- Haskell-Cafe - Haskell.org

ANNOUNCE: xmonad 0.4
by Don Stewart 18 Oct '07

18 Oct '07

The xmonad dev team is pleased to announce the 0.4 release of xmonad! http://xmonad.org xmonad is a tiling window manager for X. Windows are arranged automatically to tile the screen without gaps or overlap, maximising screen use. Window manager features are accessible from the keyboard: a mouse is optional. xmonad is written, configured and extensible in Haskell. Custom layout algorithms, key bindings and other extensions may be written by the user in Haskell, in config files. Window layouts are applied dynamically, and different layouts may be used on each workspace. Xinerama is fully supported, allowing windows to be tiled across several physical screens. Features: * Simple, intuitive user interface * Stable, fast and small memory footprint * 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 windows * XRandR support to rotate, add or remove monitors dynamically * Per-workspace layout algorithms * Per-screens custom status bars * Easy, powerful customisation and reconfiguration * Large extension library * Extensive documentation and support for hacking This is a big release, with every feature we originally proposed for xmonad implemented. Since xmonad 0.3, the following notable improvments have appeared: * Powerful "rules" system: config files may specify rules about how particular applications are handled. For example, gimp might always be placed in the floating layer, or firefox always placed on workspace 2. Gnome dock apps (such as kicker or gnome-panel) might always be placed in a status bar gap and unmanaged. * User-specified workspace tag types (not restricted to numeric keys). E.g. "web" or "www" are valid workspace tags now. * Layouts algorithms serialisable. Current workspace state preserved across restarts/reconfiguration, including user-written modules' state * User written code sandboxed from the core applicuation further, making it safer to experiment with new extensions * 100% code coverage of logic core of xmonad by its testsuite, thanks to QuickCheck and HPC. * More hooks to make writing expressive extensions easier * mod-m to shift focus to the `master' window * many new binary distributions, for various flavours of Linux and BSD, OSX is also well supported. * extensions: xmonad comes with a huge library of extensions (3 times the size of xmonad itself), contributed by viewers like you. Extensions enable pretty much arbitrary window manager behaviour to be implemented by users, in Haskell, in the config files. For more information on using and writing extensions, see the webpage. Get it! More information, screenshots, documentation, tutorials and community resources are available from the xmonad home page: http://xmonad.org The 0.4 release, and its dependencies, are available from hackage.haskell.org, here: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xmonad Brought to you by the xmonad team: Spencer Janssen Don Stewart Jason Creighton Andrea Rossato David Roundy with code contributions from: Brandon Allbery Chris Mears Shachaf Ben-Kiki Eric Mertens Alec Berryman Neil Mitchell Gwern Branwen Devin Mullins Joachim Breitner Daniel Neri Alexandre Buisse Stefan O'Rear Nick Burlett Simon Peyton Jones Peter De Wachter Hans Philipp Annen Aaron Denney Karsten Schoelzel Nelson Elhage Michael Sloan Shae Erisson Ivan Tarasov Joachim Fasting Alex Tarkovsky Michael Fellinger Christian Thiemann David Glasser Joe Thornber Kai Grossjohann Matsuyama Tomohiro Dave Harrison Daniel Wagner Juraj Hercek Ferenc Wagner Sam Hughes Jamie Webb Miikka Koskinen Brent Yorgey David Lazar nornagon Lucas Mai timthelion Robert Marlow Klaus Weidner As well as the support of a cast of hundreds on the #xmonad and #haskell IRC channels, and the wider Haskell, FP and window manager communities. Thanks to everyone for their support!

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Stack overflow in ghci
by Maurício 17 Oct '07

17 Oct '07

Hi, I get this error message when testing a function in ghci: *** Exception: stack overflow I admit I didn't care about efficiency when I wrote that function, but I'm almost sure it is not supposed to eat all my memory. Do I need to say something to ghci if I want it to use all available memory? Thanks, Maurício

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Functional Programming Books
by Dan Piponi 17 Oct '07

17 Oct '07

I was just putting together my Amazon wish list and was wondering if there are any great books on Haskell and/or functional programming that people think are must-reads. Okasaki's "Purely Functional Programming", Pierce's "Types and Programming Languages" are frequent recommendations. Smullyan's "To Mock a Mockingbird" seems like it might be a good example from the lighter end. Are there any other classics I should know about?

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generic programming tutorial?
by Greg Meredith 17 Oct '07

17 Oct '07

Haskellians, i feel like i'm chasing a rabbit down the rabbit hole, but here goes. i'm currently redoing my implementation of an evaluator for a reflective process calculus, using Haskell instead of OCaml, this time. i thought i'd give a James Cheney's FreshLib a whirl to - test out the state of the nominal machinery in Haskell - see if the nominal stuff works, practically, with my reflective account of nominal machinery i've discovered that FreshLib makes essential use of a early version of generic Haskell features. i need to bone up on generic Haskell, quickly. i've got the papers. i need to see what's being released and supported in the mainstream Haskell codebase. Is there documentation for this, or should i grovel source? Best wishes, --greg -- L.G. Meredith Managing Partner Biosimilarity LLC 505 N 72nd St Seattle, WA 98103 +1 206.650.3740 http://biosimilarity.blogspot.com

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Re: [Haskell-cafe] Suspected stupid Haskell Question
by manu 17 Oct '07

17 Oct '07

> The problem there is that nub is O(n^2). Is there a place where one can look up the complexity of Standard Libraries functions ? E.D

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Performance problem with random numbers
by ntupel 17 Oct '07

17 Oct '07

Dear all, I have implemented a small module to generate random items with a given probability distribution using the alias approach [1] and unfortunately compared to similar implementations in C++ or Java it is about 10 times slower. I have to confess that I am still in the early stages of writing Haskell programs so there is hopefully something I can do about it and I hope some helpful soul on this list can give me a hint. I have attached my implementation and a small testing routine which runs in about 5 seconds on my machine (when compiled with -O2) whereas my Java-Implementation finishes in about 0.48 seconds. Profiling indicates that the time is mostly spend in System.Random.random and System.Random.randomR so I wonder if these are slow or what else might cause the relative slowness of my implementation. Many thanks for your responses, Thoralf PS: I would also appreciate any feedback about the module from a design perspective. I bet I miss lots of good Haskell idioms. ---------------- [1] The alias methods moves probability mass of a non-uniform probability distribution around to create a uniform distribution. Lets say you have three items "a", "b", and "c" with distribution [0.2, 0.1, 0.7] then a uniform distribution would assign 1/3 to each so "a" and "b" need to be "filled up" with exactly the same probability mass that "c" has too much. Then 2 uniform random numbers are generated. The first one to pick an item and the second one to pick either the item itself if the value is in the original part or the alias otherwise. A much better explanation can be found on the web somewhere. Anyway it should not matter with regards to the performance problem I have.

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OzHaskell?!?
by Manuel M T Chakravarty 17 Oct '07

17 Oct '07

There is AngloHaskell and now AmeroHaskell. Doesn't that call for OzHaskell? http://haskell.org/haskellwiki/OzHaskell Manuel

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job opportunity
by jeff p 17 Oct '07

17 Oct '07

Hello, Here are the essential details... Location: NYC Industry: finance Salary: enough to live comfortably in Manhattan Hard Requirements: Must be able to work in the USA (we can't get you a worker's visa). Must be an expert level Haskell user; must be comfortable with monads, monad transformers, type level programming (i.e. MPTC, overlapping and undecidable instances), and lazy evaluation (i.e. know how to find and eliminate space leaks). Must have a desire to use modern PL research in the real world. Soft Requirements: Experience with low-level Haskell programming (i.e. FFI). Experience with Linux and Cygwin/Windows. Knowledge/experience in dependently typed programming. Knowledge/experience in logic programming. If anyone is interested, please contact me to find out more. thanks, Jeff

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Re: [Haskell] IN Doubt...
by ajb＠spamcop.net 17 Oct '07

17 Oct '07

[Moved to haskell-cafe] G'day all. Quoting Don Stewart <dons(a)galois.com>: > You can't pattern match 'a' and 'a' like that -- there's no implicit > unification. Since we're being nostalgic in other threads, this is #1 on my list of things I miss from Miranda. It's also high on my "things that are damned useful in 1000-line programs but would wreak silent havoc in large applications" list. Cheers, Andrew Bromage

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Help parsing dates and times
by Justin Bailey 16 Oct '07

16 Oct '07

I am trying to parse various date and time formats using the parseTime function found in (GHC 6.6.1) Data.Time.Format. The one that is giving me trouble looks like this: 2008-06-26T11:00:00.000-07:00 Specifically, the time zone offset isn't covered by the format parameters given. I can almost parse it with this: %FT%X.000 But that doesn't take into account the "-07:00" bit. I'm sure this has been solved - can someone point me to the solution? Thanks in advance. Justin

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