January 2009 - Haskell-Cafe

ANN: HDBC v2.0 now available
by John Goerzen 02 Feb '09

02 Feb '09

Hi everyone, I'm pleased to announce that HDBC v2.0 is now available. Simultaneously, HDBC-sqlite3, HDBC-postgresql, and HDBC-odbc v2.0 have also been uploaded. All may be found from Hackage, or at software.complete.org. A guide to new features and migration can be found at: http://software.complete.org/software/wiki/hdbc/NewIn20 A partial summary of it follows: New Features: * Pervasive Unicode support now part of the HDBC API and implemented by all backend drivers. Based on utf8-string and conversions between UTF-8 ByteStrings and Haskell Strings. * Full support for GHC 6.10 is new. Full support for GHC 6.8 is maintained. * Native support for the new exception handling in GHC 6.10, with CPP conditional compilation to continue supporting the old-style exceptions for users of GHC 6.8 or Hugs. * HDBC now has direct support for marshalling virtually all of the Data.Time.* types to and from SQL database date/time types. toSql and fromSql/safeFromSql now support conversions between Data.Time.* types and SqlValue. Conversions between System.Time.* types were present from the beginning and will remain. Automatic conversions are, of course, contingent on support in database engines and HDBC database backend drivers and may not be possible with all databases. * Major expansion of SqlValue to be able to carry date/time data to/from databases in terms of Data.Time.* types. + The old SqlTimeDiff and SqlEpochTime types continue to be present, but are deprecated and will be removed in a future. toSql no longer converts anything to them. The System.Time.* types are converted to the new Data.Time-based SqlValues. It should be exceptionally rare that any user code would use these types directly, but they are being retained in this version out of an abundance of caution. * Replace fromSql with safeFromSql, which returns Left on impossible conversions instead of raising an exception. + Wrote a new fromSql that behaves just like the old one, but is implemented in terms of safeFromSql. It converts the safeFromSql errors to exceptions. + The new structure made it possible to greatly enhance many error messages throughout the conversion process instances. + Removed SqlType typeclass. Re-implemented SqlValue conversions in terms of the generic infrastructure in the convertible package. Simplified code significantly due to this. * Lots of additional docs. * New skeleton test suite for HDBC itself (to be expanded upon later). Richer Date and Time Support HDBC 1.x had only two ways of getting dates and times between Haskell and a database: an epoch (an Integer representing the number of seconds since midnight Jan 1 1970 UTC) and an Integer representing a TimeDiff (a count of elapsed time). While this approach could represent a precise instant in time, it was not always the most helpful. Most notably, you might sometimes want to load date information without time, time without date, or record what timezone the time was measured within. HDBC can now convert all of these things with much greater precision. Thanks to Phil Wise for adding the first Unicode support (to HDBC-postgresql originally) and to Alson Kemp for adding the first advanced date/time marshalling support (also to HDBC-postgresql originally). The experience of adding these features to a single backend driver first made clear a good way to add them to HDBC API as a whole. -- John

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UDP
by Andrew Coppin 02 Feb '09

02 Feb '09

I'm trying to write a simple program that involves UDP. I was hoping something like this would work: module Main where import Network.Socket main = withSocketsDo main2 main2 = do s <- socket AF_INET Datagram defaultProtocol putStrLn "Waiting..." x <- recv s 100 putStrLn x Unfortunately, that doesn't work at all. It immediately throws an exception ("unknown error"). But then, the whole module seems to be completely undocumented. I managed to find a tiny amount of info online about the underlying C API, but I still don't get how the Haskell interface is supposed to be used. Any hints?

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Takusen 0.8.3 install problems
by Praki Prakash 01 Feb '09

01 Feb '09

I am trying to install Takusen 0.8.3 with ghc 6.10.1 on Ubuntu 8.04 (same issue on Win XP as well). I get the following complaint from cabal. Module `Distribution.PackageDescription' does not export `writeHookedBuildInfo' cabal: Error: some packages failed to install: Takusen-0.8.3 failed during the configure step. The exception was: exit: ExitFailure 1 Any suggestions on how to fix this issue? Thanks, Praki

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can't build testpack
by Ezekiel Smithburg 31 Jan '09

31 Jan '09

this is the error message i get: ezekiel-smithburgs-macbook-pro-15% runhaskell Setup.* build Preprocessing library testpack-1.0.0... Building testpack-1.0.0... [1 of 3] Compiling Test.QuickCheck.Instances ( src/Test/QuickCheck/Instances.hs, dist/build/Test/QuickCheck/Instances.o ) [2 of 3] Compiling Test.QuickCheck.Tools ( src/Test/QuickCheck/Tools.hs, dist/build/Test/QuickCheck/Tools.o ) [3 of 3] Compiling Test.HUnit.Tools ( src/Test/HUnit/Tools.hs, dist/build/Test/HUnit/Tools.o ) src/Test/HUnit/Tools.hs:28:36: Class `Control.Exception.Exception' used as a type In the type `Control.Exception.Exception' In the type `Control.Exception.Exception -> IO a -> IO ()' In the type `String -> Control.Exception.Exception -> IO a -> IO ()' what should i do? need this in order to build hdbc 2.0, which i'm hoping solves a problem i was having earlier (memory leak).

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Buttons and Clicks - State Monad
by guenni68 31 Jan '09

31 Jan '09

Hi, in this piece here http://moonpatio.com/fastcgi/hpaste.fcgi/view?id=1083#a1083 I'm trying to create a button that, every time when clicked, increases a counter by one and does a putStrLn of the counters current value. I'm trying to write this without any use of IORef but merely using the state monad. Can anybody show me how to do this? Günther The UI Code is wxHaskell

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Haskell Weekly News: Issue 103 - January 31, 2009
by Brent Yorgey 31 Jan '09

31 Jan '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090131 Issue 103 - January 31, 2009 --------------------------------------------------------------------------- Welcome to issue 103 of HWN, a newsletter covering developments in the [1]Haskell community. Announcements HDBC v2.0 now available. John Goerzen [2]announced that [3]HDBC v2.0 is now available. Simultaneously, [4]HDBC-sqlite3, [5]HDBC-postgresql, and [6]HDBC-odbc v2.0 have also been uploaded to Hackage. A guide to new features and migration can be [7]found here. Extensible and Modular Generics for the Masses: emgm-0.2. Sean Leather [8]announced the second major release of [9]Extensible and Modular Generics for the Masses (EMGM), a library for generic programming in Haskell using type classes and a sum-of-products view. Improvements over emgm-0.1 include type representation derivation using Template Haskell, documentation improvements, a bimap function, and more. incremental-sat-solver. Sebastian Fischer [10]announced the [11]incremental-sat-solver library, which provides an implementation of the [12]Davis-Putnam-Logemann-Loveland algorithm for the Boolean satisfiability problem. It not only allows solving Boolean formulas in one go, but also adding constraints and query bindings of variables incrementally. data-spacepart - space partitioning data structure[s] (initial release). Corey O'Connor [13]announced the [14]data-spacepart package, the goal of which is to be a collection of space partitioning data structures. Currently, there is only a simple quadtree implementation. Wired 0.2. Emil Axelsson [15]announced a new release of [16]Wired. The most important news in this release is that it now contains a 45nm cell library, which means that you can use Wired to create and analyze modern VLSI designs today! CFP Haskell Symposium 2009. Stephanie Weirich [17]announced a call for papers for the [18]2009 Haskell Symposium in Edinburgh, Scotland. The deadline for submissions is May 8. testpack (first release). John Goerzen [19]announced the release of [20]testpack, a collection of a few utilities for tests: some tools to convert QuickCheck properties into HUnit test cases, and various shortcuts and tools to increase verbosity while running tests in both QuickCheck and HUnit. convertible (first release). John Goerzen [21]announced a new package, [22]convertible. At its heart, it's a very simple typeclass that's designed to enable a reasonable default conversion between two different types without having to remember a bunch of functions. The return type from this conversion is "Either ConvertError a", and conversions are expected to do sanity checking (such as bounds checking when converting to types like Int), so as to produce neither garbage nor exceptions as part of the conversion process. The package also includes instances of the Convertible typeclass for common type conversions. working with numeric types as well as dates and times. Notably, it has code to convert between System.Time types and their Data.Time siblings, and vice versa, a capability I found annoyingly lacking in the standard library. Progress with IDE. Juergen Nicklisch-Franken [23]announced that the [24]Leksah 0.4.0 pre-release is now available. Current features include a Haskell customized editor with candy, project management support based on Cabal, a visual editor for Cabal files, navigation aids, a module browser, session support, and more. Hayoo! beta 0.3. Timo B. [25]announced the next beta version 0.3 of [26]Hayoo!, the Haskell API search engine with find-as-you-type and suggestions. Hayoo! now works even if your browser does not support JavaScript. DecisionTree 0.0. Adrian Neumann [27]announced the [28]DecisionTree package, which provides an implementation of the ID3 algorithm and can be used to classify data with discrete valued attributes. orchid-0.0.7. Sebastiaan Visser [29]announced a new release of [30]Orchid, just another Haskell Wiki. This release features a number of improvements, including a [31]filestore backend, searching, deleting and renaming support, and more. Check out the [32]demo. gitit 0.5. John MacFarlane [33]announced the latest release of [34]Gitit, the multitalented distributed wiki written in Haskell. This release uses the [35]filestore library and hence also supports a darcs backend, and also features optimizations, better search, better diffs, and more. You can check out a [36]running example. filestore 0.1. Gwern Branwen [37]announced [38]filestore 0.1, which provides a uniform, abstract, generic interface for storing versioned files on disk. It allows calling programs to use generic commands to store strings or binary data and perform various queries, such as 'what files are in this repository?' or 'what were the contents of this file at revision XXXXXXX?' or 'give me a diff of this file between revision XXXXXXX and revision YYYYYYY.' Because the interface is abstract, the calling program is insulated from the messy details of the backend (which might be a VCS or a database). Darcs and Git are fully supported. There are plans for a SQLite backend. Scurry :: A cross platform (if you put your mind to it) P2P VPN. John Van Enk [39]announced the release of [40]Scurry, a P2P VPN application written in Haskell (and a little C). Discussion Why binding to existing widget toolkits doesn't make any sense. Achim Schneider began an interesting [41]discussion on the proper approach to GUI toolkits in Haskell. Laws and partial values. Henning Thielemann began [42]a long thread on the semantics of laws (such as the monoid laws). Blog noise [43]Haskell news from the [44]blogosphere. * Sebastian Fischer: [45]Using SmallCheck to Shatter an Audacious Claim. * Xmonad: [46]Quad head xmonad. * Darcs: [47]darcs weekly news #15. * Osfameron: [48]More longest paths, and sick folds.. * Eric Kow (kowey): [49]haskell-ji. * Jeff Heard: [50]Control.Monad.IfElse. * Conal Elliott: [51]What is automatic differentiation, and why does it work?. * Luke Palmer: [52]Fun with PiSigma. * Neil Mitchell: [53]Small scripts with Haskell. * LHC Team: [54]Release notes.. * LHC Team: [55]Thoughts on a new code generator. * Xmonad: [56]contribs review: ThreeColumnsMiddle, CenteredMaster, Mosaic. * Osfameron: [57]There's the nub (snippet in Perl and Haskell). * Malcolm Wallace: [58]codec implementations. * Sebastian Fischer: [59]Fun with Infinite Global Constants. Just-in-time, memoized binomial coefficients. * Chris Done: [60]Some libgd changes. * Luke Palmer: [61]A world without orphans. Luke muses on the benefits to be gained by outlawing orphan instances. * Creighton Hogg: [62]Fear of releasing code. * LHC Team: [63]Thoughts on a new code generator. * Don Stewart (dons): [64]What is Haskell good for?. Lots of things, if this tag cloud has anything to say about it. * Arch Haskell News: [65]Haskell wiki stack in Arch. * Conal Elliott: [66]Comparing formulations of higher-dimensional, higher-order derivatives. * Conal Elliott: [67]Fostering creativity by relinquishing the obvious. * Arch Haskell News: [68]Arch Haskell News: Jan 11 2009. * Dan Piponi (sigfpe): [69]Fast incremental regular expression matching with monoids. A very cool article showing how to use fingertrees storing memoized automaton transition functions to do fast incremental regular expression matching (or, in general, fast incremental lexing). Quotes of the Week * lilac: is happy with his infinite type. it's ducks all the way across and down. * Gracenotes: You are likely to be eaten by a poset * RossMellgren: Apparently 64-bit GHC is sufficiently advanced to be indistinguishable from magic. * cjb: It's all fun and games until somebody loses an IOVar. * sigfpe: If I took some Ritalin, maybe I could write an entire book on Haskell and algebra. * ddarius: Nothing is evaluated until it is. About the Haskell Weekly News New editions are posted to [70]the Haskell mailing list as well as to [71]the Haskell Sequence and [72]Planet Haskell. [73]RSS is also available, and headlines appear on [74]haskell.org. To help create new editions of this newsletter, please see the information on [75]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [76]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51664 3. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HDBC 4. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HDBC%2Dsqlite3 5. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HDBC%2Dpostgresql 6. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HDBC%2Dodbc 7. http://software.complete.org/software/wiki/hdbc/NewIn20 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51646 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/emgm 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51564 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/incremental-sat-… 12. http://en.wikipedia.org/wiki/DPLL_algorithm 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51505 14. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/data-spacepart 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51484 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Wired 17. http://article.gmane.org/gmane.comp.lang.haskell.general/16818 18. http://haskell.org/haskell-symposium/2009/ 19. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51482 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/testpack 21. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51481 22. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/convertible 23. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51475 24. http://www.leksah.org/ 25. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51450 26. http://holumbus.fh-wedel.de/hayoo 27. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51407 28. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/DecisionTree 29. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51395 30. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/orchid 31. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/filestore 32. http://funct.org/wiki/ 33. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51392 34. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/gitit 35. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/filestore 36. http://gitit.johnmacfarlane.net/ 37. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51388 38. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/filestore 39. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51364 40. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Scurry 41. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/51478 42. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/51299 43. http://planet.haskell.org/ 44. http://haskell.org/haskellwiki/Blog_articles 45. http://www-ps.informatik.uni-kiel.de/~sebf/haskell/smallcheck-experience.ht… 46. http://xmonad.wordpress.com/2009/01/31/quad-head-xmonad/ 47. http://blog.darcs.net/2009/01/darcs-weekly-news-15.html 48. http://greenokapi.net/blog/2009/01/31/more-longest-paths-and-sick-folds/ 49. http://koweycode.blogspot.com/2009/01/haskell-ji.html 50. http://vis.renci.org/jeff/?p=96 51. http://conal.net/blog/posts/what-is-automatic-differentiation-and-why-does-… 52. http://lukepalmer.wordpress.com/2009/01/28/fun-wth/ 53. http://neilmitchell.blogspot.com/2009/01/small-scripts-with-haskell.html 54. http://lhc-compiler.blogspot.com/2009/01/release-notes.html 55. http://lhc-compiler.blogspot.com/2009/01/thoughts-on-new-code-generator.html 56. http://xmonad.wordpress.com/2009/01/27/contribs-review-threecolumnsmiddle-c… 57. http://greenokapi.net/blog/2009/01/27/theres-the-nub-snippet-in-perl-and-ha… 58. http://feeds.feedburner.com/~r/malcolm/~3/523603226/codec-implementations.h… 59. http://www-ps.informatik.uni-kiel.de/~sebf/haskell/infinite-constants.html 60. http://chrisdone.com/blog/2009/01/26/Some-libgd-changes 61. http://lukepalmer.wordpress.com/2009/01/25/a-world-without-orphans/ 62. http://abstractabsurd.blogspot.com/2009/01/fear-of-releasing-code.html 63. http://lhc-compiler.blogspot.com/2009/01/thoughts-on-new-code-generator.html 64. http://donsbot.wordpress.com/2009/01/24/what-is-haskell-good-for/ 65. http://archhaskell.wordpress.com/2009/01/25/haskell-wiki-stack-in-arch/ 66. http://conal.net/blog/posts/comparing-formulations-of-higher-dimensional-hi… 67. http://conal.net/blog/posts/fostering-creativity-by-relinquishing-the-obvio… 68. http://archhaskell.wordpress.com/2009/01/11/arch-haskell-news-jan-11-2009/ 69. http://sigfpe.blogspot.com/2009/01/fast-incremental-regular-expression.html 70. http://www.haskell.org/mailman/listinfo/haskell 71. http://sequence.complete.org/ 72. http://planet.haskell.org/ 73. http://sequence.complete.org/node/feed 74. http://haskell.org/ 75. http://haskell.org/haskellwiki/HWN 76. http://code.haskell.org/~byorgey/code/hwn/

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Re[Haskell-cafe] cursive referencing
by Belka 31 Jan '09

31 Jan '09

Hello! I'm puzzled, if in Haskell it's possible to create a (pure) data structure, consisting of 2 substructures referencing each other: ------------------------- data AA = AA { someData1 :: SomeData1 bb :: BB } data BB = BB { someData2 :: SomeData2 aa :: AA } f :: SomeData1 -> SomeData2 -> AA f somedata1 somedata2 = ?????????? -- Always True: ghci> f == aa $ bb f True ------------------------- Any ideas? Belka -- View this message in context: http://www.nabble.com/Recursive-referencing-tp21722002p21722002.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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GHCi Memory Leak in Windows Vista
by spam.andir＠gmail.com 31 Jan '09

31 Jan '09

Hi all! Environment: Windows Vista + SP1, GHC 6.10.1. Description: If use ghci.exe and run separate ghc.exe compiler process, memory leak in ghci occurred. After exhausting available memory Vista has no responding. Steps for reproduce: 1) After run GHCi, process list has 2 processes: ghci.exe (a), ghc.exe (b), 2) Then I run separated compilation process 20 times: Command Line: for /L %i in (1,1,20) do ghc -fforce-recomp -O --make "problem.hs" -o "problem.exe" Sample Haskell Program listing (problem.hs): main :: IO () main = do print $ [x | x <- [1..]] putStrLn "Hello, world!" 3) In process list (taskmgr.exe) I can see some processor activity and increasing value of "Memory (Private Working Set)" for process (b). 4) After run "Memory (Private Working Set)" increased about 100Mb. Best regards.

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darcs-client on ghc 6.10.1
by Phil 30 Jan '09

30 Jan '09

Hi, Was wondering if anyone knew if darcs-server is still maintained? The author¹s e-mail address bounces. The Haskell client is broken in ghc 6.10. I have a straightforward fix for it: phil$ darcs whatsnew hunk ./client/build 2 -ghc -Wall -O2 -o darcs-client -package network Http.hs DarcsClient.hs +ghc -Wall -O2 -o darcs-client.exe -package base-3.0.3.0 -package network Http.hs DarcsClient.hs Phil.

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UI-state, using State Monad or IORef?
by guenni68 30 Jan '09

30 Jan '09

Hi, at one point I generate n elements of dropdowns dynamically. Whenever I make a selection in any of those choices the others should also be updated, ie. the list of available choices needs to be altered. But I also need to update in place the "model" that is associated with each individual dropdown. Should I simply use IORefs for this purpose, or should I rather use a more functional code with the State Monad? Is there a tutorial or an example on how to use the State monad? Günther

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