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Haskell Weekly News: Issue 150 - February 22, 2010
by jfredett＠gmail.com 22 Feb '10

22 Feb '10

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20100222 Issue 150 - February 22, 2010 --------------------------------------------------------------------------- Welcome to issue 150 of HWN, a newsletter covering developments in the [1]Haskell community. From the very pits of Harddrive failure I return... The Haskell Weekly News Reborn! Last week, on friday, my HWN machine suffered what can only be appropriately named a unbelievably poorly timed hard drive failure, hence the lack of an HWN. I trumphently return this week with a megaedition. Tons and tons of awesome stuff happened in the last two weeks. So I won't make you wait any longer, haskellers, your Haskell Weekly News! Announcements vty-ui 0.3. Jonathan Daugherty [2]announced a new version of vty-ui, featuring a richer rendering engine, generalized text transformations, and a more functional style. darcs 2.4 release candidate 2. Reinier Lamers [3]announced a new release candidate for darcs 2.4. iteratee-parsec 0.0.1. Maciej Piechotka [4]announced the release of iteratee-parsec, a library whih provides support for parsec parsers in an Iteratee monad. concurrent-extra-0.1. Roel van Dijk [5]announced the release of concurrent-extra, which provides a few new synchronization primitives. wyvern, a Dragon Go Server 'client'. wagnerdm [6]announced wyvern, a Dragon Go Server 'client', which plays moves for you on the [7]Dragon Go Server. atom-1.0.0. Tom Hawkins [8]announced a new major release of the atom library. Call for Copy: Monad.Reader Issue 16. Brent Yorgey [9]announced the call for copy for Monad.Reader issue 16. hmatrix 0.8.3. Alberto Ruiz [10]announced a new version of hmatrix. First Atlanta Function Programming Users Group Meeting. David Vollbracht [11]announced the first Atlanta FP Group meetup. TFP 2010 - Call for Papers and Participation. Simon Marlow [12]announced a call for papers and particpation in TFP 2010, the 11th Symposium on Trends in Functional Programming. CMCS 2010: Call for Short Submissions & Call for Participation. Alexandra Silva [13]announced a call for short submissions and participation in the 10th International Workshop on Coalgebraic Methods in Computer Science. WGP 2010 Call for Papers. Bruno Oliveira [14]announced a call for papers for Workshop on Generic Programming. ICE 2010: First call for papers. Alexandra Silva [15]announced the first call for papers for ICE2010, the 3rd Interation and Concurrency Experience workshop. Call for Papers: Haskell Symposium 2010. Jeremy.Gibbons [16]announced a call for papers for the 2010 Haskell Symposium. Dungeons of Wor - a largish FRP example and a fun game, all in one! Patai Gergely [17]announced Dungeons of Wor, a Game written in Haskell using the Elerea library and Functional Reactive Techniques. Discussion The Related monad and constant values in type classes. Jonas Almstroem Duregard [18]talked about a common pattern which occurs when associating data with a type (as opposed to a value). Heterogeneous Data Structures - Nested Pairs and functional references. Guenther Schmidt [19]asked about different ways to implement heterogeonous datastructures. Blog noise [20]Haskell news from the [21]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Michael Snoyman: [22]Four HTTP Request Body Interfaces (repost). * Brent Yorgey: [23]Math.Combinatorics.Multiset. * Darcs: [24]darcs weekly news #55. * Galois, Inc: [25]Tech Talk: Modern Benchmarking in Haskell. * Ketil Malde: [26]Tools for pyrosequencing analysis. * Arch Haskell News: [27]Arch Haskell News: February 2010. * Don Stewart (dons): [28]Migrating from uvector to vector. * GHC / OpenSPARC Project: [29]Memory Barriers and GHC 6.12.1. * Darcs: [30]darcs weekly news #54. * Gergely Patai: [31]Behind the dungeons. * David Amos: [32]How to find a strong generating set. Quotes of the Week * fasta: And by cool, I mean 'that is not supposed to happen'. * uncyclopedia: Calculations which are undefined are denoted by the _|_ symbol, pronounced Bottom, which the documentation explains as the compiler giving you the finger. * Draconx|Laptop: mathematics is the art of finding different ways to write "therefore". * medfly: Cale, #haskell wants to know all your personal preferences so we can all copy you * Cale: Gentoo is a massive waste of electricity. * hobophobe: So, I can only conclude that Haskell is a memetic virus, and monads are the eggs it lays out in innocent programming forums to entice others to become infected. * benmachine: unsafeCoerce is just a generalisation of id * jmcarthur: what good is a state monad if your state is basically 'i have no idea what the hell my state is'? About the Haskell Weekly News New editions are posted to [33]the Haskell mailing list as well as to [34]the Haskell Sequence and [35]Planet Haskell. [36]RSS is also available, and headlines appear on [37]haskell.org. To help create new editions of this newsletter, please see the information on [38]how to contribute. Send stories to jfredett . at . gmail . dot . com. The darcs repository is available at darcs get [39]http://patch-tag.com/r/jfredett/HWN2/pullrepo HWN2 . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/70589 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/70563 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/70533 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/70485 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/70344 7. http://www.dragongoserver.net/ 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/70328 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/70314 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/70290 11. http://article.gmane.org/gmane.comp.lang.haskell.general/17802 12. http://article.gmane.org/gmane.comp.lang.haskell.general/17799 13. http://article.gmane.org/gmane.comp.lang.haskell.general/17791 14. http://article.gmane.org/gmane.comp.lang.haskell.general/17783 15. http://article.gmane.org/gmane.comp.lang.haskell.general/17779 16. http://article.gmane.org/gmane.comp.lang.haskell.general/17778 17. http://article.gmane.org/gmane.comp.lang.haskell.cafe/70188 18. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/70492 19. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/70450 20. http://planet.haskell.org/ 21. http://haskell.org/haskellwiki/Blog_articles 22. http://snoyberg.wordpress.com/2010/02/21/four-http-request-body-interfaces-… 23. http://byorgey.wordpress.com/2010/02/20/math-combinatorics-multiset/ 24. http://blog.darcs.net/2010/02/darcs-weekly-news-55.html 25. http://www.galois.com/blog/2010/02/19/tech-talk-modern-benchmarking-in-hask… 26. http://blog.malde.org/index.php/2010/02/19/tools-for-pyrosequencing-analysi… 27. http://archhaskell.wordpress.com/2010/02/19/arch-haskell-news-february-2010/ 28. http://donsbot.wordpress.com/2010/02/15/migrating-from-uvector-to-vector/ 29. http://ghcsparc.blogspot.com/2010/02/memory-barriers-and-ghc-6121.html 30. http://blog.darcs.net/2010/02/darcs-weekly-news-54.html 31. http://just-bottom.blogspot.com/2010/02/behind-dungeons.html 32. http://haskellformaths.blogspot.com/2010/02/how-to-find-strong-generating-s… 33. http://www.haskell.org/mailman/listinfo/haskell 34. http://sequence.complete.org/ 35. http://planet.haskell.org/ 36. http://sequence.complete.org/node/feed 37. http://haskell.org/ 38. http://haskell.org/haskellwiki/HWN 39. http://patch-tag.com/r/jfredett/HWN2/pullrepo%20HWN2

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Threading and FFI
by Yves Parès 22 Feb '10

22 Feb '10

Hello! I was wondering: is the Haskell default runtime (that which uses only one processor) scheduler able to interrupt a thread which is currently calling to a C function in order to enable another haskell thread to progress? I think it can't, because I have starvation problems when I have a thread which calls inside its loop to a C function which makes a little "sleep". BTW, what is the portable way to sleep a thread in Haskell ? Control.Concurrent.threadDelay is "GHC only". ----- Yves Parès Live long and prosper -- View this message in context: http://old.nabble.com/Threading-and-FFI-tp27611528p27611528.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Installing wx via cabal
by Dušan Kolář 22 Feb '10

22 Feb '10

Dear all, Running cabal install --global wx stops very soon with the following error. Building wxcore-0.12.1.2... [ 1 of 22] Compiling Graphics.UI.WXCore.WxcObject ( src/haskell/Graphics/UI/WXCore/WxcObject.hs, dist/build/Graphics/UI/WXCore/WxcObject.o ) [ 2 of 22] Compiling Graphics.UI.WXCore.WxcDefs ( src/haskell/Graphics/UI/WXCore/WxcDefs.hs, dist/build/Graphics/UI/WXCore/WxcDefs.o ) [ 3 of 22] Compiling Graphics.UI.WXCore.WxcClassTypes ( src/haskell/Graphics/UI/WXCore/WxcClassTypes.hs, dist/build/Graphics/UI/WXCore/WxcClassTypes.o ) [ 4 of 22] Compiling Graphics.UI.WXCore.WxcTypes ( src/haskell/Graphics/UI/WXCore/WxcTypes.hs, dist/build/Graphics/UI/WXCore/WxcTypes.o ) [ 5 of 22] Compiling Graphics.UI.WXCore.WxcClassesAL ( src/haskell/Graphics/UI/WXCore/WxcClassesAL.hs, dist/build/Graphics/UI/WXCore/WxcClassesAL.o ) ghc: out of memory (requested 1048576 bytes) cabal: Error: some packages failed to install: It seems quite strange as the machine seems to have 16GB RAM and a free swap, can I somehow put options or so? I have ghc 10.4. installed. Thanks Dusan

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games of chance
by Dupont Corentin 21 Feb '10

21 Feb '10

Hello, are you aware of a framework to find probabilities in a given game of chance, in Haskell? l would like to compute probabilities like: "roll 3 dices, sum the result, then roll 3 other dices, sum the result, what is the probability to obtain the same sum?" Cheers, Corentin

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Re: Parsing of bytestrings with non-String errors?
by Permjacov Evgeniy 21 Feb '10

21 Feb '10

On 02/21/2010 11:57 PM, haskell-cafe-request(a)haskell.org wrote: > Message: 2 > Date: Sun, 21 Feb 2010 12:36:21 +0000 > From: Magnus Therning <magnus(a)therning.org> > Subject: [Haskell-cafe] Parsing of bytestrings with non-String errors? > To: haskell-cafe <haskell-cafe(a)haskell.org> > Message-ID: <4B8128C5.6030105(a)therning.org> > Content-Type: text/plain; charset="utf-8" > > I've looked at polyparse and attoparsec and they seem to have in common that > the error always is a String. My current ideas for a project would be a lot > easier if I could just return some other type, something that I can pattern > match on. > > Is there a parser combinator library out there that works on bytestrings and > allows using a custom error type? > > Or maybe there's some very basic reason why String is so commonly used? > > You can try to play with ParsecT / ErrorT

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Re: [Haskell-cafe] Profiling
by Patai Gergely 21 Feb '10

21 Feb '10

> I tried to compile my program with -prof, but GHC just whines at me > that the packages I'm using haven't been compiled for profiling. Do I > really need to go recompile every single package I'm using with > profiling support before I can profile my program? How do I tell Cabal > to install the necessary code? (I really hope this doesn't involve > uninstalling and reinstalling everything...) Almost. You don't need to uninstall anything, just run cabal install <package> --reinstall -p for every relevant package. Gergely -- http://www.fastmail.fm - mmm... Fastmail...

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STArray newListArray
by Vojtěch Knyttl 21 Feb '10

21 Feb '10

Hello, I am trying to create STArray with newListArray like this: la x y = newListArray ((1,1),(x,y)) [(x'+y') | x' <- [1..x], y' <- [1..y]] – but it does not work: No instance for (MArray a Field m) I tried to define the type like this, but it would not work either: la :: Int -> Int -> STArray (Int,Int) Field It is obvious that I don't get the syntax of using it, so I will appreciate any suggestions. V. K.

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darcs 2.4 release candidate 2
by Reinier Lamers 21 Feb '10

21 Feb '10

Hi all, The darcs team would like to announce the immediate availability of darcs 2.4 release candidate 2. darcs 2.4 will contain many improvements and bugfixes compared to darcs 2.3.1. Highlights are the faster operation of record, revert and related commands, and the experimental interactive hunk editing. This beta is your chance to test-drive these improvements and make darcs even better. Compared to darcs 2.4 beta 3, the performance of "darcs check" and "darcs repair" has been brought up to the level of darcs 2.3.1.` The easiest way to install darcs is using the Haskell Platform [1]. If you have installed the Haskell Platform or cabal-install, you can install this beta release by doing: $ cabal update $ cabal install --reinstall darcs-beta Alternatively, you can download the tarball from http://darcs.net/releases/darcs-beta-2.3.99.2.tar.gz , and build it by hand as explained in the README file. Interactive hunk editing ------------------------ To try out interactive hunk editing, press 'e' when you are prompted with a hunk patch by 'darcs record'. You will then be shown an editor screen in which you can edit the state you want to record between the last two ruler lines. You can find more information about the hunk editing feature on http://wiki.darcs.net/HunkEditor . Reporting bugs -------------- If you have an issue with darcs 2.4 release candidate 2, you can report it via the web on http://bugs.darcs.net/ . You can also report bugs by email to bugs(a)darcs.net. What's New ---------- A list of important changes since 2.3.1 is as follows (please let me know if there's something you miss!): * Use fast index-based diffing everywhere (Petr) * Interactive patch splitting (Ganesh) * An 'optimize --upgrade' option to convert to hashed format in-place (Eric) * Hunk matching (Kamil Dworakowski, tat.wright) * Progress reporting is no longer deceptive (Roman) * A 'remove --recursive' option to remove a directory tree from revision control (Roman) * 'show files' accepts arguments to show a subset of tracked files (Luca) * A '--remote-darcs' flag for pushing to a host where darcs isn't called darcs * Many miscellaneous Windows improvements (Salvatore, Petr and others) * 'darcs send' now mentions the repository name in the email body (Joachim) * Handle files with boring names in the repository correctly (Petr) * Fix parsing of .authorspellings file (Tomáš) * Various sane new command-line option names (Florent) * Remove the '--checkpoint' option (Petr) * Use external libraries for all UTF-8 handling (Eric, Reinier) * Use the Haskell zlib package exclusively for compression (Petr) A list of issues resolved since 2.3.1: * 183: do not sort changes --summary output * 223: add --remote-darcs flag to specify name of remote darcs executable * 291: provide (basic) interactive patch splitting * 540: darcs remove --recursive * 835: 'show files' with arguments * 1122: get --complete should not offer to create a lazy repository * 1216: list Match section in ToC * 1224: refuse to convert a repo that's already in darcs-2 format * 1300: logfile deleted on unsucessful record * 1308: push should warn about unpulled patches before patch-selection * 1336: sane error message on --last "" (empty string to numbers parser) * 1362: mention repo name in mail send body * 1377: getProgname for local darcs instances * 1392: use parsec to parse .authorspelling * 1424: darcs get wrongly reports "using lazy repository" if you ctrl-c old-fashioned get * 1447: different online help for send/apply --cc * 1488: fix crash in whatsnew when invoked in non-tracked directory * 1548: show contents requires at least one argument * 1554: allow opt-out of -threaded (fix ARM builds) * 1563: official thank-you page * 1578: don't put newlines in the Haskeline prompts * 1583: on darcs get, suggest upgrading source repo to hashed * 1584: provide optimize --upgrade command * 1588: add --skip-conflicts option * 1594: define PREPROCHTML in makefile * 1620: make amend leave a log file when it should * 1636: hunk matching * 1643: optimize --upgrade should do optimize * 1652: suggest cabal update before cabal install * 1659: make restrictBoring take recorded state into account * 1677: create correct hashes for empty directories in index * 1681: preserve log on amend failure * 1709: fix short version of progress reporting * 1712: correctly report number of patches to pull * 1720: fix cabal haddock problem * 1731: fix performance regression in check and repair * 1741: fix --list-options when option has multiple names Kind Regards, the darcs release manager, Reinier Lamers [1]: You can download the Haskell platform from http://hackage.haskell.org/platform/

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Restricted categories
by Sjoerd Visscher 21 Feb '10

21 Feb '10

Hi all, I want restricted categories, just like the rmonad package provides restricted monads. The ultimate goal is to have a product category: http://en.wikipedia.org/wiki/Product_category > {-# LANGUAGE TypeOperators, TypeFamilies, MultiParamTypeClasses, FlexibleInstances, FlexibleContexts, ScopedTypeVariables, UndecidableInstances #-} > import Prelude hiding ((.), id, fst, snd) > import qualified Prelude First lets create a clone of Data.Suitable from the rmonad package, but this time for types with two arguments: > class Suitable2 m a b where > data Constraints m a b > constraints :: m a b -> Constraints m a b > withResConstraints :: forall m a b. Suitable2 m a b => (Constraints m a b -> m a b) -> m a b > withResConstraints f = f (constraints undefined :: Constraints m a b) > withConstraintsOf :: Suitable2 m a b => m a b -> (Constraints m a b -> k) -> k > withConstraintsOf v f = f (constraints v) Now we can define a restricted category: > class RCategory (~>) where > id :: Suitable2 (~>) a a => a ~> a > (.) :: (Suitable2 (~>) b c, Suitable2 (~>) a b, Suitable2 (~>) a c) => b ~> c -> a ~> b -> a ~> c (->) (or "Hask") is an instance of this class: > instance Suitable2 (->) a b where > data Constraints (->) a b = HaskConstraints > constraints _ = HaskConstraints > instance RCategory (->) where > id = Prelude.id > (.) = (Prelude..) Now on to the product category. Objects of the product category are types that are an instance of IsProduct: > class IsProduct p where > type Fst p :: * > type Snd p :: * > fst :: p -> Fst p > snd :: p -> Snd p For example: > instance IsProduct (a, b) where > type Fst (a, b) = a > type Snd (a, b) = b > fst = Prelude.fst > snd = Prelude.snd Arrows from the product of category c1 and category c2 are a pair of arrows, one from c1 and one from c2: > data (c1 :***: c2) a b = c1 (Fst a) (Fst b) :***: c2 (Snd a) (Snd b) The instance for Suitable2 restricts objects to IsProduct, and requires the Fst and Snd parts of the objects to be suitable in c1 resp. c2: > instance (IsProduct a, IsProduct b, Suitable2 c1 (Fst a) (Fst b), Suitable2 c2 (Snd a) (Snd b)) => Suitable2 (c1 :***: c2) a b where > data Constraints (c1 :***: c2) a b = (IsProduct a, IsProduct b, Suitable2 c1 (Fst a) (Fst b), Suitable2 c2 (Snd a) (Snd b)) => ProdConstraints > constraints _ = ProdConstraints Finally the RCategory instance: > instance (RCategory c1, RCategory c2) => RCategory (c1 :***: c2) where > id = withResConstraints $ \ProdConstraints -> id :***: id > -- f@(f1 :***: f2) . g@(g1 :***: g2) = > -- withResConstraints $ \ProdConstraints -> > -- withConstraintsOf f $ \ProdConstraints -> > -- withConstraintsOf g $ \ProdConstraints -> > -- (f1 . g1) :***: (f2 . g2) Here I am running into problems. I get this error: Could not deduce (Suitable2 c2 (Snd a) (Snd b), Suitable2 c1 (Fst a) (Fst b)) from the context (IsProduct b, IsProduct c, Suitable2 c1 (Fst b) (Fst c), Suitable2 c2 (Snd b) (Snd c)) arising from a use of `withConstraintsOf' In the first argument of `($)', namely `withConstraintsOf g' I don't understand this, as I thought the constraints the error is complaining about is just what withConstraintsOf g should provide. I guess there's something about the Suitable trick that I don't understand, or possibly the type families Fst and Snd are biting me. Who can help me out? Thanks. greetings, Sjoerd

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ANN: HaskellTorrent v0.0
by Jesper Louis Andersen 20 Feb '10

20 Feb '10

Hello, I am happy to announce HaskellTorrent v0.0, a concurrent bittorrent client. The current release is a rather early preview release: it can download torrents and seed them, but currently there are many optimizations and tweaks needed before it is ready for day-to-day use. In particular, we are not yet fully compliant with the bittorrent specification and need proper clients to connect to in order to operate. Basically, you install the cabal package and then run HaskellTorrent foo.torrent and it will then download the contents of the torrent to the current directory. We would like to hear about any kind of problems you might encounter. Send them to jesper.louis.andersen(a)gmail.com for now. We have only tested the software on GHC 6.10.4 and 6.12.1, mostly on Unix platforms. It is known to work on Debian/Unstable with GHC610 and GHC612. If you want to hack code, get in touch with me. There are something for any level of skill to do. *** HaskellTorrent is using the CML library to get concurrency. It easily runs some 200-300 processes when it operates and its process model is somewhat loosely inspired by the model of Erlang. Looking forward, the next goal is to optimize concurrency, memory usage and CPU usage in the client. It currently hogs resources due to naive data structure choices and some expensive correctness assertions. *** Links of interest: http://hackage.haskell.org/package/HaskellTorrent http://github.com/jlouis/haskell-torrent *** This release was brought to you by: Alex Mason: A lot of Wireprotocol and BCode serialization work through the use of the cereal package. Astro: GHC 6.12 support. Support for multi-file torrents. In addition, patches were contributed by: Jesper Louis Andersen John Gunderman Thomas Christensen -- J.

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