May 2006 - Haskell - Haskell.org

Re: Haskell Digest, Vol 33, Issue 3
by Chad Scherrer 09 May '06

09 May '06

Phil, thanks for the response. > I was thinking about the dynamic behavior of par, and there's something > > that's a little confusing to me. Am I right in understanding that (x > > `par` y) evaluates to y, and may or may not evaluate x along the way? > > The reason that par doesn't necessarily evaluate it's 1st argument is that > typical parallel Haskell programs contain vast amounts of potential > parallelism. So rather than create a relatively heavyweight thread and be > forced to administer it, e.g. schedule it for every possible expression > that could be evaluated in parallel, the expression is 'sparked', i.e. a > lightweight action that simply notes that the expression *could* be > evaluated in parallel. > I guess this comes down to how par is used. If par is used where evaluation would otherwise be entirely lazy, I wouldn't worry too much about reasoning about whether the sparked thread actually starts or not. But it would be nice to take code that has had seq introduced in some places to avoid stack overflows from excessive laziness and be able to replace seq with something else that would keep the same strictness, but evaluate in parallel. Of course, this could be done at a higher level than the cut-and-paste approach. While I've got you're attention, I wonder if you could help me understand the current state of GPH, and how it relates to recently available shared-memory parallelism available in GHC. It seems to me the ease of parallelism in Haskell could be its "killer app", at least for the folks I interact with. It would be nice if the same code could be used on GPH and parallel GHC, but I'm not sure whether that's the case. Having GHC run in parallel out of the box is great, but if it's moved to a distributed-memory system, I'm also not sure to what extent increased latency is taken into account. Thanks, Chad Scherrer "Time flies like an arrow; fruit flies like a banana" -- Groucho Marx

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how to 'accumulate' values efficiently (time and space) ?
by minh thu 09 May '06

09 May '06

Hi all, the problem is simple but i can't do it : I want to generate some values and 'accumulate' them. The meaning of 'accumulating' is not so important. The only point is that to 'accumulate' the values, I only have to know one value and the accumulator (and not all the values). The most simple example is that of adding a list of numbers. I thought that I could use a haskell list to represent the values so I could use foldr or mapM to do the accumulation (and not an imperative-style loop). Below are four attempts to solve the problem. It's not solved : in ghci, I have '*** Exception: stack overflow' with 'test1 5000000'. 5000000 is not so much for my application. How can I achieve what I want (and efficiently)? ---------------------------------------------------------------------} import Control.Monad.State import Control.Monad.ST import Data.STRef acc1, acc2, acc3 :: [Int] -> Int ---------------------------------------------------------------------- acc1 ints = foldr (+) 0 ints ---------------------------------------------------------------------- acc2 ints = execState (mapM add2 ints) 0 add2 :: Int -> State Int () add2 i = do acc <- get put (acc + i) ---------------------------------------------------------------------- acc3 ints = runST (acc3' ints :: ST s Int) acc3' ints = do accRef <- newSTRef 0 mapM (add3 accRef) ints acc <- readSTRef accRef return acc add3 accRef i = do modifySTRef accRef (+ i) ---------------------------------------------------------------------- test4' n = do let g = gen n accRef <- newSTRef 0 sRef <- newSTRef 1 acc <- acc4 g sRef accRef return acc acc4 g sRef accRef = do ret <- g sRef case ret of Nothing -> do acc <- readSTRef accRef return acc Just i -> do add3 accRef i acc4 g sRef accRef gen n sRef = do s <- readSTRef sRef let ret = if s > n then Nothing else Just 1 writeSTRef sRef (s + 1) return ret ---------------------------------------------------------------------- test1 n = acc1 $ replicate n 1 test2 n = acc2 $ replicate n 1 test3 n = acc3 $ replicate n 1 test4 n = runST (test4' n :: ST s Int) Thanks a lot, VO Minh Thu

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ANN: lambdaFeed 0.2.0 "Lambdas for all!"
by Manuel M T Chakravarty 09 May '06

09 May '06

This is to announce a new Haskell application: lambdaFeed is an RSS 2.0 feed generator. It reads news items - in a non-XML, human-friendly format - distributed over multiple channels and renders them into the RSS 2.0 XML format understood by most news aggregators as well as into HTML for inclusion into web pages. This is a very early version of the tool; hence, many desirable features are missing. However, the internal representation of RSS 2.0 feeds is already rather feature-full, including enclosure, as needed for podcats. A major shortcoming right now is that the generated HTML is quite simple, and in particular, a nice style-sheet is missing. Source is available in darcs. Check it out at http://www.cse.unsw.edu.au/~chak/haskell/lambdaFeed/ Manuel PS: The code is very hackable. Plain H98 throughout.

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QuickCheck & GADTs
by Dominic Steinitz 08 May '06

08 May '06

Has anyone got any examples of these working together? Thanks, Dominic.

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Haskell Weekly News: May 8, 2006
by dons＠cse.unsw.edu.au 08 May '06

08 May '06

Haskell Weekly News: May 8, 2006 Welcome to issue 35 of HWN, a weekly newsletter covering developments in the Haskell community. Each Monday, new editions are posted to [1]the Haskell mailing list as well as to [2]the Haskell Sequence and [3]Planet Haskell. [4]RSS is also available, and headlines appear on [5]haskell.org. 1. http://www.haskell.org/mailman/listinfo/haskell 2. http://sequence.complete.org/ 3. http://planet.haskell.org/ 4. http://sequence.complete.org/node/feed 5. http://haskell.org/ Announcements * hmake. Malcolm Wallace [6]released version 3.11 of [7]hmake, the compiler-independent project-building tool for Haskell programs. It automates recompilation analysis, based on import declarations in your files, to rebuild only those modules that are impacted by a change. It is rather like ghc's --make mode, but faster, less memory intensive, and it works with any compiler (e.g. hbc, nhc98). 6. http://article.gmane.org/gmane.comp.lang.haskell.general/13634 7. http://haskell.org/hmake * cpphs. In a busy week, Malcolm also [8]released version 1.2 of [9]cpphs, the in-Haskell implementation of the C pre-processor. The major change in this release is that the source files have been re-arranged into a cabal-ised hierarchical library namespace, so you can use cpp functionality from within your own code, in addition to the stand-alone utility. 8. http://article.gmane.org/gmane.comp.lang.haskell.general/13638 9. http://haskell.org/cpphs * Cabal 1.1. Duncan Coutts (as the new Cabal release manager) [10]announced that Cabal-1.1.4, the version shipped with GHC 6.4.2 is now available to download as [11]a separate tarball. There is also a [12]new mailing list for Cabal development discussion including patch review. This is also where patches sent via "darcs send" will end up. The Cabal team would also like to take the opportunity to invite people to get involved in Cabal development, either new features or squashing annoying bugs. 10. http://article.gmane.org/gmane.comp.lang.haskell.general/13625 11. http://haskell.org/cabal/download.html 12. http://haskell.org/mailman/listinfo/cabal-devel * DownNova-0.1. Lemmih [13]released downNova, a program designed for automating the process of downloading TV series from mininova.org. Written in Haskell, it will scan your downloaded files to find out what your interests are and download missing/new episodes to your collection. Advanced classification techniques are used to interpret the file names and 'downNova' will correctly extract series name, season number, episode number and episode title in nigh all cases. 13. http://article.gmane.org/gmane.comp.lang.haskell.general/13640 * Student SoC Application Deadline is rapidly approaching. Paolo Martini encouraged students to apply to google, using the [14]student application form, and [15]Haskell.org is looking forward to the several dozen applications we hope to receive. 14. http://article.gmane.org/gmane.comp.lang.haskell.cafe/12563 15. http://hackage.haskell.org/trac/summer-of-code/ Haskell' This section covers activity on [16]Haskell' standardisation process. * [17]Termination for FDs and ATs 16. http://hackage.haskell.org/trac/haskell-prime 17. http://thread.gmane.org/gmane.comp.lang.haskell.prime/1450/focus=1450 Discussion * Speed of Binary serialisation. Bulat Ziganshin [18]posted a comparison of Handle and Bulat's Streams IO performance, with interesting results to ponder. 18. http://article.gmane.org/gmane.comp.lang.haskell.general/13625 * GHCi-based 'eval' and the ML top level. Geoff Washburn [19]sparked a bit of a thread when wondering how to emulate the ML "top level" in Haskell. Some alternatives were proposed, including ghc-api and hs-plugins. 19. http://thread.gmane.org/gmane.comp.lang.haskell.glasgow.user/9835/focus=9835 Quote of the Week Lemmih :: Haskell is the best glue language I know. It's like super-glue. Code Watch * Wed Apr 26 11:21:14 PDT 2006 simonpj (ghc): Arrange that -fth is no longer implied by -fglasgow-exts Messages involving Template Haskell are deeply puzzling if you don't know about TH, so it seems better to make -fth an explicit flag. It is no longer switched on by -fglasgow-exts. * Fri Apr 28 06:07:18 PDT 2006 Don Stewart (packages/base): Import Data.ByteString from fps 0.5. Fast, packed byte vectors, providing a better PackedString. * Wed May 3 04:33:06 PDT 2006 Simon Marlow (packages/base): Improve performance of Integer->String conversion. See [20]. Submitted by Bertram Felgenhauer 20. http://www.haskell.org//pipermail/libraries/2006-April/005227.html Contributing to HWN You can help us create new editions of this newsletter. Please see the [21]contributing information, send stories to dons -at- cse.unsw.edu.au. The darcs repository is available at darcs get http://www.cse.unsw.edu.au/~dons/code/hwn 21. http://haskell.org/haskellwiki/HWN

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RE: [Haskell] Takusen
by Bayley, Alistair 07 May '06

07 May '06

> From: Joel Reymont [mailto:joelr1@gmail.com] > > I could not find bind variables or any examples of using them, thus > my asking. Ahh, that might be because they exist in the experimental branch only. I'll try to track down a coherent set of code for you tomorrow. Are you able to check out from SourceForge yet? > Takusen just seemed to have a more elegant API, conceptually, and > HaskellDB does not support Oracle right now. Bummer. I assumed that because HSQL had Oracle support, that would give HaskellDB support for it too (as HaskellDB works overs HSQL, AFAIK). It shouldn't take me long to fix the Oracle back-end w.r.t the latest API (it's only a few hours work :-) but as I said, spare time to work on Takusen is a bit precious for me at present. Alistair ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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Takusen
by Joel Reymont 06 May '06

06 May '06

Folks, I cannot check out Takusen from haskell-libs on Source Forge, neither an empty password nor anonymous works. Has anyone seen this? Does Takusen support SQL templates with variable bindings or is the idea that I form the SQL text myself? How should I plug in numeric ids and such into the text of the where clause, for example? Last but not least, are there any examples besides the library itself? Thanks, Joel -- http://wagerlabs.com/

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RE: [Haskell] Takusen
by Bayley, Alistair 06 May '06

06 May '06

> From: haskell-bounces(a)haskell.org > [mailto:haskell-bounces@haskell.org] On Behalf Of Joel Reymont > > Folks, > > I cannot check out Takusen from haskell-libs on Source Forge, > neither > an empty password nor anonymous works. Has anyone seen this? > > Does Takusen support SQL templates with variable bindings or is the > idea that I form the SQL text myself? How should I plug in numeric > ids and such into the text of the where clause, for example? > > Last but not least, are there any examples besides the library itself? > > Thanks, Joel I suppose I should comment on Takusen, as there hasn't been any news for a while. I don't know why you can't check out from Source Forge...sorry. Perhaps you could ask Shae to add you to the project. Oleg and I are in the process of migrating it from haskell-libs to darcs (SimonM gave us access to the repo as haskell.org, I think, some time ago). Also, the current version in the experimental branch is a bit broken at present, as Oleg redesigned the API a while ago, and I'm still catching up on the implementations. Currently PostgreSQL and Sqlite work, and Oracle... well, it's next on my list, but don't hold your breath, as I don't get a lot of spare time to work on it. I should be able to identify an appropriate older version that will compile, if you want. Support for SQL Templates... well, we support bind variables, if that's what you mean. Sounds like what you want. As for examples, there's just what's in the test modules that you'll get with the library. What's your goal with using Takusen? I hate to say it, but right now HaskellDB+HSQL is probably going to give you a better database API for Oracle, at least until I pull my finger out and finish updating the various back-ends, and complete the move to darcs. Is there something you need that HaskellDB+HSQL doesn't support? Alistair ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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DownNova-0.1
by Lemmih 05 May '06

05 May '06

Greetings, I hearby announce the release of DownNova-0.1. Description: 'downNova' is a program designed for automating the process of downloading TV series from mininova.org. It will scan your downloaded files to find out what your interests are and download missing/new episodes to your collection. Advanced classification techniques are used to interpret the file names and 'downNova' will correctly extract series name, season number, episode number and episode title in nigh all cases. This might be abused for illegally downloading copyrighted material. That is however not the intended use of this program and I do not condone such activities. Dependencies: fps: http://www.cse.unsw.edu.au/~dons/fps.html HaXml: http://haskell.org/HaXml Installation: runhaskell Setup.lhs configure [--help] runhaskell Setup.lhs build sudo runhaskell Setup.lhs install $EDITOR downnova.cfg sudo cp downnova.cfg /etc/downnova.cfg sudo cp `which downnova` /etc/cron.hourly/ Repository: darcs get http://darcs.haskell.org/~lemmih/downNova -- Friendly, Lemmih

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Haskell Workshop 2006 Second call for papers
by Andres Loeh 05 May '06

05 May '06

Apologies for multiple copies; feel free to distribute further. Cheers, Andres

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