September 2009 - Haskell-Cafe

flexible contexts problem
by Sean McLaughlin 13 Sep '09

13 Sep '09

I'm having trouble understanding the following behavior. The following program compiles: {-# OPTIONS_GHC -XMultiParamTypeClasses -XFlexibleContexts #-} import Control.Monad.State class Has α s where has :: s -> (α, s) project :: (MonadState s m, Has α s) => m α project = do (α, s) <- gets has put s return α f :: (MonadState s m, Has Int s) => m Int f = do x <- project return x However, if you replace the function f with f :: (MonadState s m, Has Int s) => m Int f = do x <- project y <- project return x then it fails with the error Could not deduce (Has α s) from the context (MonadState s m, Has Int s) arising from a use of `project' at /Users/sean/uploads/Weird.hs:16:12-18 Possible fix: add (Has α s) to the context of the type signature for `f' In a stmt of a 'do' expression: y <- project In the expression: do x <- project y <- project return x In the definition of `f': f = do x <- project y <- project return x I don't see how the second call to project could possibly make a difference. Could someone please tell me what I'm doing wrong? Thanks in advance. Sean

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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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