- Haskell-Cafe - Haskell.org

MPC 2019 final call for papers - submissions due 3rd May
by Graham Hutton 03 Apr '19

03 Apr '19

====================================================================== *** FINAL CALL FOR PAPERS -- MPC 2019 *** 13th International Conference on Mathematics of Program Construction 7-9 October 2019, Porto, Portugal Co-located with Formal Methods 2019 https://tinyurl.com/MPC-Porto ====================================================================== TIMELINE: Abstract submission 26th April 2019 Paper submission 3rd May 2019 Author notification 14th June 2019 Camera ready copy 12th July 2019 Conference 7-9 October 2019 KEYNOTE SPEAKERS: Assia Mahboubi INRIA, France Annabelle McIver Macquarie University, Australia BACKGROUND: The International Conference on Mathematics of Program Construction (MPC) aims to promote the development of mathematical principles and techniques that are demonstrably practical and effective in the process of constructing computer programs. MPC 2019 will be held in Porto, Portugal from 7-9 October 2019, and is co-located with the International Symposium on Formal Methods, FM 2019. Previous conferences were held in Königswinter, Germany (2015); Madrid, Spain (2012); Québec City, Canada (2010); Marseille, France (2008); Kuressaare, Estonia (2006); Stirling, UK (2004); Dagstuhl, Germany (2002); Ponte de Lima, Portugal (2000); Marstrand, Sweden (1998); Kloster Irsee, Germany (1995); Oxford, UK (1992); Twente, The Netherlands (1989). SCOPE: MPC seeks original papers on mathematical methods and tools put to use in program construction. Topics of interest range from algorithmics to support for program construction in programming languages and systems. Typical areas include type systems, program analysis and transformation, programming language semantics, security, and program logics. The notion of a 'program' is interpreted broadly, ranging from algorithms to hardware. Theoretical contributions are welcome, provided that their relevance to program construction is clear. Reports on applications are welcome, provided that their mathematical basis is evident. We also encourage the submission of 'programming pearls' that present elegant and instructive examples of the mathematics of program construction. SUBMISSION: Submission is in two stages. Abstracts (plain text, maximum 250 words) must be submitted by 26th April 2019. Full papers (pdf, formatted using the llncs.sty style file for LaTex) must be submitted by 3rd May 2019. There is no prescribed page limit, but authors should strive for brevity. Both abstracts and papers will be submitted using EasyChair. Papers must present previously unpublished work, and not be submitted concurrently to any other publication venue. Submissions will be evaluated by the program committee according to their relevance, correctness, significance, originality, and clarity. Each submission should explain its contributions in both general and technical terms, clearly identifying what has been accomplished, explaining why it is significant, and comparing it with previous work. Accepted papers must be presented in person at the conference by one of the authors. The proceedings of MPC 2019 will be published in the Lecture Notes in Computer Science (LNCS) series, as with all previous instances of the conference. Authors of accepted papers will be expected to transfer copyright to Springer for this purpose. After the conference, authors of the best papers from MPC 2019 and MPC 2015 will be invited to submit revised versions to a special issue of Science of Computer Programming (SCP). For any queries about submission please contact the program chair, Graham Hutton <graham.hutton(a)nottingham.ac.uk>. PROGRAM COMMITTEE: Patrick Bahr IT University of Copenhagen, Denmark Richard Bird University of Oxford, UK Corina Cîrstea University of Southampton, UK Brijesh Dongol University of Surrey, UK João F. Ferreira University of Lisbon, Portugal Jennifer Hackett University of Nottingham, UK William Harrison University of Missouri, USA Ralf Hinze University of Kaiserslautern, Germany Zhenjiang Hu National Institute of Informatics, Japan Graham Hutton (chair) University of Nottingham, UK Cezar Ionescu University of Oxford, UK Mauro Jaskelioff National University of Rosario, Argentina Ranjit Jhala University of California, USA Gabriele Keller Utrecht University, The Netherlands Ekaterina Komendantskaya Heriot-Watt University, UK Chris Martens North Carolina State University, USA Bernhard Möller University of Augsburg, Germany Shin-Cheng Mu Academia Sinica, Taiwan Mary Sheeran Chalmers University of Technology, Sweden Alexandra Silva University College London, UK Georg Struth University of Sheffield, UK CONFERENE VENUE: The conference will be held at the Alfândega Porto Congress Centre, a 150 year old former custom's house located in the historic centre of Porto on the bank of the river Douro. The venue was renovated by a Pritzer prize winning architect and has received many awards. LOCAL ORGANISERS: José Nuno Oliveira University of Minho, Portugal For any queries about local issues please contact the local organiser, José Nuno Oliveira <jno(a)di.uminho.pt>. ====================================================================== This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please contact the sender and delete the email and attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. Email communications with the University of Nottingham may be monitored where permitted by law.

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ANN: Haskell Beginners Google+ Community: "Haskell: The Haskell-Beginners Community"
by Benjamin L. Russell 02 Apr '19

02 Apr '19

Since the Google+ social network service is scheduled to be "sunset" (i.e., put out of service) on April 2, 2019, I have created a new Haskell beginners PASHpost community, "Haskell: The Haskell-Beginners Community" (see https://pashpost.com/group/haskell-the-haskell-beginners-community) and migrated a substantial portion of the original posts thereto (sans posts with missing links or irrelevant content). Feel free to join and contribute! -- Benjamin L. Russell

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Generating tagfiles for Vim
by Vanessa McHale 02 Apr '19

02 Apr '19

Hi all, I had been using hasktags for tag generation previously, however, I recently discovered that using GHCi with cabal new-repl λ:> :ctags creates a tags file that actually works with preprocessors (e.g. c2hs or alex or happy). Is there any way to run this semi-automatically? echo ':ctags' | cabal new-repl seems to work in the shell, but I'd like a vim integration if possible (also, it's slow). Cheers, Vanessa McHale

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I fell in love with System.Console.Haskeline.getExternalPrint
by Mario Lang 31 Mar '19

31 Mar '19

Hi. Since I discovered getExternalPrint, I found a ton of use cases for it. In particular, it makes it possible to write background threads that report stuff to the console without disturbing the prompt. I ended up writing a sort of uGHCi with the help of hint and the unreleased master branch of haskeline[1] to make externalPrint available from within the interpreter. Combined with Shh, this opens the door for a lot of useful functionality. Here is a simplified example based on shell programming with the help of Shh: % let watch r p = forkIO . forever $ printProc p >> readIORef r >>= OS.sleep % delay <- newIORef 10 % clock <- watch delay OS.date Sat Mar 2 21:32:28 CET 2019 Sat Mar 2 21:32:38 CET 2019 % writeIORef delay 5 Sat Mar 2 21:32:48 CET 2019 Sat Mar 2 21:32:53 CET 2019 Sat Mar 2 21:32:58 CET 2019 Sat Mar 2 21:33:03 CET 2019 % killThread clock printProc uses externalPrint from haskeline to print the output of a shell command to the console without disturbing the prompt. The OS module in this example simply exports all executables as haskell functions, thanks to the TH magic from Shh. I am relying on a pretty crude hack to make this work: (rFd, wFd) <- liftIO createPipe eprint <- getExternalPrint -- from haskeline liftIO . forkIO . forever $ do (s, bc) <- fdRead rFd 1024 eprint s -- ... -- define a function in the interpreter using hint runStmt $ "let externalPrint s = fdWrite (read " <> show (show wFd) <> ") s >> pure ()" This hack is basically the whole magic of my own hand-rolled uGHCi. I'd love to not reinvent the wheel there, and just be able to use standard GHCi to make use of externalPrint. Question is, would a similar thing be possible to implement in GHCi directly, and if so, what would be required to make this work? I am likely far too much a rooky to get this working on my own, so I am asking for help. What steps should I follow to eventually achieve my goal? I guess submitting a feature request would be a start. However, I want progress, so I am wondering: * The pipe trick is likely too hacky for GHCi. Are there any other portable alternatives for getting data from within the interpreter to the haskell process running it? * Or is there a way to serialize an IO action into the interpreter that I've missed? The problem here is the boundary between the process that runs the interpreter, and the interpreter itself. I am a bit whacky on terminology here, but as I see it, getExternalPrint returns a function that has internal state. So it isn't really possible to make such a function available from within the interpreter. Hence, the pipe hack above, which just sends the *argument* to externalPrint from the interpreter to the process running it. Any insights that might help me make that available in standard GHCi? I really think this is a pretty unique feature that would enable all sorts of interesting interactive code. [1] Haskeline < 0.8.0 doesn't allow to combine IntterpreterT from hint with InputT because of the way exceptions are done. The master branch of haskeline fixes that, so finally you can have a transformer stack that combines both, allowing for pretty simple interactive haskell interpreters with readline functionality. Thanks for that! -- CYa, ⡍⠁⠗⠊⠕

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Compose Second CFP & Keynote Speaker Announcement
by MightyByte 31 Mar '19

31 Mar '19

The April 23 submission deadline for Compose NYC is rapidly approaching, so get your submissions in soon. We are also excited to announce that we now have two confirmed keynote speakers: David Spivak - Compositional Graphical Logic Donya Quick - Making Algorithmic Music Compose is a conference focused specifically on strongly typed functional programming languages. It will be held in New York on Monday and Tuesday, June 24 -25, 2019. Registration will be open shortly. http://www.composeconference.org/2019 To get a sense of Compose, you can check out the great talks from past conferences: https://www.youtube.com/channel/UC0pEknZxL7Q1j0Ok8qImWdQ Below is our call for presentations. http://www.composeconference.org/2019/cfp/ In past years, we have also hosted an unconference over the weekend adjacent to the conference. The unconference details this year have not been finalized yet, but if you’re interested you may want to keep that in mind when making travel plans. *** Compose Conference NYC 2019 Second Call for Presentations June 24 -25, 2019 New York City The audience for Compose is people using Haskell, PureScript, OCaml, F#, SML, and other strongly typed functional programming languages who are looking to increase their skills or learn new technologies and libraries. Presentations should be aimed at teaching or introducing new ideas or tools. We are also interested in presentations aiming at taking complex concepts, such as program derivation, and putting them into productive use. However presentations on anything that you suspect our audience may find interesting are welcome. The following are some of the types of talks we would welcome: *Library/Tool Talks* — Exploring the uses of a powerful toolkit or library, be it for parsing, testing, data access and analysis, or anything else. *Production Systems* — Experience reports on deploying functional techniques in real systems; insights revealed, mistakes made, lessons learned. *Theory made Practical* — Just because it’s locked away in papers doesn’t mean it’s hard! Accessible lectures on classic results and why they matter to us today. Such talks can include simply introducing the principles of a field of research so as to help the audience read up on it in the future; from abstract machines to program derivation to branch-and-bound algorithms, the sky’s the limit. Check out the Compose YouTube channel ( https://www.youtube.com/playlist?list=PLNoHgLVTxtaoolkQo4hLy4ZsA1prUJ51m ) to see videos of talks we've had previously and get an idea of the kinds of topics we usually feature. We also welcome presentations for more formal tutorials. Tutorials should be aimed at a smaller audience of beginner-to-novice understanding, and ideally include hands-on exercises. The due date for submissions is *April 23, 2019*. We will send out notice of acceptance by *April 30th*. We prefer that submissions be via the EasyChair website ( https://easychair.org/conferences/?conf=compose2019 ). Please suggest a title, and describe the topic you intend to speak on. Talks can be either 30 or 45 minutes, please indicate how much time you would prefer to take. You may submit multiple talks if you have several ideas and are unsure which would be the most likely to be accepted. Accepted talks will be asked to submit slides for review prior to the conference. Feel free to include any additional information on both your expertise and interesting elements of your topic that would be appropriate for inclusion in the public abstract. Furthermore, if your abstract doesn't feel "final"—don't worry! We'll work with you to polish it up. If you want to discuss your presentation(s) before submitting, or to further nail down what you intend to speak on, please feel free to contact us at n...(a)composeconference.org ( n...(a)composeconference.org ). We're happy to work with you, even if you are a new or inexperienced speaker, to help your talk be great. Diversity We would like to put an emphasis on soliciting a diverse set of speakers - anything you can do to distribute information about this CFP and encourage submissions from under-represented groups would be greatly appreciated. We welcome your contributions and encourage you to apply! Best, Doug Sent via Superhuman ( https://sprh.mn/?vip=mightybyte@gmail.com )

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[Job] Cloudseal seeks Haskell Software Engineers
by Ryan Newton 30 Mar '19

30 Mar '19

Dear fellow Haskellers, We're hiring! See below. -Ryan Newton Cloudseal co-founder, Professor of Computer Science (on leave), Functional programmer for 28 years, Haskeller for 10 *========================================================* We are looking for a Haskell software engineer who is passionate about developer technologies and changing how the world tests and runs software. Cloudseal is an early-stage startup, a spin-out from academic research on reliable (deterministic) software execution. Our core technology is a new containerization mechanism for Linux/x86 programs that enables reproducible builds and functional tests that never flake. You will be joining a growing team with decades of collective experience contributing to developer tools, including the GHC compiler and ecosystem, as well as developer products at Intel and Microsoft. *Skills sought* *-------------------* We are seeking curious and independent people ready to become involved with every part of product development. We are a Haskell+Rust shop, corresponding to the high- and low-level components of our stack, respectively, with this position focused on the former. Familiarity with low-level Linux systems software is not required but would be a positive. Experience with building services (authentication, billing) is a plus for this role. You should be comfortable with modern infrastructure essentials like AWS, Docker, CI, etc. and have passable sysadmin skills. Ability to work independently as part of a distributed development team is essential. This full-time position carries an option for remote work (within the U.S.), but geographic proximity to Philadelphia, Indianapolis, or Bloomington, IN would be preferred. During a ramp-up phase we will work on site together at a higher rate (25-50% travel), after which in-person team meetups will be less frequent. *Benefits* *------------* - Competitive salary & fringe benefits - Significant early-stage stock options - Flexible working hours and vacation time *Applying* *-------------* Email your resume to jobs(a)cloudseal.io. In your message, please share links to your previous work, such as running websites or open source contributions.

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Resources/papers on lazy I/O
by Vanessa McHale 29 Mar '19

29 Mar '19

Hi all, I recently finished up writing streaming facilities via libarchive bindings and lazy bytestrings. It ended up working nicely - reading from a file lazily and then unpacking the archive was more efficient in time + allocations than reading the file all at once. That got me thinking - what exactly is wrong with lazy I/O? I've seen Oleg Kiselyov's paper (http://okmij.org/ftp/Haskell/#lazyIO-not-True) and I've run into issues myself (basically the issue here: https://stackoverflow.com/questions/31342012/read-and-writing-to-file-in-ha…) but none of those seem so pathological - the second issue could be better resolved with linear types! Are the any explanations of why Haskell *does* use lazy I/O? Laziness allows symmetries between values and generators of values - surely it is not *that* immoral to enforce this even in the IO monad? Cheers, Vanessa McHale

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Open Position: Lecturer in Cybersecurity - University of Exeter
by Achim D. Brucker 29 Mar '19

29 Mar '19

Dear all, As part of the recent expansion of the Department of Computer Science (www.ex.ac.uk/computer-science/) at the University of Exeter, we are recruiting for a new Lecturer in Cybersecurity. You will join a growing department and will contribute to a new research focus in cybersecurity. This is a *unique* opportunity to join a new cybersecurity group as founding member and to influence its future development. Application in all areas of cybersecurity are welcome. Please apply by 4th of April 2019! See the full announcement and apply here: https://jobs.exeter.ac.uk/hrpr_webrecruitment/wrd/run/ETREC107GF.open?VACAN… Feel free to contact me for informal inquires about the post. Best, Achim -- Dr. Achim D. Brucker | Chair of Cybersecurity | University of Exeter https://www.brucker.ch | https://logicalhacking.com/blog @adbrucker | @logicalhacking

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a bug in Read instance of Int?
by Javran Cheng 29 Mar '19

29 Mar '19

Hi Cafe, Not sure if there are existing discussions, but I recently run into a problem with Read instance of Int: Prelude> :set -XTypeApplications Prelude> reads @Int "123." [(123,".")] Prelude> reads @Int "123.aaa" [(123,".aaa")] Prelude> reads @Int "123.456aaa" [] -- I expected this to be [(123,".456aaa")] Prelude> reads @Double "123.234aaa" [(123.234,"aaa")] Further investigation shows that [realNumber]( http://hackage.haskell.org/package/base/docs/src/GHC.Read.html#readNumber) is used for Read instance of Int. I think what happened is that when the leading parser input can be parsed as a floating number, it will do so and commit to that decision, making backtracking impossible. I do understand that Read just need to be able to parse whatever Show can produce and is not designed to deal with raw inputs, but this is still a surprising behavior to me. When I'm using Text.ParserCombinators.ReadP, I really appreciates it that I can use `readP_to_S read` to parse simple values (integers and floating points in particular), but it bothers me that parsing Int from "123.aaa" is fine but "123.1aa" will fail simply because the not-yet-consumed part of input is different. Javran

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art exhibition in London, April 2019
by Claude Heiland-Allen 28 Mar '19

28 Mar '19

Hi all, I have an art exhibition opening soon in London, UK. https://sonicelectronicsfestival.org/exhibition/ Featuring: - raytracing in curved space - badly-played tetris - generative techno - audiovisual sliding tile puzzle - interactive graph-directed IFS - zooming hybrid fractals Opening 11th April 2019 6pm, until 27th April, at Chalton Gallery, 96 Chalton Street, Camden, London NW1 1HJ, UK. Check website for times. Two of the works are realized with Haskell: - "Wedged" implements aesthetic constraints to search tetris packings - "Hybrids" uses a formula compiler to generate C code for rendering fractals Curated by Laura Netz. Supported using public funding by the National Lottery through Arts Council England. Claude -- https://mathr.co.uk

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Call for Tutorial Proposals: ICFP 2019
by Sam Tobin-Hochstadt 28 Mar '19

28 Mar '19

CALL FOR TUTORIAL PROPOSALS ICFP 2019 24th ACM SIGPLAN International Conference on Functional Programming August 18 - 23, 2019 Berlin, Germany https://icfp19.sigplan.org/ The 24th ACM SIGPLAN International Conference on Functional Programming will be held in Berlin, Germany on August 18-23, 2019. ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. Proposals are invited for tutorials, lasting approximately 3 hours each, to be presented during ICFP and its co-located workshops and other events. These tutorials are the successor to the CUFP tutorials from previous years, but we also welcome tutorials whose primary audience is researchers rather than practitioners. Tutorials may focus either on a concrete technology or on a theoretical or mathematical tool. Ideally, tutorials will have a concrete result, such as "Learn to do X with Y" rather than "Learn language Y". Tutorials may occur after ICFP co-located with the associated workshops, from August 22 till August 23. ---------------------------------------------------------------------- Submission details Deadline for submission: May 10th, 2019 Notification of acceptance: May 17th, 2019 Prospective organizers of tutorials are invited to submit a completed tutorial proposal form in plain text format to the ICFP 2018 workshop co-chairs (Jennifer Hackett and Christophe Scholliers), via email to icfp-workshops-2019(a)googlegroups.com by May 10th, 2019. Please note that this is a firm deadline. Organizers will be notified if their event proposal is accepted by May 17, 2019. The proposal form is available at: http://www.icfpconference.org/icfp2019-files/icfp19-tutorials-form.txt ---------------------------------------------------------------------- Selection committee The proposals will be evaluated by a committee comprising the following members of the ICFP 2019 organizing committee. Tutorials Co-Chair: Jennifer Hackett (University of Nottingham) Tutorials Co-Chair: Christophe Scholliers (University of Ghent) General Chair: Derek Dreyer (MPI-SWS) Program Chair: François Pottier ( Inria, France) ---------------------------------------------------------------------- Further information Any queries should be addressed to the tutorial co-chairs ( Jennifer Hackett and Christophe Scholliers), via email to icfp-workshops-2019(a)googlegroups.com

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[TFPIE'19] Call for papers: Trends in Functional Programming in Education 2019, 11 June 2019, Vancouver, BC, CA
by Peter Achten 27 Mar '19

27 Mar '19

TFPIE 2019 Call for papers http://www.staff.science.uu.nl/~hage0101/tfpie2019/index.html (June 11th, University of British Columbia, Vancouver Canada, co-located with TFP 2019) TFPIE 2019 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 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 The pedagogy of teaching FP FP and e-learning: MOOCs, automated assessment etc. Best Lectures Ð more details below In addition to papers, we are requesting best lecture presentations. What's 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. The length of the presentation should be comparable to that of a paper. On top of the lecture itself, the presentation can also provide commentary on the lecture. Submissions 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. Papers and abstracts can be submitted via easychair at the following link: https://easychair.org/conferences/?conf=tfpie2019 After the workshop, presenters will be invited to submit (a revised version of) their article for review. The PC will select the best articles that will be published in the Electronic Proceedings in Theoretical Computer Science (EPTCS). Articles rejected for presentation and extended abstracts will not be formally reviewed by the PC. Dates Submission deadline: May 14th 2019, Anywhere on Earth. Notification: May 20th Workshop: June 11th Submission for formal review: August 18th 2019, Anywhere on Earth Notification of full article: October 6th Camera ready: November 1st Program Committee Alex Gerdes - University of Gothenburg / Chalmers Jurriaan Hage (Chair) - Utrecht University Pieter Koopman - Radboud University, the Netherlands Elena Machkasova - University of Minnesota, Morris, USA Heather Miller - Carnegie Mellon University and EPFL Lausanne Prabhakar Ragde - University of Waterloo, Waterloo, Ontario, Canada Simon Thompson - University of Kent, UK Sharon Tuttle - Humboldt State University, Arcata, USA Note: information on TFP is available at https://www.tfp2019.org/index.html

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GSoC 2019 Student Applications now open
by Jasper Van der Jeugt 26 Mar '19

26 Mar '19

Hi all, We'd like to remind you that Google has opened student applications for Google Summer of Code 2019 [1]. Applications can be submitted through their dashboard [2]. If you are thinking of applying, there is a list of ideas submitted by our wonderful community [3] that can serve as inspiration. Of course, we also welcome other proposals! Please contact us [4] if you have any other question about the program. Warm regards Jasper Van der Jeugt on behalf of the Haskell.Org Committee [1]: https://summerofcode.withgoogle.com/ [2]: https://summerofcode.withgoogle.com/dashboard/ [3]: https://summer.haskell.org/ideas.html [4]: https://summer.haskell.org/contact.html

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Munich Haskell Meeting, 2019-03-27 @ 19:30
by Leah Neukirchen 25 Mar '19

25 Mar '19

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Wednesday, March 27 at Rumpler at 19h30. For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-mar-2019/ Everybody is welcome! cu & see you perhaps tomorrow at Munich Lambda meetup, -- Leah Neukirchen <leah(a)vuxu.org> http://leahneukirchen.org/

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sublime-haskell and hsdev
by Dennis Raddle 22 Mar '19

22 Mar '19

I'm just now learning Sublime Text 3 and trying to install sublime-haskell. It requires me to build hsdev, which I did with "cabal install hsdev". However the latter operation installs version > 3 of hsdev, while sublime-haskell requires < 3. So first question, how do I build and install an earlier version of hsdev? Also, I'm not clear if sublime-haskell is integrated with stack. I use stack for everything and I've been using Intero up til now in Emacs. The docs mention stack but seem to be clearer about cabal. D

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RedMonk ranks Haskell among top 20 most popular programming languages
by Jeffrey Brown 22 Mar '19

22 Mar '19

based on GitHub and StackOverflow. https://redmonk.com/sogrady/2019/03/20/language-rankings-1-19/ -- Jeff Brown | Jeffrey Benjamin Brown Website <https://msu.edu/~brown202/> | Facebook <https://www.facebook.com/mejeff.younotjeff> | LinkedIn <https://www.linkedin.com/in/jeffreybenjaminbrown>(spammy, so I often miss messages here) | Github <https://github.com/jeffreybenjaminbrown>

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More graph algorithms for Alga & Streaming JSON/YAML parser
by Shiv 22 Mar '19

22 Mar '19

Dear mentors, I am Shiv Pratap Singh from IIIT-Allahabad, India. I am currently in 4th year and Computer Science Undergraduate. After lot of brainstorming and carefully choosing the project idea based on my skills/expertise/experience, I am highly interested in project idea mentioned in Subject of the mail. As the proposal submission date is very close, I am keen to discuss the idea in depth so that various subtasks can be finalized .If any prior contribution/patch is requirement for applying, please let me know. Please mention some resources links in order to gain insights on project. Hoping to work together! Thank you, Shiv

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[ANN] libarchive
by Vanessa McHale 21 Mar '19

21 Mar '19

Hi all, I just released libarchive (http://hackage.haskell.org/package/libarchive) which can be used to create and unpack tar archives as well as several other formats. It has a reasonably complete high-level API and full bindings to the C library. Cheers, Vanessa McHale

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Yet another binary reader (10x faster than Hackage's binary; )
by Станислав Черничкин 20 Mar '19

20 Mar '19

I was investigating Haskell’s binary serialization libraries and has found that lot of them (binary, cereal and protocol-buffers) has pretty similar design. They capable to consume lazy bytestrings and either produce result, report error or produce partial result, indicating that more input data required. Such design leads to quite complex readers, and often ends up with producing closures in runtime. If you take a close look at binary’s microbenches (binary in general bit faster than cereal, so I focused on binary) you will discover, that it triggers GC even during simple tasks, such as reading a bunch of Word64 and summing results. And it relatively slow. Binary’s performance limited to hundreds of megabytes per second even in simple scenarios, but actual memory bandwidth should allow us process gigabytes per second. So, I decided to try a different approach. My approach is based on two assumptions so if it does not suit your case it obliviously will not work for you. First – when dealing with binary data we always know exactly how many bytes we want to read. This happens because we either read a fixed size primitive type or length-prefixed variable size data (possibly not “prefixed”, but you always know expected message length from somewhere). Second – chunks of data are continuous. I.e. we working with strict bytestrings more often. Even when you processing chunked stream of data with unknown number of messages (such as Mesos RecordIO Format) you should always be able to allocate continuous memory buffer for a single entity you want to deserialize. If it’s ok for you lets go on. First thing I’ve created was so called static reader. Static – because reader knows how mush bytes it wants to consume at compile time. Such readers suitable for reading combinations of primitive values. Here the implementation https://github.com/PROTEINE-INSAIDERS/lev-tolstoy/blob/master/src/Lev/Reade… Static reader is somewhat monadic (you can use do-syntax with RebindableSyntax extension like here https://github.com/PROTEINE-INSAIDERS/lev-tolstoy/blob/master/bench/Bench/L… ) but it actually indexed monad and it unfortunately incompatible with traditional monads. Offsets and sizes are calculates at type level during the compile time and according to microbences static reader does not introduced any overhead compared to hand-written reader using the low-level indexInt64OffAddr# function ( https://github.com/PROTEINE-INSAIDERS/lev-tolstoy/blob/master/bench/Bench/H… ) Next thing was a dynamic reader. Dynamic readers are composed from static readers, they are fully monadic and allow you to read length-prefixed data structures (you read length with wrapped static reader and then perform normal monadic binding to supply a reader which reads a value). Here the implementation https://github.com/PROTEINE-INSAIDERS/lev-tolstoy/blob/master/src/Lev/Reade… I’ve discovered, that typeclasses are surprisingly fast. So, it’s completely ok to have something like “(Cursor c) => … Reader” where cursor contains functions for overflow checking and memory buffer progression. I was not able to achieve same performance when I passed buffer callbacks explicitly, possibly because of inlining of specialization magic. So, I've created ByteStringCursor ( https://github.com/PROTEINE-INSAIDERS/lev-tolstoy/blob/master/src/Lev/Reade… ) which allows to read strict bytestrings. I suppose that cursors introduce flexibility: you may read strict bytestring or you may define custom cursor for reading custom memory buffers. Finally, I’ve written some microbenches for my cases and also ported one microbench from binary. And my implementation was able to run 10x-15x faster than binary on strict bytestring. Moreover, it does not trigger GC during the run at all! You may find the project and all the benches here https://github.com/PROTEINE-INSAIDERS/lev-tolstoy So, what's the purpose of my message? It’s quite unlikely that I’ll release my code on the Hackage. This is because I’m a hobbyist Haskell developer and doing it all in my free time. But before mr. Putin will close Internet in Russia I’d like to demonstrate that it’s possible to write very fast binary deserializer taking in account several assumptions which seems quite reasonably for me. So, feel free to borrow the ideas, or share the ideas, if you know how it could be implemented better. -- Sincerely, Stanislav Chernichkin.

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Re: [Haskell-cafe] Yet another binary reader (10x faster than Hackage's binary)
by Olaf Klinke 20 Mar '19

20 Mar '19

My (admittedly limited) experience with parsers, of which deserializers are a special case, is that with complicated data structures the majority of computing time is spent transforming the raw data (i.e. chunks of bytes) into meaningful information such as Doubles, Timestamps, tree structures and so on. Of course you could argue that such conversions are not the scope of the deserializer and that these operations must be performed regardless which library one chooses. Nevertheless it somewhat relativizes the importance of the choice of serializing library. Your benchmarks do not go beyond adding integers as far as I can see, which is a relatively cheap operation. I'd be interested in a benchmark where e.g. a huge Set or an array of custom records are used. You seem to work in bioinformatics. There are plenty of examples from this field, e.g. genomic annotations. Cheers, Olaf

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Re： Yet another binary reader (10x faster thanHackage's binary; )
by Dr.Koster 20 Mar '19

20 Mar '19

These two assumptions are basically the most challenging issues stop people from getting more performance, e.g. If somehow you want to support incremental parsing, a primitive like `ensureN` probably need to do something like ``` ensureN n = Parser $ \ buf ... k -> if n < length buf then k buf ... else partial buf ... k ``` The k appear twice inside `ensureN` 's both branch, which will stop parsers from getting inline sooner or later since inlining k into both branch will produce exponential amount of code, so instead GHC will allocate k and make a jump, the best we can get is probably to try make it a joint point, so no allocation is needed, but that's the best you can get from argument passing buffers. Regards Han Dong ------------------ 原始邮件 ------------------ 发件人: "Joachim Durchholz"<jo(a)durchholz.org>; 发送时间: 2019年3月20日(星期三) 中午1:28 收件人: "haskell-cafe"<haskell-cafe(a)haskell.org>; 主题: Re: [Haskell-cafe] Yet another binary reader (10x faster thanHackage's binary; ) Am 19.03.19 um 22:58 schrieb Станислав Черничкин: > possibly because of inlining of > specialization magic. I have seen people validate this kind of assumption, by looking at the various intermediate representations of code. If you're after performance, you may want to do that. You may find that things work differently than expected, with the potential for becoming a bottleneck when stuff is scaled up (more varied datatypes in the input stream, or more complex target datatypes, stuff hidden behind "oh I don't need GC yet", that kind of finding). Regards, Jo _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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Data.Functor.Compose Combinator
by Ben Kolera 20 Mar '19

20 Mar '19

Hi, I was wondering if this function exists somewhere (i'm not attached to the name): (<<$>>) :: (Functor f) => (a -> g b) -> f a -> Compose f g b (<<$>>) mkG = Compose . fmap mkG It's handy if you're working with an applicative (e.g Reflex.Dynamic) and want to layer on top a validation type function that returns a different applicative that need composing. So I figure that it must exist somewhere! :) E.g. data Person = Person Text Email nameTextDyn :: Dynamic t Text emailTextDyn :: Dynamic t Text validEmail :: Text -> Validation (NonEmpty Text) Email validPersonDyn :: Dynamic t (Validation (NonEmpty Text) Person = getCompose $ Person <$> (pure <<$>> name) <*> (validEmail <<$>> emailTextDyn) Cheers, Ben

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Fwd: [Fwd: linux version compatible with GHC 4.3 ?]
by Damien Mattei 19 Mar '19

19 Mar '19

---------- Forwarded message --------- From: Damien Mattei <damien.mattei(a)univ-cotedazur.fr> Date: Mon, Mar 18, 2019 at 11:46 AM Subject: [Fwd: linux version compatible with GHC 4.3 ?] To: <damien.mattei(a)gmail.com> ---------- Forwarded message ---------- From: Damien Mattei <damien.mattei(a)univ-cotedazur.fr> To: Haskell Cafe <haskell-cafe(a)haskell.org> Cc: Bcc: Date: Mon, 18 Mar 2019 11:39:25 +0100 Subject: linux version compatible with GHC 4.3 ? Hi, does anyone know a linux distrib where haskell platform installs out of the box? it fails on fedora core 28 (32bits) : [root@localhost Downloads]# ghci /usr/local/haskell/ghc-8.4.3-i386/lib/ghc-8.4.3/bin/ghc: error while loading shared libraries: libtinfo.so.5: cannot open shared object file: No such file or directory but works on older system such as CentOS Linux release 7.2.1511 (Core) 64bits: [mattei@moita ~]$ cat /etc/redhat-release CentOS Linux release 7.2.1511 (Core) [mattei@moita ~]$ ghci GHCi, version 8.4.3: http://www.haskell.org/ghc/ :? for help Prelude> does it works on Ubuntu? Damien

4 3

Hard cases for "Note 5" in Haskell layout parsing
by Chris Smith 18 Mar '19

18 Mar '19

Quick question. I'm trying to resolve Haskell layout in order to provide better syntax highlighting, but without committing to building a full Haskell parser. The reason this is hard at face value is because of the "Note 5" in the relevant part of the Haskell Report, which says that a layout context closes whenever (a) the next token without closing the layout context would not be the start of any valid Haskell syntax, but (b) the current statement followed by an implicit '}' could be valid Haskell syntax. This rule is why it's okay to write "let x = 5 in x^2", even though let introduces a new layout syntax: the "in" implicitly closes it because "x = 5 in" isn't the start of any valid syntax, so the layout context is implicitly closed before the "in". Now for my question. Does anyone know other cases besides let/in where this commonly comes up? Everywhere I've seen this before uses let/in as an example, but then concludes that full parsing is needed and gives up on simpler answers. But the specific example with let/in is easily handled with a special-purpose rule that closes layout contexts as needed when an "in" keyword shows up. I cannot seem to construct any other examples, because other layout-introducing keywords have their contents at the end of syntactic element. Is there something I've missed here? I don't even care if it's a situation where something is technically valid but a horrible edge case. I'm interested in realistic counterexamples. Thanks, Chris

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Learn you a Haskell for great good! Group readnig
by Jaysinh shukla 17 Mar '19

17 Mar '19

Respected Member, I am trying to learn Haskell from the book Learn you a Haskell for great good! [1]. I livestream my reading sessions at this [2] Twitch channel. Group reading is helping me to learn better. It is way more productive than reading alone. If you are learning Haskell, please join us. If you already know Haskell, please join to teach. Teaching will give you a good revision. Don't worry about the commitment to attend each and every session. It is fine to attend sessions on the day you are available and skip the rest. The fun part is, all the sessions will be on weekends. You can watch videos of past sessions here [3]. I am trying to maintain an event calendar for upcoming sessions here [4]. Please share these resources with whoever learning the Haskell. Don't hesitate to ask your questions here or in a personal mail. Thanks! 1: http://learnyouahaskell.com 2: https://www.twitch.tv/jaysinhp 3: https://www.twitch.tv/jaysinhp/videos 4: https://www.twitch.tv/jaysinhp/events

1 0

Preferred location for symlink-bindir?
by David Banas 15 Mar '19

15 Mar '19

Hi all, In moving to the cabal 'new-install' command, is there a preferred definition for the ‘symlink-bindir’ cabal configuration variable on Mac OS X? Thanks, -db

1 0

initialization of AlexUserState
by Kees Bleijenberg 15 Mar '19

15 Mar '19

Hi All, I have a Alex lexer with wrapper "monadUserState-bytestring". The AlexUserState = AlexUserState {sheetNames:: {String], currSheet:: Int}. The lexer should check whether a found sheetname is in sheetNames. The sheetNames from AlexUserState come from outside. I want to invoke the lexer many times with different AlexUserStates. Therefore the alexInitUserState function is not what I want. I'de like to initialize the AlexUserState while starting the lexer, i.e. as a parameter to runAlex. Can that be done? Kees --- Dit e-mailbericht is gecontroleerd op virussen met Avast antivirussoftware. https://www.avast.com/antivirus

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[TFP'19] second call for papers: Trends in Functional Programming 2019, 12-14 June 2019, Vancouver, BC, CA
by Peter Achten 15 Mar '19

15 Mar '19

-------------------------------- 2 N D C A L L F O R P A P E R S -------------------------------- ====== TFP 2019 ====== 20th Symposium on Trends in Functional Programming 12-14 June, 2019 Vancouver, BC, CA https://www.tfp2019.org/index.html == Important Dates == Submission Deadline for pre-symposium formal review Thursday, March 28, 2019 Sumbission Deadline for Draft Papers Thursday, May 9, 2019 Notification for pre-symposium submissions Thursday, May 2, 2019 Notification for Draft Papers Tuesday, May 14, 1029 TFPIE Tuesday, June 11, 2019 Symposium Wednesday, June 12, 2019 – Friday, June 14, 2019 Notification of Student Paper Feedback Friday June 21, 2019 Submission Deadline for revised Draft Papers (post-symposium formal review) Thursday, August 1, 2019 Notification for post-symposium submissions Thursday, October 24, 2019 Camera Ready Deadline (both pre- and post-symposium) Friday, November 29, 2019 The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions (see below at scope). Please be aware that TFP uses two distinct rounds of submissions (see below at submission details). TFP 2019 will be the main event of a pair of functional programming events. TFP 2019 will be accompanied by the International Workshop on Trends in Functional Programming in Education (TFPIE), which will take place on June 11. == Scope == The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles: Leading-edge, previously unpublished research work Position Articles: On what new trends should or should not be Project Articles: Descriptions of recently started new projects Evaluation Articles: What lessons can be drawn from a finished project Overview Articles: Summarizing work with respect to a trendy subject Articles must be original and not simultaneously submitted for publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include, but are not limited to: Functional programming and multicore/manycore computing Functional programming in the cloud High performance functional computing Extra-functional (behavioural) properties of functional programs Dependently typed functional programming Validation and verification of functional programs Debugging and profiling for functional languages Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. Interoperability with imperative programming languages Novel memory management techniques Program analysis and transformation techniques Empirical performance studies Abstract/virtual machines and compilers for functional languages (Embedded) domain specific languages New implementation strategies Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2019 program chairs, William J. Bowman and Ron Garcia. == Best Paper Awards == To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. == Instructions to Author == Papers must be submitted at: https://easychair.org/conferences/?conf=tfp2019 Authors of papers have the choice of having their contributions formally reviewed either before or after the Symposium. == Pre-symposium formal review == Papers to be formally reviewed before the symposium should be submitted before an early deadline and receive their reviews and notification of acceptance for both presentation and publication before the symposium. A paper that has been rejected in this process may still be accepted for presentation at the symposium, but will not be considered for the post-symposium formal review. == Post-symposium formal review == Papers submitted for post-symposium review (draft papers) will receive minimal reviews and notification of acceptance for presentation at the symposium. Authors of draft papers will be invited to submit revised papers based on the feedback received at the symposium. A post-symposium refereeing process will then select a subset of these articles for formal publication. == Paper categories == There are two types of submission, each of which can be submitted either for pre-symposium or post-symposium review: Extended abstracts. Extended abstracts are 4 to 10 pages in length. Full papers. Full papers are up to 20 pages in length. Each submission also belongs to a category: research position project evaluation overview paper Each submission should clearly indicate to which category it belongs. Additionally, a draft paper submission—of either type (extended abstract or full paper) and any category—can be considered a student paper. A student paper is one for which primary authors are research students and the majority of the work described was carried out by the students. The submission should indicate that it is a student paper. Student papers will receive additional feedback from the PC shortly after the symposium has taken place and before the post-symposium submission deadline. Feedback is only provided for accepted student papers, i.e., papers submitted for presentation and post-symposium formal review that are accepted for presentation. If a student paper is rejected for presentation, then it receives no further feedback and cannot be submitted for post-symposium review. == Format == Papers must be written in English, and written using the LNCS style. For more information about formatting please consult the Springer LNCS web site (http://www.springer.com/lncs) == Program Committee == Program Co-chairs William J. Bowman University of British Columbia Ronald Garcia University of British Columbia Matteo Cimini University of Massachusetts Lowell Ryan Culpepper Czech Technical Institute Joshua Dunfield Queen's University Sam Lindley University of Edinburgh Assia Mahboubi INRIA Nantes Christine Rizkallah University of New South Wales Satnam Singh Google AI Marco T. Morazán Seton Hall University John Hughes Chalmers University and Quviq Nicolas Wu University of Bristol Tom Schrijvers KU Leuven Scott Smith Johns Hopkins University Stephanie Balzer Carnegie Mellon University Viktória Zsók Eötvös Loránd University

1 0

Annoying problem when pattern matching negative integer literals and wildcards
by Vanessa McHale 15 Mar '19

15 Mar '19

I have the following program: module Bug ( encryptionResult ) where data EncryptionResult = HasEncryption | EncryptionUnknown encryptionResult :: Int -> EncryptionResult encryptionResult 1 = HasEncryption encryptionResult -1 = EncryptionUnknown encryptionResult _ = error "Internal error." When I try to compile it with GHC I get [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:9:1: error: Multiple declarations of ‘encryptionResult’ Declared at: Bug.hs:7:1 Bug.hs:9:1 | 9 | encryptionResult _ = error "Internal error." | ^^^^^^^^^^^^^^^^ I can replicate this in Hugs, viz. ERROR "Bug.hs":7 - "encryptionResult" multiply defined However, everything compiles fine when I write module Bug ( encryptionResult ) where data EncryptionResult = HasEncryption | EncryptionUnknown encryptionResult :: Int -> EncryptionResult encryptionResult 1 = HasEncryption encryptionResult -1 = EncryptionUnknown or module Bug ( encryptionResult ) where data EncryptionResult = HasEncryption | EncryptionUnknown encryptionResult :: Int -> EncryptionResult encryptionResult 1 = HasEncryption encryptionResult 0 = EncryptionUnknown encryptionResult _ = error "Internal error." Am I doing something obviously screwy? This seems like a pretty annoying feature on the language (to the point where I assumed it was a GHC bug until I got the same behavior with Hugs) and I can't figure out why it exists. Cheers, Vanessa McHale

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How to use alex with param -g in cabal
by Kees Bleijenberg 14 Mar '19

14 Mar '19

Hi all, Alex is in the build-tools part of the cabal file. The docs of Alex says that invoking Alex with -g makes the resulting lexer significantly faster and smaller. How can I pass the -g parameter in the cabal file? Kees --- Dit e-mailbericht is gecontroleerd op virussen met Avast antivirussoftware. https://www.avast.com/antivirus

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ANN: Radicle
by Julian Arni 13 Mar '19

13 Mar '19

Today we're releasing the alpha version of Radicle. Radicle is a p2p code collaboration platform (think Github replacement). Issues, patches (like PRs) and optionally code are distributed via IPFS, without a centralized server, and with tooling that's meant to work directly from your terminal. There's a lot more info on the webpage [0]. Radicle is written in Haskell (minus the parts that are written in the Radicle language itself, though the language is implemented in Haskell), and open-source, which is why I thought to post here. [0] www.radicle.xyz

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Apply Haskell at scale in a music start-up
by Jeroen Bransen 12 Mar '19

12 Mar '19

* Dear Haskellers, Chordify is hiring! Chordify is a young and fast growing music e-learning platform that helps musicians to play their favorite music. We automatically analyse the chords of a piece of music and display them in an intuitive player. Try it yourself at: https://chordify.net/or download one of our apps https://chordify.net/app The cool thing is: our backend serving our apps and website has been written mostly in Haskell. With over 8 million users per month we apply functional programming at scale. We hope to broaden our team with a functional programmer. We are looking for people who are pro-active, independent, and creative to improve Chordify. You’d have the opportunity to be productive with advanced type-system features and powerful GHC extensions. Our back-end is powered by libraries like Servant, Persistent and Esqueleto and we distribute computation using Cloud Haskell. If you are interested in working at Chordify, please have a look at: https://jobs.chordify.net/ All the best, Jeroen Bransen *

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[OT] thoughts about OO vs. functional "philosophy"
by Dennis Raddle 12 Mar '19

12 Mar '19

I have a thought about OO vs. functional programming . I'm moderately experienced with functional languages such as Haskell and Purescript and have used OO for many years at work (Python, C++). I'm giving tutoring lessons in Python to a professional who wants to use programming as part of his work. (He's an entrepreneur.) He is eager to understand functional and OO styles within Python--he keeps asking about the real benefit of each, not content with a superficial approach. I've explained about "encapsulation": gathering related functions together and minimizing coupling to the rest of the program. He asks "why do we encapsulate?" I've explained that one reason is to help we, the programmers, be confident that our code is correct. For example, in a class we try to isolate the implementation details from the rest of the program, and the compiler helps enforce that.So when we're writing our code and confirming to ourselves it's correct, we can make simplifying assumptions. We know the rest of the program won't modify our private variables and won't access us in any way other than the interface we've presented to the world. I explained that a large program is like a corporation, and pieces of the program are like individual employees. When we write a class or function, in a sense we "become" that employee and "forget about" a lot of the details of other employees. (i.e., encapsulation). Then has asked why functional programming is helpful. I explained about referential transparency. Say we're a function: then other "employees" (other functions) can trust us with simplifying assumptions, like no side-effects. Then this thought occurred to me, which is nifty but maybe not the whole story. """ Say we're a class. Then the simplifying assumptions of OO allow *us* to trust the *rest of the program* won't mess with us. Say we're a function. Then the simplifying assumptions of functional style help the *rest of the program* trust that *we* won't mess with it. """ D

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Re: [Haskell-cafe] Informal modelling and simulation of protocols
by Doug McIlroy 11 Mar '19

11 Mar '19

> Is there some fantastic tool/library which already does everything I want? Have you looked into model checkers like Spin, which was developed for the very purpose of exhaustively checking protocols? See spinroot.com Doug McIlroy

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Machine Learning Library in Haskell
by Heet Sankesara 11 Mar '19

11 Mar '19

Hello community, Myself Heet sankesara. I am a machine learning practitioner. I've been doing it for a year. I recently learned Haskell to implement Markov Logic Networks. I found the language intuitive. It is far easier to express logic and formulas in Haskell as compared to languages like Python or R. So I decided to do some data science using it but I couldn't because there is no library like Sklearn in Python. The few libraries I found are mostly disoriented and undermanaged. I want to work on machine learning library which can be used easily and efficiently by machine learning practitioners. It would be helpful for everyone to have a dedicated machine learning library. For a practitioner, it would be easier to tweak and test the model and try different algorithms quickly. For the community, the dedicated library leads the developers to focus on it and improve it which would result in a more efficient and flexible library. The list of algorithms I am planning to implement are as follows: 1. Linear and Logistic Regression 2. Ridge Regression 3. Perceptron 4. SVM classifier and regressor (Both Linear and Non-Linear) 5. Stochastic Gradient Descent 6. K-means clustering and KNN classifier 7. Naive Bayes 8. Decision trees 9. Random Forest 10. Gradient boosting 11. Ada boost 12. Voting classifier 13. Neural Network 14. Gradient Descent, Momentum, Nesterov accelerated gradient 15. Adaptive Moment Estimation (Adam optimizer) Please consider this idea for GSoC this year. I am be happy to talk about the idea and possible algorithms that can be implemented in the upcoming summer. With regards, Heet Sankesara

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Haskell Symposium: Early Track due this Friday, March 15
by Richard Eisenberg 11 Mar '19

11 Mar '19

================================================================================ ACM SIGPLAN CALL FOR SUBMISSIONS Haskell Symposium 2019 Berlin, Germany 22--23 August, 2019 http://www.haskell.org/haskell-symposium/2019/ ================================================================================ The ACM SIGPLAN Haskell Symposium 2019 will be co-located with the 2019 International Conference on Functional Programming (ICFP). **NEW THIS YEAR**: We will be using a lightweight double-blind reviewing process. See further information below. The Haskell Symposium presents original research on Haskell, discusses practical experience and future development of the language, and promotes other forms of declarative 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; * System Demonstrations, based on running software rather than novel research results. 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. Experience reports and functional pearls 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, implementers, 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. System demonstrations 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. Submission Details ================== Early and Regular Track ----------------------- The Haskell Symposium uses a two-track submission process so that some papers can gain early feedback. Strong papers submitted to the early track are accepted outright, and the others will be given their reviews and invited to resubmit to the regular track. 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. Formatting ---------- Submitted papers should be in portable document format (PDF), formatted using the ACM SIGPLAN style guidelines. Authors should use the `acmart` format, with the `sigplan` sub-format for ACM proceedings. For details, see: http://www.sigplan.org/Resources/Author/#acmart-format It is recommended to use the `review` option when submitting a paper; this option enables line numbers for easy reference in reviews. Functional pearls, experience reports, and demo proposals should be labelled clearly as such. Lightweight Double-blind Reviewing ---------------------------------- Haskell Symposium 2019 will use a lightweight double-blind reviewing process. To facilitate this, submitted papers must adhere to two rules: 1. Author names and institutions must be omitted, and 2. References to authors’ own related work should be in the third person (e.g., not “We build on our previous work …” but rather “We build on the work of …”). The purpose of this process is to help the reviewers come to an initial judgment about the paper without bias, not to make it impossible for them to discover the authors if they were to try. Nothing should be done in the name of anonymity that weakens the submission or makes the job of reviewing the paper more difficult (e.g., important background references should not be omitted or anonymized). In addition, authors should feel free to disseminate their ideas or draft versions of their paper as they normally would. For instance, authors may post drafts of their papers on the web or give talks on their research ideas. A reviewer will learn the identity of the author(s) of a paper after a review is submitted. Page Limits ----------- The length of submissions should not exceed the following limits: Regular paper: 12 pages Functional pearl: 12 pages Experience report: 6 pages Demo proposal: 2 pages There is no requirement that all pages are used. For example, a functional pearl may be much shorter than 12 pages. In all cases, the list of references is not counted against these page limits. Deadlines --------- Early track: Submission deadline: 15 March 2019 (Fri) Notification: 19 April 2019 (Fri) Regular track and demos: Submission deadline: 10 May 2019 (Fri) Notification: 21 June 2019 (Fri) Camera-ready deadline for accepted papers: 30 June 2019 (Sun) Deadlines are valid anywhere on Earth. Submission ---------- Submissions must adhere to SIGPLAN's republication policy (http://sigplan.org/Resources/Policies/Republication/) and authors should be aware of ACM's policies on plagiarism (https://www.acm.org/publications/policies/plagiarism) The paper submission deadline and length limitations are firm. There will be no extensions, and papers violating the length limitations will be summarily rejected. Papers should be submitted through HotCRP at: https://haskell19.hotcrp.com/ Improved versions of a paper may be submitted at any point before the submission deadline using the same web interface. Supplementary material: Authors have the option to attach supplementary material to a submission, on the understanding that reviewers may choose not to look at it. This supplementary material should not be submitted as part of the main document; instead, it should be uploaded as a separate PDF document or tarball. Supplementary material should be uploaded at submission time, not by providing a URL in the paper that points to an external repository. Authors are free to upload both anonymized and non-anonymized supplementary material. Anonymized supplementary material will be visible to reviewers immediately; non-anonymized supplementary material will be revealed to reviewers only after they have submitted their review of the paper and learned the identity of the author(s). Resubmitted Papers: Authors who submit a revised version of a paper that has previously been rejected by another conference have the option to attach an annotated copy of the reviews of their previous submission(s), explaining how they have addressed these previous reviews in the present submission. If a reviewer identifies him/herself as a reviewer of this previous submission and wishes to see how his/her comments have been addressed, the principal editor will communicate to this reviewer the annotated copy of his/her previous review. Otherwise, no reviewer will read the annotated copies of the previous reviews. 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. Program Committee ================= Ki-Yung Ahn Hannam University Christiaan Baaij QBayLogic B.V. José Manuel Calderón Trilla Galois, Inc Benjamin Delaware Purdue University Richard Eisenberg (chair) Bryn Mawr College Jennifer Hackett University of Nottingham Kazutaka Matsuda Tohoku University Trevor McDonell Utrecht University Ivan Perez NIA / NASA Formal Methods Nadia Polikarpova University of California, San Diego Norman Ramsey Tufts University Christine Rizkallah University of New South Wales Eric Seidel Bloomberg LP Alejandro Serrano Mena Utrecht University John Wiegley Dfinity Foundation Thomas Winant Well-Typed LLP Ningning Xie University of Hong Kong If you have questions, please contact the chair at: rae(a)richarde.dev ================================================================================

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Informal modelling and simulation of protocols
by P Orrifolius 11 Mar '19

11 Mar '19

Hi, this will probably be a somewhat rambling, open-ended question... my apologies in advance. There are some concrete questions after I explain what I'm trying to achieve, and some of them may even make sense! I'm planning on writing a multi-party, distributed protocol. I would like to informally model the protocol itself and the environment it would run in and then simulate it to see if it achieves what I expect. Then it would need to be implemented and tested of course. I think a formal, mathematical model of the protocol would be beyond my abilities. I'm looking for any advice or tool/library recommendations I can get on the modelling and simulating part of the process and how that work could be leveraged in the implementation to reduce the work and help ensure correctness. I have some ideas of how this could work, but I don't know if I'm approaching it with a suitably Haskell-like mindset... What I envisage at the moment is defining the possible behaviour of each party, who are not homogeneous, as well as things which form the external environment of the parties but will impact their behaviour. By external things I mean, for example, communication links which may drop or reorder packets, storage devices which may lose or corrupt data, machines that freeze or slew their clock... that sort of thing. I'm also picturing a 'universal coordinator' that controls interaction of the parties/environment during simulation. Modelling each party and external as a Harel-like statechart seems plausible. Perhaps some parts could be simpler FSMs, but I think many will be reasonably complex and involve internal state. It would be nice if the simulation could, to the limit of given processing time, exhaustively check the model rather than just randomly, as per quickcheck. If at each point the universal coordinator got a list of possible next states from each party/external it could simulate the simultaneity/sequencing of events by enumerating all combinations, of every size, of individual party/external transitions and then recursing with each separate combination applied as being the next set of simultaneous state transitions. To reduce the space to exhaustively search it would be nice if any values that the parties used, and were being tested by, were abstracted. Not sure what the technical term is but I mean asserting relationships between variables in a given domain, rather than their actual value. For example, imagine a distributed vote between two nodes where each node must vote for a random integer greater than their last vote. Each node is a party in the protocol. In the current branch of the exhaustive search of the protocol a relation between node 1's existing vote, v1, and node 2's existing vote, v2, has already been asserted: v1>v2. So when the coordinator enumerates the possibilities for sets of next-state transitions, with each node n asserting vn'>vn in their individual party state transition, it will prune any search branch which doesn't satisfy the union of the assertions (v1>v2, v1'>v1, v2'>v2), and recurse into the search branch alternatives with v1'<v2', or v1'=v2', or v1'>v2'. So, some questions... Is what I'm suggesting even vaguely sensible way to approach the problem in Haskell? Or am I getting carried away and some neat tricks zipping list monoids or something will get the job done? Is there some fantastic tool/library which already does everything I want? Are there any good tools or libraries in Haskell for defining and manipulating statecharts? The sessiontypes, and sessiontypes-distributed, libraries are cool, representing the protocol at the type level... but these only handle point-to-point, two-party protocols, right? I expect that extending them would be a _serious_ amount of work. Can quickcheck do the sort of exhaustive coverage testing that I'd like? Again, not sure of the correct terminology but can quickcheck generate tests at a variable-relation assertion level? I.e. inspect the operators and boolean tests over a domain (+, ==, >=, append, length, contains, etc) and explore test cases according to whether certain relations between variables hold. Any feelings/opinions about whether Oleg Kiselyov's Typed Tagless Final Interpreter (http://okmij.org/ftp/tagless-final/index.html) work might be a useful mechanism to define the behaviour of parties within the protocol (the statecharts, basically) and then have different interpreters that enable both the testing and implementation of the protocol, to keep them more closely aligned? I read that work years ago and have wanted to try it out ever since, so I may be overlooking the fact that it's totally unsuitable! Perhaps superseded now, but if it can allow more of the protocol to be expressed at the type level that would be good. Yeah, rambling. Sorry about that. Thanks! porrifolius

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[ANNOUNCE] New release of SBV (v8.1)
by Levent Erkok 10 Mar '19

10 Mar '19

Levent Erkok <erkokl(a)gmail.com> Thu, Jul 20, 2017, 1:10 AM to Haskell I'm pleased to announce v8.1 release of SBV, a library for integrating SMT solvers into Haskell. This is a release with many new features. Some highlights: * Support for symbolic sum-types: Maybe/Either. (Thanks to Joel Burget for initiating these.) * Support for symbolic sets. * Support for uninterpreted-function values in models. * Support for validation of models coming from SMT-solvers for high-assurance. * An implementation of Dijkstra's weakest-precondition logic and a toy language for showing how to do Hoare style total-correctness proofs in SBV. * A new and better interface to the optimization engine supporting arbitrary metric spaces. * A bunch of other fixes, improvements, and examples. Full release notes are here: https://github.com/LeventErkok/sbv/blob/master/CHANGES.md Hackage: https://hackage.haskell.org/package/sbv Homepage: http://leventerkok.github.io/sbv/ Feedback and bug reports are most welcome. Happy proving! -Levent.

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Coercible between data A a b = A a b and (a, b)
by Georgi Lyubenov 07 Mar '19

07 Mar '19

Greetings! Is there any reason behind/what is the reason behind ``` data A a b = A a b ``` and ``` (a, b) ``` not being coercible? And in general all n-ary constructors not being coercible to one another? Thanks in advance! ======= Georgi

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Final steps in GHC's Trac-to-GitLab migration
by Ben Gamari 06 Mar '19

06 Mar '19

Hi everyone, Over the past few weeks we have been hard at work sorting out the last batch of issues in GHC's Trac-to-GitLab import [1]. At this point I believe we have sorted out the issues which are necessary to perform the final migration: * We are missing only two tickets (#1436 and #2074 which will require a bit of manual intervention to import due to extremely large description lengths) * A variety of markup issues have been resolved * More metadata is now preserved via labels. We may choose to reorganize or eliminate some of these labels in time but it's easier to remove metadata after import than it is to reintroduce it. The logic which maps Trac metadata to GitLab labels can be found here [2] * We now generate a Wiki table of contents [3] which is significantly more readable than GitLab's default page list. This will be updated by a cron job until underlying GitLab pages list becomes more readable. * We now generate redirects for Trac ticket and Wiki links (although this isn't visible in the staging instance) * Milestones are now properly closed when closed in Trac * Mapping between Trac and GitLab usernames is now a bit more robust As in previous test imports, we would appreciate it if you could have a look over the import and let us know of any problems your encounter. If no serious issues are identified with the staging site we plan to proceed with the migration this coming weekend. The current migration plan is to perform the final import on gitlab.haskell.org on Saturday, 9 March 2019. This will involve both gitlab.haskell.org and ghc.haskell.org being down for likely the entirety of the day Saturday and likely some of Sunday (EST time zone). Read-only access will be available to gitlab.staging.haskell.org for ticket lookup while the import is underway. After the import we will wait at least a week or so before we begin the process of decommissioning Trac, which will be kept in read-only mode for the duration. Do let me know if the 9 March timing is problematic. Cheers, - Ben [1] https://gitlab.staging.haskell.org/ghc/ghc [2] https://github.com/bgamari/trac-to-remarkup/blob/master/TicketImport.hs#L227 [3] https://gitlab.staging.haskell.org/ghc/ghc/wikis/index

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creating standalone executable with haskell
by Damien Mattei 06 Mar '19

06 Mar '19

i want to run Haskell code on a system i'm not administrator??? if i compile my haskell program rather than use interpreter (i never compile it) can i run the executable on another Linux platform which has nothing of haskell installed on it ( no runtime library,etc...) ? i already did that with Racket Scheme could it be done with GHC compiler or should i ask the system admin to install haskell platform? regards, damien

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Second call for papers, MPC 2019, Portugal
by Graham Hutton 05 Mar '19

05 Mar '19

Dear all, The next Mathematics of Program Construction (MPC) conference will be held in Portugal in October 2019, co-located with the Symposium on Formal Methods (FM). Paper submission is 3rd May 2019. Please share, and submit your best papers! Best wishes, Graham Hutton Program Chair, MPC 2019 ====================================================================== *** SECOND CALL FOR PAPERS -- MPC 2019 *** 13th International Conference on Mathematics of Program Construction 7-9 October 2019, Porto, Portugal Co-located with Formal Methods 2019 https://tinyurl.com/MPC-Porto ====================================================================== TIMELINE: Abstract submission 26th April 2019 Paper submission 3rd May 2019 Author notification 14th June 2019 Camera ready copy 12th July 2019 Conference 7-9 October 2019 KEYNOTE SPEAKERS: Assia Mahboubi INRIA, France Annabelle McIver Macquarie University, Australia BACKGROUND: The International Conference on Mathematics of Program Construction (MPC) aims to promote the development of mathematical principles and techniques that are demonstrably practical and effective in the process of constructing computer programs. MPC 2019 will be held in Porto, Portugal from 7-9 October 2019, and is co-located with the International Symposium on Formal Methods, FM 2019. Previous conferences were held in Königswinter, Germany (2015); Madrid, Spain (2012); Québec City, Canada (2010); Marseille, France (2008); Kuressaare, Estonia (2006); Stirling, UK (2004); Dagstuhl, Germany (2002); Ponte de Lima, Portugal (2000); Marstrand, Sweden (1998); Kloster Irsee, Germany (1995); Oxford, UK (1992); Twente, The Netherlands (1989). SCOPE: MPC seeks original papers on mathematical methods and tools put to use in program construction. Topics of interest range from algorithmics to support for program construction in programming languages and systems. Typical areas include type systems, program analysis and transformation, programming language semantics, security, and program logics. The notion of a 'program' is interpreted broadly, ranging from algorithms to hardware. Theoretical contributions are welcome, provided that their relevance to program construction is clear. Reports on applications are welcome, provided that their mathematical basis is evident. We also encourage the submission of 'programming pearls' that present elegant and instructive examples of the mathematics of program construction. SUBMISSION: Submission is in two stages. Abstracts (plain text, maximum 250 words) must be submitted by 26th April 2019. Full papers (pdf, formatted using the llncs.sty style file for LaTex) must be submitted by 3rd May 2019. There is no prescribed page limit, but authors should strive for brevity. Both abstracts and papers will be submitted using EasyChair. Papers must present previously unpublished work, and not be submitted concurrently to any other publication venue. Submissions will be evaluated by the program committee according to their relevance, correctness, significance, originality, and clarity. Each submission should explain its contributions in both general and technical terms, clearly identifying what has been accomplished, explaining why it is significant, and comparing it with previous work. Accepted papers must be presented in person at the conference by one of the authors. The proceedings of MPC 2019 will be published in the Lecture Notes in Computer Science (LNCS) series, as with all previous instances of the conference. Authors of accepted papers will be expected to transfer copyright to Springer for this purpose. After the conference, authors of the best papers from MPC 2019 and MPC 2015 will be invited to submit revised versions to a special issue of Science of Computer Programming (SCP). For any queries about submission please contact the program chair, Graham Hutton <graham.hutton(a)nottingham.ac.uk>. PROGRAM COMMITTEE: Patrick Bahr IT University of Copenhagen, Denmark Richard Bird University of Oxford, UK Corina Cîrstea University of Southampton, UK Brijesh Dongol University of Surrey, UK João F. Ferreira University of Lisbon, Portugal Jennifer Hackett University of Nottingham, UK William Harrison University of Missouri, USA Ralf Hinze University of Kaiserslautern, Germany Zhenjiang Hu National Institute of Informatics, Japan Graham Hutton (chair) University of Nottingham, UK Cezar Ionescu University of Oxford, UK Mauro Jaskelioff National University of Rosario, Argentina Ranjit Jhala University of California, USA Gabriele Keller Utrecht University, The Netherlands Ekaterina Komendantskaya Heriot-Watt University, UK Chris Martens North Carolina State University, USA Bernhard Möller University of Augsburg, Germany Shin-Cheng Mu Academia Sinica, Taiwan Mary Sheeran Chalmers University of Technology, Sweden Alexandra Silva University College London, UK Georg Struth University of Sheffield, UK CONFERENE VENUE: The conference will be held at the Alfândega Porto Congress Centre, a 150 year old former custom's house located in the historic centre of Porto on the bank of the river Douro. The venue was renovated by a Pritzer prize winning architect and has received many awards. LOCAL ORGANISERS: José Nuno Oliveira University of Minho, Portugal For any queries about local issues please contact the local organiser, José Nuno Oliveira <jno(a)di.uminho.pt>. ====================================================================== This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please contact the sender and delete the email and attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. Email communications with the University of Nottingham may be monitored where permitted by law.

1 0

cannot catch exception
by Kees Bleijenberg 04 Mar '19

04 Mar '19

Hi all, The program reads lots of small Text files. readCDFile handles the encoding. Below is the simplest version of readCDFile. If I call readCDFile "/home/kees/freeDB/inputError/" "blah" (the file blah does not exist) I get: Left "MyError: /home/kees/freeDB/inputError/blah: openBinaryFile: does not exist (No such file or directory)". The exception is caught by exceptionHandler If I call readCDFile "/home/kees/freeDB/inputError/" "67129209" I get freeDB: Cannot decode byte '\xa0': Data.Text.Internal.Encoding.decodeUtf8: Invalid UTF-8 stream. The exception is not caught by exceptionHandler (No "MyError: " in front). The file 67129209 is indeed bad encoded. I'am using SomeException. Still, this 'bad encoding exception' is not caught. Why? Kees import qualified Data.Text as T import System.FilePath.Posix import qualified Data.Text.Encoding as TE import qualified Data.ByteString.Lazy as B import Prelude hiding (catch) import Control.Exception main :: IO () main = do res <- readCDFile "/home/kees/freeDB/inputError/" "67129209" print res readCDFile :: FilePath -> FilePath -> IO (Either String T.Text) readCDFile baseDir fn = do catch ( do buffer <- B.readFile (combine baseDir fn) let bufferStrict = B.toStrict buffer return $ Right $ TE.decodeUtf8 bufferStrict ) exceptionHandler exceptionHandler :: SomeException -> IO (Either String T.Text) exceptionHandler e = do let err = show e return $ Left $ "MyError: " ++ err --- Dit e-mailbericht is gecontroleerd op virussen met Avast antivirussoftware. https://www.avast.com/antivirus

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Haskell wiki account request response time
by Howard B. Golden 04 Mar '19

04 Mar '19

Hi Michal, You requested a Haskell wiki account at Fri, 1 Mar 2019 16:08:10 +0100 > Date: Fri, 1 Mar 2019 16:08:10 +0100 > From: Miguel <m.i(a)gmx.at> > To: wiki-account-request(a)haskell.org > Subject: wiki-account-request > oo_miguel Then, 8 minutes, 25 seconds later, you sent this message to Haskell-Cafe: > From: m.i at gmx.at (Miguel) > Date: Fri, 1 Mar 2019 16:16:35 +0100 > Subject: [Haskell-cafe] wiki-account-request > Message-ID: <20190301151635.kkpq2m4x7fkbftqj(a)megaloman.softwarefools.com> > Hi, > Not receiving any response from the other channel I hereby request a > wiki.haskell.org account with the preferred username: "oo_miguel" > Thanks in Advance, > Michal Idziorek > Ref: > https://wiki.haskell.org/index.php?title=Special:UserLogin > "If you would like an account please email 'wiki-account-request' > (at the domain haskell dot org) or, if you find that unresponsive, > on the haskell-cafe mailing list." At Fri, 1 Mar 2019 18:36:00 +0100, Henk-Jan_van_Tuyl created your account. This was 2 hours and 28 minutes after your initial request. Generally, we create accounts within 24 hours of their request, often much sooner. All of us who create accounts are volunteers. We create accounts manually to prevent spam. Regards, Howard

1 0

PR to "double-conversion"
by Иван Николаев 02 Mar '19

02 Mar '19

Hi Bryan! May I ask you to take a look at my PR to your double-conversion library? I’ve made it about six months ago and sent you an email. A few days ago I updated it. In the PR mentioned above I’m adding several things which need your attention: 1. Conversion to bytestring and text builder. 2. Conversion of Float (using type family, but without performance degrading). 3. More benchmarks. 4. Update of the original double-conversion library. Now a bunch of 20k doubles is converted to strict bytestring in 5-8 ms using bytestring builder instead of >200-300ms using just bytestring. Cheers, Rinat

1 0

ANN: hledger-1.14
by Simon Michael 02 Mar '19

02 Mar '19

I'm pleased to announce the release of hledger 1.14! Thank you release contributors Jakob Schöttl and Jakub Zárybnický. hledger is a robust, cross-platform plain text accounting tool, for tracking money, time, stocks, cryptocurrencies or any other commodity, using double-entry accounting, private or shared plain text files, revision control, and command-line, curses or web UIs. Find out more at http://hledger.org and http://plaintextaccounting.org. Release notes summary: ---------------------- Inclusive balance assertions, commodities command, --invert option, JSON get/add support in hledger-web. For full details, see http://hledger.org/release-notes. Getting started: ---------------- All install methods are described at http://hledger.org/download . (system packages, windows binaries, docker, nix, cabal, stack, hledger-install bash script..) Some of these might take a few days to become up to date. Tutorials and all docs and support options are linked at http://hledger.org . Get help via chat in #hledger on Freenode: http://irc.hledger.org Or connect via Matrix: http://riot.hledger.org New and old users, contributors, sponsors, positive/negative feedback, always welcome! Best, -Simon

1 0

wiki-account-request
by Miguel 01 Mar '19

01 Mar '19

Hi, Not receiving any response from the other channel I hereby request a wiki.haskell.org account with the preferred username: "oo_miguel" Thanks in Advance, Michal Idziorek Ref: https://wiki.haskell.org/index.php?title=Special:UserLogin "If you would like an account please email 'wiki-account-request' (at the domain haskell dot org) or, if you find that unresponsive, on the haskell-cafe mailing list."

1 0

show in monad
by Damien Mattei 01 Mar '19

01 Mar '19

just for tracing the monad i have this : import Control.Monad import Data.Ratio import Data.List (all) import Debug.Trace newtype Prob a = Prob { getProb :: [(a,Rational)] } deriving Show instance Functor Prob where fmap f (Prob xs) = trace " Functor Prob " Prob $ map (\(x,p) -> (f x,p)) xs t flatten :: Prob (Prob a) -> Prob a flatten (Prob xs) = trace (" flatten " ++ show xs) Prob $ concat $ map multAll xs where multAll (Prob innerxs,p) = trace " multAll " map (\(x,r) -> (x,p*r)) innerxs instance Applicative Prob where pure = trace " Applicative Prob return " return (<*>) = trace " Applicative Prob ap " ap instance Monad Prob where return x = trace " Monad Prob return " Prob [(x,1%1)] m >>= f = trace " Monad Prob >>= " flatten (fmap f m) fail _ = trace " Monad Prob fail " Prob [] {- instance Applicative Prob where pure a = Prob [(a,1%1)] Prob fs <*> Prob as = Prob [(f a,x*y) | (f,x) <- fs, (a,y) <- as] instance Monad Prob where Prob as >>= f = Prob [(b,x*y) | (a,x) <- as, let Prob bs = f a, (b,y) <- bs] -} in this : flatten :: Prob (Prob a) -> Prob a flatten (Prob xs) = trace (" flatten " ++ show xs) Prob $ concat $ map multAll xs where multAll (Prob innerxs,p) = trace " multAll " map (\(x,r) -> (x,p*r)) innerxs i have this error: [1 of 1] Compiling Main ( monade.hs, interpreted ) monade.hs:22:43: error: • No instance for (Show a) arising from a use of ‘show’ Possible fix: add (Show a) to the context of the type signature for: flatten :: forall a. Prob (Prob a) -> Prob a • In the second argument of ‘(++)’, namely ‘show xs’ In the first argument of ‘trace’, namely ‘(" flatten " ++ show xs)’ In the expression: trace (" flatten " ++ show xs) Prob | 22 | flatten (Prob xs) = trace (" flatten " ++ show xs) | ^^^^^^^ Failed, no modules loaded. how can i implement a show for xs ? regards, damien

2 4

qtHaskell
by David Harley 28 Feb '19

28 Feb '19

I've made a new version of qtHaskell - version 1.1.10.1 available at the following site: http://www.isptech.co.uk/qtHaskell/download.html It comprises bindings to about 50 Qt modules and includes a version of Asteroids which uses functional reactive programming and some code running in a non-IO based monad, plus a Qt based version of Threadscope (qts). The installation of a code set of this sort can be tricky, it builds using a combination of cabal, qmake and make controled from perl. I wish it were simpler, but in most cases: ./build lite -jx will build all modules required for the demos and examples. It has currently only been tested on Linux hence, the build script which used to work on Windows will probably not work without some modification. I'll get around to that if there's any interest. It has also only been tested against regular builds of Qt 5.11/5.12 build from the qt-everywhere-src-5.11/12.x codesets. Good luck with any building and testing of qtHaskell-1.1.10.1, and I'd be delighted to get any feedback David Harley

3 2

rounding and undefined behavior
by Matt Peddie 28 Feb '19

28 Feb '19

Hi cafe, It's been my general impression that when neither Haskell nor C defines behavior in a particular situation, the behavior nonetheless matches. I was surprised to observe Prelude Data.Int> round (4294967295 :: Double) :: Int16 -1 when #include <stdio.h> #include <inttypes.h> int main(void) { double d = 4294967295; int16_t r = (int16_t) d; printf("%"PRId16"\n", r); return 0; } yields 0 when compiled and run. As far as I can tell, neither language defines what this result should be, so neither is doing anything wrong here. But I was surprised that they differ; does anyone know why Haskell's rounding operation behaves the way it does (maybe there is some historical reason)? Or can someone perhaps point me to a standards document I missed that states how the language must round out-of-bounds inputs? Regards Matt Peddie

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