.o ./Normal/BoxMuller.o ./Normal/ Framework.o ./Normal/Interface.o ./OptionCalculator.o ./Random/ Framework.o ./Random/Halton.o ./Random/Interface.o ./Random/Ranq1.o Undefined symbols: "_mtlzm1zi1zi0zi2_ControlziMonadziStateziStrict_a29_info", referenced from: _r1hl_info in Acklam.o _rGL_info in BoxMuller.o "_mtlzm1zi1zi0zi2_ControlziMonadziStateziStrict_a29_closure", referenced from: _r1hl_srt in Acklam.o _rGL_srt in BoxMuller.o "___stginit_mtlzm1zi1zi0zi2_ControlziMonadziStateziStrict_", referenced from: ___stginit_FrameworkInterface_ in FrameworkInterface.o ___stginit_FrameworkInterface_ in FrameworkInterface.o ___stginit_MonteCarloziEuropean_ in European.o ___stginit_MonteCarloziEuropean_ in European.o ___stginit_MonteCarloziFramework_ in Framework.o ___stginit_MonteCarloziFramework_ in Framework.o ___stginit_MonteCarloziLookback_ in Lookback.o ___stginit_MonteCarloziLookback_ in Lookback.o ___stginit_NormalziAcklam_ in Acklam.o ___stginit_NormalziAcklam_ in Acklam.o ___stginit_NormalziBoxMuller_ in BoxMuller.o ___stginit_NormalziBoxMuller_ in BoxMuller.o ___stginit_NormalziFramework_ in Framework.o ___stginit_NormalziFramework_ in Framework.o ___stginit_RandomziFramework_ in Framework.o ___stginit_RandomziFramework_ in Framework.o ___stginit_RandomziHalton_ in Halton.o ___stginit_RandomziHalton_ in Halton.o ___stginit_RandomziRanq1_ in Ranq1.o ___stginit_RandomziRanq1_ in Ranq1.o ld: symbol(s) not found collect2: ld returned 1 exit status make: *** [OptionCalculator] Error 1 Makefile: HC = ghc HC_OPTS = -O2 -Wall $(EXTRA_HC_OPTS) SRCS := $(shell find . -name "*.hs" -print) OBJS = $(SRCS:.hs=.o) PROG = OptionCalculator .SUFFIXES : .o .hs .hi .lhs .hc .s ${PROG} : $(OBJS) rm -f $@ $(HC) -o $@ $(HC_OPTS) $(OBJS) # Standard suffix rules .o.hi: @: .lhs.o: $(HC) -c $< $(HC_OPTS) .hs.o: $(HC) -c $< $(HC_OPTS) .o-boot.hi-boot: @: .lhs-boot.o-boot: $(HC) -c $< $(HC_OPTS) .hs-boot.o-boot: $(HC) -c $< $(HC_OPTS) clean : find . -name "*.hi" -exec rm -f {} \; find . -name "*.o" -exec rm -f {} \; rm -f ${PROG} depend : ghc -M $(HC_OPTS) $(SRCS)

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Re: [Haskell-cafe] Basic questions about concurrency in Haskell
by Sebastian Sylvan 07 Aug '09

07 Aug '09

Bringing the cafe back in. If I remember correctly tuning the GC is one of the things they worked on for the next release (in relation to parallelism).Here's a link to the paper: http://research.microsoft.com/en-us/um/people/simonpj/papers/parallel/multi… You can allocate dynamic memory on the C heap using the Foreign.Marshal.Alloc stuff. The Storable class allows you to specify alignment. However it's not clear you will need it in all cases. Most of the time IME all you really need is for "the business end" of object A and B to end up on different cache lines, padding them with the size of a cache line will accomplish that even if each object starts in the middle of a cache line. In other words, as long as you ensure that there's at least CACHE_LINE bytes difference between the last bit of data in A and the first bit of data in B, they won't exhibit false sharing. I'm not sure if any of the "standard" mutable references etc. respect this. Maybe someone can clarify? If you modify a thread-local IORef will that cause another thread to stall because it has it's own thread-local IORef on the same cache line? On Fri, Aug 7, 2009 at 12:42 PM, Thomas Witzel <witzel.thomas(a)gmail.com>wrote: > I have not yet been able to get the dev version compiled, but I'm > looking into it (basically compiles to 99% and then stops because of a > missing or defective .mk file). Anyhow, I played more with the release > version and one thing I noticed is that the GC time increases almost > linearly with the number of cores. Is there somewhere a document that > explains the overall architecture of the GHC/RTS and how in especially > the GC acts in concurrent situations ? > > As for your comment regarding the padding the data-structures, I'll of > course also need to control the alignment in such a case. Is there > such a thing as explicit dynamic memory allocation in Haskell ? > > Thanks, Thomas > > On Wed, Aug 5, 2009 at 3:16 PM, Sebastian > Sylvan<sebastian.sylvan(a)gmail.com> wrote: > > GHC doesn't have per-thread allocation so it's probably a bit tricky to > get > > that working. Plus, for parallelism it's not clear that a piece of data > is > > necessarily "owned" by one thead, since it could be produced by a spark > and > > consumed by another spark, those two independent sparks may not > necessarily > > occupy the same thread, which means that any *other* data accessed by the > > firs thread could thrash the cache. So really you'd need per-spark > > allocation areas which would probably make sparks very heavy weight. > > In other words, I think there's plenty of research that needs to be done > > w.r.t. scheduling things in time and space so as to avoid false sharing. > You > > could, of course, always chunk your work manually, and make sure that > each > > "chunk" works on a big block that won't share cache lines with anything > else > > (e.g. by padding the data structures). > > Also, while GHC does a fair bit of mutation on its own internal data > (thunks > > etc.), most of the "user data" is read-only, which should help. I.e. once > a > > cache line has been filled up, there won't be any synchronisation needed > on > > that data again. > > > > On Wed, Aug 5, 2009 at 8:04 PM, Thomas Witzel <witzel.thomas(a)gmail.com> > > wrote: > >> > >> I'll try that. I'd like to stick with it. As for the memory, although > >> its probably quite a bit of work, it should be doable to have code > >> generated where the threads have their own, non-overlapping, memory > >> pages, so that the CPUs don't go into a cache-thrashing death-match. > >> I'll spend some more time with Haskell and then go from there. > >> > >> On Wed, Aug 5, 2009 at 3:01 PM, Sebastian > >> Sylvan<sebastian.sylvan(a)gmail.com> wrote: > >> > > >> > > >> > On Wed, Aug 5, 2009 at 6:59 PM, Thomas Witzel < > witzel.thomas(a)gmail.com> > >> > wrote: > >> >> > >> >> 2. I started with the very simple nfib example given in the manual > for > >> >> Control.Parallel (Section 7.18). On my systems using multiple cores > >> >> makes the code actually slower than just using a single core. While > >> >> the manual cautions that this could be the case for certain > >> >> algorithms, I'm wondering whether this is the desired behaviour for > >> >> this example. > >> >> > >> >> I'm using ghc 6.10.4 right now. > >> > > >> > IIRC the development version of GHC has some major work to optimize > >> > concurrency, so it may be worth trying that. In particular I believe > it > >> > executes sparks in batches, to reduce the overhead (which hopefully > >> > fixes > >> > your issue). > >> > > >> > -- > >> > Sebastian Sylvan > >> > > > > > > > > > -- > > Sebastian Sylvan > > > -- Sebastian Sylvan

1 0

FFI: Problem with Signal Handler Interruptions
by Levi Greenspan 07 Aug '09

07 Aug '09

Dear list members, In February this year there was a posting "Why does sleep not work?" (http://www.haskell.org/pipermail/haskell-cafe/2009-February/055400.html) The problem was apparently caused by signal handler interruptions. I noticed the same (not with sleep though) when doing some FFI work and compiled the following test program: {-# LANGUAGE ForeignFunctionInterface #-} module Main where import Foreign.C.Types import Control.Concurrent sleep :: IO () sleep = c_sleep 3 >>= print fails :: IO () fails = sleep works :: IO () works = forkIO sleep >> return () main :: IO () main = fails >> works >> threadDelay 3000000 foreign import ccall unsafe "unistd.h sleep" c_sleep :: CUInt -> IO CUInt When compiled with GHC (using --make -threaded), it will print 3 immediately (from the "fails" function) and after 3 seconds 0 (from "works"), before it finally exits. man sleep(3) tells me that sleep returns 0 on success and if interrupted by a signal the number of seconds left to sleep. Clearly "fails" is interrupted by a signal (which seems to be SIGVTALRM). This was mentioned in the discussion from February. I would like to know why "fails" fails and "works" works, i.e. why is "sleep" not interrupted when run in a separate thread? And what can be done to make "sleep" work in the main thread? It wouldn't be wise to block SIGVTALRM, wouldn't it? Many thanks, Levi

2 4

Seeking for an extention (functional incapsulation)
by Belka 07 Aug '09

07 Aug '09

Hello, cafe visitors! :) This is a double topic: 1. Can't find any good informative resource with descriptions of Haskell extensions. Could anybody please share good one if it exists? The only "good" one I found: http://hackage.haskell.org/trac/haskell-prime/wiki/HaskellExtensions But it's a bit too old and not that full... I undestand, that Haskell is kind of "boiling" language, in a sense of being neverending experiment. It develops all the time, extensions show up and drop out. So it's not that easy to support community with a fresh information about them. But on the other side, the property (of being "boiling" language) makes such information really important for community members... I think. :) 2. Consider situation: ----------------------------------- data SomeDataType = SomeDataType { sdtField1 :: SDT_Field1Type, sdtField2 :: SDT_Field2Type} sdtField3 :: SomeDataType -> SDT_Field3Type sdtField3 sdt = f (sdtField1 sdt) (sdtField2 sdt) ----------------------------------- I induced recently, that it would be very comfortable if I could perform in a way like this: ----------------------------------- data SomeDataType = SomeDataType { sdtField1 :: SDT_Field1Type, sdtField2 :: SDT_Field2Type, sdtField3 :: SDT_Field2Type, sdtField3 = f sdtField1 sdtField2} ----------------------------------- The situation is not that rare, when dealing with nonprimitive data constructions. Moreover would be really comfortable to reduce ----------------------------------- data SomeDataType = SomeDataType_111 { sdtField1 :: SDT_Field1Type, sdtField2 :: SDT_Field2Type} | SomeDataType_222 { sdtField1 :: SDT_Field1Type, sdtField2 :: SDT_Field2Type, sdtField5 :: SDT_Field5Type} sdtField3 :: SomeDataType -> SDT_Field3Type sdtField3 sdt = case sdt of {SomeDataType_111 -> f (sdtField1 sdt) (sdtField2 sdt) ; SomeDataType_222 -> g (sdtField1 sdt) (sdtField2 sdt) (sdtField5 sdt)} \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ data SomeDataType = SomeDataType_111 { sdtField1 :: SDT_Field1Type, sdtField2 :: SDT_Field2Type, sdtField3 :: SDT_Field3Type, sdtField3 = f sdtField1 sdtField2} | SomeDataType_222 { sdtField1 :: SDT_Field1Type, sdtField2 :: SDT_Field2Type, sdtField5 :: SDT_Field5Type, sdtField3 :: SDT_Field3Type, sdtField3 = g sdtField1 sdtField2 sdtField5} ----------------------------------- Usable mechanics for realization would be: 1. Funtion similar to Data.Function.on (example: (*) `on` f = \x y -> f x * f y), but opposite - I called it under. t `under` f = \x y -> (x f) `t` (y f) 2. currying and uncurrying Is there any such extension? Belka -- View this message in context: http://www.nabble.com/Seeking-for-an-extention-%28functional-incapsulation%… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

2 6

Looking to check on some capabilities of Data.Colour
by Jeff Heard 06 Aug '09

06 Aug '09

I was wondering if Data.Colour supported Double-valued colour components > 1.0 or less than 0. I'm looking to create an HDR image processing library, and Haskell has one of the most extensive and correct colour models around, thanks to Russell. With 16bpcc or 32bpcc images, however, I need to be sure to be able to correctly calculate colour values that fall outside the usual [0.0,1.0] gamut. Does Data.Colour support this functionality? -- Jeff

2 3

A mistake in haskellwiki
by L.Guo 06 Aug '09

06 Aug '09

Hi haskellers: There is a mistake in http://www.haskell.org/haskellwiki/State_Monad It post two functions like this : evalState :: State s a -> s -> a evalState act = fst $ runState act execState :: State s a -> s -> s execState act = snd $ runState act Both the '$' operators should be '.'. Anyone would correct it ? Regards -------------- L.Guo 2009-08-06

7 7

n00b question: defining datatype
by Iain Barnett 06 Aug '09

06 Aug '09

Hi, I'm trying to get my head around datatypes, and wondering how I might define a simple "Task" datatype in Haskell. data Task = Task { title :: String, completed :: Bool } Ok, that's straightforward, but sometimes tasks become a list of tasks themselves data Task = Task { title :: String, completed :: Bool, subtasks :: [Task] } But that's not really right, because obviously, some tasks don't have subtasks. So I try this: data Task = Task { title :: String, completed :: Bool } | TaskWithSubtasks { title :: String, completed :: Bool, subtasks :: [Task] } It's a bit more accurate, but it's repeating things, which is ok with a simple type. Could anyone suggest a better way to define this? If I was using C#, which I'm far more familiar with, I could overload the constructor and refer to the smaller constructor. Is there a way to do that in Haskell, or am I still thinking too OOP? Iain

8 9

SQL Database in Haskell?
by Günther Schmidt 06 Aug '09

06 Aug '09

Hi all, is there an SQL Database in Haskell or is there a project trying to implement one? Günther

5 8

Do you understand posix well?
by Maurício CA 06 Aug '09

06 Aug '09

I've beeing writing a low-level binding to posix that can be usefull if you want to use posix but has no time to learn FFI: http://hackage.haskell.org/package/bindings-posix However, my understandment of posix is barely nothing, and I see that many of its functionality is enabled or disabled by macros, and I don't know which ones are related to what functionality. So, if you know about that: would you be able to list all macros (or at least most important ones, if there are too many) that enable all (or most) of posix? In exchange, you get a posix binding that is actually comprehensive :) Thanks, Maurício

1 0

About the import module
by xu zhang 06 Aug '09

06 Aug '09

Hi there, If I import a module and do not explicitly point out the entities I have imported. And I want the ghc to point out the entities automatically. Is there any method to do this? any methods to have the ghc point out the entities I import and export? Because there are so many files and I don't want to change them one by one, so I just want to find if there is a simple and automatic way to have the entities pointed out. Thank you in advance!

3 2

Efficient functional idiom for histogram
by Paul Moore 05 Aug '09

05 Aug '09

How would I efficiently write a function in Haskell to count occurrences of unique elements in a (potentially very large) list? For example, given the list [1,2,3,4,5,3,4,2,4] I would like the output [[1,1], [2,2], [3,2], [4,3], [5,1]] (or some equivalent representation). Clearly, this won't be possible for infinite input, but I would like it to be as efficient as possible for (lazy) input lists containing many millions of elements. So an implementation based on group . sort is not going to work. In an imperative language like Python, I'd use a dictionary as an accumulator - something like for el in input: accums[i] = accums.get(i, 0) + 1 That's about as efficient as you can hope for (assuming an efficient dictionary implementation). How would I code something equivalent in Haskell? Thanks, Paul.

12 20

Basic questions about concurrency in Haskell
by Thomas Witzel 05 Aug '09

05 Aug '09

Hello all, I'm new to Haskell, but have a good background in LISP/Scheme and do mostly C/C++ programming on a daily basis. I'm learning Haskell mainly because it provides facilities for concurrency on the language level, and I'm mainly interested in implementing parallel or massively parallel algorithms with Haskell. I have two questions that bother me. 1. Does the Haskell compiler make sure that there is no page sharing between threads, in order to avoid cache thrashing between cpus (a real killer on large SMP or ccNUMA systems) ? If so, are there functions/options to control this ? 2. I started with the very simple nfib example given in the manual for Control.Parallel (Section 7.18). On my systems using multiple cores makes the code actually slower than just using a single core. While the manual cautions that this could be the case for certain algorithms, I'm wondering whether this is the desired behaviour for this example. I'm using ghc 6.10.4 right now. Thank you for your help getting me started here. Thomas

3 2

Typeclass for functions taking different kinds of strings
by Taru Karttunen 05 Aug '09

05 Aug '09

Hello It seems like a very common issue to have an API like: foo :: String -> Foo fooBS :: ByteString -> Foo fooLBS:: L.ByteString -> Foo is there currently a library that makes unifying them easy? Below is attached one try at this, does it make sense? I'm thinking of uploading it to Hackage but would like comments first. With the library the above code is transformed into: foo :: StringLike string => string -> Foo - Taru Karttunen

3 4

Haskell interface files: Why used? What about same data in object files?
by Howard B. Golden 05 Aug '09

05 Aug '09

Hi, I am trying to understand the design of the Haskell interface files. Why are they a separate file rather than having the same data in the object file generated by the compiler? (Naively, it seems to me this would work also. Am I missing something?) Thanks. Howard B. Golden Northridge, California, USA

4 4

powerSet = filterM (const [True, False]) ... is this obfuscated haskell?
by Thomas Hartman 05 Aug '09

05 Aug '09

on haskell reddit today powerSet = filterM (const [True, False]) is said to be beautiful / mind blowing. I just don't get it. I can play with transformations until I get powerSet [] = [[]] powerSet (x:xs) = let pxs = powerSet xs in map (x:) pxs ++ pxs which is understandable to me, but no matter how long I look at the original filterM definition it just doesn't click. Is this a uniquely haskell obfu, or is there a way of reading this definition that makes sense? If anybody agrees with me, care to throw out other examples of "obfuscated haskell considered harmful"?

11 13

A problem with bytestring 0.9.1.4 "hGetBuf: invalid argument"
by kenny lu 05 Aug '09

05 Aug '09

Hi all, I've recently came across a problem when processing a large text file (around 2G in size). I wrote a Haskell program to count the number of lines in the file. module Main where import System import qualified Data.ByteString.Char8 as S -- import Prelude as S main :: IO () main = do { args <- getArgs ; case args of { [ filename ] -> do { content <- S.readFile filename ; let lns = S.lines content ; putStrLn (show $ length lns) } ; _ -> error "Usage : Wc <file>" } } I get this error, if I use the ByteString module, ./Wc a.out Wc: {handle: a.out}: hGetBuf: invalid argument (illegal buffer size (-1909953139)) Otherwise, it returns me the result. Another observation is that if I reduce the size of the file, the ByteString version works too. Is it a known limitation? Regards, Kenny A generator program that generate large file. (Warning, it is very slow, I don't know how to speed it up) -- generate a file module Main where import System import qualified Data.ByteString.Char8 as S l :: S.ByteString l = S.pack "All work, no fun, make Kenny a dull boy. " main :: IO () main = do { args <- getArgs ; case args of { [ n, fn ] -> do { let i = read n ; mapM_ (\s -> S.appendFile fn s) (take i $ repeat l) } ; _ -> return () } }

2 2

Hackage Download Rankings August 2009
by Don Stewart 05 Aug '09

05 Aug '09

Total package downloads on Hackage, by August 1 2009, http://www.galois.com/~dons/hackage/august-2009/popularity-august-2009.html All packages by month: http://www.galois.com/~dons/hackage/august-2009/hackage-august-2009.html Raw data: http://www.galois.com/~dons/hackage/august-2009/hackage-downloads-august-20… Enjoy. -- Don P.S. For reference, here's the data from March, http://www.galois.com/~dons/hackage/popularity.html and analysis at the time http://www.galois.com/blog/2009/03/23/one-million-haskell-downloads/

1 0

Cyclic data declarations
by Michal D. 04 Aug '09

04 Aug '09

I'm in the process of writing a toy compiler but I'm having some trouble trying to make my datatypes general. For example, using parsec I parse statements as: data Stmt = SIf Test [Stmt] [Stmt] | ... However, when it's time to create a control flow graph it would be nice to represent statements as (the Int's signify the node id's for either case of the if statement): data Stmt = SIf Test Int Int | ... So, in a eureka moment I decided that this should be allowable with the following declaration: data Stmt link = SIf Test link link | ... Ofcourse, the problem is trying to declare the resulting type for parsing: "parse -> Stmt [Stmt [Stmt ....]]". Any hints on whether there is a way to accomplish what I'm trying to do or do I have to bite the bullet and declare two seperate datatypes? I tried being clever and declaring a 'helper' type as "type StmtRec = Stmt [StmtRec]" but to no avail... GHC won't let it slide: "Cycle in type synonym declarations"! Cheers, Michal

6 8

Split package organization (AntTweakBar, Cabal, darcs)
by Gregory D. Weber 04 Aug '09

04 Aug '09

I'm working on a Haskell binding for AntTweakBar, a light user interface for OpenGL applications (http://www.antisphere.com/Wiki/tools:anttweakbar) I have three questions about how to organize it as a Haskell package or packages, Cabal, and darcs. First, since AntTweakBar provides support for handling events from GLUT, GLFW, and SDL, as well as customizable event handling from other sources, would it be best to divide it into four packages -- AntTweakBar (core), AntTweakBar-GLUT, AntTweakBar-GLFW, and AntTweakBar-SDL? A few other "package groups" on Hackage have taken this approach of splitting according to the user interface: for example, grapefruit-ui-gtk, reactive-glut, though not on such a large scale as I am proposing. Advantages of four packages rather than one: -- Fewer build dependencies, for example, for users who want to use just SDL and not have to install GLUT or GLFW. -- If one of the build dependencies is broken (as for example GLFW is just at the moment with the latest OpenGL), users could still build the other AntTweakBar-* packages. Disadvantages: -- More packages to install, for those who want it all. -- I might seem to be grabbing an undue share of the package namespace. And it could get way out of hand if I further split the examples from the library, making AntTweakBar-(base|GLUT|GLFW|SDL)-(lib|examples) = 8 packages! Would that be a problem? -- Possible inconvenience for the developer (see second question). Second question, assuming the four-way split is the best way to package this: my impression is that a directory can have only one cabal package file and one Setup.hs file. (http://www.haskell.org/cabal/release/cabal-latest/doc/users-guide/authors.h…, "Creating a Package") So for example I could not have, in the same directory, AntTweakBar.cabal, AntTweakBar-GLUT.cabal, etc. That means the four packages would each have to have their own directories, and it is sometimes inconvenient to be jumping back and forth between them. Any good way around that? Third question, assuming four separate directories for the four Cabal package files. Putting all four into one darcs repo (i.e., the darcs repo would have one main directory and a subdirectory for each package) seems to make it easier to coordinate development of the related packages -- for example, a single 'darcs rec -a' takes care of recording the related changes in all four subdirectories. Any reason not to do it that way? -- ___ ___ __ _ / _ \ / _ \| | | | Gregory D. Weber, Associate Professor / /_\// / | | | /\ | | Indiana University East / /_\\/ /__| | |/ \| | http://mypage.iu.edu/~gdweber/ \____/\_____/\___/\__/ Tel. (765) 973-8420; FAX (765) 973-8550

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Re: ANN: yst 0.2.1
by spoon 04 Aug '09

04 Aug '09

This sounds great! I really like using yaml for web development. However, my last use case was for a non-techie, so I created a little desktop application for editing the "yamlbase", if you excuse the neologism. I think it worked quite well, because the user was then presented with a friendly looking system ( I even wrote a little calendar widget :) without having to spend the precious moneys on dynamic hosting. In the end, everyone was very happy. Actually, it was written in Ruby, and Shoes, and the data part was a lot less powerful than the yst query language there - but I think that an analogous tool would be useful; a GUI which creates yst scripts, would make yst a very powerful tool for non-techies. John

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funct.prog. vs logic prog., practical Haskell
by Petr Pudlak 04 Aug '09

04 Aug '09

Hi all, I'd like to convince people at our university to pay more attention to functional languages, especially Haskell. Their arguments were that (1) Functional programming is more academic than practical. (2) They are using logic programming already (Prolog); why is Haskell better than Prolog (or generally a functional language better than a logic programming language)? (1) is easier to answer, there are a lots of applications at HaskellWiki, or elsewhere around the Internet, written in Haskell, OCaml, etc. Still, I welcome comments on your experience, for example, if you have written some larger-scale application in Haskell (or another a functional language) that is not at HaskellWiki, and perhaps if/why you would recommend doing so to other people. (2) is harder for me, since I've never programmed in Prolog or another language for logic programming. I'd be happy if anyone who is experienced in both Prolog and Haskell could elaborate the differences, pros & cons etc. Thanks, Petr

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