April 2010 - Haskell - Haskell.org

Monads Terminology Question
by Mark Snyder 12 Apr '10

12 Apr '10

Hello, I'm wondering what the correct terminology is for the extra functions that we define with monads. For instance, State has get and put, Reader has ask and local, etc. Is there a good name for these? I've been calling them the "non-proper morphisms" (as opposed to the "proper" morphisms unit/return and bind). But I don't know if others call them that. Is there any accepted phrase for them? Thanks, ~Mark Snyder

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Dutch HUG Day: Program and Call for Participation
by Sean Leather 11 Apr '10

11 Apr '10

[Apologies for multiple copies.] ------------------------------------------- Dutch HUG Day 24 April 2010 Ordina office Niewegein, The Netherlands ------------------------------------------- *** *** Please register! *** *** Email Sean Leather <leather(a)cs.uu.nl> by 20 April! *** INTRODUCTION To celebrate our first anniversary, the Dutch Haskell Users Group (HUG) invites Haskell and functional programming enthusiasts in the Netherlands and surrounding area to an afternoon symposium. The Dutch HUG is an informal group with monthly meetings including talks on novel applications of Haskell and socializing in the neighborhood pub. The group was founded on Sunday, April 19, 2009 at the Haskell Hackathon hosted in Utrecht. After a successful year, we renew the trend with the Dutch HUG Day. INVITATION *** Please send an email to Sean Leather <leather(a)cs.uu.nl> by Tuesday, 20 April! *** Join us for a half day of fun and functional programming! We have some great "praatjes" (the Dutch word for talks) lined up. (Just in case you were confused by my "Call for Praatjes," all talks will be in English.) Along with talks, you can join us afterwards for a buffet dinner, graciously provided by our sponsor Ordina. The registration will allow Ordina to know how many people to expect and to satisfy their security concerns. They are also looking for recruiting options and will send attendees an email describing potential opportunities. PROGRAM We are happy to announce a preliminary program. Note that the particular titles or order of talks may change, but the general schedule should remain the same. 13:00 Reception 13:30 Welcome 13:45 Lightweight Program Inversion -- Janis Voigtländer (University of Bonn) 14:00 Functional Programming in the Industry? -- Stef Joosten (Ordina, Open University of the Netherlands) 14:30 BlazeHtml: Design of a Blazingly Fast HTML Combinator Library -- Jasper van der Jeugt (Ghent University) 15:00 Functional Programming at typLAB -- Erik Hesselink (typLAB) 15:30 Break 16:00 Cλash: Haskell-ish Hardware Descriptions -- Matthijs Kooijman (formerly University of Twente) 16:30 Why Haskell Does Not Matter -- Stefan Holdermans (Vector Fabrics) 17:00 Lightweight Monadic Regions -- Bas van Dijk (Radboud University Nijmegen, Sensor Sense) 17:30 Sirenial: Type-safe SQL Wrapper -- Martijn van Steenbergen (Utrecht University) 17:40 Discussion 18:00 Dinner 19:00 Depart 19:30 Drinks LOCATION The event will be held at the Ordina office in Niewegein, a town not far south of the city of Utrecht. You can get there by train to Utrecht Centraal and tram (the Utrecht "sneltram") to P+R Westraven. Details on the location can be found at the following link, and we will put more information on our website soon. * http://www.ordina.com/Vestigingen/Nieuwegein.aspx SPONSOR We are grateful to Ordina for allowing us to host this event on their premises. They are also kindly providing drinks during the breaks and dinner afterwards for all participants. You should come and hear from our host how they make use of functional programming. * http://www.ordina.com/ in English * http://www.ordina.nl/ in het Nederlands ORGANIZERS * Sean Leather * Chris Eidhof MORE INFORMATION * Dutch HUG: http://dutchhug.nl/ * Dutch HUG Day: http://dutchhug.nl/DutchHugDay/

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ANN: haskell-src-exts 1.9.0
by Niklas Broberg 11 Apr '10

11 Apr '10

Fellow Haskelleers, I'm pleased to announce the release of haskell-src-exts-1.9.0! * On hackage: http://hackage.haskell.org/package/haskell-src-exts * Via cabal: cabal install haskell-src-exts * Darcs repo: http://code.haskell.org/haskell-src-exts 1.8.2 --> 1.9.0 =============== * OptionPragma is renamed to the more descriptive ModulePragma, and adds a constructor AnnModulePragma for handling ANN pragmas preceding module header. * Add instances for Eq/Ord/Data/Typeable for Fixity. * Add 'parseFileWithComments' and 'parseFileContentsWithComments' to L.H.Exts . * More informative error messages when HSX tags are mismatched (thanks Gracjan Polak for the patch!) Cheers, /Niklas

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ANN: hledger 0.9 released
by Simon Michael 10 Apr '10

10 Apr '10

I'm pleased to announce a new hledger release, with many bugfixes and small improvements, GHC 6.12 support, and a separate library package to make building (h)ledger-compatible tools easier. Thanks to Oliver Braun and Gwern Branwen for code contributions this release. Just in time for tax filing! :) Patches, feedback, contributions welcome. Best, -Simon home: http://hledger.org Release notes: 2010/04/10 hledger 0.9 ...................... * ghc 6.12 support * split off hledger-lib package, containing core types & utils * parsing: ignore D, C, N, tag, end tag directives; we should now accept any ledger 2.6 file * parsing: allow numbers in commodities if double-quoted, like ledger * parsing: allow transactions with empty descriptions * parsing: show a better error for illegal month/day numbers in dates * parsing: don't ignore trailing junk in a smart date, eg in web add form * parsing: don't ignore unparsed text following an amount * parsing: @ was being treated as a currency symbol * add: fix precision handling in default amounts (#19) * add: elide last amount in added transactions * convert: keep original description by default, allow backreferences in replace pattern * convert: basic csv file checking, warn instead of dying when it looks wrong * convert: allow blank/comment lines at end of rules file * print: always show zero amounts as 0, hiding any commodity/ decimal places/price, like ledger * register: fix bad layout with years < 1000 * register: fix a Prelude.head error with reporting interval, -- empty, and --depth * register: fix a regression, register should not show posting comments * register: with --empty, intervals should continue to ends of the specified period * stats: better output when last transaction is in the future * stats: show commodity symbols, account tree depth, reorder slightly * web: -fweb now builds with simpleserver; to get happstack, use - fwebhappstack instead * web: pre-fill the add form with today's date * web: help links, better search form wording * web: show a proper error for a bad date in add form (#17) * web: fix for unicode search form values * web: fix stack overflow caused by regexpr, and handle requests faster (#14) * web: look for more-generic browser executables * web: more robust browser starting (#6) * error message cleanups * more tests, refactoring, docs Stats: 58 days, 2 contributors, 102 commits since last release. Now at 3983 lines of non-test code, 139 tests, 53% coverage.

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ANNOUNCE: syb-0.2
by José Pedro Magalhães 09 Apr '10

09 Apr '10

syb: Scrap Your Boilerplate! ================================================================================ Scrap Your Boilerplate (SYB) is a library for generic programming in Haskell. It is supported since the GHC >= 6.0 implementation of Haskell. Using this approach, you can write generic functions such as traversal schemes (e.g., everywhere and everything), as well as generic read, generic show and generic equality (i.e., gread, gshow, and geq). This approach is based on just a few primitives for type-safe cast and processing constructor applications. It was originally developed by Ralf Lämmel and Simon Peyton Jones. Since then, many people have contributed with research relating to SYB or its applications. More information is available on the webpage: http://www.cs.uu.nl/wiki/GenericProgramming/SYB What's new ---------- The biggest improvements from version 0.1 are: * Reintegration of the testsuite; * Introduction of the Generics.SYB.* module hierarchy (as synonyms for their Data.Generics.* counterparts); * Adding gshows :: Data a => a -> ShowS (more efficient than gshow); * Adding gmapAccumA :: forall b d a. (Data d, Applicative a) => (forall e. Data e => b -> e -> (b, a e)) -> b -> d -> (b, a d) ; * Adding ext1B :: (Data a, Typeable1 t) => a -> (forall b. Data b => (t b)) -> a ; * Introduction of two new generic producers ('empty' and 'constrs'). The former produces an empty value of a given datatype, while the latter produces a list of values of a datatype, each using a different constructor. Features -------- * Easy generic programming with combinators * GHC can derive Data and Typeable instances for your datatypes * Comes with many useful generic functions Requirements ------------ * GHC 6.10.1 or later * Cabal 1.6 or later Download -------- Get the package: http://hackage.haskell.org/package/syb Get the source: darcs get http://code.haskell.org/syb/ Bugs & Support -------------- Please report issues or request features at the bug tracker: http://code.google.com/p/scrapyourboilerplate/issues/list For discussion about the library with the authors, maintainers, and other interested persons use the mailing list: http://www.haskell.org/mailman/listinfo/generics

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Last CfP: WWV'10
by Temur Kutsia 09 Apr '10

09 Apr '10

[Apologies if you receive multiple copies] *********************************************************** * CALL FOR PAPERS * * * * WWV 2010 * * Automated Specification and Verification of Web Systems * * 6th International Workshop * * * * Vienna University of Technology, Austria * * July 30-31, 2010 * * http://www.complang.tuwien.ac.at/WWV2010/ * *********************************************************** *************** IMPORTANT DATES *************** Abstract Submission April 12, 2010 Full Paper Submission April 19, 2010 Acceptance Notification May 23, 2010 Camera Ready June 20, 2010 Workshop July 30-31, 2010 *************** SCOPE *************** The increased complexity of Web sites and the explosive growth of Web-based applications has turned their design and construction into a challenging problem. Nowadays, many companies have diverted their Web sites into interactive, completely-automated, Web-based applications (such as Amazon, on-line banking, or travel agencies) with a high complexity that requires appropriate specification and verification techniques and tools. Systematic, formal approaches to the analysis and verification can address the problems of this particular domain with automated and reliable tools that also incorporate semantic aspects. We solicit original papers on formal methods and techniques applied to Web sites, Web services or Web-based applications, such as: * rule-based approaches to Web system analysis, certification, specification, verification, and optimization * algebraic methods for verification and certification of Web systems * formal models for describing and reasoning about Web sites * model-checking, synthesis and debugging of Web sites * analysis and verification of linked data * abstract interpretation and program transformation applied to the semantic Web * intelligent tutoring and advisory systems for Web specifications authoring * Web quality and Web metrics * Web usability and accessibility * Testing and evaluation of Web systems and applications The WWV series provides a forum for researchers from the communities of Rule-based programming, Automated Software Engineering, and Web-oriented research to facilitate the cross-fertilization and the advancement of hybrid methods that combine the three areas. The previous WWV editions were: WWV'09 (Hagenberg, Austria), WWV'08 (Siena, Italy), WWV'07 (Venice, Italy), WWV'06 (Paphos, Cyprus), and WWV'05 (Valencia, Spain). *************** LOCATION *************** WWV 2010 will be held at the Compilers and Languages Group (Complang) of the Faculty of Informatics at the Vienna University of Technology, Austria. The Complang Group is located in the center of Vienna, beside the Karlskirche and near the Opera. For more information about the Complang Group, please visit: http://www.complang.tuwien.ac.at *************** SUBMISSION *************** Submissions must be received by April 19, 2010. In addition, an ASCII version of the title and abstract must be submitted by April 12, 2010. Please submit research reports up to 15 pages in PDF, conforming to the format produced by LaTeX using the easychair.cls class file of EasyChair. The class style may be downloaded at: http://www.easychair.org/easychair.zip Submission is web-based via this link: http://www.easychair.org/conferences/?conf=wwv2010 *************** PUBLICATION *************** We will prepare workshop pre-proceedings for the workshop participants. After the workshop, an open call for a special journal issue is envisaged. *************** COMMITTEES *************** PROGRAM CO-CHAIRS: Laura Kovacs, Vienna University of Technology, Austria Temur Kutsia, Johannes Kepler University Linz, Austria PROGRAM COMMITTEE Maria Alpuente Frasnedo, Technical University of Valencia, Spain Demis Ballis, University of Udine, Italy Jorge Manuel Neves Coelho, University of Porto, Portugal Vicente Luque Centeno, Universidad Carlos III de Madrid, Spain Wlodzimierz Drabent, IPI PAN, Polish Academy of Sciences Santiago Escobar, Technical University of Valencia, Spain Moreno Falaschi, University of Siena, Italy Jens Knoop, Vienna University of Technology, Austria Laura Kovacs, Vienna University of Technology, Austria Temur Kutsia, Johannes Kepler University Linz, Austria Catherine Meadows, Naval Research Laboratory, USA *************** INVITED SPEAKER *************** Andrei Voronkov, University of Manchester, UK *************** RELATED EVENTS *************** WWV 2010 will take place after the RISC Summer 2010 conference series: http://www.risc.uni-linz.ac.at/about/conferences/summer2010/ held in Hagenberg near Linz. There are frequent train connections of about 1.5 hours between Linz and Vienna.

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Call for Contributions - Haskell Communities and Activities Report, May 2010 edition
by Janis Voigtländer 09 Apr '10

09 Apr '10

Dear all, I would like to collect contributions for the 18th edition of the ================================================================ Haskell Communities & Activities Report http://www.haskell.org/communities/ Submission deadline: 1 May 2010 (please send your contributions to hcar at haskell.org, in plain text or LaTeX format) ================================================================ This is the short story: * If you are working on any project that is in some way related to Haskell, please write a short entry and submit it. 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 in an existing project related to Haskell that has not previously been mentioned in the HCAR, 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 six months. If you have only recently been exposed to Haskell, it might be a good idea to browse the November 2009 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 submission deadline. They will then be compiled into a coherent report that is published online as soon as it is ready. As always, this is a great opportunity to update your webpages, make new releases, announce or even start new projects, or to talk about developments you want every Haskeller to know about! Looking forward to your contributions, Janis (current editor) FAQ: Q: What format should I write in? A: The required format is a LaTeX source file, adhering to the template that is available at: http://haskell.org/communities/05-2010/template.tex There is also a LaTeX style file at http://haskell.org/communities/05-2010/hcar.sty that you can use to preview your entry. If you do not know LaTeX, then use plain text. If you modify an old entry that you have written for an earlier edition of the report, you should already have received your old entry as a template (provided I have your valid email address). Please modify that template, rather than using your own version of the old entry as a template. Q: Can I include images? A: Yes, you are even encouraged to do so. Please use .jpg format, then. Q: How much should I write? A: Authors are asked to limit entries to about one column of text. This corresponds to approximately one page, or 40 lines of text, with the above style and template. A general introduction is helpful. Apart from that, you should focus on recent or upcoming developments. Pointers to online content can be given for more comprehensive or "historic" overviews of a project. Images do not count towards the length limit, so you may want to use this opportunity to pep up entries. There is no minimum length of an entry! The report aims for being as complete as possible, so please consider writing an entry, even if it is only a few lines long. Q: Which topics are relevant? A: All topics which are related to Haskell in some way are relevant. We usually had reports from users of Haskell (private, academic, or commercial), from authors or contributors to projects related to Haskell, from people working on the Haskell language, libraries, on language extensions or variants. We also like reports about distributions of Haskell software, Haskell infrastructure, books and tutorials on Haskell. Reports on past and upcoming events related to Haskell are also relevant. Finally, there might be new topics we do not even think about. As a rule of thumb: if in doubt, then it probably is relevant and has a place in the HCAR. You can also ask the editor. Q: Is unfinished work relevant? Are ideas for projects relevant? A: Yes! You can use the HCAR to talk about projects you are currently working on. You can use it to look for other developers that might help you. You can use it to write "wishlist" items for libraries and language features you would like to see implemented. Q: If I do not update my entry, but want to keep it in the report, what should I do? A: Tell the editor that there are no changes. The old entry will be reused in this case, but it might be dropped if it is older than a year, to give more room and more attention to projects that change a lot. Do not resend complete entries if you have not changed them.

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trouble with the random number generator
by Garrett Mitchener 08 Apr '10

08 Apr '10

Hi, I'm having some trouble with the standard random number generator. I re-implemented it for speed, but the same problem seems to be present in the original. The problem I'm having is in the generation of a random Double. If you go down to the function randomIvalDouble in Random.hs (and I'm looking at the one from http://darcs.haskell.org/packages/random) here's where something is going wrong: case (randomIvalInteger (toInteger (minBound::Int32), toInteger (maxBound::Int32)) rng) of (x, rng') -> let scaled_x = fromDouble ((l+h)/2) + fromDouble ((h-l) / realToFrac int32Range) * fromIntegral (x::Int32) in (scaled_x, rng') ... int32Range = toInteger (maxBound::Int32) - toInteger (minBound::Int32) I use essentially the same calculation in my implementation with l = 0 and h = 1, that is, I want to generate a random Double in the interval [0,1]. int32Range comes out to be 2^32-1. But if the pseudo-random integer x happens to be minBound, which is -2^31, then the scaled_x comes out 1/2 - 2^31/(2^32-1) = 2^31( 1/2^32 - 1/(2^32-1) ) = -1.164e-10 < 0 which is outside the required range. One of my simulations, which has been running for weeks, actually hit this, and I'd like to know if I'm just missing something or if this is a real bug. It breaks my simulation because it triggers an attempt to access element -1 of an array whose minimum index is 0, by the way. My trouble at this point is that I'd really like for my simulation results to be completely reproduceable, and I'm going to be unhappy if I have to re-implement the random generation and change it so that I have to throw out all the results I have so far. I'm also going to be unhappy if I have to insert some check that slows everything down... At any rate, if I'm right, this bug affects GHC and Hugs. But this code has surely been around long enough that someone would have found this already? But there's not a bug in hackage's trac system. Help! -- Garrett Mitchener

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Re: [Haskell-cafe] ANNOUNCE: Hac phi 2010
by Chris Casinghino 08 Apr '10

08 Apr '10

Hi Jason, > If you don't run out of space, what is the registration deadline? There's no official deadline to register with us, though we'll probably need the names a few days ahead of time to get wifi keys for everyone. We did get a hotel discount for people coming in from out of town (see the hac phi wiki page), and it's only available until April 23. I hope you can join us! --Chris

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ANNOUNCE: Hac phi 2010
by Chris Casinghino 07 Apr '10

07 Apr '10

Greetings, I am very pleased to officially announce Hac phi 2010, a Haskell hackathon/get-together to be held May 21-23 at the University of Pennsylvania in Philadelphia. The hackathon will officially kick off at 2:30 Friday afternoon, and go until 5pm on Sunday (with breaks for sleep, of course). Last year's Hac phi was a lot of fun, and many people have already expressed interest in coming back this year. I want to stress that everyone is welcome---you do not have to be a Haskell guru to attend! Helping hack on someone else's project could be a great way to increase your Haskell-fu. If you plan on coming, please officially register [1]. Registration, travel, lodging and many other details can be found on the Hac phi wiki [2]. Note that we're in a different space this year and may have to cap attendance, so register early. We're also looking for a few people interested in giving short (15-20 min.) talks, probably on Saturday afternoon. Anything of interest to the Haskell community is fair game---a project you've been working on, a paper, a quick tutorial. If you'd like to give a talk, add it on the wiki [3]. Hope to see you in Philadelphia! -The Hac φ team [1] http://haskell.org/haskellwiki/Hac_φ/Register [2] http://haskell.org/haskellwiki/Hac_φ [3] http://haskell.org/haskellwiki/Hac_φ/Talks

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