June 2008 - Haskell-Cafe

Using cabal-install
by Daniel Fischer 18 Jun '08

18 Jun '08

Is there a tutorial/user's guide for cabal-install somewhere? My limited google skills haven't found one and I really need it, because there MUST be a better way to get a package and its dependencies built and the haddock documentation generated, installed and hyperlinked than manually unpacking each .tar.gz and running cabal haddock there. Thanks, Daniel

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Bit streams
by Andrew Coppin 18 Jun '08

18 Jun '08

OK, so today I tried to write my first program using the Binary library. And I've hit a snag: It appears the library will only handle data that is byte-aligned. So if I try to write three Bool values, it uses three bytes, not three bits. Before I sit down and spend 3 months designing my own library from scratch, does anybody know of an existing library that allows you to do what Binary does, but with single-bit precision? [I presume Binary is byte-aligned for efficiency...]

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Problem building GHC 6.8.3
by Daniel Fischer 18 Jun '08

18 Jun '08

Sorry, probably stupid questions for knowledgeable folks, but after having built for a couple of hours, make died with if ifBuildable/ifBuildable base; then \ cd base && setup/Setup haddock --html-location='../$pkg' \ --hyperlink-source; \ fi Preprocessing library base-3.0.2.0... Running hscolour for base-3.0.2.0... Preprocessing library base-3.0.2.0... Running Haddock for base-3.0.2.0... Warning: The documentation for package rts-1.0 is not installed. No links to it will be generated. Setup: Haddock's internal GHC version must match the configured GHC version make[1]: *** [doc.library.base] Fehler 1 make[1]: Leaving directory `/home/dafis/HasCom/ghc-6.8.3/libraries' make: *** [stage1] Fehler 2 So, what is Haddock's internal GHC version? Is it the version, haddock was built with? And what is the configured GHC version, is it the one I'm trying to build or the one I'm building with? If the former, I seem to have landed in a circulus vitiosus, if the latter, that is the GHC, haddock was built with, too. For the record: dafis@linux:~/HasCom/ghc-6.8.3> haddock --version Haddock version 2.1.0, (c) Simon Marlow 2006 Ported to use the GHC API by David Waern 2006-2008 How should I proceed now? Thanks, Daniel

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First Call for Papers: DSL WC
by Emir Pasalic 18 Jun '08

18 Jun '08

IFIP Working Conference on Domain Specific Languages (DSL WC) July 15-17, 2009, Oxford CALL FOR PAPERS Domain-specific languages are emerging as a fundamental component of software engineering practice. DSLs are often introduced when new domains such as web-scripting or markup come into existence, but it is also common to see DSLs being introduced and adopted for traditional domains such as parsing and data description. Developing software using DSLs has many benefits. DSLs are often designed based on existing notations that are already in use by experts in a given domain. As such, successful DSLs often reduce or eliminate the effort needed to transform the concept or innovation produced by the domain expert into an executable artifact or even a deliverable software product. DSL implementations can capture and mechanize a significant portion of the repetitive and mechanical tasks that a domain expert traditionally needed to perform in order to produce an executable. DSLs can in many cases capture and make widely available special expertise that only top specialists in a given domain might have. By capturing expert knowledge and reducing repetitive tasks, DSLs often also lead to software that is significantly more portable, more reliable and more understandable than it would otherwise be. DSLs can be viewed as having a dual role to general-purpose languages: whereas general purpose languages try to do everything as well as possible, DSLs are designed to find a domain where they can solve some class of problems -- no matter how small -- in the best possible way. Widely known examples of DSLs include Matlab, Verilog, SQL, LINQ, JavaScript, PERL, HTML, Open GL, Tcl/Tk, Macromedia Director, Mathematica/Maple, AutoLisp/AutoCAD, XSLT, RPM, Make, lex/yacc, LaTeX, PostScript, Excel, among many others. But while these tools have been widely successful, they still fall short of realizing the full idea behind them. The goal of this conference is to explore the extent to which incorporating modern principles of language design and software engineering can benefit existing and future domain-specific languages. The ultimate goal of using DSLs is to improve programmer productivity and software quality. Often, this is achieved by reducing the cost of initial software development as well as maintenance costs. These improvements - programs being easier to write and maintain - materialize as a result of domain-specific guarantees, analyses, testing techniques, verification techniques, and optimizations. * Paper Criteria Papers are sought addressing the research problems, fundamental principles, and practical techniques of DSLs, including but not limited to: - Foundations, including semantics, formal methods, type theory, and complexity theory - Language design, ranging from concrete syntax to semantic and typing issues - Software engineering, including domain analysis, software design, and round-trip engineering - Software processes, including metrics for software and language evaluation - Implementation techniques, including parsing, compiling, and program generation - Program analysis and automated transformation - Reverse engineering, re-engineering, design discovery, automated refactoring - Hardware/software codesign - Programming environments, including visual languages, debuggers, and testing infrastructure - Teaching DSLs and the use of DSLs in teaching - Case studies, including engineering, bioinformatics, hardware specification languages, parallel computing languages, real-time and embedded systems, and networked and distributed domains Papers will be judged on the depth of their insight and the extent to which they translate specific experience into general lessons for domain-specific language designers and implementers, and software engineers. Papers can range from the practical to the theoretical; where appropriate, they should refer to actual languages, tools, and techniques, provide pointers to full definitions and implementations, and include empirical data on results. * Important Dates - December 14th, 2008: Abstract submission due. Firm, will not have any extensions - December 21st, 2008: Paper submission deadline. Firm, will not have any extensions - February 23rd, 2009: Author notification of decisions - March 22nd, 2009: Camera ready manuscripts due * Program Committee - Jon Bentley, Avayalabs - Martin Erwig, Oregon State University - Jeff Gray, University of Alabama at Birmingham - Robert Grimm, New York University - Jim Grundy, Intel Strategic CAD Labs - Tom Henzinger, EPFL - Sam Kamin, UIUC - Dick Kieburtz, Portland State University - Ralf Lämmel, University of Koblenz - Julia Lawall, University of Copenhagen - Benjamin Pierce, University of Pennsylvania - Vivek Sarkar, Rice University - Jeremy Siek, University of Colorado at Boulder - José Nuno Oliveira, University of Minho - Doaitse Swierstra, Utrecht University - Walid Taha (Chair), Rice University - Eelco Visser, Delft University - William Waite, University of Colorado at Boulder - Stephanie Weirich, University of Pennsylvania * Organizers - General Chair: Jeremy Gibbons, Oxford University - Publicity Chair: Emir Pasalic, LogicBlox

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Haskell Weekly News: Issue 73 - June 18, 2008
by Brent Yorgey 18 Jun '08

18 Jun '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20080618 Issue 73 - June 18, 2008 --------------------------------------------------------------------------- Welcome to issue 73 of HWN, a newsletter covering developments in the [1]Haskell community. The Google Summer of Code is in full swing, preparations are underway for ICFP and the eleventh ICFP Programming Contest, and cabal-install is oh-so-sexy. It's an exciting time to be a part of the Haskell community! Community News Andy Gill has completed his move from Portland, OR to Kansas. Luke Palmer (luqui) has [2]begun work for [3]Anygma, Peter Verswyvelen's startup using Haskell (among other languages) to ``generate easy-to-use tools for creating audio-visual 2D/3D content.'' Congrats to Andy and Luke on their new beginnings! Announcements Final CFP: 2008 Haskell Symposium. Andy Gill [4]announced the final call for papers for the [5]2008 Haskell Symposium. The deadline is the 23rd of this month; please submit a paper! cabal-install. Duncan Coutts [6]announced the release of [7]cabal-install-0.5, along with the release of Cabal-1.4 to support it. It features an improved command line interface, smarter upgrading, and is made of win. If you are still stuck in the dark ages of runhaskell Setup configure blah blah, then the imperative monkeys have already won. ICFP programming contest. Tim Chevalier [8]announced the eleventh annual [9]ICFP programming contest, to be held from Friday, July 11, 2008 to Monday, July 14, 2008. Are you ready? c.h.o trac. Ian Lynagh [10]announced that it is now possible for projects on [11]community.haskell.org to [12]create themselves a trac, providing a bug tracking system and wiki. random-access-list. Stephan Friedrichs [13]announced an [14]implementation of Chris Okasaki's random-access lists, providing typical list operations (cons, head, tail) in O(1) and indexed random-access in O(log n). GHC version 6.8.3. Ian Lynagh [15]announced a [16]new patchlevel release of [17]GHC, containing a number of bugfixes relative to 6.8.2. Printf-TH. Marc Weber [18]announced that he has taken over maintenance of the [19]Printf-TH library, which implements a printf function via [20]Template Haskell, in order to guarantee that wrong argument types or the wrong number of arguments will result in compile time errors. Mueval. Gwern Branwen [21]announced the release of the [22]mueval package, providing a standalone executable for evaluating Haskell expressions based on the GHC API. Topkata. Christoph Bauer [23]announced the release of [24]Topkata, a simple OpenGL game written in Haskell. The goal is to guide a ball through a labyrinth to the opposite corner. Haddock Trac. David Waern [25]announced a new [26]bug-tracker and wiki for the [27]Haddock project. Fortress talk. Jeff Polakow [28]announced that a [29]talk on [30]Fortress, a new OO/functional language from Sun, will take place on Wednesday, June 25 at 6:30pm in Manhattan, New York, USA. ieee-0.2. Patrick Perry [31]announced the release of [32]ieee, a library that provides approximate comparison of floating point numbers based, NaN-aware minimum and maximum, and a type class for approximate comparisons. Google Summer of Code Hoogle 4. Neil Mitchell (ndm) is [33]working on Hoogle 4, recently adding support for generating Hoogle databases to [34]Haddock, using the GHC API. This week he plans to work on database creation and text searches. DPH physics engine. Roman Cheplyaka (Feuerbach) is [35]working on a physics engine using [36]Data Parallel Haskell, recently adding rotations, represented by quaternions. Next he plans to handle collisions properly with respect to rotation, and to add documentation. Generic tries. Jamie Brandon is writing a library for efficient maps using generalized tries. He has come up with a preliminary API and is [37]asking for feedback. Cabal dependency framework. Andrea Vezzosi (Saizan) is working on a make-like dependency analysis framework for Cabal, recently refining the core model, that has built its first sources in the testing environment. The next step will be dealing with preprocessor chaining. Language.C. Benedikt Huber (visq) is working on Language.C, a standalone parser/pretty printer library for C99. The test suite is finished, the parser and pretty printer support most GNU extensions, and all failing tests of gcc.dg are documented. GHC API. Thomas Schilling (nominolo) is working on improvements to the GHC API. GHC plugins. Maximilian Conroy Bolingbroke is working on dynamically loaded plugins for GHC. Discussion Low-level array performance. Dan Doel began a [38]discussion about the [39]fannkuch benchmark and the current state of Haskell support for fast low-level array operations. 1/0. Evan Laforge began a lively [40]discussion about Infinity, NaN, and Haskell's support for the IEEE floating-point standard. Documenting the impossible. Andrew Coppin began a [41]discussion on the relative merits of {-# IMPOSSIBLE #-} pragmas, calls to 'error' and 'assert', the use of tools like [42]Catch, and other methods of annotating impossible cases. Blog noise [43]Haskell news from the [44]blogosphere. * [45]PE Problem #1 in Haskell * [46]osfameron: Countdown words game solver in Haskell * [47]Algebraic Data Types in JavaScript * [48]Finance and Haskell * [49]Well-Typed.Com: New Cabal and cabal-install releases * [50]Neil Mitchell: GSoC Hoogle: Week 3 * [51]Max Bolingbroke: Compiler Plugins For GHC: The First Week * [52]Dan Piponi (sigfpe): Categories of polynomials and comonadic plumbing * [53]Roman Cheplyaka: Status report: week 3 * [54]Thomas DuBuisson (TomMD): Static Buffers Considered Harmful Quotes of the Week * ddarius: Here's the short guide to Haskell for OO programmers: Haskell isn't at all an OO language. * swalters: I'm starting to believe that learning haskell is mostly about carefully crafting small and clever functions and then finding out that they are already part of the standard library. About the Haskell Weekly News New editions are posted to [55]the Haskell mailing list as well as to [56]the Haskell Sequence and [57]Planet Haskell. [58]RSS is also available, and headlines appear on [59]haskell.org. Headlines are available as [60]PDF. To help create new editions of this newsletter, please see the information on [61]how to contribute. Send stories to byorgey at seas dot upenn dot edu. The darcs repository is available at darcs get [62]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://luqui.org/blog/archives/2008/06/18/new-job/ 3. http://anygma.com/ 4. http://article.gmane.org/gmane.comp.lang.haskell.general/16249 5. http://haskell.org/haskell-symposium/2008 6. http://article.gmane.org/gmane.comp.lang.haskell.cabal.devel/3267 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/cabal-install 8. http://article.gmane.org/gmane.comp.lang.haskell.general/16238 9. http://icfpcontest.org/ 10. http://article.gmane.org/gmane.comp.lang.haskell.general/16241 11. http://community.haskell.org/ 12. http://community.haskell.org/admin/using_project.html#trac 13. http://article.gmane.org/gmane.comp.lang.haskell.general/16237 14. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/random-access-li… 15. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/14645 16. http://haskell.org/ghc/docs/6.8.3/html/users_guide/release-6-8-3.html 17. http://www.haskell.org/ghc/ 18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41293 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Printf-TH 20. http://www.haskell.org/th/ 21. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41265 22. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mueval 23. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41263 24. http://home.arcor.de/chr_bauer/topkata.html 25. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41249 26. http://trac.haskell.org/haddock 27. http://www.haskell.org/haddock/ 28. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41235 29. http://lisp.meetup.com/59 30. http://research.sun.com/projects/plrg/ 31. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41201 32. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ieee 33. http://neilmitchell.blogspot.com/2008/06/gsoc-hoogle-week-3.html 34. http://www.haskell.org/haddock/ 35. http://physics-dph.blogspot.com/2008/06/status-report-week-3.html 36. http://www.haskell.org/haskellwiki/GHC/Data_Parallel_Haskell 37. http://article.gmane.org/gmane.comp.lang.haskell.libraries/9259 38. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/14637 39. http://shootout.alioth.debian.org/gp4/benchmark.php?test=fannkuch 40. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41368 41. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41295 42. http://www-users.cs.york.ac.uk/~ndm/catch/ 43. http://planet.haskell.org/ 44. http://haskell.org/haskellwiki/Blog_articles 45. http://jdfrens.blogspot.com/2008/06/pe-problem-1-in-haskell.html 46. http://osfameron.vox.com/library/post/countdown-words-game-solver-in-haskel… 47. http://w3future.com/weblog/stories/2008/06/16/adtinjs.xml 48. http://blog.gmosx.com/2008/06/finance-and-haskell.html 49. http://blog.well-typed.com/2008/06/new-cabal-and-cabal-install-releases/ 50. http://neilmitchell.blogspot.com/2008/06/gsoc-hoogle-week-3.html 51. http://blog.omega-prime.co.uk/2008/06/15/compiler-plugins-for-ghc-the-first… 52. http://sigfpe.blogspot.com/2008/06/categories-of-polynomials-and-comonadic.… 53. http://physics-dph.blogspot.com/2008/06/status-report-week-3.html 54. http://tommd.wordpress.com/2008/05/25/static-buffers-considered-harmful/ 55. http://www.haskell.org/mailman/listinfo/haskell 56. http://sequence.complete.org/ 57. http://planet.haskell.org/ 58. http://sequence.complete.org/node/feed 59. http://haskell.org/ 60. http://code.haskell.org/~byorgey/code/hwn/archives/20080618.pdf 61. http://haskell.org/haskellwiki/HWN 62. http://code.haskell.org/~byorgey/code/hwn/

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Fast sorting with Bytestring
by gsauthof＠TechFak.Uni-Bielefeld.DE 18 Jun '08

18 Jun '08

Hi, I played a bit around with the nice bytestring package. At some point I implemented a simple sorting program, because I needed line-sorting a file with a custom line-compare function. I was a bit surprised, that the resulting code is very fast. A lot of faster than sorting via GNU sort (with the standard line-compare function). Then I got suspicious and tested standard GNU sort against a trivial standard sort implementation in Haskell using bytestring. The Haskell implementation looks like: > module Main > where > import qualified Data.ByteString.Lazy.Char8 as B > import Data.List > main = do > c <- B.getContents > let l = B.lines c > let r = sort l > B.putStr $ B.unlines r Sorting a file of '[]'-strings I get: time ./sort < brackets > /dev/null # ~ 0.01 s time sort < brackets > /dev/null # ~ 14 s Ok, strane ... Well, let's test with some 'normal' text: time ./sort < bible > /dev/null # ~ 0.4 s time sort < bible > /dev/null # ~ 0.56 s Ok, not that different. But with Haskell you often expect to get very slow code compared to an implementation in C. And I am surprised, that the Haskell is fast _and_ nice to read - because for example the ultra fast 'wc -l' Haskell implementation from the Haskell-Wiki uses some insider-knowledge about bytestring, and looks to a beginner not that intuitive, I guess. ./sort is the shown Haskell implementation. I used ghc 6.8.2, installed bytestring 0.9.1.0 as a user-local package (don't now I this superseeds the global bytestring package), compiled via ghc -O2. The tests are run at a Pentium M 1.3 GHz computer. As GNU sort I tested the version from coreutils 6.9. You can get the test files from: http://www.techfak.uni-bielefeld.de/~gsauthof/stuff/brackets.gz http://www.techfak.uni-bielefeld.de/~gsauthof/stuff/bible.gz (obviously, you have to gunzip them after downloading ...) Of course, the naive Haskell implementation doesn't care about locales (i.e. collating locale sequences), but this shouldn't explain the observed differences sorting the brackets file. Best regards Georg Sauthoff -- Fortune : 'Real programmers don't comment their code. It was hard to write, it should be hard to understand.' ;)

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working with Random.randoms
by Stephen Howard 18 Jun '08

18 Jun '08

Hi List, I am a newcomer doing my obligatory struggling with Haskell's type system, and I've got a nut I've not been able to crack. Given: import Random random_test :: Int -> String random_test n = do g <- getStdGen take n (randoms g)::String I'm expecting that I ought to be able to pass this action an integer and get back a random string that long (given, not all characters may be printable). But GHCI tells me: RandomTest.hs:7:4: Couldn't match `[]' against `IO' Expected type: [] Inferred type: IO In a 'do' expression: g <- getStdGen In the definition of `random_test': random_test n = do g <- getStdGen take n (randoms g) :: String And yet, when I run these lines in GHCI by hand, things seem to work (though the string is the same set of random characters each time, another bit that I need to solve): Prelude> :module Random Prelude Random> g <- getStdGen Prelude Random> take 5 (randoms g)::String "\1025049\315531\882767\1032009\334825" I'm guessing that randoms is returning an IO type but I'm not sure how to go about extracting the String to return to the calling action. Changing the type signature to Int -> IO String only gives me a different error. Where am I going wrong? thanks, Stephen

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Re: [Haskell-cafe] Lambda and closures in PHP -- could someone please comment?
by PR Stanley 18 Jun '08

18 Jun '08

Blimey! Talk about rearranging the deckchairs :-) With respect, do you not think it'd be wiser for the community to deal with a total lack of proper type checking, the lack of any notion of the general concept of a function, or a whole range of other fundamental issues in PHP first before worrying about closures and lambda functions? I'm no language purist but PHP really does take the biscuit. My personal views and not in any way representing the list . Paul At 17:45 17/06/2008, you wrote: >Hi, > >The PHP community is discussing the adding of closures and lambdas to >the language, see the proposal at http://wiki.php.net/rfc/closures > >If someone with knowledge of both languages could take a quick look it >would be great. > >Thanks a lot > >Karoly Negyesi > >Ps. I am not a member of the PHP internals team, I am just a PHP >developer but I am very very interested in getting these in my >favourite language. >_______________________________________________ >Haskell-Cafe mailing list >Haskell-Cafe(a)haskell.org >http://www.haskell.org/mailman/listinfo/haskell-cafe

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Something like scan1
by Achim Schneider 18 Jun '08

18 Jun '08

Is there a generalisation of scan1, such that eg. foo (+) [0,1] (1,2) = [0,1,1,2,3,5,8,13,...] ? I came up with it while thinking about the equivalence of laziness and strictness resp. pull and push. To be more specific, I was thinking about ArrowLoop and how that beast generalises over time-varying values. It's some kind of helixoid fixed point (which might not help at all if your visualisation is incompatible with mine). -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited.

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Haskell data types and Storable class
by Galchin, Vasili 18 Jun '08

18 Jun '08

Hello, I am reading the FFI spec. Something is unclear to me. Let's assume we have data A = {b:B, .......} and data B ={ .............} both of which belong to class Storable. In the A instance of Storable I want to do a poke and peek of "b" into and out-of, respectively, B. How do I write the poke and peek function of "b" in the "instance Storable A"? thank you, Vasili

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