June 2009 - Haskell - Haskell.org

Using unsafePerformIO safely
by Hector Guilarte 24 Jun '09

24 Jun '09

Hello, I made a GCL compiler using Alex and Happy and now I'm making the interpreter to that program. Here's the deal: First of all, I'm no expert in the usage of monads. Now: Whenever a "show" instruction is found in any GCL program while the interpretation is being done it is supposed to print on the stdout the string or the aritmetic expresion it was called with, so I guessed I need to run an IO operation and continue the interpretation of my program. I managed to do this using unsafePerformIO and `seq` like is shown below. My question is: Is it safe to use it this way? So far it is working great, but I need to be sure I'm using it in a "safe" way. Like I said, I'm no expert in monads and the System.IO.Unsafe documentation says: " *unsafePerformIO* :: IO<http://www.haskell.org/ghc/docs/latest/html/libraries/base/System-IO.html#t…>a -> a This is the "back door" into the IO<http://www.haskell.org/ghc/docs/latest/html/libraries/base/System-IO.html#t…>monad, allowing IO<http://www.haskell.org/ghc/docs/latest/html/libraries/base/System-IO.html#t…>computation to be performed at any time. For this to be safe, the IO<http://www.haskell.org/ghc/docs/latest/html/libraries/base/System-IO.html#t…>computation should be free of side effects and independent of its environment. " I don't know if the IO computation I'm doing is free of side effects and independent of its enviroment :s. (is just hPutStr stdout ....) Also I've read something about my code not being executed for sure or something like that. Can somebody check the code and tell me if I'm "safe" with it? Thanks a lot! Here's the code: -- Tabla is my Symbol Table of the program being interpreted evalInstruccion:: Instruccion -> Tabla -> Tabla evalInstruccion (ShowY showY) tabla = myRunIO (evalShow showY tabla) evalInstruccion _ tabla = tabla -- There are many other Instructions here missing wich are not relevant to my question {-# NOINLINE myRunIO #-} myRunIO:: (Tabla, IO()) -> Tabla myRunIO tupla = ((unsafePerformIO (snd tupla)) `seq` (fst tupla)) -- Here's the unsafePerformIO.... Am I safe? evalShow:: ShowY -> Tabla -> (Tabla, IO()) evalShow (ShowS string) tabla = (tabla,(hPutStr stdout string)) evalShow (ShowE expr) tabla = (tabla,(hPutStr stdout (show (evalExpr expr tabla)))) -- Don't worry about evalExpr, it works and returns an Int

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(no subject)
by Stephanie Weirich 24 Jun '09

24 Jun '09

===================================================================== Call for Participation ACM SIGPLAN Haskell Symposium 2009 http://haskell.org/haskell-symposium/2009/ Edinburgh, Scotland, 3 September 2009 ===================================================================== The ACM SIGPLAN Haskell Symposium 2009 will be co-located with the 2009 International Conference on Functional Programming (ICFP). The purpose of the Haskell Symposium is to discuss experiences with Haskell and future developments for the language. The scope of the symposium includes all aspects of the design, semantics, theory, application, implementation, and teaching of Haskell. Preliminary program: * http://haskell.org/haskell-symposium/2009/schedule.html REGISTRATION IS NOW OPEN: * http://www.regmaster.com/conf/icfp2009.html * Early registration deadline: July 30, 2009 Local arrangements (including travel and accommodation): * http://www.haskell.org/haskellwiki/ICFP_2009_Local_Arrangements * Conference reservation/rate deadline: July 20, 2009 * ICFP09 & Haskell 09 coincides with the final week of the Edinburgh Festival, one of the premier arts and cultural festivals in the world. The opportunity to attend the Festival is a plus! Due to the popularity of Edinburgh during the festival period, we strongly recommend booking accommodation early. See you in Edinburgh, Stephanie Weirich Haskell 2009 Program Chair ===================================================================== p.s., don't forget about the ICFP Programming Contest this weekend!! * http://www.icfpcontest.org * Friday, June 26 to Monday, June 29 * Organizers: Computer Systems Design Laboratory (University of Kansas)

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Haskell on the iPhone
by Ryan Trinkle 24 Jun '09

24 Jun '09

Dear Haskellers, Recently, there's been a groundswell of activity in the Haskell community regarding the Haskell's use in developing iPhone games. The iPhone is a powerful, innovative platform (with a great monetization scheme, to boot), and it's not surprising that many of us would want to develop apps for it in our favorite language. I am proud to announce today that my company, iPwn Studios Inc., is currently preparing to release an open source patch to GHC that allows it to output binaries for iPhone OS. The patch will be released under a BSD license as soon as possible and hopefully integrated into the GHC main-line in the near future. As the first (to my knowledge) Haskell-based game studio, iPwn Studios is committed to giving back to the Haskell community through open source - contributing to a rising tide that lifts us all. I would like to take this opportunity to propose the creation of a haskell-iphone mailing list, so that all Haskellers working with the iPhone - whether for profit or for pleasure - can come together to make Haskell a force to be reckoned with in the burgeoning iPhone App marketplace. Best wishes, Ryan Trinkle President, iPwn Studios Inc. P.S.: If you wish to be involved in the preparation of the GHC patch or in the creation of iPwn Studios' first game, don't hesitate to contact me by email (ryant5000(a)gmail.com) AIM (RyanT5000), or IRC (RyanT5000 on irc.freenode.net)

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ANNOUNCE: happstack-0.3.2
by Matthew Elder 24 Jun '09

24 Jun '09

Announcing happstack-0.3.2: It was released several days ago to hackage, but here is the official announcement! List of recorded changes (many improvements were not documented): * Modularization of the example application using the component system * All packages now require Cabal >= 1.6 * Repository metadata added to cabal description * Moved Combined Logging from Happstack.Server to Happstack.Server.AccessLog.Combined * Added Happstack.Util.Mail: a simple email interface which utilizes a smarthost * SimpleHTTP: look and lookPairs now assume utf-8 from the browser * Space leak fixed in Happstack.Util.Timeout * A fix for an issue where alphanumeric Accept-Encoding Requests made the parser fail * Fixes for some command-line browsers such as links * Guards now have fall-through semantics * Various updates & additions to documentation * Code beautification * Bugfix to Happstack.Util.Cron to accept intervals up to maxBound * addition of a strict version of fileServe "fileServeStrict" * fileServe (lazy) behaves more reliably now and escapes before any filters can be applied Regards, Matthew Elder

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ANNOUNCE: sendfile-0.1
by Matthew Elder 24 Jun '09

24 Jun '09

Announcing sendfile-0.1: A library which exposes zero-copy sendfile functionality in a portable way. http://hackage.haskell.org/package/sendfile-0.1 Right now it supports natively linux 2.6+ (maybe older too) and windows 2000+ -- on other platforms it will fall back seamlessly to a portable haskell implementation. Please test it out and send your experiences / bug reports to HAppS(a)googlegroups.com. Patches for other platforms also welcome (but please preserve the existing style). Recommended initial testing steps: cabal install sendfile wget http://patch-tag.com/r/sendfile/snapshot/current/content/raw/test.hs runghc test.hs open http://127.0.0.1:8000 in your web browser and see if test.hs was rendered properly (firefox recommended) see which mode it was rendered in (stdout will say one of WIN32_SENDFILE, LINUX_SENDFILE, or PORTABLE_SENDFILE) Happy Hacking! Matthew Elder

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Re: [Haskell-cafe] Re: ANN: haskell-src-exts-1.0.0
by Niklas Broberg 23 Jun '09

23 Jun '09

Hi Maurício, > How far is Unicode from beeing parsed? It doesn't seem to be > a huge step (from my ill-informed viewpoint), and it would > not let behind those who are happy to be able to declare names > in their own native language. (Oh, and sorry for resorting to > politically correct blackmail...) Unicode in identifiers and symbols actually already works, assuming you don't use the non-Unicode-aware parseFile, parseFileWithExts or parseFileWithMode (which all use Prelude.readLine). What doesn't work is to use the Unicode versions of special symbols like ->, => etc. I'm waiting for a stable and blessed unicode-aware text package to replace utf8-string, before we have one of those then my support would only be half-hearted at best. But in the mean time you can use the readLine provided by utf8-string, and then parseFileContents on that, which should give you the politically correct names. ;-) Cheers, /Niklas

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INAP 2009: 2nd Call for Papers
by Pedro Salgueiro 23 Jun '09

23 Jun '09

[apologies for cross-posting; please distribute] --- (PLEASE DISTRIBUTE) ------------------------------------------------------------ Second Call for Papers INAP 2009 18th International Conference on Applications of Declarative Programming and Knowledge Management November 5-7, 2009 Evora, Portugal http://www.di.uevora.pt/inap2009/ http://inap.dialogengines.com/ ------------------------------------------------------------ Organized by the Portuguese AI Society (APPIA), the INAP Committee and the Society of Logic Programming (GLP e.V.) == Overview == Declarative Programming is a family of advanced paradigms for the modeling and solving of complex problems. These specification and implementation methods have attracted more and more attention over the past years, e.g. in the domains of databases and natural language processing, for modeling and the processing of combinatorial problems, and for establishing systems for the web. == INAP 2009 == INAP is a communicative and dense forum for intensive discussion of applications of important technologies related to Prolog, Logic and Constraint Programming as well as closely related advanced software. It comprehensively covers the impact of programmable logic solvers in the Internet Society, its underlying technologies, and leading edge applications in industry, commerce, government, and societal services. INAP 2009 continues a tradition of successful workshops cast around the applications of declarative programming, which were held in Kobe (1997), Tokyo (1995, 1996, 1998 - 2001), Potsdam (2004), Fukuoka (2005) and Wuerzburg (2007). We invite the submission of high quality papers on the described topics, especially, but not exclusively, on different aspects of Declarative Programming, Constraint Processing and Knowledge Management as well as their use for Distributed Systems and the Web: - Knowledge Management, e.g. Data Mining, Decision Support, Deductive Databases - Distributed Systems and the Web, e.g. Agents and Concurrent Engineering, Semantic Web - Constraints, e.g. Constraint Systems, Extensions of Constraint (Logic) Programming - Theoretical Foundations, e.g. Deductive Databases, Nonmonotonic Reasoning - Systems and Tools for Academic and Industrial Use - Knowledge-based Web Services - Logic Solvers and Applications == Workshop Format == The technical program of the workshop will include invited presentations (to be announced), regular technical sessions with presentations of the accepted papers, system demonstrations and a panel discussion. == Conference Venue == The conference will be held at the University of Evora, Portugal in November 5-7, 2009. Evora is a nice and quiet historical city located in the south of Portugal that can be reached from Lisbon by train or coach in under 2 hours. It is a small city of 60.000 inhabitants, 120 km inland from Lisbon and classified by Unesco as World Heritage. The University of Evora was established in the 16th Century and is the 2nd oldest Portuguese University. The social program is promising since the region is very rich in historical sites (Stone Age, Roman, Medieval and Renaissance remains) and also offers a very special gastronomy. See http://en.wikipedia.org/wiki/%C3%89vora for more information. == Important Dates == Paper Submission Deadline: June 29, 2009 Notifications to Authors: August 17, 2009 Camera-ready Version Deadline: September 14, 2009 INAP 2009 Workshop: November 5-7, 2009 == Submission Guidelines == Participants should submit a paper (maximum 15 pages, PDF format), describing their work in topics relevant to the workshop. Accepted papers will be presented during the workshop. At least one author of an accepted contribution is expected to register for the workshop, and present the paper. All submissions should include the author's name(s), affiliation, complete mailing address, and email address. Authors are requested to prepare their submissions, following the LNCS/LNAI Springer format. Please see: http://www.springer.de/comp/lncs/authors.html for further details. The submission should be submitted through the electronic submission site: http://www.easychair.org/conferences/?conf=inap2009 The deadline for receipt of submissions is June 29, 2009. Papers received after this date will not be reviewed. Eligible papers will be peer-reviewed by at least three members of the Program Committee. Authors will be notified via email of the results by August 17, 2009. Authors of accepted papers are expected to improve their paper based on reviewers' comments and to send a camera ready version of their manuscripts by September 14, 2009. Accepted papers will be included in the workshop proceedings, which will be distributed to the participants. As in previous editions, we plan to publish selected papers in a proceedings volume in the Springer Lecture Notes in Artificial Intelligence (LNAI) series. == Organizing Committee == Vitor Nogueira vbn AT di.uevora.pt Salvador Abreu spa AT di.uevora.pt Pedro Salgueiro pds AT di.uevora.pt Universidade de Evora Portugal == Program Committee == Salvador Abreu, University of Evora, Portugal (co-chair) Sergio Alvarez, Boston College, USA Philippe Codognet, CNRS/JFLI, Tokyo, Japan Vitor Santos Costa, University of Porto, Portugal Daniel Diaz, University of Paris I, France Ulrich Geske, University of Potsdam, Germany Gopal Gupta, UT Dallas, USA Petra Hofstedt, Technical University of Berlin, Germany Ulrich Neumerkel, Technical University of Vienna, Austria Vitor Nogueira, University of Evora, Portugal Enrico Pontelli, New Mexico State University, USA Irene Rodrigues, University of Evora, Portugal Carolina Ruiz, Worcester Polytechnic Institute, USA Dietmar Seipel, University of Wuerzburg, Germany (co-chair) Terrance Swift, CENTRIA, Portugal Hans Tompits, Technical University of Vienna, Austria Masanobu Umeda, Kyushu Institute of Technology, Japan Armin Wolf, Fraunhofer FIRST, Berlin, Germany Osamu Yoshie, Waseda University, Japan == Contact Information == inap2009(a)di.uevora.pt Universidade de Evora Departamento de Informatica Largo dos Colegiais, 2 7004-516 Evora - PORTUGAL

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ANN: Reusable Corecursive Queues via Continuations
by Leon Smith 23 Jun '09

23 Jun '09

In a purely functional setting, real-time queues are traditionally thought to be much harder to implement than either real-time stacks or amortized O(1) queues. In “Circular Programs and Self-Referential Structures,” [1] Lloyd Allison uses corecursion to implement a queue by defining a lazy list in terms of itself. This provides a simple, efficient, and attractive implementation of real-time queues. Now, control-monad-queue is available on hackage [2], which offers this technique in a reusable library. As Allison's queue is not fully persistent, it cannot be a first class value; rather they are encoded in specific algorithms written in an extended continuation passing style, and the use of continuations seems necessary in order to abstract the corecursive queue operations. Also, a substantially revised draft of the associated paper, "Lloyd Allison's Corecursive Queues: Why Continuations Matter" is now available. [3] This paper will appear in the upcoming Monad Reader issue 14, and comments would be most appreciated. It derives a reusable implementation in an explicit continuation-passing style from Allison's original code, demonstrates an alternate reusable implementation in direct style using mapCont, and argues that mapCont cannot be expressed in terms of callCC, return, and (>>=). Finally, this approach performs well in practice, when compiled with optimization using GHC. However, performance has regressed from GHC 6.8.3 to 6.10.3, and there is a curious performance anomaly associated with the generalized corecursive abstraction. [1] http://www.csse.monash.edu.au/~lloyd/tildeFP/1989SPE/ [2] http://hackage.haskell.org/package/control-monad-queue [3] http://blog.melding-monads.com/2009/06/22/control-monad-queue/ Best, Leon

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ANN: haskell-src-exts-1.0.0
by Niklas Broberg 23 Jun '09

23 Jun '09

Fellow Haskelleers, It is with great pleasure I hereby announce the first stable release of the haskell-src-exts package, version 1.0.0! haskell-src-exts is a package for Haskell source code manipulation. In particular it defines an abstract syntax tree representation, and a parser and pretty-printer to convert between this representation and String. It handles (almost(*)) all syntactic extensions to the Haskell 98 standard implemented by GHC, and the parsing can be parametrised on what extensions to recognise. I wish to thank the glorious Haskell community, for giving me the chance to work on this project as part of Haskell.org's GSoC programme, but also for simply being such a nice place to be! Special thanks to everyone who helped me with testing and bug reports during the final stretch of release candidates, in particular the many excellent reports from Ganesh Sittampalam, Sebastian Fischer, and Neil Mitchell who is also mentoring the project. You're all awesome! haskell-src-exts-1.0.0: ================= Via cabal: cabal install haskell-src-exts-1.0.0 Via darcs: darcs get http://code.haskell.org/haskell-src-exts On hackage: http://hackage.haskell.org/package/haskell-src-exts-1.0.0 Changes from 0.5.7, the last release candidate: ====================================== * CPP lines are no longer ignored, which means haskell-src-exts will now invariably give a parse error on files with CPP pragmas in them. CPP is not supported by haskell-src-exts, and this is more intuitive than parsing e.g. all branches of an #if pragma, which is invariably give unintended results. * Fixed a stupid introduced bug where extensions passed int he parse mode were ignored. * fromParseOk is now exported, not just defined (doh). * ScopedTypeVariables now implies TypeOperators, as per GHC. I'm sure there are more implications that are missing from haskell-src-exts, I will add them as I find out about them. Thanks once again, and Happy Haskell Hacking to all! Cheers, /Niklas (*) The only two exceptions are NewQualifiedOperators and UnicodeSyntax.

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ICFP09 Call for Participation
by Matthew Fluet (ICFP Publicity Chair) 22 Jun '09

22 Jun '09

===================================================================== Call for Participation The 14th ACM SIGPLAN International Conference on Functional Programming (ICFP 2009) http://www.cs.nott.ac.uk/~gmh/icfp09.html Edinburgh, Scotland, 31 August - 2 September 2009 ===================================================================== ICFP 2009 provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. The conference covers the entire spectrum of work, from practice to theory, including its peripheries. Preliminary program: * Accepted papers: + http://web.cecs.pdx.edu/~apt/icfp09_accepted_papers/accepted.html * Invited speakers: + Guy Steele -- Organizing Functional Code for Parallel Execution: or, foldl and foldr Considered Slightly Harmful + Benjamin Pierce -- Lambda, the Ultimate TA: Using a Proof Assistant to Teach Programming Language Foundations +Dan Piponi -- Commutative Monads, Diagrams and Knots Schedule including related workshops: * Aug 30: ACM SIGPLAN Workshop on ML * Aug 30: ACM SIGPLAN Workshop on Generic Programming * Aug 31-Sep 2: ICFP09 * Sep 3: ACM SIGPLAN Haskell Symposium * Sep 3: ACM SIGPLAN Developer Tracks on Functional Programming * Sep 4: Commercial Users of Functional Programming * Sep 4: ACM SIGPLAN Workshop on Mechanizing Metatheory * Sep 4: ACM SIGPLAN Workshop on Approaches and Applications of Inductive Programming * Sep 5: ACM SIGPLAN Erlang Workshop * Sep 5: ACM SIGPLAN Developer Tracks on Functional Programming * Sep 5: ACM SIGPLAN Haskell Implementors Workshop Registration information: * http://www.regmaster.com/conf/icfp2009.html * Early registration deadline: July 30, 2009 Local arrangements (including travel and accommodation): * http://www.haskell.org/haskellwiki/ICFP_2009_Local_Arrangements * Conference reservation/rate deadline: July 20, 2009 * ICFP09 coincides with the final week of the Edinburgh International Festival, one of the premier arts and cultural festivals in the world. The opportunity to attend the Festival is a plus! Due to the popularity of Edinburgh during the festival period, we strongly recommend booking accommodation early. Conference organizers: * General Chair: Graham Hutton (University of Nottingham) * Program Chair: Andrew Tolmach (Portland State University) * Local Arrangements Chairs: Philip Wadler (University of Edinburgh), Kevin Hammond (University of St Andrews), and Gregory Michaelson (Heriot-Watt University) * Workshop Co-Chairs: Christopher Stone (Harvey Mudd College), and Michael Sperber (DeinProgramm) * Programming Contest Chair: Andrew Gill (University of Kansas) * Publicity Chair: Matthew Fluet (Toyota Technological Institute at Chicago) ===================================================================== ===================================================================== And, don't forget about the ICFP Programming Contest this weekend!! * http://www.icfpcontest.org * Friday, June 26 to Monday, June 29 * Organizers: Computer Systems Design Laboratory (University of Kansas)

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