- Haskell - Haskell.org

HDBC Transactions with Sqlite3
by Tom Hawkins 15 Jan '06

15 Jan '06

I have HDBC running with Sqlite3, but I'm getting a SqlError due to a locked table. Please excuse my SQL ignorance, but what may be causing the problem? In SQL, are we not allowed to select, update, and delete from a table within a single transaction? If not, what are the rules for transactions? Thanks for any help! -Tom SELECT * FROM freeKey; SELECT * FROM nextKey; INSERT INTO nextKey VALUES (1); SELECT * FROM freeKey; SELECT * FROM nextKey; UPDATE nextKey SET key = 2 WHERE key = 1; SELECT * FROM freeKey; SELECT * FROM nextKey; UPDATE nextKey SET key = 3 WHERE key = 2; INSERT INTO freeKey VALUES (0); INSERT INTO freeKey VALUES (1); SELECT * FROM freeKey; DELETE FROM freeKey WHERE key = 0; SqlError {seState = "", seNativeError = 1, seErrorMsg = "step: database table is locked"}

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Looking for a random-access sequence data structure
by Duncan Coutts 13 Jan '06

13 Jan '06

Hi all, I've been looking around (unsuccessfully) for an efficient data structure to implement a sequence data type with indexed insert/delete/lookup. lookup :: Sequence a -> Int -> Maybe a insert :: Sequence a -> Int -> a -> Sequence a delete :: Sequence a -> Int -> Sequence a Obviously I can implement this with ordinary lists in O(n) time for each operation. It seems that this could be done in O(log n) time for each operation. This seems like a fairly common collection signature to want but to my surprise I've not been able to find any existing implementations that support it. There are several that have almost all the necessary operations. For example the Data.Map supports all of these except insert. Okasaki's random access lists only support inserting elements at the head of the list. I'd guess that some kind of (balanced) binary search tree where each node is annotated with the number of nodes below it could support all these operations. Duncan

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ANN: HDBC (Haskell Database Connectivity)
by John Goerzen 13 Jan '06

13 Jan '06

Hi, I'm pleased to announce the first alpha release (I could call it a "developer's preview", but then I don't wear a suit) of HDBC. HDBC is the Haskell Database Connectivity library. It is patterned after Perl's DBI. I wrote it from scratch -- this is not a reimplementation of HSQL -- because several design decisions in HSQL have been causing me trouble. I am also announcing the first alpha release of the Sqlite3 backend driver for HDBC. I anticipate writing backend drivers for the same databases HSQL supports (though probably not Sqlite2), but it should be easier for others to write HDBC drivers as well. To answer a potential FAQ, HDBC does not attempt to do what HaskellDB does, though HDBC could potentially replace HSQL as the underlying layer of choice in HaskellDB. I'm including the README below, which goes into a bit more detail. To get HDBC: darcs get --partial http://darcs.complete.org/hdbc To get the Sqlite3 driver: darcs get --partial http://darcs.complete.org/hdbc-sqlite3 Welcome to HDBC, Haskell Database Connectivity. HDBC is modeled loosely on Perl's DBI interface, though it has also been influenced by Python's DB-API v2, JDBC in Java, and HSQL in Haskell. Features of HDBC ---------------- HDBC provides an abstraction layer between Haskell programs and SQL relational databases. This lets you write database code once, in Haskell, and have it work with any number of backend SQL databases (MySQL, Oracle, PostgreSQL, ODBC-compliant databases, etc.) HDBC is a from-scratch effort. It is not a reimplementation of HSQL, though its purpose is the same. Some features HDBC has which HSQL lacks include: * Ability to use replacable parameters to let one query be executed multiple times (eliminates the need for an "escape" function) * Ability to access returned rows by column number * Ability to read data from the SQL server on-demand rather than reading the entire result set up front * HUnit testsuite for each backend driver * Well-defined standard API and easy backend driver implementation Features on the TODO list which will appear shortly include: * Support for translation between Haskell and SQL types * Lazy reading of the entire result set (think hGetContents, but for the results of SELECT) * Support for querying metadata (column names, types, etc.) * Additional infrastructure for querying database server properties * Add-on package to integrate with MissingH (filesystem in a database, backend for AnyDBM, etc.) HDBC Drivers ------------ The following HDBC drivers exist: Sqlite v3, darcs get --partial http://darcs.complete.org/hdbc-sqlite3 More will be coming shortly. -- John Goerzen December 20, 2005

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New look for haskell.org: MediaWiki
by John Peterson 11 Jan '06

11 Jan '06

As everyone has noticed during the "making Haskell more open" discussion, MediaWiki was suggested as a better wiki technology for haskell.org. Ashley Yakeley has generously installed MediaWiki and we would like to migrate the main pages of haskell.org into this wiki. The migration is not complete - only the front page is finished - but I'd like to make this public now so that there's time for comments. In the end, this will allow anyone to come in and fix up the main haskell.org pages - the people, the projects, the help for beginners, whatever you want. Olaf and I will then step back and let the community work directly on the entire site without having to bother us (a big advantage!). This will also impact the old Haskell wiki. Rather than try to automatically convert the old wiki to the new one, we're going to ask the community to come in and do this for us. In particular, the new wiki is under the GNU FDL so the licenses are not necessarily compatible. We will keep the two wikis going "side by side" for a while but in the long term I hope all content migrates to MediaWiki (we won't be deprecating the Trac stuff - this will stay as is). I believe that MediaWiki is more professional looking and has a nice separation of documentation and discussion that MoinMoin lacks. I hope that this will result in better wiki content and a more organized site. Moving content by hand will give us all a chance to spruce up the existing content as it moves (and get rid of all the ugly CamelCase page names!). I expect that it will take another week or so for the rest of the haskell.org pages to move into the new wiki - at that point we'll "flip the switch" and take down the old pages (but not the old wiki yet) and change the main page to point into the MediaWiki. Content that isn't being maintained by Olaf and I will stay as before although I hope that more and more pages will move into the wiki and we won't have to give out accounts to people on haskell.org just to host projects. The new wiki isn't yet visible from the front page but you can find it at http://haskell.org/haskellwiki/Haskell For you style sheet gurus, the style sheet itself is also in the wiki at http://haskell.org/haskellwiki/MediaWiki:Quiet.css If anyone wants to help move the main pages over, drop me an email and I'll coordinate things. Feel free to start adding stuff to the new wiki. It won't be visible to the outside world immediately but you can get it ready for the switch over. This isn't a completely "done deal" - there is still time to object to the whole thing or make suggestions. Nothing will be visible to the outside world until we make the switch later. But I believe this will result in a much better site and also make life a lot easier for Olaf and I. (And I apologize to everyone that's asked for updates to haskell.org recently - I've been avoiding them to concentrate on this!). I'm sure some of the MediaWiki settings still need to be tweaked. Send me mail if something in the configuration of MediaWiki needs to be changed. A big thanks again to Ashley! John

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MonadPlus vs. Monoid
by Twan van Laarhoven 10 Jan '06

10 Jan '06

I was wondering, in the MonadPlus documentation it says that: * mzero is the identity of mplus (and some extra conditions) * mplus is an associative operation While for Monoid we have: * mempty is identity of mappend * mappend is an associative operation MonadPlus is of course a 'stronger' assertion. But why is not every instance of MonadPlus also an instance of Monoid? > instance MonadPlus m => Monoid (m a) where > mempty = mzero > mappend = mplus The only type that is an instance of both is [a]. But I see no reason why it there should not be a Monoid instance for other MonadPlus types. In particular, an instance for Maybe could be useful with a writer monad when you are only interested in the first result. Twan

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Re: [Haskell] GHC and GLUT
by Wolfgang Jeltsch 10 Jan '06

10 Jan '06

Am Montag, 9. Januar 2006 10:56 schrieb Axel Simon: > On Fri, 2006-01-06 at 22:37 +0100, Wolfgang Jeltsch wrote: > > Hello again, > > > > now that I had installed libsm-dev and libxmu-dev, building a Gears > > binary worked well. Since the problem didn't seem related to the GHC > > version, I deinstalled the GHC backports and installed GHC from sarge > > again which is 6.2.2. > > > > However, with GHC 6.2.2 I got these error messages during compiling > > Gears.hs: > > > > /tmp/ghc10821.hc: In function `sfcm_ret': > > /tmp/ghc10821.hc:1098: warning: assignment discards qualifiers from > > pointer target type > > /tmp/ghc10821.hc: In function `sfcf_ret': > > /tmp/ghc10821.hc:1216: warning: assignment discards qualifiers from > > pointer target type > > /tmp/ghc10821.hc: In function `sfc8_ret': > > /tmp/ghc10821.hc:1334: warning: assignment discards qualifiers from > > pointer target type > > /tmp/ghc10821.hc: In function `Main_info_entry': > > /tmp/ghc10821.hc:1443: warning: assignment discards qualifiers from > > pointer target type > > > > What does this have to say? > > You probably already got an answer. It's to do with const modifiers that > ghc cannot produce correctly since FFI declarations do not take const > modifiers. There was a discussion about this, but all solutions were too > intrusive with respect to the net gain (removing some warnings). So the warnings are harmless? But why don't they occur with GHC 6.4? > Axel. Best wishes, Wolfgang

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Haskell Performance Resource
by Simon Marlow 10 Jan '06

10 Jan '06

There has been a lot of talk about Haskell performance recently, particularly in relation to the shootout benchmarks, with many useful techniques being mentioned. Some of this information is already available in various bits of documentation, and some of it is only emitted in small nuggets by people like me when they are prodded in the right places (sorry :-). So I felt motivated to start organising some pages on the wiki where we can collect performance-related wisdom. Here it is: http://haskell.org/haskellwiki/Haskell_Performance_Resource The content is quite thin right now, but I hope others will start adding stuff (and by all means fiddle with the structure too - nothing's set in stone). I've added some material from GHC's user guide, and I plan to move the rest of the performance-related material from there in due course. Cheers, Simon

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Re: ANN: HDBC (Haskell Database Connectivity)
by oleg＠pobox.com 10 Jan '06

10 Jan '06

Axel Simon wrote, in response to Keean Schupke > > dbConnectWith :: DbName -> (DbHandle -> IO Result) -> Result > > dbConnectWith name workFn = do > > handle <- dbConnectTo name > > workFn handle `finally` dbDisconnect handle > > > > In this way you avoid finalizers... and everthing is safe providing you > > only export the "with" style functions from the library... Here's an > > example from the library, the connect function: > > I suppose you meant to write "result" rather than "Result". This style > of functions is only safe if the user ensures that DbHandle is never > returned as part of the result. You should have that in your > documentation. It seems using types to enforce the policy that a data base handle cannot ever `leak' out might be a better idea, in Haskell. It is quite straight-forward to do so: cf. the design of the ST monad guarantees that an STRef cannot `leak' out in the result of runST. Monadic Regions (implemented in Haskell) generalize the idea to multiple nested regions: a pointer (or any other resource, e.g., a database cursor) allocated in one region can be used in nested regions but cannot leak outside of the region that created it (Or, to be more precise, cannot be used outside -- and so, can be safely deallocated when the region is exited). Incidentally, the difficulty with finalizers was precisely the argument for using enumerators rather than cursors in database APIs. Takusen has implemented that idea; takusen currently supports Sqlite, PostgreSQL and Oracle, has a test suite. Its performance test shows that takusen can retrieve 2 million rows from a table without running out of memory.

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AMAST 2006 2nd Call for Papers
by Varmo Vene 09 Jan '06

09 Jan '06

SECOND CALL FOR PAPERS 11th International Conference on Algebraic Methodology and Software Technology, AMAST '06 colocated with MPC '06 Kuressaare, Estonia, 5-8 July 2006 http://cs.ioc.ee/mpc-amast06/amast/ Background The major goal of the AMAST conferences is to promote research that may lead to the setting of software technology on a firm, mathematical basis. This goal is advanced by a large international cooperation with contributions from both academia and industry. The virtues of a software technology developed on a mathematical basis have been envisioned as being capable of providing software that is (a) correct, and the correctness can be proved mathematically, (b) safe, so that it can be used in the implementation of critical systems, (c) portable, i.e., independent of computing platforms and language generations, and (d) evolutionary, i.e., it is self-adaptable and evolves with the problem domain. The previous conferences were held in Iowa City, Iowa, USA (1989, 1991 and 2000), Twente, The Netherlands (1993), Montreal, Canada (1995), Munich, Germany (1996), Sydney, Australia (1997), Manaus, Amazonia, Brazil (1998), Reunion Island, France (2002) and Stirling, UK (2004, colocated with MPC' 04). The 2006 conference will be held at Kuressaare, Estonia, colocated with MPC '06. The conference series has become widely known for disseminating academic and industrial achievements within the broad AMAST areas of interest. Through these meetings AMAST has attracted an international following among researchers and practitioners interested in software technology, programming methodology and their algebraic and logical foundations. Important dates * Submission of abstracts: 27 January 2006 * Submission of full papers: 3 February 2006 * Notification of authors: 17 March 2006 * Camera-ready version: 14 April 2006 Topics Topics of interest include, but are not limited to, the following: * Software technology: systems software technology, application software technology, concurrent and reactive systems, formal methods in industrial software development, formal techniques for software requirements/design, evolutionary software/adaptive systems. * Programming methodology: logic programming, functional programming, object paradigms, constraint programming and concurrency, program verification and transformation, programming calculi, specification languages and tools, formal specification and development case studies. * Algebraic and logical foundations: logic, category theory, relation algebra, computational algebra, algebraic foundations for languages and systems, coinduction, theorem proving and logical frameworks for reasoning, logics of programs, algebra and coalgebra. * Systems and tools (for system demonstrations or ordinary papers): software development environments, support for correct software development, system support for reuse, tools for prototyping, component based software development tools, validation and verification, computer algebra systems, theorem proving systems. Submission and publication Two kinds of submissions are solicited for this conference: technical papers and system demonstrations. Papers may report academic or industrial progress, and papers which deal with both are especially well-regarded. Submission is in two stages. Abstracts (plain text) must be submitted by 27 January 2006. Full papers (pdf) adhering to the llncs style and not longer than 15 pages (6 pages for system demonstrations) must be submitted by 3 February 2006. The web-based submission system is open. Papers must report previously unpublished work and not be submitted concurrently to another conference with refereed proceedings. Accepted papers must be presented at the conference by one of the authors. All papers will be refereed by the programme committee, and will be judged based on their significance, technical merit, and relevance to the conference. The proceedings of AMAST '06 will be published in the Lecture Notes in Computer Science series of Springer-Verlag. Programme Committee Michael Johnson, Macquarie University (co-chair) Varmo Vene, University of Tartu (co-chair) Luís Barbosa, Universidade do Minho Gilles Barthe, INRIA Sophia-Antipolis Michel Bidoit, École Normale Supérieure de Cachan Gregor v. Bochmann, University of Ottawa Manfred Broy, Technische Universität München Cristian Calude, University of Auckland Christine Choppy, Université Paris Nord Arthur Fleck, University of Iowa Marcelo Frias, Universidad de Buenos Aires Nicolas Halbwachs, Université Grenoble I / CNRS Anne Haxthausen, Technical University of Denmark Antonia Lopes, Universidade de Lisboa Michael Mislove, Tulane University Peter Mosses, University of Wales Swansea Monica Nesi, Università degli Studi di L'Aquila Rocco De Nicola, Università degli Studi di Firenze Anton Nijholt, Universiteit Twente Dusko Pavlovic, Kestrel Institute Jaco van de Pol, CWI Charles Rattray, University of Stirling Teodor Rus, University of Iowa Giuseppe Scollo, Università degli Studi di Verona Carolyn Talcott, SRI International Andrzej Tarlecki, Warsaw University Ken Turner, University of Stirling Irek Ulidowski, University of Leicester Martin Wirsing, Ludwig-Maximilians-Universität München AMAST steering committee Egidio Astesiano, Universita degli Studi di Genova Robert Berwick, MIT Zohar Manna, Stanford University Michael Mislove, Tulane University Anton Nijholt, University of Twente Maurice Nivat, Universite Paris 7 Charles Rattray, University of Stirling Teodor Rus, University of Iowa Giuseppe Scollo, Universita degli Studi di Verona Michael Sintzoff, Universite Catholique de Louvain Jeannette Wing, Carnegie Mellon University Martin Wirsing, Ludwig-Maximilians-Universitaet Muenchen Michael Johnson, Macquarie University (chair) Venue Kuressaare (pop. 16000) is the main town on Saaremaa, the second-largest island of the Baltic Sea. Kuressaare is a charming seaside resort on the shores of the Gulf of Riga highly popular with Estonians as well as visitors to Estonia. The scientific sessions of MPC/AMAST 2006 will take place at Saaremaa Spa Hotel Meri, one among the several new spa hotels in the town. The social events will involve a number of sites, including the 14th-century episcopal castle. Accommodation will be at Saaremaa Spa Hotels Meri and Ruutli. To get to Kuressaare and away, one must pass through Tallinn (pop. 402000), Estonia's capital city. Tallinn is famous for its picturesque medieval Old Town, inscribed on UNESCO's World Heritage List. Local organizers MPC/AMAST 2006 is organized by Institute of Cybernetics, a research institute of Tallinn Univ. of Technology. The local organizers are Tarmo Uustalu (chair), Monika Perkmann, Juhan Ernits, Ando Saabas, Olha Shkaravska, Kristi Uustalu. Contact email addresses: mike(at)ics.mq.edu.au, varmo(at)cs.ut.ee.

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ANN: hdbc-odbc
by John Goerzen 09 Jan '06

09 Jan '06

I am pleased to be able to announce the first version of hdbc-odbc, the ODBC backend for HDBC. With this driver, you can use HDBC to connect to any database for which ODBC drivers exist, including such databases as MySQL, Oracle, MS SQL Server, etc. I have tested it against PostgreSQL and would appreciate "make test-ghc6" results with more (see testsrc/SpecificDB.hs for the place to specify your connect string.) hdbc-odbc is available for download from: http://quux.org/devel/hdbc People interested in development should use the darcs repo: darcs get --partial http://darcs.complete.org/hdbc-odbc -- John Goerzen Author, Foundations of Python Network Programming http://www.amazon.com/exec/obidos/tg/detail/-/1590593715

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