December 2011 - Haskell-Cafe

ANNOUNCE: Anansi 0.4.2 (literate programming pre-processor)
by John Millikin 18 Dec '11

18 Dec '11

Anansi is a preprocessor for literate programs, in the model of NoWeb or nuweb. Literate programming allows both computer code and documentation to be generated from a single unified source. Home page: https://john-millikin.com/software/anansi/ Hackage: http://hackage.haskell.org/package/anansi-0.4.2 ----- This release has a couple cool new features, suggested by Dirk Laurie. Markdown loom =============== Markdown, a lightweight markup language similar to ReStructuredText, is used often on web forums. Use [[ :loom anansi.markdown ]] in your documents to enable. User-defined line pragmas ======================== Users can now add, modify, and disable line pragmas in tangled output based on file extension. This makes it much easier to combine code and data in a single source file. By default, line pragmas are enabled for the C, C++, C#, Haskell, Perl, and Go languages. Customizing the pragma format is easy. Use the ${line}, ${path}, and ${quoted-path} substitutions in an :option. This example code will insert comments into tangled Python code: ------------------------------------------- :# Insert comments into any tangled output file with a name ending in ".py" :option anansi.line-pragma-py=# Generated from ${path} line ${line} ------------------------------------------- To disable line pragmas for a particular file type, just set its pragma format to an empty string: ------------------------------------------- :option anansi.line-pragma-pl= -------------------------------------------

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Announce: The Haskell Platform 2011.4
by Don Stewart 18 Dec '11

18 Dec '11

We're pleased to announce the release of the Haskell Platform: a single, standard Haskell distribution for everyone. Download the Haskell Platform 2011.4.0.0: http://haskell.org/platform/ The specification, along with installers (including Windows, Apple and Unix installers for a full Haskell environment) are available. The Haskell Platform is a single, standard Haskell distribution for every system, in the form of a blessed library and tool suite for Haskell distilled from the thousands of libraries on Hackage, along with installers for a wide variety of systems. It saves developers work picking and choosing the best Haskell libraries and tools to use for a task. When you install the Haskell Platform, you get the latest stable compiler, an expanded set of core libraries, additional development tools, and cabal-install – so you can download anything else you need from Hackage. What you get is specified here: http://hackage.haskell.org/platform/contents.html Thanks! -- The Platform Infrastructure Team P.S. Special thanks to Mark Lentczner for his excellent work on this release.

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ANNOUNCE: hxournal-0.5.0.0 - A pen notetaking program written in haskell
by Ian-Woo Kim 18 Dec '11

18 Dec '11

Hi, everyone, I am very pleased to announce a pen notetaking program: hxournal, which is written entirely in haskell using gtk2hs. I uploaded the package on hackage. This program accompanies with two library packages, xournal-parser and xournal-render for parsing and rendering xournal format file. http://hackage.haskell.org/package/hxournal http://hackage.haskell.org/package/xournal-parser http://hackage.haskell.org/package/xournal-render Installing hxournal should be very simple: > cabal update > cabal install hxournal hxournal can be currently regarded as a clone of xournal, which is a notetaking program developed in C. (See http://xournal.sourceforge.net) As xournal, hxournal can take wacom tablet X11 input in subpixel unit so that it can result in very smooth notetaking experience. Currently, basic pen operations and eraser operations, file open/save operations, rectangular selection, cut/copy/paste operations have been implemented. So the application is semi-usable. The file format is the same as xournal but gunzipped. So to view/edit xoj files generated from xournal, just gunzip the xoj files and read them in hxournal. Gunzipped xoj files generated from hxournal are readable in xournal program. One NEW special feature of hxournal compared with xournal: This program can make a split view (horizontal and vertical and arbitrary combination of them) of the same document similarly to emacs buffers and windows. Please try Horizontal/Vertical Split in View menu of the program. This will be convenient when notetaking a long document. The git repository is located at https://www.github.com/wavewave/hxournal The program web page and development web/wiki pages will be announced soon (it will be linked from package webpage on hackage anyway) and the detailed manual will be presented there. Thank you for your interest. Enjoy haskell notetaking! Ian-Woo Kim

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I've just heard of a neat security measure that when you compile the code it generates different object code...
by KC 17 Dec '11

17 Dec '11

... with the same functionality. Thus, your program would be a moving target to hackers. Would this be challenging with ghc? -- -- Regards, KC

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Typechecking Using GHC API
by Sh NJP 17 Dec '11

17 Dec '11

Hi, I do some pre-processing on a normal Haskell code ( -F ). The pre-processor needs to know the type of each expression. What are the possibilities to do so? Can I use GHC API to employ GHC type checker? If yes, any good tutorial? Is it too naive to think of a function, f :: String -> AnnotatedAST , that takes Haskell code and returns its corresponding abstract syntax tree annotated with types? Thanks, /shayan

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gtk2hs: adding widget during runtime
by Gary Klindt 17 Dec '11

17 Dec '11

Hello Haskellers, currently I work with the gtk2hs library to create a graphical user interface. Everything works fine, but there is one problem: How can I insert widgets into boxes during runtime? I tried something like: main = do initGUI window <- windowNew box <- vBoxNew True 0 l1 <- labelNew $ Just "label eins" bc <- buttonNewWithLabel "insert!" onClicked bc $ (\b -> do lh <- labelNew $ Just "neues label!" boxPackStart b lh PackNatural 0 widgetQueueDraw lh widgetQueueDraw b ) box boxPackStart box l1 PackNatural 0 boxPackStart box bc PackNatural 0 containerAdd window box widgetShowAll window onDestroy window mainQuit mainGUI That compiles fine, but the GUI never shows a "neues label!". What I want is a widget W, which takes a list L, and produces sub widgets for each element. There are also some Entry widgets and a button B. By clicking on that button B, I want to add an element to the list L, and add a sub widget to the widget W. Thank you for reading, Gary

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What happens if you get hit by a bus?
by Michael Litchard 17 Dec '11

17 Dec '11

I'm learning what it means to be a professional Haskell programmer, and contemplating taking on side jobs. The path of least resistance seems to be web applications, as that is what I do at work. I've been investigating what some web developers have to say about their trade. One article addresses the question above. His answer was that he uses RoR which has a large community and he is therefore easily replaceable. My question, for freelancers in general, and web developers in particular is this: How do you address this question? I imagine potential clients would need to be assuaged of their fears that hiring me would lead to a lock-in situation at best, and no one to maintain a code base at worst. Lock-in won't be part of my business model, also sooner or later we part ways with the client. When the client wonders, "What happens then?", what is a good answer?

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Dutch national FP day, January 6, Utrecht
by S D Swierstra 16 Dec '11

16 Dec '11

On http://www.cs.uu.nl/wiki/bin/view/FPDag2012/WebHome you will find the program and registration information about the next Dutch National Functional Programming day, on January 6, Utrecht University. Please forward this mail to anyone interested. Any questions can be directed to me. Hoping to meet you all, Doaitse Swierstra

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Proposal to incorporate Haskell.org
by Don Stewart 16 Dec '11

16 Dec '11

Hello everyone. The haskell.org committee[1], in the interest of the long-term stability of the open source Haskell community infrastructure, has decided to incorporate haskell.org as a legal entity. This email outlines our recommendation, and seeks input from the community on this decision. The committee's proposal is that haskell.org incorporate as an entity under the Software Freedom Conservancy umbrella organization (the same group that Darcs joined recently): http://sfconservancy.org/ If we proceed with this move, haskell.org will be a legal entity, and registered as a non-profit, allowing us to more directly accept (US tax-deductible) donations, and to invest in assets that benefit the Haskell open source community. We welcome your feedback on the proposal attached below. -- Don Stewart (on behalf of the Haskell.org committee) ------------------------------------------------------------------------ = A proposal for the incorporation of Haskell.org = In recent years, haskell.org has started to receive assets, e.g. money from Google Summer Of Code, donations for Hackathons, and a Sparc machine for use in GHC development. We have also started spending this money: in particular, on hosting haskell.org itself. There is also interest in running fundraising drives for specific things such as Hackathon sponsorship and hosting fees. However, haskell.org doesn't currently exist as a legal entity, meaning that these assets have had to be held on our behalf by other entities, such as Galois and various universities. This leads to tricky situations, with no-one being sure who should decide how the haskell.org assets can be used. To solve these problems, we propose that haskell.org applies to become a member project of the Software Freedom Conservancy (SFC) <http://conservancy.softwarefreedom.org/>. The SFC is a non-profit organization that provides free financial and administrative services to open source projects. Additionally, it has 501(c)(3) status, meaning donations from the US are tax-deductible. The SFC would hold haskell.org's money and other assets, and would be able to accept donations on behalf of haskell.org. The haskell.org committee, as described here [2], will make decisions on spending assets and other decisions related to governing the non-profit. Before proceeding, we are inviting input from the community in the form of specific objections or queries regarding the plan. We've tried to answer some of the most likely questions: Q: Does this mean that my Haskell project must now be covered by a copyleft licence such as GPL? A: No, but Haskell projects using haskell.org resource should use an Open Source licence <http://www.opensource.org/licenses/alphabetical>. Q: Will it still be possible to use community.h.o to host non-open-source material, such as academic papers? A: An overall minority of such content, as is the current situation, is not a problem. Q: Will it still be possible to have job ads on the haskell.org mailing lists and website? A: Yes. Q: Will this affect our ability to host the Haskell Symposium <http://www.haskell.org/haskell-symposium/> and Industrial Haskell Group<http://industry.haskell.org/> webpages within haskell.org? A: No. Q: What will be the relationship between haskell.org and other organizations such as the Haskell Symposium and Industrial Haskell Group? A: Those organisations will continue to exist as separate entities. Q: If an umbrella non-profit organisation "The Haskell Foundation" was created, would haskell.org be able to join it? A: Yes. It's likely that in such a scenario, the Haskell Foundation would become the owner of the haskell.org domain name, with the cost divided between the members. The entity that is part of the SFC would be renamed "community.haskell.org" in order to avoid confusion. [1]: http://www.haskell.org/haskellwiki/Haskell.org_committee [2]: http://www.haskell.org/haskellwiki/Haskell.org_committee#Operation

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DB vs read/show for persisting large data
by C K Kashyap 16 Dec '11

16 Dec '11

Hi, It has been on my todo list for some time now. I'd like to write a GTD tool that has dependency tracking support. Haskell seems like a good choice for this. I was wondering if there has been any past attempts with this? One thing that has been bothering me has been this - the persistence of data. Should I use sqlite(or someother DB) or should I use Haskell's read/show functions to read from and write to a file? I am slightly not inclined towards NOT using DB because I want to implement all the business logic in Haskell. I want to avoid having to generate SQL. It'll be great if I could get some feedback on the "read/show" approach - is this even a viable option? Regards, Kashyap

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