December 2009 - Haskell-Cafe

Upgraded to GHC 6.12 and can't find anything
by Gregory Propf 28 Dec '09

28 Dec '09

I finally compiled and installed GHC 6.12 on my Linux system and it seems to be failing to find a lot of things. Notably these import Control.Monad import Control.Monad.State import Control.Monad.Trans import Control.Parallel Worked fine under 6.10. Any clues?

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Control.Parallel missing
by Mitar 28 Dec '09

28 Dec '09

Hi! A friend of mine tried to learn Haskell and asked me for an advice because he had problems with Haskell in 5 steps: http://www.haskell.org/haskellwiki/Haskell_in_5_steps Under "Write your first parallel Haskell program" section there is "import Control.Parallel" which is simply missing in 6.12 and also it is not in documentation anymore: http://www.haskell.org/ghc/docs/latest/html/libraries/index.html I know that we have moved now to Haskell Platfrom so you can install it additionally (probably), but for a novice it is not really nice that example programs do not compile out of the box. Maybe we could extend this 4th step also with an introduction to Cabal? Mitar

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ANNOUNCE: CPython / libpython bindings
by John Millikin 28 Dec '09

28 Dec '09

CPython, the primary implementation of the Python language, has a C API for embedding Python into applications and writing extension modules[1]. The cpython[2] package is a binding to this API. It's not a complete binding yet -- there's a couple areas where I haven't figured out how to represent the C-ish idioms -- so it's not yet possible to do things like implement extension modules[3], run code directly from a file[4], or compile Python strings to code[4]. Hackage can't build docs because it doesn't have the Python development libraries installed, so I've uploaded them to <http://ianen.org/haskell/bindings/cpython/api-documentation/>. If you encounter any build errors, or have wishes / ideas on which parts of the API to add to the binding, please say so. I will add parts as I figure them out, but wanted to get a working version out ASAP so people can play with it. [1] http://docs.python.org/3.1/c-api/ [2] http://hackage.haskell.org/package/cpython/ [3] http://docs.python.org/3.1/c-api/module.html#initializing-c-modules [4] http://docs.python.org/3.1/c-api/veryhigh.html

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time of day
by Brian Denheyer 28 Dec '09

28 Dec '09

Hi All, What's the best way to get the year/month/day/hour/min/sec of the current time ? I've become mired in confusion with Time, Data.Time, DateTime and I think there is even an old-time. Might be a couple of calendar libraries in there, not quite sure... Thanks, Brian

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install-dirs on Mac OS X
by Mark Lentczner 27 Dec '09

27 Dec '09

I have been thinking about the location of installed Haskell package files on Mac OS X. The choice of location affects: GHC & other Haskell implementations Haskell Platform Cabal & cabal-install Haddock If all those agreed on directory locations and layouts, I think the state of Haskell on Mac OS X would be nicer for users. In particular, my hope is for users to end up with an automatically complete Haddock documentation incorporating everything they install. 1) Packages the user installs --global I noticed that the default location for global installation with cabal is on Mac OS X is /usr/local: install-dirs global -- prefix: /usr/local This then intermingles all the Haskell package files along with all sorts of other things that live in /usr/local and environs. While this is arguably convenient for executables that end up in /usr/local/bin (in most people's PATH), it does make things less than tidy, and harder to clean up. Taking a cue from the various preinstalled language systems on Mac OS X, up over in /Library might be a better place: Python puts installed packages in: /Library/Python/<version>/site-packages Ruby puts installed packages in: /Library/Ruby/Gems/<version> /Library/Ruby/Site/<version> Java appears to use /Library/Java/Extensions and has a link to the packages that come the framework as: /Library/Java/Home Perl put installed packages in: /Library/Perl/<version> I suggest that the default place for global installs on Mac OS X be: /Library/Haskell/ Since cabal already by default interposes the compiler version into the lib dir, path, there doesn't appear to be a need to put a <version> dir level near the top. 2) Structure of package pieces I notice that cabal/cabal-install's default layout of where a package's pieces go, and GHC's layout of its base packages don't agree. Further, cabal/cabal-install's are not set up so that one can easily delete an installed package without hunting down its parts. cabal/cabal-install defaults the parts as follows: executables: --prefix--/bin libraries: --prefix--/lib/--pkgid--/--compiler-- data: --prefix--/share/--pkgid-- doc: --prefix--/share/doc/--pkgid--/ html: --prefix--/share/doc/--pkgid--/html That's at least four directories you need to hunt down if you want to clean out a package, and rummaging through bin to figure out which things to remove. (Not to mention libexec, which isn't used by any packages on my system, so I can't say where it goes...) GHC/Haskell Platform use a different layout: executables: --prefix--/bin libraries: --prefix--/lib/--compiler--/--pkgid-- data: --prefix--/share/--pkgid-- doc: --prefix--/share/doc/ghc/libraries/--pkgid--/ html: --prefix--/share/doc/ghc/libraries/--pkgid--/ I think it best if everything for a package is in one place - making removal very easy: executables: --prefix--/packages/--pkgid--/bin libraries: --prefix--/packages/--pkgid--/lib/--compiler-- data: --prefix--/packages/--pkgid--/share doc: --prefix--/packages/--pkgid--/doc html: --prefix--/packages/--pkgid--/doc I put the "packages" level at the top, so that other things, like a master Haddock index dir could be put easily directly under the prefix. 3) Symlinks for binaries This does suggest that it would be nice for the symlink-bindir facility (is that in cabal itself, or added by cabal-install?) to have a version for --global installs. Users could then either set something like: symlink-global-bindir: /usr/local/bin in .cabal/config. Or symlink-global-bindir: /Library/Haskell/bin and then put that in their PATH 4) Quick access to the Framework I like Java's convenience link 'Home', and suggest that /Library/Haskell/GHC be a symlink to where the framework's package files are stored: /Library/Frameworks/GHC.framework/Versions/Current/usr/ Other implementations could use the same idea. Having this here would also (I suspect) help in getting Haddock to be able to find all the bits needed to generate a comprehensive index. Thoughts? I'd be happy to help by supplying patches for various tools to normalize all this on some agreed upon layout. I admit that I'm a bit unclear where the directory choices are being made: Haskell Platform's build process, or GHC's? Cabal's defaults or cabal-install's? And then clearly parts of Haddock. Given the number of tools that need to agree, seems best that we hash it out (here or in the wiki) first, before making patches. - Mark (mtnviewmark) Mark Lentczner http://www.ozonehouse.com/mark/ mark(a)glyphic.com

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Video for Linux (v4l) library for Haskell
by Christopher Done 27 Dec '09

27 Dec '09

Hackage and Google turn up nothing¹, so I am asking here; has anyone written a v4l library for Haskell? I have been reading the v4l documentation² and I am ready to implement a Haskell interface for webcams, but it would be a waste of effort if someone's already got one knocking about. I could hack on theirs! Cheers! Christopher Done ¹ In fact, the only Google result is a posting to this mailing list asking if there is a v4l library to which the single response is "no, write an FFI interface". ² http://pages.cpsc.ucalgary.ca/~sayles/VFL_HowTo/ and http://pages.cpsc.ucalgary.ca/~sayles/VFL_HowTo/Video4LinuxAPI.html

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Installing Haskell on Windows 7
by Thomas Hühn 27 Dec '09

27 Dec '09

[Please excuse me if I seem to be a bit frustrated. I am. I have tried to transcribe a live Haskell platform installation session, but I don't remember details of my past attempts to get cabal working. If you have any questions: shoot.] Hi I've been trying to install GHC and some libraries on Windows 7 for some time now, to no avail. I'm on Windows 7 Home Premium here, and I'd like to install all Haskell-related stuff in C:\Weiteres\Haskell (cabal --user installations ending up in C:\Users\Thomas\AppData\Roaming\cabal is fine). Actually I would like to make system-wide package installations (maybe in C:\Weiteres\Haskell\cabal), but not even --user is working fine so far, so I postpone that. I see two basic options: * Haskell Platform (older release, but all relevant libs bundled with it) * ghc and libs installed by hand (newer release, but more hassle) For the first option I expect a nice installer that just does everything for me, for the second option I'm going along with the instructions in Real World Haskell's appendix. So far, none of it worked. ghc is fine (mostly), but cabal is a total mess. I've just tried the second option and actually I've got quite far, until the network library didn't install. I don't have any specifics anymore. And whichever option I choose I can only make --user installs with cabal (but I'd be willing to settle for that). Okay, let's skip all this "manual installation stuff", on to the beginner-friendly first option: Haskell platform I specify the destination folder "C:\Weiteres\Haskell\Platform" and just go with the default selection of checkboxes. Now I'm trying ghci from the start menu... okay, it works. Entering Windows' command prompt I now enter "cabal update". There is a newer version of cabal-install available. I'm ignoring that for now. I don't want to mess up a tested, working cabal-install version and deviate from the Haskell Platform release just yet. Now "cabal install hakyll --user": C:\Users\Thomas>cabal install hakyll --user Resolving dependencies... Downloading pandoc-1.3... [1 of 1] Compiling Main ( C:\Users\Thomas\AppData\Local\Temp\pandoc- 1.35032\pandoc-1.3\Setup.hs, C:\Users\Thomas\AppData\Local\Temp\pandoc-1.35032\p andoc-1.3\dist\setup\Main.o ) Linking C:\Users\Thomas\AppData\Local\Temp\pandoc-1.35032\pandoc-1.3\dist\setup\ setup.exe ... Configuring pandoc-1.3... Preprocessing library pandoc-1.3... Preprocessing executables for pandoc-1.3... Building pandoc-1.3... src\Text\Pandoc\Shared.hs:121:7: Could not find module `System.IO.UTF8': There are files missing in the `utf8-string-0.3.6' package, try running 'ghc-pkg check'. Use -v to see a list of the files searched for. cabal: Error: some packages failed to install: hakyll-0.2 depends on pandoc-1.3 which failed to install. pandoc-1.3 failed during the building phase. The exception was: exit: ExitFailure 1 That went well. :-( "ghc-pkg check": C:\Users\Thomas>ghc-pkg check There are problems in package binary-0.5.0.2: import-dirs: C:\Users\Thomas\AppData\Roaming\cabal\binary-0.5.0.2\ghc-6.10.4 oesn't exist or isn't a directory library-dirs: C:\Users\Thomas\AppData\Roaming\cabal\binary-0.5.0.2\ghc-6.10.4 doesn't exist or isn't a directory file Data\Binary.hi is missing file Data\Binary\Put.hi is missing file Data\Binary\Get.hi is missing file Data\Binary\Builder.hi is missing cannot find libHSbinary-0.5.0.2.a on library path There are problems in package digest-0.0.0.8: import-dirs: C:\Users\Thomas\AppData\Roaming\cabal\digest-0.0.0.8\ghc-6.10.4 oesn't exist or isn't a directory library-dirs: C:\Users\Thomas\AppData\Roaming\cabal\digest-0.0.0.8\ghc-6.10.4 doesn't exist or isn't a directory file Data\Digest\CRC32.hi is missing file Data\Digest\Adler32.hi is missing cannot find libHSdigest-0.0.0.8.a on library path There are problems in package template-0.1.1.1: import-dirs: C:\Users\Thomas\AppData\Roaming\cabal\template-0.1.1.1\ghc-6.10. doesn't exist or isn't a directory library-dirs: C:\Users\Thomas\AppData\Roaming\cabal\template-0.1.1.1\ghc-6.10 4 doesn't exist or isn't a directory file Text\Template.hi is missing cannot find libHStemplate-0.1.1.1.a on library path There are problems in package utf8-string-0.3.6: import-dirs: C:\Users\Thomas\AppData\Roaming\cabal\utf8-string-0.3.6\ghc-6.10 4 doesn't exist or isn't a directory library-dirs: C:\Users\Thomas\AppData\Roaming\cabal\utf8-string-0.3.6\ghc-6.1 .4 doesn't exist or isn't a directory file Codec\Binary\UTF8\String.hi is missing file Codec\Binary\UTF8\Generic.hi is missing file System\IO\UTF8.hi is missing file System\Environment\UTF8.hi is missing file Data\String\UTF8.hi is missing file Data\ByteString\UTF8.hi is missing file Data\ByteString\Lazy\UTF8.hi is missing cannot find libHSutf8-string-0.3.6.a on library path There are problems in package zip-archive-0.1.1.4: import-dirs: C:\Users\Thomas\AppData\Roaming\cabal\zip-archive-0.1.1.4\ghc-6. 0.4 doesn't exist or isn't a directory library-dirs: C:\Users\Thomas\AppData\Roaming\cabal\zip-archive-0.1.1.4\ghc-6 10.4 doesn't exist or isn't a directory file Codec\Archive\Zip.hi is missing cannot find libHSzip-archive-0.1.1.4.a on library path There are problems in package haddock-2.4.2: import-dirs: c:/builds/slave/x86-win-stable/build/ghc-6.10.4\haddock-2.4.2 do sn't exist or isn't a directory library-dirs: c:/builds/slave/x86-win-stable/build/ghc-6.10.4\haddock-2.4.2 d esn't exist or isn't a directory file Distribution\Haddock.hi is missing file Haddock\DocName.hi is missing file Haddock\Types.hi is missing file Haddock\InterfaceFile.hi is missing file Haddock\Exception.hi is missing file Haddock\Utils.hi is missing file Haddock\GHC\Utils.hi is missing cannot find libHShaddock-2.4.2.a on library path The following packages are broken, either because they have a problem listed above, or because they depend on a broken package. binary-0.5.0.2 digest-0.0.0.8 template-0.1.1.1 utf8-string-0.3.6 zip-archive-0.1.1.4 haddock-2.4.2 Excuse me? Broken packages right after installation? Okay, reinstalling them all (with --user --reinstall"). Except haddock: C:\Users\Thomas>cabal install haddock --user --reinstall Resolving dependencies... cabal: cannot configure haddock-2.6.0. It requires ghc >=6.12 && <6.14 There is no available version of ghc that satisfies >=6.12 && <6.14 *sigh* I'm starting to think about the manual installation of ghci and the libs again... but I won't do it, because it gives me all other kinds of pain (like "let's ship the mingw tool chain, but don't enter it into the PATH, the user will certainly know where to find ar.exe and how to make cabal use it when building a package"). I'm failing there just as much as here with the Platform. Okay, let's forget about haddock. Back to hakyll: "cabal install hakyll --user" Ends with: Linking dist\build\markdown2pdf\markdown2pdf.exe ... Created man\man1\pandoc.1 Created man\man1\hsmarkdown.1 Created man\man1\html2markdown.1 Created man\man1\markdown2pdf.1 setup.exe: CreateDirectory: permission denied (Zugriff verweigert) cabal: Error: some packages failed to install: hakyll-0.2 depends on pandoc-1.3 which failed to install. pandoc-1.3 failed during the final install step. The exception was: exit: ExitFailure 1 Okay, remember that cabal-install was out of date? "cabal install cabal-install" ends with: Linking dist\build\cabal\cabal.exe ... cabal: Error: some packages failed to install: cabal-install-0.6.4 failed during the final install step. The exception was: CreateDirectory: permission denied (Zugriff verweigert) Would be nice to know which directory cabal-install tried to create, don't you think? (This was just thrown in to show why I've only user user installations so far). Okay, the same with "--user" succeeds. Yay! Let's try pandoc again: Linking dist\build\markdown2pdf\markdown2pdf.exe ... Created man\man1\pandoc.1 Created man\man1\hsmarkdown.1 Created man\man1\html2markdown.1 Created man\man1\markdown2pdf.1 setup.exe: CreateDirectory: permission denied (Zugriff verweigert) cabal: Error: some packages failed to install: pandoc-1.3 failed during the final install step. The exception was: exit: ExitFailure 1 *sigh* What is cabal trying to do outside the battle-proven AppData-Cabal directory anyways? Let's revisit the phrase "beginner-friendly first option". :-/ Just for fun's sake, let's have a look into cabal's config file, since I seem to have some directory trouble: install-dirs user -- prefix: C:\Users\Thomas\AppData\Roaming\cabal -- bindir: $prefix\bin -- libdir: $prefix -- libsubdir: $pkgid\$compiler -- libexecdir: $prefix\$pkgid -- datadir: "C:\\Program Files (x86)\\Haskell" -- datasubdir: $pkgid -- docdir: $prefix\doc\$pkgid -- htmldir: $docdir\html -- haddockdir: $htmldir install-dirs global -- prefix: "C:\\Program Files (x86)\\Haskell" -- bindir: $prefix\bin -- libdir: $prefix -- libsubdir: $pkgid\$compiler -- libexecdir: $prefix\$pkgid -- datadir: "C:\\Program Files (x86)\\Haskell" -- datasubdir: $pkgid -- docdir: $prefix\doc\$pkgid -- htmldir: $docdir\html -- haddockdir: $htmldir I certainly don't have a "C:\\Program Files (x86)\\Haskell" folder. Might that result in problems? I don't know, because I have no clue what's supposed to be in the datadir. But then again I shouldn't have to meddle with some installed configuration file, especially since there has been no warning that I had to do that and very especially since I entered my destination folder upon installation. Maybe it's okay, but it kind of makes me nervous. And God knows what else I haven't stumbled upon yet. (I changed those directory entries to the ghc installation directory when I tried the second option and couldn't make it work either.) Has anyone who is *not* a Haskell/ghc/cabal expert been able to install Haskell satisfactorily on Windows 7? What are my options now? Any stupid mistakes I made? Waiting for the next release of the Haskell Platform (whenever that might happen)? Giving up, selling RWH on ebay and preparing New Year's Eve celebrations? Thomas

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: cabal install SDL
by Lie Ryan 27 Dec '09

27 Dec '09

================================================================ C:\Windows\system32>cabal install SDL Resolving dependencies... [1 of 1] Compiling Main ( C:\Users\LIERYA~1\AppData\Local\Temp\SDL-0.5.93108\SDL-0.5.9\Setup.lhs, C:\Users\LIERYA~1\AppData\Local\Temp\SDL-0.5.93108\SDL-0.5.9\dist\setup\Main.o ) C:\Users\LIERYA~1\AppData\Local\Temp\SDL-0.5.93108\SDL-0.5.9\Setup.lhs:2:2: 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" Linking C:\Users\LIERYA~1\AppData\Local\Temp\SDL-0.5.93108\SDL-0.5.9\dist\setup\setup.exe ... Warning: defaultUserHooks in Setup script is deprecated. Configuring SDL-0.5.9... setup.exe: sh: runGenProcess: does not exist (No such file or directory) cabal: Error: some packages failed to install: SDL-0.5.9 failed during the configure step. The exception was: exit: ExitFailure 1 ================================================================ I searched on google, it says some modules (e.g. SDL) requires a unix-shell to run the ./configure script. I do have Cygwin on the machine, but I installed GHC/Haskell Platform on the host machine (not on Cygwin). If I installed the SDL package inside cygwin using cabal, would cabal installs the SDL on the Cygwin environment or on the host machine? (i.e. can I use the resultant SDL-binding outside Cygwin?)

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HList and Data Types a la carte?
by Günther Schmidt 27 Dec '09

27 Dec '09

Hi, is there a connection between HList and Data Types a la Carte? Are both approaches pursuing the same goal? Or is it more like trying to compare apples and pears? Günther

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Mixing internal functions and datatypes with externally available ones
by DPX-Infinity 27 Dec '09

27 Dec '09

Hello. I'm writing a library - some kind a wrapper around SDL library, an engine. For example, I have a module Graphics.UI.SDL.XEngine.State and functions modifyState and setColor in it. These functions are using "global" variable of type IO (IORef XState). I want to use the first function in Graphics.UI.SDL.XEngine.General and Graphics.UI.SDL.XEngine.Drawing modules and I don't want this function to be accessible from a program which uses my library, but I need to make the function setColor visible from everywhere. Is there a simple way to do such thing? Or maybe I should restructure my library?

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