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PLMW at ICFP: Call for Scholarship Applications (due 17 May)
by Sam Tobin-Hochstadt 07 May '19

07 May '19

ACM SIGPLAN Programming Languages Mentoring Workshop Co-located with ICFP'19 PLMW web page: https://icfp19.sigplan.org/home/PLMW-ICFP-2019 The purpose of the programming languages mentoring workshop (PLMW) is to encourage senior undergraduate and early career (first or second year) to pursue careers in programming language research. We are specifically interested in attracting groups who have traditionally not had the opportunity to participate in research in functional programming. This workshop will be a combination of learning about the work being done in several areas of programming language research and mentoring with respect to helping students prepare for graduate school and the rest of their career. We will bring together leaders in programming language research from academia and industry to give talks on the kind of research typically performed after obtaining a Ph.D. The workshop will engage students, specifically interested in programming language research, in a process of imagining how they might contribute to the world. We especially encourage women and underrepresented minority students to attend PLMW. This workshop is part of the activities surrounding ICFP, the International Conference on Functional Programming, and takes place the day before the main conference. One goal of the workshop is to make ICFP conference more accessible to newcomers. We hope that participants will stay through the entire conference. ## Travel Scholarship Applications (Due 17 May) Please fill out this form by 17 May to apply for travel funding. https://forms.gle/QEvBateG7PRywB336 See the PLMW web page for additional details. The workshop registration is open to all. Students with alternative sources of funding are welcome.

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Haskell Platform / GHC 8.6.5
by Philipp Hausmann 07 May '19

07 May '19

Hi All I noticed that the Windows Download Link on https://www.haskell.org/platform/windows.html points to the 8.6.3 version. When can we expect an updated Haskell Platform release to be available? To give some background, we had some trouble where students got Access Violation crashes on Windows machines using GHC 8.6.3 which is fixed on GHC 8.6.5. In the end we updated to GHC 8.6.5 using the Binary GHC release, but this is quite ugly as it requires fiddling with the PATH... Best, Philipp

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Final CFP: Haskell Symposium due this Friday
by Richard Eisenberg 07 May '19

07 May '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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ARM builds of GHC
by Vanessa McHale 06 May '19

06 May '19

Hi all, Are there any plans to release/distribute ARM builds of GHC for the 8.8.* series? The most recent GHC to have ARM binaries distributed seems to be 8.4.2, which regrettably has a bug that makes it unsuitable for my purposes. Cheers, Vanessa McHale

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[ANNOUNCEMENT] 11th International School on Rewriting (ISR'19), 1-6 July 2019, MINES ParisTech, France
by Johannes Waldmann 06 May '19

06 May '19

Dear Cafe - if your're using Haskell, you are using (term) rewriting: both first order (pattern matching on algebraic data types) and higher order (lambda calculus). Here is your chance to get the fundamentals right, and see more applications: the 11th International School on Rewriting (ISR'19), 1-6 July 2019, MINES ParisTech, France. https://isr2019.mines-paristech.fr/ Deadline for early registration: May 17 full text of call for participation http://lists.tcs.ifi.lmu.de/pipermail/loginf/2019/001723.html - J.W.

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Call for Participation: Compose Conference [NYC, Jun 22- 23 2019]
by Gershom B 03 May '19

03 May '19

=============================================== Call for Participation Compose Conference 2019 Mon June 24 - Tue June 25 2019 (Unconference on Sat Jun 22 - Sun Jun 23) New York, NY http://www.composeconference.org/2019 =============================================== The practice and craft of functional programming :: Conference Compose is a conference for typed functional programmers, focused specifically on Haskell, OCaml, F#, SML, and related technologies. Typed functional programming has been taken up widely, by industry and hobbyists alike. For many of us it has renewed our belief that code should be beautiful, and that programming can be as enjoyable as it is practical. Compose is about bringing together functional programmers of all levels of skill and experience — from technical leads to novices, and from long-time hackers to students just getting started. It will feature a two days of great and wide-ranging talks * Invited Keynotes Donya Quick - Making Algorithmic Music David Spivak - Compositional Graphical Logic * Accepted Talks and Tutorials Kenny Foner - Functors of the World, Unite! Phillip Carter - The anatomy of the F# tools for Visual Studio Sebastien Mondet - Genspio: Generating Shell Phrases In OCaml Justin Le - Applicative Regular Expressions using the Free Alternative Gaetano Checinski - Buckaroo SAT - Solving a partially revealed SAT problem for Package Management Richard Feldman - From Rails to Elm and Haskell Samuel Gélineau - Stuck macros: deterministically interleaving macro-expansion and typechecking Vaibhav Sagar - Yes, IHaskell Can Do That! Fintan Halpenny - Bowl Full of Lentils Aditya Siram - A Tase Of ATS Ward Wheeler, Alex Washburn, Callan McGill - Phylogenetic Software in Haskell Igor Trindade Oliveira - Type Driven Secure Enclave Development using Idris David Christiansen - Bidirectional Type Checking Chris Smith - Teaching the intersection of mathematics and functional programming Brandon Kase - Fast Accumulation on Streams James Koppel - The Best Refactoring You’ve Never Heard Of Allister Beharry - Using Dependent Types in an F# DSL for Linear Algebra Diego Balseiro - Bridge Haskell and ReasonML in Production * Full abstracts: http://www.composeconference.org/2019/program * Conference Registration: https://www.eventbrite.com/e/new-york-compose-2019-tickets-56751182314 * Unconference Registration: https://www.eventbrite.com/e/new-york-compose-unconference-2019-tickets-603… * Follow @composeconf on twitter for news: https://twitter.com/composeconf * On freenode irc, chat with fellow attendees at #composeconference * Corporate sponsorships are welcome. Current sponsors list forthcoming. * Policies (diversity and anti-harassment): http://www.composeconference.org/conduct * Email us with any questions at info(a)composeconference.org * Please forward this announcement to interested parties and lists.

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Static linking against X11
by Vanessa McHale 01 May '19

01 May '19

Hi all, I'm trying to cross-compile xmobar for aarch64-linux-gnu. The cross compiler that comes with my version of Ubuntu works with a later GLIBC than the host platform, so I figured I'd make a static executable instead - this approach had worked with e.g. cabal-install. Unfortunately, I get the following: Resolving dependencies... Build profile: -w ghc-8.6.4 -O1 In order, the following will be built (use -v for more details): - xmobar-vanessa-0.1.0.0 (exe:xmobar) (first run) Preprocessing executable 'xmobar' for xmobar-vanessa-0.1.0.0.. Building executable 'xmobar' for xmobar-vanessa-0.1.0.0.. Linking /home/vanessa/programming/haskell/done/xmobar-vanessa/dist-newstyle/build/aarch64-linux/ghc-8.6.4/xmobar-vanessa-0.1.0.0/x/xmobar/build/xmobar/xmobar ... /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /usr/local/lib/aarch64-linux-gnu-ghc-8.6.4/rts/libHSrts.a(Linker.o): in function `internal_dlopen': /home/vanessa/cross/ghc-8.6.4/rts/Linker.c:600:0: error: warning: Using 'dlopen' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /home/vanessa/.cabal/store/ghc-8.6.4/network-3.1.0.0-b60cf17d11d7eda024959ae28f710f94d7565bcd8e3372f04f32d2600769c2c1/lib/libHSnetwork-3.1.0.0-b60cf17d11d7eda024959ae28f710f94d7565bcd8e3372f04f32d2600769c2c1.a(HsNet.o): in function `hsnet_getaddrinfo': HsNet.c:(.text+0x10): warning: Using 'getaddrinfo' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/lib/../lib/libX11.a(xcb_io.o): in function `require_socket': /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_io.c:68:0: error: undefined reference to `xcb_take_socket' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/lib/../lib/libX11.a(xcb_io.o): in function `poll_for_event': /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_io.c:245:0: error: undefined reference to `xcb_poll_for_event' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_io.c:243: undefined reference to `xcb_poll_for_queued_event' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/lib/../lib/libX11.a(xcb_io.o): in function `poll_for_response': /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_io.c:284:0: error: undefined reference to `xcb_poll_for_reply64' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/lib/../lib/libX11.a(xcb_io.o): in function `_XSend': /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_io.c:499:0: error: undefined reference to `xcb_writev' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/lib/../lib/libX11.a(xcb_io.o): in function `_XEventsQueued': /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_io.c:364:0: error: undefined reference to `xcb_connection_has_error' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/lib/../lib/libX11.a(xcb_io.o): in function `_XReadEvents': /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_io.c:441:0: error: undefined reference to `xcb_connection_has_error' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_io.c:400: undefined reference to `xcb_wait_for_event' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/lib/../lib/libX11.a(xcb_io.o): in function `_XAllocIDs': /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_io.c:549:0: error: undefined reference to `xcb_generate_id' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/lib/../lib/libX11.a(xcb_io.o): in function `_XReply': /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_io.c:609:0: error: undefined reference to `xcb_wait_for_reply64' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/lib/../lib/libX11.a(ClDisplay.o): in function `XCloseDisplay': /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/ClDisplay.c:71:0: error: undefined reference to `xcb_disconnect' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/lib/../lib/libX11.a(OpenDis.o): in function `OutOfMemory': /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/OpenDis.c:705:0: error: undefined reference to `xcb_disconnect' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/lib/../lib/libX11.a(OpenDis.o): in function `XOpenDisplay': /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/OpenDis.c:255:0: error: undefined reference to `xcb_get_setup' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/OpenDis.c:498: undefined reference to `xcb_get_maximum_request_length' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/lib/../lib/libX11.a(xcb_disp.o): in function `_XConnectXCB': /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_disp.c:69:0: error: undefined reference to `xcb_parse_display' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_disp.c:76: undefined reference to `xcb_connect_to_display_with_auth_info' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_disp.c:81: undefined reference to `xcb_get_file_descriptor' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_disp.c:84: undefined reference to `xcb_generate_id' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_disp.c:92: undefined reference to `xcb_connection_has_error' /usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: /tmp/cpkg-2c6d48cdbb4678ca/libX11-1.6.7/src/xcb_disp.c:78: undefined reference to `xcb_connect' collect2: error: ld returned 1 exit status `aarch64-linux-gnu-gcc' failed in phase `Linker'. (Exit code: 1) I looked in libX11.a with nm /usr/aarch64-linux-gnu/lib/libX11.a | rg 'xcb_take_socket' which yields U xcb_take_socket which, as I understand, means that something is screwed up in the X11 static linking (but I know less about systems programming and linkers than Haskell). Does anyone know how to fix such a problem? Cheers, Vanessa McHale

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Trying to find a Haskell unikernel project which is not HaLVM.
by Magicloud Magiclouds 01 May '19

01 May '19

Hi, About half an year ago, while I was digging a sanity check issue in 8.6.1, I accidently got a Trac mentioning a Haskell unikernel project. The name is H prefixed (apparently), and a bit of long. Now I am trying to dig more on that project, but could not find it anywhere. Does anyone have a clue? Thanks. -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

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Repa array and Data.Vector.Storable.Mutable.
by PICCA Frederic-Emmanuel 01 May '19

01 May '19

Hello I would like a function which allows to freeze a Mutable Vector into a Repa array. of type Array F DIM2 a It seems to me that the the foreignPtr ownership should be transfer to the Repa Array, but I can not find a way to do this... So what is the proper way to achieve this ? thansk for your help. Frederic

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Agda's BUILTIN Naturals in Haskell
by Georgi Lyubenov 30 Apr '19

30 Apr '19

Hey, Is there any way to do something similar to what Agda does with natural numbers via BUILTIN pragmas? More precisely I want to have correct-by-construction natural numbers, that at runtime are treated as `Integer`s. My initial idea was to abuse rewrite rules to turn `data N = Z | S N` into `Integer` terms somehow, but I'm not sure if this is possible. ======= Georgi

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MPC 2019 deadline extension
by Graham Hutton 30 Apr '19

30 Apr '19

====================================================================== DEADLINE EXTENSION TO *10 MAY* -- 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 7th May 2019 (AoE) (extended) Paper submission 10th May 2019 (AoE) (extended) 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 7th May 2019. Full papers (pdf, formatted using the llncs.sty style file for LaTex) must be submitted by 10th 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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PPDP'19 Deadline extension
by Ekaterina Komendantskaya 28 Apr '19

28 Apr '19

DEADLINE EXTENSION TO *10 MAY* - PPDP 2019 21st International Symposium on Principles and Practice of Declarative Programming 7–9 October 2019, Porto, Portugal Collocated with FM'19 http://ppdp2019.macs.hw.ac.uk ====================================================================== Important Dates --------------- Title and abstract registration 4 May 2019 (AoE) (extended) Paper submission 10 May 2019 (AoE) (extended) Rebuttal period (48 hours) 10 June 2019 (AoE) (extended) Author notification 20 June 2019 (extended) Final paper version 15 July 2019 Conference 7–9 October 2019 About PPDP ---------- The PPDP 2019 symposium brings together researchers from the declarative programming communities, including those working in the functional, logic, answer-set, and constraint handling programming paradigms. The goal is to stimulate research in the use of logical formalisms and methods for analyzing, performing, specifying, and reasoning about computations, including mechanisms for concurrency, security, static analysis, and verification. See http://ppdp2019.macs.hw.ac.uk for further information and information. Invited Speakers ---------------- Amal Ahmed Northeastern University, USA Title: TBA Naoki Kobayashi The University of Tokyo, Japan Title: 10 Years of the Higher-Order Model Checking Project Submission page: ---------------- https://easychair.org/conferences/?conf=ppdp19

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Type information in MVars
by Georgi Lyubenov 28 Apr '19

28 Apr '19

Hi, There are obviously a lot of cool tricks you can do with phantom parameters, but they are all lost when you start looking at a `MVar` holding a type with a phantom parameter. Is there any way to track this type-level information, while still being able to write/read values from multiple threads? ======= Georgi

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ANN: network-3.1.0.0, network-2.8.0.1
by Evan Borden 26 Apr '19

26 Apr '19

Announcing the release of network-3.1.0.0 <http://hackage.haskell.org/package/network-3.1.0.0> and network-2.8.0.1 <http://hackage.haskell.org/package/network-2.8.0.1>. *Version 3.1.0.0* - Made GC of socket safer.(#399 <https://github.com/haskell/network/pull/399>) - Deprecating fdSocket. Use withFdSocket instead to ensure that sockets are GCed in proper time. (#399 <https://github.com/haskell/network/pull/399>) *Version 2.8.0.1* - Ensure that accept returns a correct sockaddr for unix domain. (#400 <https://github.com/haskell/network/pull/400>) - Avoid out of bounds writes in pokeSockAddr. (#400 <https://github.com/haskell/network/pull/400>) As always thank you to network's contributors and bug reporters.

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[Job] Interos is hiring Haskell developers (Arlington, VA and Menlo Park, CA)
by John Evans 26 Apr '19

26 Apr '19

When I posted this on reddit, someone suggested I post it here as well, so: Interos Solutions, Inc. is a fast-growing venture backed company with an AI-driven SaaS application that delivers our commercial and government customers unique insight into their ever-changing business ecosystems. The core of our platform is the compilation, analysis and visualization of dynamically changing big data collected across open source, proprietary and public data sources. By continuously analyzing our "real-time" data stream we provide our customers with unique insights into their business relations, supply chains and other third-party activities. To accelerate the growth of our application, we are putting together a team of Haskell engineers, data analysts, data scientists, UI/UX professionals and product managers. We are committed to building a world class product organization that leverages tools like Haskell and latest machine learning techniques to achieve outsized results as individuals and as a team. Salary and benefits are competitive for the areas. We have offices in Arlington, VA and Menlo Park, CA. We are unable to consider remote employees at this time. https://interos.applicantpro.com/jobs/986652-306361.html https://interos.applicantpro.com/jobs/1004858-306361.html https://interos.applicantpro.com/jobs/1004874-306361.html We are also hiring for Business Analysts, Data Analysts, Data Visualization, DevOps engineers and Data Scientists, email me for links to those opportunities.

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[ANNOUNCE] GHC 8.8.1-alpha1 is now available
by Ben Gamari 25 Apr '19

25 Apr '19

Hello everyone, The GHC team is pleased to announce the first alpha release of GHC 8.8.1. The source distribution, binary distributions, and documentation are available at https://downloads.haskell.org/~ghc/8.8.1-alpha1 A draft of the release notes is also available [1]. This release is the culmination of over 3000 commits by over one hundred contributors and has several new features and numerous bug fixes relative to GHC 8.6: * Profiling now works correctly on 64-bit Windows (although still may be problematic on 32-bit Windows due to platform limitations; see #15934) * A new code layout algorithm for amd64's native code generator * The introduction of a late lambda-lifting pass which may reduce allocations significantly for some programs. * Further work on Trees That Grow, enabling improved code re-use of the Haskell AST in tooling * More locations where users can write `forall` (GHC Proposal #0007) * Further work on the Hadrian build system This release starts the pre-release cycle for GHC 8.8. This cycle is starting quite a bit later than expected due recent work on GHC's CI and release infrastructure. See the GHC Blog [2] for more on this. As always, if anything looks amiss do let us know. Happy compiling! Cheers, - Ben [1] https://downloads.haskell.org/ghc/8.8.1-alpha1/docs/html/users_guide/8.8.1-… [2] https://www.haskell.org/ghc/blog/20190405-ghc-8.8-status.html

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CDelta and Haskell
by Tysha Moore 25 Apr '19

25 Apr '19

Haskell Developers, We at Pyrofex Corporation are working on an exciting new project called CDelta (cdelta.io <http://cdelta.io/>), a transaction based blockchain that will compete with Visa and Venmo. This blockchain is written in Haskell and we are looking for build a team of Haskell developers here in Utah to bring this project to fruition. Our job description is below. We would LOVE to hear from you. Cryptocurrency Software Engineer Are you ready to work for a company of engineers, managed by engineers, and focused on engineers and the work they can do? Your opportunity to work with a brilliant team that’s developing world-changing technology is here—seize it! At Pyrofex, we do things differently: we hire great engineers, give them the tools to do great things, and expect them to do so. We are invested in each team member's growth and foster a workplace that celebrates accomplishments and hard work by focusing on our engineers and what they need in order to be successful. Pyrofex is hiring. Show us your best work. About Us Pyrofex Corporation is changing the blockchain game and quickly growing a world-class team to do it. As one of Utah Valley’s first cryptocurrency startups, founded in 2016 by ex-Googlers Mike Stay and Nash Foster, Pyrofex is busy creating next-generation blockchain platforms that are simple, secure, and always reliable. We take pride in our work. We set high expectations for everyone, from our founders to each team member, and as a result we deliver extraordinary products and services. At Pyrofex, we hire for strength, not for lack of weakness. We hire for capability and talent, not specific knowledge of a tool or language. We hire people who have a passion for quality and innovation. Each team member achieves great things in an environment supporting both independence and collaboration. About You You collaborate well with others to design and architect our complex systems. You take the amorphous sets of needs and use cases and distill these into written designs and specifications. You demonstrate a fastidious attention to detail, knowledge of your programming tools, and the ability to regularly produce working, correct code. You are interested in building high-performance, high-bandwidth networks, and solving interesting problems. Pyrofex hires engineers at all levels of experience—from current students to engineers with decades of experience. Our engineers have worked on compilers, system software, distributed data storage, service and reliability, and JavaScript language security features through their careers. The path each of us has taken to get here is unique and we suspect the same will be true of our best employees. We are most interested in hiring strong programmers with experience working with large datasets and peer-to-peer networking. We desire to hear from candidates with experience with functional programming (Scala, Clojure, F#, SCheme, Haskell) and encryption technology. Our most successful candidates also have a background in computer science, but if you think this job is for you, we'll take a look. About the Job Developers on our team design, implement, test, deploy, and manage a variety of systems and products using technologies like Haskell, GNU/Linux, and C/C++. The engineers on this team will design, implement, test, deploy, and manage a large-scale global software system using Linux and the JVM. Pyrofex builds cryptocurrency systems and large-scale distributed and decentralized applications. If this sounds good to you, then e-mail us at jobs(a)pyrofex.net <mailto:jobs@pyrofex.net> with the subject line, “AWW MAN! I CAN”T WAIT!!!” and your resume or linkedin profile. We would also enjoy a cover letter telling us about your work ethic and your favorite project. If you can send us examples of your code, that would be most excellent. Tysha Moore Talent Acquisition Specialist Pyrofex Corporation

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Why are && and || right-associative?
by Richard Eisenberg 24 Apr '19

24 Apr '19

Hi café, Why are && and || in the Prelude right-associative? This contradicts my expectation and the way these work in other languages. That said, I can't think of any harm in it. This came up from a question asked by a student, and I have no idea why the design is this way. Thanks, Richard

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[ANNOUNCE] GHC 8.6.5 is now available
by Ben Gamari 24 Apr '19

24 Apr '19

Hello everyone, The GHC team is proud to announce the release of GHC 8.6.5. The source distribution, binary distributions, and documentation are available at https://downloads.haskell.org/~ghc/8.6.5 Release notes are also available [1]. This release fixes a handful of issues with 8.6.4: - Binary distributions once again ship with Haddock documentation including syntax highlighted source of core libraries (#16445) - A build system issue where use of GCC with `-flto` broke `configure` was fixed (#16440) - An bug affecting Windows platforms wherein XMM register values could be mangled when entering STG has been fixed (#16514) - Several Windows packaging issues resulting from the recent CI rework. (#16408, #16398, #16516) Do note that due to linking issues (see #15934) profiling will be rather unreliable on Windows. This will be fixed in 8.8.1. As always, if anything looks amiss do let us know. Happy compiling! Cheers, - Ben [1] http://downloads.haskell.org/~ghc/8.6.5/docs/html/users_guide/8.6.5-notes.h…

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Munich Haskell Meeting, 2019-04-25 @ 19:30
by Leah Neukirchen 23 Apr '19

23 Apr '19

Dear all, This week, our monthly Munich Haskell Meeting will take place again on Thursday, April 25 at Cafe Puck 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-apr-2019/ Everybody is welcome! cu, -- Leah Neukirchen <leah(a)vuxu.org> http://leahneukirchen.org/

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Problem on exception and laziness
by Magicloud Magiclouds 23 Apr '19

23 Apr '19

Hi, I am aware that laziness sometimes may cause exception handling in unexpected ways. Recently I have such a problem that I cannot figure out how to fix (simply). I have a function `watch` that parse the content of /proc/. And I use `catch` to wrap `readFile` call, since the data in /proc/ could be gone any time. ```Haskell wrap2Maybe :: IO a -> IO (Maybe a) wrap2Maybe f = catch ((<$>) Just $! f) (\(_ :: IOException) -> return Nothing) watch args = do mStat <- wrap2Maybe (readFile ("/proc/" </> fp </> "stat")) >>= return . flip (>>=) parseStat print mStat watch args ``` But occasionally, my tool exits with message: GoM: /proc/1484/stat: hGetContents: does not exist (No such process) Since above code is the only `readFile` call which leads to hGetContents, I could not figure out what else should I do to catch the error. -- 竹密岂妨流水过山高哪阻野云飞

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how do I intercalate for Data.Text.Lazy.Builder
by Javran Cheng 22 Apr '19

22 Apr '19

Hi Cafe, Just a quick question, the title says it all: how do I intercalate for the Builder? Given what it does, it makes sense that things like `intercalate` should be out of the box, yet I feel the export list of Builder is very limited. -- Javran (Fang) Cheng

2 2

When does ICFP open registration?
by Alexey Raga 22 Apr '19

22 Apr '19

Hello, For bureaucracy reasons, it may be a time in our company to start sorting out ICFP trips/tickets. Does anyone have any information about when the registration may be opening? I couldn't find anything on their website, and I couldn't find any contact details on that website either, so asking here just in case if anyone knows :) Best Regards, Alexey Raga

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Re: [Haskell-cafe] Is there already a lib to parse a line of string with a pattern and generate key-value map or a record?
by Olaf Klinke 19 Apr '19

19 Apr '19

You could emulate this with some custom parser combinators on top of any monadic parser combinator library such as attoparsec or megaparsec. keyed :: (Ord key, Functor parser) => key -> parser a -> parser (Map key a) keyed key = fmap (singleton key) Then, assuming 'char' and 'digitChar' exists in the parser library, you may write integer = some digitChar logline = fmap mconcat $ sequence [ keyed "year" (integer <* char '/'), keyed "month" (integer <* char '/'), keyed "day" (integer <* char ' '), -- etc. ] Olaf

2 2

-fdefer-type-errors
by Bill Hallahan 18 Apr '19

18 Apr '19

Hi, I'm trying to use the -fdefer-type-error flag, discussed in an ICFP paper from 2012: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.366.841&rep=rep1&t… <http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.366.841&rep=rep1&t…> On page 2, the paper has an example, showing that fdefer-type-errors will allow a the first element to be extracted fro a tuple, even if the second element does not correctly typecheck: ghci> let foo = (True, ’a’ && False) Warning: Couldn’t match ‘Bool’ with ‘Char’ ghci> :type foo (Bool, Bool) ghci> fst foo True However, with GHC 8.2.2, I get an error when trying to do this: GHCi, version 8.2.2: http://www.haskell.org/ghc/ :? for help Prelude> let foo = (True, 'a' && False) <interactive>:1:18: warning: [-Wdeferred-type-errors] • Couldn't match expected type ‘Bool’ with actual type ‘Char’ • In the first argument of ‘(&&)’, namely ‘'a'’ In the expression: 'a' && False In the expression: (True, 'a' && False) Prelude> :type foo foo :: (Bool, Bool) Prelude> fst foo *** Exception: <interactive>:1:18: error: • Couldn't match expected type ‘Bool’ with actual type ‘Char’ • In the first argument of ‘(&&)’, namely ‘'a'’ In the expression: 'a' && False In the expression: (True, 'a' && False) (deferred type error) Does anyone know the reason for the change in the behavior? Is there any way to get back to the old behavior, i.e. allow the first element of the tuple to still be extracted? Ideally, I would like to get the errors given by defer-type-errors to be as fine-grained/close-to-the-source as possible. Thanks, Bill Hallahan

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Is there already a lib to parse a line of string with a pattern and generate key-value map or a record?
by Magicloud Magiclouds 18 Apr '19

18 Apr '19

Hi, I saw this function in some web tools, pretty useful when parsing log or so. So I wonder if Haskell has similar libs already. Sample: Input line: "2019/04/17 17:27 User magicloud runs command ls." Pattern: "${year}/${month}/${day} ${hour}:${minute} User ${username} runs command ${command}." Output: toList [ ("year", "2019"), ("month", "04") , etc ] -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

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monad example
by Damien Mattei 17 Apr '19

17 Apr '19

hello, i still seaching a good monad example and after passed the classic tutorial about Maybe monad or State monad which is found in almost 90% of the litterature i try to learn in deep the example of monad that talk about probability ( http://learnyouahaskell.com/for-a-few-monads-more ) for this i try to trace the calls of the inner monad definition like in the file, i give the file in attachment (monade.hs) and the output has a lot of garbage data, not the nicer way to display it,sorry. What i can not figure out is at what stage the program construct the [Tails,Heads] , [Heads,Heads] ... etc i do not know, if someone could explain me in detail the action of a <- coin b <- loadedCoin return [a,b] step by step it would be of great help... Regards, Damien note: here is the ouput: *Main> :load monade.hs [1 of 1] Compiling Main ( monade.hs, interpreted ) Ok, one module loaded. *Main> flipTwoVal Prob {getProb = (Monad Prob >>= flatten (fmap f m) Functor Prob Functor Prob (f x,1 % 2) flatten multAll map ... p= 1 % 2 (Monad Prob >>= flatten (fmap f m) Functor Prob Functor Prob (f x,1 % 10) flatten multAll map ... p= 1 % 10 Monad Prob return) [ flatten multAll (1 % 10*1 % 1) flatten multAll (1 % 2*1 % 10) ([Heads,Heads],1 % 20) Functor Prob (f x,9 % 10) flatten multAll map ... p= 9 % 10 Monad Prob return) , flatten multAll (9 % 10*1 % 1) flatten multAll (1 % 2*9 % 10) ([Heads,Tails],9 % 20) Functor Prob (f x,1 % 2) flatten multAll map ... p= 1 % 2 (Monad Prob >>= flatten (fmap f m) Functor Prob Functor Prob (f x,1 % 10) flatten multAll map ... p= 1 % 10 Monad Prob return) , flatten multAll (1 % 10*1 % 1) flatten multAll (1 % 2*1 % 10) ([Tails,Heads],1 % 20) Functor Prob (f x,9 % 10) flatten multAll map ... p= 9 % 10 Monad Prob return) , flatten multAll (9 % 10*1 % 1) flatten multAll (1 % 2*9 % 10) ([Tails,Tails],9 % 20)]} *Main> flipTwoVal Prob {getProb = [([Heads,Heads],1 % 20),([Heads,Tails],9 % 20),([Tails,Heads],1 % 20),([Tails,Tails],9 % 20)]}

1 0

shake and cmd argument dependency
by PICCA Frederic-Emmanuel 17 Apr '19

17 Apr '19

Hello, I am writting a program which execute some scientific task via shake. liftIO $ shake shakeOptions{ shakeFiles=shakeFiles' , shakeReport=["/tmp/shake.html"] , shakeVerbosity=Diagnostic} $ do want [toFilePath uploaded] -- execute xdsme and deal with input dependencies toFilePath xml %> \_out -> do need (map toFilePath is) processXdsMe cwd' cell sg mr mo rdir images -- upload the result into the Databse toFilePath uploaded %> \_out -> actionXml xml b c uploaded processXdsMe :: Path Abs Dir -> Maybe Cell -> Maybe SpaceGroup -> Maybe Resolution -> Maybe Optimize -> Path Rel File -> String -> Action () processXdsMe cwd' mcell msg mr mo rdir images = cmd opts args where opts :: [CmdOption] opts = px1Opts ++ [Cwd . fromAbsDir $ cwd', AutoDeps] args = xdsMePath : catMaybes params params :: [Maybe String] params = [ Just "--brute" , Just "--weak" , Just "--xml" , Just ("-p" ++ fromRelFile rdir) , fmap (\(Cell a b c alpha beta gamma) -> printf "-c%f,%f,%f,%f,%f,%f" a b c alpha beta gamma) mcell , fmap (\sg -> "-s" ++ unpack sg) msg , fmap (\(Resolution r) -> printf "--resolution %f" r) mr , fmap (\o -> printf "--optimize %d" (fromEnum o)) mo , Just images ] actionXml :: Path Abs File -> Beamline -> SomeDataCollection -> Path Abs File -> Action () actionXml xml b c uploaded = do need [toFilePath xml] container <- liftIO . fromFile . toFilePath $ xml -- post processing let attachment = _autoProcProgramAttachment . _autoProcProgramContainer $ container attachment' <- liftIO $ runReaderT (toRuchePath attachment) b _ <- copyAttachment' attachment attachment' let container' = (autoProcProgramContainer . autoProcProgramAttachment .~ attachment') container -- replace attachement -- upload into ISPYB liftIO $ storeAutoProcIntoISPyB c NoAnomalous container' cmd_ ("touch" :: String) (toFilePath uploaded) My users want to change the arguments in the processXdsMe cmd args. How can I teach shake to rebuild a rules when the argument of the cmd change ? thanks for your help. Cheers

2 1

GHC 8.8 and MonadFail proposal
by Kazu Yamamoto 17 Apr '19

17 Apr '19

Hello, I built the GHC 8.8 branch and tried to use it. I was very surprised because many packages cannot be built due to the removal of the "fail" method from the Monad typeclass. GHC 8.6 (with -Wcompat) does not warn even if "fail" is defined. I had no chance to notice this change. Isn't this change too radical? The same thing happened in GHC 8.4 due to Semigroup. I could not notice this change beforehand because I did not know the "-Wcompat" option. In my opinion, we should have included "-Wcampat" in "-Wall". Anyway, if I understand correctly, "-Wcompat" does not help in the MonadFail case. I'm a fan of both proposal. But I feel that no period of warnings is not a good approach. --Kazu

2 1

Compose Conference tickets are now available
by MightyByte 16 Apr '19

16 Apr '19

I'm pleased to announce that ticket sales are now open for both the New York Compose Conference and Unconference happening June 22 - 25. See our website for more details: http://www.composeconference.org/ There is one week left until the talk submission deadline. So, if you would like to submit a talk, make sure you get it in before April 23 at 11:59PM EDT. Part of our mission is to be as open and inclusive as possible. To support this, we have a limited number of volunteer tickets available if you would like to attend but the ticket price is an obstacle for you. Email us at nyc(a)composeconference.org with some information about you, your situation, and what you would like to get out of the conference and we will work with you. Sent via Superhuman ( https://sprh.mn/?vip=mightybyte@gmail.com )

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PPDP'19 Final CFP
by Ekaterina Komendantskaya 12 Apr '19

12 Apr '19

FINAL CALL FOR PAPERS -- PPDP 2019 21st International Symposium on Principles and Practice of Declarative Programming 7–9 October 2019, Porto, Portugal Collocated with FM'19 http://ppdp2019.macs.hw.ac.uk ====================================================================== Important Dates --------------- Title and abstract registration 26 April 2019 (AoE) Paper submission 3 May 2019 (AoE) Rebuttal period (48 hours) 3 June 2019 (AoE) Author notification 14 June 2019 Final paper version 15 July 2019 Conference 7–9 October 2019 About PPDP ---------- The PPDP 2019 symposium brings together researchers from the declarative programming communities, including those working in the functional, logic, answer-set, and constraint handling programming paradigms. The goal is to stimulate research in the use of logical formalisms and methods for analyzing, performing, specifying, and reasoning about computations, including mechanisms for concurrency, security, static analysis, and verification. Invited Speakers ---------------- Amal Ahmed Northeastern University, USA Title: TBA Naoki Kobayashi The University of Tokyo, Japan Title: 10 Years of the Higher-Order Model Checking Project Scope ----- Submissions are invited on all topics related to declarative programming, from principles to practice, from foundations to applications. Topics of interest include, but are not limited to - Language Design: domain-specific languages; interoperability; concurrency, parallelism and distribution; modules; probabilistic languages; functional languages; reactive languages; database languages; knowledge representation languages; languages with objects; language extensions for tabulation; metaprogramming. - Implementations: abstract machines; interpreters; compilation; compile-time and run-time optimization; memory management. - Foundations: types; logical frameworks; monads and effects; semantics. - Analysis and Transformation: partial evaluation; abstract interpretation; control flow; data flow; information flow; termination analysis; resource analysis; type inference and type checking; verification; validation; debugging; testing. - Tools and Applications: programming and proof environments; verification tools; case studies in proof assistants or interactive theorem provers; certification; novel applications of declarative programming inside and outside of CS; declarative programming pearls; practical experience reports and industrial application; education. For further information, please visit: http://ppdp2019.macs.hw.ac.uk

1 0

Newtype, Data.Text and instance declarations...
by Guy-Laurent Subri 12 Apr '19

12 Apr '19

Hi all, There are a few things that I don't understand involving Data.Text and instance declarations... I'm building a small web app to practise Haskell and am using the SQLite.Simple library. I have defined a few types and functions like so: ''' data BookmarkDB = BookmarkDB Connection Table newtype Table = Table Text instance ToField Table where toField = SQLText initDB :: FilePath -> Table -> IO BookmarkDB initDB fp table = do let query = Query ("CREATE TABLE IF NOT EXISTS :table " <> " (url TEXT, tags TEXT, date INTEGER)") conn <- open fp executeNamed conn query [":table" := table] return $ BookmarkDB conn table ''' 1. My first question is about the instance declaration. Why would ''' instance ToField Table where toField = SQLText ''' return this error ? ''' Couldn't match type ‘Table’ with ‘Text’ Expected type: Table -> SQLData Actual type: Text -> SQLData • In the expression: SQLText In an equation for ‘toField’: toField = SQLText In the instance declaration for ‘ToField Table’ ''' I've noticed that if I write ''' instance ToField Table where toField (Table t) = SQLText t ''' I have no error and it compiles. I don't get it, what is 'toField' supposed to receive except a Table? 2. My second question is concerning the initDB function. If I write it that way, the code compiles, but I get an error during execution: bkmrk: SQLite3 returned ErrorError while attempting to perform prepare "CREATE TABLE IF NOT EXISTS :table (url TEXT, tags TEXT, date INTEGER)": near ":table": syntax error I don't understand what is wrong with the code and I doubt that my query is wrong because everything works with the last code snippet I wrote (see question #3). 3. Trying to get around the error I've noticed a few things. If I try to write this instead: ''' initDB :: FilePath -> Table -> IO BookmarkDB initDB fp table = do let query = Query ("CREATE TABLE IF NOT EXISTS " <> table <> " (url TEXT, tags TEXT, date INTEGER)") conn <- open fp execute_ conn query return $ BookmarkDB conn table ''' it doesn't compile because table is of type Table and not Data.Text.Internal.Text, which I get, but I don't know what is the Haskell way of resolving this. I've also noticed that this will help: ''' initDB :: FilePath -> Table -> IO BookmarkDB initDB fp t@(Table table) = do let query = Query ("CREATE TABLE IF NOT EXISTS " <> table <> " (url TEXT, tags TEXT, date INTEGER)") conn <- open fp execute_ conn query return $ BookmarkDB conn t ''' But I *really* don't get why! The most confusing part for me is that the last initDB function will do exactly what I want it to do, but I am unable to understand why it works...Why am I able to concatenate the 'table' now and not before and why is 't' of a different type than 'table'? All of this is very confusing and I find myself unable to reason about it. Sorry if this is a big/messy question. I hope everything is clear enough to answer... Thank you all!

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[CfP] Functional High-Performance and Numerical Computing 2019
by Marco Zocca 11 Apr '19

11 Apr '19

===================================================== Call for Papers (Extended Abstracts and Full Papers) ACM SIGPLAN Workshop on Functional High-Performance and Numerical Computing (FHPNC), Berlin, August 18, 2019 Satellite event of the 24th ACM SIGPLAN International Conference on Functional Programming (ICFP 2019) 18 - 23 August, 2019 ===================================================== https://icfp19.sigplan.org/home/FHPNC-2019#Call-for-Papers The ACM SIGPLAN International Workshop on Functional High-Performance and Numerical Computing aims to bring together researchers and practitioners exploring or employing the use of functional or declarative programming languages or techniques in scientific computing, and specifically in the domains of high-performance computing and numerical programming. The purpose of the meeting is to enable sharing of results, experiences, and novel ideas about how high-level, declarative techniques can help make high-performance, distributed/parallel, or numerically-intensive code dealing with computationally challenging problems easier to write, read, maintain, or portable to new hardware architectures. Areas of interest include, but are not limited to: * relevant compiler technologies * runtime systems (including fault tolerance mechanisms and those supporting distributed or parallel computation) * domain-specific languages (embedded or standalone) * type systems * formal methods * software libraries (e.g. for exact or interval arithmetic). ## Submission details Submissions should fall into one of two categories: * Regular research papers (up to 12 pages) * Extended abstracts (1 - 2 pages) The bibliography will not be counted against the page limits for either category. Regular research papers are expected to present novel and interesting research results, and will be included in the formal proceedings. Extended abstracts should report work in progress that the authors would like to present at the workshop; they will be evaluated primarily for relevance and interest. Extended abstracts will be distributed to workshop attendees but will not be published in the formal proceedings. We welcome submissions from PC members (with the exception of the PC Chair), but these submissions will be held to a higher standard. Submission is handled through the HotCRP site. All submissions should be in portable document format (PDF) and formatted using the ACM SIGPLAN style guidelines. Submissions written with LaTeX are required to use the ‘acmart’ format and the two-column ‘sigplan’ subformat (not to be confused with the one-column ‘acmlarge’ subformat!). Extended Abstracts must be submitted with the label ‘Extended abstract’ clearly in the title. ## Publication The proceedings of FHPNC 2019 will be published in the ACM Digital Library. ## Related links * Author Information and LaTeX templates : http://www.sigplan.org/Resources/Author/ * Attendee Code of Conduct: http://www.sigplan.org/Resources/Policies/CodeOfConduct/

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Possible ghc bug
by Michel Haber 10 Apr '19

10 Apr '19

Hello Cafe, I was trying to load a module containing this function in ghci: "add x y = wrap $ unwrap x + unwrap y" with the following extensions activated: ConstraintKinds DataKinds DeriveFunctor DuplicateRecordFields FlexibleContexts FlexibleInstances GADTs KindSignatures MultiParamTypeClasses PolyKinds TypeFamilies TypeOperators AllowAmbiguousTypes And it loaded without problem. So then I tested its type with ":t add", which gave: add :: (Num a, Newtype a b1, Newtype a b2, Newtype a b3) => b2 -> b3 -> b1 Then I added this signature to the function in the module. This caused ghci to refuse to load it and give the following error: src/Exercises.hs:55:11: error: • Could not deduce (Newtype Integer b1) arising from a use of ‘wrap’ from the context: (Num a, Newtype a b1, Newtype a b2, Newtype a b3) bound by the type signature for: add :: forall a b1 b2 b3. (Num a, Newtype a b1, Newtype a b2, Newtype a b3) => b2 -> b3 -> b1 at src/Exercises.hs:54:1-74 • In the expression: wrap $ unwrap x + unwrap y In an equation for ‘add’: add x y = wrap $ unwrap x + unwrap y | 55 | add x y = wrap $ unwrap x + unwrap y | ^^^^^^^^^^^^^^^^^^^^^^^^^^ src/Exercises.hs:55:18: error: • Could not deduce (Newtype Integer b2) arising from a use of ‘unwrap’ from the context: (Num a, Newtype a b1, Newtype a b2, Newtype a b3) bound by the type signature for: add :: forall a b1 b2 b3. (Num a, Newtype a b1, Newtype a b2, Newtype a b3) => b2 -> b3 -> b1 at src/Exercises.hs:54:1-74 • In the first argument of ‘(+)’, namely ‘unwrap x’ In the second argument of ‘($)’, namely ‘unwrap x + unwrap y’ In the expression: wrap $ unwrap x + unwrap y | 55 | add x y = wrap $ unwrap x + unwrap y | ^^^^^^^^ src/Exercises.hs:55:29: error: • Could not deduce (Newtype Integer b3) arising from a use of ‘unwrap’ from the context: (Num a, Newtype a b1, Newtype a b2, Newtype a b3) bound by the type signature for: add :: forall a b1 b2 b3. (Num a, Newtype a b1, Newtype a b2, Newtype a b3) => b2 -> b3 -> b1 at src/Exercises.hs:54:1-74 • In the second argument of ‘(+)’, namely ‘unwrap y’ In the second argument of ‘($)’, namely ‘unwrap x + unwrap y’ In the expression: wrap $ unwrap x + unwrap y | 55 | add x y = wrap $ unwrap x + unwrap y | ^^^^^^^^ Failed, no modules loaded. This does not make sense to me, since I only used the signature that ghci itself gave me. Is this a bug? if not, could someone please explain this behaviour to me? Thanks, Michel

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ANN: gitlab-haskell
by Rob Stewart 10 Apr '19

10 Apr '19

This new gitlab-haskell library provides read/write access to data on a GitLab server, using the GitLab web API. The library provides access to: branches, commits, groups, issues, jobs, members, merge requests, pipelines, projects, repositories, repository files and users. JSON responses are parsed into typed Haskell values for convenience. https://hackage.haskell.org/package/gitlab-haskell-0.1.0.0 -- Rob Stewart

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Re: [Haskell-cafe] streaming with logs / metadata
by Olaf Klinke 10 Apr '19

10 Apr '19

>> Anything beyond the Functor instance for (Either e), though, models exceptions that abort the computation as soon as the first Left arises. You seem to use the type in a different way which may be one reason why you do not find your functions implemented elsewhere. For logging or warnings, most Haskellers use something like a writer monad transformer. The underlying monad, >> >> Writer w a = (w,a) > > That's the thing I was saying destroys streaming. The problem is that > it returns ([log], [a]), instead of [Either log a], so the > interleaving has been lost. > Evan, When you say interleaving, do you think of lists like the following? [Left warning1,Right value 1,Left warning 2,Right value2,...] The above is isomorphic to [(warning1,value1),(warning2,value2),...] I don't think that the writer monad destroys streaming. Below is a somewhat contrived, but ordinary use case. {-- begin example --} import Control.Monad.Writer -- from mtl type Log = [String] -- some Monoid half :: Int -> Writer Log Int half x = case x `quotRem` 2 of (y,0) -> return y (y,1) -> writer (y,["Warning: "++(show x)++" was uneven."]) stream :: [Int] stream = 4:8:5:3:7:2: error "broken stream" (ys,warnings) = runWriter (mapM half stream) {-- end example --} ghci> -- load the example above ghci> ys [2,4,2,1,3,1*** Exception: broken stream ghci> mapM_ putStrLn warnings Warning: 5 was uneven. Warning: 3 was uneven. Warning: 7 was uneven. *** Exception: broken stream You see that there is some output before the error is reached, proving that both ys and warnings could be consumed in a streaming manner. Here it is important that the Log monoid's `mappend` function is not strict in the second argument. It would not, for example, work with Log = Data.Sequence.Seq String With mtl you could easily throw in a State monad component that keeps track of the position in the stream, so that warning messages can hint at the place where the warning originated. Olaf

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[Announcement] Copilot 3.0, a hard realtime C generator and runtime verification framework
by Frank Dedden 09 Apr '19

09 Apr '19

Dear all, We are very pleased to announce the release of Copilot 3.0, a stream-based DSL for writing and monitoring embedded C programs, with an emphasis on correctness and hard realtime requirements. Copilot is typically used as a runtime verification framework, where programs serve as specifications to the system we want to monitor. Additional libraries provide utility functions for temporal logic (LTL, PTLTL and MTL), clocks and voting algorithms. Over the years, Copilot has been used at the Safety Critical Avionics Systems Branch of NASA Langley Research Center for monitoring test flights of drones. This new release contains a number of additional features that make writing programs easier: * The extended language with support for monitoring and generating structs and arrays in a type-safe manner. * A completely rewritten C99 code generator to support the new features. * Significant improvements on the quality and readability of the output code, which help in traceability and certification of the code. * Internal simplifications for a more future proof codebase. Copilot is available on hackage [1]. For more information, including documentation, examples and links to the source code, please visit the webpage [2]. Kind regards, The Copilot developers: - Frank Dedden (maintainer) - Alwyn Goodloe (maintainer) - Ivan Perez [1] http://hackage.haskell.org/package/copilot [2] https://copilot-language.github.io

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OO "dot" notation and records...
by Nicholls, Mark 09 Apr '19

09 Apr '19

Is there something in Haskell like this? I could do with getting OO like intelisense going...i.e. you have some values, the types are inhered in my environment, and the available functions prompt the programmer. (I'm not a big Haskell user, but I'm trying to "sell" it as an alternative for F# and scala in an industrial context). CONFIDENTIALITY NOTICE This e-mail (and any attached files) is confidential and protected by copyright (and other intellectual property rights). If you are not the intended recipient please e-mail the sender and then delete the email and any attached files immediately. Any further use or dissemination is prohibited. While MTV Networks Europe has taken steps to ensure that this email and any attachments are virus free, it is your responsibility to ensure that this message and any attachments are virus free and do not affect your systems / data. Communicating by email is not 100% secure and carries risks such as delay, data corruption, non-delivery, wrongful interception and unauthorised amendment. If you communicate with us by e-mail, you acknowledge and assume these risks, and you agree to take appropriate measures to minimise these risks when e-mailing us. MTV Networks International, MTV Networks UK & Ireland, Greenhouse, Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be Viacom, Viacom International Media Networks and VIMN and Comedy Central are all trading names of MTV Networks Europe. MTV Networks Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.

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looking for yesod-auth example with LTS-13
by Johannes Waldmann 09 Apr '19

09 Apr '19

Dear Cafe, I am trying to update some legacy code, and I have trouble getting yesod-auth to work under LTS-13. It worked with LTS-10. I think the error in this demonstration project (not mine) is related to what I am seeing: https://github.com/TobyGoodwin/auth38/issues/1 My actual code (and error message) is here https://gitlab.imn.htwk-leipzig.de/autotool/all0/issues/565 but "auth38" is certainly easier to reproduce. I was unable to apply this idea: https://stackoverflow.com/questions/23188494/yesod-subsites-and-forms/29394… (which seems dated - the HandlerT type is gone?) Any ideas? Thanks - J.W.

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Package takeover intent - dyre
by Fraser Tweedale 09 Apr '19

09 Apr '19

The dyre[1] package is unmaintained for 5 years. I would like to contribute to it or take over maintainership, but have been unable to contact the maintainer (Cc'd). Pursuant to wiki[2] I am announcing my intention to take over the package. [1] https://hackage.haskell.org/package/dyre [2] https://wiki.haskell.org/Taking_over_a_package Thanks, Fraser

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[ANNOUNCE] comprehensions-ghc: ApplicativeComprehensions as a GHC plugin
by Matthew Farkas-Dyck 09 Apr '19

09 Apr '19

https://hackage.haskell.org/package/comprehensions-ghc See description for instructions how to use. A comprehension makes more sense than a `do` expression for `Applicative` types — `ApplicativeDo` relies on a kludge: checking whether the last expression has the form `pure _` or `return _`. Indeed, for an `Applicative` term, it can ultimately (modulo aliases, let-expressions, η-expansion, etc) have no other! So far, however, the plugin merely rewrites each comprehension as a `do` expression. (It ignores comprehensions with features which can't be converted.) My most compelling use case so far has been context-free-parsing records (for examples: with `optparse-applicative` or `regex-applicative`). It lets one write the following: `[Options {..} | foo <- parseFoo, bar <- parseBar]` Cheers, happy hacking ☺

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Re: [Haskell-cafe] streaming with logs / metadata
by Olaf Klinke 08 Apr '19

08 Apr '19

Dear Evan, Probably you want to have a look whether the mtl package has something for you. Anything beyond the Functor instance for (Either e), though, models exceptions that abort the computation as soon as the first Left arises. You seem to use the type in a different way which may be one reason why you do not find your functions implemented elsewhere. For logging or warnings, most Haskellers use something like a writer monad transformer. The underlying monad, Writer w a = (w,a) for some monoid w, is exceptionally versatile because of the function Functor f => Writer w (f a) -> f (Writer w a) which in combination with traverse lets you move the (Writer w) type in and out of nested types easily. Cheers, Olaf

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GHC extensions
by Michel Haber 08 Apr '19

08 Apr '19

Hello Cafe, So I've been learning a bit about the GHC extensions from https://github.com/i-am-tom/haskell-exercises. But the lessons say nothing about how the extensions work behind the scenes. For example, I've assumed that RankNTypes would require something similar to dynamic dispatch in imperative languages in order to work. But this is just an assumption. So I was wondering where I can get a quick succinct read (or a summary at least) about how these extensions are implemented, as well as their performance cost (or gain!). Also if someone knows other tutorials and lessons for these, and other extensions, please feel free to share them :p Thank you, Michel :)

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[ANNOUNCE] GHC 8.6.5-rc1 is now available
by Ben Gamari 08 Apr '19

08 Apr '19

Hello everyone, The GHC team is proud to announce the first release candidate of 8.6.5. The source distribution, binary distributions, and documentation are available at https://downloads.haskell.org/~ghc/8.6.5-rc1 This release fixes a handful of issues with 8.6.4: - Binary distributions once again ship with Haddock documentation including syntax highlighted source of core libraries (#16445) - A build system issue where use of GCC with `-flto` broke `configure` was fixed (#16440) - An bug affecting Windows platforms wherein XMM register values could be mangled when entering STG has been fixed (#16514) - Several Windows packaging issues resulting from the recent CI rework. (#16408, #16398, #16516) Since this is a relatively small bugfix release we are bypassing the alpha releases and moving right to the release candidate stage. If all goes well the final release will be cut next week. As always, if anything looks amiss do let us know. Happy testing! Cheers, - Ben

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[ANN] Haskell.Org Discourse Instance
by Jasper Van der Jeugt 08 Apr '19

08 Apr '19

Hello all, We would like to announce a new discourse-based forum for the Haskell community, at: https://discourse.haskell.org/ This is inspired by the Rust, Nix and Elm discourse instances, where these forums have had a strong positive effect on the community. We will run this as a "beta" for 6 months and then evaluate its usefulness. It is meant as an extra alternative to Haskell-cafe, reddit and Haskell IRC, but it does not replace any of those. Discourse is completely open source and easily accessible using an email client. We would like to thank the Haskell.Org admin team for provisioning a server and Matthew Pickering for suggesting this and doing the hard work setting up the instance. Warm regards, Jasper Van der Jeugt on behalf of the Haskell.Org Committee

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streaming with logs / metadata
by Evan Laforge 08 Apr '19

08 Apr '19

I have a pattern that's come up several times, and I'm wondering if there's a name for it, or a better way to do it. It has to do with processing streams, which in the presence of laziness and the absence of effects can be done with just lists. For instance, imagine a parser that produces [Token], then various processing stages that go [Token] -> [x], [x] -> [y], [y] -> [Output]. If I have a transform function that works on a single element 1:1 and is stateless, then I can express it with 'map'. If it needs simple state, then I can switch 'map' for 'mapAccumL', which is just a specialization of the State monad. If it needs to know the next element, I can compose a 'zipNext' (zip xs (drop 1 xs)) on the front. If it returns multiple elements, there's concatMap, and of course mapM for arbitrary monads. Now suppose it needs warnings, or logging, so to preserve streaming I wind up with '[Either e a] -> [Either e b]'. I still want to do all the same stuff, but factor out the Lefts so I don't have to be explicitly passing through all the time. So I start reimplementing the usual list functions: module E where map :: (a -> b) -> [Either e a] -> [Either e b] mapE :: (a -> Either e b) -> [Either e a] -> [Either e b] concatMap :: (a -> [b]) -> [Either e a] -> [Either e b] concatMapE :: (a -> [Either e b]) -> [Either e a] -> [Either e b] mapAccumL :: (state -> a -> (state, Either e b)) -> state -> [Either e a] -> (state, [Either e b]) And of course the monadic / applicative variants: mapM :: Applicative m => (a -> m b) -> [Either e a] -> [Either e b] mapEM :: Monad m => (a -> m (Either e b)) -> [Either e a] -> m [Either e b] ... etc. But to deal with supplying extra state, or looking into the future or filtering I have to reinvent those too: zip :: [a] -> [Either e b] -> [Either e (a, b)] zip{2,3,4,...} :: ... zipNexts :: [Either e a] -> [Either e (a, [a])] filter :: (a -> Bool) -> [Either e a] -> [Either e a] The zips become asymmetrical, but they're in service of a common pattern which I'm not sure how to describe, but is used to get the Lefts out of the way. E.g. if a duration can be derived from a Right value, to annotate Rights with start times: 'E.zip (scanl (+) 0 (map durationOf (Either.rights xs))) xs'. It's a bit unsatisfying because it relies on the transformation preserving 1:1 with its input, or at least new elements are added only at the end and I can ignore them. 'scanl . map' happens to have this property, but it's not obvious or guaranteed. My questions are, is this a known pattern? Is there an implementation on hackage, or at least a good thing to call it? And then, is there a a way to construct these functions systematically, or to compose them from smaller parts? The 1:1 stateless ones like 'map' and 'mapM' work out nicely because they're just 'fmap . fmap' or 'traverse . traverse', and I can implement 'concatMapM' and then implement a lot of other kinds of maps as specializations, though efficiency may suffer. But for the zips and filters and takeWhiles I wind up just rewriting the recursion. They feel ad-hoc and unsatisfying, that if I were more clever I would figure out how to abstract out the Lefts in one spot, once and for all. There is a general way to get all of the '[a] -> [b]' functions into '[Either e a] -> [Either e b]', and that's to partitionsEithers, apply second, then concat, but of course it spoils streaming and is inefficient if there are lots of Lefts. Still, it's the only way I can think of to get those Lefts out of the picture in a modular way. Using a Writer I think is equivalent. There's a similar problem with being able factor out annotations, similar to the way I want to factor out logs / warnings / other metadata above. E.g. if we have '[(annot, a)] -> [(annot, b)]' then we start with a simple fmap.fmap, but any more complicated transforms means you either have to intersperse the "ignore annotation" logic and clutter things up with 'snd's and 'second's everywhere, or come up with a whole new map filter zip toolkit.

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Call for Contributions--First miniKanren and Relational Programming Workshop
by William Byrd 05 Apr '19

05 Apr '19

DEADLINE: 15 May 2019, (Any time in the world) WEBSITE: https://icfp19.sigplan.org/home/minikanren-2019 LOCATION: Berlin, Germany (co-located with ICFP) DATE: 22 August 2019 The 2019 First miniKanren and Relational Programming Workshop is calling for submissions. Full papers are due 15 May 2019. Authors will be notified by 15 June 2019. Camera-ready versions are due 30 June 2019. All deadlines are (23:59 UTC-12), "Anywhere on Earth". The miniKanren and Relational Programming Workshop is a new workshop for the miniKanren family of relational (pure constraint logic programming) languages: miniKanren, microKanren, core.logic, OCanren, Guanxi, etc. The workshop solicits papers and talks on the design, implementation, and application of miniKanren-like languages. A major goal of the workshop is to bring together researchers, implementors, and users from the miniKanren community, and to share expertise and techniques for relational programming. Another goal for the workshop is to push the state of the art of relational programming---for example, by developing new techniques for writing interpreters, type inferencers, theorem provers, abstract interpreters, CAD tools, and other interesting programs as relations, which are capable of being "run backwards," performing synthesis, etc. Submission Information Submission Page: https://minikanren19.hotcrp.com/ Paper submissions must use the format acmart and its sub-format acmlarge. They must be in PDF, printable in black and white on US Letter size. Microsoft Word and LaTeX templates for this format are available at: http://www.sigplan.org/Resources/Author/ As this is the first iteration of the workshop, we want to encourage all kinds of submissions. We expect short papers as well as longer papers. As a rough guideline, with the new ACM format a short paper would be 2 to 7 pages and a long paper 8 to 25 pages. Authors are encouraged to publish any code associated to their papers under an open source license, so that reviewers may try the code and verify the claims. Proceedings will be printed as a Technical Report at Harvard University. Publication of a paper at this workshop is not intended to replace conference or journal publication, and does not preclude re-publication of a more complete or finished version of the paper at some later conference or in a journal. Sincerely, William E. Byrd, General Chair Nada Amin, Program Committee Chair Program Committee: Claire Alvis, Sparkfund Tom Gilray, University of Alabama, Birmingham Jason Hemann, Northeastern University Eric Holk, Google Kanae Tsushima, National Institute of Informatics

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Call for Contributions: Summer BOB 2019 [Aug 21, Berlin, deadline May 17]
by Matthias Fischmann 05 Apr '19

05 Apr '19

[Online version of this email: https://bobkonf.de/2019-summer/cfc.html] Summer BOB Conference 2019 "What happens when we use what's best for a change?" http://bobkonf.de/2019-summer/cfc.html Berlin, August 21 co-located with ICFP 2019 Call for Contributions Deadline: May 17, 2019 You are engaged in software development or software architecture, and have an interesting story to tell about an advanced tools, technique, language or technology that you're using? Or a gnarly problems that these tools fail to address but should? Summer BOB is a one-time-only event, in the spirit of the spectacular Winter BOB. The International Conference on Functional Programming is coming to town, and Summer BOB will be right in the middle of it, on the last day of ICFP proper, prior to all the workshops. Summer BOB will feature two tracks: one from practitioners, and one from researchers, and foster communication and cross-pollination between these communities. If you share our vision and want to contribute, submit a proposal for a talk! NOTE: The conference fee will be waived for presenters. Travel expenses will not be covered (for exceptions see "Speaker Grants"). Topics ------ We are looking for talks about best-of-breed software technology, e.g.: - functional programming - persistent data structures and databases - types - formal methods for correctness and robustness - abstractions for concurrency and parallelism - metaprogramming - probabilistic programming - math and programming - controlled side effects - beyond REST and SOAP - effective abstractions for data analytics - … everything really that isn’t mainstream, but you think should be. Presenters should provide the audience with information that is practically useful for software developers. We're especially interested in experience reports. Other topics are also relevant, e.g.: - demos and how-tos - reports on problems that cutting-edge languages and tools should address but don't - overviews of a given field Requirements ------------ We accept proposals for presentations of 45 minutes (40 minutes talk + 5 minutes questions), as well as 90 minute tutorials for beginners. The language of presentation should be either English. Your proposal should include (in your presentation language of choice): - An abstract of max. 1500 characters. - A short bio/cv - Contact information (including at least email address) - A list of 3-5 concrete ideas of how your work can be applied in a developer's daily life - additional material (websites, blogs, slides, videos of past presentations, …) - Don't be confused: The system calls a submission event. Submit here ----------- https://bobcfc.active-group.de/bob2019-summer/cfp Speaker Grants -------------- BOB has Speaker Grants available to support speakers from groups under-represented in technology. We specifically seek women speakers and speakers who are not be able to attend the conference for financial reasons. Shepherding The program committee offers shepherding to all speakers. Shepherding provides speakers assistance with preparing their sessions, as well as a review of the talk slides. Organisation ------------ - Direct questions to contact at bobkonf dot de - Proposal deadline: May 17, 2019 - Notification: May 31, 2019 - Program: June 14, 2019 Program Committee ----------------- - Matthias Fischmann, zerobuzz UG - Matthias Neubauer, SICK AG - Nicole Rauch, Softwareentwicklung und Entwicklungscoaching - Michael Sperber, Active Group - Stefan Wehr, factis research Scientific Advisory Board - Annette Bieniusa, TU Kaiserslautern - Torsten Grust, Uni Tübingen - Peter Thiemann, Uni Freiburg More information here: http://bobkonf.de/2019-summer/programmkomitee.html

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Hackage Down
by Ara Adkins 04 Apr '19

04 Apr '19

Is anybody else unable to access Hackage? I'm seeing a 502 bad gateway. _ara

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Feedback on plan for checking code requirements in a GHC plugin
by Chris Smith 03 Apr '19

03 Apr '19

Hey everyone, I'm converging on a design for a new feature of CodeWorld, the Haskell-based educational programming environment that I teach with. I'm wondering if anyone has done something like this before. The goal is that when I give an assignment in a class (e.g., "modify this starting code to generalize the repeated pattern using a function"), I want the user to see a checklist of assignment requirements when they run the code. A prototype implementation is here: https://code.world/haskell#PpwpTF1wv3qIvwhohCfvSrQ There are all sorts of possible requirements, such as: "No lines longer than 80 characters", or "there must be a function called foo", or "all top-level definitions must have type signatures", or "your code must define at least 10 top-level variables, and use at least 3 where clauses", or "your definition of var should be equivalent to this one" (see Joachim Breitner's inspection testing work), or even "the function f must satisfy this QuickCheck property". It's been suggested that the requirements language also include the ability to match patterns in the AST, which I think is a good idea. The current prototype uses a pre-compile step that parses the code using haskell-src-exts, and doesn't implement dynamic requirements (runtime-evaluated) at all. My ultimate plan, though, is to send these requirements to GHC via a plugin, then have it evaluate the static ones at compile time, and generate code to check the dynamic ones. Finally, the plugin would add new code to the beginning of main that will invoke a configurable function with the results of the requirement check (hard-coding the static ones, and evaluating dynamic ones on the fly). (In the CodeWorld environment, this function would display the checklist in the web UI, for example.) Has anyone done anything like this before? Any wisdom to share, or ideas to contribute? Thanks, Chris

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