- Haskell-Cafe - Haskell.org

GHCi timing statistics
by David Rush 05 Mar '15

05 Mar '15

Hi all - Is it my imagination, or are the statistics printed by GHCi when :set +s has been enabled entirely spurious when SMP parallelism is turned on? I'm trying to determine if I am actually getting any improvement, and - both by the wall clock and by the reported statistics I don't seem to be; however, the reported statistics don't seem to line up very well with the wall clock time. An additional oddity that I've noted is that my algorithm's reference implementation - which simply can't run in parallel due to a foolishly introduced data dependency - still seems to kick 16 CPUs well into the 90%+ utilization range when I have +RTS -N. This code has no parallelism primitives in it whatsoever. I realize that I'm not being terribly rigorous in my description here, but that is partly because I am not sure how to report on this yet. I think my next step is going to be to build a standalone executable to check using the Unix time command. For reference I am running Haskell platform from Debian Jessie on a 16- core amd64 system with 29GiB or RAM available. This would appear to be GHC 7.6.3 :( - d

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Design of protocol implementation?
by Magnus Therning 05 Mar '15

05 Mar '15

By now I've written a couple of implementations of (reply / response) protocols in Haskell. They all basically follow the same pattern: 1. One message type with a constructor for each, e.g. data Message = PingMsg | ... 2. One reply type with a constructor for each, e.g. data Reply = PingReply | ... 3. Any message or reply containing data has a constructor taking an argument of a type for that data, e.g. data Message = ... | SendDataMsg SendDataD | ... data SendDataD = SendDataD ByteString 4. The raw data is received from somewhere and passed through a parser written using attoparsec. 5. The messages are rendered into ByteString using ByteString.Builder. So, in essence something like this: +------+ +----------+ +-------+ +------------+ +------+ | read | --> | parse | --> | stuff | --> | render | --> | send | | raw | | into | +-------+ | to | | raw | +------+ | Messages | | ByteString | +------+ +----------+ +------------+ I'm curious to hear about other ways to handle protocols. Are there any papers written on implementing protocols using FP in particular? The protocols I've faced are rather simple things, what about more complicated ones, e.g. multi-layered protocols (ala IP - TCP)? /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus In order to understand recursion you must first understand recursion.

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(no subject)
by S J Rajath Krishna 05 Mar '15

05 Mar '15

I would like to create an account with the following user name User name : "raxerz" (Without the quotes) Thanks,S J Rajath Krishna

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ghci and dynamically linking to Objective-C objects on Mac OS X
by Sean Seefried 05 Mar '15

05 Mar '15

Hi all, I fear I might be unaware of something I should be. Say I have a file objc_util.m with the following contents: #include <Foundation/Foundation.h> void ns_log(const char *s) { NSString *str = [NSString stringWithUTF8String:s]; NSLog(@"%@", str); } I also have a file Main.hs with contents: {-# LANGUAGE ForeignFunctionInterface #-} module Main where import Foreign.C.Types import Foreign.C.String foreign import ccall "ns_log" cNSLog :: CString -> IO () nsLog s = withCString s cNSLog I compile objc_util.m with: gcc -c objc_util.m And then I try to open it up in GHCi. ghci objc_util.o Main.hs -framework Foundation I add the flag '-frame Foundation' in the hopes that symbols in objc_util.o will get resolved dynamically. However I get: GHCi, version 7.8.3: 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 object (static) objc_util.o ... ghc: panic! (the 'impossible' happened) (GHC version 7.8.3 for x86_64-apple-darwin): Loading temp shared object failed: dlopen(/var/folders/pv/pfxcyy117v31vt6lsshtgr_w0000gn/T/ghc33546_0/ghc33546_1.dylib, 9): Symbol not found: _OBJC_CLASS_$_NSString Referenced from: /var/folders/pv/pfxcyy1 17v31vt6lsshtgr_w0000gn/T/ghc33546_0/ghc33546_1.dylib Expected in: flat namespace in /var/folders/pv/pfxcyy117v31vt6lsshtgr_w0000gn/T/ghc33546_0/ghc33546_1.dylib Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug However, I have found a work around to this. If I do this: ln -s /System/Library/Frameworks/Foundation.framework/Foundation Foundation.o and then run ghci Foundation.o objc_util.o Main.hs I get this: GHCi, version 7.8.3: 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 object (static) Foundation.o ... done Loading object (static) objc_util.o ... done final link ... done Everything has worked! And I can happily run 'nsLog' from GHCi and have it appear in the 'Console' app. However, it doesn't seem like I should have to do this. Where am I going wrong? Sean

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[TFPIE 2015] 2nd call for papers
by Peter Achten 05 Mar '15

05 Mar '15

Trends in Functional Programming in Education (TFPIE 2015) 2nd Call for papers https://wiki.science.ru.nl/tfpie/TFPIE2015 The 4th International Workshop on Trends in Functional Programming in Education, TFPIE 2015, will be held on June 2, 2015 in Sophia-Antipolis in France. It is co-located with the Symposium on Trends in Functional Programming (TFP 2015) which takes place from June 3 - 5. *** Goal *** The goal of TFPIE is to gather researchers, teachers and professionals that use, or are interested in the use of, functional programming in education. TFPIE aims to be a venue where novel ideas, classroom-tested ideas and work-in-progress on the use of functional programming in education are discussed. The one-day workshop will foster a spirit of open discussion by having a review process for publication after the workshop. The program chair of TFPIE 2015 will screen submissions to ensure that all presentations are within scope and are of interest to participants. Potential presenters are invited to submit an extended abstract (4-6 pages) or a draft paper (up to 16 pages) in EPTCS style. The authors of accepted presentations will have their preprints and their slides made available on the workshop's website/wiki. Visitors to the TFPIE 2015 website/wiki will be able to add comments. This includes presenters who may respond to comments and questions as well as provide pointers to improvements and follow-up work. After the workshop, presenters will be invited to submit (a revised version of) their article for review. The PC will select the best articles for publication in the journal Electronic Proceedings in Theoretical Computer Science (EPTCS). Articles rejected for presentation and extended abstracts will not be formally reviewed by the PC. TFPIE workshops have previously been held in St Andrews, Scotland (2012), Provo Utah, USA (2013), and Soesterberg, The Netherlands (2014). *** Program Committee *** Peter Achten, Radboud University Nijmegen, The Netherlands Edwin Brady, University of St Andrews, UK Johan Jeuring, Utrecht University and Open University, The Netherlands (Chair) Shriram Krishnamurthi, Brown University, US Rita Loogen, Philipps-Universität Marburg, Germany Marco Morazan, Seton Hall University, US Norman Ramsey, Tufts University, US *** Submission Guidelines *** TFPIE 2015 welcomes submissions describing techniques used in the classroom, tools used in and/or developed for the classroom and any creative use of functional programming (FP) to aid education in or outside Computer Science. Topics of interest include, but are not limited to: - FP and beginning CS students - FP and Computational Thinking - FP and Artificial Intelligence - FP in Robotics - FP and Music - Advanced FP for undergraduates - Tools supporting learning FP - FP in graduate education - Engaging students in research using FP - FP in Programming Languages - FP in the high school curriculum - FP as a stepping stone to other CS topics - FP and Philosophy *** Best Lectures *** In addition to papers, we request “best lecture” presentations. What is your best lecture topic in an FP related course? Do you have a fun way to present FP concepts to novices or perhaps an especially interesting presentation of a difficult topic? In either case, please consider sharing it. Best lecture topics will be selected for presentation based on a short abstract describing the lecture and its interest to TFPIE attendees. *** Submission *** Papers and abstracts can be submitted via easychair at the following link: https://easychair.org/conferences/?conf=tfpie2015 It is expected at at least one author for each submitted paper will attend the workshop. *** Important Dates *** April 7, 2015: Early Registration for TFP closes April 27, 2015: Submission deadline for draft TFPIE papers and abstracts May 3 2015: Notification of acceptance for presentation ?? (Probably May 22 2015): Registration for TFPIE closes - as does late registration for TFP June 2, 2015: Presentations in Sophia-Antipolis, France July 7, 2015: Full papers for EPTCS proceedings due. September 1, 2015: Notification of acceptance for proceedings September 22, 2015: Camera ready copy due for EPTCS Submission of an abstract implies no obligation to submit a full version; abstracts with no corresponding full versions by the full paper deadline will be considered as withdrawn.

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Haskell Weekly News
by Kim-Ee Yeoh 04 Mar '15

04 Mar '15

*Top picks:* Jasper Van der Jeugt <http://jaspervdj.be/posts/2015-02-24-lru-cache.html> shows how you can write an intuitive, obviously correct LRU cache perfectly polymorphic in both the key and value types of the cache lookup function. (Reddit discussion.) <http://www.reddit.com/r/haskell/comments/2wz4tj/writing_an_lru_cache_in_has…> Core is broken! Well, no, ticket 9858 <https://ghc.haskell.org/trac/ghc/ticket/9858> reported previously is still open, and it's about translating an exotic species of Haskell into Core. But Javran Cheng <https://ghc.haskell.org/trac/ghc/ticket/10121> found out that the documented specification of Core's operational semantics is incomplete. Neil Mitchell <http://neilmitchell.blogspot.com/2015/02/making-withsocketsdo-unnecessary.h…> removes the error-prone wart of withSocketsDo <http://hackage.haskell.org/package/network-2.6.0.2/docs/Network.html#v:with…> in Windows network programming. Moving in for the kill is the triple combo of evaluate, NOINLINE, and unsafePerformIO. (Reddit discussion.) <http://www.reddit.com/r/haskell/comments/2x7js6/making_withsocketsdo_unnece…> Can you write a sorting algorithm? Can you write a fancy sorting algorithm? Can you write a sorting algorithm so fancy it hides a subtle bug? Can you write a sorting algorithm so fancy that it hides a bug so subtle <https://github.com/timjb/haskell-timsort/commit/d9c3e1e454c7d338320f8c2aa12…> that it evades even QuickCheck because the smallest testcase is 2^49 big? But the good news is that QuickCheck doesn't see any regression in the bugfix. (Hacker News discussion.) <https://news.ycombinator.com/item?id=9100107#up_9112425> The consequence of misspelling pragmas <https://ghc.haskell.org/trac/ghc/ticket/10106>, Or: when stumped on a compile error, turn on -Werror to see if you aren't missing something obvious. *Quote of the week:*garry__cairns <https://twitter.com/garry__cairns/status/571087073739976704>: The trouble with learning #haskell is the more I expose myself to it the more I dislike what I have to work with to pay the bills. *Repo of the week: *Kalium <https://github.com/int-index/kalium>: Turn Pascal <https://int-index.github.io/kalium/examples.html> into Haskell -- Kim-Ee

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Haskell 2015: 2nd Call for Papers
by Ben Lippmeier 04 Mar '15

04 Mar '15

===================================================================== ACM SIGPLAN CALL FOR SUBMISSIONS Haskell Symposium 2015 Vancouver, Canada, 3-4 September 2015, directly after ICFP http://www.haskell.org/haskell-symposium/2015 ===================================================================== ** The Haskell Symposium has an early track this year ** ** See the Submission Timetable for details. ** The ACM SIGPLAN Haskell Symposium 2015 will be co-located with the International Conference on Functional Programming (ICFP 2015) in Vancouver, Canada. The Haskell Symposium aims to present original research on Haskell, discuss practical experience and future development of the language, and to promote other forms of denotative programming. Topics of interest include: * Language Design, with a focus on possible extensions and modifications of Haskell as well as critical discussions of the status quo; * Theory, such as formal semantics of the present language or future extensions, type systems, effects, metatheory, and foundations for program analysis and transformation; * Implementations, including program analysis and transformation, static and dynamic compilation for sequential, parallel, and distributed architectures, memory management, as well as foreign function and component interfaces; * Libraries, that demonstrate new ideas or techniques for functional programming in Haskell; * Tools, such as profilers, tracers, debuggers, preprocessors, and testing tools; * Applications, to scientific and symbolic computing, databases, multimedia, telecommunication, the web, and so forth; * Functional Pearls, being elegant and instructive programming examples; * Experience Reports, to document general practice and experience in education, industry, or other contexts. Papers in the latter three categories need not necessarily report original academic research results. For example, they may instead report reusable programming idioms, elegant ways to approach a problem, or practical experience that will be useful to other users, implementors, or researchers. The key criterion for such a paper is that it makes a contribution from which other Haskellers can benefit. It is not enough simply to describe a standard solution to a standard programming problem, or report on experience where you used Haskell in the standard way and achieved the result you were expecting. More advice is available via the Haskell wiki: (http://wiki.haskell.org/HaskellSymposium/ExperienceReports) Regular papers should explain their research contributions in both general and technical terms, identifying what has been accomplished, explaining why it is significant, and relating it to previous work, and to other languages where appropriate. In addition, we solicit proposals for: * System Demonstrations, based on running software rather than novel research results. These proposals should summarize the system capabilities that would be demonstrated. The proposals will be judged on whether the ensuing session is likely to be important and interesting to the Haskell community at large, whether on grounds academic or industrial, theoretical or practical, technical, social or artistic. Please contact the program chair with any questions about the relevance of a proposal. Travel Support: =============== Student attendees with accepted papers can apply for a SIGPLAN PAC grant to help cover travel expenses. PAC also offers other support, such as for child-care expenses during the meeting or for travel costs for companions of SIGPLAN members with physical disabilities, as well as for travel from locations outside of North America and Europe. For details on the PAC program, see its web page (http://pac.sigplan.org) Proceedings: ============ Accepted papers will be included in the ACM Digital Library. Authors must grant ACM publication rights upon acceptance (http://authors.acm.org/main.html) Authors are encouraged to publish auxiliary material with their paper (source code, test data, etc.); they retain copyright of auxiliary material. Accepted proposals for system demonstrations will be posted on the symposium website, but not formally published in the proceedings. All accepted papers and proposals will be posted on the conference website one week before the meeting. Publication date: The official publication date of accepted papers is the date the proceedings are made available in the ACM Digital Library. This date may be up to two weeks prior to the first day of the conference. The official publication date affects the deadline for any patent filings related to published work. Submission Details: =================== Submitted papers should be in portable document format (PDF), formatted using the ACM SIGPLAN style guidelines (http://www.acm.org/sigs/sigplan/authorInformation.htm) The text should be in a 9-point font in two columns. The length is restricted to 12 pages, except for "Experience Report" papers, which are restricted to 6 pages. Papers need not fill the page limit -- for example, a Functional Pearl may be much shorter than 12 pages. Each paper submission must adhere to SIGPLAN's republication policy, as explained on the web. Demo proposals are limited to 2-page abstracts, in the same ACM format as papers. "Functional Pearls", "Experience Reports", and "Demo Proposals" should be marked as such with those words in the title at time of submission. The paper submission deadline and length limitations are firm. There will be no extensions, and papers violating the length limitations will be summarily rejected. A link to the paper submission system will appear on the Haskell Symposium web site closer to the submission deadline. Submission Timetable: ===================== Early Track Regular Track System Demos ---------------- ------------------- --------------- 13th March Paper Submission 1st May Notification 19th May Abstract Submission 22nd May Paper Submission 5th June Resubmission Demo Submission 26th June Notification Notification Notification 19th July Final papers due Final papers due Deadlines stated are valid anywhere on earth. In this iteration of the Haskell Symposium we are trialling a two-track submission process, so that some papers can gain early feedback. Papers can be submitted to the early track on 13th March. On 1st May, strong papers are accepted outright, and the others will be given their reviews and invited to resubmit. On 5th June early track papers may be resubmitted, and are sent back to the same reviewers. The Haskell Symposium regular track operates as in previous years. Papers accepted via the early and regular tracks are considered of equal value and will not be distinguished in the proceedings. Although all papers may be submitted to the early track, authors of functional pearls and experience reports are particularly encouraged to use this mechanism. The success of these papers depends heavily on the way they are presented, and submitting early will give the program committee a chance to provide feedback and help draw out the key ideas. Program Committee: =================== Mathieu Boespflug - Tweag I/O Edwin Brady - University of St Andrews Atze Dijkstra - Utrecht University Tom DuBuisson - Galois Torsten Grust - University of Tuebingen Patrik Jansson - Chalmers University of Technology Patricia Johann - Appalachian State University Oleg Kiselyov - Tohoku University Edward Kmett - McGraw Hill Financial Neelakantan Krishnaswami - University of Birmingham Ben Lippmeier (chair) - Vertigo Technology Hai (Paul) Liu - Intel Labs Garrett Morris - University of Edinburgh Dominic Orchard - Imperial College London Matt Roberts - Macquarie University Tim Sheard - Portland State University Joel Svensson - Indiana University Edsko de Vries - Well Typed =====================================================================

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ANN: ZuriHac 2015: registration is open
by Alexander Bernauer 04 Mar '15

04 Mar '15

Hi everybody, it is my pleasure to announce that the registration for ZuriHac 2015 <https://wiki.haskell.org/ZuriHac2015> is open now. If you want to participate in this year's Haskell Hackathon in Zurich, please fill out this form <http://goo.gl/forms/L24NgFRvCw>. Make sure to wait for a confirmation email afterwards before booking. The event can only host around 90 participants. We will confirm registrations at a first come first served basis. Please spread the word. Hope to see you soon! Alex

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Re: [Haskell-cafe] [Haskell] Constraint Satisfaction Problem
by Henning Thielemann 04 Mar '15

04 Mar '15

On Wed, 4 Mar 2015, K Sai Anirudh wrote: > Hello, > > I tried to solve simple constraint satisfaction problem. This is my code " http://pastebin.com/VAaRYSEA " . > This gives solution for present list of domains, but when I change the domain of 'd' in the list 'ld' then I > get error. I think the error is in line 52. I indexed the first value, but I tried filtering the results > where all the variables are assigned and I get error. I think this fits better to Haskell Cafe <haskell-cafe(a)haskell.org> where I send this reply, too.

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Help needed
by S J Rajath Krishna 03 Mar '15

03 Mar '15

I am a newbie to contributing to open source.I need help or the procedure for the following. 1.Replying to a thread2.Creating an account with the forum that will help me get started off for GSOC 2015. I apologize if this is not the right forum to be posting this, please direct me to the right forum. Thanks,S J Rajath Krishna

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