- Haskell-Cafe - Haskell.org

instance Monad (Either String) in Prelude or Data.Either?
by Evan Laforge 12 Sep '09

12 Sep '09

Is there any particular reason to not move the instance to the prelude? A module was failing when imported from one place and ok when imported from another, so I spent a frustrating 10 minutes searching for the instance. I couldn't find a way to search haddock for instances (not even grep on the html), nor hoogle, nor anything else. Finally I turned to google and found a couple of haskell-cafe threads with people wondering why other people's code failed for them. This was especially frustrating because I knew I had written my own instance when I originally couldn't find it, then removed my own when I did find it, then forgot where I found it *two times* so I knew it existed, just not where. So this is the third time I've done this search. Now I have a few commented 'import Control.Monad.Error ()' scattered about in a few "low level" modules to try to make sure it's visible everywhere and next time I go hunting I can look in my own modules. If orphan instances are discouraged, shouldn't the instance for Monad Either be declared where Either is? This should probably go for Functor Either too. I notice that Monad Maybe is in Prelude, and it would be a pain if it weren't. If there's no particular reason to not move it, I'll do a libraries proposal... or since it involves the prelude should this be haskell-prime?

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Haskell Weekly News: Issue 130 - September 12, 2009
by Joe Fredette 12 Sep '09

12 Sep '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090912 Issue 130 - September 12, 2009 --------------------------------------------------------------------------- Welcome to issue 130 of HWN, a newsletter covering developments in the [1]Haskell community. Welcome to issue 130 of HWN! In the last week, HWN has gotten a new editor, me! I'm Joe Fredette (jfredett on IRC, reddit, and everywhere else), and I'll be taking over for Brent (byorgey) from now on. I think I speak for the whole community when I thank him for his excellent work on the HWN and associated tools. I have a few ideas about how I want to change HWN for the better, and hopefully you'll like them too! So, without further ado, The Haskell Weekly News! Announcements Looking for a new HWN editor. Brent Yorgey [2]went looking for a new editor for the HWN, and that's how you got me! See the editorial for more details. CfPart: FMICS 2009, 2-3 November 2009. Christophe Joubert [3]announced FMICS 2009 - FIRST CALL FOR PARTICIPATION, 14th International Workshop on Formal Methods for Industrial Critical Systems. November 2-3, 2009 Call for Posters: APLAS 2009. Kiminori Matsuzaki [4]announced a CALL FOR POSTER PRESENTATIONS The Seventh ASIAN Symposium on Programming Languages and Systems (APLAS 2009) December 14 - 16, 2009 Seoul National University, Seoul, Korea. hecc-0.1. Marcel Fourn√© [5]announced the first release of hecc, the Elliptic Curve Cryptography Library for Haskell. Implemented are affine, projective, jacobian and modified jacobian point formats with the basic operations. Included as an Example is a basic ECDH as well as a basic speed test. HLint 1.6.8. Neil Mitchell [6]announced HLint 1.6.8. HLint is a tool for suggesting improvements to your source code. It suggests the use of library functions you may have been unaware of, finds patterns of recursion that are really folds/maps, hints about extensions you aren't using and much more. HLint is now one of the top 20 applications on Hackage, and is used by the darcs project to improve and statically check their code base. A Levenberg-Marquardt implementation. Bas van Dijk [7]announced the release of a Haskell binding to Manolis Lourakis's C levmar library. This library implements the Levenberg-Marquardt algorithm which is an iterative technique that finds a local minimum of a function that is expressed as the sum of squares of nonlinear functions. It has become a standard technique for nonlinear least-squares problems and can be thought of as a combination of steepest descent and the Gauss-Newton method. CCA-0.1. Paul L [8]announced that a library for Causal Commutative Arrows (CCA) has been uploaded to Hackage DB. It implements CCA normalization using Template Haskell and a modified arrow pre- processor (based on arrowp) to generate outout that Template Haskell can parse. It's highly experimental since we are still fiddling with several design choices, and by no means we imply Template Haskell is the best choice to implement CCA. Any suggestion or comment is welcome! graphviz-2999.5.0.0. Ivan Lazar Miljenovic [9]announced version 2999.5.0.0 of the graphviz package for Haskell. This is what I like to think of as the 'Hey, this is almost getting to be a decent library!' version. The graphviz package provides bindings to the GraphViz suite of programs by providing the ability to generate and parse GraphViz's Dot language as well as wrappers around the tools themselves. uvector-algorithms 0.2. Dan Doel [10]announced version 0.2 of the uvector-algorithms package. The package so far has implementations of several sorting and selection algorithms for use on the mutable arrays from the uvector library, as well as combinators for applying them to immutable arrays. dbmigrations 0.1. Jonathan Daugherty [11]announced dbmigrations, A library and program for the creation, management, and installation of schema updates (called migrations) for a relational database. In particular, this package lets the migration author express explicit dependencies between migrations and the management tool automatically installs or reverts migrations accordingly, using transactions for safety. This package is written to support any HDBC-supported database, although at present only PostgreSQL is fully supported. Palindromes 0.1. Johan Jeuring [12]announced Palindromes, a package for finding palindromes in files. Visit the [13]homepage The primary features of Palindromes include: A linear-time algorithm for finding exact palindromes, A linear-time algorithm for finding text palindromes, ignoring spaces, case of characters, and punctuation symbols. Discussion Averting QuickCheck Madness. Christopher Lane Hinson Christopher Hinson [14]asked about best practices with regards to QuickCheck, and it's inclusion/exclusion as a dependency for end-user programs. How to customize dyre recompile? Andy Stewart Andy Stewart [15]asked about how to customize Dyre's settings to do a whole-program recompilation. Externally derive instance of Data? Dimitry Golubovsky Dimitry Golubovsky [16]asked about stand-alone deriving for third-party datatypes. Parallel parsing & multicore. Anakim Border Anakim Border [17]talked about parallel parsing, specifically about a parser he had put together, which led to a discussion of Edward Kmett's recent talks at BAHUG. Ph.D position, Utrecht University, the Netherlands. S.Doaitse [18]announced Vacancy PhD student on Realizing Optimal Sharing in the Functional Language Implementations Utrecht University, The Netherlands. Blog noise [19]Haskell news from the [20]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Eric Kow (kowey): [21]Cabal-Installing graphical apps on MacOS X. * Don Stewart (dons): [22]Improving Data Structures with Associated Types. * Manuel M T Chakravarty: [23]Haskell Arrays, Accelerated.. * Galois, Inc: [24]Tech Talk: Building Systems That Enforce Measurable Security Goals. * Kevin Reid (kpreid): [25]GSoC conclusion.. * Neil Brown: [26]Boids Simulation: Part 1. * Paul Potts: [27]MacPorts, Snow Leopard, and GHC == Sadness. * Andrew Calleja: [28]Haskell IDEs on Windows. * Sean Leather: [29]"Upwards and downwards accumulations on trees" translated into Haskell. * Xmonad: [30]The Design and Implementation of XMonad. * Galois, Inc: [31]Tech Talk: Constructing a Universal Domain for Reasoning About Haskell Datatypes. * Well-Typed.Com: [32]Slides from the IHG talk at CUFP. * Alex McLean: [33]Hackpact Documentation. This links to part one of a two part series. * Bas van Gijze: [34]Cannibals, Missionaries and the State Monad pt. 1. * Magnus Therning: [35]Wrapping IO. This links to part one of a two part series. * Don Stewart (dons): [36]Stream Fusion for Haskell Arrays. * Tom Schrijvers: [37]EffectiveAdvice: AOP, mixin inheritance, monads, parametricity, non-interference, .... * Johan Jeuring: [38]Finding palindromes. * Neil Brown: [39]Concurrent vs Parallel vs Sequential. * Don Stewart (dons): [40]DEFUN 2009: Multicore Programming in Haskell Now!. * Don Stewart (dons): [41]The Haskell Platform: Status Report: Haskell Symposium 2009. Quotes of the Week * lispy: All haskell lists have less than 400 elements * Jafet: The C preprocessor is purely dysfunctional * edwardk: so the -> is matched on the outside, but the -> and , fail to match on the inside, unification fails, dogs and cats start living together in harmony, general chaos. * yaxu: [about lambdabot] an irc bot that no-one understands the workings of has to be a fine precursor to artificial intelligence * Gracenotes: all in all, you're just another brick in the -Wall About the Haskell Weekly News New editions are posted to [42]the Haskell mailing list as well as to [43]the Haskell Sequence and [44]Planet Haskell. [45]RSS is also available, and headlines appear on [46]haskell.org. To help create new editions of this newsletter, please see the information on [47]how to contribute. Send stories to jfredett . at . gmail . dot . com. The darcs repository is available at darcs get [48]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63133 3. http://article.gmane.org/gmane.comp.lang.haskell.general/17476 4. http://article.gmane.org/gmane.comp.lang.haskell.general/17483 5. http://article.gmane.org/gmane.comp.lang.haskell.general/17482 6. http://article.gmane.org/gmane.comp.lang.haskell.general/17481 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63283 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63233 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63219 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63205 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63187 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63157 13. http://www.jeuring.net/Palindromes/ 14. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63146 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63143 16. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63314 17. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63223 18. http://article.gmane.org/gmane.comp.lang.haskell.general/17478 19. http://planet.haskell.org/ 20. http://haskell.org/haskellwiki/Blog_articles 21. http://koweycode.blogspot.com/2009/09/cabal-installing-graphical-apps-on.ht… 22. http://donsbot.wordpress.com/2009/09/11/improving-data-structures-with-asso… 23. http://justtesting.org/post/185173082 24. http://www.galois.com/blog/2009/09/10/jaegermeasurablesecurit/ 25. http://kpreid.livejournal.com/16930.html 26. http://chplib.wordpress.com/2009/09/08/boids-simulation-part-1/ 27. http://praisecurseandrecurse.blogspot.com/2009/09/macports-snow-leopard-and… 28. http://lambdacolyte.wordpress.com/2009/09/08/haskell-ides-on-windows/ 29. http://feedproxy.google.com/~r/splonderzoek/~3/4E8TZPDZ-aM/ upwards-and-downwards-accumulations-on.html 30. http://xmonad.wordpress.com/2009/09/09/the-design-and-implementation-of-xmo… 31. http://www.galois.com/blog/2009/09/08/huffman_universaldomain/ 32. http://blog.well-typed.com/2009/09/slides-from-the-ihg-talk-at-cufp/ 33. http://yaxu.org/hackpact-documentation/ 34. http://adoseoflogic.blogspot.com/2009/07/cannibals-missionaries-and-state-m… 35. http://therning.org/magnus/archives/738 36. http://donsbot.wordpress.com/2009/09/07/stream-fusion-for-haskell-arrays/ 37. http://tomschrijvers.blogspot.com/2009/09/effectiveadvice-aop-mixin-inherit… 38. http://johanjeuring.blogspot.com/2007/08/finding-palindromes.html 39. http://chplib.wordpress.com/2009/09/06/concurrent-vs-parallel-vs-sequential/ 40. http://donsbot.wordpress.com/2009/09/05/defun-2009-multicore-programming-in… 41. http://donsbot.wordpress.com/2009/09/05/the-haskell-platform-status-report-… 42. http://www.haskell.org/mailman/listinfo/haskell 43. http://sequence.complete.org/ 44. http://planet.haskell.org/ 45. http://sequence.complete.org/node/feed 46. http://haskell.org/ 47. http://haskell.org/haskellwiki/HWN 48. http://code.haskell.org/~byorgey/code/hwn/

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Just to let people know
by Jeff Heard 12 Sep '09

12 Sep '09

lhs2TeX does not compile with the latest version of base. complaints about Control.Exception abound

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ANNOUNCE: Palindromes 0.1
by Johan Jeuring 12 Sep '09

12 Sep '09

Palindromes ============================================== Palindromes is a package for finding palindromes in files. Visit the homepage http://www.jeuring.net/Palindromes/ Features -------- The primary features of Palindromes include: * Linear-time algorithm for finding exact palindromes * Linear-time algorithm for finding text palindromes, ignoring spaces, case of characters, and punctuation symbols. Requirements ------------ Palindromes has the following requirements: * GHC version 6.8.1 or later - It has been tested with version 6.10.1. * Cabal library version 1.2.1 or later - It has been tested with version 1.6.0.1. Download & Installation ----------------------- * Use cabal-install cabal install palindromes * If you don't have cabal-install, you must download the Palindromes package from HackageDB and install it manually. Get the `tar.gz` file and decompress it. http://hackage.haskell.org/package/palindromes Once downloaded, use the following commands for configuring, building, and installing the library. runghc Setup.lhs configure runghc Setup.lhs build runghc Setup.lhs install * Get the source: svn checkout https://subversion.cs.uu.nl/repos/staff.johanj.palindromes/ Documentation ------------- The API is documented using Haddock and available on the Palindromes package site. Examples -------- You can find example palindromes, on which Palindromes has been tested, in the `examples` directory of the source distribution. https://subversion.cs.uu.nl/repos/staff.johanj.palindromes/trunk/examples/p… Bugs & Support -------------- To report bugs, use the Google Code project page for Palindromes. http://code.google.com/p/palindromes/ For general concerns and questions, email the author: johan at jeuring.net Licensing --------- Palindromes is licensed under the so-called BSD3 license. See the included `LICENSE` file. Credits ------- Palindromes is based on the functional program developed by Johan Jeuring in his PhD thesis. The current author and maintainer of Palindromes is Johan Jeuring. http://www.jeuring.net/

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hmatrix on os x
by Ben 12 Sep '09

12 Sep '09

hello -- i've been having a heck of a time installing hmatrix on mac os x. i've seen the help pages including http://mit.edu/harold/Public/easyVisionNotes.html but they haven't helped me. my setup is haskell platform 2009.2.0.2 (ghc 6.10.4) os x 10.5 macports -- i've tried installing gsl and gsl-devel to no avail. i've tried cabal install with various options, to no avail. has anyone else have luck with this? best, ben

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Haskell Platform install fails on mtl
by Lyle Kopnicky 12 Sep '09

12 Sep '09

OK, I was able to build the Haskell Platform on Ubuntu 9.04 with GHC 6.10.4. But when I try to install it, I get an error: Registering haskell-platform-2009.2.0.2... Reading package info from "dist/inplace-pkg-config" ... done. Writing new package config file... done. ************************************************** * Building each component completed successfully. * * Now do "sudo make install" ************************************************** lwk@lwk-desktop:~/downloads/haskell-platform-2009.2.0.2$ sudo make install [sudo] password for lwk: scripts/install.sh Installing mtl-1.1.0.2... Error: The mtl-1.1.0.2/Setup script does not exist or cannot be run make: *** [install] Error 2 - Lyle

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Re: [Haskell-cafe] Unable to install Haskell Platform without editline
by Lyle Kopnicky 11 Sep '09

11 Sep '09

On Fri, Sep 11, 2009 at 12:01 PM, Judah Jacobson <judah.jacobson(a)gmail.com>wrote: > The above editline requirement is for the editline C library, not the > Haskell bindings: > http://www.thrysoee.dk/editline > > My guess is that you need to install a recent version of the > libedit-dev package. > After installing libedit-dev, the rest of the build worked. Thanks! Now I'm having a new problem, that I'll post in another thread. - Lyle

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Unable to install Haskell Platform without readline
by Lyle Kopnicky 11 Sep '09

11 Sep '09

Hi folks, I just installed GHC 6.10.4 on Ubuntu 9.04 32-bit, and then tried to install the Haskell Platform from source. It built quite a bit of stuff, with many warnings but no errors, and then finally died with the error below. To install editline, I need cabal, which is of course why I installed the Platform. I read an earlier thread from May that said that editline came with GHC 6.10.2, so the Platform didn't work with 6.10.3, but was soon to be updated. Now the web site<http://hackage.haskell.org/platform/contents.html>for the Platform says it comes with 6.10.4, so I assumed it should work with 6.10.4, but apparently it still has this problem of still missing editline. Am I doing something wrong? checking editline/readline.h usability... no checking editline/readline.h presence... no checking for editline/readline.h... no checking editline/editline.h usability... no checking editline/editline.h presence... no checking for editline/editline.h... no checking readline/readline.h usability... yes checking readline/readline.h presence... yes checking for readline/readline.h... yes checking for sign of read_history result on error... negative checking for rl_completion_matches... no checking for completion_matches... no configure: error: editline not found, so this package cannot be built See `config.log' for more details. Error: Configuring the editline-0.2.1.0 package failed make: *** [build.stamp] Error 2 - Lyle

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Re: Unable to install Haskell Platform without editline
by Lyle Kopnicky 11 Sep '09

11 Sep '09

I mean editline, not readline. On Fri, Sep 11, 2009 at 11:46 AM, Lyle Kopnicky <lists(a)qseep.net> wrote: > Hi folks, > > I just installed GHC 6.10.4 on Ubuntu 9.04 32-bit, and then tried to > install the Haskell Platform from source. It built quite a bit of stuff, > with many warnings but no errors, and then finally died with the error > below. > > To install editline, I need cabal, which is of course why I installed the > Platform. I read an earlier thread from May that said that editline came > with GHC 6.10.2, so the Platform didn't work with 6.10.3, but was soon to be > updated. Now the web site<http://hackage.haskell.org/platform/contents.html>for the Platform says it comes with 6.10.4, so I assumed it should work with > 6.10.4, but apparently it still has this problem of still missing editline. > > Am I doing something wrong? > > checking editline/readline.h usability... no > checking editline/readline.h presence... no > checking for editline/readline.h... no > checking editline/editline.h usability... no > checking editline/editline.h presence... no > checking for editline/editline.h... no > checking readline/readline.h usability... yes > checking readline/readline.h presence... yes > checking for readline/readline.h... yes > checking for sign of read_history result on error... negative > checking for rl_completion_matches... no > checking for completion_matches... no > configure: error: editline not found, so this package cannot be built > See `config.log' for more details. > > Error: > Configuring the editline-0.2.1.0 package failed > make: *** [build.stamp] Error 2 > > - Lyle >

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Re: [Haskell-cafe] Essentials about type classes?
by Kim-Ee Yeoh 11 Sep '09

11 Sep '09

Hi Fredrik, Temaran wrote: > > data Dar = Dar String String > deriving (Show, Eq) > > class Bar a where > foo :: a -> Int > > instance Bar Dar where > foo(Dar n c) = length c > > but it keeps generating the same error; > > ERROR "./Bar.hs":16 - Inferred type is not general enough > *** Expression : foo > *** Expected type : a -> Int > *** Inferred type : Dar -> Int > You're missing indentation. Instead of declaring foo as a member of the typeclass, your code says it's a top-level function fully-polymorphic in the first parameter. That's why defining it later as foo (Dar ...) gives the error message it does. -- View this message in context: http://www.nabble.com/Essentials-about-type-classes--tp25393728p25405022.ht… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Control.Exception base-3/base-4 woes
by Neil Brown 11 Sep '09

11 Sep '09

Hi, In my CHP library I need to do some exception catching. I want the library to work on GHC 6.8 (with base-3 -- this is the current version in Ubuntu Hardy and Jaunty, for example) and GHC 6.10 (which comes with base-4). But base-3 and base-4 need different code for exception catching (whether it's importing Control.OldException or giving a type to the catch method). Here's what I currently do -- my Haskell file contains this: #if __GLASGOW_HASKELL__ >= 609 import qualified Control.OldException as C #else import qualified Control.Exception as C #endif My cabal file contains this (it used to say just "base,..." but Hackage complained at me the other day when I tried to upload that): Build-Depends: base >= 3 && < 5, ... This works on two machines: one is 6.8+base-3, the other is 6.10+base-3&base-4, where cabal seems to use base-4. However, I have had a bug report (now replicated) which stems from a different 6.10+base-3&base-4 machine where cabal picks base-3 instead. The real problem is that the #if is based on GHC version, but really it should be based on which base-* library is being used. I know the code works with base-3 (use Control.Exception) and base-4 (use Control.OldException) but I can't get the build process right to alter the code based on which base-* library is being used. Can anyone tell me how to fix this? I don't think that changing to always use Control.Exception would fix this, because I need to give a different type for catch in base-3 to base-4, so there's still the incompatibility to be dealt with. Thanks, Neil.

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Externally derive instance of Data?
by Dimitry Golubovsky 11 Sep '09

11 Sep '09

Hi, Given a datatype defined somewhere in a third-party package, without deriving (Data) specified. Is it possible, in my module which is importing that datatype from that package, to auto-derive instance of Data for the said datatype? The goal is not to recompile the package just because an auto-derived instance is needed. Or no way other than to recompile the package? Thanks. -- Dimitry Golubovsky Anywhere on the Web

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Problem installing OpenGL
by Seb 11 Sep '09

11 Sep '09

Hi, I'm having trouble installing OpenGL through cabal. It fails when it tries to install OpenGLRaw with this error message: cabal: Missing dependency on a foreign library: * Missing C library: GL I'm running OS X Leopard and have Xcode 3.1.3 installed. Do i have to install something separate or is cabal just not looking in the right places?

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Resolving overloading loops for circular constraint graph
by Stefan Holdermans 10 Sep '09

10 Sep '09

Manuel, Simon, I've spotted a hopefully small but for us quite annoying bug in GHC's type checker: it loops when overloading resolving involves a circular constraint graph containing type-family applications. The following program (also attached) demonstrates the problem: {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE TypeFamilies #-} type family F a :: * type instance F Int = (Int, ()) class C a instance C () instance (C (F a), C b) => C (a, b) f :: C (F a) => a -> Int f _ = 2 main :: IO () main = print (f (3 :: Int)) My guess is that the loop is caused by the constraint C (F Int) that arises from the use of f in main: C (F Int) = C (Int, ()) <= C (F Int) Indeed, overloading can be resolved successfully by "black-holing" the initial constraint, but it seems like the type checker refuses to do so. Can you confirm my findings? I'm not sure whether this is a known defect. If it isn't, I'd be more than happy to issue a report. Since this problem arises in a piece of very mission-critical code, I would be pleased to learn about any workarounds. Thanks in advance, Stefan

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Fwd: Re[Haskell-cafe] [2]: memoization
by Alberto G. Corona 10 Sep '09

10 Sep '09

instead o that you can use a key such is: key :: a -> Int key = unsafePerformIO . hashStableName . makeStableName that is defined for any kind of data then, a unique key for the pair f x could be: key1 f x=(key f , key x) However my experience is that ocassionally gives different hashes for the same object, so maybe a few registers will be duplicated. 2009/9/10 <mf-hcafe-15c311f0c(a)etc-network.de> > On Thu, Sep 10, 2009 at 05:23:26AM -0700, staafmeister wrote: > > To: haskell-cafe(a)haskell.org > > From: staafmeister <g.c.stavenga(a)uu.nl> > > Date: Thu, 10 Sep 2009 05:23:26 -0700 (PDT) > > Subject: Re: Re[Haskell-cafe] [2]: memoization > > > > > > > > Hi Bulat, > > > > > > Bulat Ziganshin-2 wrote: > > > > > > Hello staafmeister, > > > > > > Thursday, September 10, 2009, 3:54:34 PM, you wrote: > > > > > >> What do you think about such a function? This function is > > > > > > a bit of refactoring > > > > > > -- "global variable" in haskell way > > > cache = unsafePerformIO $ newIORef M.empty > > > > > > memo f x = unsafePerformIO$ do > > > m <- readIORef cache > > > case M.lookup x m of > > > Just y -> return y > > > Nothing -> do let res = f x > > > writeIORef cache $ M.insert x > res m > > > return res > > > > > > memo2 = curry . memo . uncurry > > > > > > > This doesn't work and is exactly what I'm afraid the compiler is going to > > do. Cache needs to > > be associated with the function f. > > > > Otherwise one would get conflicts > > then make the cache object store functions together with values. > > > cache = unsafePerformIO $ newIORef M.empty > > memo f x = unsafePerformIO$ do > m <- readIORef cache > case M.lookup (mkKey f, x) m of > Just y -> return y > Nothing -> do let res = f x > writeIORef cache $ M.insert (mkKey > f, x) res m > return res > > memo2 = curry . memo . uncurry > > This leaves mkKey. Since functions are neither Ord nor Show, you'd > have to hack something together yourself. Perhaps an explicit > argument to memo? > > memo :: (Ord a) => String -> (a -> b) -> a -> IO b > memo fname f x = unsafePerformIO$ do > m <- readIORef cache > case M.lookup (fname, x) m of > Just y -> return y > Nothing -> do let res = f x > writeIORef cache $ M.insert (fname, > x) res m > return res > > there is probably a better and more elegant solution, but this should > at least work. right? > > > matthias > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Re: Snow Leopard breaks GHC
by Brian Sniffen 10 Sep '09

10 Sep '09

Having edited the Haskell Platform's /usr/bin/ghc in place, most packages install fine. I'm still having trouble with Pandoc, even given the advice: > Once cabal works, options --ld-option=-m32 (and also --gcc-option=-m32) > may be used. These options may also be passed to "./Setup configure" The problem appears to come when linking an incompatible zlib version: src/Text/Pandoc/ODT.hs:49:26: Exception when trying to run compile-time code: user error (Codec.Compression.Zlib: incompatible zlib version) Code: ($) makeZip "data" </> "odt-styles" In the first argument of `read', namely `$(makeZip $ "data" </> "odt-styles")' In the expression: read ($(makeZip $ "data" </> "odt-styles")) In the definition of `refArchive': refArchive = read ($(makeZip $ "data" </> "odt-styles")) The same problem occurs when making any call to Codec.Archive.Zip or Codec.Compression.Zlib. I do have a universal zlib installed by MacPorts, as well as the universal zlib that shipped with Snow Leopard and the universal zlib that came with Cabal. I'm not sure whether this message indicates that TH code is searching a different library path than non-TH code or what. Advice is most welcome. I'm particularly interested in finding out which zlib versions are being found at the construction of Codec.Compression.Zlib and at runtime (Pandoc compile time). -- Brian Sniffen http://evenmere.org/~bts/ <bts(a)evenmere.org>

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retrieving arguments for functions from a heterogenous list (HList)
by Andrew U. Frank 10 Sep '09

10 Sep '09

I have a number of functions which have some arguments and produce a single result. all the arguments are in a heterogenous list and the results should update the list. this appears somewhat similar to the keyword-argument solution for functions proposed by oleg kiselyov in 2004. i would like to have a method to convert the functions f :: A -> B -> C g:: A -> D -> C -> B (for example) to f' :: argTypes -> H -> H g' :: argTypes -> H -> H where H is a heterogenous list containing A, B, C, D (and others) and argTypes is another heterogenous list containing the types of the arguments, which are used to retrieve the data from the list (with .!!.) - the result has the correct type and is updated in the list with .@@. . naively this could be done by some functins fx (recursing over the list of arguments) storing the last argument in the HList: fx :: (HList l) => op -> HCons e l -> H -> H fx op HNil uod = uod .@@. op fx op (HCons a as) uod = fx (op arg) as uod where arg = uod .!!. a this code does not compile, because HNil and HCons do not match (they are different data types, not a union type). code that compiles looks like class (HList l, HList k , HUpdateAtHNat n e k k, HType2HNat e k n , HLookupByHNat n k e ) => HCall e n f l k | l k -> n where hcall :: f -> l -> k -> k -- not general instance ( HNat n , HUpdateAtHNat n e UoD UoD, HType2HNat e UoD n , HLookupByHNat n UoD e ) => HCall e n e HNil UoD where hcall opv HNil k = hcall0 opv k instance (HCall e n f l UoD , HLookupByHNat n UoD e, HType2HNat e n UoD ) => HCall e n (e -> f) (HCons a l) UoD where hcall op (HCons a l) k = hcall (op arg) l k where arg = hLookupByHNat n k n = hType2HNat (toProxy arg) k :: n hcall0 :: ( HUpdateAtHNat n f UoD UoD, HType2HNat f H n, HCall e n f HNil UoD) => f -> H -> H hcall0 op k = hUpdateAtHNat n (const op undefined) k `asTypeOf` k where n = hType2HNat (toProxy op) k where i factored out the terminating call, which is probably wrong. i would like to use it as: showPop4 :: (HList hNil, HCall Population n (District -> Population) (hConst District hNil) UoD) => (hCons District hNil) -> UoD -> UoD showPop4 arg uod = hcall showPop2 arg uod unfortunately, calls to this function result in 'cannot deduce' compilation error; it seems that some of the intermediate types are not known. i appreciate any help! andrew

1 0

Dutch HUG: meeting tomorrow in Utrecht
by Tom Lokhorst 10 Sep '09

10 Sep '09

Hi everyone, I want to remind all functional programmers currently in The Netherlands of the Dutch Haskell User Group [1, 2] meeting tomorrow at 19:00 [3]. The meeting will be in Booth Hall [4] of the Utrecht University Library, where we'll have three talks. There's free car parking [5] at the library, and it's easily accessible by bike and bus [6]. Also, to stay on top of Dutch HUG related news, please subscribe to the mailing list [2]. See you tomorrow! - Tom Lokhorst [1]: http://www.haskell.org/haskellwiki/Dutch_HUG [2]: http://groups.google.com/group/dutch-hug [3]: http://www.mail-archive.com/haskell-cafe@haskell.org/msg64036.html [4]: http://www.uu.nl/EN/library/contact/university_library/zaalverhuur/Pages/de… [5]: http://www.uu.nl/EN/library/contact/university_library/Parkeren/Pages/defau… [6]: http://www.uu.nl/EN/library/contact/university_library/plattegrondenrou/Pag…

1 0

Would you mind explain such a code ?
by zaxis 10 Sep '09

10 Sep '09

myFoldl :: (a -> b -> a) -> a -> [b] -> a myFoldl f z xs = foldr step id xs z where step x g a = g (f a x) I know myFoldl implements foldl using foldr. However i really donot know how it can do it ? Please shed a light one me, thanks! -- View this message in context: http://www.nabble.com/Would-you-mind-explain-such-a-code---tp25377949p25377… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

5 6

better error message for "undefined"
by Andrew U. Frank 10 Sep '09

10 Sep '09

the haskell prelude introduces the type undefined and contains a remark to the effect that compilers are expected to intrudocue a meaningful error message. GHC just prints 'Prelude undefined' which is not very informativ. is there a way to have different kinds of undefined? such that i get a message which one was hit. something like writing in the code 'unefined 'my error 123' which prints 'undefined - my error 123' when it is accidentally hit. i searched the web, but found nothing. any suggestions? thanks a lot! andrew

3 2

Bounded parMap
by Anakim Border 10 Sep '09

10 Sep '09

Hi, lately I've been working on a parallel parser whose core is something like this: pMap parse blocks where pMap is a map-like function sparking independent computations over the elements of the "blocks" list. The actual implementation used Control.Parallel.Strategies: map parse blocks `using` parListChunk n rnf In a recent post [1], however, Edward Kmett noted that such code is cache oblivious because the "blocks" list is traversed independently by the map and by the sparks. It may therefore happen that the first spark starts to be evaluated when the map is already at the end of the list. Moreover, all the sparks are generated almost instantaneously even if only a few of them can be evaluated concurrently (I'm assuming here that the length of the list is bigger than the number of available native threads, but that seems reasonable). To solve this issue I imagined an alternative "par" primitive sparking a new computation in parallel when a native thread is free to perform its evaluation and otherwise blocking. It turns out it is possible to implement something like this in a library; have a look at the BoundedParMap module here: http://github.com/akborder/HsMakefileParser/ The code uses unsafe operations, so I'm not sure it can be completely trusted. Given however that the "boundedParMap" function combines deterministically the results of multiple applications of a pure function, it should remain referentially transparent. To measure performances I made two versions of my parser (Makefile.hs), one keeping Control.Parallel.Strategies as before and the other using BoundedParMap. I built them (ghc -O2 -threaded; ghc 6.11.20090907) and run them on a quad-core system (+RTS -N4) over a list generating 48 sparks. Running each implementation 10 times I got the following run times: Control.Parallel.Strategies: 1.328 +- 0.1 BoundedParMap: 1.095 +- 0.12 BoundedParMap seems to be faster, especially considering that the total number of sparks (48) is quite small. Do you think that the difference is actually due to better caching (both in the list traversing and because the runtime system deals with less sparks at any time) or to something else I'm missing? -- AB [1] http://www.haskell.org/pipermail/haskell-cafe/2009-September/066158.html

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Re: Would you mind explain such a code ?
by oleg＠okmij.org 10 Sep '09

10 Sep '09

> I know myFoldl implements foldl using foldr. However i really donot know how > it can do it ? You will probably like Graham Hutton A Tutorial on the Universality and Expressiveness of Fold JFP, 1999. http://www.cs.nott.ac.uk/~gmh/fold.pdf Section 5.1 (actually, suml in Section 5) of the paper explains how the expression of foldl in terms of foldr can be _calculated_. The result is correct by construction.

1 0

Parallel parsing & multicore
by Anakim Border 10 Sep '09

10 Sep '09

Hi, I've put together a parser that works like this: - the full input is read into a strict ByteString; - such string is split into a number of lines; - each line is fed (independently) to a parser based on Parsec (version 3). Running the serial version of the parser (compiled with -O2 optimizations) on a rather large file, I get the following: $ ./Parser +RTS -s 2,175,464,100 bytes allocated in the heap 49,293,632 bytes copied during GC 5,297,560 bytes maximum residency (6 sample(s)) 1,406,800 bytes maximum slop 16 MB total memory in use (0 MB lost due to fragmentation) Generation 0: 4140 collections, 0 parallel, 0.39s, 0.42s elapsed Generation 1: 6 collections, 0 parallel, 0.05s, 0.07s elapsed INIT time 0.00s ( 0.00s elapsed) MUT time 1.93s ( 1.99s elapsed) GC time 0.44s ( 0.48s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 2.37s ( 2.47s elapsed) %GC time 18.7% (19.5% elapsed) Alloc rate 1,127,336,508 bytes per MUT second Productivity 81.2% of total user, 78.1% of total elapsed The profile report: COST CENTRE MODULE %time %alloc >>=_a6OH Text.Parsec.Prim 20.6 13.0 tokenPrimEx Text.Parsec.Prim 16.5 20.8 fmap_a6Qj Text.Parsec.Prim 15.5 3.6 parserBind Text.Parsec.Prim 12.4 9.3 mplus_a6KS Text.Parsec.Prim 10.3 10.6 notFollowedBy Text.Parsec.Combinator 3.1 4.4 [...] shows that the biggest part of the execution time is spent in the parser (not in the read & line split operations, as expected). Given that each line is parsed independently, I used the following code: map parse lines `using` parListChunk 250 rnf to spark a separate computation for each group of 250 lines. I made the datatype used by the parser an instance of NFData, so that the "rnf" strategy should force a complete evaluation. The threaded version running on 2 cores is moderately faster than the serial one: $ ./Parser +RTS -s -N2 2,377,165,256 bytes allocated in the heap 36,320,944 bytes copied during GC 6,020,720 bytes maximum residency (6 sample(s)) 6,933,928 bytes maximum slop 21 MB total memory in use (0 MB lost due to fragmentation) Generation 0: 2410 collections, 0 parallel, 0.33s, 0.34s elapsed Generation 1: 6 collections, 4 parallel, 0.06s, 0.05s elapsed Parallel GC work balance: 1.83 (2314641 / 1265968, ideal 2) Task 0 (worker) : MUT time: 2.43s ( 1.19s elapsed) GC time: 0.02s ( 0.02s elapsed) Task 1 (worker) : MUT time: 2.15s ( 1.19s elapsed) GC time: 0.29s ( 0.30s elapsed) Task 2 (worker) : MUT time: 2.37s ( 1.19s elapsed) GC time: 0.07s ( 0.08s elapsed) Task 3 (worker) : MUT time: 2.45s ( 1.19s elapsed) GC time: 0.00s ( 0.00s elapsed) INIT time 0.00s ( 0.00s elapsed) MUT time 2.06s ( 1.19s elapsed) GC time 0.39s ( 0.39s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 2.45s ( 1.58s elapsed) %GC time 15.7% (24.9% elapsed) Alloc rate 1,151,990,234 bytes per MUT second Productivity 84.2% of total user, 130.2% of total elapsed The speedup is smaller than what I was expecting given that each unit of work (250 input lines) is completely independent from the others. Changing the size of each work unit did not help; garbage collection times are small enough that increasing the minimum heap size did not produce any speedup either. Is there anything else I can do to understand why the parallel map does not provide a significant speedup? Thanks, AB

4 10

Fixed length list type?
by Job Vranish 10 Sep '09

10 Sep '09

Does anyone know of a hackage package that has fixed length list type that is an instance of Applicative, Foldable and Traversable? (a list type that somehow encodes its length in the type) I've found lots of fixed length list types, but non that are members of the common typeclasses. I've implement one here: http://github.com/jvranish/FixedList/blob/6c861a12ba5d17481fd22cdb1f90404ab… But am I just duplicating work that is already out there? Thanks, - Job

1 0

Darcs 2.3 and NFS
by Lewis-Sandy, Darrell 09 Sep '09

09 Sep '09

I am trying to set up darcs so that I can share patches between the many machines that I use for application development and testing. The machines have various operating systems (Windows XP, Windows 2000, Windows Vista, Ubuntu 9.04 32-bit, Ubuntu 64 bit, etc). I have a windows file share that is accessible to all the machines, and has been permanently mounted as a CIFS share on the Linux machines. I would like to use that drive for a centralized repository. Since all machines have access to that share I assumed that I could use darcs without setting up either http or ssh access. I have built darcs 2.3 on the Ubuntu 9.04 (Jaunty) 32 bit box and am able to execute darcs commands against any local folders, but am consistently getting an error message when I try to push or put to the NFS: darcs: ./_darcs/tentative_pristine-0:rename: already exists (File exists) Likewise when I navigate to the mounted share folder and attempt a get or pull. Has anyone else encountered this problem?

2 1

problems with HOC install from svn
by John Velman 09 Sep '09

09 Sep '09

I'm unable to build HOC from the svn read-only checkout. Here are some details of what I'm doing. I'm running OS X 10.5.8 on an intel iMac with Xcode is 3.1.3. Haskel and Cabal are from the Haskel platform, haskell-platform-2009.2.0.2-i386.dmg I got Parsec 3.0 from Hackage. I checked out HOC using the svn command at http://code.google.com/p/hoc/source/checkout and checked out revision 411. Configure goes OK except for the complaint: ---- Setup.hs:1:0: Warning: In the use of `defaultUserHooks' (imported from Distribution.Simple): Deprecated: "Use simpleUserHooks or autoconfUserHooks, unless you need Cabal-1.2 compatibility in which case you must stick with defaultUserHooks" ---- But when I try to build, I get, after a bunch of apparently successful things: ----------- Loading package binary-0.5.0.1 ... <command line>: can't load .so/.DLL for: HSbinary-0.5.0.1 (dlopen(libHSbinary-0.5.0.1.dylib, 9): image not found) ----------- I certainly can't find libHSbinary... of any version on my computer, dylib or not. Tried looking in the /Library/Frameworks/GHC.Framework stuff, also did a find . -iname "*libHS* and found libHSGLFW..., libHSparsec-3.0.0. (also tried this in my home directory). What is this, and how do I get it? Best, John Velman

2 4

ANNOUNCE: CCA-0.1
by Paul L 09 Sep '09

09 Sep '09

I'm pleased to annouce that a library for Causal Commutative Arrows (CCA) has been uploaded to Hackage DB. It implements CCA normalization using Template Haskell and a modified arrow pre-processor (based on arrowp) to generate outout that Template Haskell can parse. It's highly experimental since we are still fiddling with several design choices, and by no means we imply Template Haskell is the best choice to implement CCA. Any suggestion or comment is welcome! -- Regards, Paul Liu Yale Haskell Group http://www.haskell.org/yale

3 2

Deconstructing types
by Louis Wasserman 09 Sep '09

09 Sep '09

Yo, I don't know a thing about SYB, Data.Data, or Data.Typeable, mostly because I'm an efficiency fanatic. Nevertheless, I'd like to know whether or not there's a way to deconstruct a (mostly) arbitrary type, into tuples, unions, etc. using this framework. Any thoughts? Louis Wasserman wasserman.louis(a)gmail.com

3 8

Strange type error (tfp package + GADTs)
by Emil Axelsson 09 Sep '09

09 Sep '09

Hi Café, Can anyone explain why `add1` is rejected in the code below (which uses the tfp package): import Types.Data.Num data A n where A :: NaturalT n => Int -> A n getA :: A n -> Int getA (A n) = n add1 :: NaturalT (m:+:n) => A m -> A n -> A (m:+:n) add1 (A a) (A b) = A (a+b) add2 :: NaturalT (m:+:n) => A m -> A n -> A (m:+:n) add2 a b = A (getA a + getA b) add3 :: NaturalT (m:+:n) => A m -> A n -> A (m:+:n) add3 (A a) _ = A a `add2` and `add3` are accepted. As far as I can see, `add2` is equivalent to `add1` except that it delegates the pattern matching to the function `getA`. If I only pattern match on one of the arguments, as in `add3`, things are also fine. Thanks! / Emil

1 1

ANN: fclabels-0.4.0 - First class accessor labels.
by Sebastiaan Visser 09 Sep '09

09 Sep '09

Hello all, IFCP is a really inspiring place to hang/hack around with your fellow Haskell hackers. So, straight from Edinburgh, I proudly present a new release of fclabels[1,2], your favourite record selector package. This version is joint work with Chris Eidhof and Sjoerd Visscher. This package has been around for a while but has been changed almost entirely now. Naming is different and has a far more consistent usage. This library might look cryptic at first sight, but give it a try it is not that hard. There are more package around that serve the same purpose (like the Lenses package which was uploaded a few days ago), but I'm convinced the simplicity and elegance of fclabels will strike you all. ;-) The package description is included below. Documentation can be found in the package itself or on Hackage. Gr, -- Sebastiaan Visser [1] Hackage: http://hackage.haskell.org/package/fclabels [2] Github: http://github.com/sebastiaanvisser/fclabels/tree/master * package description * First class labels that act as bidirectional records fields. The labels are fully composable and can be used to get, set and modify part of datatypes in a consistent way. The label datatype, conveniently called `:->', is an instance of the `Category' type class meaning it has a proper identity and composition. The library has support for automatically deriving labels from record selectors that start with an underscore. Labels can be used in a pure functional setting or be applied to mutable state in some state monad.

2 2

ANNOUNCE: graphviz-2999.5.0.0
by Ivan Lazar Miljenovic 09 Sep '09

09 Sep '09

I am pleased to announce version 2999.5.0.0 [1] of the graphviz [2] package for Haskell. This is what I like to think of as the "Hey, this is almost getting to be a decent library!" version :p [1] http://hackage.haskell.org/packages/archive/graphviz/2999.5.0.0/graphviz-29… [2] http://hackage.haskell.org/package/graphviz The graphviz package provides bindings to the GraphViz [3] suite of programs by providing the ability to generate and parse GraphViz's Dot [4] language as well as wrappers around the tools themselves. [3] http://www.graphviz.org/ [4] http://www.graphviz.org/doc/info/lang.html This is an almost complete re-write of the previously released version (2999.1.0.2): I do not mean that this version was re-written from scratch, but substantial portions of the library have been improved or replaced. As such, current users of this library will unfortunately have to update their code that uses it. The major changes (becuase there's probably heaps of smaller changes I've forgotten about) are: * Parsing and printing of Dot code was re-written to use the new ParseDot and PrintDot classes rather than the old Parseable class and the Show class. What this means for the end-user is that quotation problems should finally all be resolved (I hope...). In particular, proper quotation of String values is now done automagically: if it is found that the String to be printed requires quoting (because it does not match the format required for non-quoted String values), then quotes within the String are escaped and the entire String is quoted. As part of this, the Data.GraphViz.ParserCombinators module has been moved to Data.GraphViz.Types.Parsing. * Re-write the various Dot* datatypes in Data.GraphViz.Types. Sub-graphs/clusters are now their own entity rather than being part of DotNode and the Node ID type is now a type parameter rather than being just Int. Sub-graphs/clusters can now also be parsed. DotGraph and DotSubGraph now both contain a "DotStatements" value, which in turn contains global attributes, subgraphs, nodes and edges. * The various conversion functions in Data.GraphViz now come in two flavours: the unprimed versions take in a Bool indicating if the graph is directed or not; the primed versions attempt to automatically detect this. Also add cluster support for the graph -> dot -> graph conversion-style functions, as requested by Nikolas Mayr. * Allow custom arrow types as supported by GraphViz; as requested by Han Joosten. * Fixed a bug in HSV-style Color values where Int was used instead of Double; spotted by Michael deLorimier. * Properly resolved the situation initially spotted by Neil Brown: Matthew Sackman was following Dot terminology for an edge `a -> b' when using "head" for `b' and "tail" for `a' (this is presumably because the head/tail of the arrow are at those nodes). DotEdge now uses "from" and "to" avoid ambiguity; the various Attribute values still follow upstream usage. This should hopefully be the last update that is such an intrusive change. The next release will most likely contain updates on how to specify a particular output to use (including variants), with most of the rest remain as-is. -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

1 0

Takusen: *** Exception: readUTF8Char: illegal UTF-8 character 252
by Günther Schmidt 09 Sep '09

09 Sep '09

Hi all, I'm trying to use Takusen ODBC on Windows. I'm using a German WinXP Pro and try to connect to an MS Access database. As soon as I try to do some inserts the above mentioned exception shows up. Does anyone know a work around for this? Günther

2 1

HList and Type signatures / synonyms
by Günther Schmidt 09 Sep '09

09 Sep '09

Hi, I keep accumulating values and right now use plain tuples for that. I end up with a 12 element tuple and things are a bit messy. I'd like to use extensible Records from HList instead, thing is I'd like to keep putting type signatures in my code. As it turns out that seems to be where it gets messy with HList. Is there a simple way to do this? Günther PS: Does anyone know why there are Label-n modules in HList, and which one to use?

5 5

ANNOUNCE: uvector-algorithms 0.2
by Dan Doel 08 Sep '09

08 Sep '09

Greetings, It is my pleasure to announce version 0.2 of the uvector-algorithms package. The package so far has implementations of several sorting and selection algorithms for use on the mutable arrays from the uvector library, as well as combinators for applying them to immutable arrays. New developments in this version include: - A simple benchmarking program for testing the performance of the algorithms (it's what I use to measure them, but I only have one computer to run it on, so perhaps other folks might want to see how it works on their machine) - A testing program, written with quick check to verify properties of the algorithms - Several bugs found and fixed due to the above tests and using HPC to verify good program coverage - Combinators for Schwartzian transform - Reworking radix sort to be more amenable to optimization. It's now around twice as fast. - A Radix instance for strict pairs, and a radix sortBy - Merge sort is now slightly faster due to memcpy in uvector :) The library can be found at hackage: http://hackage.haskell.org/package/uvector-algorithms or in its darcs repository: http://code.haskell.org/~dolio/uvector-algorithms/ As always, I can be notified of any issues. Enjoy. -- Dan

1 0

ForeignFunPtr
by Maurício CA 08 Sep '09

08 Sep '09

Hi, We have ForeignPtr. Why isn't there a corresponding ForeignFunPtr? Thanks, Maurício

2 3

Looking for a new HWN editor
by Brent Yorgey 08 Sep '09

08 Sep '09

Executive summary: * I'm looking for someone to take over as HWN editor * It is highly automated and doesn't take as much time as you might think (about 3-4 hours/week on average) * You DON'T need to be a Haskell guru * It is far from a thankless job and is a fun way to provide an appreciated service to the community! Read on for more details! ------------------------------------------------------------------------- Hi all, As you probably know, I've been the editor of the Haskell Weekly News for a little over a year now, and I've decided that it's time for me to move on to other things. So, I'm looking for someone to volunteer to take over as HWN editor. Why might you want to do this? It's true that there is no concrete reward. But judging from the number of comments I have received from people over the past year, the HWN provides a valuable and appreciated service to the Haskell community: there are many who simply don't have time to read the mailing lists, but like to know about new libraries, compiler releases, interesting discussions, and other major goings-on in the community. What does the editorship entail? Thanks to some automated tools developed specifically for the job, it doesn't take as much time as you might think: usually about 4 hours per week; most of that is spent simply reading/skimming various Haskell mailing lists to pick out items for the HWN. The process generally goes like this: * pick out funny quotes from the IRC channel using an automated tool * pick out Haskell-related blog posts using an automated tool * pick out announcements and discussions from the mailing list with an automated tool, writing a short blurb for each (usually this just involves cutting and pasting from the announcement itself, with a bit of editing to make it flow * compile text and HTML versions with an automated tool * post to sequence.complete.org and the mailing list. There are much more detailed instructions written up, and of course I'll be happy to provide detailed help and support for the first few weeks of the new editor's tenure. I should emphasize that the HWN editor does NOT need to be a Haskell guru. In fact, this could be an ideal job for someone who is relatively new to Haskell and the community, but would like to contribute in a tangible way. I also want to emphasize that with the change in editorship, the HWN need not remain exactly the same: if you have exciting ideas about changes to make to the format or content, be my guest! The HWN will be whatever you make of it. So, let me know if you are interested! There won't be any formal interview process; the first person to contact me who wants to do it, gets the job. But of course, if you are not sure and want more information, feel free to email me with questions. -Brent

3 3

Ph.D position, Utrecht University, the Netherlands
by S. Doaitse Swierstra 08 Sep '09

08 Sep '09

Subject: Ph.D position, Utrecht University, the Netherlands =================================================== Vacancy PhD student on Realizing Optimal Sharing in the Functional Language Implementations Utrecht University, The Netherlands. =================================================== Within the Software Technology group of the Information and Computing Sciences department of Utrecht University there is a vacancy for a PhD student to work on the efficient implementation of functional languages. The position is funded by NWO, the Netherlands Organization for Scientific Research. ----------------------------------------------------------------------------------------- Project summary: Lambda-calculus and term rewriting are models of computation lying at the basis of functional programming languages. Both possess syntactic meta-theories based on analyzing rewrite steps. Unfortunately, naive implementations are inefficient, since subterms are frequently copied. To overcome this problem in both theoretical systems and actual implementations, duplicate work is avoided by using graph-based term representations, in which identical subterms can be (but not always are) shared. The question arises whether graph-representations and their reductions that are optimal in a theoretical sense can also be practical from an implementer's point of view. However, so far it is unclear whether nice theoretical ideas combine well with existing implementation methods. The overall-goal of this project is to answer this question in a back-and-forth communication between theoretical concepts and practical realizations. Starting points are the recent work on the optimal Lambdascope implementation based on context sharing, and the Haskell implementation developed at Utrecht University. One of the open problems is whether the Lambdascope framework can be extended to efficiently represent sets of mutually recursive definitions. Another, whether global program analysis can discover where Lambdascope-based approaches solve problems due to insufficient sharing. If both questions can be solved, we want to combine Lambdascope-based implementations with conventional frameworks, and investigate how efficient the resulting implementations become. The unique combination of the theoretical depth from the Logic department and the implementation skills and compiler infrastructure from the Computer Science department make Utrecht University the optimal surroundings for such a project. ----------------------------------------------------------------------------------------- Project leaders are Prof.dr. Doaitse Swierstra and dr. Vincent van Oostrom (principal investigator). The project will be executed in close cooperation between * the Software Technology group (http://www.cs.uu.nl/wiki/Center) of the Information and Computing Sciences department (http://www.cs.uu.nl/ ) * and the Theoretical Philosophy group (http://www.uu.nl/EN/faculties/Humanities/research/researchinstitutes/zeno/r… ) of the Philosophy department (http://www.phil.uu.nl/) and between * the more practically oriented PhD student and * the more theory oriented postdoc. ----------------------------------------------------------------------------------------- Requirements: Master degree in Computer Science, Logic, or equivalent. Good knowledge of functional programming, and several advanced computer science techniques. Knowledge of lambda-calculus implementations, Haskell, and compiler construction will be useful. Both theory and software development based on this should appeal to you. Terms of employment: the PhD student should start as soon as possible, but no later than January 1, 2010. The position is for four years (after one year there will be an evaluation), full-time. Gross salary starts with € 2042,-- per month in the first year and increases to € 2612,-- in the fourth year of employment. The salary is supplemented with a holiday bonus of 8% and an end-of-year bonus of 3%. In addition we offer: a pension scheme, partially paid parental leave, facilities for child care, flexible employment conditions in which you may trade salary for vacation days or vice versa. Conditions are based on the Collective Employment Agreement of the Dutch Universities: http://www.vsnu.nl/Workstudy/Universities-as-employers-/Collective-Labour-A… More information: * about the project can be found on http://www.cs.uu.nl/wiki/bin/view/Center/OptimalSharing * about the Software Technology group on http://www.cs.uu.nl/wiki/Center * about the Information and Computing Sciences department on http://www.cs.uu.nl/ * about this vacancy can be obtained from Doaitse Swierstra (doaitse(a)cs.uu.nl , +31 6 4613 6929). Send your application in pdf (or another non-proprietary format) to mailto:SciencePenO@uu.nl with a cc to mailto:doaitse@cs.uu.nl. on or before Sept 31, 2009. Mention vacancy nr 62910. _______________________________________________ St-staff mailing list St-staff(a)cs.uu.nl http://mail.cs.uu.nl/mailman/listinfo/st-staff

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ANNOUNCE: dbmigrations 0.1
by Jonathan Daugherty 08 Sep '09

08 Sep '09

dbmigrations is: A library and program for the creation, management, and installation of schema updates (called migrations) for a relational database. In particular, this package lets the migration author express explicit dependencies between migrations and the management tool automatically installs or reverts migrations accordingly, using transactions for safety. This package is written to support any HDBC-supported database, although at present only PostgreSQL is fully supported. To get started, see the included README and MOO.TXT files and the usage output for the "moo" command. Get it from Hackage: http://hackage.haskell.org/package/dbmigrations Or get the source with darcs: http://repos.codevine.org/dbmigrations/ This package is motivated by the need for a framework-independent, solid tool to manage database schema changes in a clean way without assuming a linear sequence of changes assumed by existing tools. dbmigrations lets you manage a forest of schema changes. Future work will include an hscurses-based tool to visualize and manipulate available migrations and their dependencies and support for other database engines. Please don't hesitate to send patches, feedback, and criticism directly to me at drcygnus AT gmail DOT com. I'd like to say thanks to Josh Hoyt and Jason Dagit for suggesting improvements, providing support, and showing me how beautiful Haskell is. Thanks! Enjoy! -- Jonathan Daugherty

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High memory consumption of "print"
by Peter Robinson 08 Sep '09

08 Sep '09

The following toy program consumes either 25MB or 70MB, depending on whether the line print "done" is a comment or code. (Using only 1 OS thread increases memory consumption to 130MB when the print is active vs 25MB when inactive.) What am I doing wrong? --------------------- module Main where import Control.Concurrent import Control.Concurrent.STM import Control.Concurrent.STM.TChan import System.Environment import Control.Applicative main = do n <- read . head <$> getArgs tvar <- newTVarIO 0 tchan <- newTChanIO tids <- sequence [ forkIO (test tchan tvar i) | i <- [1..10^n] ] waitForAll tchan $! length tids where waitForAll _ 0 = return () waitForAll tchan len = do atomically $ readTChan tchan waitForAll tchan (len-1) test :: TChan () -> TVar Int -> Int -> IO () test tchan tvar i = do atomically $ do val <- readTVar tvar if val+1 == i then do writeTVar tvar i writeTChan tchan () else retry print "done" --------------------- ghc --make -O2 teststm.hs -threaded && ./teststm 4 +RTS -sstderr

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Failure to build curl bindings on alpha
by Erik de Castro Lopo 08 Sep '09

08 Sep '09

Hi all, I am the Debian Maintainer of the haskell curl bindings which is failing to build on the alpha CPU with the following error: [7 of 8] Compiling Network.Curl.Easy ( Network/Curl/Easy.hs, dist/build/Network/Curl/Easy.o ) Network/Curl/Easy.hs:218:0: On Alpha, I can only handle 32 bytes of non-floating-point arguments to foreign export dynamic When checking declaration: foreign import ccall safe "wrapper" mkProgress :: ProgressFunction -> IO (FunPtr ProgressFunction) Network/Curl/Easy.hs:221:0: On Alpha, I can only handle 32 bytes of non-floating-point arguments to foreign export dynamic When checking declaration: foreign import ccall safe "wrapper" mkDebugFun :: DebugFunctionPrim -> IO (FunPtr DebugFunctionPrim) The GHC version is 6.10.4 and the full Debian build log is here: https://buildd.debian.org/fetch.cgi?&pkg=haskell-curl&ver=1.3.5-2&arch=alph… I am correct to suspect that this is a bug in ghc rather than in haskell-curl? Any other useful clues or information? Cheers, Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

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Re: Looking for a new HWN editor
by John Lato 08 Sep '09

08 Sep '09

I'd just like to say a big "Thank you" to Brent for his service as the HWN editor. I appreciate it very much and always look forward to HWN. Thanks for all your work, Brent. Cheers, John > > Message: 11 > Date: Sat, 5 Sep 2009 17:26:08 -0400 > From: Brent Yorgey <byorgey(a)seas.upenn.edu> > Subject: [Haskell-cafe] Looking for a new HWN editor > > Hi all, > > As you probably know, I've been the editor of the Haskell Weekly News > for a little over a year now, and I've decided that it's time for me > to move on to other things. So, I'm looking for someone to volunteer > to take over as HWN editor. > > -Brent

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How to use Template Haskell build Map?
by Andy Stewart 08 Sep '09

08 Sep '09

Hi all, I have below instances: instance PageViewState DiredViewState where instance PageViewState StringViewState where I can use Language.Haskell.Exts.Parser scan above instances got list: typeList :: [Type] typeList = [TyCon (UnQual (Ident "DiredViewState")),TyCon (UnQual (Ident "DiredViewState"))] So question is how to use Template Haskell and above `typeList` build below `Map` at compile-time? tagmap = M.fromList [(typeIdOf StringViewState, Exists (Dict :: PageViewStateDict StringViewState)) ,(typeIdOf DiredViewState, Exists (Dict :: PageViewStateDict DiredViewState))] Thanks! -- Andy

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How to generate the .chi file for c2hs?
by Magicloud Magiclouds 08 Sep '09

08 Sep '09

Hi, I want to make a binding of a gtk function, which returns a X11 type. gtk2hs is made by c2hs, which is OK to give me the .chi file. Well, X11 is not. So if I make my binding c2hs style, I have to make a .chi file for X11 myself. How to do it? -- 竹密岂妨流水过山高哪阻野云飞

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Re: [Haskell-cafe] ANNOUNCE: Palindromes 0.1
by Johan Jeuring 07 Sep '09

07 Sep '09

On 07 Sep 2009, at 21:21, Rafael Cunha de Almeida wrote: > Johan Jeuring wrote: >> Palindromes >> ============================================== >> >> Palindromes is a package for finding palindromes in files. >> >> Visit the homepage >> >> http://www.jeuring.net/Palindromes/ >> > > A few options are not working well: Thanks. Both errors have been corrected in version 0.1.1. And I moved it from category Algorithm to category Algorithms. -- Johan > $ ./palindromes --h > ********************* > * Palindrome Finder * > ********************* > palindromes: --h: openFile: does not exist (No such file or directory) > $ cat f > socorram-me subi no onibus em marrocos > $ ./palindromes -tl f > ********************* > * Palindrome Finder * > ********************* > Usage: > > palindrome [command-line-options] input-file > > The following options are available: > --h: This message > -p : Print the longest palindrome (default) > -ps: Print the longest palindrome around each position in the input > -l : Print the length of the longest palindrome > -ls: Print the length of the longest palindrome around each position > in the input > -t : Print the longest palindrome ignoring case, spacing and > punctuation > -tl: Print the length of the longest text palindrome > $ > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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haskelldb and Debian
by Joachim Breitner 07 Sep '09

07 Sep '09

Hi Haskell-DB-interested people, we are still on our way to get the Haskell coverage on Debian back in a good shape. One of the open issues is haskelldb, haskelldb-dynamic and haskelldb-hsql-*. All of these are on 0.10 [1] and do not build with ghc-6.10. It seems that at least haskelldb itself has a 0.12 which does build, but the others do not. Thus, some questions: * Are the haskelldb-hsql-* and haskelldb-dynamic packages still maintained? If so, is there a release expected soon? If not, we will have to remove these from Debian. * Without the hsql-* packages, the haskelldb package itself is useless, correct? So we need to package the hdbc series. Are these maintained actively? * Anything else to consider? Greetings, Joachim [1] http://packages.debian.org/search?suite=sid&arch=any&searchon=sourcenames&k… -- 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

2 1

Cabal install specific version of a package
by Grigory Sarnitskiy 07 Sep '09

07 Sep '09

How to install specific version of a package (derive 0.1.4)?

3 2

Problem on existential type.
by Magicloud Magiclouds 07 Sep '09

07 Sep '09

Hi, I am trying out existential type, some sample code works well. Well, my own code could not be compiled with message: Grid.hs:45:11: Kind error: `GridWidget' is applied to too many type arguments In the type `GridWidget widget' In the type `(GridWidget widget) -> (widget -> t) -> t' In the type signature for `liftGW': liftGW :: (GridWidget widget) -> (widget -> t) -> t The code is: {-# OPTIONS -fglasgow-exts #-} module Grid where import Graphics.UI.Gtk data GridWidgetType = GridLabel | GridTextView data GridWidget = forall widget. (WidgetClass widget) => GridWidget widget --GWLabel Label -- | GWTextView TextView gridNew defaultWidget = do self <- fixedNew -- gw <- gridWidgetNew defaultWidget -- gridAddWidget self gw (0, 0) -- self `on` realize $ do -- (ww, wh) <- liftGW gw widgetGetSize -- (w, h) <- widgetGetSize self -- mapM_ (\x -> -- mapM_ (\y -> do -- gw <- gridWidgetNew defaultWidget -- liftGW gw $ \gw -> fixedPut self gw (x * ww, y * wh) -- ) [0..floor (h / wh)] -- ) [0..floor (w / ww)] return self -- gridSetWidget self (x, y) widget = do -- w <- gridGetWidget self (x, y) -- if w == widget -- then return () -- else do -- (w, h) <- widgetGetSize w -- gw <- gridWidgetNew widget -- fixedPut self gw (x * w, y * h) -- widgetDestroy w -- gridWidgetNew GridLabel = labelNew Nothing >>= return . GW -- gridWidgetNew GridTextView = textViewNew >>= return . GW -- gridAddWidget grid (GWLabel label) (x, y) = fixedPut grid label (x, y) -- gridAddWidget grid (GWTextView textView) (x, y) = fixedPut grid textView (x, y) liftGW :: (GridWidget widget) -> (widget -> t) -> t liftGW (GridWidget label) f = f label liftGW (GridWidget textView) f = f textView -- 竹密岂妨流水过山高哪阻野云飞

5 5

How to Create Data Type of memory
by Akshay Dave 07 Sep '09

07 Sep '09

Hi All, I am stuck in converting the transition semantics in Haskell. Please let me know how to define memory data types in Haskell( like we define pointer in C). Prompt help would be greatly appreciated. Sincerely, Akshay _________________________________________________________________ Get back to school stuff for them and cashback for you. http://www.bing.com/cashback?form=MSHYCB&publ=WLHMTAG&crea=TEXT_MSHYCB_Back…

2 4

"Conceptual Mathematics"
by Vasili I. Galchin 07 Sep '09

07 Sep '09

Hello, "Conceptual Mathematics" has been advertised as accessible to high school students. I would like to collect where this book is being taught to high school students and how it is taught(heuristics). I am interested in teaching it to students locally but I realize that these students to be very gifted. Any advice and especially real world experience would be appreciated. Thank you, Vasili

1 0

How to Create Data Type of memory
by Akshay Dave 07 Sep '09

07 Sep '09

Hi All, I am stuck in converting the transition semantics in Haskell. Please let me know how to define memory data types in Haskell( like we define pointer in C). Prompt help would be greatly appreciated. Sincerely, Akshay _________________________________________________________________ Hotmail® is up to 70% faster. Now good news travels really fast. http://windowslive.com/online/hotmail?ocid=PID23391::T:WLMTAGL:ON:WL:en-US:…

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