August 2008 - Haskell-Cafe

Scripting COM Components from Haskell - GreenCard on Hackage
by Günther Schmidt 07 Aug '08

07 Aug '08

Hi, does anybody know if the Greencard package / lib is the same software that is mentioned in the paper "Scripting COM Components from Haskell"? http://research.microsoft.com/~simonpj/papers/com.ps.gz I managed to install the hackage Greencard package on XP with GHC 6.8.3 but it seems to be quite different from what the paper describes. Günther

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Network.CGI Content header problem in Firefox.
by Edward Ing 07 Aug '08

07 Aug '08

Hi, I am doing some tests with Haskell to produce CGI programmes. I am running Microsoft IIS 5.0 as the weberver executing haskell compile executables that are cgi. If I set the header with a content type, Firefox always reports the content-type as application/octet-stream, and tries to initiate a download. IExplorer 6.0 does not report the type at all. It seems like the setHeader function does not result in sending headers. Has anyone seen this problem. Code snippet here ==== main :: IO() main = runCGI $ handleErrors cgiMain cgiMain :: CGI CGIResult cgiMain = do x <- getVars y <- getInputs prog <- progURI query <- queryURI request <- requestURI path <- pathInfo inputs <- getInputs setHeader("Content-type" "text/plain") setCookie (Cookie "bbb" "hello" Nothing Nothing Nothing False ) liftIO (putStr "asdfasdf") output $ (uris "prog" prog) ++ (uris "query" query) ++ (uris "request" request) ++ "\npath: " ++ path ++ "\n" ++ (varsToString inputs) ++(varsToString x) ++ "\n\nVars\n"++ (varsToString y)

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the Haskell "with" "pattern"?
by Galchin, Vasili 07 Aug '08

07 Aug '08

Hello, 1) Is there a common assumed semantics across all of the Haskell "with" things? withString? withData? 2) If the answer to 1) is yes, then does this imply some kind of polymorphism? Couldn't "with" be "reduced" to a higher order function then ?? Kind regards, Vasili

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DEFUN 2008 (Developer Tracks on Functional Programming): Call for participation
by Matthew Fluet (ICFP Publicity Chair) 06 Aug '08

06 Aug '08

ACM SIGPLAN 2008 Developer Tracks on Functional Programming http://www.deinprogramm.de/defun-2008/ Victoria, BC, Canada, 25, 27 September, 2008 Held in conjunction with ICFP 2008: http://www.icfpconference.org/icfp2008/ DEFUN 2008 is the event for developers using functional languages: Recognized experts on functional programming technologies share their knowledge and professional skills in talks and tutorials in 10 exciting tracks. Find out how to best make functional programming work in your development project! Acquire new development skills! Learn about other functional languages! The DEFUN program (attached) has tracks with the following types of presentations: - Half-day general language tutorials for specific functional languages, given by recognized experts for the respective languages. - Half-day tutorials on specific techniques or the use of specific technologies in functional programming. - 45-minute "how-to" talks that provide specific information on how to solve specific problems using functional programming. These talks focus on concrete examples, but provide useful information for developers working on different projects or in different contexts. The developer tracks are complementary to ICFP itself (which is for researchers). They are anchored by CUFP, the Haskell Symposium, and the Erlang workshop. Organizers Kathleen Fisher AT&T Labs Simon Peyton Jones Microsoft Research Mike Sperber (co-chair) DeinProgramm Don Stewart (co-chair) Galois PROGRAM: Note: The sessions of a given morning or afternoon are concurrent. The markers (M1, M2, A1, A2, etc.) mark a particular session, and correspond to the designations on the registration forms. Note that the talks M5 together constitute a session. DAY 1 - 25 SEPTEMBER, 2008 MORNING SESSION M1 (Tutorial): Practical Erlang Programming Francesco Cesarini Erlang Training and Consulting M2 (Tutorial): A Gentle Introduction to Functional Information Visualization Jefferson Heard Renaissance Computing Institute, University of North Carolina M3 (Tutorial): JavaScript: from basics to building custom frameworks Sameer Sundresh and Erik Hinterbichler University of Illinois Urbana-Champaign and Pattern Insight, Inc. AFTERNOON SESSION A1 (Tutorial): Erlang DBG and the Trace Biff Tamas Nagy Erlang Training and Consulting A2 (Tutorial): Erlang QuickCheck Tutorial Thomas Arts IT University of Gothenburg and Quviq A3 (Tutorial): Practical and Portable Programming in Scheme Donovan Kolbly TippingPoint Technologies DAY 2 - 27 SEPTEMBER 2008 MORNING SESSION M4 (Tutorial): Real World Haskell Bryan O'Sullivan M5 (Talks): Ten one-liners: handling power series in Haskell Doug McIlroy Dartmouth Incremental multi-level input processing with left-fold enumerator Oleg Kiselyov How we locate wild animals with a functional program Ryan Newton MIT AFTERNOON SESSION A4 (Tutorial): Using QuickCheck and HPC - Obtaining Quality Assurance for Haskell Code Andy Gill Kansas University Koen Claessen Chalmers A5 (Tutorial): Introduction to F# Don Syme and Chris Smith Microsoft Research

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helping you contribute to darcs (poll results so far)
by Eric Y. Kow 06 Aug '08

06 Aug '08

Dear Haskellers, Last Friday, I had posted a message asking how the darcs community could a better job recruiting developers to hack on darcs. Thanks for all the great responses! I am gratified by the suggestions you have offered, as well as the recent uptick in community involvement. The responses so far fall along three themes: offering new features, improving code accessibility and shaking up the community: Features - GUI (david48, Bit Conner) - splitting/merging (Luke Palmer, Ben Franksen) - binary file handling (Jason Dusek) - ... already does what I want (Allan Clark, Andrew Coppin) Code accessibility - split into libs (Neil Mitchell) - unit tests! (Ashley Moran) - code documentation (Lele Gaifax) - patch theory docs (Apfelmus, Ferenc Wagner) - inherent simplicity of model, cf git (Austin Seipp) Community - release announcements (Brandon Allbery, Neil Mitchell, Don Stewart) - showing ways to help (Wren Ng Thorton, Ferenc Wagner) - announcing our need for help (Wren Ng Thorton) - easier entry point to darcs code, à la xmonad (Petr Rockai) - more active leadership (Don Stewart, Lele Gaifax) One thing which is clear is that the darcs team have failed to communicate effectively: the code is not as well-documented as it should be, patch theory is still not defined clearly or rigorously enough for Haskellers, the recent release announcements gave people the impression that darcs was being abandoned, and we haven't made it clear that we needed your help. We need your help ----------------- Hopefully one thing is clearer after this discussion. We definitely need your help! What we need most of all are some Haskell optimisation gurus to join the project, even in a minor way. Darcs 2 offers some huge improvements in safety and core efficiency. Unfortunately, these improvements are overshadowed by poor performance. Paradoxically speaking, darcs 2 just isn't fast enough for people to notice how much faster it has gotten! We need somebody to comb through our code and spot the silly things which are making performance suffer. Is there something too strict? Too lazy? Are going about IO completely the wrong way? There is no patch theory needed for this! Anybody with an eye for performance should be able to rip into this code and find something to fix. If you are not an optimisation guru, there are still loads of ways to help. For starters, you could help us to improve our support for Windows, or maybe some of the ProbablyEasy bugs: http://bugs.darcs.net/issue?@columns=title,id,activity,status,assignedto&@f… We will communicate better -------------------------- The darcs 2 release announcement was very frank, but it also painted an inaccurate picture of the situation. Here is a clearer picture: we are all still very interested in darcs and want to keep using it! If you have a large repository and you cannot wait for us to fix performance bugs, we wish you the best with git (etc). But if darcs can handle your repository, we hope you stick around. It is true that David is taking a lower profile, but this just means that he is not following every discussion on the mailing list or every new bug and feature request. David is still receiving patches and reviewing them on a daily basis, providing the usual technical insight. So keep sending those patches! That's all for now ------------------ I am going to leave things here for now, despite all the interesting points we could still address and see where else the discussion leads. In my next reply, I hope to address some of the more of suggestions you have offered. Thanks again! -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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Looking for a more functional way to do this
by Jefferson Heard 06 Aug '08

06 Aug '08

Working with HOpenGL and GLUT, I find myself approaching a common problem with a common solution that I don't really like all that much, as it reeks of procedural programming. Basically the problem is that of complex program state, such that when the user provides input to the program in the form of a mouse click or a typed string or character, the program updates its internal state to reflect this, whether that's changing the rotation, scale, or position of a screen element, or deciding what data to have loaded from disc. What I often do is something that looks like this: data ProgramState = ProgramState { some_associative_data :: Map String String , position :: GL.Vector3 Float , look_at :: GL Vector3 Float , selectables :: Map GLuint NamedObject } render :: IORef ProgramState -> IO () render state = do st <- readIORef state ... handleMouseClicks :: IORef ProgramState -> GLUT.KeyboardMouseHandler handleMouseClicks state ... = do st <- readIORef state ... main = do ... let st = ProgramState { Map.empty ... } render' = render st mouse' = handleMouseClicks st GLUT.renderCallback $= render GLUT.keyboardMouseCallback $= Just mouse' and so on and so forth. Generally there are not fewer than 5 and not more than about 32 variables that I have to track between mouse clicks, and there's all this boilerplate code as well. I'm searching for a better way to do this, and I feel sure there is one. I'm considering using Template Haskell or possibly SYB to generate this code, but it also seems like I also ought to be able to declare some kind of state monad or continuation monad that can encapsulate ProgramState without having to declare an explicit structure for it everytime. For one thing, I'd like to genericize this code and write something akin to Processing for Haskell (http://www.processing.org)

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Haskell Weekly News: Issue 80 - August 6, 2008
by Brent Yorgey 06 Aug '08

06 Aug '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20080806 Issue 80 - August 6, 2008 --------------------------------------------------------------------------- Welcome to issue 80 of HWN, a newsletter covering developments in the [1]Haskell community. Community News Brent Yorgey (byorgey, your friendly neighborhood HWN editor) has completed a move to Philadelphia and looks forward to starting a PhD in the programming languages group at U Penn next month. Roman Cheplyaka (Feuerbach) won second prize at the 2008 [2]International Mathematics Competition! Announcements prof2dot, version 0.4.1. Gregory Wright [3]announced the release of prof2dot, a graphical profiling tool for use with GHC. prof2dot is a filter that takes the profiling output generated by running a GHC-compiled program with the "+RTS -pix -RTS", option and turns it into a graphviz dot file. GHC switching to git. Simon Marlow [4]announced that the GHC team has made the decision to switch the version control system hosting the GHC repository from darcs to git. Haddock 2.2.1. David Waern [5]announced the release of version 2.2.1 of Haddock, the Haskell documentation tool. Haskore tutorial. jinjing is creating [6]a Haskore tutorial while learning it. Suggestions and corrections are welcome. Hoogle 4 beta. Neil Mitchell [7]announced the availability of beta versions of Hoogle 4, both a [8]web client and [9]command-line version. Testing and [10]feedback welcome! Design your own xmonad shirt. David Lazar has prepared a design on [11]spreadshirt under Designs > Computer > Programming. Choose the color and other formatting and get your very own custom xmonad shirt! Google Summer of Code Progress updates from participants in the 2008 [12]Google Summer of Code. Generic tries. Jamie Brandon is working on a library for efficient maps using generalized tries. This week, he has worked on implementing AVL trees and has created several [13]more [14]benchmarks. Hoogle 4. Neil Mitchell (ndm) is working on [15]Hoogle 4. [16]This week, he finished up type search, which now gives much better results than Hoogle 3. He also [17]released a [18]public beta version of the command-line interface. [19]Bug reports or feature requests are welcome. DPH physics engine. Roman Cheplyaka (Feuerbach) is working on a [20]physics engine using [21]Data Parallel Haskell. [22]Last week, he won second prize at the 2008 International Mathematics Competition; while he was away he also found time to read several papers on broad phase collision detection and to begin thinking about [23]general convex polyhedra. GHC plugins. Max Bolingbroke is working on dynamically loaded plugins for GHC. Cabal dependency framework. Andrea Vezzosi (Saizan) is working on a [24]make-like dependency analysis framework for Cabal. Language.C. Benedikt Huber (visq) is [25]working on Language.C, a standalone parser/pretty printer library for C99. GHC API. Thomas Schilling (nominolo) is working on [26]improvements to the GHC API. Discussion poll: how can we help you contribute to darcs?. Eric Kow (kowey) [27]asked how the darcs team could better encourage more people to contribute, precipitating a long and productive discussion with many good suggestions. Jobs Lectureship in Functional Programming, Nottingham. Graham Hutton [28]announced an opening for a Lecturer (Assistant Professor) in the Functional Programming Lab in Nottingham, a recently formed research group that comprises Thorsten Altenkirch, Graham Hutton, Henrik Nilsson, four research fellows, and eleven PhD students. Applications from the Haskell community are encouraged! The closing date for applications is Friday, 15th August 2008. Blog noise [29]Haskell news from the [30]blogosphere. * Roman Cheplyaka: [31]Physics and polyhedra. * Chris Done: [32]Kibro: Haskell, lighttpd and fastcgi. * Neil Mitchell: [33]Hoogle 4.0 web client preview. * >>> Sven Heyll: [34]Lazy Evaluation (there be dragons and basement cats). * Clifford Beshers: [35]Two-dimensional zip. * Brent Yorgey: [36]Philadelphia!. * Luke Plant: [37]Haskell API docs suck. A lot.. * Neil Mitchell: [38]Hoogle 4.0 release (beta, command line). * Mikael Johansson (Syzygy-): [39]The end of the line. * Jamie Brandon: [40]Yet more mini benchmarks. * Douglas M. Auclair (geophf): [41]Combinators in Haskell. * Holumbus: [42]Search Packages. * Douglas M. Auclair (geophf): [43]How do I get better?. * Neil Mitchell: [44]GSoC Hoogle: Week 10. * Dan Piponi (sigfpe): [45]Hopf Algebra = Group + Monad. * >>> Ayumilove: [46]Haskell Programming Tutorial Part 4. * Douglas M. Auclair (geophf): [47]Trivial Monad solutions. * Douglas M. Auclair (geophf): [48]Trivial Monad solutions (cont.). * Douglas M. Auclair (geophf): [49]Orators' exercise. * Roman Cheplyaka: [50]Status report: week 9-10. * Matthew Sackman: [51]Reflections on the ICFP Programming Contest 2008. * Jamie Brandon: [52]More benchmarks. * Chris Done: [53]GHCi on Acid (GOA). * Audrey Tang: [54]Pugs now builds again from SVN.. * "FP Lunch": [55]An ad-hoc approach to productive definitions. * Ketil Malde: [56]A plan for Bloom filters. * Audrey Tang: [57]Pugs.hs is back.. * Holumbus: [58]OpenSearch Available Again. Quotes of the Week * shepheb: don't forget YMCArray * matthew-_: you know I increasingly think I'm a very bad haskell programmer - I spend all my time programming at the type level, which is basically untyped. So I just write untyped programs, that happen to run at compile time. * SyntaxNinja: just picture monads as tiny, silly, luminous, and devious sprites who fly around your haskell code carrying state from one piece of code to another. I don't think that'll help, but it can't hurt. * poetix: Avoiding lambdas is pointless <-- *groan* * kzm: My program contains a bug. How ungrateful, after all I've done for it. * sw17ch: FunPtrs do not live up to their name About the Haskell Weekly News New editions are posted to [59]the Haskell mailing list as well as to [60]the Haskell Sequence and [61]Planet Haskell. [62]RSS is also available, and headlines appear on [63]haskell.org. Headlines are available as [64]PDF. To help create new editions of this newsletter, please see the information on [65]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [66]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://imc-math.org/ 3. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/14821 4. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/14819 5. http://www.haskell.org//pipermail/haskell-cafe/2008-August/045791.html 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/42861 7. http://neilmitchell.blogspot.com/2008/08/hoogle-40-web-client-preview.html 8. http://haskell.org/hoogle/beta/ 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hoogle 10. http://code.google.com/p/ndmitchell/issues/list 11. http://spreadshirt.com/ 12. http://hackage.haskell.org/trac/summer-of-code/wiki/SoC2008 13. http://jamiiecb.blogspot.com/2008/08/more-benchmarks.html 14. http://jamiiecb.blogspot.com/2008/08/yet-more-mini-benchmarks.html 15. http://code.haskell.org/hoogle/ 16. http://neilmitchell.blogspot.com/2008/08/gsoc-hoogle-week-10.html 17. http://neilmitchell.blogspot.com/2008/08/hoogle-40-release-beta-command-lin… 18. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hoogle 19. http://code.google.com/p/ndmitchell/issues/list 20. http://haskell.org/haskellwiki/Hpysics 21. http://www.haskell.org/haskellwiki/GHC/Data_Parallel_Haskell 22. http://physics-dph.blogspot.com/2008/08/status-report-week-9-10.html 23. http://physics-dph.blogspot.com/2008/08/physics-and-polyhedra.html 24. http://code.haskell.org/~Saizan/cabal 25. http://www.sivity.net/projects/language.c/wiki/ 26. http://hackage.haskell.org/trac/ghc/wiki/GhcApiStatus 27. http://www.haskell.org//pipermail/haskell-cafe/2008-August/045701.html 28. http://article.gmane.org/gmane.comp.lang.haskell.general/16365 29. http://planet.haskell.org/ 30. http://haskell.org/haskellwiki/Blog_articles 31. http://physics-dph.blogspot.com/2008/08/physics-and-polyhedra.html 32. http://chrisdone.com/blog/2008/08/06/kibro-haskell-lighttpd-and-fastcgi/ 33. http://neilmitchell.blogspot.com/2008/08/hoogle-40-web-client-preview.html 34. http://sheyll.blogspot.com/2008/08/lazy-evaluation-there-be-dragons-and.html 35. http://cliffordbeshers.blogspot.com/2008/08/two-dimensional-zip.html 36. http://byorgey.wordpress.com/2008/08/04/philadelphia/ 37. http://lukeplant.me.uk/blog.php?id=1107301692 38. http://neilmitchell.blogspot.com/2008/08/hoogle-40-release-beta-command-lin… 39. http://blog.mikael.johanssons.org/archive/2008/08/the-end-of-the-line/ 40. http://jamiiecb.blogspot.com/2008/08/yet-more-mini-benchmarks.html 41. http://logicaltypes.blogspot.com/2008/08/combinators-in-haskell.html 42. http://holumbus.fh-wedel.de/blog/?p=14 43. http://logicaltypes.blogspot.com/2008/08/how-do-i-get-better.html 44. http://neilmitchell.blogspot.com/2008/08/gsoc-hoogle-week-10.html 45. http://sigfpe.blogspot.com/2008/08/hopf-algebra-group-monad.html 46. http://www.5min.com/Video/Ayumilove-Haskell-Programming-Tutorial-Part-4-328… 47. http://logicaltypes.blogspot.com/2008/05/trivial-monad-solutions.html 48. http://logicaltypes.blogspot.com/2008/05/trivial-monad-solutions-cont.html 49. http://logicaltypes.blogspot.com/2008/05/orators-exercise.html 50. http://physics-dph.blogspot.com/2008/08/status-report-week-9-10.html 51. http://www.wellquite.org/icfp_contest_2008_reflections.html 52. http://jamiiecb.blogspot.com/2008/08/more-benchmarks.html 53. http://chrisdone.com/blog/2008/08/01/ghci-on-acid-goa/ 54. http://pugs.blogs.com/pugs/2008/08/pugs-now-builds.html 55. http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=109 56. http://blog.malde.org/index.php/2008/07/31/a-plan-for-bloom-filters/ 57. http://pugs.blogs.com/pugs/2008/07/pugshs-is-back.html 58. http://holumbus.fh-wedel.de/blog/?p=13 59. http://www.haskell.org/mailman/listinfo/haskell 60. http://sequence.complete.org/ 61. http://planet.haskell.org/ 62. http://sequence.complete.org/node/feed 63. http://haskell.org/ 64. http://code.haskell.org/~byorgey/code/hwn/archives/20080806.pdf 65. http://haskell.org/haskellwiki/HWN 66. http://code.haskell.org/~byorgey/code/hwn/

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GHC Feature or Bug: f x = (`head` x, ())
by Jeremy Shaw 06 Aug '08

06 Aug '08

Hello, GHC is happy to compile this code: > f x = (`head` x, ()) but Hugs does not like it, and Section 3.5 of the Haskell Report does not give any obvious indications that it is valid. Numerous people have suggested that some additional parens are required: > f x = ((`head` x), ()) Is this GHC behavior intentional? If not, is it perhaps a happy accident? Or is it ambigious in some way with out the additional parenthesis ? I am curious because trhsx (the preprocessor for HSP/HSX) currently does not accept this construct. If it is a bug in GHC (that will eventually be fixed), then we can leave trhsx alone. If it is a feature, then a precise definition of the adjusted syntax would be helpful. (Or, if this construct is valid H98, an explaination of how to read the report correctly). Thanks! j.

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Re: [haskell-art] Haskore Tutorial
by Vikrant 06 Aug '08

06 Aug '08

Hi, I get this error. I think have zlib installed! what package should I install to compile cabal on my machine (ubuntu - 8.04) Configuring cabal-install-0.5.2... Setup: At least the following dependencies are missing: zlib >=0.4 status of zlib on my machine is as following bahs$ aptitude search zlib p gambas2-gb-compress-bzlib2 - The Gambas bzlib2 component p gambas2-gb-compress-zlib - The Gambas zlib compression component p libcompress-raw-zlib-perl - low-level interface to zlib compression l p libcompress-zlib-perl - Perl module for creation and manipulation p libio-compress-zlib-perl - Perl interface to zlib p libio-zlib-perl - IO:: style interface to Compress::Zlib p libjzlib-java - Reimplementation of zlib in pure java i libzlib-ruby - transitional dummy package v libzlib-ruby1.8 - i zlib-bin - compression library - sample programs i zlib1g - compression library - runtime p zlib1g-dbg - compression library - development i A zlib1g-dev - compression library - development i zlibc - Uncompressing C Library Regards, Vikrant 2008/8/5 jinjing <nfjinjing(a)gmail.com> > What I did was to compile from source: > > http://hackage.haskell.org/trac/hackage/wiki/CabalInstall > > notice the darcs repo? > > http://darcs.haskell.org/cabal-install/ > > I used > > runghc Setup configure --user --prefix=$HOME > > to keep packages in user space, i.e. inside ~/.cabal folder. > > > On Wed, Aug 6, 2008 at 1:00 AM, Sebastian Menge > <sebastian.menge(a)uni-dortmund.de> wrote: > > Am Tue, 5 Aug 2008 22:10:16 +0530 > > schrieb Vikrant <vikrant.patil(a)gmail.com>: > > > >> well, How do I get cabal! on my ubuntu installation it gives me error > >> saying libghc6-cabal-dev depends ghc < 6.6.1 but 6.8.2 installed! > > > > Thats a known bug, but I cant remeber my workaround. Anyways I have > > installed > > > > libhugs-cabal-bundled > > > > IIRC from a gutsy-repository > > > > HTH, Sebastian. > > _______________________________________________ > > haskell-art mailing list > > haskell-art(a)lurk.org > > http://lists.lurk.org/mailman/listinfo/haskell-art > > > _______________________________________________ > haskell-art mailing list > haskell-art(a)lurk.org > http://lists.lurk.org/mailman/listinfo/haskell-art >

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Haskell garbage collector notes?
by Galchin, Vasili 06 Aug '08

06 Aug '08

hello, Is http://hackage.haskell.org/trac/ghc/wiki/GarbageCollectorNotes a reliable source of info on the ghc garbage collector? thx, vasili

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