August 2009 - Haskell-Cafe

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 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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

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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

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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

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