November 2010 - Haskell

[ANNOUNCE] Parallel Haskell project underway
by Dmitry Astapov 15 Nov '10

15 Nov '10

Parallel Haskell project underway GHC HQ and Well-Typed are pleased to report that work has started on the MSR-funded project to push the real-world use of parallel Haskell. We will be working with four industrial partners over the next two years, with the aim of demonstrating that parallel Haskell can be employed successfully in industrial projects. The participating organizations are: * Dragonfly (New Zealand) * IIJ Innovation Institute Inc. (Japan) * Los Alamos National Laboratory (USA) * Willow Garage Inc. (USA) Each group is working on their own project, applying parallel Haskell and their domain-specific expertise. In addition to providing advice on Haskell tools and techniques, we will work with these partners to identify and resolve any issues that are hindering progress. We are prepared to handle issues covering anything from the compiler and runtime system, through to platform, tool and library problems. All the participants are working on complex, real-world problems. Three projects involve scientific problems, and the fourth involves network servers. Three of the projects are targeting single-node SMP systems, while the fourth is targeting clusters. In two cases, Haskell will be directly pitted against existing code written in C or C++. Project progress reports will be posted to the Well-Typed blog [1] and to the new Parallel Haskell mailing list [2]. [1]: http://www.well-typed.com/blog/ [2]: http://groups.google.com/group/parallel-haskell == Dragonfly == http://www.dragonfly.co.nz/ Participants: Finlay Thompson, Edward Abraham Cloudy Bayes: Hierarchical Bayesian modeling in Haskell The Cloudy Bayes project aims to develop a fast Bayesian model fitter that takes advantage of modern multiprocessor machines. It will support model descriptions in the BUGS model description language (WinBUGS, OpenBUGS, and JAGS). It will be implemented as an embedded domain specific language (EDSL) within Haskell. A wide range of model hierarchical Bayesian model structures will be possible, including many of the models used in medical, ecological, and biological sciences. Cloudy Bayes will provide an easy to use interface for describing models, running Monte Carlo Markov chain (MCMC) fitters, diagnosing performance and convergence criteria as it runs, and collecting output for post-processing. Haskell's strong type system will be used to ensure that model descriptions make sense, providing a fast, safe development cycle. == IIJ Innovation Institute Inc. == http://www.iij-ii.co.jp/en/ Participants: Kazu Yamamoto Haskell is suitable for many kinds of domain, and GHC's support for lightweight threads makes it attractive for concurrency applications. An exception has been network server programming because GHC 6.12 and earlier have an IO manager that is limited to 1024 network sockets. The upcoming GHC 7 has a new IO manager implementation that gets rid of this limitation. This project will implement several network servers to demonstrate that Haskell is suitable for network servers that handle a massive number of concurrent connections. == Los Alamos National Laboratory == http://www.lanl.gov/ Participants: Michael Buksas, Timothy M. Kelley This project will use parallel Haskell to implement high-performance Monte Carlo algorithms, a class of algorithms which use randomness to sample large or otherwise intractable solution spaces. The initial goal is a particle-based MC algorithm suitable for modeling the flow of radiation, with application to problems in astrophysics. From this, the project is expected to move to identification of suitable abstractions for expressing a wider variety of Monte Carlo algorithms, and using models for different physical phenomena. == Willow Garage == http://www.willowgarage.com/ Participants: Ryan Grant Distributed Rigid Body Dynamics in ROS Willow Garage seeks a high-level representation for a distributed rigid body dynamics simulation, capable of excellent parallel speedup on current and foreseeable hardware, yet linking to existing optimized libraries for low-level message passing and matrix math. This project will drive API, performance, and profiling tool requirements for Haskell's interface to the Message Passing Interface (MPI) specification, an industry-standard in High Performance Computing (HPC), as used on clusters of many nodes. Competing internal initiatives use C++/MPI and CUDA directly. Willow Garage aims to lay the groundwork for personal robotics applications in everyday life. ROS (Robot Operating System - ROS.org) is an open source, meta-operating system for your robot. -- Dmitry Astapov Well-Typed LLP, http://www.well-typed.com/

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Gtk2Hs 0.12.0 released
by Axel Simon 11 Nov '10

11 Nov '10

Dear all, the Gtk2Hs team is happy to announce a new release of the core packages glib, gio, pango, cairo, and gtk all in version 0.12.0. Andy Steward has put in a lot of effort to add many new functions to gtk, thereby getting close to covering the full Gtk+ API. John Obbele has kindly investigated into fixing some memory leaks. These new packages should build with Cabal 0.10.0, that is, with the upcoming ghc 7 release. Please note that you need to manually install gtk2hs-buildtools before attempting to install any of the packages above! If in doubt, please read the INSTALL instructions found on our web-site: http://haskell.org/gtk2hs/download/ Comments and feedback welcome. Axel (on behalf of the Gtk2Hs team) About Gtk2Hs ------------ Gtk2Hs is a set of Haskell bindings to many of the libraries included in the Gtk+/Gnome platform. Gtk+ is an extensive and mature multi- platform toolkit for creating graphical user interfaces. GUIs written using Gtk2Hs use themes to resemble the native look on Windows. Gtk is the toolkit used by Gnome, one of the two major GUI toolkits on Linux. On Mac OS programs written using Gtk2Hs are run by Apple’s X11 server but may also be linked against a native Aqua implementation of Gtk. Gtk2Hs features: • Automatic memory management (unlike some other C/C++ GUI libraries, Gtk+ provides proper support for garbage-collected languages) • Unicode support • High quality vector graphics using Cairo • Extensive reference documentation • An implementation of the “Haskell School of Expression” graphics API • Bindings to many other libraries that build on Gtk: gio, GConf, GtkSourceView 2.0, glade, gstreamer, vte, webkit (released separately)

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Haskell Weekly News: Issue 158 - November 10, 2010
by Daniel Santa Cruz 11 Nov '10

11 Nov '10

Welcome to issue 158 of the HWN, a newsletter covering developments in the [1]Haskell community in the week of October 31 - November 06. I'd like to start things off with a quote from Jeremy O'Donoghue this past week on a thread that produced plenty of laughs: Haskell was developed by Isaac Newton in the 15th Century as a tool to help his investigations into the Alchemic arts. It was rediscovered in the 1980s by three Cambridge undergraduates who were browsing through Newton's laboratory notebooks looking for smutty jokes in the margins, and has since developed into an elaborate joke perpetrated by elite computer scientists who believe that predictable order of execution is contrary to natural law. The current version of Haskell is Haskell 1714, which adds syntactic sugar for Zygohistomorphic Premorphisms to the original language definition of 1693. This week we had 378 messages posted to Haskell-Cafe (up 76 from last week!), 30 stories posted to Reddit (1 more than last week), 40 questions posted to StackOverflow (15 more than last week), and 96 updates to Hackage (11 more than last week). Busy busy week! From all the noise in the intertubes, it sounds like BelHac was awesome. There were plenty of kudos to Jasper Van der Jeugt for how well things went. Jasper posted a [2]summary blog, and we also have some [3]pictures from the event. Announcements Will Sonnex [4]updated Zeno, a fully automated inductive theorem proving tool for Haskell programs. Gregory D. Weber [5]updated Sifflet, a visual, functional programming language and support system for students learning about recursion. Mario BlaÅ¾eviÄ/= [6]updated monad-coroutine and SCC to version 0.6. The monad-coroutine package exports a generic monad transformer: Coroutine: Functor s => MonadTrans (Coroutine s). Johan Tibell informed us that he has [7]merged network-bytestring into the network package. This means that efficient and correct networking using ByteString is available as part of the standard network package. By far, the most popular thread this week in -cafe was a thread entitled [8]"Haskell is a scripting language inspired by Python." As you can imagine, many could not resist! The thread diverted into some interesting historical notes about Haskell. Top Reddit Stories * Learn You a Haskell: Zippers Domain: learnyouahaskell.com Score: 91, Comments: 44 On Reddit: http://www.reddit.com/r/haskell/comments/e0qqz/learn_you_a_haskell_zippers/ Original: http://learnyouahaskell.com/zippers * Neat Haskell commenting trick Domain: self.haskell Score: 78, Comments: 6 On Reddit: http://www.reddit.com/r/haskell/comments/dyvsi/neat_haskell_commenting_tric… Original: /r/haskell/comments/dyvsi/neat_haskell_commenting_trick/ * Haskell Halloween! Domain: i.imgur.com Score: 53, Comments: 5 On Reddit: http://www.reddit.com/r/haskell/comments/dyznc/haskell_halloween/ Original: http://i.imgur.com/t7qWf.jpg * Circular wavefronts Domain: claudiusmaximus.goto10.org Score: 39, Comments: 3 On Reddit: http://www.reddit.com/r/haskell/comments/e02vp/circular_wavefronts/ Original: http://claudiusmaximus.goto10.org/cm/2010-11-02_circular_wavefronts.html * Optimizing Haskell Loops With LLVM Domain: dmpots.com Score: 35, Comments: 1 On Reddit: http://www.reddit.com/r/haskell/comments/e1yfn/optimizing_haskell_loops_wit… Original: http://www.dmpots.com/blog/2010/11/05/optimizing-haskell-loops-with-llvm.ht… * Obtaining the name of a function in Haskell Domain: mainisusuallyafunction.blogspot.com Score: 24, Comments: 3 On Reddit: http://www.reddit.com/r/haskell/comments/e1i3q/obtaining_the_name_of_a_func… Original: http://mainisusuallyafunction.blogspot.com/2010/11/obtaining-name-of-functi… * Generative Type Abstraction and Type-level Computation Domain: cis.upenn.edu Score: 17, Comments: 2 On Reddit: http://www.reddit.com/r/haskell/comments/dzx80/generative_type_abstraction_… Original: http://www.cis.upenn.edu/~sweirich/newtypes.pdf * Relations rather than functions - where to learn about them? Domain: self.haskell Score: 17, Comments: 17 On Reddit: http://www.reddit.com/r/haskell/comments/e1520/relations_rather_than_functi… Original: /r/haskell/comments/e1520/relations_rather_than_functions_where_to_learn/ * Haskellers.com: Special Interest Groups feature active Domain: haskellers.com Score: 16, Comments: 2 On Reddit: http://www.reddit.com/r/haskell/comments/dzkel/haskellerscom_special_intere… Original: http://www.haskellers.com/news/6/ * The Utrecht Haskell Compiler now in github Domain: github.com Score: 16, Comments: 2 On Reddit: http://www.reddit.com/r/haskell/comments/e26ar/the_utrecht_haskell_compiler… Original: https://github.com/uhc/uhc Top StackOverflow Questions * how to do this in haskell? Question (votes: 0, answers: 1): Read on SO: http://stackoverflow.com/questions/4106247/how-to-do-this-in-haskell * Haskell define Merge using mapReduce Question (votes: 0, answers: 1): Read on SO: http://stackoverflow.com/questions/4099627/haskell-define-merge-using-mapre… * Real GHC RTS memory usage Question (votes: 0, answers: 1): Read on SO: http://stackoverflow.com/questions/4088351/real-ghc-rts-memory-usage * reading file and accessing in haskell (functional programming language) Question (votes: 0, answers: 2): Read on SO: http://stackoverflow.com/questions/4074342/reading-file-and-accessing-in-ha… * Converting tree types Question (votes: 0, answers: 2): Read on SO: http://stackoverflow.com/questions/4073091/converting-tree-types * Printing Binary Tree per Layer in a List Question (votes: 0, answers: 3): Read on SO: http://stackoverflow.com/questions/4068681/printing-binary-tree-per-layer-i… * Comparing Bool Value in Matrix Question (votes: 0, answers: 2): Read on SO: http://stackoverflow.com/questions/4063553/comparing-bool-value-in-matrix * Converting Int to Integer Question (votes: 0, answers: 3): Read on SO: http://stackoverflow.com/questions/4061777/converting-int-to-integer * Integrating Haskell with .Net? Question (votes: 1, answers: 3): Read on SO: http://stackoverflow.com/questions/4111467/integrating-haskell-with-net * Putting existentials into monad Question (votes: 1, answers: 1): Read on SO: http://stackoverflow.com/questions/4106793/putting-existentials-into-monad Quotes of the week * Luke Palmer:Also they "don't scale well", which I guess means that they don't make it inconvenient to design badly. * merijn: <dankna> someday we'll need meta-software that converts from obsolete languages into modern ones <merijn> Don't we call that compilers? * dolio: Let's spawn a thread every time we want to and two booleans. * ray: how about a language where you program with unit vectors: orientation oriented programming * Axman6: Haskell is easy, you just apply functions to arguments, and then you apply them to other arguments. Axman6's girlfriend: I don't like conflict * monochrom: in soviet haskell, functions run you * geheimdienst: in soviet russia, i remember lambdabot's quotes * Funktorsalat: sum is just the free monoid functor applied to the mediating arrow of the terminality of () * geheimdienst: ah, yes. now we have to make a lambdacat captioned "kittehs no bery gud at speling. we says leksah fur lexer and monad fur moniod in catagory of ennobunktors" * Vanadium: That tripped my C++ highlight. * jmcarthur: what you just typed isn't even well typed About the Haskell Weekly News New editions are posted to [9]the Haskell mailing list as well as to [10]the Haskell Sequence and [11]Planet Haskell. [12]RSS is also available, and headlines appear on [13]haskell.org. To help create new editions of this newsletter, please send stories to dstcruz * at * gmail * dot * com. The code used to produce this version of the newsletter is not yet publicly available, as it is a complete hack designed to get things started again. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://jaspervdj.be/posts/2010-11-09-belhac-summary.html 3. http://www.flickr.com/groups/1566670@N23/ 4. http://article.gmane.org/gmane.comp.lang.haskell.general/18277 5. http://article.gmane.org/gmane.comp.lang.haskell.general/18279 6. http://article.gmane.org/gmane.comp.lang.haskell.general/18281 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/82798 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/82995 9. http://www.haskell.org/mailman/listinfo/haskell 10. http://sequence.complete.org/ 11. http://planet.haskell.org/ 12. http://sequence.complete.org/node/feed 13. http://haskell.org/

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ANNOUNCE: The Fibon benchmark suite (v0.2.0)
by David Peixotto 10 Nov '10

10 Nov '10

I'm pleased to announce the release of the Fibon benchmark tools and suite. Fibon is a set of tools for running and analyzing benchmark programs in Haskell. Most importantly, it includes an optional set of benchmark programs including many programs taken from the Hackage open source repository. The source code for the tools and benchmarks are available on github https://github.com/dmpots/fibon http://github.com/dmpots/fibon-benchmarks The Fibon tools (without the benchmarks) are available on hackage. http://hackage.haskell.org/package/fibon The package needs to be unpacked and built in place to be able to run any benchmarks. It can be used with the official Fibon benchmarks or you can create your own suite and just use Fibon to run and analyze your benchmark programs. Some more documentation is available on the fibon wiki https://github.com/dmpots/fibon/wiki Fibon Tools =================================================================== Fibon is a pure Haskell framework for running and analyzing benchmark programs. Cabal is used for building the benchmarks. The benchmark harness, configuration files, and benchmark descriptions are all written in Haskell. The benchmark descriptions and run configurations are all statically compiled into the benchmark runner to ensure that configuration errors are found at compile time. The Fibon tools are not tied to any compiler infrastructure and can build benchmarks using any compiler supported by cabal. However, there are some extra features available when using GHC to build the benchmarks: * Support in config files for using an inplace GHC HEAD build * Support in `fibon-run` for collecting GC stats from GHC compiled programs * Support in `fibon-analyse` for reading GC stats from Fibon result files The Fibon Benchmark Suite =================================================================== The Fibon benchmark suite currently contains 34 benchmarks from a variety of sources. The individual benchmarks and lines of code are given below. Dph _DphLib 316 Dotp 308 Qsort 236 QuickHull 680 Sumsq 72 ------------------------------ TOTAL 1612 Hackage Agum 786 Bzlib 432 Cpsa 11582 Crypto 4486 Fgl 3834 Fst 4532 Funsat 16085 Gf 23970 HaLeX 4035 Happy 5833 Hgalib 819 Palindromes 496 Pappy 7313 QuickCheck 4495 Regex 6873 Simgi 5134 TernaryTrees 722 Xsact 2783 ------------------------------ TOTAL 104210 Repa _RepaLib 8775 Blur 77 FFT2d 89 FFT3d 103 Laplace 274 MMult 133 ------------------------------ TOTAL 9451 Shootout BinaryTrees 63 ChameneosRedux 96 Fannkuch 27 Mandelbrot 68 Nbody 192 Pidigits 26 SpectralNorm 97 ------------------------------ TOTAL 569

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ANNOUNCE: Haskell Communities and Activities Report (19th ed., November 2010)
by Janis Voigtländer 09 Nov '10

09 Nov '10

On behalf of all the contributors, I am pleased to announce that the Haskell Communities and Activities Report (19th edition, November 2010) is now available in PDF and HTML formats: http://haskell.org/communities/11-2010/report.pdf http://haskell.org/communities/11-2010/html/report.html Many thanks go to all the people that contributed to this report, both directly, by sending in descriptions, and indirectly, by doing all the interesting things that are reported. I hope you will find it as interesting a read as I did. If you have not encountered the Haskell Communities and Activities Reports before, you may like to know that the first of these reports was published in November 2001. Their goal is to improve the communication between the increasingly diverse groups, projects, and individuals working on, with, or inspired by Haskell. The idea behind these reports is simple: Every six months, a call goes out to all of you enjoying Haskell to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and sometimes in time for the actual deadline ;-) to the call. The editor collects all the contributions into a single report and feeds that back to the community. When I try for the next update, six months from now, you might want to report on your own work, project, research area or group as well. So, please put the following into your diaries now: ---------------------------------------- End of April 2011: target deadline for contributions to the May 2011 edition of the HC&A Report ---------------------------------------- Unfortunately, many Haskellers working on interesting projects are so busy with their work that they seem to have lost the time to follow the Haskell related mailing lists and newsgroups, and have trouble even finding time to report on their work. If you are a member, user or friend of a project so burdened, please find someone willing to make time to report and ask them to "register" with the editor for a simple e-mail reminder in April (you could point me to them as well, and I can then politely ask if they want to contribute, but it might work better if you do the initial asking). Of course, they will still have to find the ten to fifteen minutes to draw up their report, but maybe we can increase our coverage of all that is going on in the community. Feel free to circulate this announcement further in order to reach people who might otherwise not see it. Enjoy! Janis Voigtlaender <hcar at haskell.org>

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CfP: JOURNAL OF APPLIED LOGIC, Special Issue on Automated Specification and Verification of Web Systems
by Temur Kutsia 08 Nov '10

08 Nov '10

[Apologies for multiple copies] ======================================================================== JOURNAL OF APPLIED LOGIC Special Issue on Automated Specification and Verification of Web Systems http://www.risc.uni-linz.ac.at/people/tkutsia/jal-wwv.html ======================================================================== SCOPE ----- This special issue of the Journal of Applied Logic is related to the topics of the workshop WWV'10: Automated Specification and Verification of Web Systems, which took place in Vienna on July 30-31, 2010. Both participants of the workshop and other authors are invited to submit contributions. The increased complexity of Web sites and the explosive growth of Web-based applications has turned their design and construction into a challenging problem. Nowadays, many companies have diverted their Web sites into interactive, completely-automated, Web-based applications (such as Amazon, on-line banking, or travel agencies) with a high complexity that requires appropriate specification and verification techniques and tools. Systematic, formal approaches to the analysis and verification can address the problems of this particular domain with automated and reliable tools that also incorporate semantic aspects. We solicit original papers on logic-based methods and techniques applied to Web sites, Web services or Web-based applications, such as: * Rule-based approaches to Web systems analysis, certification, specification, verification, and optimization * Algebraic methods for verification and certification of Web systems * Formal models for describing and reasoning about Web systems * Model-checking, synthesis and debugging of Web systems * Abstract interpretation and program transformation applied to the semantic Web * Intelligent tutoring and advisory systems for Web specifications authoring * Web quality and Web metrics * Web usability and accessibility * Testing and evaluation of Web systems and applications SUBMISSION ---------- We expect original articles (typically 15-25 pages; submission of larger papers will be evaluated depending on editorial constraints) that present high-quality contributions that have not been previously published and that must not be simultaneously submitted for publication elsewhere. Submissions must comply with JAL's author guidelines. They must be written in English and should be prepared using the Elsevier LaTeX package. Submissions are encouraged via the EasyChair submission system: http://www.easychair.org/conferences/?conf=jalwwv2010. IMPORTANT DATES --------------- * Submission of papers: March 7, 2011. * Notification: June 6, 2011. GUEST EDITORS -------------- * Laura Kov�cs (Vienna University of Technology) * Temur Kutsia (RISC, Johannes Kepler University Linz)

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Re: [Haskell] ANN: blaze-builder-0.2.0.0
by Simon Meier 08 Nov '10

08 Nov '10

Hi Antoine, Can the same technique be ported over to the binary package, or is it > somehow interface incompatible? > I'm not exactly sure what you mean by the same technique. If you mean using blaze-builder instead of Data.Binary.Builder as the Monoid that the Put writer monad in the Binary typeclass is using, then, yes, you can because Blaze.ByteString.Builder is a drop-in replacement for Data.Binary.Builder. However, in that case you loose some of the speedup of blaze-builder with respect to Data.Binary.Builder. The results https://gist.github.com/664979#file_comparison_to_binary_package.txt of the throughput benchmark (ported from the binary package) https://github.com/meiersi/blaze-builder/blob/master/benchmarks/BenchThroug… essentially show that you should not use the Put monad but the underlying Monoid directly for serialization. In my opinion, it is also not necessary to have a Writer monad (Put) by default. The only real benefit it brings is the nice do-notation. However, for the syntax we would rather go for a MonoidCatSyntax extension that introduces a 'cat' keyword analogously to the 'do' keyword. That's an extension which would also come in very handy for blaze-html and possibly other mappend-heavy applications. If you mean the Write abstraction, then its a partial yes. You can port it to binary, but I'm not sure how big the win is going to be. The current Data.Binary.Builder implementation suffers the problem that each builder needs to know the strategy for output construction and hence, the whole state of output construction. Passing all that data around makes its `mappend` implementation quite slow. I'd thought I'd heard rumbles a while back about a desire the change > the implementation of 'binary', but I don't know what happened to > that. I also heard some rumbles, but nothing concrete. Perhaps one of the 'binary' developers could comment on that issue? best regards, Simon

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ANN: blaze-builder-0.2.0.0
by Simon Meier 07 Nov '10

07 Nov '10

The blaze-builder library provides an abstraction of buffered output of byte streams and several convenience functions to exploit it. For example, it allows to efficiently serialize Haskell values to lazy bytestrings with a large average chunk size. The large average chunk size allows to make good use of cache prefetching in later processing steps (e.g. compression) and reduces the sytem call overhead when writing the resulting lazy bytestring to a file or sending it over the network. Note that blaze-builder was inspired by the Data.Binary.Builder module provided by the binary package. It was originally developed with the specific needs of the blaze-html package in mind. Since then it has been restructured to serve as a drop-in replacement for Data.Binary.Builder, which it *improves upon both in speed as well as expressivity.* See the following blog-post for more details: http://lambda-view.blogspot.com/2010/11/blaze-builder-library-faster.html best regards, Simon Meier

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ANNOUNCE: coroutine-enumerator
by Mario Blažević 05 Nov '10

05 Nov '10

The newly released coroutine-enumerator package can be used as a bridge between the enumerator and monad-coroutine packages. It provides two-way conversion functions between an Iteratee and an Await-suspending coroutine, and also between an Enumerator and a Yield-suspending coroutine. As a little example, the following program combines the http-enumerator, monad-coroutine, and SCC packages using the coroutine-enumerator package to print out all lines from the Hackage database containing substring "enumerator": > import Control.Exception.Base (SomeException) > import Control.Monad.Trans.Class (lift) > > import Data.ByteString (ByteString) > import Data.Text.Encoding (decodeUtf8) > > import Network.HTTP.Enumerator > > import Control.Monad.Coroutine > import Control.Monad.Coroutine.SuspensionFunctors > import Control.Monad.Coroutine.Nested > import Control.Monad.Coroutine.Enumerator > > import Control.Concurrent.SCC.Sequential > > main = httpRedirect (\_ _-> coroutineIteratee consumer) =<< parseUrl address > > address = "http://hackage.haskell.org/packages/archive/pkg-list.html" > > consumer :: Coroutine (Await [ByteString]) IO (Either SomeException ((), [ByteString])) > consumer = pipe translator (consume worker) >> return (Right ((), [])) > > translator :: Functor f => Sink IO (EitherFunctor (Await [a]) f) a -> Coroutine (EitherFunctor (Await [a]) f) IO () > translator sink = do chunks <- liftParent await > if null chunks > then lift (putStrLn "END") > else putList chunks sink >> translator sink > > worker :: Consumer IO ByteString () > worker = toChars >-> foreach (line `having` substring "enumerator") > (append (fromList "\n") >-> toStdOut) > suppress > > toChars :: Monad m => Transducer m ByteString Char > toChars = oneToOneTransducer decodeUtf8 >-> coerce Alternatively, the worker coroutine can parse the XML database and print out all elements whose any attribute value contains the substring "enumerator": > worker = toChars > >-> parseXMLTokens > >-> foreach (xmlElementHavingTagWith (xmlAttributeValue `having` substring "enumerator") > `nestedIn` xmlElementContent) > (coerce >-> toStdOut) > suppress

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ANNOUNCE: version 0.6 of monad-coroutine and SCC
by Mario Blažević 05 Nov '10

05 Nov '10

Packages monad-coroutine and SCC have been upgraded to version 0.6 on Hackage. The monad-coroutine package exports a generic monad transformer Coroutine: Functor s => MonadTrans (Coroutine s). A Coroutine-transformed monad can suspend at any point, returning its resumption wrapped in the functor s. There are also some functions for manipulating and running coroutines, as well as a couple of useful suspension functors such as Yield and Await. Version 0.6 of monad-coroutine makes running pairs of coroutines simpler by adding several predefined resolvers. The new version of Streaming Component Combinators (a.k.a. SCC) is mostly about performance enhancements. The coroutines now communicate through chunks of data rather than individual items, which reduces the coroutine switching overhead. The module hierarchy has been reorganized for easier use, but the exported type and function names have mostly remained the same. Both packages have been tested with GHC 6.12.3 and 7.0.

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