- Haskell-Cafe - Haskell.org

Re: [Haskell-beginners] folds -- help!
by Adrian Neumann 14 Mar '09

14 Mar '09

That's why I said "for appropriate g and f". But I see that my wording was misleading. However you can say: > foldl' oplus alpha bs =(foldr f id bs) alpha where > f a g = \alpha -> g (alpha `oplus` a) > > foldr' oplus alpha bs = (foldl f id bs) alpha where > f g a = \alpha -> g (a `oplus` alpha) And it works as long as oplus is strict in both arguments. Am 10.03.2009 um 21:54 schrieb John Dorsey: > Adrian Neumann wrote: > >> Notice that there is no difference between >> >> foldr g a >> foldl f a >> >> (for appropriate g and f) if g and f are strict in both arguments. > > Be careful... as apfelmus noted elsewhere in this thread, that's > not (in > general) true. > > Prelude> foldr (^) 2 [3,5] > 847288609443 > Prelude> foldl (^) 2 [3,5] > 32768 > > The reason? Integer exponentiation (^) isn't associative and > commutative. So the first is (3 ^ (5^2)) = 3^25, while the second is > ((2 ^ 3) ^ 5) = 2^15. > > Cheers, > John > > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://www.haskell.org/mailman/listinfo/beginners

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Haskell Weekly News: Issue 109 - March 14, 2009
by Brent Yorgey 14 Mar '09

14 Mar '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090314 Issue 109 - March 14, 2009 --------------------------------------------------------------------------- Welcome to issue 109 of HWN, a newsletter covering developments in the [1]Haskell community. Congratulations to the authors of RWH on their [2]Jolt award! Some cool libraries released this week (as usual), and some really cool PhD [3]opportunities at Strathclyde. Also, it seems that I was censured last week for not including any quotes in the HWN, which is because tunes.org (which hosts the #haskell logs) was down while I was putting it together. So, this time I've included quotes going back two weeks, I HOPE YOU'RE HAPPY Community News Tom DuBuisson (TomMD) has [4]moved to Portland and will be starting a PhD at Portland State soon. Announcements darcs fundraising drive - only $720 left to go!. Eric Kow [5]announced that [6]donations are still being accepted to help pay for travel to the upcoming Haskell hackathon. So far we have raised $280, so we're almost a third of the way there. Think you can help? Vintage BASIC 1.0. Lyle Kopnicky [7]announced the initial release of [8]Vintage BASIC, an interpreter for microcomputer-era BASIC. Fully unit-tested, it faithfully implements the common elements of the language. On the web site, you can find 102 games from the classic book BASIC Computer Games, all of which run flawlessly. Have fun! ThreadScope: Request for features for the performance tuning of parallel and concurrent Haskell programs. Satnam Singh [9]requested feedback on infrastructure for logging run-time events and a graphical viewer program called [10]ThreadScope. The goal is for these features to make it into the next release of GHC. torch-0.1. Yusaku Hashimoto [11]announced a new unit test framework, [12]torch-0.1. sparsebit 0.5 - Sparse Bitmaps for Pattern Match Coverage. Ki Yung Ahn [13]announced the release of the [14]sparsebit library. This library packages the functional peal paper [15]Sparse Bitmaps for Pattern Match Coverage submitted to ICFP 2009 by Ki Yung Ahn and Tim Sheard. happs-tutorial 0.8. Crieghton Hogg [16]announced the release of [17]happs-tutorial 0.8, which is compatible with [18]happstack-0.2. A number of changes have occurred in this release, including general code cleanup, migration to the new Happstack.Server.SimpleHTTP API, and more. Future 1.1.0 concurrency library. ChrisK [19]announced the [20]future package, which ought to do what C++ standard futures/promises do, plus a bit more. The main operation is forkPromise :: IO a -> IO (Promise a), which sets the "IO a" operation running in a fresh thread; the eventual result can be accessed in many ways (non-blocking, blocking, blocking with timeout). Holumbus-MapReduce 0.0.1. Stefan Schmidt [21]announced three new libraries: [22]Holumbus-MapReduce, [23]Holumbus-Distribution, and [24]Holumbus-Storage, which provide tools for building distributed systems. These libraries are used as the backbone of the [25]Holumbus search engine. Turbinado V0.6. Alson Kemp [26]announced the release of [27]Turbinado 0.6, a Rails-ish Model-View-Controller web serving framework for Haskell. New features include support for CGI serving, statically compiled Layouts, Views, and Controllers, lower case paths, support for cookies and encrypted cookie sessions, easier installation, and support for GHC 6.10. iteratee-0.1.0. John Lato [28]announced the hackage release of [29]iteratee-0.1.0. This library implements enumerators and iteratees [30]as proposed by Oleg Kiselyov. Harpy 0.4.4 - Runtime code generation for x86 machine code. Dirk Kleeblatt [31]announced the release of [32]Harpy 0.4.1, a library for runtime code generation for x86 machine code. The new release features additional Eq instances, support for new prefetching instructions, and some bug fixes. Discussion Suggestion for a Haskell mascot. Maur�cio [33]suggested using a sloth as the Haskell mascot. If you would like to know how to say 'sloth' in just about every language ever, read this thread. Jobs Microsoft PhD Scholarship at Strathclyde. Conor McBride [34]announced another PhD opportunity at Strathclyde, sponsored by Microsoft Research, to investigate the practical and theoretical impact of extending Haskell's type system with numeric expressions (representing sizes, or ranges, or costs, for example) and constraints capturing richer safety properties than are currently managed by static typing. Blog noise [35]Haskell news from the [36]blogosphere. * Braden Shepherdson: [37]Pimp Your XMonad #4: Urgency Hooks. * Thomas M. DuBuisson: [38]Explicit Parallelism via Thread Pools. * Ketil Malde: [39]Current developments. Ongoing development of the biohaskell libraries for bioinformatics. * Philip Wadler: [40]Cafe Scientifique. Philip will be giving a talk, "Proofs are Programs: 19th Century Logic and 21st Century Computing", on Monday in Edinburgh. * Yi: [41]Yi 0.6.0 Release Notes. * Alson Kemp: [42]ANNOUNCE: Turbinado V0.6. * GHC / OpenSPARC Project: [43]Thread activity plotting. * Real-World Haskell: [44]We won a Jolt Award!. * Real-World Haskell: [45]Real World Haskell on the Kindle 2. * Christophe Poucet (vincenz): [46]Bootstrapping cabal. * Gtk2HS: [47]Mickinator File Manager. * Osfameron: [48](rough) Grids in Haskell. Some notes on representing 2D grids in Haskell. * Manuel M T Chakravarty: [49]These graphs summarise the performance of Data Parallel Haskell.... * GHC / OpenSPARC Project: [50]Project midpoint. * GHC / OpenSPARC Project: [51]The GNU Debugger and me. * Don Stewart (dons): [52]Evolving faster Haskell programs. Using genetic algorithms to find optimal flag combinations. * Xmonad: [53]Xmonad and the Gimp. * Xmonad: [54]xmonad on eee. * Mark Wassell: [55]Conversations with a type checker. * Holumbus: [56]Holumbus-MapReduce on Hackage. Some neat libraries for building distributed systems! * Darcs: [57]darcs weekly news #20. * Nick Mudge: [58]First Bay Area Haskell Meeting. * Dan Piponi (sigfpe): [59]Dinatural Transformations and Coends. Quotes of the Week * mmorrow: when i first saw haskell i was like "holy shitfork! that's what i've been trying to do in C for forever!" * pastah: the maybe monad is like cheating. everything is so awesomelly easy. * wli: Monads are like constipation. Comonads are like Ex-Lax. * TomMD: Never trust IO. * Axman6: let blah f x = f (blah f x) in blah ("blah "++) "" * MyCatVerbs: Lazy IO is implemented in terms of unsafePerformIO, you, you, you silly bipedal carbon-based organism. * MyCatVerbs: Amdahl's law is mostly to be used for making people feel depressed. * Axman6: -ddump-occur-anal <- another terrible name... * AchimSchneider: Finite automata don't go bottom in any case, at least not if you don't happen to shoot them and their health drops below zero. * ski: the truth (semantics), the whole truth (completeness), and nothing but the truth (soundness) * f4hy: wait you can do a show on an infinite list?! (I am starting to think haskell is not a programming language, it is evil wizardry) * Baughn: concat $ forM [(1,2), (4,5)] $ \(a,b) -> show (b,a+b) About the Haskell Weekly News New editions are posted to [60]the Haskell mailing list as well as to [61]the Haskell Sequence and [62]Planet Haskell. [63]RSS is also available, and headlines appear on [64]haskell.org. To help create new editions of this newsletter, please see the information on [65]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [66]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://www.realworldhaskell.org/blog/2009/03/12/we-won-a-jolt-award/ 3. http://article.gmane.org/gmane.comp.lang.haskell.general/16944 4. http://tommd.wordpress.com/2009/03/13/explicit-parallelism-via-thread-pools/ 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/54758 6. http://www.darcs.net/donations.html 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/54652 8. http://www.vintage-basic.net/ 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/54521 10. http://raintown.org/threadscope 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/54445 12. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/torch 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/54436 14. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/sparsebit 15. http://kyagrd.dyndns.org/wiki/SparseBitmapsForPatternMatchCoverage 16. http://www.haskell.org//pipermail/haskell-cafe/2009-March/057305.html 17. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happs%2Dtutorial 18. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happstack 19. http://article.gmane.org/gmane.comp.lang.haskell.cafe/54409 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/future 21. http://article.gmane.org/gmane.comp.lang.haskell.cafe/54325 22. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Holumbus%2DMapRe… 23. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Holumbus-Distrib… 24. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Holumbus-Storage 25. http://www.holumbus.org/redmine/wiki/holumbus 26. http://article.gmane.org/gmane.comp.lang.haskell.general/16953 27. http://www.turbinado.org/ 28. http://article.gmane.org/gmane.comp.lang.haskell.general/16945 29. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/iteratee 30. http://okmij.org/ftp/Haskell/Iteratee/ 31. http://article.gmane.org/gmane.comp.lang.haskell.general/16942 32. http://uebb.cs.tu-berlin.de/harpy/ 33. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/54418 34. http://article.gmane.org/gmane.comp.lang.haskell.general/16944 35. http://planet.haskell.org/ 36. http://haskell.org/haskellwiki/Blog_articles 37. http://braincrater.wordpress.com/2009/03/14/pimp-your-xmonad-4-urgency-hook… 38. http://tommd.wordpress.com/2009/03/13/explicit-parallelism-via-thread-pools/ 39. http://blog.malde.org/index.php/2009/03/13/current-developments/ 40. http://wadler.blogspot.com/2009/03/cafe-scientifique.html 41. http://yi-editor.blogspot.com/2009/03/yi-060-release-notes.html 42. http://www.alsonkemp.com/haskell/announce-turbinado-v06/ 43. http://ghcsparc.blogspot.com/2009/03/thread-activity-plotting.html 44. http://www.realworldhaskell.org/blog/2009/03/12/we-won-a-jolt-award/ 45. http://www.realworldhaskell.org/blog/2009/03/13/real-world-haskell-on-the-k… 46. http://cpoucet.wordpress.com/2009/03/12/bootstrapping-cabal/ 47. http://haskell.org/gtk2hs/archives/2009/03/10/mickinator-file-manager/ 48. http://greenokapi.net/blog/2009/03/10/rough-grids-in-haskell/ 49. http://justtesting.org/post/85103645 50. http://ghcsparc.blogspot.com/2009/03/project-midpoint.html 51. http://ghcsparc.blogspot.com/2009/03/gnu-debugger-and-me.html 52. http://donsbot.wordpress.com/2009/03/09/evolving-faster-haskell-programs/ 53. http://xmonad.wordpress.com/2009/03/08/xmonad-and-the-gimp/ 54. http://xmonad.wordpress.com/2009/03/08/xmonad-on-eee/ 55. http://www.poundstone.org/blog/?p=23 56. http://holumbus.fh-wedel.de/blog/?p=18 57. http://blog.darcs.net/2009/03/darcs-weekly-news-20.html 58. http://nickmudge.info/?post=115 59. http://blog.sigfpe.com/2009/03/dinatural-transformations-and-coends.html 60. http://www.haskell.org/mailman/listinfo/haskell 61. http://sequence.complete.org/ 62. http://planet.haskell.org/ 63. http://sequence.complete.org/node/feed 64. http://haskell.org/ 65. http://haskell.org/haskellwiki/HWN 66. http://code.haskell.org/~byorgey/code/hwn/

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Vim support for cabal
by Pavel Perikov 14 Mar '09

14 Mar '09

Hi café ! I googled for some kind of vim support for cabal but found nothing. I mean syntax highlighting of .cabal and probably integration with haskellmode. Did anyone hear about such thing? Pavel

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Re: [Haskell-cafe] ANNOUNCE: Vintage BASIC 1.0
by Lyle Kopnicky 14 Mar '09

14 Mar '09

I've posted a new version, 1.0.1, that has a usage message if you run it with no arguments. There is a package for Windows now (not just a binary) as well as Linux. Both packages include documentation and example programs. Thanks for pointing that out! On Fri, Mar 13, 2009 at 1:31 AM, Wolfgang Jeltsch < jeltsch(a)informatik.tu-cottbus.de> wrote: > When running the executable, nothing happens. The executable should show a > usage message instead. Where are the BASIC programs? I think, you have to > grab them from the source. They should be installed, too. > > Best wishes, > Wolfgang >

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Re: [Haskell-cafe] Abuse of the monad [was: monadic logo]
by Andrew Wagner 14 Mar '09

14 Mar '09

Can you expand on this a bit? I'm curious why you think this. On Thu, Mar 12, 2009 at 10:13 AM, Thomas Davie <tom.davie(a)gmail.com> wrote: > > On 12 Mar 2009, at 15:04, Gregg Reynolds wrote: > > At risk of becoming the most hated man in all Haskelldom, I'd like to >> suggest that the Haskell logo not use lambda symbols. Or at least not as >> the central element. Sorry, I know I'm late to the party, but the thing is >> there is nothing distinctive about lambda; it's common to all FPLs. >> Besides, Lisp/Scheme already have that franchise. >> >> What is distinctive about Haskell it's use of the monad. The Pythagorean >> monad symbol is wonderfully simple: >> > No, what's distinctive about Haskell is usually the abuse of the monad. > > Encouraging people to think Haskell is all about monadic programming even > more is a recipe for disaster. > > Just my 2¢ > > Bob_______________________________________________ > > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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reddit.com/r/haskell_proposals: Relevance to Google Summer of Code?
by fallintothis 14 Mar '09

14 Mar '09

NOTE: This message was originally posted to the subreddit in question (and has been slightly modified), where I was told that I should post the question on haskell-cafe. See http://www.reddit.com/r/haskell_proposals/comments/847by/ask_relevance_to_g… I'm currently researching the possibility of applying for the Google Summer of Code[1] and (by way of dons's post[2]) have found myself perusing the Haskell Proposals subreddit for project ideas. As an accepted MS CS student, I've spent my undergraduate life annoying professors by using a slew of different programming languages -- most recently, Haskell. While not altogether unfamiliar with the language, I rather doubt (or at least try to honestly question) how useful a contributor I'd be to some of the larger projects that have been posted (e.g., the Immix garbage collector[3] or loop unrolling[4]), despite some of their acceptances as tickets on the Summer of Code Trac[5] and my deep interest in compiler & language theory. There are projects that match other interests of mine and (in my approximation) my experience level, but they also tend to be smaller. For example, the reddit-alike[6] or wiki-embedded Haddock[7]. So, background sap-story notwithstanding, I suppose my general question is: with respect to the aforementioned Summer of Code post, is this subreddit meant to be a place for appropriate SoC projects? It doesn't feel quite like it is, but I would be excited to work on some of those that I indicated. The telltale sign for a project's worthiness seems to be that a ticket is already opened on the Trac that spells out the appropriateness, but this is limiting. More obviously, to test the fitness of a project, should the idea be opened as a ticket for the cursory review of others? Should someone who wants to do Summer of Code work be at any particular level of experience ("dive into GHC's backend" versus "use Haskell to hack on a project")? Intuitively, 1 summer's worth of work could probably be found in any corner of code that meshes with any student's expertise and interests -- even a reddit-alike can actually be a lot of work. But the catch (for me) is that when familiarity is relatively low, it's hard to come up with such ideas. I realize that applications are competitive against other students, so the range of acceptable submissions would depend more on the other applicants, but I think it's also important to address haskell.org's ethos with regards to who they're looking for. If there's a more appropriate place to post this question (ha! singular) I'm more than happy to transplant it. [1] http://code.google.com/soc/ [2] http://www.reddit.com/r/programming/comments/7zfog/anybody_done_the_google_… [3] http://www.reddit.com/r/haskell_proposals/comments/7wjsc/implement_the_immi… [4] http://www.reddit.com/r/haskell_proposals/comments/7z1uf/implement_loop_unr… [5] http://hackage.haskell.org/trac/summer-of-code/wiki/Soc2009 [6] http://www.reddit.com/r/haskell_proposals/comments/7u48x/a_simple_redditlik… [7] http://www.reddit.com/r/haskell_proposals/comments/7qnwq/haddock_with_embed…

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Pointless functors
by Martijn van Steenbergen 13 Mar '09

13 Mar '09

Bonjour café, Are there any functors f for which no point/pure/return :: a -> f a exists? Thank you, Martijn.

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Applicative combinators from Parsec
by Martijn van Steenbergen 13 Mar '09

13 Mar '09

Hello, Looking at Parsec 3 I see: > chainr1 :: (Stream s m t) => ParsecT s u m a -> > ParsecT s u m (a -> a -> a) -> ParsecT s u m a > chainr1 p op = scan where > scan = do x <- p; rest x > rest x = (do f <- op; y <- scan; return (f x y)) <|> return x > But if I remove the type signature and let GHC infer it for me, I get a much more generic type: > chainr1 :: (Alternative m, Monad m) => m a -> m (a -> a -> a) -> m a But we don't really need m to be a monad since we're only doing applicative operations, so after some rewriting we get: > chainr1 :: Alternative f => f a -> f (a -> a -> a) -> f a > chainr1 p op = scan where > scan = flip id <$> p <*> rest > rest = (flip <$> op <*> scan) <|> pure id Would it be a good idea to: 1) make the Parsec combinators as generic as possible and 2) move the really generic applicative ones to Control.Applicative? Thanks, Martijn.

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Re: [Haskell-cafe] Natural Numbers: Best implementation?
by Brandon S. Allbery KF8NH 13 Mar '09

13 Mar '09

On 2009 Mar 12, at 22:54, Mark Spezzano wrote: > I was wondering what the best way to implement Natural number would > be. Is there a package which already does this? type-level on Hackage. > 2. Use the type > data Natural = Zero | Succ !Natural One of the reasons people use type-level naturals is to get laziness; you've made this strict. Is there a reason? -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery(a)kf8nh.com system administrator [openafs,heimdal,too many hats] allbery(a)ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH

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Re: [Haskell-cafe] ANNOUNCE: Vintage BASIC 1.0
by Lyle Kopnicky 13 Mar '09

13 Mar '09

On Fri, Mar 13, 2009 at 1:31 AM, Wolfgang Jeltsch < jeltsch(a)informatik.tu-cottbus.de> wrote: > When running the executable, nothing happens. The executable should show a > usage message instead. Where are the BASIC programs? I think, you have to > grab them from the source. They should be installed, too. > Thanks for your feedback, and for checking out Vintage BASIC! I will add a usage message, as you suggested. Currently the usage is only described in the User's Guide. There are no options; you just give it the name of one or more BASIC source files. (Naturally this extends to doing nothing when supplied with zero source files.) The BASIC games are at http://www.vintage-basic.net/games.html. There is a tarball of all the games (bcg.tar.gz<http://www.vintage-basic.net/downloads/bcg.tar.gz>) as well. These are separated from the Vintage BASIC distribution for legal reasons. Vintage BASIC is copyrighted by me under a BSD license. The games were written by many authors and compiled into a book copyrighted by Creative Computing. I have secured permission from the editor to post the games. I do not wish to imply that they are covered by the same license as the interpreter. If anyone has any suggestions as to how to make the process simpler, I'd be happy to hear it. Thanks, Lyle P.S. I need to get my other e-mail account subscribed to this list....

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