January 2007 - Haskell

Accessing files without typing the entire path name
by Neena Kaushik 13 Jan '07

13 Jan '07

Hello, I am trying to set up the hugs search path so that all the files from a particular directory can be loaded without giving the entire path name. I tried the following Hugs.Base> :set -P.:{Home}/lib/hugs/packages/*:/usr/local/lib/hugs/packages/*:{Hugs}/libraries:{Hugs}/packages/*:{Hugs}/oldlib:/home/nkaushik/coen70/lab1 Hugs.Base> :load lab1.hs Error - Unable to open file "lab1.hs" Hugs.Base> :load /home/nkaushik/coen70/lab1/lab1.hs Main> Could someone please help me ? Thanks. Regards, Neena Kaushik

1 0

ESSLLI 2007 Student Session - Final Call for Papers
by Ville Nurmi 12 Jan '07

12 Jan '07

[Our apologies for multiple postings of this announcement.] ESSLLI 2007 STUDENT SESSION FINAL CALL FOR PAPERS August 6-17 2007, Dublin, Ireland Deadline: February 11, 2007 http://www.loria.fr/~sustreto/stus07/ We are pleased to announce the Student Session of the 19th European Summer School in Logic, Language and Information, which will be held in Dublin, Ireland on August 6-17, 2007. We invite submission of papers in the areas of Logic, Language and Computation for presentation at the Student Session and for appearance in the proceedings. AIM Student Session exists to bring together young researchers to present and discuss their work in progress with a possibility to get feedback from senior researchers. SUBMISSION Only original publications are accepted, previous published works are not allowed. All authors of the paper must be students: undergraduate (before the completion of the Masters degree) or graduate (before the completion of the PhD degree). Papers can be submitted either for oral (20min talk+10 min discussion), or poster presentation. There are three subject areas: Logic and Language (lola), Language and Computation (laco) and Logic and Computation (loco). The submissions should be sent by email before 11 February 2007 to dmitry.sustretov(a)loria.fr (the message should have subject "ESSLLI STUS submission") along with an identification file in plain text of the following format: Title: title of the submission First author: firstname lastname Affiliation: affiliation of the first author E-mail: e-mail of the first author ...... Last author: firstname lastname Affiliation: affiliation of the last author E-mail: e-mail of the last author Abstract: (5 lines) Subject area: Logic and Language or Language and Computation or Logic and Computation Modality: Poster or Oral The submission should be in one of the following formats: PostScript, PDF or RTF. (In case of acceptance, the final version of the paper will have to be submitted in LaTeX format.) The papers must use single column A4 size pages, 11pt or 12pt fonts, and standard margins, and may not exceed 7 pages of length exclusive of references. The paper and identification file should be named by the following convention: category-modality-last name(s) of author(s) (for example, "loco-oral-martin.pdf" and "loco-oral-martin.txt"). At least one of the authors of the paper must register as a participant of ESSLLI. Accepted papers will be published in the proceedings which will be available during ESSLLI. TIMELINE Submission deadline: February 11, 2007 Notification of authors: April 20, 2007 Full paper deadline: May 20, 2007 ESSLLI: August 6-17, 2007 PROGRAM COMMITTEE Chairs: Ville Nurmi, University of Helsinki Dmitry Sustretov, LORIA Area experts: Paul Buitelaar (Language & Computation) Valentin Goranko (Logic & Computation) Carl Pollard (Logic & Language) Co-chairs: Logic & Computation Bryan Renne, City University of New York Levan Uridia, University of Amsterdam Language & Computation Luciana Benotti, INRIA Lorraine Michael Kaisser, University of Edinburgh Logic & Language Jana Häussler, University of Konstanz Miltiadis Kokkonidis, University of Oxford CONTACT The Student Session webpage is the place for relevant information. http://www.loria.fr/~sustreto/stus07/ Feel free to contact the chairs for any questions about the submissions or the Student Session in general. Ville Nurmi Phone: +358 9 191 51497 Fax: +358 9 191 51400 E-mail: ville.v.nurmi(a)helsinki.fi Dmitry Sustretov Phone: +33 3 83 59 20 35 Fax: +33 3 83 41 30 79 E-mail: dmitry.sustretov(a)loria.fr

1 0

state of HaXml?
by nr＠eecs.harvard.edu 11 Jan '07

11 Jan '07

I have some XML things to take care of, and I had hoped to use a nice functional language with combinators. But I'm having trouble getting HaXml to do anything useful. Here is a program that I wrote just to read in the XML and prettyprint it. But it fails with an error message. The 'expat' tool 'xmlwf' claims the XML is well formed, and the XML was generated from gpsbabel, a tool I trust to behave properly. And yet: : nr@curlycoat 10429 ; xmlwf 2006-12-27-backup.gpx : nr@curlycoat 10430 ; $AWD/Main 2006-12-27-backup.gpx Main: Parse error: unexpected EOF Here is Main.hs: module Main where import qualified Text.XML.HaXml as X import qualified Text.XML.HaXml.Parse as XP import qualified Text.XML.HaXml.Pretty as XPP import qualified IO import qualified System load :: String -> IO X.Document load fn = do handle <- IO.openFile fn IO.ReadMode contents <- IO.hGetContents handle IO.hClose handle return $ XP.xmlParse fn contents main = do [xml] <- System.getArgs d <- load xml IO.putStrLn $ show $ XPP.document $ d I'm using HaXml version 1.13.2-5 as distributed by Debian, with GHC 6.6. Does anyone have thoughts or suggestions? Is there software I should prefer to HaXml? (I notice that HaXml does not understand XML Schema, which I seem to be stuck with...) Norman

12 13

Beautiful concurrency: Santa Claus v2
by Simon Peyton-Jones 11 Jan '07

11 Jan '07

Friends I had lots of useful feedback about my paper "Beautiful concurrency"; thank you. I've revised it quite heavily, and have just put up a revised draft, Version 2. If you want to take a look, either for the first time, or to see what I've done in response to your suggestions, look here: http://haskell.org/haskellwiki/Talk:SantaClausProblemV2 The code is online there too. If you give your real name somewhere in your text (or email it to me), I'll add you to the acknowledgements at the end of the chapter. I'm missing some from the previous Talk page; notably, I'd like to acknowledge Steven807, Tibbe, Fanf, Garious, Rycee, Brecknell, Mvanier, Gaal, Fernando, Gknauth, EngineerScotty, BoAdler. If you'd like a mention, let me know who you are. Thanks again for your input. I must do this with all my papers! Simon

1 0

Haskell 98 syntax question
by "Sascha Böhme" 10 Jan '07

10 Jan '07

Hello, referring to the Haskell 98 report as available in the Internet, I have a short question. Section 4.1.3 (Syntax of Class Assertions and Contexts) contains the rule: class -> qtycls tyvar | qtycls ( tyvar atype1 ... atypen ) (n>=1) Is there a (simple) practical example of a Haskell type expression using the second line of the above rule? Thanks a lot, Sascha -- Der GMX SmartSurfer hilft bis zu 70% Ihrer Onlinekosten zu sparen! Ideal für Modem und ISDN: http://www.gmx.net/de/go/smartsurfer

3 2

ANNOUNCE: lhs2tex-1.12
by Andres Loeh 09 Jan '07

09 Jan '07

lhs2TeX version 1.12 ==================== We are pleased to announce a new release of lhs2TeX, a preprocessor to generate LaTeX code from literate Haskell sources. lhs2TeX includes the following features: * Highly customized output. * Liberal parser -- no restriction to Haskell 98. * Generate multiple versions of a program or document from a single source. * Active documents: call Haskell to generate parts of the document (useful for papers on Haskell). * A manual explaining all the important aspects of lhs2TeX. Changes (w.r.t. lhs2TeX 1.11) ----------------------------- * Compatible with ghc-6.6. * Compatible with cabal-1.1.6; traditional configure/make installation should still work. Thanks to Brian Smith for submitting a patch to improve the Cabal experience on Windows. Requirements and Download ------------------------- A source distribution is available from http://www.iai.uni-bonn.de/~loeh/lhs2tex/ It has been verified to build on Linux and MacOSX, but should also work on Windows. Binaries will be made available on request. You need a recent version of GHC (6.4.2 is tested, older versions might work) to build lhs2TeX, and, of course, you need a TeX distribution to make use of lhs2TeX's output. The program includes a configuration that is suitable for use with LaTeX. In theory, there should be no problem to generate code for other TeX flavors, such as plainTeX or ConTeXt. Happy lhs2TeXing, Andres Loeh and Ralf Hinze lhs2TeX(a)andres-loeh.de ralf(a)informatik.uni-bonn.de

1 0

Haskell Weekly News: January 09, 2007
by dons＠cse.unsw.edu.au 09 Jan '07

09 Jan '07

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20070109 Issue 56 - January 09, 2007 --------------------------------------------------------------------------- Welcome to issue 56 of HWN, a weekly newsletter covering developments in the [1]Haskell community. More libraries and applications for the new year, and the Haskell Hackathon gets underway! 1. http://haskell.org/ Announcements Happy: LALR(1) parser generator. Simon Marlow [2]announced version 1.16 of [3]Happy, the parser generator system for Haskell. Changes from version 1.15 to 1.16 include switching to Cabal, a new %error directive, new production forms, and attribute grammar support. Happy version 1.16 is required for building GHC version 6.6 and later. 2. http://article.gmane.org/gmane.comp.lang.haskell.general/14726 3. http://www.haskell.org/happy/ Alex: lexical analyser generator. Simon Marlow [4]announced version 2.1.0 of [5]Alex. Changes in Alex 2.1.0 vs. 2.0.1 include switching to Cabal, and slight changes to the error semantics. 4. http://article.gmane.org/gmane.comp.lang.haskell.general/14728 5. http://www.haskell.org/alex/ rdtsc: reading IA-32 time register. Martin Grabmueller [6]announced version 1.0 of [7]package rdtsc has just been released. This small package contains one module called [8]'Rdtsc.Rdtsc', providing the function 'rdtsc' for accessing the 'rdtsc' machine register on modern IA-32 processors. This is a 64-bit counter which counts the number of processor cycles since the machine has been powered up. Using this instruction, you can make very precise time measurements which are independent of the actual CPU frequency. 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/18095/ 7. http://uebb.cs.tu-berlin.de/~magr/projects/rdtsc/ 8. http://uebb.cs.tu-berlin.de/~magr/darcs/rdtsc/ monadLib 3.0. Iavor Diatchki [9]announced a new version of [10]monadLib, a collection of standard monad implementations. Some of the changes compared to the previous version: the whole library is in a single module MonadLib.hs (~500 lines); simpler and more symmetric API; removed the (generic) monadic combinators; removed the search transformer; rewrote some transformers in the 'traditional' way (exceptions and output); there is an optional module that defines base monads corresponding to each transformer. 9. http://article.gmane.org/gmane.comp.lang.haskell.general/14714 10. http://www.csee.ogi.edu/~diatchki/monadLib Shellac 0.6. Robert Dockins [11]announced a simultaneously release of the following related packages: Shellac 0.6 Shellac-readline 0.3 and Shellac-vty 0.1. [12]Shellac is a framework for building read-eval-print style shells which uses configurable backend plugins. The major new feature of this release is the new Shellac-vty backend package, which uses the [13]new Vty library terminal I/O directly. It currently has basic line editing keybindings, paging, and a command history. The main package and Shellac-readline updates consist of minor API updates. 11. http://article.gmane.org/gmane.comp.lang.haskell.general/14715 12. http://www.eecs.tufts.edu/~rdocki01/shellac.html 13. http://members.cox.net/stefanor/vty/ IntelliJIDEA for Haskell. Tony Morris [14]announced syntax highlighting support for [15]Haskell in IntellijIDEA, released under a BSD licence. 14. http://article.gmane.org/gmane.comp.lang.haskell.general/14719 15. http://www.workingmouse.com/research/IntelliJIdea%2DHaskell/ Yampa + GADT for GHC 6.6. Joel Reymont [16]announced a cabalized [17]version of Yampa + GADT for GHC 6.6. Joel also sought comments on cabalisation, testing and example for this package. 16. http://article.gmane.org/gmane.comp.lang.haskell.cafe/18215 17. http://wagerlabs.com/yampa HNOP. Ashley Yakeley [18]updated the status of [19]HNOP, the Haskell library for doing nothing. It has recently been split into two Cabal packages: 'nop', a library of no-op services, and 'hnop', a program that uses nop to do nothing. Both packages can be found in darcs. The two packages are intended to be templates for Cabal projects, so I'm interested in making them as canonical and 'best practices' for packaging libraries and executables. 18. http://article.gmane.org/gmane.comp.lang.haskell.general/14720 19. http://semantic.org/hnop/ Haskell' This section covers the [20]Haskell' standardisation process. * [21]Rough draft of informal pattern-guard (qualifiers) explanations 20. http://hackage.haskell.org/trac/haskell-prime 21. http://article.gmane.org/gmane.comp.lang.haskell.prime/1982 Discussion instance Monad Set, using GADTs. Roberto Zunino [22]announced a definition of the Set datatype, with the usual operations, such that it can be made a member of the Monad class. 22. http://article.gmane.org/gmane.comp.lang.haskell.cafe/18118 GADTs are expressive. Jim Apple [23]described a data type which holds only those terms of the untyped lambda calculus that are reducible to normal form, using GADTs 23. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/18210/focus=18210 Hackage interface. Ross Paterson [24]set up (temporarily) a simple first cut at an [25]interface to the Hackage package database. On a related note, there was some [26]discussion for home pages for Hackage projects, and collecting statistics. 24. http://article.gmane.org/gmane.comp.lang.haskell.libraries/6025 25. http://ross-paterson.dyndns.org/~ross/hackage/ 26. http://article.gmane.org/gmane.comp.lang.haskell.libraries/6035 Conference roundup The Haskell Hackathon. Hac 2007 [27]is being held this week, January 10-12th, in Oxford, with around 20 Haskell coders from across the world gathering to hack on libraries and practical tools for Haskell. Work is planned for at least hackage, Cabal, bytestrings, binary IO, http, GHC, YHC, Hoogle, DrHaskell, WinHugs, GHCi debugger, crypto, QuickCheck 2, Haddock and more besides. Notably, some graduates from this year's Google Summer of Code projects will be attending, with plans to integrate their work into the main project branches. Happy hacking everyone! 27. http://haskell.org/haskellwiki/Hac_2007 Blog noise [28]Haskell news from the blogosphere. * [29]Liberating Myself from the von Neumann Style * [30]First impressions of Haskell: Whoa! * [31]Comparing Gzip Code Reduction * [32]Simple demonstration of Haskell FFI * [33]Does Functional Programming Matter? * [34]2006 in review * [35]Haskell script to replace tabs * [36]Functional programming is functional * [37]The shock of the forgotten * [38]Category theory * [39]Does Haskell need macros? * [40]On darcs * [41]Learning things * [42]Folds for imperative programmers * [43]Dammit all! I've been blubbed * [44]Getting started with installing third-party Haskell packages * [45]A Nice Way to Learn FP * [46]Learning Haskell * [47]Haskell and Eclipse * [48]Haskell and Eclipse: building a server executable * [49]What makes a programming language more productive? * [50]Composability and Productivity * [51]Arithmetic coding in Haskell * [52]A quick and dirty theorem prover in Haskell * [53]Haskell is Fun! * [54]2007, the year of software reliability? * [55]Haskell, bondage-and-discipline and separation-of-concerns programming * [56]Type systems as safety belts * [57]It's Haskell! * [58]Two promising Haskell projects: Vital and Pivot * [59]Exceptions and interrupts 28. http://planet.haskell.org/ 29. http://blogs.nubgames.com/code/?p=4 30. http://blogs.nubgames.com/code/?p=15 31. http://blogs.nubgames.com/code/?p=16 32. http://blog.acolyte.co.za/articles/2007/01/01/simple-demonstration-of-haske… 33. http://denkspuren.blogspot.com/2007/01/does-functional-programming-matter.h… 34. http://koweynlg.blogspot.com/2006/12/state-of-thesis-2006-12-31.html 35. http://chill-yo.blogspot.com/2007/01/haskell-code-replace-tabs.html 36. http://gearon.blogspot.com/2006/10/functional-programming-is-functional.html 37. http://www.serpentine.com/blog/2007/01/01/the-shock-of-the-forgotten/ 38. http://comblog.net/hnbeck/archive/2007/01/05/2384.aspx 39. http://neilmitchell.blogspot.com/2007/01/does-haskell-need-macros.html 40. http://simulacra.in/2007/01/darcs/ 41. http://koweynlg.blogspot.com/2007/01/zommmmbieeee.html 42. http://blog.tmorris.net/folds-for-imperative-programmers/ 43. http://withoutane.com/rants/2007/01/damn-you-haskell 44. http://www.serpentine.com/blog/2007/01/05/getting-started-with-installing-t… 45. http://monadnation.blogspot.com/2007/01/nice-way-to-learn-fp.html 46. http://www.timeblog.net/2007/01/06/haskell/ 47. http://cohatoe.blogspot.com/2006/12/simple-example-walkthrough-ii.html 48. http://cohatoe.blogspot.com/2007/01/building-server-executable.html 49. http://kawagner.blogspot.com/2007/01/what-makes-programming-language-more.h… 50. http://cogito.blogthing.com/2007/01/07/composablility-and-productivity/ 51. http://vandreev.wordpress.com/2007/01/07/arithmetic-coding/ 52. http://vandreev.wordpress.com/2006/12/24/quick-and-dirty-theorem-prover/ 53. http://onthebalcony.wordpress.com/2007/01/08/haskell-is-fun/ 54. http://jguk.org/2007/01/2007-year-of-software-reliability.html 55. http://syntaxfree.wordpress.com/2007/01/08/haskell-bondage-and-discipline-a… 56. http://programming.reddit.com/info/xbc7/comments/cxfs0 57. http://e-scribe.com/news/322 58. http://factor-language.blogspot.com/2007/01/two-promising-haskell-projects.… 59. http://www.weaselhat.com/2007/01/08/exceptions-and-interrupts/ Quotes of the Week * Eric: The Haskell [code] contains no redundancy. In fact, in all the [Haskell] code I've written, in both production and play, each idea is expressed once and only once. It is the Zen ideal of perfect code. And thats never happened to me before. * nostrademons: Haskell is in a similar position [to Scala] - a complex language with many sustaining innovations - but it has one major disruptive innovation. Purity. Now, the question is whether that can be leveraged in a way that makes it useful in some market that existing imperative languages can't reach. My bets are on concurrency... * Excedrin: Isn't OO deprecated? * dpiponi: [monochrom] Nevermind monads. Use arrows. Come join the Dart Side! [dpiponi] Never mind arrows. Use comonads. Cojoin the other side. * nilsi: #haskell is better than Google * sigfpe: I think Haskell is a great language for short attention spans. You can get so much done in one line before you get bored. * timthelion: Oh wait, I LOVE foldr!! And I have only been learning Haskell for hours * kowey: All the things with guards are just there to siphon off the weirdos * Eric: [Haskell] astonishes me at every turn with its beauty and elegance. I've never felt such power. Haskell has brought back a joy in programming that I didnt even know I was missing. * Paul Johnson: Mutable state is actually another form of manual memory management: every time you over-write a value you are making a decision that the old value is now garbage, regardless of what other part of the program might have been using it. About the Haskell Weekly News Each week, new editions are posted to [60]the Haskell mailing list as well as to [61]the Haskell Sequence and [62]Planet Haskell. [63]RSS is also available, and headlines appear on [64]haskell.org. Headlines are available as [65]PDF. To help create new editions of this newsletter, please see the [66]contributing information. Send stories to dons at cse.unsw.edu.au. The darcs repository is available at darcs get [67]http://www.cse.unsw.edu.au/~dons/code/hwn 60. http://www.haskell.org/mailman/listinfo/haskell 61. http://sequence.complete.org/ 62. http://planet.haskell.org/ 63. http://sequence.complete.org/node/feed 64. http://haskell.org/ 65. http://www.cse.unsw.edu.au/~dons/code/hwn/archives/20070109.pdf 66. http://haskell.org/haskellwiki/HWN 67. http://www.cse.unsw.edu.au/~dons/code/hwn

1 0

ANNOUNCE: Alex version 2.1.0
by Simon Marlow 08 Jan '07

08 Jan '07

I am pleased to announce version 2.1.0 of Alex, the lexical analyser generator for Haskell. Changes in Alex 2.1.0 vs. 2.0.1: * Switch to a Cabal build system: you need a recent version of Cabal (1.1.6 or later). If you have GHC 6.4.2, then you need to upgrade Cabal before building Alex. GHC 6.6 is fine. * Slight change in the error semantics: the input returned on error is before the erroneous character was read, not after. This helps to give better error messages. Distributions can be obtained from Alex's home page: http://www.haskell.org/alex/ Alex is distributed under a BSD-style license. Cheers, Simon

1 0

Fast Packed Strings Question
by Dominic Steinitz 07 Jan '07

07 Jan '07

After a lay off from Haskell for a few months and preparatory to Hac 07, I thought I had better check my laptop was appropriately set up. However, I encountered the following: C:\Documents and Settings\Owner\crypto>Setup build Preprocessing library Crypto-3.1.0... Preprocessing executables for Crypto-3.1.0... Building Crypto-3.1.0... Data/Digest/SHA1.hs:36:17: Could not find module `Data.ByteString': it was found in multiple packages: fps-0.8 base What's the story with fast packed strings these days? Is it now part of base and I shouldn't have installed it? If not, can someone remind me how I hide the module in base? Thanks, Dominic.

2 1

HNOP Status
by Ashley Yakeley 06 Jan '07

06 Jan '07

For code designed not to do anything, HNOP has high hopes. I have recently split the project into two Cabal packages: "nop", a library of no-op services, and "hnop", a program that uses nop to do nothing. Both packages can be found in this repository: darcs get http://semantic.org/hnop/ First and foremost the two packages are intended to be templates for Cabal projects, so I'm interested in making them as canonical and "best practices" as possible. I'm not so interested in showing off clever Haskell programming idioms for doing nothing, unless there's some expository benefit relating to the Cabal or Haddock infrastructure. For instance, in the nop package, "runhaskell Setup test" works. It runs "make" in the "test" directory, which compiles a program and runs it, and then diffs it against reference output. But should I be using QuickCheck or something here? Is there some well-known or Cabal-approved way to run tests on a package? Please send me patches licensed under the simple permissive license in the LICENSE files if you have any improvements. Or I can move this to darcs.haskell.org if it's appropriate. -- Ashley Yakeley Seattle, WA

2 1