April 2007 - Haskell - Haskell.org

One-year INRIA post-doctoral position
by Frederic Blanqui 11 Apr '07

11 Apr '07

A one-year INRIA post-doctoral position is available: Title: Generation of construction functions guaranteeing algebraic invariants on concrete data types Aim: Although concrete data types are very useful in defining complex data structures, they are not always sufficient to adequately specify the data structures required by some algorithms. Often, only a subset of the concrete data type is in fact used since some invariants between the components are mandatory to ensure the correctness of the program. Now, many invariants can be described by using some equational theory. For instance, a sorted list is a particular representative of the equivalence class of lists modulo commutativity. The usual way to solve this problem is to use abstract data types or, better, private data types if one does not want to lose the ability of doing pattern matching. We propose to study the automatic generation of certified construction functions guaranteeing algebraic invariants on concrete data types, and develop an extension of OCaml with relational data types, that is, data types with invariants described by user defined equations. More information and online application on: http://www.talentsplace.com/syndication1/inria/frpostdoc/details.html?id=PG… Competences and profile: The position involves research and development in the area of functional programming, rewriting theory (in particular Knuth-Bendix completion) and, possibly, interactive theorem proving (experience with a proof assistant such as Coq is welcome). Speaking french is not necessary. Requirements: Candidates are required to hold a PhD degree between May 2006 and June 2007. Salary: the monthly gross salary is approx. EUR 2,150. Environment: - laboratory: LORIA (http://www.loria.fr/) - team: Protheo (http://protheo.loria.fr/) - project: Quotient (http://quotient.loria.fr/) - location: Nancy, in the East of France is at 1:30 from Paris by tren, 1:30 from Luxembourg airport by car, and 1:30 from Germany and Belgium. Application deadline: 1st July 2007. Contact: Frederic Blanqui (http://www.loria.fr/~blanqui/) More information about INRIA post-doctoral positions: http://www.inria.fr/travailler/opportunites/postdoc/postdoc.en.html

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ANN: System.FilePath 1.0
by Neil Mitchell 10 Apr '07

10 Apr '07

Hi, Finally, here is a System.FilePath 1.0 release! The FilePath library is a library for manipulating FilePaths in a cross platform way on both Windows and Unix. Home page: http://www-users.cs.york.ac.uk/~ndm/filepath/ Darcs repo: http://darcs.haskell.org/packages/filepath/ Haddock: http://www.cs.york.ac.uk/fp/haddock/filepath/ This version will be included in GHC 6.6.1 and all future major Haskell compilers. THINGS TO NOTE: * There are no longer Version_0_10 interfaces - the interface is now stable, please use System.FilePath. * The library is now "filepath", not "FilePath" I would upload this libary to Hackage, but Cabal won't work with sdist on my machine, so I can't. If someone else wants to, please feel free. Thanks Neil

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What's with Network.Socket?
by ROBERT DOUGLAS HOELZ 10 Apr '07

10 Apr '07

Is Network.Socket buggy/incomplete? I'm trying to implement an NNTP module in Haskell, but it seems the Network.Socket module doesn't convert the native byte order to network byte order, so the connection gets denied. When I reverse the bytes in the address by hand and try to connect, it locks up. What's wrong? Thanks, Rob Hoelz

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Call for Contributions - HC&A Report (May 2007 edition)
by Andres Loeh 10 Apr '07

10 Apr '07

Dear Haskellers, it is nearly time for the twelfth edition of the ================================================================ Haskell Communities & Activities Report http://www.haskell.org/communities/ Submission deadline: 2 May 2007 (please send your contributions to hcar at haskell.org, in plain ASCII or LaTeX format) ================================================================ This is the short story: * If you are working on any project that is in some way related to Haskell, write a short entry and submit it to the me. Even if the project is very small or unfinished or you think it is not important enough -- please reconsider and submit an entry anyway! * If you are interested any project related to Haskell that has not previously been mentioned in the HC&A Report, please tell me, so that I can contact the project leaders and ask them to submit an entry. * Feel free to pass on this call for contributions to others that might be interested. More detailed information: The Haskell Communities & Activities Report is a bi-annual overview of the state of Haskell as well as Haskell-related projects over the last, and possibly the upcoming 6 months. If you have only recently been exposed to Haskell, it might be a good idea to browse the November 2006 edition -- you will find interesting topics described as well as several starting points and links that may provide answers to many questions. Contributions will be collected until the beginning of May. They will be compiled into a coherent report which will appear sometime near the end of May. As always, this is a great opportunity to update your webpages, make new releases, announce of even start new projects, or to point at some developments you want every Haskeller to see! As the purpose of the report is to collect recent or current activities, I encourage you to update all existing summaries and reports. I will probably drop any topics that have not had any activity for the past year, i.e., since June 2006, but I would very much prefer you to present an updated description of the topic. Of course, new entries are more than welcome. Reports should generally be kept brief and informative, ranging from a few sentences to a few hundred words, to keep the whole report reasonably sized. Looking forward to your contributions, Andres (current editor) ----------------------------------- topics New suggestions for current hot topics, activities, projects, etc. are welcome - especially with names and addresses of potential contacts, but here is a non-exclusive list of likely topics (see also http://www.haskell.org/communities/topics.html ): General Haskell developments Haskell implementations Haskell extensions Standardization (Haskell', ...) Documentation Libraries Papers and Books Feedback Summaries of discussions in specialist mailing lists Conference reports Community activities Other Haskell information channels (TMR, Sequence, HWN, ...) Announcements Upcoming Haskell events Everything that's new or has had new releases Ongoing projects Reports on what's happening behind the scenes Confirmations that projects are still maintained Calls for contributions and contributors Tutorials Tools and Applications Released and unreleased Haskell applications Tools useful for Haskell programmers Experiences with using Haskell for a project Commercial uses of Haskell Even if your topic is not listed in this list, there's a good chance it has a place in the Report. Please get in touch with me. If you want to see an entry that hasn't been there in the past, but you are not the maintainer of the project, then please encourage the maintainers to write an entry/update, or ask permission to write the entry yourself. -------------------------- what should I write? That depends on your topic, but as a general rule, it shouldn't take you long. A simple sentence or two about your use of Haskell could go into the "Individual Haskellers" section. If you're a company, or if you're working on a project using Haskell as the implementation language, a paragraph on that could go into the "Applications" section. A typical summary report about a tool/library/project/application/... would be between 1 and 3 paragraphs of ASCII text (what's it about? major topics and results since the last report? current hot topics? major goals for the next six months?) plus pointers to material for further reading (typically to a home page, or to mailing list archives, specifications and drafts, implementations, meetings, minutes, ...). Browsing through previous editions should give you a good idea of the variety of possibilities, ranging from very brief to extensive. For those who prefer templates to fill in, the report is edited in LaTeX, and an entry template might look something like this: \begin{hcarentry}{(MYSTUFF)} \report{(MY NAME)} \status{(PROJECT STATUS IN ONE LINE)} \participants{(PARTICIPANTS OTHER THAN MYSELF)}% optional \makeheader Put the text here. What's following are suggestions for the content of an entry. (WHAT IS IT?) (WHAT IS ITS STATUS? / WHAT HAS HAPPENED SINCE LAST TIME?) (CAN OTHERS GET IT?) (WHAT ARE THE IMMEDIATE PLANS?) \FurtherReading \url{(PROJECT URL)} \end{hcarentry} This template and a style file to preview your document are available at http://haskell.org/communities/05-2007/template.tex http://haskell.org/communities/05-2007/hcar.sty

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ANNOUNCE: Haskell SWF generation library
by Jeremy Shaw 08 Apr '07

08 Apr '07

Hello, I would like to take this opportunity to announce the availability of an Adobe Shockwave Flash (SWF) library for Haskell: darcs get http://www.n-heptane.com/nhlab/repos/haskell-swf/ The library is a bit old and crufty, and it is not really release quality code. The cabal files are out of date, etc. But, I thought I would get it out there in case people wanted to play with it. (I have heard some noise on #haskell about it). It is primarily useful for compiling ActionScript assembly into a .swf file. If anyone is interested in improving the library, the most sensible starting places would be: 1) Update the code to use the new Binary library 2) Create a better API for creating assemble macros 3) Add support for the new Flash 9 action script virtual machine (AVM2). I currently implement 'macros' by defining a function like, > popArray :: [SwfAssembly] > popArray = > [ ActionPushFloat 0.0 -- Array.pop takes no arguments > , ActionStackSwap > , ActionPushString "pop" -- Call the pop() method > , ActionCallMethod > ] And then using it like: > bindArg (STG.AtomVar var) = > (ActionPushDuplicate : > popArray ++ > [ ActionPushString (escape var) > , ActionGetVariable > , ActionSetVariable > ]) This is clearly, pretty lame. :) j. ps. I also have the beginnings of a YHC.Core -> SWF compiler. It can currently compile this simple program: > main = > case id (Just 'a') of > (Just c) -> displayPrimitive c > Nothing -> displayPrimitive 'f' Unfortunately, it does not yet implement garbage collecting, updates, proper environment saving, and other essential features. It also generates some pretty inefficient code. I am going to try to get the current version 'working', and then do a better implementation based on everything I learned from my first attempt at a Haskell compiler. I should note that this is different than the Haskell -> Javascript compiler that is already in YHC. I am targeting the flash virtual machine byte-code directly, not the higher level actionscript (aka, ecmascript) code. I pushed what I currently have at: http://www.n-heptane.com/nhlab/repos/yhc/ the code is in the directory: http://www.n-heptane.com/nhlab/repos/yhc/src/translator/avm2/ First build yhc normally, then cd into that directory and run make. Hopefully that will work for you.

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ANN: Haskell Cryptographic Library 4.0.3
by Dominic Steinitz 07 Apr '07

07 Apr '07

I should like to announce the release of a new version of the Haskell Cryptographic Library based on the proposal at http://www.haskell.org/haskellwiki/Crypto_Library_Proposal. See http://www.haskell.org/crypto/ for more details. There is now no dependency on NewBinary. The downside is the library contains no support for ASN.1 which will be released in separate package. Dominic.

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Fixpoint combinator without recursion
by Edsko de Vries 06 Apr '07

06 Apr '07

Hey, It is well-known that negative datatypes can be used to encode recursion, without actually explicitly using recursion. As a little exercise, I set out to define the fixpoint combinator using negative datatypes. I think the result is kinda cool :) Comments are welcome :) Edsko {- Definition of the fixpoint combinator without using recursion Thanks to Dimitri Vytiniotis for an explanation of the basic principle. -} module Y where {-# NOINLINE app #-} data Fn a = Fn (Fn a -> Fn a) | Value a -- Application app :: Fn a -> Fn a -> Fn a app (Fn f) x = f x -- \x -> f (x x) delta :: Fn a -> Fn a delta f = Fn (\x -> f `app` (x `app` x)) -- Y combinator: \f -> (\x -> f (x x)) (\x -> f (x x)) y :: Fn a -> Fn a y f = delta f `app` delta f -- Lifting a function to Fn lift :: (a -> a) -> Fn a lift f = Fn (\(Value x) -> Value (f x)) -- Inverse of lift unlift :: Fn a -> (a -> a) unlift f = \x -> case f `app` Value x of Value y -> y -- Fixpoint combinator fix :: ((a -> a) -> (a -> a)) -> (a -> a) fix f = unlift (y (Fn (\rec -> lift (f (unlift rec))))) -- Example: factorial facR f n = if n == 1 then 1 else n * f (n - 1) fac = fix facR

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-compiler-options vs {#-LANGUAGE Flags-#}
by S. Alexander Jacobson 05 Apr '07

05 Apr '07

In theory, Haskell modules should contain all information necessary to interpret/compile them properly. In practice, many modules don't because their authors are flagging required language extensions in build systems rather than in module sources. This practice causes problems because then it becomes much hard to move modules between packages or to use a particular module outside of a particular build system context. I experience this problem when I use SearchPath to build HAppS applications. For example, $ sp runhaskell MyModule.hs will recursively download imported modules into a local directory and then run: $ runhaskell -i.haskell-cache MyModule.hs If all the imported modules contain all the right flags in their source then MyModule.main will just run (no need for manual recursion of through a cabal package depency tree!). If some of the imported modules do not include the correct flags, then an error message will result and I am then forced to do: $ sp runhaskell MyModule.hs -cpp -fglasgow-exts -etc And this is bad because (1) some of the modules may not want a particular extension turned on and (2) it is annoying to the user to have to guess at required extensions until they are all added on the command line. Problem (1) is probably small as evidenced by cabals use of global extensions without much complaint. Problem (2) is bigger. Most other modern languages e.g. Java, Python, Perl, Ruby, etc. don't rely on the compiler/interpreter command line options to designate language extensions. Neither should haskell. The correct answer, I believe, is to require that module authors put flags in the module themselves where they belong. At very least it should be considred bad style not to have them in your code and really what would make more sense is for compiler writers to disable command line flags that specify lanaguge-extensions. -Alex- PS Until this is resolved, though it is a hack, I will probably have searchpath automatically add all ghc language extension flags to the command line if the user is using ghc, runghc, or ghci i.e.: "-cpp -fth -fglasgow-exts -fallow-undecidable-instances -fallow-incoherent-instances -fallow-overlapping-instances" Another solution would be to have searchpath map files also carry cabal file URLs and get the flag from there, but some people still use makefiles or other randomness and I would like to make Searchpath work with java, perl,python, and ruby without much change.

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ANNOUNCE: Debian library
by Jeremy Shaw 05 Apr '07

05 Apr '07

Hello, I would like to announce the availability of the a library for interacting with the Debian system. This library does not (currently) depend on dpkg or apt for any functionality. Contributions are welcome. You should probably send an email first to make sure you are not duplicating any of our currently unreleased code. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/debian-1.2 Well-Support Modules: + Parsing/Printing Debian control files using Strings or ByteStrings + Parsing/Printing sources.list files (including support for the wacky sources.list escaping mechanism) + Comparing Debian version numbers. (pure Haskell code, includes support for ~). + A data type for encoding Debian relations. For example: foo (>= 1.2) | bar (<= 3.0), baz + Check if a version satisfies a version requirement. For example: does 1.2 satisfy (>= 1.1) Experimental Modules: + A dependency resolver. Answers the question: Given a relation and a Debian Packages file, what packages do I need to install to satisfy the relation. For example, what packages do I need to install from sid to satisfy the relation: foo, bar (>= 1.1) | baz (>= 1.4) There are few things that are not yet handled: + proper support for architectures (easy) + installing the packages onto an existing system when no packages need to be removed. (medium) + figuring out what packages to remove from an existing install when one or more packages must absolutely be removed in order to satisfy the requested relation. This requires user interaction, since no heuristic can determine which set of packages you would be least upset to see removed from your system. (difficult). It is currently suitable for finding packages in a distribution that could never be installed, or for creating a chroot that contains a certain set of packages. Coming Soon: Linspire.Debian.ChangeLog - a module for parsing Debian Changelogs. (Code existis, but needs to be updated to support a newer version of the time library) A bunch of modules for dealing the Repository management, such as creating Packages/Sources files, installing new packages into an existing distribution, repository signing and more. These modules are largely working, but need to be refactored into standalone libraries. They are currently too tightly integrated with the autobuilder framework. A revision control system agnostic API for checking out source, and assigning a 'version' number to the source. With backend support for darcs, svn, tla, mercurial, quilt, uri, and apt. These modules also need to be pried out of the autobuilder. Known Issues: + Handling of comments in control files is a bit of hack. + There is some code which blindly ignores the Architecture. I believe this is limited to the Dependencies module. Should be easy to rectify. + The modules are currently in the Linspire.* module path. This is bogus. In the future they will be moved to a more suitable location. Getting Source / Submitting Patches: Currently the only way to get the source is through hackage. If there is demand, we can make the source available via tla or darcs. For now, just submit any patches as a .diff. j.

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ANNOUNCE: storylen
by Dino Morelli 05 Apr '07

05 Apr '07

storylen - story word count and categorization storylen is a command-line utility that counts the words in files and classifies them into story types (short story, novella, novel...) Its operation and output are very similar to the *nix program wc This is really only useful for books in plain ascii text, of which I have amassed quite a few. I imagine not many people will find it useful. But it's short, was fun to write and uses Data.ByteString. For those interested, enjoy. darcs get http://ui3.info/darcs/storylen http://ui3.info/d/proj/storylen.html -- .~. Dino Morelli /V\ email: dino(a)ui3.info /( )\ irc: dino- ^^-^^ preferred distro: Debian GNU/Linux http://www.debian.org

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