- Haskell-Cafe - Haskell.org

Real-time garbage collection for Haskell
by Luke Palmer 09 Mar '10

09 Mar '10

I have seen some proposals around here for SoC projects and other things to try to improve the latency of GHC's garbage collector. I'm currently developing a game in Haskell, and even 100ms pauses are unacceptable for a real-time game. I'm calling out to people who have seen or made such proposals, because I would be willing to contribute funding and/or mentor a project that would contribute to this goal. Also any ideas for reducing this latency in other ways would be very appreciated. Thanks, Luke

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file descriptors and handles
by Mathijs Kwik 09 Mar '10

09 Mar '10

Hi all, Today I had a look at chapter 20 of RWH. The extended example (stripped down HSH) in the end is great. I think I understand it, but I have some questions left: the master process closes the client-sided FD's. it uses fdToHandle for the other sides of the pipe to get a handle to stdIn and stdOut on the client process. it writes to the stdIn handle and closes it afterwards. - doesn't it need to close the fd as well? the stdOut handle gets used when reading the command output (using hGetContents) - doesn't the handle need to get closed? or will this happen automatically if hGetContents finds EOF ? - and also here, shouldn't the fd get closed? More general: what happens when closing a handle when there's still output left? Will reading further output throw an exception or just think it's EOF? And what happens when closing the underlying FD? will the handle "break"? or will it close automatically? Thanks for any help Mathijs

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ptys and hGetContent problem
by Mathijs Kwik 08 Mar '10

08 Mar '10

Hi all, I found this blogpost from Bryan O'Sullivan http://www.serpentine.com/blog/2008/09/30/unix-hacking-in-haskell-better-ps… and I wanted to try it out. Before moving to an interactive command (which needs pty), I just did a small test for "ls -l /" to see if it worked. I got it to compile, but when running, it throws an exception when reaching the end of the output (in this case because I evaluate the length to force reading all). Main: /dev/ptmx: hGetContents: hardware fault (Input/output error) Please have a look at the hpaste to see what I did: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=23343 What's wrong? :) My guess is that hGetContents doesn't receive a nice EOF when the process exits (ls doesn't stay around waiting for input), but I have no idea on how to fix this. And further... If I do want to use an interactive program which needs input, how do I send ctrl-d or ctrl-c? tail -f needs ctrl-c (or I need to kill the process) Thanks for any help Mathijs PS: I know about libexpect, it's not useful for what I wanna do (multiple processes, having 'answers' from 1 be used to decide what to input the other, without ending the 'answer' process)

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Books for "advanced" Haskell
by Günther Schmidt 08 Mar '10

08 Mar '10

Hi all, there seems to be a huge number of things that monads can be used for. And there are lots of papers, blog posts, etc. describing that, some more or less accessible. Apart from monads there are of course also Applicative Functors, Monoids, Arrows and what have you. But in short the Monad thingy seems to be the most "powerful" one of them all. Is there a book that specializes on Monads? A Haskell-Monad book? Günther

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Haskell Weekly News: Issue 152 - March 08, 2010
by jfredett＠gmail.com 08 Mar '10

08 Mar '10

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20100308 Issue 152 - March 08, 2010 --------------------------------------------------------------------------- Welcome to issue 152 of HWN, a newsletter covering developments in the [1]Haskell community. Hello Haskellers, this week brings updates to some standards (like Parsec), as well as some new tunes to the Haskell songbook. WAI and Yesod were released, giving some new options for Haskell-based web applications, Don Stewart made some improvements to his Genetic Optimizer system to include options from GHC's new LLVM backend, and I made some serious progress on the new HWN software. Speaking of the new software, there have been numerous reports of warts and other unfortunate things with the current editions of the HWN. Fear not, these warts are well known and being worked on intently. Unfortunately, it's somewhat difficult to fix them given the current publication software, however, in the new-and-improved version that (hopefully) should be entering use soon, these warts will be removed. So, without further interuption about the stylistic content, Haskellers, your Haskell Weekly News! Announcements Bluetile 0.3.1. Jan Vornberger [2]announced Bluetile, an adaptation of xmonad for the masses. Bluetile aims to make tiling window managers accessible by drawing on standard window manager conventions and idioms. ED: This is not technically an announcement, but it's very cool and everyone should check it out! yesod 0.0.0 (web framework). Michael Snoyman [3]announced the release of yesod, a web framework based on WAI. wai-0.0.0 (Web Application Interface). Michael Snoyman [4]announced the first release of wai, a library implementing the WAI protocol. iteratee-parsec 0.0.2. Maciej Piechotka [5]announced iteratee-parsec, a library which allows for parsec parsers in the IterateeG monad. Parsec 3.1.0. Derek Elkins [6]announced a new release of Parsec, containing many improvments due (primarily) to Antoine Latter. Progression-0.3 (supporting benchmarking in Haskell). Neil Brown [7]announced a new release of Progression. Progression is a utility built on top of Criterion for recording benchmarks for several version of your code. Ghent Functional Programming Group: First Meeting on April 1, 2010. Jeroen Janssen [8]announced the first meeting of the Ghent Functional Programming group, see the post for location and time details. PhD position in Functional Programming at Chalmers (deadline 2010-04-07). Patrik Jansson [9]announced an opening for a PhD student at Chalmers, working in Functional Programming and DSELs. VSTTE 2010: Verified Software -- Third Call for Papers. Gudmund Grov [10]announced a third CFP for VSTTE 2010, the Third International Conference on Verified Software: Theories, Tools, and Experiments. barchart-0.1.1. Sebastian Fischer [11]announced barchart, a command line program with an associated library for generating bar charts. Call for Participation: CHR Summer School. Jon Sneyers [12]announced a call for participation in the CHR Summer School on Programming and Reasoning with Rules and Constraints. Discussion Free theorem - what do we need it for. Maciej Piechotka [13]asked about Free Theorems and what they were good for. Has anybody translated Douglas Hofstadter's Scientific American articles introducting Scheme to a general audience into Haskell? Benjamin L. Russell [14]asked if anyone had considered translating Douglas Hofstadter's SciAm articles introducting Scheme to Haskell. Evolving Faster Haskell Programs (now with LLVM!). Don Stewart [15]our resident speed demon is at it again, harnessing the new LLVM backend of GHC and the power of Natural Selection to make his programs go even faster. Blog noise [16]Haskell news from the [17]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Neil Brown: [18]Synchronous Channels using MVars. * "FP Lunch": [19]Causal Semantics of (A)FRP. * Darcs: [20]darcs weekly news #56. * Dan Piponi (sigfpe): [21]Products, Limits and Parametric Polymorphism. * Bryn Keller: [22]Real World Haskell. * Isaac Dupree: [23]Next Project, Move doc-parsing to from GHC to Haddock. * Isaac Dupree: [24]Summer of Code Wrap-Up.. * Isaac Dupree: [25]Status update. * Isaac Dupree: [26]platform progress. * Isaac Dupree: [27]another boring update, & question :-). * Isaac Dupree: [28]How To Navigate Your Code:. * Michael Snoyman: [29]Persistence. * Neil Brown: [30]Choice over Events using STM. * Michael Snoyman: [31]Tweedle Beetle Battle. * Galois, Inc: [32]The Semantics of Asynchronous Exceptions. * Bryan O'Sullivan: [33]What's in a parser? Attoparsec rewired (2/2). * Bryan O'Sullivan: [34]What's in a parsing library? (1/2). * Neil Brown: [35]Progression 0.3: Bar Charts and Normalisation. Quotes of the Week * edwardk: heh, i'm amused the ParsecT that Antoine Latter put together is in the form of a right kan extension ;) * Philippa: <TR1N1TY> I'm selling botz and backdoors <Philippa> I'm selling bans * samlee (via reddit): haha those ghc options are longer than actual program About the Haskell Weekly News New editions are posted to [36]the Haskell mailing list as well as to [37]the Haskell Sequence and [38]Planet Haskell. [39]RSS is also available, and headlines appear on [40]haskell.org. To help create new editions of this newsletter, please see the information on [41]how to contribute. Send stories to jfredett . at . gmail . dot . com. The darcs repository is available at darcs get [42]http://patch-tag.com/r/jfredett/HWN2/pullrepo HWN2 . References 1. http://haskell.org/ 2. http://www.bluetile.org/ 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/71314 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/71184 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/71144 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/71122 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/71041 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/70981 9. http://article.gmane.org/gmane.comp.lang.haskell.general/17842 10. http://article.gmane.org/gmane.comp.lang.haskell.general/17841 11. http://article.gmane.org/gmane.comp.lang.haskell.general/17831 12. http://article.gmane.org/gmane.comp.lang.haskell.general/17825 13. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/71117 14. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/71022 15. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/70967 16. http://planet.haskell.org/ 17. http://haskell.org/haskellwiki/Blog_articles 18. http://chplib.wordpress.com/2010/03/08/synchronous-channels-using-mvars/ 19. http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=369 20. http://blog.darcs.net/2010/03/darcs-weekly-news-56.html 21. http://blog.sigfpe.com/2010/03/products-limits-and-parametric.html 22. http://www.xoltar.org/?p=36 23. http://haddock2009.wordpress.com/2009/07/21/next-project-move-doc-parsing-t… 24. http://haddock2009.wordpress.com/2009/08/26/summer-of-code-wrap-up/ 25. http://haddock2009.wordpress.com/2009/05/12/status-update/ 26. http://haddock2009.wordpress.com/2009/05/20/platform-progress/ 27. http://haddock2009.wordpress.com/2009/05/26/another-boring-update-question/ 28. http://haddock2009.wordpress.com/2009/06/23/how-to-navigate-your-code/ 29. http://www.snoyman.com/blog/entry/persistence/ 30. http://chplib.wordpress.com/2010/03/04/choice-over-events-using-stm/ 31. http://www.snoyman.com/blog/entry/tweedle-beetle-battle/ 32. http://www.galois.com/blog/2010/03/04/the-semantics-of-asynchronous-excepti… 33. http://www.serpentine.com/blog/2010/03/03/whats-in-a-parser-attoparsec-rewi… 34. http://www.serpentine.com/blog/2010/03/03/whats-in-a-parsing-library-1/ 35. http://chplib.wordpress.com/2010/03/02/progression-0-3-bar-charts-and-norma… 36. http://www.haskell.org/mailman/listinfo/haskell 37. http://sequence.complete.org/ 38. http://planet.haskell.org/ 39. http://sequence.complete.org/node/feed 40. http://haskell.org/ 41. http://haskell.org/haskellwiki/HWN 42. http://patch-tag.com/r/jfredett/HWN2/pullrepo%20HWN2

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Re: [Haskell] Recursive definition of fibonacci with Data.Vector
by Henning Thielemann 08 Mar '10

08 Mar '10

On Sun, 7 Mar 2010, Edgar Z. Alvarenga wrote: > Hello, > > why I can't define a recursive vector using Data.Vector, like in > the example: > > import qualified Data.Vector as V > > let fib = 0 `V.cons` (1 `V.cons` V.zipWith (+) fib (V.tail v)) Since I liked to have both element-wise lazy construction and packed data, I created a data-structure for that purpose: http://code.haskell.org/storablevector/Data/StorableVector/Cursor.hs However, those vectors/arrays are finite, but could be extended to a chunky infinite structure.

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ghc leaking memory?
by Joachim Breitner 08 Mar '10

08 Mar '10

Hi, in Debian, we are having some problems building large libraries (such as agda, highlighting-kate, xmonad-contrib) on weaker architectures (sparc, armel, s390) which compile with -fvia-C, especially when building the profiling libraries. In the case of highlighting-kate, there were really issues with the code: A huge list of words which ghc seemed to try to inline caused it consuming a lot of memory. But in the case of agda, it even fails with relatively small modules: https://buildd.debian.org/fetch.cgi?pkg=agda&arch=sparc&ver=2.2.6-3&stamp=1… Now, looking at the memory gauge on my computer while compiling such a program with Cabal (which compiles all modules in one ghc call), it looks like it is steadily increasing. I’d expect ghc to free a lot of memory when it is done with a module, but this does not seem to be the case. Is this a bug (i.e. memory leak) in ghc or expected behavior? Is there a way to make Cabal build each module on its own? Are there any fixes or work-arounds? Greetings, Joachim -- Joachim "nomeata" Breitner Debian Developer nomeata(a)debian.org | ICQ# 74513189 | GPG-Keyid: 4743206C JID: nomeata(a)joachim-breitner.de | http://people.debian.org/~nomeata

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how to write a function to send a string to a tuple
by Pradeep Wickramanayake 08 Mar '10

08 Mar '10

Hi, Im having problems with sending a string to a tuple. My string contains integers and strings The whole string stay as ("test,dfdf",3,"dfsf") sortList2 :: String -> String sortList2 (x:xs) | x == ',' = "" | otherwise = [x] ++ sortList2 xs The above function separating each words from the string Now I need to put them to a tuple putList :: String -> (Int, String, String, Int, Int) putList (x:xs) |xs /="" = sortList2 ++ putList xs I wrote something like above. But I really have no clue how to continue. Can someone help me. It's a big help

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Haskell platform for GHC 6.12.1?
by Peter Verswyvelen 08 Mar '10

08 Mar '10

Using GHC 6.12.1 on Windows currently is hard, since one must compile the latest version of cabal-install, which is a nightmare to do for a typical windows user (install mingw, msys, utils like wget, download correct package from hackage, compile them in correct order, etc etc) What's the status of the Haskell platform for the latest and greatest Glasgow Haskell Compiler?

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Re: [Haskell] Recursive definition of fibonacci with Data.Vector
by Don Stewart 08 Mar '10

08 Mar '10

edgar: > Hello, > > why I can't define a recursive vector using Data.Vector, like in > the example: > > import qualified Data.Vector as V > > let fib = 0 `V.cons` (1 `V.cons` V.zipWith (+) fib (V.tail v)) > There's a typo: fib = 0 `V.cons` (1 `V.cons` V.zipWith (+) fib (V.tail fib)) Which let's it typecheck. But I don't think this is a sensible use of vectors. In fact, infinite vectors make no sense, as far as I can tell -- these are fundamentally bounded structures. GHC even optimizes it to: fib = fib (literally!). $ time ./A A: <<loop>> -- Don

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