- Haskell-Cafe - Haskell.org

ANNOUNCE: xmonad 0.9 is now available!
by Don Stewart 26 Oct '09

26 Oct '09

http://xmonad.org The xmonad dev team is pleased to announce xmonad 0.9! We think this is a great release. The headlines: * Actions.SpawnOn: Windows go to the workspace they were launched on, even if you're no longer viewing that workspace. Especially handy for slow-launching applications like Firefox * Actions.GridSelect: graphically go to, select, do things with windows, workspaces, prompts ... * Many new window layouts: http://is.gd/4BzAI * Many new scriptable actions: http://is.gd/4BzCN * Focus changes across screens with mouse movement, no longer requiring a click, even for empty workspaces. * Improved xmobar/dzen statusbar functions, easier to use, more compositional * New --restart command line flag to restart a running xmonad process. * Supports for multi-module local configuration files * Support for user-defined X event handling * xmonad comes with 180 extensions for enhancing functionality * Over 3000 commits have been made to the project. Extensive change logs: http://haskell.org/haskellwiki/Xmonad/Notable_changes_since_0.8 About: xmonad is a leading tiling window manager, known for its lightness, reliability, extensibility and efficiency. It supports true multiheaded tiling, and rich, rapid customisation. It is also highly portable, running on regular desktops, laptops, netbooks, phones, game consoles, the OLPC, and more. Features: * Very stable, fast, small and simple. * Automatic window tiling and management * First class keyboard support: a mouse is unnecessary * Full support for tiling windows on multi-head displays * Full support for floating, tabbing and decorated windows * Full support for Gnome and KDE utilities * XRandR support to rotate, add or remove monitors * Per-workspace layout algorithms * Per-screens custom status bars * Compositing support * Powerful, stable customisation and reconfiguration * Large extension library * Excellent, extensive documentation * Large, active development team, support and community Get it! Information, screenshots, documentation, tutorials and community resources are available from the xmonad home page: http://xmonad.org The 0.9 release, and its dependencies, are available from hackage.haskell.org: http://hackage.haskell.org/package/xmonad xmonad packages are available in pretty much every package system, including. Debian, Gentoo, Arch, Ubuntu, OpenBSD, NetBSD, FreeBSD, Gobo, NixOS, Source Mage, Slackware and 0.9 packages will appear in coming days (some are already available). On the fly updating to xmonad 0.9 is supported, without losing your session! You can even use cabal-install: $ cabal update $ cabal install xmonad-0.9 $ cabal install xmonad-contrib-0.9 $ xmonad --recompile mod-q Extensions: xmonad comes with a huge library of extensions (now around 15 times the size of xmonad itself), contributed by viewers like you. Extensions allow for all sorts of functionality and enhancements to the window manager, via Haskell in your config file. For more information on using and writing extensions see the webpage. The library of extensions is available from hackage: http://hackage.haskell.org/cgi-bin/xmonad-contrib Full documentation for using and writing your own extensions: http://xmonad.org/documentation.html This release brought to you by the xmonad dev team: Spencer Janssen Don Stewart Adam Vogt Brent Yorgey Daniel Wagner Devin Mullins Daniel Schoepe Braden Shepherdson Nicolas Pouillard Roman Cheplyaka Gwern Branwen Lukas Mai Featuring code contributions from over 80 developers: Aaron Denney Jason Creighton Alec Berryman Alex Tarkovsky Alexandre Buisse Andrea Rossato Austin Seipp Bas van Dijk Ben Voui Brandon Allbery Chris Mears Christian Thiemann Clemens Fruhwirth Daniel Neri Anders Engstrom Dave Harrison David Glasser David Lazar Dmitry Kurochkin Dominik Bruhn Dougal Stanton Eric Mertens Ferenc Wagner Jan Vornberger Hans Philipp Annen Ivan Tarasov Ivan Veselov Jamie Webb Jeremy Apthorp Malebria Joachim Breitner Joachim Fasting Joe Thornber Joel Suovaniemi Juraj Hercek Justin Bogner Kai Grossjohann Karsten Schoelzel Klaus Weidner Mathias Stearn Mats Jansborg Matsuyama Tomohiro Michael Fellinger Michael Sloan Miikka Koskinen Neil Mitchell Nelson Elhage Nick Burlett Quentin Moser Nils Anders Danielsson Peter De Wachter Robert Marlow Sam Hughes Shachaf Ben-Kiki Shae Erisson Simon Peyton Jones Stefan O'Rear Tom Rauchenwald Valery V. Vorotyntsev Will Farrington Yaakov Nemoy timthelion Rickard Gustafson Trevor Elliott Ian Zerny Ivan Miljenovic Marco e Silva Michal Janeczek David Roundy Wirt Wolff Max Rabkin Sean Escriva Norbert Zeh Alexey Khudyakov Ismael Carnales Luis Cabellos Konstantin Sobolev Dmitry Astapov Andres Salomon Aleksandar Dimitrov Ilya Portnov Michal Trybus Travis Hartwell As well as the support of many others on the #xmonad and #haskell IRC channels, and the wider Haskell and window manager communities. Thanks to everyone for their support!

6 5

ANN: GPipe-TextureLoad 1.0.0 and GPipe 1.0.3
by Tobias Bexelius 26 Oct '09

26 Oct '09

I've uploaded a new version of GPipe as well as a utility package for loading textures. GPipe 1.0.3: * Fixes a major bug in the shader generation GPipe-TextureLoad 1.0.0: * Helps loading GPipe textures from file. It is based on the stb-image package, and supports subsets of the JPG, PNG, TGA, BMP and PSD formats. _________________________________________________________________ Hitta kärleken nu i vår! http://dejting.se.msn.com/channel/index.aspx?trackingid=1002952

1 0

Fortran mixed mode arithmetic expressions -> Haskell
by michael rice 26 Oct '09

26 Oct '09

Translating Fortran mixed mode arithmetic expressions into Haskell is quite a challenge. Believe it or not c=10.**(11-int(alog10(r)+10)) translates to let c = (**) 10.0 $ fromIntegral $ subtract 11 $ truncate $ (+) (logBase 10.0 r) 10.0 I finally broke the expression below into two parts (k1 & k2) to ease translation. I get it that Haskell is expecting to subtract two Integers and is instead being given an Integer and a Double. What must I do to make this work? Are there any guidelines for doing this kind of translation work? Michael ================ Prelude> let mm = 2 Prelude> let k1 = 3*mm+2 Prelude> let k2 = (/) 150 119 Prelude> let k = k1 - k2 <interactive>:1:13: Couldn't match expected type `Integer' against inferred type `Double' In the second argument of `(-)', namely `k2' In the expression: k1 - k2 In the definition of `k': k = k1 - k2 Prelude> :t 150/119 150/119 :: (Fractional t) => t Prelude>

6 9

any haskellers in chicago? Impromptu lakeview meetup tomorrow (tuesday) evening.
by Thomas Hartman 26 Oct '09

26 Oct '09

I'm visiting chicago, and found one other haskeller interested in a haskell meetup tomorrow 7:30 pm lakeview cafe intelligentsia. email thomashartman1 at gmail if you'd like to hook up! this is a relaxed occasion with no fixed agenda other than birds of a feather flocking home. thomas.

1 0

ANN: attempt-0.0.0
by Michael Snoyman 26 Oct '09

26 Oct '09

Hello, I'm happy to announce the first release of the attempt package[1]. It is meant to solve the "how should I represent a failure" issue. It is based on extensible exceptions and provides a monad, a monad transformers and helper functions to replace many standard, unsafe functions like head. This release should be considered unstable as the API is still open to some change, but is quite usable. I have a blog post [2] which includes an example walk through of how to use this library. It covers most of what is available. Comments are most welcome. I would like this to be a suitable replacement for the ubiquitous Maybe, (Either String) and ad-hoc Result data types so often used to report a failure. I'd be very happy to improve the package for the general community. Michael [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/attempt [2] http://blog.snoyman.com/2009/10/25/introduction-to-attempt-error-reporting-…

2 2

ANN: HoleyMonoid-0.1
by Martijn van Steenbergen 26 Oct '09

26 Oct '09

Hello! I'm happy to announce the first release of HoleyMonoid, a datatype that helps you build monoids with holes in them. The holes are filled in later using normal function application. For example: > > let holey = now "x = " > . later show > . now ", y = " > . later show > > run holey 3 5 > "x = 3, y = 5" The library is available on Hackage: http://hackage.haskell.org/package/HoleyMonoid Thanks to David Menendez for the name and Sjoerd Visscher for help with rewriting and simplifying. :-) Martijn.

1 0

example of PortMidi use
by erik flister 26 Oct '09

26 Oct '09

hey mike- i think the trouble with your program is that it sends all the events as fast as possible and then terminates -- it is insensitive to their timestamps. probably portmidi's buffer receives them all, starts the first one, and then is destroyed before ever emitting the corresponding off message, leaving the first note hung. i've just been learning haskell and have been using portmidi as a vehicle. here's a demo i've been working on, it seems to work well. it uses Data.Heap (http://hackage.haskell.org/package/heap) as a priority queue to manage the timestamp scheduling and allow you to schedule events nonmonotonically (portmidi expects you to handle this). it also shows how to use the random generator i noticed you asked about. http://code.google.com/p/h1ccup/source/browse/trunk/theory/haskell/src/PMTe… i would really appreciate any style/design critiques that anyone could offer! some specific q's: 1) the 'addNote' function has a local predicate 'match', which winds up being called on every member in the queue twice -- but memoizing it would be hard because it is used by the heap's higher order functions ('filter' and 'partition'). how should i handle this? can i expect/rely on any auto-memoizing? 2) because a noteOff event in midi turns off a note no matter how many previous noteOns occurred, 'addNote' needs to be careful to not schedule a noteOff during a previously scheduled note, and remove any previously scheduled noteOff that would prematurely cut off the new note. the alg is a little tricky and it would be nice to "prove" its correctness -- and there are enough degrees of freedom that QuickCheck would not explore the relevant corner cases. how would one approach this from a curry-howard perspective? 3) i would like the most natural possible musical EDSL, but currently have to write things like 'Dotted $ Triplet $ NoteDur Eighth' rather than 'Dotted Triplet Eighth'. it would be worse if i added a layer of symbols to prevent arbitrary nesting and ordering of 'Dotted' and 'Triplet'. can this be addressed? 4) threadDelay seems to have a resolution of 10ms. isn't that awfully high? (i'm on OSX 10.5.8, ghc 6.10.3). could this possibly because i forkIO the producer, but not the consumer (only the consumer threadDelays)? 5) ski on #haskell wrote 'asksTo' for me (see http://tunes.org/~nef//logs/haskell/09.08.06) -- but it is not as polymorphic as we'd like -- it only works for ReaderT's instead of all MonadReader's. 'asksTo' is for accessing more than one MVar simultaneously inside a ReaderT, one needs to avoid nesting liftIO's (see http://hpaste.org/fastcgi/hpaste.fcgi/view?id=7915) why not allow nested liftIO's, and if there is a good reason, is there a more general solution than asksTo? 6) i would (neurotically) like to work under 'default ()', but this causes zillions of problems that i can't figure out. is there a good strategy for getting all your numbers to work polymorphically? 7) i want to write as paradigmatically as possible, so style advice is very helpful! i've tried to follow the guidelines from the wiki. i didn't see any opportunities to define a new monad, but maybe there are some? the 'addNote' and 'drain' functions, which do the queueing and dequeuing, seem uglier than necessary -- any way to decompose them better? -e On Wed, 14 Oct 2009, Michael Mossey wrote: > Can someone give me an example of Sound.PortMidi use? I'm having trouble. > This program has bugs---makes sound only intermittently, and seems to have > set up some kind of loop that is sending midi messages continuously even > after terminating the program: import Sound.PortMidi import Foreign.C msgs = [ (0::CULong,PMMsg 0x9c 0x40 0x40) , (500, PMMsg 0x8c 0x40 0x40) , (1000, PMMsg 0x9c 0x41 0x40) , (1500, PMMsg 0x8c 0x41 0x40) ] main = do let deviceId = 12 initialize >>= print getDeviceInfo deviceId >>= print startTime <- time let evts = map (\(t,msg) -> PMEvent msg (t+startTime)) msgs result <- openOutput deviceId 10 case result of Right err -> putStrLn ("After open: " ++ show err) Left stream -> do result <- writeEvents stream evts putStrLn ("After write: " ++ show result) close stream return () terminate >>= print

1 0

Re: ghci can't find Paths_ module created by cabal
by Thomas Hartman 26 Oct '09

26 Oct '09

from my bash hints file: thartman@ubuntu:~/haskellInstalls/gitit>thartman_ghci_with_data_files Loading a package with data files in ghci See http://neilmitchell.blogspot.com/2008/02/adding-data-files-using-cabal.html Snip: The above method works well after a program has been installed, but is harder to work with while developing a program. To alleviate these problems, we can add our own Paths module to the program, for example: module Paths_hoogle where getDataFileName :: FilePath -> IO FilePath getDataFileName = return Place this module alongside all the other modules. While developing the program our hand-created Paths module will be invoked, which says the data is always in the current directory. When doing a Cabal build, Cabal will choose its custom generated Paths module over ours, and we get the benefits of Cabal managing our data. 2009/10/21 Robin Green <greenrd(a)greenrd.org>: > I'm trying to run cabal-install in ghci so I can run it under the ghci > debugger. However I try it, though, I always get one of these two > errors: > > /src/greenrd/darcs/cabal-install/Main.hs:70:17: > Could not find module `Paths_cabal_install': > Use -v to see a list of the files searched for. > Failed, modules loaded: none. > > or > > <command line>: > Could not find module `Main': > Use -v to see a list of the files searched for. > > -- > Robin > _______________________________________________ > Libraries mailing list > Libraries(a)haskell.org > http://www.haskell.org/mailman/listinfo/libraries >

2 1

How come pattern match does not recognize this code style?
by Magicloud Magiclouds 26 Oct '09

26 Oct '09

Hi, In case of this: case bala of [ bala , bala , bala ] -> bala bala bala _ -> bala ghc 6.10.4 would fail to compile, because of the wrong indent of line ", bala". -- 竹密岂妨流水过山高哪阻野云飞

3 3

ANN: GlomeVec, IcoGrid
by Jim Snow 26 Oct '09

26 Oct '09

I just uploaded two packages to hackage. The first package [1] is the vector library used by my haskell ray-tracer, Glome, which has been neglected of late. It's one of the first things I ever wrote in Haskell, so some of the code looks a little strange to me now, but it works pretty well for a wide variety of computational geometry tasks. I also included a perlin noise implementation. I released GlomeVec so that I would have a reasonable vector library to work off of for my other project, which is the IcoGrid library [2]. IcoGrid (Icosahedron Grid) is a library for dealing with grids of hexagons and pentagons wrapped around a sphere. Individual grid cells are identified by an integer, and the library can find all the neighbors of a given cell, it can find all the places where three cells intersect at a point, and it can also tell you where in 3-D space the center of the cell is. (The cells are positioned on the surface of a sphere with unit 1.) The one very useful function I haven't implemented yet is, given an arbitrary point, find the cell that the point "belongs" in. I posted a screenshot on the Haskell wiki [3] showing an OpenGL application I wrote that uses IcoGrid. My initial goal was to write some sort of simple environmental simulator that can eventually be made into a game. The grid turned out to be a pretty big project by itself, so I turned it into a stand-alone library. Both libraries have haddock docs, but they aren't showing up on hackage. Is there a trick to tell hackage it needs to generate docs, or do I just need to wait for a cron job to run? -jim [1] http://hackage.haskell.org/package/GlomeVec [2] http://hackage.haskell.org/package/IcoGrid [3] http://www.haskell.org/haskellwiki/IcoGrid

1 0