- Haskell-Cafe - Haskell.org

unsafeDestructiveAssign?
by John Lato 13 Aug '09

13 Aug '09

Hi Job, I don't think this hypothetical function could exist; you may as well call it "notEverSafeOhTheHumanity" and be done with it. Since Haskell provides no guarantees about when (if ever) any given function/data will be evaluated, you would need some mechanism to tell the compiler that a data chunk has a certain value at one time and a different value at another. The language provides this in the IO (and ST) monads. So the function would need to live within IO, and you don't gain anything. If you try to take it outside of IO, with e.g. unsafePerformIO, then the compiler will no longer treat it like IO and the result is free to be evaluated whenever, so you're back where you started. Also, keep in mind that purity is a language requirement in Haskell and such a function really would "break everything". Specifically, you would get differing output depending on the exact transformations performed by the compiler, which in general would be difficult to predict in advance, probably not the same between different compiler versions, changed by compiler flags and phases of the moon, etc. I have an example in a darcs repo somewhere... Cheers, John > From: Job Vranish <jvranish(a)gmail.com> > Subject: Re: [Haskell-cafe] unsafeDestructiveAssign? > > Ga! Before to many people start flooding me responses of "This is really > dumb idea don't do it!" I would like to clarify that for the most part > IKnowWhatI'mDoing(TM) > > I am well aware of the usual ST/IORefs as the usual solutions to data > mutability in haskell. > I very very much understand purity, and why it is a good thing, and why we > should try to stay away from IO and ST as much as possible. > I am very much away that even if I had such a function that it will probably > break everything. > I am not just trying to make things run faster. > > What I am trying to do is hyper unusual and I really do need an > unsafeHorribleThings to do it. > > - Job

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ANNOUNCE: GLFW-0.4.1
by Paul L 13 Aug '09

13 Aug '09

I'm glad to announce a new version of GLFW, 0.4.1, has been uploaded to HackageDB. Notable changes include: * workaround for a FFI bug that affects GHC < 6.10 on 64-bit machines. * fix for the compilation problem on OS X for GHC > 6.10.1 * compatibility fix to work with both OpenGL 2.3.0.0 and older versions. * choice of a "dynamic" flag to link with dynamic GLFW C library instead. * a number of other fixes, cleanups and improvements. Many thanks goes to Brian Lewis, Sönke Hahn, and other people who sent in bug reports, patches, and suggestions. If you have any problem with this new version, you can either reply this email, or send to my other account (paul at thev.net) -- Regards, Paul Liu Yale Haskell Group http://www.haskell.org/yale

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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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