October 2010 - Haskell-Cafe

If Python now has a good email library; how challenging is it to call Python from Haskell?
by caseyh＠istar.ca 28 Oct '10

28 Oct '10

:)

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New repo location for the network package
by Johan Tibell 28 Oct '10

28 Oct '10

Hi all, To ease my maintenance burden, I've moved the network package repo to: http://github.com/haskell/network Patches are accepted either in the git mbox format, as normal (diff) patch files, or as GitHub pull requests. P.S. If you want to get added to the haskell GitHub organization, just drop me an email. Johan

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Re: [Haskell-cafe] concurrency vs. I/O in GHC
by John Lato 28 Oct '10

28 Oct '10

From: Claude Heiland-Allen <claudiusmaximus(a)goto10.org> > > On 23/10/10 23:17, Donn Cave wrote: > > Quoth Claude Heiland-Allen<claudiusmaximus(a)goto10.org>, > > ... > >> The conclusion I drew was that "unsafe" foreign functions block the > >> current "capability" (OS thread) and any "threads" (Haskell forkIO etc) > >> currently scheduled on that capability, but other capabilities and > >> threads continue executing as normal. > > ... until GC time when all capabilities must be ready. (?) > That's quite interesting. Thanks very much to everyone who contributed to this. I think my understanding of the interactions between threads and foreign functions has deepened considerably. I may be able to accomplish what I want after all. I am somewhat surprised that all capabilities must be ready for GC; I thought with the parallel GC that wouldn't be necessary. But I don't know much about GC implementations so I try not to let their behavior surprise me too much. John

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Map constructor in a DSL
by Dupont Corentin 28 Oct '10

28 Oct '10

Hello café, I have a little DSL in my program as follow. Now I'd like to add a Map constructor in it. Thats where I would need help! > data Obs a where > AllPlayers :: Obs [Int] > Plus :: (Num a) => Obs a -> Obs a -> Obs a > And :: Obs Bool -> Obs Bool -> Obs Bool > Vote :: Obs String -> Obs Int -> Obs Bool > *Map :: (Obs a -> Obs b) -> Obs [a] -> Obs [b]* > -- and others Here is the evaluator for Obs: > evalObs :: Obs a -> Evaluator a > evalObs (Konst a) = return $ pure a > evalObs (Not a) = liftE not (evalObs a) > evalObs (Plus a b) = liftE2 (+) (evalObs a) (evalObs b) > evalObs (Minus a b) = liftE2 (-) (evalObs a) (evalObs b) > evalObs (Time a b) = liftE2 (*) (evalObs a) (evalObs b) > evalObs (And a b) = liftE2 (&&) (evalObs a) (evalObs b) > evalObs (Or a b) = liftE2 (||) (evalObs a) (evalObs b) > evalObs (Equ a b) = liftE2 (==) (evalObs a) (evalObs b) > evalObs (If a b c) = liftE3 (if3) (evalObs a) (evalObs b) (evalObs c) How you can see it is quite neat... But how can I write the evaluator for Map? Actually I have some half baked solution, 15 lines long that I don't dare to show ;) Actually compiling code excerpt is here: http://hpaste.org/40897/map_contstructor_in_a_dsl Thanks for your help. Corentin Below is some helper code: type Evaluator a = StateT Game Comm a (Either Actions a) -- | Combined lifters for Evaluator liftE = liftM . liftA liftE2 = liftM2 . liftA2 liftE3 = liftM3 . liftA3 instance Applicative (Either Actions) where pure x = Right x (Right f) <*> (Right x) = Right $ f x (Right _) <*> (Left u) = Left u (Left u) <*> (Right _) = Left u (Left u) <*> (Left v) = Left $ u ++ v

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Re: [Haskell-cafe] New repo location for the network package
by John Lato 28 Oct '10

28 Oct '10

> > From: Magnus Therning <magnus(a)therning.org> > > On Wed, Oct 27, 2010 at 22:53, Johan Tibell <johan.tibell(a)gmail.com> > wrote: > > Hi all, > > > > To ease my maintenance burden, I've moved the network package repo to: > > > > Â Â http://github.com/haskell/network > > > > Patches are accepted either in the git mbox format, as normal (diff) > > patch files, or as GitHub pull requests. > > > > P.S. If you want to get added to the haskell GitHub organization, just > > drop me an email. > > Ah, the use of github is spreading :-) > > If I, as the developer of the FOO Haskell package, want to move to use > github, can I get a source repo under that organisation as well? > I'm asking since I am considering taking some of my packages from > patch-tag to github (it's really github I want, it's unfortunate that > it also means I'll have to leave darcs), it would then be nice to have > those repos as a part of the haskell organisation. > Similarly, what's the remit of the Haskell organization on github? Is the intention to be an umbrella for any haskell package, or more restricted? I have the same question as Magnus (although in my case I took over something on github; if I could move to darcs and preserve history I would). John

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Test command line programs
by Dupont Corentin 28 Oct '10

28 Oct '10

Hello again café, I have a command line program that takes input from various handles (actually network sockets) like this: > s <- hGetLine h > etc. I'd like to unit test this. How can I do? I'd like to inject data on the handle so that all the input chain is tested. How are command line programs' IO automatically tested usually? Another little question: How can I access the name of a function inside a function (for Trace purpose)? I have to use the CPP preprocessor? Thanks for hints, Corentin

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ANN: language-java-0.1.0
by Niklas Broberg 28 Oct '10

28 Oct '10

Hi café, I found myself in need of a source manipulation suite for Java code. A hackage search turned up nothing, so I wrote one: http://hackage.haskell.org/package/language-java I'm sure there are a number of bugs waiting to be discovered, my own testing hasn't been overly extensive. I'm setting up a trac, will follow up with its location once it's up. Known short-coming: Annotations are not yet supported. Cheers, /Niklas

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On being called a troll
by Günther Schmidt 28 Oct '10

28 Oct '10

Hi everyone, this post is to argue my own case. Today I have made the most upsetting experience of being called a troll, twice. I have posted to this list for over 3 years now and until lately it was an enlightening experience. The responses to my questions have usually been helpful and friendly. But for some time now, I have noticed that the tone on this list has changed. It seems to have become ok to respond quite brutally and without regard for the other persons feelings. It also seems to have become ok to chime in. For some reason it has become acceptable to politicalize a subject at the earliest convenience and take the gloves off. I am 42 now and am surprised how much this still hurts, after all I survived the schoolyard bullies and who would have thought that these times would ever come again? I urge you, my fellow haskellers, to show some restraint when we are dealing with one another on this list. And to think twice before you launch a personal attack. Günther

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Need programming advice for Network Protocol Parsing
by Günther Schmidt 27 Oct '10

27 Oct '10

Hi all, I'd like to write a client app that communicates with a server over TCP/IP. My question is in regard which parser to use for the servers responses. I'm quite familiar with parsec (2.x) but I'm not sure if it's the right choice for this. The code would necessarily constantly be switching between checking for input, interpreting and then responding. Any suggestions? Günther

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Haskell Weekly News: Issue 156 - October 27, 2010
by Daniel Santa Cruz 27 Oct '10

27 Oct '10

Welcome to issue 156 of the HWN, a newsletter covering developments in the [1]Haskell community in the week of October 17 - 28. I did not manage to filter out good posts from Haskell-Cafe this week. If you see a thread in -cafe that you think would be good to share with the community, please do share it with me. I need to find a better way of keeping up with the mountain of posts to that list. There were a total of 34 new stories posted to the Haskell Reddit channel (+10), 47 new questions taged with Haskell in StackOverflow (+20), and 332 messages posted to Haskell-Cafe (-76). So, what was hot last week? Announcements John Hughes [2]announced that the Functional Programming group at Chalmers is recruiting a postdoctoral researcher for a two year position, starting as soon as possible. Wouter Swierstra [3]called for workshop and co-located event proposals for the ICFP 2011 in Tokyo, Japan. Zhong Shao [4]informed us that the Department of Computer Science at Yale University is seeking applicants for a PostDoc and PhD positions in the broad area of certified software. Josh Tripplett wrote in to tell us about Ore, a [5]packaging system for Ruby inspired by Haskell's Cabal! According to [6]this haskell community calendar, there are 2 events to take note happening next week: The Haskell Communities & Activities Report submission deadline on Nov 1, and BelHac (in Ghent, Belgium) on Nov 5 - 7. Top Reddit Stories * The Haskell Platform is now in Ubuntu Domain: packages.ubuntu.com Score: 58, Comments: 5 On Reddit: http://www.reddit.com/r/haskell/comments/dtffi/the_haskell_platform_is_now_… Original: http://packages.ubuntu.com/maverick/haskell-platform * ghcjs: Haskell to Javascript: now released Domain: github.com Score: 36, Comments: 4 On Reddit: http://www.reddit.com/r/haskell/comments/dujnb/ghcjs_haskell_to_javascript_… Original: http://github.com/sviperll/ghcjs#readme * GHC Blog: New directions for Template Haskell Domain: hackage.haskell.org Score: 32, Comments: 3 On Reddit: http://www.reddit.com/r/haskell/comments/dtav8/ghc_blog_new_directions_for_… Original: http://hackage.haskell.org/trac/ghc/blog/Template%20Haskell%20Proposal * A brief tale of faster equality Domain: serpentine.com Score: 27, Comments: 10 On Reddit: http://www.reddit.com/r/haskell/comments/dt76u/a_brief_tale_of_faster_equal… Original: http://www.serpentine.com/blog/2010/10/19/a-brief-tale-of-faster-equality/ * MTL 2.0 has been uploaded good bye old mtl, hello monads-fd! Domain: hackage.haskell.org Score: 25, Comments: 6 On Reddit: http://www.reddit.com/r/haskell/comments/dx8ml/mtl_20_has_been_uploaded_goo… Original: http://hackage.haskell.org/package/mtl-2.0.0.0 * Haskell Rapid Transit Domain: mtnviewmark.wordpress.com Score: 23, Comments: 4 On Reddit: http://www.reddit.com/r/haskell/comments/duqp0/haskell_rapid_transit/ Original: http://mtnviewmark.wordpress.com/2010/10/21/haskell-rapid-transit/ * mathblog: A program for creating and managing a static, mathematically-inclined weblog Domain: hackage.haskell.org Score: 20, Comments: 0 On Reddit: http://www.reddit.com/r/haskell/comments/duh1o/mathblog_a_program_for_creat… Original: http://hackage.haskell.org/package/mathblog-0.2 * Lazy Type-Level Programming: nice trick by Max Bolingbroke Domain: haskell.org Score: 20, Comments: 1 On Reddit: http://www.reddit.com/r/haskell/comments/duu54/lazy_typelevel_programming_n… Original: http://www.haskell.org/pipermail/haskell-cafe/2010-October/085307.html * Let's build a compiler (in Haskell): Part 12 - Introducing the State Monad Domain: alephnullplex.appspot.com Score: 19, Comments: 14 On Reddit: http://www.reddit.com/r/haskell/comments/du38c/lets_build_a_compiler_in_has… Original: http://alephnullplex.appspot.com/blog/view/2010/10/19/lbach-introducing-the… * What's the status of Haskell on the iPhone? Domain: self.haskell Score: 18, Comments: 5 On Reddit: http://www.reddit.com/r/haskell/comments/dsyij/whats_the_status_of_haskell_… Original: /r/haskell/comments/dsyij/whats_the_status_of_haskell_on_the_iphone/ Top StackOverflow Questions * Question (votes: 33, answers: 8): Best explanation for Languages without Null Read on SO: http://stackoverflow.com/questions/3989264/best-explanation-for-languages-w… * Question (votes: 16, answers: 6): Saving my running toplevel for later Read on SO: http://stackoverflow.com/questions/3966925/saving-my-running-toplevel-for-l… * Question (votes: 10, answers: 2): What's the difference between undefined in Haskell and null in Java? Read on SO: http://stackoverflow.com/questions/3962939/whats-the-difference-between-und… * Question (votes: 9, answers: 2): Is FC++ used by any open source projects? Read on SO: http://stackoverflow.com/questions/3995942/is-fc-used-by-any-open-source-pr… * Question (votes: 8, answers: 3): What is the difference between forall a. [a] and [forall a. a]? Read on SO: http://stackoverflow.com/questions/3961851/what-is-the-difference-between-f… * Question (votes: 6, answers: 5): In Haskell, is there any way to express that a type should be an instance of a typeclass in more than one way? Read on SO: http://stackoverflow.com/questions/3998732/in-haskell-is-there-any-way-to-e… * Question (votes: 5, answers: 3): Pure exceptions in Haskell Read on SO: http://stackoverflow.com/questions/3961536/pure-exceptions-in-haskell * Question (votes: 5, answers: 1): How to use fromInteger with no implicit prelude in Haskell? Read on SO: http://stackoverflow.com/questions/3969413/how-to-use-frominteger-with-no-i… * Question (votes: 5, answers: 7): Is this Fibonacci sequence function recursive? Read on SO: http://stackoverflow.com/questions/3980756/is-this-fibonacci-sequence-funct… * Question (votes: 5, answers: 1): Any Sparse Linear Algebra package in Haskell? Read on SO: http://stackoverflow.com/questions/3995323/any-sparse-linear-algebra-packag… Quotes of the Week If you'd like to have a quote you see in IRC here, use the following syntax: @remember WhoSaidIt Quote. I'm currently scrapping IRC logs to find this data, so don't worry if lambdabot doesn't cooperate. * chrisdone: Production of two-handed use langes Schwerts with long flambard blades and heavily category-theoretically decorated guards, katzbalgers, axes, mail and Macedonian quality defence pikes. Lambda Knights need to be prepared for the inevitable battle against success. HackageDB Updates Who contributed, and what got uploaded? * AlbertoRuiz: hmatrix-special * AlessandroVermeulen: lhs2TeX-hl * AlexanderSolla: Facts * AlexeyKhudyakov: histogram-fill, monoid-statistics, mwc-random-monad * AntonKholomiov: csound-expression, temporal-media * AristidBreitkreuz: monadLib-compose, xml-monad * AycanIrican: hweblib * BasVanDijk: concurrent-extra, dstring, explicit-iomodes, explicit-iomodes-bytestring, explicit-iomodes-text, repr, string-combinators, threads, usb, usb-enumerator * BryanOSullivan: text * ChrisKuklewicz: regex-tdfa, regex-tdfa-unittest * ClaudeHeilandAllen: gmndl, qd * DanielDiaz: HaTeX * DonaldStewart: plugins * EugeneKirpichov: splot * GregWeber: xss-sanitize * HenkJanVanTuyl: GeBoP * HolgerReinhardt: amqp * HugoPacheco: pointless-rewrite * JamesCook: priority-queue, queue * JeremyShaw: formlets-hsp * JoelCrisp: bindings-gts * JohanTibell: network * JohnMillikin: anansi, cpython, enumerator-fd, enumerator, enumerator-tf, yajl-enumerator, yajl * JonathanDaugherty: mathblog * JudeNagurney: augeas * KetilMalde: a50, flower * MagnusTherning: archlinux, archlinux-web, cabal2arch * MasatakeDaimon: bindings-audiofile, bindings-EsounD * MichaelIlseman: yaml-light * MichaelSnoyman: authenticate, convertible-text, data-object-json, data-object, data-object-yaml, hamlet, mime-mail, wai-handler-devel, wai-handler-webkit, web-encodings, yesod-auth, yesod * MichelBoucey: ip6addr * NeilMitchell: hlint * OlegBelozeorov: xmms2-client-glib, xmms2-client * OscarFinnsson: text-xml-qq * PeterSimons: vty * PetrRockai: darcs-fastconvert * RoelVanDijk: base-unicode-symbols, containers-unicode-symbols * RyanNewton: wordsetdiff * SimonMarlow: stm * StephenBlackheath: hexpat * StephenTetley: wumpus-basic, wumpus-microprint, wumpus-tree * ThomasDuBuisson: control-event, crypto-api, gps, hsXenCtrl, ipc * TomHawkins: fountain * ViktorDevecseri: bloxorz About the Haskell Weekly News New editions are posted to [7]the Haskell mailing list as well as to [8]the Haskell Sequence and [9]Planet Haskell. [10]RSS is also available, and headlines appear on [11]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://article.gmane.org/gmane.comp.lang.haskell.general/18252 3. http://article.gmane.org/gmane.comp.lang.haskell.general/18260 4. http://article.gmane.org/gmane.comp.lang.haskell.general/18261 5. http://postmodern.github.com/2010/10/25/mining-rubygems-from-ore.html 6. https://sites.google.com/site/haskellcommunitycalendar/ 7. http://www.haskell.org/mailman/listinfo/haskell 8. http://sequence.complete.org/ 9. http://planet.haskell.org/ 10. http://sequence.complete.org/node/feed 11. http://haskell.org/

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