July 2007 - Haskell - Haskell.org

Irrefutable patterns allowing mutually dependent functions.
by Michael Speer 27 Jul '07

27 Jul '07

Some time ago I wrote to this list linking to a regular expression engine I was writing in order to learn the Haskell programming language. I had noted the ability to send a single functions output into it as the its input and had tried using this property of the language in a rather winding way to transform a string regular expression into an integer based array of rules approximating DFAs. At the time I just smashed the stack as mutually dependent functions called one another recursively, each depending on the output of the other to execute. I didn't know a way around this, or even if Haskell provided a way around this. Yesterday a link from reddit to a site concerning `irrefutable patterns` caused me to jump back to the code and see if they allowed for what I wanted. They did. The working code can be found here : http://rx-haskell.googlecode.com/svn/trunk/rx.hs The link goes to a simple regular expression matcher a little under 200 lines long that can accept a regex string with operands (*), (*?), (?), (??), (+) and grouping using parenthesis. I hope to update the code with bracketed ranges and things soon. Any comments, questions, or criticisms from the list would be highly appreciated. - Michael Speer .

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Nirvana
by Andrzej Jaworski 27 Jul '07

27 Jul '07

Hi, I guess most of you have already watched this laughing contest: http://download.microsoft.com/download/c/d/2/cd213f37-2a1d-4b79-80a6-fc8297… s_Language_MSRCam2007.wmv It offers first hand information that the usefulness of Haskell as programming language amounts exactly to 0. This is a big surprise for me. On the contrary, I think Haskell has been getting too expressive at the expense of fundamental issues left neglected like relatively weak module system. But here up comes another surprise - this complex fancy but pragmatic sugar developed to support human reasoning was selected to manage alien low level environment. Yet another shock comes form worshiping C, C#, Java as perpetually useful. So, it seems Okasaki wrote for an alternative world. This is becoming incomprehensible for me and I shall retreat to mathematics. But perhaps my impressions could stir up some useful discussion here, as I have great sympathy for you guys:-) Best regards, -Andrzej

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ANNOUNCE: Gtk2Hs version 0.9.12 released
by Duncan Coutts 27 Jul '07

27 Jul '07

Gtk2Hs - A GUI Library for Haskell based on Gtk+ Version 0.9.12 is now available from: http://haskell.org/gtk2hs/download/ The source tarball and an installer for Windows are available. Packages for various platforms should become available soon, hopefully including Debian, Fedora, Gentoo, FreeBSD and Darwin. Changes since 0.9.11: * ps, pdf and svg cairo backends are now supported * drag & drop support added * can run mainGUI in GHCi after :reload * Graphics.SOE.Gtk now works with threaded rts and GHCi * Windows build now includes OpenGL and SourceView packages * c2hs no longer chokes on some system headers (eg glibc-2.4) * various bug fixes and minor code cleanups * major overhaul of the code generator (will help binding Gtk+ 2.10) Gtk2Hs feature highlights: * automatic memory management * Unicode support * nearly full coverage of Gtk+ 2.8 API * support for several additional Gtk+/Gnome modules: * Glade visual GUI builder * cairo vector graphics library * SVG rendering for cairo * OpenGL extension (works with HOpenGL) * GConf, Gnome's system for storing app preferences * SourceView, code editor widget with syntax highlighting * the Mozilla browser rendering engine in a widget * an implementation of the Graphics.SOE API * extensive haddock API reference documentation * multi-platform support with native look * LGPL licence Platforms and requirements: * builds from source on Linux, Windows, MacOS X, FreeBSD and Solaris * builds with GHC 6.2 - 6.6.1 * works with Gtk+ version 2.0 through to 2.10 * SVG support requires librsvg version 2.16 or later Please report all problems to gtk2hs-devel(a)sourceforge.net Contributions and feedback are also most welcome. Windows release notes: The installer expects GHC 6.6.1. As always if you need a build for a different version of GHC then that's possible by building from source. The windows build now includes the gtkglext and sourceview packages, but not svgcairo as that has pretty heavy dependencies. This makes the download a bit bigger, but on the other hand currently it includes support for only one GHC version, so overall the installer is rather smaller than in the last release. Duncan (on behalf of the Gtk2Hs team)

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View patterns in GHC: Request for feedback
by Dan Licata 26 Jul '07

26 Jul '07

Hi everyone, Simon PJ and I are implementing view patterns, a way of pattern matching against abstract datatypes, in GHC. Our design is described here: http://hackage.haskell.org/trac/ghc/wiki/ViewPatterns If you have any comments or suggestions about this design, we'd love to hear them. You can respond to this list (and we can take it to haskell-cafe if the thread gets long) or, if you prefer, directly to me. Thanks! -Dan

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KPS'07: Einladung zum Kolloquium Programmiersprachen
by Clemens Grelck 25 Jul '07

25 Jul '07

Our sincere apologies to all non German speaking readers of this mailing list for this workshop invitation in German. ====================================================================== Einladung zur Teilnahme KPS'07 Kolloquium Programmiersprachen und Grundlagen der Programmierung Timmendorfer Strand 10.-12. Oktober 2007 Anmeldeschluss: 1. August 2007 http://www.isp.uni-luebeck.de/kps07 Liebe Kollegen, das 14. Kolloquium Programmiersprachen und Grundlagen der Programmierung setzt eine traditionelle Reihe von Arbeitstagungen fort, die 1980 von den Forschungsgruppen der Professoren Friedrich L. Bauer (TU München), Klaus Indermark (RWTH Aachen) und Hans Langmaack (CAU Kiel) ins Leben gerufen wurde. Heute präsentiert sich die Veranstaltung allen interessierten deutschsprachigen Wissenschaftlern als ein offenes Forum zum zwanglosen Austausch neuer Ideen und Ergebnisse aus den Forschungsbereichen Programmiersprachen sowie Grundlagen des Programmierens. Wir würden uns freuen, Sie als Teilnehmer des 14. Kolloquiums Programmiersprachen und Grundlagen der Programmierung vom 10. bis zum 12. Oktober 2007 im Hotel Atlantis in Timmendorfer Strand an der Ostsee begrüßen zu können. Mit besten Wünschen Dr. Annette Stümpel und Dr. Clemens Grelck Institut für Softwaretechnik und Programmiersprachen Universität zu Lübeck http://www.isp.uni-luebeck.de

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math library for Haskell
by Lloyd Allison 25 Jul '07

25 Jul '07

Am I looking in the wrong place (http://haskell.org/ghc/docs/latest/html/libraries/ ) or just not seeing it, but I was hoping there would be a math library for Haskell that would include, e.g., a Gamma function and the like. -L --

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List averaging function [was: View patterns in GHC: Request for feedback]
by Brent Yorgey 24 Jul '07

24 Jul '07

Hi Man, "Difficult" is a relative term -- with study and practice, what one once considered difficult can become easy. With that said, it is true that beginners to Haskell might find it difficult to define an average function correctly since Haskell is (for good reason) picky about numeric types. If you post some specific code you are having trouble with I'm sure someone would be happy to help you. You can also join the #haskell IRC channel on freenode.net; it is populated by lots of helpful, friendly people who can answer your questions about Haskell in real-time. cheers, -Brent On 7/24/07, Manuel Hernandez <hg.manuel(a)gmail.com> wrote: > > Dear Haskellers, > why is so difficult to define a function to compute the average of > a list of > numbers?? > > Warm regards!!! > > Man > > > > > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell > >

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PLAN-X 2008 first call for papers and demos
by Ioana Manolescu 20 Jul '07

20 Jul '07

Call for Papers and Demos ========================= PLAN-X 2008 --- Programming Language Techniques for XML ACM SIGPLAN Workshop colocated with POPL 2008 San Francisco, California, USA - 9 January 2008 http://gemo.futurs.inria.fr/events/PLANX2008/ The PLAN-X 2008 workshop is the forum to present and discuss bleeding-edge research at the intersection of programming language and data base technology with an emphasis on tree-shaped data structures and their XML representation. Topics of interest are all aspects of XML processing and querying: theories, methodologies, paradigms, language designs, types, analyses, runtime aspects, implementations, tools, applications. This edition of PLAN-X is particularly interested in blending the XML processing approaches developed by the programming languages and data management communities. Expressive power and high performance are among the common goals that these communities pursue. We encourage the submission of crosscutting contributions that apply techniques from one community to problems from the other. The primary criteria for paper selection are originality, relevance, and timeliness to ensure that we can enjoy reports on ongoing and unfinished work with high potential in the workshop. Submissions =========== We seek submissions in two categories * regular papers (10 pages, 30 minutes presentation) * demo papers (4 pages, 10 minutes plenary presentation + 30 minutes slot for individual discussions shared with other demos) For details see the submission instructions on http://gemo.futurs.inria.fr/events/PLANX2008/?page=subm Important Dates =============== Submission deadline 15 October 2007 Notification 30 November 2007 Final papers due 14 December 2007 Program Committee ================= Veronique Benzaken Université de Paris-Sud 11, France Alin Deutsch University of California, San Diego, USA Wenfei Fan University of Edinburgh, UK Mary Fernandez ATT Research, USA Haruo Hosoya University of Tokyo, Japan Ralf Lämmel Universität Koblenz, Germany Sebastian Maneth National ICT and UNSW, Sydney, Australia Jim Melton Oracle Corporation, USA Michael Schwartzbach University of Aarhus, Denmark Jérôme Vouillon CNRS, France Ioana Manolescu (general chair) Gemo group, INRIA Futurs, France Peter Thiemann (program chair) University of Freiburg, Germany

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Progress in StaticDTD
by Marcel Manthe 18 Jul '07

18 Jul '07

Hello, in StaticDTD we are moving to complete statical validness against a DTD. For a (compile time) function that uses our generic combinators, we can garuantee the following: - The content model for each element is enforced (this is done by checking a type-level determined finite automaton for each content model) - The attributes are validated (not so their values yet). The check function facilitates a type-level mergesort algorithm. We are using a HList like structure and so these garuantees also hold with higher order functions. The implementation can be found at http://m13s07.vlinux.de/darcs/StaticDTD/v2 It is a mess and all of the infrastructure around it is still missing, but it shows that the concept might work. We hope to have a well-working release in very few months. Some words about related work: - WASH/HTML [1] was the original inspiration for us. It checks proper nesting of elements, but not the content model. It is a HTML, not a 'all DTDs of XML' library - HaXml [2] has two modes: one with generic combinators, which are not type-safe in respect to a DTD, and one where validity is enforced by regex-like Haskell abstract data types. With them, pattern matching can be used. - HSXML [3] has generic combinators and checkes for some nesting-properties. - BinaryNumbers.hs [4] is a great type-level implemention of numeric calculation and we are using it in our library for defining complete order and enumerate the states of a DFA. As a side-effect of our work we hope to put the type-level functions in a small seperate 'type-level programming' library, for common use. Comments are very welcome. Marcel Manthe [1] http://www.informatik.uni-freiburg.de/~thiemann/WASH/#washhtml [2] http://www.cs.york.ac.uk/fp/HaXml/ [3] http://okmij.org/ftp/Scheme/xml.html#typed-SXML [4] http://okmij.org/ftp/Haskell/types.html#binary-arithm -- View this message in context: http://www.nabble.com/Progress-in-StaticDTD-tf4106801.html#a11678520 Sent from the Haskell - Haskell mailing list archive at Nabble.com.

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Power series in a nutshell
by Doug McIlroy 17 Jul '07

17 Jul '07

For lovers of things small and beautiful, http://www.cs.dartmouth.edu/~doug/powser.html boils down basic operations on power series with numeric coefficients to the bare minimum--each is a one-liner. Included are overloaded arithmetic operators, integration, differentiation, functional composition, functional inverse and coercion from scalars. --A telling demonstration of the power of lazy evaluation and of Haskell's attunement to math. Doug McIlroy

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