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Lens with merge (Semigroup)
by Tony Morris 05 Sep '11

05 Sep '11

A regular Lens can be represented as follows: data CoState a = CoState (a -> b) a newtype Lens a b = Lens (a -> CoState b a) I once read about a lens representation that permits a general "merge" operation. I forget where I read it -- I think it was #haskell IRC. However, as I recall, perhaps incorrectly, the merge operation involves a Semigroup[1] and helps to overcome the fact that Lens is not an Arrow and so does not have a (&&&) operation. I am interested to know what this Lens operation is and the associated merge operation. [1] -- Approximate data SemigroupT f a = SemigroupT (a -> a -> f a) -- Tony Morris http://tmorris.net/

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Call for papers: Programming languages meets program verification
by Nikhil Swamy 05 Sep '11

05 Sep '11

PLPV 2012 The Sixth ACM SIGPLAN Workshop Programming Languages meets Program Verification 24th January, 2012 Philadelphia, USA (Affiliated with POPL 2012) http://research.microsoft.com/en-us/um/people/nswamy/plpv12 -------------------------------------------------------------------------------- Overview The goal of PLPV is to foster and stimulate research at the intersection of programming languages and program verification, by bringing together experts from diverse areas like types, contracts, interactive theorem proving, model checking and program analysis. Work in this area typically attempts to reduce the burden of program verification by taking advantage of particular semantic or structural properties of the programming language. Examples include dependently typed programming languages, which leverage a language's type system to specify and check richer than usual specifications or extended static checking systems which incorporate contracts with either static or dynamic contract checking. We invite submissions on all aspects, both theoretical and practical, of the integration of programming language and program verification technology. To encourage cross-pollination between different communities, we seek a broad scope for PLPV. In particular, submissions may have diverse foundations for verification (Type-based, Hoare-logic-based, Abstract Interpretation-based, etc.), target different kinds of programming languages (functional, imperative, object-oriented, etc.), and apply to diverse kinds of program properties (data structure invariants, security properties, temporal protocols, resource constraints, etc.). -------------------------------------------------------------------------------- Important Dates: Submission: 11th October, 2011 Notification: 8th November, 2011 Final Version: 15th November, 2011 Workshop: 24th January, 2012 -------------------------------------------------------------------------------- Submissions We seek submissions of up to 12 pages related to the above topics---shorter submissions are also welcome. Submissions may describe new work, propose new challenge problems for language-based verification techniques, or present a known idea in an elegant way (i.e., a pearl). Submissions should be prepared with SIGPLAN two-column conference format (http://www.sigplan.org/authorInformation.htm) Submitted papers must adhere to the SIGPLAN republication policy (http://www.sigplan.org/republicationpolicy.htm) Concurrent submissions to other workshops, conferences, journals, or similar forums of publication are not allowed. To submit a paper, access the submission site at http://www.easychair.org/conferences/?conf=plpv2012. -------------------------------------------------------------------------------- Publication Accepted papers will be published by the ACM and will appear in the ACM Digital library. -------------------------------------------------------------------------------- Program Committee Amal Ahmed Indiana University Lennart Augustsson Standard Chartered Koen Claessen Chalmers (co-chair) Martin Giese University of Oslo Daniel Licata Carnegie Mellon University Peter MÃ¼ller ETH Zurich Aleksandar Nanevski IMDEA Matthieu Sozeau INRIA Nikhil Swamy Microsoft Research (co-chair) David Walker Princeton University Dana Xu INRIA -------------------------------------------------------------------------------- Previous PLPVs: http://plpv.org

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Final CFP: PADL'12 - Practical Aspects of Declarative Languages 2012
by Claudio Russo 05 Sep '11

05 Sep '11

[Apologies if you receive multiple copies.] Final Call for Papers ===================== 14th International Symposium on Practical Aspects of Declarative Languages (PADL 2012) http://research.microsoft.com/~crusso/padl12 Philadelphia, Pennsylvania, USA, January 23-24, 2012 Co-located with ACM POPL'12 Abstract/Paper submission deadline: September 10th/17th, 2011 Conference Description ====================== Declarative languages build on sound theoretical bases to provide attractive frameworks for application development. These languages have been successfully applied to many different real-world situations, ranging from data base management to active networks to software engineering to decision support systems. New developments in theory and implementation have opened up new application areas. At the same time, applications of declarative languages to novel problems raise numerous interesting research issues. Well-known questions include designing for scalability, language extensions for application deployment, and programming environments. Thus, applications drive the progress in the theory and implementation of declarative systems, and benefit from this progress as well. PADL is a forum for researchers and practitioners to present original work emphasizing novel applications and implementation techniques for all forms of declarative concepts, including, functional, logic, constraints, etc. Topics of interest include, but are not limited to: * Innovative applications of declarative languages * Declarative domain-specific languages and applications * Practical applications of theoretical results * New language developments and their impact on applications * Declarative languages and Software Engineering * Evaluation of implementation techniques on practical applications * Practical experiences and industrial applications * Novel uses of declarative languages in the classroom * Practical extensions such as constraint-based, probabilistic, and reactive languages. PADL'12 welcomes new ideas and approaches pertaining to applications and implementation of declarative languages. In this occasion PADL is co-located, as traditionally, with ACM POPL, which will be held immediately following PADL, January 25-27. The symposium will be held in Philadelphia, Pennsylvania, USA. Important Dates and Submission Guidelines ========================================= Abstract Submission: September 10, 2011 Paper Submission: September 17, 2011 Notification: October 22, 2011 Camera-ready: November 5, 2011 Symposium: January 23-24, 2012 Authors should submit an electronic copy of the full paper in PDF using the Springer LNCS format. The submission will be done through EasyChair conference system. If electronic submission is impossible, please contact the program chairs for information on how to submit hard copies. All submissions must be original work written in English. Submissions must be unpublished and not submitted for publication elsewhere. Work that already appeared in unpublished or informally published workshops proceedings may be submitted. PADL'12 will accept both technical and application papers: * Technical papers must describe original, previously unpublished research results. Technical papers must not exceed 15 pages in Springer LNCS format. * Application papers are a mechanism to present important practical applications of declarative languages that occur in industry or in areas of research other than Computer Science. Application papers will be published in the Springer-Verlag conference proceedings, and will be presented in a separate session. Application papers are expected to describe complex and/or real-world applications that rely on an innovative use of declarative languages. Application descriptions, engineering solutions and real-world experiences (both positive and negative) are solicited. The limit for application papers is 6 pages in Springer LNCS format. Program Committee ================= Marcello Balduccini, Intelligent Systems Department, Kodak Research Labs Edwin Brady, University of St Andrews, Scotland Henning Christiansen, Roskilde University, Denmark Agostino Dovier, University of Udine, Italy Matthew Flatt, University of Utah, USA Gopal Gupta, University of Texas at Dallas, USA John Hughes, Chalmers University of Technology, Sweden; Quviq AB Gabriele Keller, University of New South Wales, Australia Lunjin Lu, Oakland University, USA Marc Pouzet, École normale supérieure, France Ricardo Rocha, University of Porto, Portugal Andreas Rossberg, Google Germany GmbH, Germany Claudio Russo, Microsoft Research Cambridge, UK (co-chair) Kostis Sagonas, Uppsala University, Sweden; NTUA, Greece Satnam Singh, Microsoft Research Cambridge, UK Zoltan Somogyi, University of Melbourne, Australia Eijiro Sumii, Tohoku University, Japan Terrance Swift, Universidade Nova de Lisboa, Portugal; Johns Hopkins University, USA Andrew Tolmach, Portland State University, USA Jan Wielemaker, University of Amsterdam, The Netherlands Roland Yap, National University of Singapore, Republic of Singapore Kwangkeun Yi, Seoul National University, Korea Neng-Fa Zhou, Brooklyn College, City University of New York, USA (co-chair) Contacts ======== For additional information about papers and submissions, please contact the Program Chairs: Claudio Russo Microsoft Research Cambridge,UK Email: crusso <AT> microsoft <DOT> com Neng-Fa Zhou Brooklyn College, The City University of New York, USA Email: zhou <AT> sci <DOT> brooklyn <DOT> cuny <DOT> edu With the Cooperation of ======================= The Association for Logic Programming (ALP) ACM SIGPLAN Microsoft Research, Cambridge ===================================

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Real CMS Application in Haskell
by Haisheng Wu 05 Sep '11

05 Sep '11

Hello guys, I googled for a real open source CMS application in Haskell but have no luck. So I'm wondering if Haskell is used very little in Web development area. Thanks. -Simon

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Enumeratee that generates data
by tsuraan 05 Sep '11

05 Sep '11

I'm trying to write a program whose network behaviour is analogous to a web proxy. A client connects to my server and gives me some data, my server connects to an upstream server and gives data to it, my server gets data from upstream, and gives data to the client. I'd like to write this using the enumerator library, since it seems like it should be possible to do that cleanly. Now, the guts of an echo server are pretty easy: runIteratee $ enumSocket cs sock $$ iterSocket sock That's just plain pretty. You can even put interesting data tranformations (Enumeratees) in there to make it behave a bit differently. What I'd like to do is have an Enumeratee that connects to the upstream server, forwards the request, and then uses one of the Data.Enumerator.List functions to generate a response that is the response from the upstream server. It doesn't look like this is possible though, since Enumeratees are pretty much one output per input. Is my basic model broken here? It's occurred to me that what I actually want to do is tie the enumSocket clientSock to an iterSocket upstreamSock, do the reverse, and then do two runIteratee calls (one in a forkIO, I guess?). That seems uglier, I'm not sure if there would be complications in making sure both Iteratees stop running correctly. Is that the right way to do, or am I just missing some capability that Enumeratees have?

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ANNOUNCE: Hs2lib-0.5.5
by Phyx 04 Sep '11

04 Sep '11

What is it? ======== A preprocessor and library which allow you to create dynamic libs from arbitrary annotated Haskell programs with one click. It also allows you to use the generated lib in C, C++ and C# just by including the generated header files. At a minimum it can be considered the inverse of c2hs. Where to get it? ============ You can get it from Hackage (http://hackage.haskell.org/package/Hs2lib) or by using cabal (cabal install Hs2lib). Documentation, Mailing List, Source, etc ======================= Go to http://mistuke.wordpress.com/category/hs2lib/ for information. Or for a tutorial http://www.scribd.com/doc/63918055/Hs2lib-Tutorial What's New? ========= - Currently Supported: * Autogerates free functions for any StablePtr used. * Added support for memory leak tracing with the --debug flag http://mistuke.wordpress.com/2011/08/09/tracing-lexer-memory-leaks/ * Fixed a bug in the library that caused an error in marshalling * No longer frees strings, in order to prevent heap corruptions on calls from c# * Fixed an issue with lists and type synonyms * Fixed an alignment issue with stdcall * Renamed the hs2c# pragma to hs2cs * Fixed an error in parsing pragmas * Fixed a majot marshalling bug having to do with lists of pointer types * Started on an implementation of an automatic test generator to test exported functions. * Re-arranged the namespaces generated in C#. Now Functions and types are put in different namespaces. - Not Currently supported: * Infix constructors * Control over the autogenerated free functions for StablePtr * Exporting of type/functions with the same name in different modules * Exporting polymorphic functions Details ===== A more detailed documentation will follow in the next few weeks. Why is the first version 0.4.8? -------------- This project has been in development for a very long time. Nearly two years on and off. It was developed mainly to facilitate the creation of Visual Haskell 2010. This is just the first public release of this tool.

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Any good topics for Master Thesis
by Haisheng Wu 04 Sep '11

04 Sep '11

Dear Haskellers, I'm a master student major of computer science and trying to find any topics for my master thesis. My mentor suggest me to find any topic I'm interested in. Therefore I'm thinking whether there are some topics related to FP and Haskell. Especially use such technology to solve problems rather than theory research. Appreciate any suggestions / ideas! -Simon

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ANN: EclipseFP 2.1.0 released
by JP Moresmau 04 Sep '11

04 Sep '11

Hello Haskellers, Version 2.1.0 of the EclipseFP project (Eclipse plugins for Haskell development) has been released. Based mainly on the work Alejandro Serrano did for his GSoC project, this release features a lot of enhancements: - A package/module browser - Hoogle integration: select a identifier in your code and jump to its hoogle definitions - HLint integration: jump directly to HLint errors and warnings - Profiling graphs: run an executable with profiling flags and its the resulting graphs - SourceGraph: generate SourceGraph reports - Better auto completion information And of course some bug fixes. Please go to http://eclipsefp.github.com/, the new website Alejandro designed for more information and installation instructions. Feedback welcome! -- JP Moresmau http://jpmoresmau.blogspot.com/

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Configuration Problem and Plugins
by M. George Hansen 03 Sep '11

03 Sep '11

Greetings, I'm a Python programmer who is relatively new to Haskell, so go easy on me :) I have a program that uses (or will use) plugins to render output to the user in a generic way. I'm basing the design of the plugin infrastructure on the Plugins library, and have the following interface: data Renderer = Renderer { initialize :: IO (), destroy :: IO (), render :: SystemOutput -> IO () } The program loads plugins at the start and runs the initialize function, and then enters the main loop where it repeatedly calls the render function with output to display. When the program exits the main loop, it calls the destroy function to clean up any resources used by the plugin. You can probably already see my problem: how do I pass initialization information created in the initialize function to the render function? I'm vaguely aware of some solutions to the typical "configuration problem", such as implicit arguments or explicitly passing the configuration data through the function call hierarchy. As far as I can tell, neither of these approaches would work because the program can't know at compile time what, if any, configuration data is used by the plugin. I suppose I could pass a Dynamic up the call chain and let the plugin decode it in the render function, but that seems a little kludgy to me. Any thoughts would be greatly appreciated. -- M. George Hansen

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ANN: hledger-web 0.15.1 (& hledger 0.15)
by Simon Michael 03 Sep '11

03 Sep '11

I've made a bugfix release of the hledger-web package, to fix build problems. hledger-web 0.15.1: * web: add missing Hledger.Web.Options to cabal file * web: tighten up dependencies to reduce build problems And here's another new dependency I forgot to mention: flot, the js charting library. The rest of this mail is a repeat of yesterday's announcement, since that one seriously confused google groups, gmane, and perhaps your mailreader (pro tip: don't re-edit old announcements with Mail.app's cmd-shift-d. :) -Simon Date: 2011/9/1 Subject: ANN: hledger 0.15 I'm pleased to announce hledger 0.15! This release includes work by Trygve Laugstøl, Dmitry Astapov, Clint Adams, Johann Klähn and myself. hledger is a library and set of user tools for working with financial data (or anything that can be tracked in a double-entry accounting ledger.) It is a haskell port and friendly fork of John Wiegley's Ledger. hledger provides command-line, curses and web interfaces, and aims to be a reliable, practical tool for daily use. Given a plain text file describing transactions of money or any other commodity, it will print the chart of accounts, account balances, or just the transactions you're interested in. It can also help you record new transactions, or convert CSV data from your bank. Home: http://hledger.org IRC: irc://irc.freenode.net/#ledger Install: cabal update; cabal install hledger [hledger-web hledger-vty hledger-chart hledger-interest] Platform-specific binaries, which are time-consuming to make and support, are now provided on request to financial donors - a great way to give back and help pay hosting costs! Best, -Simon Release notes for 0.15: * hledger's options are now modal, providing better help (using cmdargs) * hledger now lists and runs any hledger-* add-ons found in the user's path * case insensitivity of filter patterns has been fixed * parsing: `alias`/`end aliases` directives, for renaming accounts, are supported, like ledger's but a bit more powerful; also an `--alias` option for renaming on the fly * parsing: the `account` directive now preserves posting type (normal/virtual/balanced virtual) * parsing: the `pop` directive is supported as an alias for `end tag`, like ledger * parsing: `P` (historical price) directives can contain a (ignored) numeric time zone, like ledger * parsing: the leading `!` in directives is now optional and deprecated, like ledger * parsing: entries with a negative amount in the first posting now infer the correct balancing amount * parsing: bad date checking is more accurate * balance: collapsing of boring accounts to one line can be disabled with `--no-elide` * balance: fix a wrong precision regression from last release * convert: standard input can be converted * convert: an alternate rules file can be specified with `--rules` * convert: `account2-field` can be used when the CSV file specifies both accounts * convert: `description-field` can have a custom format and combine multiple CSV fields * convert: `in-field` and `out-field` support CSV files that use two amount columns * convert: don't fail when there's no default journal file * web: the web interface has been overhauled/cleaned up * web: account register views are now transaction-based, like gnucash etc., and show accurate historical balances when possible * web: simple balance charts are displayed (using flot) * web: more expressive and consistent search patterns, using a new matching engine * web: add form uses currently focussed account as default, redirects to itself, formats status messages better * web: sidebar now shows empty/boring accounts too * web: now uses warp and a newer yesod * api simplifications * importable Hledger, Hledger.Web, Hledger.Vty and Hledger.Chart modules * the basic reports are now provided by hledger-lib for easier reuse * new api use examples: `equity.hs`, `uniquify.hs` * some old base 3 support has been dropped * the old -s flag has been dropped Stats: Release contributors: Simon Michael, Trygve Laugstøl, Dmitry Astapov, Clint Adams, Johann Klähn 132 days, 314 commits, 18 end-user features and 6 end-user bugfixes since last release. 210 unit & functional tests and 55% unit test coverage (hledger, hledger-lib packages). 7642 lines of code (all packages).

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