March 2012 - Haskell - Haskell.org

ANNOUNCE: join (UHac <$> DHD)
by Sean Leather 13 Mar '12

13 Mar '12

You can still join us at the DHD >>= UHac, but the time is running out. http://www.haskell.org/haskellwiki/DHD_UHac Deadline: April 1 (no fooling!) We've also have a few updates: * We put the DHD program up, at least as much of it as we have. http://www.haskell.org/haskellwiki/DHD_UHac/DHD_Program * As you can see from the program, there is still room for more speakers. In particular, we'd like to hear from people coming outside Utrecht and the Netherlands. We'd also like to see more lightning talks. Send Sean an email with your idea: leather(a)cs.uu.nl * UHac on Friday has moved to a "new" location. Actually, it's the same location as on Saturday and Sunday, so that should make things easier. See you in Utrecht! The Organizers: Sean Leather Jurriën Stutterheim Jurriaan Hage P.S. Make sure your Monad is also a Functor. P.P.S. Apologies for multiple copies.

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PhD and postdoc positions in regular expressions and types
by Fritz Henglein 13 Mar '12

13 Mar '12

Two PhD and postdoc positions are available at DIKU, the Department of Computer Science at the University of Copenhagen, in the Project *Kleene Meets Church (KMC): Regular Expressions and Types*. The overall objective of KMC is to investigate the type-theoretical foundations for the prevalent use of regular expressions (and related grammars) for extracting information from an input, not just classifying it into accepting/nonaccepting; to explore and demonstrate guaranteed safety and expressiveness of programming with regular expressions as types; and to drastically improve semantic predictability and computational scalability vis a vis commonly used regular expression processing tools such as Perl. Application deadline: *March 31st, 2012*. For information on the positions and application requirements, please see http://diku.dk/english/about/vacancies

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PhD position at Radboud University, The Netherlands - NECTOP project
by Peter Achten 12 Mar '12

12 Mar '12

Dear all, Please find attached information about a PhD position at the Model Based Software Development department of the Computer and Information Sciences Institute at the Radboud University, The Netherlands. With kind regards, on behalf of Rinus Plasmeijer, Peter Achten

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ANNOUNCE: freesect-0.0.5
by Ras Far 11 Mar '12

11 Mar '12

Hi, I'm pleased to announce my first package, freesect, which is a Haskell syntax extension to generalise sections. Please visit the homepage http://www.fremissant.net/freesect for more information. The package is also available on Hackage. Some previous discussion occurred on the haskell-cafe thread http://www.mail-archive.com/haskell-cafe@haskell.org/msg97643.html It's been an exhilarating experience! Kind Regards, Andrew Seniuk (rasfar on #haskell)

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ANNOUNCE: diagrams 0.5
by Brent Yorgey 09 Mar '12

09 Mar '12

I am pleased to announce the release of version 0.5 of diagrams [1], a full-featured framework and embedded domain-specific language for declarative drawing. Check out the gallery [2] for examples of what it can do! [1] http://projects.haskell.org/diagrams [2] http://projects.haskell.org/diagrams/gallery.html Highlights of this release include: - A new diagrams-contrib [3] package of user-contributed modules, which so far contains code for tree drawing, Apollonian gaskets, planar tilings, "wrapped" layout, and turtle graphics. - Experimental support for animation, built on top of the new active [4] library. - Numerous small additions and improvements, including more general rounded rectangle shapes and better text support. - Much better performance in some common situations, such as laying out a very long list of diagrams using 'cat' and related combinators. - Added support for GHC 7.4. See the release notes [5] for complete details, and the diagrams wiki [6] for help migrating code from 0.4 to 0.5 (changes should be minimal). [3] http://hackage.haskell.org/package/diagrams%2Dcontrib [4] http://hackage.haskell.org/package/active [5] http://projects.haskell.org/diagrams/releases.html [6] http://www.haskell.org/haskellwiki/Diagrams/Migrate0.5 Try it out ---------- For the truly impatient: cabal install gtk2hs-buildtools cabal install diagrams Diagrams is supported under GHC 6.12, 7.0, 7.2, and 7.4. However, getting cairo to build can be tricky on some platforms; see the diagrams wiki [8] for more information and workarounds regarding specific platforms. (A new native SVG backend is in the works, targeted for the 0.6 release.) To get started with diagrams, read the quick tutorial [9], which will introduce you to the fundamentals of the framework. For those who are even less impatient but want to really dig in and use the power features, read the user manual [10]. [7] http://projects.haskell.org/gtk2hs/development/#development [8] http://www.haskell.org/haskellwiki/Diagrams [9] http://projects.haskell.org/diagrams/tutorial/DiagramsTutorial.html [10] http://projects.haskell.org/diagrams/manual/diagrams-manual.html Get involved ------------ Subscribe to the project mailing list [11], and/or come hang out in the #diagrams IRC channel on freenode.org for help and discussion. Make some diagrams. Fix some bugs [12]. Submit your cool examples for inclusion in the gallery or your cool code for inclusion in the diagrams-contrib package! [11] http://groups.google.com/group/diagrams-discuss [12] http://code.google.com/p/diagrams/issues/list Happy diagramming! Brought to you by the diagrams team: - Peter Hall - Ian Ross - Michael Sloan - Ryan Yates - Brent Yorgey with contributions from: - Sam Griffin - Claude Heiland-Allen - John Lato - Vilhelm Sjoberg - Luite Stegeman - Kanchalai Suveepattananont - Scott Walck

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[ANN] gtk2hs-0.12.3
by wagnerdm＠seas.upenn.edu 09 Mar '12

09 Mar '12

Hello all! I'm pleased to announce the release of gtk2hs, the definitive Haskell bindings to Gtk+. This release includes GHC-7.4 support, as well as the new widgetRestore{Fg,Bg,Text,Base} bindings. Get it from the Hackage nearest you! cabal update cabal install gtk2hs-buildtools cabal install gio gtk All the best. - the gtk2hs team

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Re: [Haskell] Displaying trees in Haskell
by John Lato 08 Mar '12

08 Mar '12

> From: Luana Fagarasan <luana_0105(a)yahoo.com> > > Hello, > > I am quite new to Haskell and I am seeking the best way to > display trees graphically when using Haskell. I have looked on > the web, but am still not clear! IMHO Haskell is a good language for this sort of task; there are several graphics libraries that I would consider fairly mature and reliable. I have a project that uses "diagrams" (http://hackage.haskell.org/package/diagrams) to draw a tree; the code is: > import Diagrams.Prelude > > drawTree (Node dt children) = > fmap (queryFunc $ nodePath dt) (circle 1 > # scaleY 0.5 > # fc darkblue > # lw 0.1 > # lc deepskyblue > # pad 1.1 > # named (show $ nodePath dt) > ) > === > (hcat' with {sep = 0.2} (map drawTree children) # centerX) drawTree could be understood as "draw the current node on top of the diagram produced by applying the node's children to drawTree". This function just draws each node as an oval. "#" is a diagrams-provided operator to apply parameters to a diagram. The "queryFunc" and "named" stuff is to enable queries into the diagram, so that mouse click coordinates can be converted into a label for the node (as retrieved by "nodePath"). Depending on what you want to display for each node, the image could be as simple or complex as you would like. Probably the most full-featured diagrams backend uses Cairo, so your drawings can be rendered in any format Cairo supports (including GTK widgets). Other backends are also available although I don't know as much about them. HTH, John Lato

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[Haskell-cafe] Monad.Reader #20 call for copy
by Edward Z. Yang 07 Mar '12

07 Mar '12

I'm pleased to announce that I, Edward Z. Yang, will be taking over Brent Yorgey's role as lead editor of the Monad Reader! Call for Copy: The Monad.Reader - Issue 20 -------------------------------------------- Whether you're an established academic or have only just started learning Haskell, if you have something to say, please consider writing an article for The Monad.Reader! The submission deadline for Issue 20 will be: **Monday, March 5** The Monad.Reader ~~~~~~~~~~~~~~~~ The Monad.Reader is a electronic magazine about all things Haskell. It is less formal than journal, but somehow more enduring than a wiki- page. There have been a wide variety of articles: exciting code fragments, intriguing puzzles, book reviews, tutorials, and even half-baked research ideas. Submission Details ~~~~~~~~~~~~~~~~~~ Get in touch with me if you intend to submit something -- the sooner you let me know what you're up to, the better. Please submit articles for the next issue to me by e-mail (ezyang(a)mit.edu) Articles should be written according to the guidelines available from http://themonadreader.wordpress.com/contributing/ Please submit your article in PDF, together with any source files you used. The sources will be released together with the magazine under a BSD license. If you would like to submit an article, but have trouble with LaTeX please let me know and we'll work something out.

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Displaying trees in Haskell
by Luana Fagarasan 07 Mar '12

07 Mar '12

Hello, I am quite new to Haskell and I am seeking the best way to display trees graphically when using Haskell. I have looked on the web, but am still not clear! For those interested, please find more detailed information below. Regards, Luana Fagarasan Further information: I am writing a theorem prover in Haskell as my final year project. This is very loosely based on the HAL theorem prover described in "ML for the working programmer" by Larry Paulson. I would like to display the proof tree (containing the main goal as the root and subgoals that were developed along the way as leaves/nodes), once a proof is found. More generally I would be interested in understanding more about GUIs when using Haskell.

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Higher types in contexts
by Barney Hilken 06 Mar '12

06 Mar '12

Is there any deep reason why I can't write a polymorphic type in a context? I think the record update problem can be (sort of) solved if you could write: class Has r Rev (forall a. [a] -> [a]) => HRClass r where setHRClass :: (forall a.[a] -> [a]) -> r -> r but polymorphic types are not allowed in contexts. Is this one of the problems SPJ considers "Hard" or is it a feasible extension? Barney.

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