- Haskell-Cafe - Haskell.org

[ANN] PAM library, Iptables web-interface
by Evgeny Tarasov 10 Jul '11

10 Jul '11

Hello! I'd like to announce my project called Iptadmin. It's a web interface for linux Iptables firewall [1]. It supports just few Iptables options by now. The main feature of Iptadmin is user friendly help messages. Iptadmin works in a daemon mode. It doesn't keep any auxiliary information in a system, firewall configuration is taken from the «iptables-save» script. All changes is made by Iptables calling. Firewall rules are saved by «/etc/init.d/iptables save» script. Several linux distributions such as Debian require additional Iptables configuration. Iptadmin uses PAM [2] authentication. Access is granted for root and for any other user with membership in «iptadmin» system group. Iptadmin is written using Happstack, so it doesn't support https yet. To prevent sending system password by network in plain text, the web interface is listening only on loopback network interface. In order to access Iptadmin remotely user should setup https proxying using external web server. There is also dedicated library for parsing and printing Iptables rules [3]. While working on Iptadmin I've implemented library with subset of PAM api bindings[4]. A code of my project is licensed under BSD3. Sources are uploaded to hackage [3,4,5]. More information can be found on a project homepage[6]. [1] http://www.netfilter.org/ [2] http://www.kernel.org/pub/linux/libs/pam/ [3] http://hackage.haskell.org/package/iptables-helpers-0.3 [4] http://hackage.haskell.org/package/pam-0.1 [5] http://hackage.haskell.org/package/iptadmin-1.0.0 [6] http://iptadmin.confmgr.org -- Best regards, Evgeny Tarasov

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Cabal uninstall
by Andrew Pennebaker 10 Jul '11

10 Jul '11

Please add an automated uninstall option for Cabal packages. It's a pain to remove them manually, and the user expectation based on other package managers (Gem, Aptitude, MacPorts, Homebrew, Yum, Emerge) is that "cabal uninstall"/"cabal remove" does the intuitive thing: remove packages and their dependencies. Cheers, Andrew Pennebaker www.yellosoft.us

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Re: [Haskell-cafe] Call for GUI examples - Functional Reactive Programming
by John Lato 09 Jul '11

09 Jul '11

From: Chris Smith <cdsmith(a)gmail.com> > > On Fri, 2011-07-08 at 08:08 +0200, Heinrich Apfelmus wrote: > > Do you know any *small GUI programs* that you would *like* to see > > *implemented with Functional Reactive Programming?* > > This isn't really a specific application, but what I'd like to see most > from FRP is an example of something that involves moving between windows > and dialog boxes. All of the GUI-based FRP examples I've seen so far > involve interactions in a specific GUI layout. It's unclear to me how > FRP extends into a situation like: > > - There's a starting window showing several options for what to do > - When the user chooses an option, that window closes, and a new one > opens with that activity. > - In response to some actions, dialog boxes appear with their own > interactions. > > It's not clear to me if anyone in FRP has an idea of how stuff like this > fits in. Is there some FRP trick to handle this declaratively? Or > would you just say each move to a new window ends or pauses one network > of events and behaviors, and starts a new one? I can show you how I've been handling this with reactive-banana and gtk2hs. As a small example, the "File->Open" command is meant to open a new project. The codez: > maybeEvent0 :: Typeable a => Action -> IO (Maybe a) -> NetworkDescription (Event a) > maybeEvent0 act ops = do > (addHandler, runHandlers) <- liftIO newAddHandler > liftIO $ on act actionActivated $ ops >>= maybe (return ()) runHandlers > fromAddHandler addHandler > -- | Load a saved project file > openHandler :: ActionGroup -> Window -> NetworkDescription (Event (String, HTree)) > openHandler actGrp _win = do > act <- liftIO openAction > liftIO $ actionGroupAddActionWithAccel actGrp act Nothing > maybeEvent0 act openProjectDialog > openProjectDialog :: IO (Maybe (String, HTree)) > openProjectDialog = do > fc <- fileChooserDialogNew (Just "Select a project file") > Nothing > FileChooserActionOpen > [] > fileChooserSetSelectMultiple fc False > dialogAddButton fc stockCancel ResponseCancel > dialogAddButton fc stockOk ResponseOk > widgetShowAll fc > resp <- dialogRun fc > case resp of > ResponseOk -> runMaybeT $ do > fp <- MaybeT $ fileChooserGetFilename fc > liftIO $ widgetDestroy fc > (fp, ) <$> liftIO (readProject fp) > _ -> widgetDestroy fc >> return Nothing The `openHandler` function connects the Gtk signal to the reactive-banana framework. This uses the helper `maybeEvent0`, which filters an IO action and triggers a reactive-banana Event when that IO action actually returns a value. I've been using this pattern for most of my modal dialogs, and I think it works very well. The one dialog I haven't used it for is the starting window, which is straight-line imperative code. I don't yet have any non-modal dialogs or alternate windows, but there shouldn't be a problem. There's nothing special about which window a widget is in; it can be connected to the FRP framework just like a widget in the main window. John L.

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Re: [Haskell-cafe] NLP libraries and tools?
by wren ng thornton 09 Jul '11

09 Jul '11

On 7/7/11 3:50 AM, Aleksandar Dimitrov wrote: > It's actually a shame we're discussing this on -cafe and not on -nlp. Then > again, maybe it's going to prompt somebody to join -nlp, and I'm gonna CC it > there, because some folks over there might be interested, but not read -cafe. Quite :) > When you mentioned Arabic for producing sentences that go on for ages > you don't really need to go that far. I have had the doubtful pleasure of > reading Kant and Hegel in their original versions. In German, it is sometimes > still considered good style to write huge sentences. I once made it a point, > just to stick it to a Kant-loving-person, to produce a sentence that spanned 2 > whole pages (A4.) It wasn't even difficult. The Romans were big fans of that too (though there's only a small group of folks interested in doing NLP on Latin these days). I've only read Hegel et al. in translation, but the Latin I've read falls nicely into the notion of "span". It doesn't, however, always fall nicely into a clause-based approach like Japanese does. Then again, that could be due to the poetic/rhetorical nature of the texts in question. I wonder if there's been any computational attempt to make the notion of span or discourse atoms rigorous enough for pragmatic use... > I'm very much a "works for me" person in these matters. Mostly because I'm tired > of linguists fighting each other over trivial matters. Give me something I can > work with already! I can't help but be a (meta)theorist. But then, I'm of the firm opinion that theory must be grounded in actual practice, else it belongs more to the realm of theology than science. -- Live well, ~wren

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video for linux two (v4l2) bindings
by Claude Heiland-Allen 09 Jul '11

09 Jul '11

Greetings all, I uploaded 4 new packages that may be of interest: bindings-linux-videodev2 0.1 - bindings to Video For Linux Two (v4l2) kernel interfaces http://hackage.haskell.org/package/bindings-linux-videodev2-0.1 bindings-mmap 0.1 - bindings to mmap for POSIX http://hackage.haskell.org/package/bindings-mmap-0.1 bindings-libv4l2 0.1 - bindings to libv4l2 for Linux http://hackage.haskell.org/package/bindings-libv4l2-0.1 v4l2-examples 0.1 - video for linux two examples http://hackage.haskell.org/package/v4l2-examples-0.1 The first wraps the low-level structures and ioctls of the V4L2 API. The second wraps the raw mmap/munmap functions and constants (which I couldn't seem to find on hackage, only higher level wrappers which I couldn't use for various reasons). It would make more sense for this to be folded into bindings-posix at some point. The third wraps libv4l2, which provides an interface very similar to the use of V4L2 ioctls, but the library adds extra capabilities behind the scenes (I'm led to believe colour space conversion is one of them) which is hopefully useful. And the last is a crude example dumping frames from a video device (like a webcam) to stdout in YUV4MPEG2 format. The code is *very* low-level and imperative (almost a direct translation from the C example provided on the linuxtv API reference), there is plenty of room for a much nicer layer to (for example) get video data into RePa arrays or OpenGL textures. As these are raw bindings, documentation is best found upstream. Thanks to Maurício C. Antunes's package for making this possible, I recommend it: http://hackage.haskell.org/package/bindings-DSL Claude -- http://claudiusmaximus.goto10.org

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Re: [Haskell-cafe] Call for GUI examples - Functional Reactive Programming
by Daniel Patterson 08 Jul '11

08 Jul '11

Forgot to cc the list On Jul 8, 2011, at 11:20 AM, Daniel Patterson wrote: > On Jul 8, 2011, at 3:51 AM, Heinrich Apfelmus wrote: >> Jason Dagit wrote: >>> Heinrich Apfelmus wrote: >>>> Do you know any *small GUI programs* that you would *like* to see >>>> *implemented with Functional Reactive Programming?* >>>> >>>> I would love to hear your examples, so that I can try to convert them to FRP >>>> style and test my library against them! >>> How about a GUI for darcs? >> >> This would involve a lot of functionality unrelated to GUIs. Could you break it down to a minimal "GUI-only" example that still gets the point across? > > > What about something that just showed the list of patches for a given repository, which would update when the repository changed? That is deadly simple, but could still be somewhat useful (ie, have it track a relatively central repo, and running on a screen somewhere in the metaphorical office). It would also be wonderful to start on a GUI for darcs, and I could say it might interest _me_ in taking a stab at improving it :) And it might be an example of the kind of open system that was mentioned earlier > > Daniel

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Using Acid-State for IPC?
by Dmitri O.Kondratiev 08 Jul '11

08 Jul '11

Hi, I am wondering if Acid-State (http://hackage.haskell.org/package/acid-state) can be used to share data between processes running in different address spaces? For example, one demon system process (not thread!) periodically collects data from Web and stores it in a list. On regular intervals this process checkpoints the list to a disk file. Another independent process randomly starts and reads this list from the checkpoint file. Can this simple scenario be done with Acid-State? Any conflicts accessing checkpoint file from two system processes simultaneously? What other Haskell libs can be used for such a task? Thanks!

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CfP: Haskell Workshop in Leipzig, Germany, October 7
by Johannes Waldmann 08 Jul '11

08 Jul '11

Call for submissions for our local Haskell Workshop in Leipzig, Germany. Tutorials, talks, demonstrations ... everything welcome. Workshop language is German (mainly), and English (by request). Submission deadline: August 20, Workshop date: October 7 http://portal.imn.htwk-leipzig.de/events/hal6-haskell-workshop Best regards, Johannes Waldmann.

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Diagnose stack space overflow
by Logo Logo 08 Jul '11

08 Jul '11

Hi, For the following error: Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize -RTS' to increase it. I want to find out the culprit function and rewrite it tail-recursively. Is there a way to find out which function is causing this error other than reviewing the code manually? Thanks, Loganathan

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ANNOUNCE: hacphi satellite in berlin july 29-31
by Matthias Fischmann 08 Jul '11

08 Jul '11

yet another hackathon: in case you wanted to join the philadelphia haskell hackathon but decided it's too far away (or in case you happen to be anywhere near and think this is a great opportunity), please join us in berlin: http://haskell.org/haskellwiki/Hac_%CF%86#Berlin_satellite admission is free. we have limited seats, so don't wait too long! hope to see you there, cheers, matthias

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Re: [Haskell-cafe] Diagnose stack space overflow
by John Lato 08 Jul '11

08 Jul '11

> From: Logo Logo <saraslogo(a)gmail.com> > > Hi, > > For the following error: > > Stack space overflow: current size 8388608 bytes. > Use `+RTS -Ksize -RTS' to increase it. > > I want to find out the culprit function and rewrite it tail-recursively. Is > there a way to find out which function is causing this error other > than reviewing the code manually? > I'd like to point out that a stack-space overflow in Haskell isn't quite the same thing as in other functional languages. In particular, it's possible for tail-recursive functions to overflow the stack because of laziness. Consider this tail-recursive sum function: > trSum :: [Int] -> Int > trSum l = go 0 l > where > go acc [] = acc > go acc (x:xs) = go (acc+x) xs It's tail-recursive. But if you enter this in ghci and run it, you'll find that it uses increasing stack space, and will likely cause a stack overflow for large enough inputs. The problem is that the accumulator 'acc' isn't strict and builds up a thunk of the form: 0+n1+n2+...+nn The solution is to add strictness. For this example, a '!' on the accumulator will do. GHC will sometimes spot cases where extra strictness is helpful (it'll figure this one out when compiled with -O), but it often needs help. I'd recommend Edward Yang's series of blog posts about debugging, space leaks, and the Haskell heap. One useful article is http://blog.ezyang.com/2011/05/anatomy-of-a-thunk-leak/ , but you may want to start at the beginning of the heap series. John L.

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Re: [Haskell-cafe] NLP libraries and tools?
by wren ng thornton 08 Jul '11

08 Jul '11

On 7/7/11 3:38 AM, Aleksandar Dimitrov wrote: > On Wed, Jul 06, 2011 at 07:27:10PM -0700, wren ng thornton wrote: >> I definitely agree with the iteratees comment, but I'm curious about the >> leaks you mention. I haven't run into leakiness issues (that I'm aware of) >> in my use of ByteStrings for NLP. > > The issue is this: strict ByteStrings retain pointers to the original chunk. The > chunk is probably bigger than you'd want to keep in memory, if you, say, wanted > to just keep one or two words. In my case, the chunk was some 65K (that was my > Iteratee chunk size.) Oh, that issue. Yeah, I maintain an intern table and make sure that the copy in the table is a trimmed copy instead of keeping the whole string alive. I guess I should factor that part of my tagger out into a separate package :) I didn't know if you meant there was a technical issue, e.g. something about the fact that ByteStrings uses pinned memory (whereas Text doesn't IIRC). -- Live well, ~wren

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NVIDIA's CUDA and Haskell
by Vasili I. Galchin 08 Jul '11

08 Jul '11

Hi, NVIDIA's CUDA library seems to be really hot in the massively parallel world: http://www.nvidia.com/object/cuda_home_new.html. I realize that given CUDA seems to be implemented in an extension of ANSI C that it is pervaded by statefulness. However, is there any effort to build "a bridge" between Haskell and CUDA, foreign language bindings or maybe better yet a monad to encapsulate state?? Kind regards, Vasili

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Jenkins/Hudson support for GHC warnings?
by Bryan O'Sullivan 07 Jul '11

07 Jul '11

Hi, folks - I know there are quite a few Haskell projects using the Jenkins (formerly Hudson) continuous build system, and I wonder if anyone has figured out how to get it reliably collecting errors and warnings from GHC. The standard warnings plugin<https://wiki.jenkins-ci.org/display/JENKINS/Warnings+Plugin>does a bad job - it tends to identify random (sometimes even empty) bits of build output as warnings. If you've configured it to behave better with GHC / hpc / QuickCheck / cabal-install, you'd be doing us a great service by sharing your tricks! Thanks, Bryan.

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how to change a process name
by Kazu Yamamoto 07 Jul '11

07 Jul '11

Hello, I would like to know how to change a process name in Haskell. When we are programming in C, we can change it by overriding argv on Unix. But I cannot find the same way to do in Haskell. Can anyone suggest how in Haskell? I'm not talking about the result of System.Environment.getProgName but talking about the process name which we can see by the "ps" command. Thanks. --Kazu

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Web Framework to Show Experimental Data
by Dmitri O.Kondratiev 07 Jul '11

07 Jul '11

Hi! I am looking for the Haskell libraries to quickly create some Web Framework to Show Experimental Data. Please share your experience and ideas. What tools would you chose for such a framework: == Architecture There are several unsynchronized processes: 1) Finder - demon that periodically searches and collects JSON data from the Web and stores this data in some sort of Archive (DB). 2) Processor - demon that periodically process new data from Archive collected by Finder and stores results of its work in the same Archive. 3) Web application that shows processed data in a browser. == General Requirements *** Main requirement - simplicity and high speed of development *** - Max Data storage capacity - 10 Mb - Max number of Web users - 50 - Web UI shows what Archive has at the moment of user request. == Web UI Requirements - Multi-page view of long data sets (some sort of scrolling) - Simple graphs and charts (desirable) == Questions 1) What to use for the Archive? Though input data is in JSON format, data generated from it is binary vectors. Not sure that CouchDB is a good choice in this case. What simple (Haskell lib + DB) combination one may advise that support concurrent read / write access with simple locking (don't need full transactional support)? 2) Web framework? Don't need AJAX, just basic stuff but simple and easy to code forms? Thanks!

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CFP: PADL'12 - Practical Aspects of Declarative Languages 2012
by Claudio Russo 07 Jul '11

07 Jul '11

[Apologies if you receive multiple copies.] Call for Papers =============== 14th International Symposium on Practical Aspects of Declarative Languages (PADL 2012) http://research.microsoft.com/~crusso/padl12 Philadelphia, Pennsylvania, USA, January 23-24, 2012 Co-located with ACM POPL'12 Abstract/Paper submission deadline: September 10th/17th, 2011 Conference Description ====================== Declarative languages build on sound theoretical bases to provide attractive frameworks for application development. These languages have been successfully applied to many different real-world situations, ranging from data base management to active networks to software engineering to decision support systems. New developments in theory and implementation have opened up new application areas. At the same time, applications of declarative languages to novel problems raise numerous interesting research issues. Well-known questions include designing for scalability, language extensions for application deployment, and programming environments. Thus, applications drive the progress in the theory and implementation of declarative systems, and benefit from this progress as well. PADL is a forum for researchers and practitioners to present original work emphasizing novel applications and implementation techniques for all forms of declarative concepts, including, functional, logic, constraints, etc. Topics of interest include, but are not limited to: * Innovative applications of declarative languages * Declarative domain-specific languages and applications * Practical applications of theoretical results * New language developments and their impact on applications * Declarative languages and Software Engineering * Evaluation of implementation techniques on practical applications * Practical experiences and industrial applications * Novel uses of declarative languages in the classroom * Practical extensions such as constraint-based, probabilistic, and reactive languages. PADL'12 welcomes new ideas and approaches pertaining to applications and implementation of declarative languages. In this occasion PADL is co-located, as traditionally, with ACM POPL, which will be held immediately following PADL, January 25-27. The symposium will be held in Philadelphia, Pennsylvania, USA. Important Dates and Submission Guidelines ========================================= Abstract Submission: September 10, 2011 Paper Submission: September 17, 2011 Notification: October 22, 2011 Camera-ready: November 5, 2011 Symposium: January 23-24, 2012 Authors should submit an electronic copy of the full paper in PDF using the Springer LNCS format. The submission will be done through EasyChair conference system. If electronic submission is impossible, please contact the program chairs for information on how to submit hard copies. All submissions must be original work written in English. Submissions must be unpublished and not submitted for publication elsewhere. Work that already appeared in unpublished or informally published workshops proceedings may be submitted. PADL'12 will accept both technical and application papers: * Technical papers must describe original, previously unpublished research results. Technical papers must not exceed 15 pages in Springer LNCS format. * Application papers are a mechanism to present important practical applications of declarative languages that occur in industry or in areas of research other than Computer Science. Application papers will be published in the Springer-Verlag conference proceedings, and will be presented in a separate session. Application papers are expected to describe complex and/or real-world applications that rely on an innovative use of declarative languages. Application descriptions, engineering solutions and real-world experiences (both positive and negative) are solicited. The limit for application papers is 6 pages in Springer LNCS format. Program Committee ================= Marcello Balduccini, Intelligent Systems Department, Kodak Research Labs Edwin Brady, University of St Andrews, Scotland Henning Christiansen, Roskilde University, Denmark Agostino Dovier, University of Udine, Italy Matthew Flatt, University of Utah, USA Gopal Gupta, University of Texas at Dallas, USA John Hughes, Chalmers University of Technology, Sweden; Quviq AB Gabriele Keller, University of New South Wales, Australia Lunjin Lu, Oakland University, USA Marc Pouzet, École normale supérieure, France Ricardo Rocha, University of Porto, Portugal Andreas Rossberg, Google Germany GmbH, Germany Claudio Russo, Microsoft Research Cambridge, UK (co-chair) Kostis Sagonas, Uppsala Univeristy, Sweden Satnam Singh, Microsoft Research Cambridge, UK Zoltan Somogyi, University of Melbourne, Australia Eijiro Sumii, Tohoku University, Japan Terrance Swift, Universidade Nova de Lisboa, Portugal; Johns Hopkins University, USA Andrew Tolmach, Portland State University, USA Jan Wielemaker, University of Amsterdam, The Netherlands Roland Yap, National University of Singapore, Republic of Singapore Kwangkeun Yi, Seoul National University, Korea Neng-Fa Zhou, Brooklyn College, City University of New York, USA (co-chair) Contacts ======== For additional information about papers and submissions, please contact the Program Chairs: Claudio Russo Microsoft Research Cambridge,UK Email: crusso <AT> microsoft <DOT> com Neng-Fa Zhou Brooklyn College, The City University of New York, USA Email: zhou <AT> sci <DOT> brooklyn <DOT> cuny <DOT> edu With the Cooperation of ======================= The Association for Logic Programming (ALP) ACM SIGPLAN ===================================

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Installation failure crypto-api on MAC
by Neil Davies 07 Jul '11

07 Jul '11

Hi Anyone out there seen this - building > Building crypto-api-0.6.3... > [2 of 9] Compiling Crypto.CPoly ( Crypto/CPoly.hs, dist/build/Crypto/CPoly.o ) several minutes later > ghc: could not execute: /usr/bin/gcc looks like it is silently running out of memory (I understand that this particular module is tough for the compiler due to the large 'constant' table inside it) I'm using "The Glorious Glasgow Haskell Compilation System, version 7.0.3" on (uname -a follows) Darwin mac-server-a.local 10.7.0 Darwin Kernel Version 10.7.0: Sat Jan 29 15:17:16 PST 2011; root:xnu-1504.9.37~1/RELEASE_I386 i386 Suggestions anyone? Neil

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Re: [Haskell-cafe] NLP libraries and tools?
by wren ng thornton 07 Jul '11

07 Jul '11

On 7/6/11 5:58 PM, Aleksandar Dimitrov wrote: > On Wed, Jul 06, 2011 at 09:32:27AM -0700, wren ng thornton wrote: >> On 7/6/11 9:27 AM, Dmitri O.Kondratiev wrote: >>> Hi, >>> Continuing my search of Haskell NLP tools and libs, I wonder if the >>> following Haskell libraries exist (googling them does not help): >>> 1) End of Sentence (EOS) Detection. Break text into a collection of >>> meaningful sentences. >> >> Depending on how you mean, this is either fairly trivial (for English) or >> an ill-defined problem. For things like determining whether the "." >> character is intended as a full stop vs part of an abbreviation; that's >> trivial. > > I disagree. It's not exactly trivial in the sense that it is solved. It is > trivial in the sense that, usually, one would use a list of know abbreviations > and just compare. This, however, just says that the most common approach is > trivial, not that the problem is. Perhaps. I recall David Yarowsky suggesting it was considered solved (for English, as I qualified earlier). The solution I use is just to look at a window around the point and run a standard feature-based machine learning algorithm over it[1]. Memorizing known abbreviations is actually quite fragile, for reasons you mention. This approach will give you accuracy in the high 90s, though I forget the exact numbers. [1] With obvious features like whether the following word is capitalized, whether the preceding word is capitalized, length of the preceding word, whether there's another period after the next word,... >> But for general sentence breaking, how do you intend to deal with >> quotations? What about when news articles quote someone uttering a few >> sentences before the end-quote marker? So far as I'm aware, there's no >> satisfactory definition of what the solution should be in all reasonable >> cases. A "sentence" isn't really very well-defined in practice. > > As long as you have one routine and stick to it, you don't need a formal > definition every linguist will agree on. Computational Linguists (and their > tools,) more often than not, just need a dependable solution, not a correct one. But the problem is that what constitutes an appropriate solution for computational needs is still very ill-defined. For example, the treatment of quotations will depend on the grammar theory used in the tagger, parser, translator, etc. The quality of output is often quite susceptible to EOS being meaningfully[2] distributed. Thus, what constitutes a "dependable" solution often varies depending on the task in question.[3] Also, a lot of the tools in this area assume there's some sort of punctuation marking the end of sentences, even if it's unreliable as an EOS indicator. That works well enough for languages with European-like orthographic traditions, but it falls apart quite rapidly when moving to East Asian languages (e.g., Burmese, Thai,...). And languages like Japanese or Arabic can have "sentences" that go on forever, but are best handled by chunking them into clauses. [2] In a statistical sense, relative to the structure of the model. [3] Personally, I think the idea of having a single EOS type is the bulk of the problem. If we allowed for different kinds of EOS in grammars then the upstream tools could handle sentence fragments better, which would make it easier to make fragment breaking reliable. >> I've been working over the last year+ on an optimized HMM-based POS >> tagger/supertagger with online tagging and anytime n-best tagging. I'm >> planning to release it this summer (i.e., by the end of August), though >> there are a few things I'd like to polish up before doing so. In >> particular, I want to make the package less monolithic. When I release it >> I'll make announcements here and on the nlp@ list. > > I'm very interested in your progress! Keep us posted :-) Will do :) -- Live well, ~wren

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Re: [Haskell-cafe] NLP libraries and tools?
by wren ng thornton 07 Jul '11

07 Jul '11

On 7/6/11 6:45 PM, Aleksandar Dimitrov wrote: > One hint, if you ever find yourself reading in quantitative linguistic data with > Haskell: forget lazy IO. Forget strict IO, except your documents aren't ever > bigger than a few hundred megs. In case you're not keeping the whole document in > memory, but you're keeping some stuff in memory, never keep it around in > ByteStrings, but use Text or SmallString (ByteStrings will invariably leak space > in this scenario.) Learn how to use Iteratees and use them judiciously. I definitely agree with the iteratees comment, but I'm curious about the leaks you mention. I haven't run into leakiness issues (that I'm aware of) in my use of ByteStrings for NLP. -- Live well, ~wren

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GHC/ARM registerised port
by Karel Gardas 07 Jul '11

07 Jul '11

Hello, Stephen Blackheath, David Terei and me are working together on ARM registerised port of GHC. The port is using LLVM as a code generator and is kind of working already. (GHCi support still missing) If you are curious and would like to try the code, please read last two paragraphs containing instructions what to do here[1]. This blog[2] is my personal attempt to document the project at least from my point of view. If you would just like to go straight to the code for code review or to follow progress directly, then github.com repo[3] is the right link for you. Thanks for testing, bug reporting and/or patches! Karel [1]: http://ghcarm.wordpress.com/2011/07/06/armv7-thumb-vfpv3-support-and-github… [2]: http://ghcarm.wordpress.com/ [3]: https://github.com/kgardas/ghc

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[Haskell-Cafe] Constructive Probability Theory and RandProc's σ-algebras
by Edward Kmett 07 Jul '11

07 Jul '11

On Sun, Jul 3, 2011 at 11:05 AM, David Banas <dbanas(a)banasfamily.net> wrote: > v0.4 of `RandProc` has just been posted to Hackage: > http://hackage.haskell.org/package/randproc [NB: I transfered this discussion from haskell to haskell-cafe, and started another thread] I have been spending some time exploring constructive probability theory in Haskell, and I have a couple of observations about working with random processes in a constructive setting: Necessarily because you are working in Haskell, a constructive setting, your σ-algebras can't be actual σ-algebras! =/ Notably, they aren't closed under *countable* union/intersection/complement, but merely finite union/intersection/complement, and Gray and Davisson's horrified objections from the bottom of page 39 on Random Processes applies: If a class of sets is only a field rather than a σ-field, that is, if it > satisfies only (3.1) and (3.2), then there is no guarantee that the class > will contain all limits of sets. Hence, for example knowing that a class of > sets contains all half-open intervals of the form (a,b] for a and b finite > does not ensure that it will also contain points or singleton sets! In fact, > it is straightforward to show that the collection of all such half-open > intervals together with the complements of such sets and all finite unions > of the intervals and complements forms a field. The singleton sets, however, > are not in the field. (See exercise 3.4) > Thus if we tried to construct a probability theory based on only a field, > we might have probabilites defined for events such as (a,b) meaning "the > output voltage of a measurement is between a and b" yet not have > probabilities defined for a singleton set {a} meaning "the output voltage is > exactly a." By requiring that the event space be a σ-field instead of only a > field, we are assured that all such limits are indeed events. This limitation, while from some perspective annoying is intrinsic to tackling the problem intuitionistically. Practically, this means you need to be careful when rederiving most of the later results, because you are limited to what you can prove in a constructive measure theory. In particular the approaches of YK Chan, Brian Weatherson, and Glenn Shafer to intuitionistic probability theory are probably appropriate reading. Personally, I don't think this is all that bad, we get some nice properties by being in a constructive setting. Weatherson noted that your measure becomes additive without problems from Dutch book arguments in an intuitionistic setting, because P(A v not A) is not necessarily 1! You may recall that recall that additivity would imply that P(A v B) = P(A) + P(B), given that A and B are disjoint, but that it tends to fall apart in classical probability theory. Intuitionistically, however, this is fine. That is to say that if you placed bets that payed out with market rate interest at a rational booking agent on both whether P = NP and P /= NP, it isn't just as good as having placed a bet on truth, because intuitionistically it is possible that neither of those bets may ever pay out, but in a classical setting P (P = NP v P /= NP) = P(True) = 1, so we lose additivity to gain the excluded middle. The cost of additivity is giving up or refining a lot of results from that text that talk about the limit of a random process. That and that the "σ-fields" in question are mere fields. ;) I am interested in exploring the consequences of this further. -Edward

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Re: [Haskell-cafe] NLP libraries and tools?
by wren ng thornton 07 Jul '11

07 Jul '11

On 7/6/11 8:46 PM, Richard O'Keefe wrote: >> I've been working over the last year+ on an optimized HMM-based POS >> tagger/supertagger with online tagging and anytime n-best tagging. I'm >> planning to release it this summer (i.e., by the end of August), though >> there are a few things I'd like to polish up before doing so. In >> particular, I want to make the package less monolithic. When I release it >> I'll make announcements here and on the nlp@ list. > > One of the issues I've had with a POS tagger I've been using is that it > makes some really stupid decisions which can be patched up with a few > simple rules, but since it's distributed as a .jar file I cannot add > those rules. How horrid. I assume the problem is really that the trained model is in the jar and you can't do your own training? Or is this a Brill-like tagger where you really mean to add new rules? If an HMM-based tagger is amenable, you could try switching to Daniël de Kok's Java port of TnT: https://github.com/danieldk/jitar The tagger I'm working on does support being hooked up to a Java client (i.e., consumer of tagging info), but it's fairly ugly due to Java's refusal to believe in IPC. -- Live well, ~wren

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Haskell Weekly News: Issue 189
by Daniel Santa Cruz 07 Jul '11

07 Jul '11

Welcome to issue 189 of the HWN, a newsletter covering developments in the Haskell community during the week of June 26 to July 2, 2011. It seems that it was a pretty quiet week in the mailing list. There were no significant announcements made, and the number of threads was low by comparison. Hope everyone is having a great week! You can find the HTML version at: http://contemplatecode.blogspot.com/2011/07/haskell-weekly-news-issue-189.h… Quotes of the Week * iwtu: [#haskell] is a good channel. Really. People are helpful and don't deserve killing or eating * [Cale] Finite dimensional vector spaces over a field F are algebras for the monad of F-linear combinations of elements of a set. [ivanm] oooohhhhh.... _now_ I get you! * [quicksilver] C++ templates can embed arbitrary computation at compile time [quicksilver] that alone tells you something about the complexity of the compiler [edwardk] yeah. they were accidentally turing complete. (whoops!) ;) [quicksilver] edwardk: OOPS I ACCIDENTALLY THE WHOLE TARPIT * bos: other companies use expensive firewalls and crypto hardware to protect their intellectual secrets. edwardk uses category theory! * ManuelChakravarty: After all, you can import any C function with a pure type which also allows you to wreak arbitrary havoc. We enable the user to disguise arbitrary machine code as a Haskell function of essentially arbitrary type. In comparison, `unsafePerformIO' seems angelic. * NihilistDandy: The best part of Haskell is that 80% of module names can be turned into clever blog titles. * AlanPerlis: We will never run out of things to program as long as there is a single program around. Top Reddit Stories * Here be dragons: advances in problems you didn't even know you had Domain: serpentine.com, Score: 78, Comments: 8 On Reddit: http://goo.gl/4RC1W Original: http://goo.gl/Pc0nd * A Gentle Introduction to Category Theory Domain: citeseerx.ist.psu.edu, Score: 33, Comments: 25 On Reddit: http://goo.gl/nb6yJ Original: http://goo.gl/ItUef * Step-wise evaluation of simple Haskell code to hpaste (via Stepeval) Domain: chrisdone.com, Score: 33, Comments: 4 On Reddit: http://goo.gl/VaPXN Original: http://goo.gl/NhWLC * Debugging compilers with optimization fuel Domain: blog.ezyang.com, Score: 30, Comments: 1 On Reddit: http://goo.gl/uUEct Original: http://goo.gl/tSk0e * Fully-Funded PhD Studentship in Functional Programming Domain: cs.nott.ac.uk, Score: 23, Comments: 5 On Reddit: http://goo.gl/Xa231 Original: http://goo.gl/zIvZe * Using Snap in Production! Domain: cdsmith.wordpress.com, Score: 21, Comments: 20 On Reddit: http://goo.gl/KgKxY Original: http://goo.gl/kZ5hp * Monads from Comonads Domain: comonad.com, Score: 19, Comments: 1 On Reddit: http://goo.gl/1yxKe Original: http://goo.gl/R9PyX * Haskell plugin for IntelliJ IDEA Domain: code.google.com, Score: 18, Comments: 7 On Reddit: http://goo.gl/DUiWy Original: http://goo.gl/H1goQ * Barnes & Hut simulator in Haskell! Domain: mortenlysgaard.com, Score: 16, Comments: 4 On Reddit: http://goo.gl/qTKlT Original: http://goo.gl/a5EAb * How do you deal with "long" function bodies? Domain: self.haskell, Score: 12, Comments: 29 On Reddit: http://goo.gl/sRQy0 Top StackOverflow Questions * Bentley-Ottmann Algorithm in Haskell? votes: 31, answers: 1 Read on SO: http://goo.gl/wyJNY * Haskell approaches to error handling votes: 22, answers: 3 Read on SO: http://goo.gl/I2dVG * is point free code more efficient, or just terser? votes: 16, answers: 2 Read on SO: http://goo.gl/em3uu * Are distinct open and close delimiters syntactically necessary? votes: 9, answers: 7 Read on SO: http://goo.gl/roNWE * How to persist large data for efficient deserialization in Haskell votes: 8, answers: 1 Read on SO: http://goo.gl/ixalr * Building with runtime flags using cabal and ghc votes: 6, answers: 1 Read on SO: http://goo.gl/UyrBs About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. Until next time, Daniel Santa Cruz References 1. http://www.reddit.com/r/haskell/comments/ic3qx/here_be_dragons_advances_in_… 2. http://www.serpentine.com/blog/2011/06/29/here-be-dragons-advances-in-probl… 3. http://www.reddit.com/r/haskell/comments/icogq/a_gentle_introduction_to_cat… 4. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.78.7317&rep=rep1&t… 5. http://www.reddit.com/r/haskell/comments/iezj6/stepwise_evaluation_of_simpl… 6. http://chrisdone.com/posts/2011-07-02-stepeval-hpaste.html 7. http://www.reddit.com/r/haskell/comments/iacth/debugging_compilers_with_opt… 8. http://blog.ezyang.com/2011/06/debugging-compilers-with-optimization-fuel/ 9. http://www.reddit.com/r/haskell/comments/ie6by/fullyfunded_phd_studentship_… 10. http://www.cs.nott.ac.uk/~gmh/phd-advert.html 11. http://www.reddit.com/r/haskell/comments/iby54/using_snap_in_production/ 12. http://cdsmith.wordpress.com/2011/06/28/im-using-snap-in-production/ 13. http://www.reddit.com/r/haskell/comments/iao3l/monads_from_comonads/ 14. http://comonad.com/reader/2011/monads-from-comonads/ 15. http://www.reddit.com/r/haskell/comments/ib4zu/haskell_plugin_for_intellij_… 16. http://code.google.com/p/ideah/ 17. http://www.reddit.com/r/haskell/comments/idlza/barnes_hut_simulator_in_hask… 18. http://mortenlysgaard.com/wordpress/?p=17 19. http://www.reddit.com/r/haskell/comments/icelh/how_do_you_deal_with_long_fu… 20. http://stackoverflow.com/questions/6487632/bentley-ottmann-algorithm-in-has… 21. http://stackoverflow.com/questions/6537766/haskell-approaches-to-error-hand… 22. http://stackoverflow.com/questions/6494443/is-point-free-code-more-efficien… 23. http://stackoverflow.com/questions/6542724/are-distinct-open-and-close-deli… 24. http://stackoverflow.com/questions/6556042/how-to-persist-large-data-for-ef… 25. http://stackoverflow.com/questions/6505648/building-with-runtime-flags-usin…

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Re: [Haskell-cafe] NLP libraries and tools?
by wren ng thornton 07 Jul '11

07 Jul '11

On 7/6/11 9:27 AM, Dmitri O.Kondratiev wrote: > Hi, > Continuing my search of Haskell NLP tools and libs, I wonder if the > following Haskell libraries exist (googling them does not help): > 1) End of Sentence (EOS) Detection. Break text into a collection of > meaningful sentences. Depending on how you mean, this is either fairly trivial (for English) or an ill-defined problem. For things like determining whether the "." character is intended as a full stop vs part of an abbreviation; that's trivial. But for general sentence breaking, how do you intend to deal with quotations? What about when news articles quote someone uttering a few sentences before the end-quote marker? So far as I'm aware, there's no satisfactory definition of what the solution should be in all reasonable cases. A "sentence" isn't really very well-defined in practice. > 2) Part-of-Speech (POS) Tagging. Assign part-of-speech information to each > token. There are numerous approaches to this problem; do you care about the solution, or will any one of them suffice? I've been working over the last year+ on an optimized HMM-based POS tagger/supertagger with online tagging and anytime n-best tagging. I'm planning to release it this summer (i.e., by the end of August), though there are a few things I'd like to polish up before doing so. In particular, I want to make the package less monolithic. When I release it I'll make announcements here and on the nlp@ list. > 3) Chunking. Analyze each tagged token within a sentence and assemble > compound tokens that express logical concepts. Define a custom grammar. > > 4) Extraction. Analyze each chunk and further tag the chunks as named > entities, such as people, organizations, locations, etc. > > Any ideas where to look for similar Haskell libraries? I don't know of any work in these areas in Haskell (though I'd love to hear about it). You should try asking on the nlp@ list where the other linguists and NLPers are more likely to see it. -- Live well, ~wren

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(no subject)
by Ian Childs 06 Jul '11

06 Jul '11

Suppose I have two terms s and t of type "a" and "b" respectively, and I want to write a function that returns s applied to t if "a" is an arrow type of form "b -> c", and nothing otherwise. How do i convince the compiler to accept the functional application only in the correct instance? Thanks, Ian

3 7

Arrow instance of function type [a] -> [b]
by Markus Läll 06 Jul '11

06 Jul '11

Hi! Is it possible to define an Arrow instance of list to list functions? Something like import Control.Arrow import Control.Category type X a b = [a] -> [b] instance Category X where id = map Prelude.id g . f = g Prelude.. f instance Arrow X where arr f = map f first f = unzip >>> first f >>> uncurry zip The problem is that it's not allowed to use partially applied type synonyms. It is however possible to define a type synonym which value is a partially applied type, but I haven't been able to figure out if I could somehow use that fact in defining the X... Is it at all possible, or is a newtype the only way to do it? -- Markus Läll

4 3

Automatic Reference Counting
by Thomas Davie 06 Jul '11

06 Jul '11

Hi guys, Apple recently announced a new static analysis in Clang called ARC (Automatic Reference Counting). The idea is to provide what GC provides (zero memory management code by the programmer), but not to incur the runtime penalty of having to have the GC run. It seems to be extremely effective in objective-C land. I was wondering if any of the compiler gurus out there could comment on the applicability of this kind of analysis to Haskell. Dropping the GC and hence stopping it blocking all threads and killing parallel performance seems like nirvana. The one major problem that's still left with ARC is that it does not solve the retain cycle problem of reference counting. Programmers must insert a "weak" keyword to break cycles in their data graphs. Could even this analysis be automated statically? Could we put up with a language extension that added this annotation? I'd love to hear some comments from people more-experienced-than-I on this. Thanks Tom Davie

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How to ensure code executes in the context of a specific OS thread?
by Jason Dagit 06 Jul '11

06 Jul '11

Hello, I'm trying to get some GUI code working on OSX and numerous forums around the internet keep reiterating that on OSX to correctly handle GUI events you need to use the original thread allocated to your process to check for events and to call the Cocoa framework functionality. Specifically, using a secondary thread (even a bound thread) is not sufficient with the Cocoa framework. I looked at the threading documentation in Control.Concurrent for GHC and it's not clear to me if this is even possible with GHC without restricting to the non-threaded RTS. This means that using the GUI library from GHCI is not an option and using multiple OS threads in the final application is also not possible. This means that some FFI libraries will be unusable. My main question is, is there a way around this so that I could, for example, use the library from GHCI? My second question is, if there is no current workaround then how can we remedy this situation? It seems like there could be an api function like: runOnOriginalThread :: IO a -> IO a This function would be similar to runInBoundThread except it would be guaranteed to run on the original thread allocated to the ghc/ghci process. I believe the above primitive would be sufficient. I'll worry about filing a bug or making a libraries proposal after I have a better understanding of what must be done. Thanks, Jason

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Re: [Haskell-cafe] How to ensure code executes in the context of a specific OS thread?
by John Lato 06 Jul '11

06 Jul '11

Message: 23 > Date: Wed, 06 Jul 2011 10:14:56 +0100 > From: Simon Marlow <marlowsd(a)gmail.com> > Subject: Re: [Haskell-cafe] How to ensure code executes in the context > of a specific OS thread? > To: Jason Dagit <dagitj(a)gmail.com>, cvs-ghc(a)haskell.org, Haskell > Cafe > <haskell-cafe(a)haskell.org> > Message-ID: <4E142790.8090009(a)gmail.com> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > On 05/07/2011 20:33, Ian Lynagh wrote: > > On Tue, Jul 05, 2011 at 08:11:21PM +0100, Simon Marlow wrote: > >> > >> In GHCi it's a different matter, because the main thread is running > >> GHCi itself, and all the expressions/statements typed at the prompt > >> are run in forkIO'd threads (a new one for each statement, in fact). > >> If you want a way to run command-line operations in the main thread, > >> please submit a feature request. I'm not sure it can be done, but > >> I'll look into it. > > > > We already have a way: -fno-ghci-sandbox > > Aha, I'd forgotten about that! Thanks Ian. > > Simon > IIRC a lot of people have had trouble running GUI apps from within GHCi on OS X, whether they're GLUT, Gtk2hs, WxHaskell, or native, and several users consider this a large obstacle. I know that I haven't been successful with gtk2hs. However, at this suggestion I just tried running a gtk2hs app I'm developing with the -fno-ghci-sandbox flag, and it worked perfectly. Thanks very much, Ian. John L.

1 0

Re: [Haskell-cafe] function terms
by oleg＠okmij.org 06 Jul '11

06 Jul '11

Ian Childs wrote: > I have a function that returns a witness to 's :: Term a' and 't :: > Term b' having the same type, if they do, but I am wondering how to > extend this to the first argument of an arrow type. Basically you have to write the deconstruct that takes (TRepr a), the witness for type a, and returns either Nothing or Just (exists b1 b2. (EQ a (b1->b2), TRepr b1, TRepr b2)) That is, if the type a is indeed an arrow type, you return the triple: the witnesses for the argument and the result types and the witness for the equality of a and b1->b2. Problems like these often occur in type-checking (or in de-serialization of a typed term from an untyped representations). The following page discusses two (GADT and GADT-less) solutions: http://okmij.org/ftp/tagless-final/course/course.html#type-checking Specifically, http://okmij.org/ftp/tagless-final/course/Typ.hs defines such an arrow witness, names `AsArrow'. Both approaches are essentially equivalent -- and both are quite complex. It really takes a couple of hours to explain either of them. I don't believe a simple solution exists.

1 0

ANNOUNCE: test-framework-doctest 0.1
by Sakari Jokinen 05 Jul '11

05 Jul '11

test-framework-doctest [1] provides a wrapper for running doctests [2] in test-framework [3]. This uses the newly minted API exposed by doctest 0.4 that Simon Hengel just announced [4]. The current incarnation of the package is a very rudimentary. Patches are more than welcome [5]. Many thanks to Simon Hengel for working with me on this. [1] http://hackage.haskell.org/package/test-framework-doctest [2] http://hackage.haskell.org/package/doctest-0.4.0 [3] http://hackage.haskell.org/package/test-framework-0.4.0 [4] http://www.haskell.org/pipermail/haskell-cafe/2011-July/093748.html [5] https://github.com/sakari/test-framework-doctest Sakari

2 1

Searching of several substrings (with Data.Text ?)
by Tillmann Vogt 05 Jul '11

05 Jul '11

Hi, For my font library I need A function that can handle ligatures. It can be explained best with an example: f ["Th", "ff", "fi", "fl", "ffi"] "The fluffiest bunny" should be evaluated to ["Th", "e", " ", "fl", "u", "ffi", "e", "s", "t", " ", "b", "u", "n", "n", "y" ] I looked at Data.Text http://hackage.haskell.org/packages/archive/text/0.5/doc/html/Data-Text.html and http://hackage.haskell.org/packages/archive/stringsearch/0.3.3/doc/html/Dat… but they don't have a function that can search several substrings in one run. I guess that searching a text again and again for every substring is not very efficient and it can be done in one run. Although I may figure this out myself I think such a function could be so common that someone has done it or can give me some tips. Thanks

5 5

ANN: Monad.Reader Issue 18
by Brent Yorgey 05 Jul '11

05 Jul '11

I am pleased to announce that Issue 18 of The Monad.Reader is now available [1]. Issue 18 consists of the following three articles: * "MapReduce as a Monad" by Julian Porter * "Fun with Parallel Monad Comprehensions" by Tomas Petricek * "Attributed Variables: Their Uses and One Implementation" by Douglas M. Auclair Feel free to browse the source files. You can check out the entire repository using darcs (or simply visit the below URL in your browser): darcs get http://code.haskell.org/~byorgey/TMR/Issue18 Enjoy! [1] http://themonadreader.files.wordpress.com/2011/07/issue18.pdf

1 0

Haskell and Databases
by Tobias Schoofs 05 Jul '11

05 Jul '11

I am studying Haskell database libraries. In particular I am looking at haskelldb and the Takusen Database.Enumerator library. In haskelldb, there are very good ideas aiming to represent database objects as (typeable) Haskell objects, instead of embedding SQL in plain strings. This is really an interesting approach that overcomes the hiatus between the database there and the processing logic here. Unfortunately, the library cannot deal with some obvious issues related to this concept; conflicts arise, for instance, when Haskell keywords are used as names of attributes or tables or when the same name is used for an attribute and for a table (which is perfectly legal in SQL). Also, haskelldb cannot cope with peculiarities of popular database tables, such as ISAM tables - which are case sensitive. Another, more conceptual issue, is the lack of database cursors. Database programs, usually, do not just issue isolated SQL statements, but implement a processing logic with nested queries and DML statements. A DB library should provide control structures to ease this kind of processing. A library that tackles this issue, is the Takusen Database.Enumerator, again, a library with very strong ideas. Unfortunately, in Takusen there is nothing like the haskelldb DSL. Concerning, cursors, Takusen uses iterators to stream query results. This makes a lot of sense. The iterators, however, cannot be used to implement the nesting of queries. The user has to provide an additional action which is responsible for all the cursor-related logic. The tools provided to deal with cursors resemble very much the instructions found in other database-oriented languages, such as PL/SQL. This leads to verbose code where cursor control is implemented in a quite "imperative" way. The user, however, should be concerned with getting her queries right, not with the "technical" details of fetching from cursors. In summary, what I miss is a database library that - integrates haskelldb approach with - a "functional-style" cursor concept Is anybody working on something like this? Thanks, Tobias

6 6

haskell; json-rpc
by Комар Максим 05 Jul '11

05 Jul '11

Apologize in advance for the English language. I'm working with json-rpc interface (http://json-rpc.org/) via http. Requests and responses look like this: -> {"jsonrpc" : "2.0", "id" : "1", "method" : "user.authenticate", "params" : { "user" : "myUser", "password" : "myPassword" }} <- {"jsonrpc":"2.0","result":"97d4b59d2f2fbf703bb7aa257aae5254","id":"1"} -> {"jsonrpc" : "2.0", "id" : "2", "method" : "user.getObjects", "auth" : "97d4b59d2f2fbf703bb7aa257aae5254", "params" : { "alias" : "myUser" }} <- {"jsonrpc":"2.0","result":[{"userid":"3","alias":"myUser","name":"lala", "surname":"lala","passwd":"c5aba41f671a02a3c8a6f10a2a7d8a19", "url":"myUrl","autologin":"1","autologout":"0","lang":"ru_ru", "refresh":"30","type":"1","theme":"css_bb.css","attempt_failed":"0", "attempt_ip":"0.0.0.0","attempt_clock":"1282502966", "rows_per_page":"50"}],"id":"2"} How can i describe in Haskell my task? P.S. The first request is required for authentication (field "auth" in the following queries). Using the second query, I want to know "userid"). P.P.S. My first approach is to describe rpc query as following: data RpcQuery = RpcQuery { rpcVersion :: String, rpcId :: String, rpcMethod :: String, rpcAuth :: String, rpcParams :: AuthUser } deriving (Show) data AuthUser = AuthUser { authUser :: String, authPassword :: String } deriving (Show) instance JSON AuthUser where showJSON au = makeObj [ ("user", showJSON $ authUser au) , ("password", showJSON $ authPassword au) ] readJSON (JSObject obj) = let jsonObjAssoc = fromJSObject obj in do user <- mLookup "user" jsonObjAssoc >>= readJSON password <- mLookup "password" jsonObjAssoc >>= readJSON return $ AuthUser { authUser = user , authPassword = password } readJSON _ = fail "" But this scheme is not extended.

1 0

Haskell Implementors Workshop 2011, Second CFT
by Ben Lippmeier 05 Jul '11

05 Jul '11

Call for Talks ACM SIGPLAN Haskell Implementors' Workshop http://haskell.org/haskellwiki/HaskellImplementorsWorkshop/2011 Tokyo, Japan, September 23rd, 2011 The workshop will be held in conjunction with ICFP 2011 http://www.icfpconference.org/icfp2011/ Important dates Proposal Deadline: 22nd July 2011 Notification: 8th August 2011 Workshop: 23rd September 2011 The Haskell Implementors' Workshop is to be held alongside ICFP 2011 this year in Tokyo, Japan. There will be no proceedings; it is an informal gathering of people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure. This relatively new workshop reflects the growth of the user community: there is a clear need for a well-supported tool chain for the development, distribution, deployment, and configuration of Haskell software. The aim is for this workshop to give the people involved with building the infrastructure behind this ecosystem an opportunity to bat around ideas, share experiences, and ask for feedback from fellow experts. We intend the workshop to have an informal and interactive feel, with a flexible timetable and plenty of room for ad-hoc discussion, demos, and impromptu short talks. Scope and target audience ------------------------- It is important to distinguish the Haskell Implementors' Workshop from the Haskell Symposium which is also co-located with ICFP 2011. The Haskell Symposium is for the publication of Haskell-related research. In contrast, the Haskell Implementors' Workshop will have no proceedings -- although we will aim to make talk videos, slides and presented data available with the consent of the speakers. In the Haskell Implementors' Workshop we hope to study the underlying technology. We want to bring together anyone interested in the nitty gritty details necessary to turn a text file into a deployed product. Having said that, members of the wider Haskell community are more than welcome to attend the workshop -- we need your feedback to keep the Haskell ecosystem thriving. The scope covers any of the following topics. There may be some topics that people feel we've missed, so by all means submit a proposal even if it doesn't fit exactly into one of these buckets: * Compilation techniques * Language features and extensions * Type system implementation * Concurrency and parallelism: language design and implementation * Performance, optimisation and benchmarking * Virtual machines and run-time systems * Libraries and Tools for development or deployment Talks ----- At this stage we would like to invite proposals from potential speakers for a relatively short talk. We are aiming for 20 min talks with 10 mins for questions and changeovers. We want to hear from people writing compilers, tools, or libraries, people with cool ideas for directions in which we should take the platform, proposals for new features to be implemented, and half-baked crazy ideas. Please submit a talk title and abstract of no more than 200 words to benl(a)cse.unsw.edu.au We will also have a lightning talks session which will be organised on the day. These talks will be 2-10 minutes, depending on available time. Suggested topics for lightning talks are to present a single idea, a work-in-progress project, a problem to intrigue and perplex Haskell implementors, or simply to ask for feedback and collaborators. Organisers ---------- * Rebekah Leslie (Portland State University) * Ben Lippmeier - co-chair (University of New South Wales) * Andres Loeh (Well-Typed LLP) * Oleg Lobachev (University of Marburg) * Neil Mitchell - co-chair (Standard Chartered) * Dimitrios Vytiniotis (Microsoft Research)

1 0

ANNOUNCE: doctest-0.4.0
by Simon Hengel 04 Jul '11

04 Jul '11

I just uploaded a new version of doctest[1] to Hackage. WHAT IS doctest? ================ doctest is a port of Python's doctest[2] to Haskell. It can be used to verify, that examples in Haddock comments[3] do still work. This also provides you with a simple mechanism to write unit test, without the burden of maintaining a dedicated test suite. A basic example of usage is at [4]. WHAT'S NEW IN THIS VERSION? =========================== doctest's functionality is now exposed as a library, this allows for integration with existing test frameworks. Sakari Jokinen is working on integration with test-framework[5]. Thanks to Sakari Jokinen for both, his contributions to the doctest API and his work on test-framework-doctest! Cheers, Simon [1] http://hackage.haskell.org/package/doctest [2] http://docs.python.org/library/doctest.html [3] http://www.haskell.org/haddock/doc/html/ch03s08.html#id566093 [4] https://github.com/sol/doctest-haskell#readme [5] https://github.com/sakari/test-framework-doctest

1 0

Haskell Platform on Ubuntu: Installation Problems
by Dmitri O.Kondratiev 04 Jul '11

04 Jul '11

Hi, I am trying to install Haskell Platform on latest Ubuntu desktop: ( uname -a: Linux frigate 2.6.38-8-generic #42-Ubuntu SMP Mon Apr 11 03:31:24 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux ) I started with installing GHC. Ubuntu could only install version 6.12.3: without Cabal! Now I am trying to install haskell-platform which is a separate package. Ubuntu suggests to insatll version 2010.1.0.0.1 and fails (see bellow). What sould I do now to get GHC + Cabal? Should I: 1) De-insatll GHC 6.12.3 and all related libraries and try then installing Haskell Platform again? 2) Should I install Caball separately and forget about Haskell Platform? 3) Provide somehow for two different installations? Thanks! === Installation errors: This error could be caused by required additional software packages which are missing or not installable. Furthermore there could be a conflict between software packages which are not allowed to be installed at the same time. haskell-platform: Depends: ghc6 (< 6.12.1+) but 6.12.3-1ubuntu7 is to be installed Depends: libghc6-cgi-dev (>= 3001.1.7.2) but 3001.1.7.2-1build1 is to be installed Depends: libghc6-fgl-dev (< 5.4.2.2+) but 5.4.2.2-2build2 is to be installed Depends: libghc6-glut-dev (< 2.1.2.1+) but 2.1.2.1-1build1 is to be installed Depends: libghc6-haskell-src-dev (< 1.0.1.3+) but 1.0.1.3-2build1 is to be installed Depends: libghc6-html-dev (< 1.0.1.2+) but 1.0.1.2-3build2 is to be installed Depends: libghc6-hunit-dev (< 1.2.2.1+) but 1.2.2.1-2build2 is to be installed Depends: libghc6-mtl-dev (< 1.1.0.2+) but 1.1.0.2-10build2 is to be installed Depends: libghc6-network-dev (< 2.2.1.7+) but 2.2.1.7-1build2 is to be installed Depends: libghc6-opengl-dev (< 2.2.3.0+) but 2.2.3.0-2build2 is to be installed Depends: libghc6-parallel-dev (< 2.2.0.1+) but 2.2.0.1-1build1 is to be installed Depends: libghc6-parsec2-dev (< 2.1.0.1+) but 2.1.0.1-2build2 is to be installed Depends: libghc6-quickcheck2-dev (< 2.1.0.3+) but 2.1.0.3-1build2 is to be installed Depends: libghc6-regex-base-dev (< 0.93.1+) but 0.93.1-8build1 is to be installed Depends: libghc6-regex-compat-dev (< 0.92+) but 0.92-6build2 is to be installed Depends: libghc6-regex-posix-dev (< 0.94.1+) but 0.94.1-2build1 is to be installed Depends: libghc6-stm-dev (< 2.1.1.2+) but 2.1.1.2-5build2 is to be installed Depends: libghc6-xhtml-dev (>= 3000.2.0.1) but 3000.2.0.1-6build2 is to be installed Depends: libghc6-zlib-dev (< 0.5.2.0+) but 0.5.2.0-4build2 is to be installed Depends: libghc6-http-dev (>= 40000009) but 40000009-2build1 is to be installed Depends: libghc6-deepseq-dev (< 1.1.0.0+) but 1.1.0.0-2build1 is to be installed Depends: alex (< 2.3.3+) but 2.3.3-1 is to be installed Depends: happy (< 1.18.4-2+) but 1.18.4-2 is to be installed Depends: haddock but it is a virtual package

3 6

IterIO: How to write use my inumReverse
by John Ky 04 Jul '11

04 Jul '11

Hi Haskell Cafe, I've defined the following reverse echo server that echos text back in reverse: module Programs.TcpEchoIterServer where import Control.Concurrent import Control.Exception import Control.Monad import Control.Monad.Trans import Data.IterIO import Data.IterIO.Inum import Network import System.IO import System.IO.Error (isEOFError) import qualified Data.ByteString.Lazy as L import qualified Data.ByteString.Lazy.Char8 as C iterHandle' :: (MonadIO m) => Handle -> IO (Iter L.ByteString m (), Onum L.ByteString m a) iterHandle' = iterHandle main = withSocketsDo $ do sListen <- listenOn (PortNumber 8000) putStrLn "Listening on Port 8000" forkIO $ forever $ do (sSession, hostname, port) <- accept sListen hSetBuffering sSession NoBuffering putStrLn ("Connected to " ++ hostname ++ ":" ++ show port) forkIO $ do (iter, enum) <- iterHandle' sSession enum |$ inumLines .| inumReverse .| inumUnlines .| iter putStrLn "Press <CTRL-D> to quit." exitOnCtrlD iterLines :: (Monad m) => Iter L.ByteString m [L.ByteString] iterLines = do line <- lineI return [line] iterUnlines :: (Monad m) => Iter [L.ByteString] m L.ByteString iterUnlines = (L.concat . (++ [C.pack "\n"])) `liftM` dataI iterReverse :: (Monad m) => Iter [L.ByteString] m [L.ByteString] iterReverse = do lines <- dataI return (map L.reverse lines) inumLines = mkInum iterLines inumUnlines = mkInum iterUnlines inumReverse = mkInum iterReverse exitOnCtrlD = try getLine >>= either (\e -> unless (isEOFError e) $ ioError e) (const exitOnCtrlD) It all works fine. My question is: Is it possible to rewrite inumReverse to be this: iterReverse :: (Monad m) => Iter L.ByteString m L.ByteString iterReverse = do line <- dataI return (L.reverse line) inumReverse = mkInum iterReverse And still be able to use it in the line: enum |$ inumLines .| {-- inumReverse goes in here somehow --} .| inumUnlines .| iter The reason I ask is that the Haskell function reverse has the type [a] -> [a], not [[a]] -> [[a]]. I thought perhaps the alternative inumReverse is cleaner than the original as it behaves more similarly to Haskell's own reverse function. Cheers, -John

2 1

Data.Time
by Tony Morris 04 Jul '11

04 Jul '11

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I recently set out to write a library that required a decent time library. Having only had a flirt with Data.Time previously, I assumed it would be robust like many other haskell libraries. I don't know about consensus, but I have been massively let down. I won't go in to the details, since this is not the point -- I don't wish to complain - -- I wish to get on with it. So, assuming the consensus is in agreement, is there a reasonable alternative to Data.Time (I looked on hackage and nothing seemed to have come close)? Am I wrong in assuming Data.Time is pretty useless? If I am right, and there is no alternative, I see no option but to take an excursion into writing my own. Ultimately, I am just trying to avoid this. Tips welcome. - -- Tony Morris http://tmorris.net/ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk4Ggx4ACgkQmnpgrYe6r61BRQCfbn+1jqNSjR+lxM+4h3gpvAMM VskAoKxqDCETyVAaOdoYDmFJGz1fOGd/ =IC7O -----END PGP SIGNATURE-----

8 13

Re: [Haskell-cafe] How to ensure code executes in the context of a specific OS thread?
by Jason Dagit 04 Jul '11

04 Jul '11

On Sun, Jul 3, 2011 at 10:31 PM, David Barbour <dmbarbour(a)gmail.com> wrote: > > On Jul 3, 2011, Jason Dagit <dagitj(a)gmail.com> wrote: >> >> to correctly handle GUI events you need to use the original thread >> allocated to your process to check for events and to call the Cocoa >> framework functionality. >> >> I looked at the threading documentation in Control.Concurrent for GHC and >> it's not clear to me if this is even possible with GHC without restricting >> to the non-threaded RTS. > > The 'main' thread in GHC is the bound thread initially allocated to the > process. That doesn't seem to be the case for GHCI. > You can easily establish an event-loop in the main thread, and feed > events from other threads. Consider using Control.Concurrent.Chan. > If you need feedback, things get a bit trickier because you'll have special > cases based on whether you're starting in the main thread. Yes, that might work for compiled programs. What about GHCI? Jason

1 0

Re: [Haskell-cafe] How to ensure code executes in the context of a specific OS thread?
by David Barbour 04 Jul '11

04 Jul '11

On Jul 3, 2011, Jason Dagit <dagitj(a)gmail.com> wrote: > to correctly handle GUI events you need to use the original thread > allocated to your process to check for events and to call the Cocoa > framework functionality. > > I looked at the threading documentation in Control.Concurrent for GHC and > it's not clear to me if this is even possible with GHC without restricting > to the non-threaded RTS. > The 'main' thread in GHC is the bound thread initially allocated to the process. You can easily establish an event-loop in the main thread, and feed events from other threads. Consider using Control.Concurrent.Chan. If you need feedback, things get a bit trickier because you'll have special cases based on whether you're starting in the main thread. Regards, Dave

1 0

GUI Program Hangs in GHCI
by Jason Dagit 04 Jul '11

04 Jul '11

Hello, I have a GUI program that when I compile it and run it there are no problems. When I load it into GHCI and type, "main", it loads the main window but there are no window decorations and the program hangs to the point where I have to kill the ghci process. You see a spinning cursor when you mouse over the window. I found this old email regarding gtk2hs: http://web.archiveorange.com/archive/v/nDNOvMeDATtTGn026lbI I recompiled the program to use -threaded but the behavior is unchanged (if the email above describes my problem then I expected the compiled version to start having issues). What else can cause the hangs I'm seeing? I'm using the GLFW-b library on hackage and the program I'm trying to run are any of the executables from the nehe-tuts package (also on hackage). To reproduce my hangs, I think you need OSX (I didn't test this on windows or linux), and then type the following: {{{ mkdir -p ~/tmp/test cd ~/tmp/test cabal update cabal-dev install-deps nehe-tuts cabal unpack nehe-tuts cabal-dev ghci nehe-tuts-0.2.3/lesson01.hs *Main> main }}} Doing a force quit on ghci gives me a stack trace via the OSX crash reporting system. You'll find the relevant bits from that at the end of this email. What debugging techniques do I have at my disposal for figuring out what is going wrong here? At least one person has suggested that possibly ghci and the GUI bits of glfw are competing for input and conflicting with each other. If that's the case, how could I be sure and what would I do about it? Thanks, Jason {{{ Process: ghc [48045] Path: /Library/Frameworks/GHC.framework/Versions/7.0.3-x86_64/usr/lib/ghc-7.0.3/ghc UID: 502 Thread 84d5f8 DispatchQueue 1 User stack: 47 __semwait_signal + 10 (in libSystem.B.dylib) [0x7fff8760ef8a] Kernel stack: 46 semaphore_wait_continue + 0 [0x22a88f] 1 lo_alltraps + 454 [0x2a1976] 1 i386_astintr + 47 [0x2aacb4] 1 ast_taken + 247 [0x219432] 1 bsd_ast + 806 [0x48fea8] 1 postsig + 432 [0x48cfff] 1 exit1 + 449 [0x48187a] 1 task_terminate_internal + 242 [0x22ca4d] 1 ipc_space_destroy + 177 [0x215868] 1 ipc_right_clean + 397 [0x215256] 1 mach_notify_no_senders + 75 [0x23ff7b] 1 mach_msg_send_from_kernel_proper + 90 [0x21e0cb] 1 ipc_kmsg_send + 105 [0x210a86] 1 ipc_kobject_server + 267 [0x21dbfc] 1 iokit_notify + 154 [0x284eed] 1 iokit_client_died + 85 [0x571527] 1 com.apple.GeForce 6.3.0 + 47083 [0x830867eb] 1 com.apple.GeForce 6.3.0 + 305981 [0x830c5b3d] 1 com.apple.GeForce 6.3.0 + 258633 [0x830ba249] 1 OSObject::release() const + 25 [0x506759] 1 OSObject::taggedRelease(void const*) const + 32 [0x50673e] 1 com.apple.GeForce 6.3.0 + 253194 [0x830b8d0a] 1 com.apple.GeForce 6.3.0 + 251919 [0x830b880f] 1 com.apple.NVDAResman 6.3.0 + 453556 [0x83689bb4] 1 com.apple.NVDAResman 6.3.0 + 445937 [0x83687df1] 1 com.apple.NVDAResman 6.3.0 + 302211 [0x83664c83] 1 com.apple.NVDAResman 6.3.0 + 249957 [0x83658065] 1 com.apple.NVDAResman 6.3.0 + 112888 [0x836368f8] 1 com.apple.NVDAResman 6.3.0 + 111718 [0x83636466] 1 com.apple.nvidia.nv50hal 6.3.0 + 623157 [0x83e1a235] 1 com.apple.nvidia.nv50hal 6.3.0 + 605845 [0x83e15e95] 1 com.apple.nvidia.nv50hal 6.3.0 + 606056 [0x83e15f68] Thread 84d67e DispatchQueue 2 User stack: 46 start_wqthread + 13 (in libSystem.B.dylib) [0x7fff875edfc5] 46 _pthread_wqthread + 353 (in libSystem.B.dylib) [0x7fff875ee128] 46 _dispatch_worker_thread2 + 252 (in libSystem.B.dylib) [0x7fff875ee7fe] 46 _dispatch_queue_invoke + 185 (in libSystem.B.dylib) [0x7fff875eecd4] 46 kevent + 10 (in libSystem.B.dylib) [0x7fff875ed12a] Kernel stack: 46 kevent + 97 [0x47a681] Thread 84d5f9 User stack: 46 kevent64 + 10 (in libSystem.B.dylib) [0x7fff87687512] Kernel stack: 46 kevent + 97 [0x47a681] Thread 84d5fa User stack: 46 ??? [0x10681d9e8] 38 ??? [0x10a60403b] 37 CGLFlushDrawable + 67 (in OpenGL) [0x7fff819d3261] 37 gldFinish + 874 (in GeForceGLDriver) [0x2000d728a] 37 glcNoop + 1072 (in OpenGL) [0x7fff819d491c] 37 CGSFlushSurfaceWithOptions + 396 (in CoreGraphics) [0x7fff88fb81f9] 37 _CGSFlushSurfaceInline + 210 (in CoreGraphics) [0x7fff88fb848c] 37 mach_msg_trap + 10 (in libSystem.B.dylib) [0x7fff875d429a] 1 glfwSwapBuffers + 69 (in libglfw.dylib) [0x1036f6ba5] 1 _glfwPlatformPollEvents + 132 (in libglfw.dylib) [0x1036f26c4] 1 -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 155 (in AppKit) [0x7fff88135751] 1 _DPSNextEvent + 103 (in AppKit) [0x7fff88135ba5] 8 ??? [0x109fc6d03] 8 glFlush_Exec + 133 (in GLEngine) [0x11c5b7150] 8 gldUpdateDispatch + 13841 (in GeForceGLDriver) [0x2000d6711] 8 IOConnectCallMethod + 325 (in IOKit) [0x7fff81ae3328] 8 io_connect_method + 490 (in IOKit) [0x7fff81b26ad2] 8 mach_msg_trap + 10 (in libSystem.B.dylib) [0x7fff875d429a] Kernel stack: 32 ipc_mqueue_receive_continue + 0 [0x210d84] 12 lo64_mach_scall + 77 [0x2a255d] 12 thread_setuserstack + 405 [0x295c17] 8 mach_msg_overwrite_trap + 274 [0x216f84] 8 ipc_kmsg_send + 105 [0x210a86] 8 ipc_kobject_server + 244 [0x21dbe5] 8 iokit_server_routine + 4669 [0x286610] 8 is_io_connect_method + 467 [0x56e2b3] 8 IOUserClient::externalMethod(unsigned int, IOExternalMethodArguments*, IOExternalMethodDispatch*, OSObject*, void*) + 909 [0x56d9ff] 8 shim_io_connect_method_scalarI_structureO + 455 [0x56d160] 8 com.apple.GeForce 6.3.0 + 49337 [0x830870b9] 8 com.apple.GeForce 6.3.0 + 310514 [0x830c6cf2] 8 com.apple.GeForce 6.3.0 + 64383 [0x8308ab7f] 8 IOLockSleep + 39 [0x53633c] 8 lck_mtx_sleep + 87 [0x221d42] 8 thread_block + 33 [0x227654] 8 thread_block_reason + 331 [0x2275c6] 8 thread_dispatch + 1966 [0x227327] 8 machine_switch_context + 659 [0x2a9adb] 4 mach_msg_overwrite_trap + 586 [0x2170bc] 4 ipc_mqueue_receive + 89 [0x211dc4] 4 thread_block + 33 [0x227654] 4 thread_block_reason + 309 [0x2275b0] 4 thread_go + 1961 [0x22698c] 4 thread_setrun + 1360 [0x225bba] 4 machine_idle + 239 [0x2ad0f5] 1 call_continuation + 28 [0x2a179c] 1 idle_thread + 58 [0x22812e] 1 thread_run + 118 [0x22743b] 1 thread_dispatch + 1347 [0x2270bc] 1 ml_set_interrupts_enabled + 47 [0x2a45e3] 1 lo_allintrs + 302 [0x2a1c2e] 1 interrupt + 182 [0x2ab419] 1 lapic_interrupt + 108 [0x2b32b2] 1 mp_kdp_exit + 860 [0x2b4506] 1 sync_iss_to_iks + 124 [0x2aabf6] Thread 84d623 User stack: 46 __semwait_signal + 10 (in libSystem.B.dylib) [0x7fff8760ef8a] Kernel stack: 46 semaphore_wait_continue + 0 [0x22a88f] }}}

2 4

Strange context reduction with partial application and casting
by Wonchan Lee 04 Jul '11

04 Jul '11

Hi cafe, I found some strange phenomenon when I was hanging around with GHCi. Please see the following interaction: GHCi, version 7.0.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. Prelude> let f a b c d = a == b && c == d Prelude> :t f f :: (Eq a, Eq a1) => a -> a -> a1 -> a1 -> Bool Prelude> let g = f 1 Prelude> :t g g :: Integer -> () -> () -> Bool Here I expect that the type of g is (Eq a) => Integer -> a -> a -> Bool. But suddenly all the context in the type is gone and I have some strange thing with unit type in it. I tried another example to get what I expected at the first time: Prelude> let g = f :: (Eq a) => Int -> Int -> a -> a -> Bool Prelude> :t g g :: Int -> Int -> () -> () -> Bool The resulting type was different from one that I want to cast into. I know that Haskell tries to reduce the context in the type when there's sufficient information to do it. However, this goes too far from what I think normal. Is this intended behavior or just a bug?

5 5

Confused about my IterIO code
by John Ky 04 Jul '11

04 Jul '11

Hi Hakell Cafe, I'm struggling to understand my unambitious IterIO code that somehow manages to work. Basically I run an echo server that is supposed to read from a socket line by line and write back to the socket with all the characters in the line reversed: import Control.Exception import Control.Monad import Control.Monad.Trans import Data.IterIO import Data.IterIO.Inum import Network import System.IO import System.IO.Error (isEOFError) import qualified Data.ByteString.Lazy as L import qualified Data.ByteString.Lazy.Char8 as C iterHandle' :: (MonadIO m) => Handle -> IO (Iter L.ByteString m (), Onum L.ByteString m a) iterHandle' = iterHandle main = withSocketsDo $ do sListen <- listenOn (PortNumber 8000) putStrLn "Listening on Port 8000" forkIO $ forever $ do (sSession, hostname, port) <- accept sListen hSetBuffering sSession NoBuffering putStrLn ("Connected to " ++ hostname ++ ":" ++ show port) forkIO $ do (iter, enum) <- iterHandle' sSession enum |$ inumReverseLines .| iter putStrLn "Press <CTRL-D> to quit." exitOnCtrlD inumReverseLines :: (Monad m) => Inum L.ByteString L.ByteString m a inumReverseLines = mkInum $ do line <- lineI return (L.reverse (L.concat [line, C.pack "\n"])) exitOnCtrlD = try getLine >>= either (\e -> unless (isEOFError e) $ ioError e) (const exitOnCtrlD) When I run it, it does this: asdfghc7@hoggy-nn:/home/hoggy$ nc localhost 8000 1234 4321 4321 1234 abcde edcba The red lines are the replies from my echo server. But all I've done is: enum |$ inumReverseLines .| iter inumReverseLines = mkInum $ do line <- lineI return (L.reverse (L.concat [line, C.pack "\n"])) No attempt was made to reverse more than one line - at least as far as I can see. What have I done wrong that it should work so well? Also, is there a better way to do this? Cheers, -John

3 3

ANNOUNCE: regex-applicative-0.1
by Roman Cheplyaka 03 Jul '11

03 Jul '11

I am glad to announce the initial release of regex-applicative. Hackage: http://hackage.haskell.org/package/regex-applicative Repository: https://github.com/feuerbach/regex-applicative Issues: https://github.com/feuerbach/regex-applicative/issues regex-applicative is aimed to be an efficient and easy to use parsing combinator library based on regular expressions. Perl programmers often use regular expressions for parsing, even if it is not an appropriate tool for the job, because Perl has so good support for regexps. The opposite seems to be valid about Haskell programmers -- they use parsing combinators (which recognize context-free or even context-sensitive grammars), even when the language is actually regular! Hopefully, this library will improve the situation. This is an early preview release. Some features are lacking, and performance is probably not very good yet. Among the features that we are going to support in future versions are: * Non-greedy operators * Search-and-replace functionality * Error reporting The implementation is heavily based on the ideas from "A Play on Regular Expressions" by Sebastian Fischer, Frank Huch and Thomas Wilke. http://sebfisch.github.com/haskell-regexp/regexp-play.pdf -- Roman I. Cheplyaka :: http://ro-che.info/

1 0

Fwd: Data.Time
by Daniel Patterson 03 Jul '11

03 Jul '11

sent from wrong account - message follows: > I've found most of the time library to be quite useful, but the parsing to be worthless (I've tried to get someone to prove me wrong already, and would be happy if someone could on this thread!). > > Specifically, the formatTime function, if it ever strips out padding (by zeros or spaces), results in a time that is unparseable. The fact that formatTime and parseTime are not capable of being inverses of each other seems like a major flaw, when you think that this is not a parseable date: > > 2011/1/30 (because the month must be padded by zeros). > > Even though it is very easy to print, and occurs commonly in the world. > > Because of this, I use formatTime to write my times, and then have a custom parser to parse them back out. Which makes me think that this is a broken library > > On Jun 27, 2011, at 10:37 AM, <briand(a)aracnet.com> <briand(a)aracnet.com> wrote: > >> On Mon, 27 Jun 2011 11:15:28 +0300 >> Yitzchak Gale <gale(a)sefer.org> wrote: >> >>> >>> The biggest shortcoming, in my opinion, is that the documentation >>> assumes that the reader is very familiar with the Haskell type >>> system, and with viewing type signatures and instance lists as an >>> integral and central part of the documentation. >>> >>> In particular, Haskell's standard numeric type classes and the >>> conversion functions between them play a central role in the API >>> of Data.Time. But you wouldn't realize that unless you have read >>> the type signatures and instance lists in the Haddocks very >>> carefully, and have thought about it for a while. >> >> This is exactly right. >> >>> >>> Another problem, as Malcolm pointed out, is that because of the >>> sheer size of the library, a quick-start guide for the common >>> cases would be extremely helpful for newcomers. >> >> That would be very, very helpful. I had a few working examples things were much better. Finding a starting place, any starting place, proved to be quite elusive. Also the fact that asking for the current time traps you in IO hell, doesn't help, although it's clear that it should be that way. >> >> Brian >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >

4 5

Printing the empty list.
by Joshua Ball 02 Jul '11

02 Jul '11

GHCi seems to be clever about some things: If I try to print the empty list in ghci, I encounter no problems: Prelude> [] [] Prelude> show [] "[]" Prelude> print [] [] Even though the type of the list is clearly unknown, it must be picking SOME type. (why does it print [] instead of "")? If I write a program in a file and load it in main = print [] Then I get the ambiguous type variable error that I would expect. Why doesn't ghci generate this error at the prompt? -- Borrow my books: http://goo.gl/UBbSH

6 6

Period of a sequence
by michael rice 02 Jul '11

02 Jul '11

MathWorks has the function seqperiod(x) to return the period of sequence x. Is there an equivalent function in Haskell? Michael

4 3