- Haskell-Cafe - Haskell.org

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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Test
by Ian Lynagh 30 Nov '10

30 Nov '10

A1

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Re: [Haskell-cafe] DPH and GHC 7.0.1
by Andrew Coppin 30 Nov '10

30 Nov '10

On 29/11/2010 01:42 AM, Manuel M T Chakravarty wrote: > Andrew Coppin: >> I was wondering about this myself, actually. I'm especially surprised since I thought the DPH implementation was hard-wired into the compilter itself (in which case, how can you distribute it seperately?) >> >> Then again, I've never yet even tried using DPH. (The wiki page looks very out of date, so I don't know how much to trust its information.) > As David said, we will release the DPH libraries separately, but at the same time as GHC 7.0.2. DPH consists essentially of two components (a) the vectoriser, a program transformer hardwired into GHC and (b) the DPH libraries. At the request of the Haskell Platform people we separated the DPH library packages from the standard GHC distribution and will distribute them via Hackage. > > The wiki page will be updated in time for that release. > > Manuel I would have thought that the two components would be so tightly coupled that this wouldn't work. But then again, you presumably know a lot more about it than I ever will. Anyway, thanks for the clarification.

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System.Console.Haskeline
by michael rice 30 Nov '10

30 Nov '10

How do I load this module? Michael ============= *Main> :m + System.Console.Haskeline <no location info>: Could not find module `System.Console.Haskeline': it is not a module in the current program, or in any known package. *Main>

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Crazy idea, building ghc with cabal?
by Joris Putcuyps 30 Nov '10

30 Nov '10

Hello Could it be done and would it be interesting, building 'ghc' using cabal? * 'lhc' does it * Use 'cabal-rpm' and 'cabal2arch' to create packages for linux distributions * As ordinary user, install specific versions in your home directory. cabal install ghc => $HOME/.cabal/bin/ghc * Get base packages as a dependency. Greetings Joris

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Transparent identity instances
by Jafet 29 Nov '10

29 Nov '10

Hi, Does it make sense to declare a transparent identity instance for Functor, Applicative, Monad, etc? For example, I might want to generalize ($) = (<*>) where > ($) :: (a -> b) -> a -> b > (<*>) :: (Functor f) => f (a -> b) -> f a -> f b The traditional definition makes Identity a newtype: > newtype Identity a = Identity a > instance Applicative Identity where > pure a = Identity a > (Identity f) <*> (Identity a) = Identity (f a) But using this instance becomes unwieldy. If using Identity was transparent, eg. if it was a type synonym > {-# LANGUAGE TypeSynonymInstances #-} > type Identity a = a > instance Applicative Identity where > -- something like > pure a = a > f <*> a = f a But GHC does not accept type synonym instances unless they are fully applied. Is it sound for such an instance to exist? If so, how might it be defined? -- Jafet

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