June 2020 - Haskell-Cafe

stack: pandoc fails to build as dependency
by Olaf Klinke 06 Aug '20

06 Aug '20

Dear cafe, I am baffled to learn that stack does not provide builds as reproducible as advertised. I have a project that depends on pandoc. It builds fine on my Debian 9 machine. Then I check out the project on a Debian 8 machine. Downloading and building pandoc-2.7.3 with the latest stack-2.1.3 on the Debian 8 machine runs fine. Now I create a new project, using the same stack.yaml as in the pandoc-2.7.3 package, except now pandoc-2.7.3 is an extra-dep. The project's only module contains nothing but: module Test where import Text.Pandoc Building this project with the same stack results in a linker error: pandoc > Preprocessing executable 'pandoc' for pandoc-2.7.3.. pandoc > Building executable 'pandoc' for pandoc-2.7.3.. pandoc > [1 of 2] Compiling Main pandoc > [2 of 2] Compiling Paths_pandoc pandoc > Linking .stack-work/dist/x86_64-linux/Cabal-2.4.0.1/build/pandoc/pandoc ... pandoc > collect2: error: ld returned 1 exit status pandoc > `gcc' failed in phase `Linker'. (Exit code: 1) This seems to be independent of the LTS version (the stack.yaml in pandoc-2.7.3 says lts-13.17 although lts-13.17 contains pandoc-2.5 and pandoc-2.7.3 is available only in 14.9). Can somebody hint what I am doing wrong? Should I file a bug report? Thanks Olaf

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Haskell Love Conference (the 31st of July & 1st of August, 2020)
by Ida Bzowska 20 Jul '20

20 Jul '20

Hi There! We are organizing the online event on Haskell language https://haskell.love, free to attend. The CFP for the event has started (ends on the 1st of July, 2020), please consider joining https://konfy.care/cfp Tickets (free) will be available soon, follow us on twitter https://twitter.com/_haskellove for the updates and feel free to hop on our slack http://tinyurl.com/haskelloveslack λCheers Ida Bzowska

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Linking + zstd on FreeBSD
by Vanessa McHale 09 Jul '20

09 Jul '20

I tried linking against zstd within a Vagrant simulating FreeBSD. I get the following: ld: error: duplicate symbol: XXH64 >>> defined at xxhash.c >>> xxhash.o:(XXH64) in archive /home/vagrant/.cabal/store/ghc-8.8.3/zstd-0.1.2.0-c8ee757c8e8a7307779ab3cfbc91f3445940e16bbf8f9916f4c90432a0ac499e/lib/libHSzstd-0.1.2.0-c8ee757c8e8a7307779ab3cfbc91f3445940e16bbf8f9916f4c90432a0ac499e.a >>> defined at xxhash.c:693 (/wrkdirs/usr/ports/lang/ghc/work/ghc-8.8.3/rts/xxhash.c:693) >>> RTS.o:(.text.XXH64+0x0) in archive /usr/local/lib/ghc-8.8.3/rts/libHSrts.a ... I am using GHC version 8.8.3_1 and cabal-install 3.0 installed by 'sudo pkg install ...' (I was trying to run cabal install language-dickinson) Cheers, Vanessa McHale

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Is there a handy refl or refl generator for converting GADT types?
by chris done 02 Jul '20

02 Jul '20

Hi all, I have stages in my compiler that convert e.g. Global Renamed -> Global Generated, etc. where certain constructors are available in certain stages. data GlobalRef s where FromIntegerGlobal :: GlobalRef s FromDecimalGlobal :: GlobalRef s InstanceGlobal :: !InstanceName -> GlobalRef Resolved E.g. after type class resolution is done, the InstanceGlobal constructor is available. But instances can't appear in the AST at other stages. In three stages, I've had to copy/paste this code: + refl = + case name of + FromIntegerGlobal -> FromIntegerGlobal + FromDecimalGlobal -> FromDecimalGlobal Because if I just put `name` then GHC will complain that the types are different, which is correct. But a straight-forward pattern match gives GHC the proof that they can be converted. Is there a handy way already implemented that could derive either this code or this proof for me? Cheers, Chris

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ICFP 2020: Second Call for Student Volunteers
by Victor Lanvin 29 Jun '20

29 Jun '20

Please don't hesitate to share this information with your students, classmates or colleagues! ICFP'20 SECOND CALL FOR STUDENT VOLUNTEERS =========================================== ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. The conference covers the entire spectrum of work, from practice to theory, including its peripheries. In order to smoothly run the conference, associated workshops, and tutorials, we need student volunteers to help out on the practical aspect of the organization. All the events associated with ICFP'20 will take place **virtually** from Sun 23 - Fri 28 August 2020. Even though the event will be virtual, we will more than ever need the help of student volunteers to make sure everything runs smoothly. In return, as an ICFP 2020 Student Volunteer, you will interact closely with researchers, academics and practitioners from various disciplines and meet other students from around the world. While the exact structure of the conference is still being worked on, job assignments for student volunteers will include but will not be restriced to: 1- Assisting with technical sessions, workshops, tutorials and panels. 2- Helping to get speakers prepped and ready for broadcast. 3- Managing the various slack channels and social activities. To be considered as a Student Volunteer for ICFP, please fill in the following application form. https://forms.gle/YPsgEb4qiqnuHteB7 The permanent link to this form can be found on the official conference website. https://icfp20.sigplan.org/track/icfp-2020-student-volunteering The deadline for the second round of applications is July 19th, 2020 AoE. The notification will be on July 21st. Positive notifications given in the first round are firm and the second round is only for spots not filled by the first round. If your application was not accepted in the first round, it will automatically be included in the 2nd round.

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PEP622
by Olaf Klinke 28 Jun '20

28 Jun '20

An excerpt from PEP622 [1]: > Let us start from some anecdotal evidence: isinstance() is one of the > most called functions in large scale Python code-bases (by static > call count). In particular, when analyzing some multi-million line > production code base, it was discovered that isinstance() is the > second most called builtin function (after len()). Even taking into > account builtin classes, it is still in the top ten. Most of such > calls are followed by specific attribute access. > > There are two possible conclusions that can be drawn from this > information: > > * Handling of heterogeneous data (i.e. situations where a variable > can take values of multiple types) is common in real world code. > * Python doesn't have expressive ways of destructuring object data > (i.e. separating the content of an object into multiple variables). > I just want to say a big thank you to the Haskell creators for giving us a tool to efficiently write real world code (as it is called above). [1] https://www.python.org/dev/peps/pep-0622/#rationale-and-goals

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Munich Virtual Haskell Meeting, 2020-06-30 @ 19:30
by Leah Neukirchen 28 Jun '20

28 Jun '20

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Tuesday, June 30 at 19:30. **Due to meetup limitations in Bavaria, this meeting will take place online!** For details see here: http://muenchen.haskell.bayern/dates.html A Google Meet link to join the room will be provided on Tuesday. Everybody is welcome, especially the Haskellers from Bavaria that do not usually come to our Munich meetings due to travel distance! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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Second Call for Papers: Reactive and Event-Based Languages and Systems (REBLS 2020)
by Ivan Perez 26 Jun '20

26 Jun '20

SECOND CALL FOR PAPERS 7th Workshop on Reactive and Event-based Languages and Systems (REBLS 2020) co-located with the SPLASH Conference Chicago, Illinois, USA Sun 15 - Fri 20 November 2020 Website: https://2020.splashcon.org/home/rebls-2020 IMPORTANT DATES Submission Deadline: 24 Jul 2020 Author Notification: 24 Aug 2020 Camera Ready Deadline: 25 Sep 2020 INTRODUCTION Reactive programming and event-based programming are two closely related programming styles that are becoming more important with the ever increasing requirement for applications to run on the web or on mobile devices, and the advent of advanced High-Performance Computing (HPC) technology. A number of publications on middleware and language design -- so-called reactive and event-based languages and systems (REBLS) -- have already seen the light, but the field still raises several questions. For example, the interaction with mainstream language concepts is poorly understood, implementation technology is still lacking, and modularity mechanisms remain largely unexplored. Moreover, large applications are still to be developed, and, consequently, patterns and tools for developing large reactive applications are still in their infancy. This workshop will gather researchers in reactive and event-based languages and systems. The goal of the workshop is to exchange new technical research results and to better define the field by developing taxonomies and discussing overviews of the existing work. We welcome all submissions on reactive programming, functional reactive programming, and event- and aspect- oriented systems, including but not limited to: * Language design, implementation, runtime systems, program analysis, software metrics, patterns and benchmarks. * Formal models for reactive and event-based programming. * Study of the paradigm: interaction of reactive and event-based programming with existing language features such as object-oriented programming, pure functional programming, mutable state, concurrency. * Modularity and abstraction mechanisms in large systems. * Advanced event systems, event quantification, event composition, aspect-oriented programming for reactive applications. * Functional Reactive Programming (FRP), self-adjusting computation and incremental computing. * Synchronous languages, modeling real-time systems, safety-critical reactive and embedded systems. * Applications, case studies that show the efficacy of reactive programming. * Empirical studies that motivate further research in the field. * Patterns and best-practices. * Related fields, such as complex event processing, reactive data structures, view maintenance, constraint-based languages, and their integration with reactive programming. * Implementation technology, language runtimes, virtual machine support, compilers. * IDEs, Tools. The format of the workshop is that of a mini-conference. Participants can present their work in slots of 30 mins with Q&A included. Because of the declarative nature of reactive programs, it is often hard to understand their semantics just by looking at the code. We therefore also encourage authors to use their slots for presenting their work based on live demos. SUBMISSIONS REBLS encourages submissions of two types of papers: * Full papers: papers that describe complete research results. These papers will be published in the ACM digital library. * In-progress papers: papers that have the potential of triggering an interesting discussion at the workshop or present new ideas that require further systematic investigation. These papers will not be published in the ACM digital library. Format: * Submissions should use the ACM SIGPLAN Conference acmart Format with the two-column, sigplan Subformat, 10 point font, using Biolinum as sans-serif font and Libertine as serif font. All submissions should be in PDF format. If you use LaTeX or Word, please use the ACM SIGPLAN acmart Templates. The page http://www.sigplan.org/Resources/Author/#acmart-format contains instructions for authors, and a package that includes an example file acmart-sigplan.tex. * Authors are required to explicitly specify the type of paper in the submission (i.e., full paper, in-progress paper). * Full papers can be *up to* 12 pages in length, excluding references. In-progress papers can be *up to* 6 pages, excluding references. Papers do not need to make use of all pages, but they will be summarily rejected if they exceed the page limits. Instructions for the Authors: * Papers should be submitted through: https://rebls20.hotcrp.com/ * For fairness reasons, all submitted papers should conform to the formatting instructions. Submissions that violate these instructions will be summarily rejected. * Program Committee members are allowed to submit papers, but their papers will be held to a higher standard. * Papers must describe unpublished work that is not currently submitted for publication elsewhere as described by SIGPLAN’s Republication Policy (http://www.sigplan.org/Resources/Policies/Republication) Submitters should also be aware of ACM’s Policy and Procedures on Plagiarism. * All submissions are expected to comply with the ACM Policies for Authorship detailed at https://www.acm.org/publications/authors/information-for-authors. PROGRAM COMMITTEE Ivan Perez (PC Chair; NIA) Alan Jeffrey, Mozilla Research. Christiaan Baaij, QBayLogic. César Sánchez, IMDEA Software. Daniel Winograd-Cort, Target Corp. Edward Amsden, Black River Software, LLC. Guerric Chupin, University of Nottingham. Heinrich Apfelmus. Jonathan Thaler, University of Applied Sciences Vorarlberg. Louis Mandel, IBM Research. Manuel Bärenz, sonnen eServices GmbH. Marc Pouzet, Université Pierre et Marie Curie. Mark Santolucito, University of Yale. Neil Sculthorpe, University of Nottingham Trent. Noemi Rodrigues, Pontifícia Universidade Católica do Rio de Janeiro Oleksandra Bulgakova, Sukhomlynsky Mykolaiv National University Patrick Bahr, University of Copenhagen Takuo Watanabe, Tokyo Institute of Technology Tetsuo Kamina, Oita University Tom Van Cutsem, Nokia Bell Labs Yoshiki Ohshima, HARC / Y Combinator Research ORGANIZING COMMITTEE Guido Salvaneschi, TU Darmstadt, Germany Wolfgang De Meuter, Vrije Universiteit Brussel, Belgium Patrick Eugster, Universita della Svizzera Italiana, Switzerland Francisco Sant'Anna, Rio de Janeiro State University, Brazil Lukasz Ziarek, SUNY Buffalo, United States For any questions, please use the form on the website or contact the Chair at ivan.perezdominguez(a)nasa.gov

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[HIW'20] Second Call for Talks
by Ben Gamari 24 Jun '20

24 Jun '20

Hello everyone, Haskell Implementors Workshop is calling for talk proposals. Co-located with ICFP, HiW is an ideal place to describe a Haskell library, a Haskell extension, compiler, works-in-progress, demo a new Haskell-related tool, or even propose future lines of Haskell development. The deadline for submissions is July 2nd 2020. Call for Talks ============== The 12th Haskell Implementors’ Workshop is to be held alongside ICFP 2020 this year. It is a forum for people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure, to share their work and discuss future directions and collaborations with others. Talks and/or demos are proposed by submitting an abstract, and selected by a small program committee. There will be no published proceedings. The workshop will be informal and interactive, with open spaces in the timetable and room for ad-hoc discussion, demos and lightning talks. Scope and Target Audience ------------------------- It is important to distinguish the Haskell Implementors’ Workshop from the Haskell Symposium which is also co-located with ICFP 2020. The Haskell Symposium is for the publication of Haskell-related research. In contrast, the Haskell Implementors’ Workshop will have no proceedings – although we will aim to make talk videos, slides and presented data available with the consent of the speakers. The Implementors’ Workshop is an ideal place to describe a Haskell extension, describe works-in-progress, demo a new Haskell-related tool, or even propose future lines of Haskell development. Members of the wider Haskell community encouraged to attend the workshop – we need your feedback to keep the Haskell ecosystem thriving. Students working with Haskell are specially encouraged to share their work. The scope covers any of the following topics. There may be some topics that people feel we’ve missed, so by all means submit a proposal even if it doesn’t fit exactly into one of these buckets: - Compilation techniques - Language features and extensions - Type system implementation - Concurrency and parallelism: language design and implementation - Performance, optimization and benchmarking - Virtual machines and run-time systems - Libraries and tools for development or deployment Talks ----- We invite proposals from potential speakers for talks and demonstrations. We are aiming for 20-minute talks with 5 minutes for questions and changeovers. We want to hear from people writing compilers, tools, or libraries, people with cool ideas for directions in which we should take the platform, proposals for new features to be implemented, and half-baked crazy ideas. Please submit a talk title and abstract of no more than 300 words. Submissions can be made via HotCRP at https://icfp-hiw20.hotcrp.com/ until July 2nd (anywhere on earth). We will also have lightning talks session. These have been very well received in recent years, and we aim to increase the time available to them. Lightning talks be ~7mins and are scheduled on the day of the workshop. Suggested topics for lightning talks are to present a single idea, a work-in-progress project, a problem to intrigue and perplex Haskell implementors, or simply to ask for feedback and collaborators. Logistics --------- Due to the on-going COVID-19 situation, ICFP (and, consequently, HIW) will be held remotely this year. However, the organizers are still working hard to provide for a great workshop experience. While we are sad that this year will lack the robust hallway track that is often the highlight of HIW, we believe that this remote workshop presents a unique opportunity to include more of the Haskell community in our discussion and explore new modes of communicating with our colleagues. We hope that you will join us in making this HIW as vibrant as any other. Program Committee ----------------- - Andrey Mokhov (Newcastle University) - Ben Gamari (Well-Typed LLP) - Christian Baaij (QBayLogic) - George Karachalias (Tweag I/O) - Klara Marntirosian (KU Leuven) - Matthew Pickering (Univeristy of Bristol) - Ryan G.L. Scott (Indiana University Bloomington) Best wishes, ~ Ben

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[ANN] Enpuzzled - iOS/Android Haskell game
by Miriam 18 Jun '20

18 Jun '20

Hi everyone! After years of work, thousands of commits, and over 100 uploads to iTunes and Android, we are very happy to finally announce Enpuzzled, a Haskell game for iOS and Android. Enpuzzled is a brain teaser that anyone can enjoy quietly, so there is no timer and no rush: it's just you against the board. The game is suitable for all audiences and requires no permissions to run, as part of our recent movement 'Safe2Play'. iTunes: https://apps.apple.com/us/app/enpuzzled/id1460083994 Google Play: https://play.google.com/store/apps/details?id=uk.co.keera.games.enpuzzled Web page: https://enpuzzled.haskell.games Official announcement: https://keera.co.uk/2020/06/18/enpuzzled-released-for-android-and-ios/ Issue tracker: https://github.com/keera-studios/enpuzzled Support/questions: support(a)keera.co.uk Safe2Play: https://keera.co.uk/2020/06/17/safe2play-caring-for-privacy-in-an-interconn… This is our second self-published mobile Haskell game, and one more small step in a long way towards making Haskell a real possibility for game programming. You can find some technical details in the official announcement. We would like to publicly thank all beta testers, who patiently tried version after version, and all the people who supported the development in different ways. If you'd like to support the development of more Haskell games, please consider buying Enpuzzled and/or spreading the word. We currently have three more games at different stages of development. You can follow the development on our website and on social networks, where we will also post calls for early testers. Have fun, and happy Haskelling! Miriam, Keera Studios

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