March 2009 - Haskell-Cafe

Purely Functional Data Structures
by Gü?nther Schmidt 09 Mar '09

09 Mar '09

Hi, is the above mentioned book still *the* authority on the subject? I bought the book, read about 10 pages and then put it back on the shelf. Um. In my app I have to deal with 4 csv files, each between 5 - 10 mb, and some static data. I had put all that data into an Sqlite3 database and used SQL on it. But, as the requirements keep changing the SQL becomes a bit messy. I guess we've all had that experience. So I'm wondering if I will find clues in this book how to do my querying and handling of moderately large data in a more haskellish way and be able to drop the SQL. Your suggestions appreciated. Günther

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How to make a dock window for xmonad using gtk2hs?
by Magicloud Magiclouds 09 Mar '09

09 Mar '09

Hi, I am using gtk2hs to make some sidebar thing for xmonad. Well, after I tried a few ways, I still cannot make it dock like xmobar. It just covered other windows at the edge of the screen. Could someone give me a sample or something I could learn from? Thanks. -- 竹密岂妨流水过山高哪阻野云飞

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STG's? [was: I want to write a compiler]
by Rick R 08 Mar '09

08 Mar '09

Where can I find more information on STGs? Google search doesn't bring up anything too enlightening. My curiosity was piqued by http://www.cs.chalmers.se/~gedell/ssc/index.html. Of course it doesn't indicate how these should be built or the format. On Sun, Mar 8, 2009 at 6:41 PM, Loup Vaillant <loup.vaillant(a)gmail.com>wrote: > Thanks to the courage you all gave me, I found the strength to go on. > > Template instantiation seems to be the easiest path, so I decided to > follow it. I think I solved the problem about primitives and FFI I > though it had. Namely, how the hell do I compile primitive calls with > an arbitrary number of arguments. > > Starting from the Tutorial of Peyton Jones and Lester, I added a new > node type to help guide the order of evaluation. Basically, this "Seq" > node takes the address of two other nodes. It pushes them both on the > stack, like an application node would. (That is because I don't want a > dump, but I could as well create a new stack and and push the previous > one on the dump.) > > Note the nodes which are evaluated this way must not have a functional > head normal form (primitive or supercombinator). That would leak past > the beginning of the stack. > > When the node is finally evaluated (e.g. points to a HNF, like a boxed > integer), the topmost and second topmost pointers on the stack are > swapped. (or the topmost pointer of the stack and the topmost pointer > of the topmost stack on the dump are swapped). > > With a suitable compilation scheme, that should guarantee that > primitives have their arguments already evaluated. (And avoid infinite > loops). > > Now, I just have to implement it. :-) > > Cheers, > Loup. > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- We can't solve problems by using the same kind of thinking we used when we created them. - A. Einstein

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ANN : happs-tutorial 0.8
by Creighton Hogg 08 Mar '09

08 Mar '09

Hello, I'd like to announce the release of the happstack-0.2 compatible release of happs-tutorial on hackage and available for perusing on tutorial.happstack.com. A number of changes occurred in this release: * General cleanup of code for readability * Migration to the new Happstack.Server.SimpleHTTP api * Addition of a chapter on multimaster, the Spread Toolkit based system for syncing your applications across multiple Happstack instances. * Revised chapters on introducing Happstack.Server and Happstack.State, with an emphasis on simple, well-commented examples showing the orthogonality of these separate libraries. * Minor bug fixes Cheers, Creighton

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Cabal and package changelog
by Manlio Perillo 08 Mar '09

08 Mar '09

Hi. The Cabal package description includes a property `license-file`. This property may be used by Hackage to provide a link to the license file. However I would like to have a `changelog-file`, too. So that from Hackage I can quickly check what's changed with the new version of a package. Is this feasible? Thanks Manlio Perillo

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Looking for literature
by Gü?nther Schmidt 08 Mar '09

08 Mar '09

Hi all, I'm trying to catch up with all the wonderful Haskell Types, classes, Abstract Data Types, Algebraic Data Types, Types that give peoples headaches and all the other, deeper stuff I have been happily putting off. Now to look smart I have a bookshelf full of books for smart people and TaPL is amoung them. Should I try that or will RWH teach me enough to get by? Günther

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cabal-install 0.6.2 does not bootstrap with ghc-6.10.1 debian distribution
by Ahn, Ki Yung 08 Mar '09

08 Mar '09

Dear Haskellers and especially who are working on cabal-install and debian packaging, I sometimes clean up .ghc and .cabal in my home directory to start from scratch because of dependency loopholes (cabal-install does not have remove option yet, so it's hard to fix when such loophole happens). Today, I had some time in the airport and decided to start from scratch again because of the dependency loophole with process 1.0.1.1 and haddock. I downloaded the most recent version of cabal-install the version 0.6.2, and found out that the ./bootstrap.sh does not work. So, I had to bootstrap from version 0.6.2 and do "cabal update" and "cabal upgrade cabal-install" to upgrade to 0.6.2. I am not sure whether this is a cabal-install problem or debian dstribution ghc-6.10.1 packaging probelm, since I have not tried to test this with any other ghc-6.10.1 distribution. If anyone who are not using debian distribution ghc-6.10.1 (e.g., general linux binary ghc-6.10.1 or source compiled one) can try bootstrapping cabal-install 0.6.2 from scratch also finds the same problem, I think someone should make a ticket for cabal-install. Thanks, Ahn, Ki Yung

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Looking for a co-founder for a startup using Haskell
by Ed McCaffrey 08 Mar '09

08 Mar '09

Hello, I'm turning a project involving music into a startup, and I will be using Haskell for most and possibly all of it. I had an angel investor interested until the market collapse forced him to turn his focus away from new investments. Other investors I have spoken with want me to contact them again when it is further developed; basically, I think that I am optimistic at the prospect of funding with the right team. I am looking for one or more co-founders in the Boston, MA, area who would be willing to work on this full-time in the near future, after funding is secured, and in their spare time until then. Since many investors are currently moving towards larger investments in growth-stage companies, I am going to apply to incubators who specialize in early-stage companies. Anyone who wants more info send a reply to ed(a)edmccaffrey.net Thanks, Ed McCaffrey ed(a)edmccaffrey.net

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Re: [Haskell] string type class
by Duncan Coutts 08 Mar '09

08 Mar '09

On Fri, 2009-03-06 at 19:16 +0000, Chris Kuklewicz wrote: > Matthew Pocock wrote: > > It seems every time I look at hackage there is yet another stringy > > datatype. For lots of apps, the particular stringy datatype you use > > matters for performance but not algorithmic reasons. Perhaps this is a > > good time for someone to propose a stringy class? > > Not likely. > > I did define my own (private) class for regular expressions, to abstract over > String, the ByteStrings, and Seq Char. But it is used in one place and is a > wart that should be removed. > > The simple task of looping over the contents of a String (once, forward) is > quite different from a Strict ByteString (using an index and a lookup). > > This means for decent efficiency I need two copies of my code, hand specialized > to each case. > > "tail" or "(x:xs)" : very efficient for String (no allocation) > "tail" or "uncons" : not efficient for ByteString (allocation, might as well > convert to [Char] head/tail/uncons on a strict or lazy ByteString is perfectly ok. I would recommend it over using length+index. If you are using tail in a tail recursion then ghc can almost always optimise it to unbox the various ByteString components and so there is no allocation of fresh BS constructors, just adjusting offsets and lengths held in registers. It's also possible to use unsafeHead and unsafeTail if you've checked for null. Duncan

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3D Rendering Engine in Haskell (Re: [Haskell-cafe] FRP + physics / status of hpysics)
by Peter Verswyvelen 08 Mar '09

08 Mar '09

Awesome! When you say you took Ogre as a base, do you mean your engine will be able to load the meshes and material files, or are you also wrapping the C++ code base? Did you also consider Collada? 2009/3/8 Csaba Hruska <csaba.hruska(a)gmail.com> > Hi! > > This should be a bit offtopic, but now I'd like to announce that I'm > working on a 3D rendering rengine in Haskell. > I take ogre3d (www.ogre3d.org) as a base. My code can import import a > subset of ogre model files (currently xml version) and material scripts > (http://www.ogre3d.org/docs/manual/manual_14.html#SEC23) > You can easily import an existing 3d content or create new one because > there are ogre exporter plugins for every major modeler programs. > Currently I have some working code. I hope I'll be ready to release it in a > month. It should act as graphical backend for FRP libraries. > I use yampa in the example program but it's just an option, only example > program depends on it. > > Cheers, > Csaba Hruska > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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