December 2010 - Haskell-Cafe

Managing multiple installations of GHC
by Robert Clausecker 02 Dec '10

02 Dec '10

Hi folks! I want to test the new version 7 of GHC, but don't want to replace the packaged version 6.12 with it. I'm not very advanced with the internals of GHC and have some problems. So these are my questions: I installed GHC into a subdir of my homedir, let's call it ~/ghc7. How can I install additional libs there? How can I install GHC 7 parallel to GHC 6.12 with the option to choose? My OS is GNU/Linux, my Distro is Ubuntu (Lucid). Thank you very much, yours Robert Clausecker

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doesDirectoryExist is always returning False
by Marcelo Sousa 02 Dec '10

02 Dec '10

Hi, I'm having currently a problem with System.Directory in my mac os. System Version: Mac OS X 10.6.5 Kernel Version: Darwin 10.5.0 Prelude System.Directory> let dirTest = do {dir <- getCurrentDirectory; doesDirectoryExist dir} Prelude System.Directory> dirTest False I noticed also that I can't change the searchable field in the permissions record. Prelude System.Directory> getPermissions "." Permissions {readable = True, writable = True, executable = True, searchable = False} I tried different versions of directory and filepath packages but with no success at the moment. Any suggestions?! Regards, Marcelo Sousa

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Haskell Weekly News: Issue 160 - December 1, 2010
by Daniel Santa Cruz 01 Dec '10

01 Dec '10

Welcome to issue 160 of the HWN, a newsletter covering developments in the [1]Haskell community in the week of November 21 - 27. My apologies for proving a much shorter version of the weekly news this time around. I'm really short on time this week, but decided to send this abbreviated version rather than skipping it. Hope to resume full coverage next week. Cheers! Top Reddit Stories * Lisk - Lisp and Haskell Domain: chrisdone.com Score: 70, Comments: 83 On Reddit: http://www.reddit.com/r/haskell/comments/ec0kp/lisk_lisp_and_haskell/ Original: http://chrisdone.com/posts/2010-11-25-lisk-lisp-haskell.html * lazycatmanatee is building a enormous suite of graphical, desktop apps in Haskell. Here's the screenshot feed Domain: flickr.com Score: 58, Comments: 11 On Reddit: http://www.reddit.com/r/haskell/comments/eb5kd/lazycatmanatee_is_building_a… Original: http://www.flickr.com/photos/48809572@N02/ * Category theory for Haskell programmers Domain: geoffhulette.wordpress.com Score: 49, Comments: 7 On Reddit: http://www.reddit.com/r/haskell/comments/eatd6/category_theory_for_haskell_… Original: http://geoffhulette.wordpress.com/2010/11/22/category-theory-for-haskell-pr… * Duck typing in Haskell Domain: chrisdone.com Score: 45, Comments: 10 On Reddit: http://www.reddit.com/r/haskell/comments/ea99a/duck_typing_in_haskell/ Original: http://chrisdone.com/posts/2010-11-22-duck-typing-in-haskell.html * GHC 7 I/O manager status update: bugs fixed, performance improved, plans afoot! Domain: serpentine.com Score: 41, Comments: 0 On Reddit: http://www.reddit.com/r/haskell/comments/ecls3/ghc_7_io_manager_status_upda… Original: http://www.serpentine.com/blog/2010/11/27/ghc-7-io-manager-status/ * And here I thought they were using Haskell... Domain: i.imgur.com Score: 34, Comments: 11 On Reddit: http://www.reddit.com/r/haskell/comments/ebgnj/and_here_i_thought_they_were… Original: http://i.imgur.com/ApzhX.png * Fun with monad comprehensions Domain: blog.n-sch.de Score: 33, Comments: 9 On Reddit: http://www.reddit.com/r/haskell/comments/ecu0w/fun_with_monad_comprehension… Original: http://blog.n-sch.de/2010/11/27/fun-with-monad-comprehensions/ * The 'text' package has been accepted into the Haskell Platform! Domain: self.haskell Score: 31, Comments: 20 On Reddit: http://www.reddit.com/r/haskell/comments/eb7fd/the_text_package_has_been_ac… Original: /r/haskell/comments/eb7fd/the_text_package_has_been_accepted_into_the/ * Yesod 0.6.3 Released Domain: docs.yesodweb.com Score: 24, Comments: 1 On Reddit: http://www.reddit.com/r/haskell/comments/e9jfd/yesod_063_released/ Original: http://docs.yesodweb.com/blog/yesod-0-6-3/ * how subtraction works for combinatorial species Domain: byorgey.wordpress.com Score: 24, Comments: 2 On Reddit: http://www.reddit.com/r/haskell/comments/ec5mx/how_subtraction_works_for_co… Original: http://byorgey.wordpress.com/2010/11/24/species-subtraction-made-simple/ Top StackOverflow Questions * Avoiding namespace pollution in Haskell votes: 14, answers: 3 http://stackoverflow.com/questions/4260507/avoiding-namespace-pollution-in-… * Keeping State in a Stateless world votes: 7, answers: 2 http://stackoverflow.com/questions/4259800/keeping-state-in-a-stateless-wor… * Updating a Big State Fast in Haskell votes: 7, answers: 2 http://stackoverflow.com/questions/4265660/updating-a-big-state-fast-in-has… * What is the most efficient purely functional algorithm for generating all prefixes of a list? votes: 7, answers: 2 http://stackoverflow.com/questions/4290370/what-is-the-most-efficient-purel… * How can I make a graphical command line in haskell/gtk2hs? votes: 6, answers: 2 http://stackoverflow.com/questions/4281984/how-can-i-make-a-graphical-comma… * Point-free form versus style votes: 5, answers: 3 http://stackoverflow.com/questions/4235741/point-free-form-versus-style * How to catch (and ignore) a call to the error function? votes: 4, answers: 2 http://stackoverflow.com/questions/4243117/how-to-catch-and-ignore-a-call-t… * Persistent console history in ghci votes: 4, answers: 1 http://stackoverflow.com/questions/4249351/persistent-console-history-in-gh… * Common Lisp equivalent to Haskell's main function? votes: 4, answers: 2 http://stackoverflow.com/questions/4285718/common-lisp-equivalent-to-haskel… * How can I write a MST algorithm (Prim or Kruskal) in Haskell? votes: 4, answers: 3 http://stackoverflow.com/questions/4290163/how-can-i-write-a-mst-algorithm-… About the Haskell Weekly News New editions are posted to [2]the Haskell mailing list as well as to [3]the Haskell Sequence and [4]Planet Haskell. [5]RSS is also available, and headlines appear on [6]haskell.org. To help create new editions of this newsletter, please send stories to dstcruz * at * gmail * dot * com. The code used to produce this version of the newsletter is not yet publicly available, as it is a complete hack designed to get things started again. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://www.haskell.org/mailman/listinfo/haskell 3. http://sequence.complete.org/ 4. http://planet.haskell.org/ 5. http://sequence.complete.org/node/feed 6. http://haskell.org/

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Who's in charge of the new Haskell.org server?
by Christopher Done 01 Dec '10

01 Dec '10

If someone will allow me to send them an extension for WikiMedia I will write one. It shouldn't be complex at all, so code review will be trivial. Please let me know! I'm sure other people here are interested to know who to go to to get things like this done. It would be cool to write an extension to support an embedded Haskell prompt (e.g. tryhaskell.org abd http://haskell.quplo.com/) inside the wiki. It's possible to extend the parser to support custom token types[1], so this could be a neat addition. For instance, the _Blow your mind_ article is full of examples, you can link to them with tryhaskell.org[3], but that's not as cool, why not make these runnable inside the page? :-) If tryhaskell.orgever goes down the script can just fall back to displaying code. Ciao [1]: http://www.mediawiki.org/wiki/Category:Parser_extensions [2]: http://haskell.org/haskellwiki/Blow_your_minds [3]: http://tryhaskell.org/?input=foldr%20(\a%20~(x,y)%20-%3E%20(a:y,x))%20([],[…

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Unable to install packages
by Roland Senn 01 Dec '10

01 Dec '10

I learned a little bit Haskell with Hugs on Windows and now I want to develop on Linux. I installed the Haskell Platform on Unbunto 10.10. There were no problems. Then I tried to install Leksah with sudo cabal install leksah --global It failed with: Resolving dependencies... /tmp/gtksourceview2-0.11.12661/gtksourceview2-0.11.1/Gtk2HsSetup.hs:25:0: warning: #warning Setup.hs is guessing the version of Cabal. If compilation of Setup.hs fails use -DCABAL_VERSION_MINOR=x for Cabal version 1.x.0 when building (prefixed by --ghc-option= when using the 'cabal' command) [1 of 2] Compiling Gtk2HsSetup ( /tmp/gtksourceview2-0.11.12661/gtksourceview2-0.11.1/Gtk2HsSetup.hs, /tmp/gtksourceview2-0.11.12661/gtksourceview2-0.11.1/dist/setup/Gtk2HsSetup.o ) [2 of 2] Compiling Main ( /tmp/gtksourceview2-0.11.12661/gtksourceview2-0.11.1/Setup.hs, /tmp/gtksourceview2-0.11.12661/gtksourceview2-0.11.1/dist/setup/Main.o ) Linking /tmp/gtksourceview2-0.11.12661/gtksourceview2-0.11.1/dist/setup/setup ... Configuring gtksourceview2-0.11.1... Preprocessing library gtksourceview2-0.11.1... Building gtksourceview2-0.11.1... [ 1 of 13] Compiling Graphics.UI.Gtk.SourceView.Signals ( dist/build/Graphics/UI/Gtk/SourceView/Signals.hs, dist/build/Graphics/UI/Gtk/SourceView/Signals.o ) Graphics/UI/Gtk/SourceView/Signals.chs:51:46: Module `System.Glib.UTFString' does not export `maybePeekUTFString' cabal: Error: some packages failed to install: gtksourceview2-0.11.1 failed during the building phase. The exception was: ExitFailure 1 leksah-0.8.0.8 depends on gtksourceview2-0.11.1 which failed to install. I searched the Internet on "gtksourceview2 maybePeekUTFString" and found a patch: http://www.mail-archive.com/gtk2hs-devel@lists.sourceforge.net/msg00971/gtk… As a newby with the Haskell tools, I searched the Internet on how to install a patch. I found dpm and I tried to install it with: sudo cabal install dpm --global It failed with: configure: error: in `/tmp/terminfo-0.3.1.31936/terminfo-0.3.1.3': configure: error: curses headers could not be found, so this package cannot be built See `config.log' for more details. cabal: Error: some packages failed to install: DPM-0.2.1 depends on terminfo-0.3.1.3 which failed to install. darcs-2.5 depends on terminfo-0.3.1.3 which failed to install. haskeline-0.6.3.2 depends on terminfo-0.3.1.3 which failed to install. terminfo-0.3.1.3 failed during the configure step. The exception was: ExitFailure 1 So after installing Haskell Platform, I only found broken packages! What can I do to install Leksah?

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Cabal sdist bug patch
by John D. Ramsdell 01 Dec '10

01 Dec '10

So as far as I can tell, it's easy to fix the cabal sdist bug. The module that generates a distribution simply has to use insntallOrdinaryFile when copying files, not the version of copyFile that is exported by Distribution.Simple.Util. I'll respond to the open ticket with this patch later today. John $ diff -ur ocabal-1.8 cabal-1.8 Only in cabal-1.8: .darcs-boring diff -ur ocabal-1.8/Distribution/Simple/SrcDist.hs cabal-1.8/Distribution/Simple/SrcDist.hs --- ocabal-1.8/Distribution/Simple/SrcDist.hs 2010-12-01 11:16:00.629309262 -0500 +++ cabal-1.8/Distribution/Simple/SrcDist.hs 2010-12-01 11:18:37.449933651 -0500 @@ -78,7 +78,7 @@ ( Version(versionBranch) ) import Distribution.Simple.Utils ( createDirectoryIfMissingVerbose, withUTF8FileContents, writeUTF8File - , copyFiles, copyFileVerbose + , installOrdinaryFile, installOrdinaryFiles , findFile, findFileWithExtension, matchFileGlob , withTempDirectory, defaultPackageDesc , die, warn, notice, setupMessage ) @@ -341,6 +341,12 @@ createDirectoryIfMissingVerbose verbosity True (takeDirectory targetFile) copyFileVerbose verbosity file targetFile +copyFileVerbose :: Verbosity -> FilePath -> FilePath -> IO () +copyFileVerbose = installOrdinaryFile + +copyFiles :: Verbosity -> FilePath -> [(FilePath, FilePath)] -> IO () +copyFiles = installOrdinaryFiles + printPackageProblems :: Verbosity -> PackageDescription -> IO () printPackageProblems verbosity pkg_descr = do ioChecks <- checkPackageFiles pkg_descr "." $

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[ANNOUNCE] A general data-flow framework
by Mitar 01 Dec '10

01 Dec '10

Hi! I have just published my library which provides a general data-flow framework: http://hackage.haskell.org/package/Etage Sadly it requires current GHC HEAD branch because of this: http://hackage.haskell.org/trac/ghc/ticket/1769 Short description: A general data-flow framework featuring nondeterminism, laziness and neurological pseudo-terminology. It can be used for example for data-flow computations or event propagation networks. It tries hard to aide type checking and to allow proper initialization and cleanup so that interfaces to input and output devices (data or events producers or consumers) can be made (so that created models/systems/networks can be used directly in real world applications, for example robots). I am more than open to any suggestions and comments. Mitar

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ANN: HaLVM 1.0: the Haskell Lightweight Virtual Machine
by Adam Wick 01 Dec '10

01 Dec '10

Galois, Inc. is pleased to announce the immediate release of the Haskell Lightweight Virtual Machine (or HaLVM), version 1.0. The HaLVM is a port of the GHC runtime system to the Xen hypervisor, allowing programmers to create Haskell programs that run directly on Xen's "bare metal." Internally, Galois has used this system in several projects with much success, and we hope y'all will have an equally great time with it. What might you do with a HaLVM? Pretty much anything you want. :) Explore designs for operating system decomposition, examine new notions of mobile computation with the HaLVM and Xen migration, or find interesting network services and lock them inside small, cheap, single-purpose VMs. The HaLVM is the result of many years of effort, by many people inside Galois. Although it is not yet totally bug-free, we have decided that broad adoption wins over perfection and thus we are releasing it for general review. As such, there will be some rough edges, and we urge you to read the documentation to understand the platforms we test on. We are releasing the HaLVM under a non-restrictive BSD3 license. You can find it here: http://halvm.org We welcome user feedback, feature requests, bug notices, patches, and feature additions; see the page above for guidelines on getting involved. Finally, we'd like to give many things to the GHC and Xen communities, without which this work would not be possible. If you have any questions or concerns, please don't hesitate to contact the HaLVM's maintainers at halvm-devel(a)community.galois.com. Have a lovely day! - Adam

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