March 2011 - Haskell-Cafe

ANNOUNCEMENT: nehe-tuts 0.2.0, new release
by Jason Dagit 28 Mar '11

28 Mar '11

What is the nehe-tuts package? In 1999 Jeff Molofee, aka NeHe, wrote a series of tutorials on how to get started with basic OpenGL. In 2005, I ported the code for these tutorial pages to Haskell. You can find NeHe's original tutorials here: http://nehe.gamedev.net/default.asp Since that time, we have seen the adoption of Cabal, the rise of Hackage, a major refactoring of the Haskell OpenGL bindings, major revisions to the official OpenGL spec, and major changes to GHC. Through all of that my tutorial conversions have continue to compile with GHC by explicitly requesting Haskell98, but they are starting to bit rot and GHC complains that I use deprecated features. This release represents an effort to modernize the haskell version of these tutorials. I have stopped using the OpenGL package and now instead use the easier/cleaner OpenGLRaw bindings. Instead of GLUT, I use GLFW-b bindings. This means windows users can 'cabal install' this package and run the examples with just the Haskell Platform. No extra libraries need to be manually installed. All the dependencies can be installed from Hackage. I've also replaced some of the uglier bits that I wrote with nicer libraries like bytestring and cereal. These tutorial need further updates in order to match the latest in OpenGL specifications. The tutorials are still written using OpenGL's immediate mode, but that was deprecated in OpenGL 3.x so it's possible that in the future these examples won't be supported by your graphics card. Updating these examples to not rely on deprecated APIs should be easy, but I wanted an intermediate modernization release first. Enjoy! Jason

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ANNOUNCEMENT: xmobar 0.13
by Jose A. Ortega Ruiz 27 Mar '11

27 Mar '11

I'm happy to announce the release of xmobar 0.13. xmobar is a lightweight, text-based system monitor for un*x systems. See http://projects.haskell.org/xmobar/ for the whole story. ## Version 0.13 (March 28, 2011) _New features_ - New `Volume` monitor displaying ALSA soundcards information, by Thomas Tuegel. - New `ThermalZone` plugin substituting `Thermal` and using linux's *sysfs* interface (you need this one if you're using a kernel version equal to or above 2.6.37). See [issue 44]. - xmobar app new has WM_CLASS, WM_NAME and _NET_WM_PID xprops ([issue 38]). _Incompatible changes_ - In the process of solving [issue 14], we've broken those configurations that rely on including alignment separators in the input fed to `StdinReader`. - The MPD plugin does not accept host and port options anymore: use the environment variables MPD_HOST and MPD_PORT instead. - The `Mail` plugin now takes a second parameter (a string) specifying its alias. As a side-effect, this solves [issue 30]. _Bug fixes_ - [issue 14]: `StdinReader` and other plugins accepting external input don't get confused anymore when characters from `alignSep` appear in their input. - [issue 27]: `BottomSize` placement now respects its width argument. - [issue 28]: Compilation in Mac OS X fixed. - [issue 30]: `Mail` plugin can be specified anywhere in commands list. - [issue 36]: Battery monitor now supports non-standard locations of the `/sys/class/power_supply/AC/online` file. - [issue 40]: Battery monitor now supports the new power_now, that replaces current_now in linux kernels for v. 2.36 and above. - [issue 42]: More accurate net monitor rates. - DiskIO, Cpu and MultiCpu monitors are also more accurate now. - Text is now correctly centered vertically. - `FullBM` border spec fixed. Happy monitoring, jao -- Computer games don't affect kids; I mean if Pac Man affected us as kids, we would all be running around in darkened rooms, munching magic pills, and listening to repetitive electronic music. - Kristian Wilson, Nintendo Inc.

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why are trading/banking industries seriously adopting FPLs???
by Vasili I. Galchin 27 Mar '11

27 Mar '11

Hello, I am very curious about the readiness of trading and banking industries to adopt FPLs like Haskell: http://talenteze.catsone.com/careers/index.php?m=portal&a=details&jobOrderI….... I currently work in the computer security(intrusion detection). My colleagues are totally ignorant concerning the foundations/motivations of FPLs. (Ironically http://www.galois.com participates in the computer security arena!). Why are are trading/banking diving into FPLs? Regards, Vasili

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Three Google Summer of Code project proposals
by Johan Tibell 27 Mar '11

27 Mar '11

Hi, I'd like to advertise three Google Summer of Code projects that I recently added to the list [1] of proposed projects: *** Build multiple Cabal packages in parallel *** http://hackage.haskell.org/trac/summer-of-code/ticket/1594 Many developers have multi-core machines but Cabal runs the build process in a single thread, only making use of one core. If the build process could be parallelized build times could be cut by perhaps a factor of 2-8, depending on the number of cores and opportunity of parallel execution available. *** Simpler support for isolated/sandboxed Cabal builds *** http://hackage.haskell.org/trac/summer-of-code/ticket/1590 cabal-dev and capri allow developers to build packages in their own sandboxes, using a separate package database for each. This allows for isolated builds and prevents breakages due e.g. package upgrades. Merging cabal-dev into Cabal allows us to share lots of code and makes the feature more accessible to developers. *** Convert the text package to use UTF-8 internally *** http://hackage.haskell.org/trac/summer-of-code/ticket/1595 When the text package was created, early benchmarks showed that using UTF-16 as the internal representation for Unicode code points was the fastest. The package still uses UTF-16 internally. The benchmarks might not have given a complete picture of the performance implications of using different internal encodings: all benchmarks were run on input data that used the same encoding as used internally, but most real world data uses UTF-8. If the benchmarks would also have taken the cost of decoding and encoding from and to UTF-8 the results might have been different. The goal of this project is to revisit the choice of internal encoding. I encourage any interested students to have a look at the three proposals (and the other proposals on the list), discuss them on this list, and sign up for GSoC (after March 28). 1. http://hackage.haskell.org/trac/summer-of-code/report/1 Cheers, Johan

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Re: [Haskell-cafe] timezone-series and timezone-olson
by Yitzchak Gale 27 Mar '11

27 Mar '11

Hi Manfred, I am copying this response to the Haskell Cafe mailing list. Manfred Lotz wrote: > ...I'm trying to figure out how to use your > packages to get the time in a different timezone. > Do you have an example how to do that? What I want for example is to > provide the timezone preferably like this: US/Eastern, and get the time > information like for example this: > > US/Eastern DST EDT 2011.03.27 05:20:52 > > The pieces I like to get are: Summertime indicator, TZ abbrev and the > date resp. time in that timezone. If you are willing to hard-code the offset of the timezone, you don't need my packages. You only need them if you need your program to reflect accurately whether summer time is/was in effect at the given time at the given location, or if the timezone changed at some time in history. I assume that you are starting with a UTCTime object, constructed in one of the usual ways using the time package. Get the timezone information provided by the operating system. On anything other than Windows, that means reading the timezone file for that zone. On Windows the information is in the registry, but unfortunately we don't have an interface for reading it from there yet. The best I can suggest for now is to copy timezone files from a non-Unix computer. Assuming you have the timezone file that you need - let's say it is in the directory /usr/share/zoneinfo as typical for Linux and Mac - here is how to code it: do ... tzs <- getTimeZoneSeriesFromOlsonFile "/usr/share/zoneinfo/America/New_York" let usEastern = utcToLocalTime' tzs utc Then, to format the time as you require, use the formatTime function from the time package. Hope this helps, Yitz

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NFData instance for Numeric.LinearAlgebra Matrix
by Tad Doxsee 27 Mar '11

27 Mar '11

Hello, Is there already an instance of NFData (from Control.DeepSeq in the deepseq package) for the type Matrix (from Numeric.LinearAlgebra in the hmatrix package) somewhere? If not, how does one define one? (The data declaration for Matrix is in a hidden module, Data.Packed.Internal.Matrix, if that makes any difference). Thanks, Tad

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ANN: unix-bytestring 0.3.4
by wren ng thornton 27 Mar '11

27 Mar '11

-------------------------------------------- -- unix-bytestring 0.3.4 -------------------------------------------- The unix-bytestring package offers a full selection of Unix/Posix-specific functions for reading and writing ByteStrings to Fds. -------------------------------------------- -- Changes (since 0.3.2) -------------------------------------------- * For all the low-level functions (fd*Buf) there are now safer versions (tryFd*Buf) which return errors via Either Errno, instead of throwing IOError exceptions. These will be of particular interest to the maintainers of iteratee, iteratee-mtl, and liboleg. * All the low-level functions (and the appropriate higher-level analogues) now check that the ByteCount or Int arguments are positive. If they're negative or zero then they return immediately (saying that zero bytes were read/written, returning an empty ByteString, etc). Note that this behavior is different than the functions in @unix@ which only check if they're equal to zero, or don't check at all. -------------------------------------------- -- Future work -------------------------------------------- * The readv(2) and writev(2) functions have a number of corner cases that throw errors (e.g., if you have too many iovecs where "too many" could mean >16) but these can be detected beforehand, or worked around by making multiple calls. Unfortunately, finding out what the limit is (or whether the linked version of libc does its own workarounds) is pretty tricky and platform-dependent. So I'll work on figure that out and making some safer wrappers. -------------------------------------------- -- Links -------------------------------------------- Homepage: http://code.haskell.org/~wren/ Hackage: http://hackage.haskell.org/package/unix-bytestring Darcs: http://community.haskell.org/~wren/unix-bytestring Haddock (Darcs version): http://community.haskell.org/~wren/unix-bytestring/dist/doc/html/unix-bytes… -- Live well, ~wren

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help with dynamic load
by Rob Nikander 27 Mar '11

27 Mar '11

Hi all, I'm trying to use the 'plugins' package. Since I already posted to stackoverflow I'll just link to that. I posted a simple program that I thought would work, but mostly doesn't. Any pointers, appreciated. http://stackoverflow.com/questions/5427777/help-with-haskell-dynamic-plugin… thanks, Rob

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Functional dependence nightmare
by Edgar Gomes Araujo 26 Mar '11

26 Mar '11

Hi, I'm running in errors that, I think, is related with functional dependence. But I don't know how to interpret or solve them. I have basically 3 types: Edge, Face and Simplex (Tetrahedron) and I want to combined them in a class type such that: - Edge and Face will produce a convex hull - Face and Simplex will produce a Delaunay triangulation under the same MCB (Marriage Before Conquer) algorithm. I first tried to use Multiparameter type class with functional dependence relation: class SubUnit subUnit unit | subUnit -> unit, unit -> subUnit where buildUnit :: ActiveSubUnit subUnit -> [Point] -> Maybe unit build1stUnit :: Plane -> [Point] -> [Point] -> [Point] -> Maybe unit getAllSubUnits :: unit -> [ActiveSubUnit subUnit] subUnitPos :: BoxPair -> subUnit -> Position but then I decide to go for a GADT form (If someone wants to try to compile it, one can get the complete code on GitHub: http://github.com/EdgarGomes/DeUni) : class SubUnit subUnit where type Unit subUnit :: * buildUnit :: ActiveSubUnit subUnit -> [Point] -> Maybe (Unit subUnit) build1stUnit :: Plane -> [Point] -> [Point] -> [Point] -> Maybe (Unit subUnit) getAllSubUnits :: Unit subUnit -> [ActiveSubUnit subUnit] subUnitPos :: BoxPair -> subUnit -> Position In both cases I get a couple of errors like: src/DeUni.hs:265:39: Couldn't match type `Unit subUnit3' with `Unit subUnit2' NB: `Unit' is a type function, and may not be injective Expected type: Unit a Actual type: Unit subUnit2 In the expression: un In the expression: [un] In the first argument of `return', namely `(([un], fromList $ getAllSubUnits un) :: SubUnit a => ([Unit a], SetActiveSubUnits a))' src/DeUni.hs:265:39: Couldn't match type `Unit (ActiveSubUnit subUnit3)' with `Unit subUnit2' NB: `Unit' is a type function, and may not be injective Expected type: Unit a Actual type: Unit subUnit2 In the expression: un In the expression: [un] In the first argument of `return', namely `(([un], fromList $ getAllSubUnits un) :: SubUnit a => ([Unit a], SetActiveSubUnits a))' src/DeUni.hs:265:44: Could not deduce (a1 ~ ActiveSubUnit subUnit3) from the context (SubUnit a) bound by the type signature for mbc :: SubUnit a => [Point] -> SetActiveSubUnits a -> Box -> StateMBC a [Unit a] at src/DeUni.hs:(260,1)-(317,53) or from (SubUnit a1) bound by an expression type signature: SubUnit a1 => ([Unit a1], SetActiveSubUnits a1) at src/DeUni.hs:265:37-117 `a1' is a rigid type variable bound by an expression type signature: SubUnit a1 => ([Unit a1], SetActiveSubUnits a1) at src/DeUni.hs:265:37 Expected type: SetActiveSubUnits a Actual type: Set (ActiveSubUnit subUnit3) In the expression: fromList $ getAllSubUnits un In the first argument of `return', namely `(([un], fromList $ getAllSubUnits un) :: SubUnit a => ([Unit a], SetActiveSubUnits a))' ..... ..... Any help is more than welcome! Cheers, Edgar Gomes (LambdaSteel)

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Re: [Haskell-cafe] ANNOUNCE: version 0.7 of monad-parallel, monad-coroutine and SCC
by Mario Blažević 26 Mar '11

26 Mar '11

On 11-03-26 12:27 AM, Steven Shaw wrote: > Hi Mario, > > I wondered if you had an application in mind for your incremental > parser library in Haskell? A little while ago I was following the > development of an open source text editor for Mac OS X called > Kod[.app]. They were wanting an incremental parser to help with > correct+fast syntax highlighting and the like. Looks like they decided > on gazelle written in C. I though you might find it of interest. > > https://groups.google.com/forum/#!msg/gazelle-users/RfE-lSmqb7c/vrqdPaOIoMwJ > <https://groups.google.com/forum/#%21msg/gazelle-users/RfE-lSmqb7c/vrqdPaOIo…> > http://www.reverberate.org/gazelle/ > > Is that the kind of thing you had in mind for your incremental parser > library in Haskell? The application I had in mind for the incremental parser is already using it, it's the new version of the streaming component combinators framework. More generally, though, its main purpose is the efficient communication between coroutine-like things like enumerators and iteratees. They tend to produce and consume data in chunks, but the producer's idea of proper chunk boundaries often doesn't match the consumer's. So instead of fetching raw chunks, the consumer uses incremental parser to abstract the producer's boundaries away. I did not have text editors or parsing "big" languages in mind when I wrote the library, but I suppose it could be used there as well. Among my vague plans were to provide a bridge for the enumerator and coroutine libraries, and to write a proper incremental XML parser. Thanks for the links, I wasn't aware of these projects.

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