- Haskell-Cafe - Haskell.org

Final Call for the early round of Papers for the Haskell Symposium 2021
by Hage, J. (Jurriaan) 23 Apr '21

23 Apr '21

Dear all, This is the first call for the *regular* round of papers for the upcoming Haskell Symposium. Please forward to anyone that you believe might be interested. The deadline for this round is May 21. Apologies for receiving multiple copies of this announcement. Best regards, Jurriaan Hage Chair ================================================================================ ACM SIGPLAN CALL FOR SUBMISSIONS Haskell Symposium 2021 ** virtual ** Thu 26 -- Fri 27 August, 2021 http://www.haskell.org/haskell-symposium/2021/ ================================================================================ The ACM SIGPLAN Haskell Symposium 2021 will be co-located with the 2021 International Conference on Functional Programming (ICFP). Due to COVID-19 it will take place **virtually** this year. Like last year, we will be using a lightweight double-blind reviewing process. See further information below. Different from last year is that we offer a new submission category: the tutorial. Details can be found 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; * Tutorials, to document how to use a particular language feature, programming technique, tool or library within the Haskell ecosystem; * 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. A new submission category for this year's Haskell Symposium is the tutorial. Like with the experience report and the functional pearl, the key criterion for such a paper is that it makes a contribution from which other Haskellers can benefit. What distinguishes a tutorial is that its focus is on explaining an aspect of the Haskell language and/or ecosystem in a way that is generally useful to a Haskell audience. Tutorials for many such topics can be found online; the distinction here is that by writing it up for formal review it will be vetted by experts and formally published. 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. If your contribution is not a research paper, please mark the title of your experience report, functional pearl, tutorial or system demonstration as such, by supplying a subtitle (Experience Report, Functional Pearl, Tutorial Paper, System Demonstration). Submission Details ================== 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, tutorials and demo proposals should be labelled clearly as such. Lightweight Double-blind Reviewing ---------------------------------- Haskell Symposium 2021 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 Tutorial: 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 --------- Regular track and demos: Submission deadline: 21 May 2021 (Fri) Notification: 23 June 2021 (Wed) 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) Program Committee members are allowed to submit papers, but their papers will be held to a higher standard. 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://haskell21.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 can distinguish between 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 conference chair 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. Proceedings =========== Accepted papers will be included in the ACM Digital Library. Their authors will be required to choose one of the following options: - Author retains copyright of the work and grants ACM a non-exclusive permission-to-publish license (and, optionally, licenses the work with a Creative Commons license); - Author retains copyright of the work and grants ACM an exclusive permission-to-publish license; - Author transfers copyright of the work to ACM. For more information, please see ACM Copyright Policy (http://www.acm.org/publications/policies/copyright-policy) and ACM Author Rights (http://authors.acm.org/main.html) Accepted proposals for system demonstrations will be posted on the symposium website but not formally published in the proceedings. 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. Artifacts ========= Authors of accepted papers are encouraged to make auxiliary material (artifacts like source code, test data, etc.) available with their paper. They can opt to have these artifacts published alongside their paper in the ACM Digital Library (copyright of artifacts remains with the authors). If an accepted paper's artifacts are made permanently available for retrieval in a publicly accessible archival repository like the ACM Digital Library, that paper qualifies for an Artifacts Available badge (https://www.acm.org/publications/policies/artifact-review-badging#available) Applications for such a badge can be made after paper acceptance and will be reviewed by the PC chair. Program Committee ================= Edwin Brady University of St Andrews Koen Claessen Chalmers University of Technology Dominique Devriese Vrije Universiteit Brussel Andy Gill University of Kansas Jurriaan Hage (chair) Universiteit Utrecht Zhenjiang Hu Peking University Ranjit Jhala University of California Patricia Johann Appalachian State University Yukiyoshi Kameyama University of Tsukuba George Karachalias Tweag Ralf Laemmel University of Koblenz-Landau Daan Leijen Microsoft Research Ben Lippmeier Ghost Locomotion Neil Mitchell Facebook Alberto Pardo Universidad de la Republica, Uruguay Matt Roberts Macquarie University Janis Voigtlaender University of Duisburg-Essen Nicolas Wu Imperial College London If you have questions, please contact the chair at: j.hage(a)uu.nl ================================================================================

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Richard Eisenberg inspired dependent type hacking and some questions
by Clinton Mead 21 Apr '21

21 Apr '21

My apologies for the (kind of) cross post, I originally put a similar question on the Haskell <https://www.reddit.com/r/haskell/comments/mv6m5s/hacking_richard_eisenbergs…> Reddit <https://www.reddit.com/r/haskell/comments/mv6m5s/hacking_richard_eisenbergs…> I'm never sure the best place to post these sorts of things. Inspired by some of the code <https://github.com/goldfirere/video-resources/tree/main/2021-04-20-vectors> from one of Richard Eisenberg's weekly videos <https://www.youtube.com/watch?v=WHeBxSBY0fc> (which I always eagerly await!) I made some adjustments to his code here <https://gist.github.com/clintonmead/dc6233afb14cb04a3e1ae2b44bd0bf08>. Basically the attempt is to be able to deal with compile time known length lists and runtime only known length lists as uniformly as possible, as the logic is the same in both cases. In addition, allowing us to do things like `safeHead (x : xs)` regardless whether we know the length of `xs` at runtime or compile time, because it should never fail. My attempt makes things a bit messier, adding an extra constructor in the runtime case, and then naturally this means all the functions have to be extended to specifically pattern matched on this constructor. I'm trying to wrap my head around dependent types, and I did buy the ebook version of "Type-Driven Development in Idris", but I've never used Idris before so perhaps I'm having some trouble making these examples more concrete. The vague idea I've seemed to have heard is that dependent types blurs the distinction between "values" and "types", so in Idris my thought was as a result we get rid of this messy hacky distinction between the two that's required in Haskell. Can we actually do this and how? And indeed, can we do this in Haskell as well? Does the current GHC type system give us tools to allow what I've designed without bloating all the functions by having to deal with this extra constructor match? Thanks, Clinton

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IntelliJ Haskell plugins?
by Gregory Guthrie 21 Apr '21

21 Apr '21

Does anyone have experience with and a recommendation for the best Haskell for the IntelliJ IDE?

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GLR parser for Haskell?
by Benjamin Redelings 21 Apr '21

21 Apr '21

Hi, I've been looking at the Haskell parser in ghc/compiler/GHC/Parser.y. It relies on post-processing pretty heavily, both to determine the type of parsed expressions (i.e. is "(x,y)" a pattern or expression?) and to reject invalid syntax (i.e. field declarations are parsed as a type, but this is rejected during postprocessing I think, except in constructor declarations). This makes the grammar rather hard to read. To quote [1]: > Insteadof describingthe languageto be parsed,thegrammardescribes > theprocessused to parseit; it'smore like a hand-crafted parsing > program,butcrammed into Backus-Naur Form. Does anybody know if there is another version of the parser generator uses grammar rules that are closer to the grammar rules in the 2010 report? Maybe a GLR grammar? Also, I see that Happy is able to generate GLR parsers. I'm curious if GLR parsers aren't being used just because they are slow, or if there is some other reason they are hard to use. I am not an expert on parsing or grammars, so any insight would be appreciated. Thanks! -BenRI [1] https://escholarship.org/uc/item/8559j464

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Bx 2021 - FINAL CALL FOR PAPERS
by Meng Wang 21 Apr '21

21 Apr '21

Dear Haskellers, Lenses is Bx and our own Edward Kmett will be giving the keynote! Please consider submitting. Best regards, Meng Bx 2021 - FINAL CALL FOR PAPERS ********************************************************************************** 9th International Workshop on Bidirectional Transformations (Bx 2021) as part of the STAF conference (June 21, 2021) running virtually, Western Norway University of Applied Sciences, Bergen, Norway http://bx-community.wikidot.com/bx2021:home ********************************************************************************** * Important dates: * Abstract submission: April 27, 2021 * Paper Submission: May 4, 2021 ********************************************************************************** OVERVIEW ========================================= Bidirectional transformations (bx) are a mechanism for maintaining the consistency between two or more related (and heterogeneous) sources of information (i.e., relational databases, software models and code, or any other artefacts following standard or domain-specific formats). The strongest argument in favour of bx is its ability to provide a synchronization mechanism that is guaranteed to be correct by construction. Bx has been attracting a wide range of research areas and communities, with prominent presence at top conferences in several different fields (namely databases, programming languages, software engineering, and graph transformation). Nowadays, the fast-growing complexity of software- or data- intensive systems has forced the industry and the academy to use and investigate different development techniques to manage the many different aspects of the systems. Researchers are actively investigating the use of bidirectional approaches to tackle a diverse set of challenges with various applications including model-driven software development, visualization with direct manipulation, big data, databases, domain-specific languages, serializers, and data transformation, integration and exchange. Bx 2021 is a dedicated venue for bx in all relevant fields and is part of a workshop series that was created in order to promote cross-disciplinary research and awareness in the area. As such, since its beginning in 2012, the workshop has rotated between venues in different fields. KEYNOTE ========================================= We are happy to announce our keynote speaker: Edward Kmett. TOPICS ========================================= The aim of the workshop is to bring together researchers and practitioners, established and new, interested in bx from different perspectives, including but not limited to: * bidirectional programming languages and frameworks * software development with bx * data and model synchronization * view updating * inter-model consistency analysis and repair * data/schema (or model/metamodel) co-evolution * coupled software/model transformations * inversion of transformations and data exchange mappings * domain-specific languages for bx * analysis and classification of requirements for bx * bridging the gap between formal concepts and application scenarios * analysis of efficiency of transformation algorithms and benchmarks * model-driven and model-based approaches * survey and comparison of bx technologies * case studies and tool support CATEGORIES OF SUBMISSIONS ========================================= Five categories of submissions are considered: * Full Research Papers (13-15 pages) - in-depth presentations of novel concepts and results - applications of bx to new domains - survey papers providing novel comparisons between existing bx technologies and approaches, case studies * Tool Papers (7-8 pages) - guideline papers presenting best practices for employing a specific bx approach (with a specific tool) - presentation of new tools or substantial improvements to existing ones - qualitative and/or quantitative comparisons of applying different bx approaches and tools * Experience Report (7-8 pages) - sharing experiences and lessons learned with bx tools/frameworks/languages - how bx is used in (research/industrial/educational) projects * Short Papers (5 pages) - work in progress - small focused contributions - position papers and research perspectives - critical questions and challenges for bx * Talk Proposals (2 pages) - proposed lectures about topics of interest for bx - existing work representing relevant contributions for bx - promising contributions that are not mature enough to be proposed as papers of the other categories If your submission is not a Full Research Paper, please include the intended submission category in the Title field of EasyChair’s submission form. Tool papers, experience reports and short papers will be mapped to the short paper category in CEUR (having between 5-9 standard pages, 1 standard page = 2500 characters), whereas full research papers will be mapped to the regular paper category in CEUR (having at least 10 standard pages). The bibliography is excluded from the page limits. All papers are expected to be self-contained and well-written. Tool papers are not expected to present novel scientific results, but to document artifacts of interest and share bx experience/best practices with the community. Experience papers are expected to report on lessons learnt from applying bx approaches, languages, tools, and theories to practical application case studies. Extended abstracts should primarily provoke interesting discussion at the workshop and will not be held to the same standard of maturity as regular papers; short papers contain focused results, positions or perspectives that can be presented in full in just a few pages, and that correspondingly contain fewer results and that therefore might not be competitive in the full paper category. Talk proposals are expected to present work that is of particular interest to the community and worth a talk slot at the workshop. We strongly encourage authors to ensure that any (variants of) examples are present in the bx example repository at the time of submission, and, for tool papers, to allow for reproducibility with minimal effort, either via a virtual machine (e.g., via Share) or a dedicated website with relevant artifacts and tool access. All submissions will be peer-reviewed by at least three members of the program committee. If a submission is accepted, at least one author is expected to participate in the workshop to present it. Authors of accepted tool paper submissions are also expected to be available to demonstrate their tool at the event. PROCEEDINGS ========================================= The workshop proceedings (in a STAF 2021 joint volume for workshops), including all accepted papers (except talk proposals), shall be submitted after the conference to CEUR-WS.org for online publication. Pre-prints of all papers will be available via the workshop website at the beginning of the conference. Papers must follow the CEUR one column style available at: http://ceur-ws.org/Vol-XXX/CEURART.zip or https://www.overleaf.com/latex/templates/template-for-submissions-to-ceur-w… and must be submitted via EasyChair: https://easychair.org/conferences/?conf=bx2021 Please also ensure that your submission is legible when printed on a black and white printer. In particular, please check that colors remain distinct and font sizes are legible. Submissions not complying with the above guidelines may be excluded from the reviewing process without further notice. IMPORTANT DATES ========================================= Abstract submission: April 27, 2021 Paper submission: May 4, 2021 Author notification: May 25, 2021 Early registration: May 27, 2021 Workshop: June 21, 2021 PROGRAM CO-CHAIRS ========================================= The workshop is co-organized by Meng Wang (University of Bristol, UK) and Leen Lambers (Hasso Plattner Institute at the University of Potsdam, Germany). In case of questions, please contact the PC chairs at bx2021(a)easychair.org . Please find further information w.r.t. the Bx 2021 workshop at: http://bx-community.wikidot.com/bx2021:home and STAF 2021 conference at: https://staf2021.hvl.no/ PROGRAM COMMITTEE ========================================= Ravi Chugh, University of Chicago, USA Anthony Cleve, University of Namur, Belgium Alcino Cunha, University of Minho, Portugal Romina Eramo, University of L'Aquila, Italy Michael Johnson, Macquarie University, Australia Hsiang Shang Ko, Academia Sinica, Taiwan Ralf Lämmel, University of Koblenz-Landau, Germany Kazutaka Matsuda, Tohoku University, Japan Fernando Orejas, Universitat Politècnica de Catalunya, Spain Roly Perera, Alan Turing Institute, UK Perdita Stevens, The University of Edinburgh, UK Tarmo Uustalu, Reykjavik University, Iceland Jens Weber, University of Victoria, Canada Bernhard Westfechtel, University of Bayreuth, Germany ========================================= _____________________________________ Leen Lambers Senior Researcher at System Analysis and Modeling Group https://hpi.de/giese/personen/dr-leen-lambers.html _____________________________________ Hasso-Plattner-Institut für Digital Engineering gGmbH Universität Potsdam Prof.-Dr.-Helmert-Str. 2-3 D-14482 Potsdam, Germany _____________________________________ Amtsgericht Potsdam, HRB 12184 Geschäftsführung: Prof. Dr. Christoph Meinel _____________________________________ _______________________________________________ Bx mailing list Bx(a)inf.ed.ac.uk http://lists.inf.ed.ac.uk/mailman/listinfo/bx

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International Conference on Recent Theories and Applications in Transportation and Mobility - (RTATM 2021) Prague
by matteo＠confscience.com 20 Apr '21

20 Apr '21

Call for papers ************************************************* International Conference on Recent Theories and Applications in Transportation and Mobility - (RTATM 2021) Prague - Czech Republic, October 14-15, 2021 https://confscience.com/rtatm/ All papers accepted in RTATM 2021 will be published in Springer CCIS (Communications in Computer and Information Science). CCIS is abstracted/indexed in Scopus, SCImago, EI-Compendex, Mathematical Reviews, DBLP, Google Scholar, and Thomson Reuters Conference Proceedings Citation (Former ISI Proceedings) *************************************************************************** IMPORTANT DATES: - Paper Submission: April 20, 2021 (extended) - Acceptance Notification: July 1, 2021 - Final Manuscript Due: September 1, 2021 *************************************************************************** The RTATM 2021 conference will be held in Conjunction with: International Conference on Applied Data Science and Intelligence (ADSI 2021) International Conference on Informatics Revolution for Smarter Healthcare (IRSH 2021) *************************************************************************** TOPICS: Authors are invited to submit their original papers to address the topics of the conference, including but not limited to: FUNDAMENTALS AND THEORIES - Modelling and Simulation Algorithms - Vehicular Wireless Medium Access Control - V2X communications - Routings and Protocols for Connected Vehicles - Mobility Models and Architectures - Distribution Strategies - Traffic Incident Management Systems - Bio-Inspired Approaches - Optimization and Collaboration - Automatic Control in Vehicular Networks - Energy-aware Connected Mobility - Programming Languages - Sustainable Transportation - Multimodal Transportation Networks and Systems - Systemsb Integration - Driver Behavior Models and Simulation - Human Factors and Travel Behaviour - Green Mobility - Regulations and Bylaws for Intelligent - Transportation and Mobility SMART TRANSPORTATION AND LOGISTICS - Mobility Management - Connected Vehicles - VANETs - Predictive Logistics - Spatio-Temporal Event Tracking - Decision Support Systems - Emergency Management - Logistics and E-Commerce - Supply Chain Design and Execution - Supply Chain Management - Advanced Planning Systems - Fleet Management - Multi-Agent Systems - Machine Learning for Smart Logistics - Intelligent Infrastructures - Real-time Analysis of Comprehensive Supply Chain Data - Smart Synchronization of Logistics Processes - New Approaches for Cost Transparency - Big Data for Smart Logistics - Logistics 4.0 - Mobile Networks - Next-Generation Smart Logistics - Performance Management Approaches - Tests and Deployment - Software Defined Networks - Smart Freight Management - Smart Shipment Management - Smart Warehousing - Smart Inventory management DATA AND SERVICES - Real-Time transportation Data Acquisition - Event Detection and Monitoring - Data Warehouses for connected mobility - Data mining and Data analytics - Data Worthiness in Connected Vehicles - Data Trustworthiness for effective transportation and mobility - Road Traffic Data Analytics - Structured and Unstructured Data for Connected Mobility - Volunteered Geographic Information (VGI) - Data Representation for Connected Mobility - Transportation Data Mining - Transportation and mobility Data Visualization - Cognitive and Context-aware Intelligence - Transportation Decision Support Systems - Mobility as a Service (MaaS) - Intelligent Transportation Services - Smart Mobility Services - Big Data and Vehicle Analytics - Massive Data Management - Collective and connected Intelligence - Next Generation Services - Driver Behaviour Analysis - Geo-Spatial Services - Service-Oriented Architecture (SOA) - Web and Mobile Services SAFETY, SECURITY, AND HAZARD MANAGEMENT - Security Issues in Vehicular Communications - Safety Applications of Connected Vehicles - Weather-related Safety solutions - V2V, V2I and I2V Road Safety Applications - Connected Mobility for Hazard Management - Risk Management - Road Traffic Crashes Analytics - Traffic Jam Prediction - Resource Allocation for Hazard Management - Trust and Privacy Issues in Logistics - Management of Exceptional Events - New approaches to Networking Security for Transportation Applications - Failure modes, human factors, software safety - Automated Failure Analysis - Performance and Human Error Analysis - Design and Reliability of Control Systems - Dispersion Modelling Software - Quantification of Risk *************************************************************************** OUTSTANDING PAPERS: Based on the peer review scores as well as the presentations at the conference, the authors of outstanding papers will be invited to extend their works for a potential publication in journals special issues with high impact factors. *************************************************************************** PAPER SUBMISSION: Papers must be submitted electronically as PDF files via easychair (https://easychair.org/conferences/?conf=rtatm2021) All papers will be peer reviewed. Length of Full papers: 12-15 pages long (written in the LNCS/CCIS one-column page format, 400 words per page) Length of Short papers: less than 12 pages For more information, please refer to the conference website: https://confscience.com/rtatm/ *************************************************************************** CONTACT For more information, please send an email to info-rtatm(a)confscience.com

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Trick to have existential type work in this case?
by YueCompl 19 Apr '21

19 Apr '21

Dear Cafe, I believe there should exist some trick that I haven't learned, to have this compile: module PoC.Existential where import Data.Dynamic import qualified Data.Vector.Storable as VS import Foreign import Prelude -- * Necessary artifacts data Series a = Series { seriesLen :: IO Int, readSeries :: Int -> IO a } data SomeArray = forall a. (Typeable a, VS.Storable a) => SomeArray { arrayCap :: Int, arrayPtr :: ForeignPtr a } class ManagedArray t where arrayAtTheMoment :: t -> IO SomeArray data SomeManagedArray = forall t. (Typeable t, ManagedArray t) => SomeManagedArray t In following, I can confirm it works with the nested `do` block flattened (as shown later), but I really need it in the more complex real case, so please bear with me. -- * Things not working managedArrayAsSeries :: SomeManagedArray -> IO Dynamic managedArrayAsSeries (SomeManagedArray ma) = do vec <- do SomeArray cap fp <- arrayAtTheMoment ma return $ VS.unsafeFromForeignPtr0 fp cap let len = return $ VS.length vec rs i = return $ vec VS.! i return $ toDyn $ Series len rs The error: src/PoC/Existential.hs:36:5: error: • Couldn't match type ‘a’ with ‘a0’ ‘a’ is a rigid type variable bound by a pattern with constructor: SomeArray :: forall a. (Typeable a, Storable a) => Int -> ForeignPtr a -> SomeArray, in a pattern binding in a 'do' block at src/PoC/Existential.hs:35:5-20 Expected type: IO (VS.Vector a0) Actual type: IO (VS.Vector a) • In a stmt of a 'do' block: return $ VS.unsafeFromForeignPtr0 fp cap In a stmt of a 'do' block: vec <- do SomeArray cap fp <- arrayAtTheMoment ma return $ VS.unsafeFromForeignPtr0 fp cap In the expression: do vec <- do SomeArray cap fp <- arrayAtTheMoment ma return $ VS.unsafeFromForeignPtr0 fp cap let len = return $ VS.length vec rs i = return $ vec VS.! i return $ toDyn $ Series len rs • Relevant bindings include fp :: ForeignPtr a (bound at src/PoC/Existential.hs:35:19) | 36 | return $ VS.unsafeFromForeignPtr0 fp cap | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ While these more trivial things work as expected: -- * Things working managedArrayAsSeries' :: SomeManagedArray -> IO Dynamic managedArrayAsSeries' (SomeManagedArray ma) = do SomeArray cap fp <- arrayAtTheMoment ma let vec = VS.unsafeFromForeignPtr0 fp cap let len = return $ VS.length vec rs i = return $ vec VS.! i return $ toDyn $ Series len rs arrayAsSeries :: SomeArray -> Dynamic arrayAsSeries (SomeArray cap fp) = colAsSeries $ SomeColumn $ VS.unsafeFromForeignPtr0 fp cap arrayAsSeries' :: SomeArray -> Dynamic arrayAsSeries' (SomeArray cap fp) = do let vec = VS.unsafeFromForeignPtr0 fp cap len = return $ VS.length vec rs i = return $ vec VS.! i toDyn $ Series len rs data SomeColumn = forall a. (Typeable a, VS.Storable a) => SomeColumn (VS.Vector a) colAsSeries :: SomeColumn -> Dynamic colAsSeries (SomeColumn colVec) = toDyn $ Series len rs where len = return $ VS.length colVec rs i = return $ colVec VS.! i Please teach me the trick! Thanks with regards, Compl

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How to move files?
by ☂Josh Chia (謝任中) 16 Apr '21

16 Apr '21

I'm trying to write to a temp file in /tmp and then move it to another location that may be in /tmp. If I use System.Directory.renameFile and the final location is in another filesystem, I'll get an error "renameFile:renamePath:rename: unsupported operation (Invalid cross-device link)". If I copy to the new location and then remove the temp file, but the new location is also in /tmp, I am doing an unnecessary copy (instead of mv), which is inefficient. I don't know how to detect whether two filepaths are in the same filesystem. What's the best way to move the file if possible but copy-and-delete if necessary? Josh

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[ANN] wai-handler-hal-0.1.0.0 - Wrap a WAI Application to run on AWS Lambda
by Jack Kelly 15 Apr '21

15 Apr '21

I have just pushed an initial release of wai-handler-hal[1] to Hackage. This library lets you run `wai` `Application`s on AWS Lambda, using the proxy integration features of an API Gateway REST API. This allows you to write your APIs using tools like `servant`, test them locally using `warp`, and then build deployment binaries using `hal`. There's an especially nice payoff when you use `servant`: it's very easy to test the entire API locally using `warp`, but then split endpoints into individual Lambda binaries. This means you can assign minimal IAM policies to each Lambda when you deploy to AWS. The library code, an example API, example deployment code (in AWS CDK[2]), and extensive documentation are all available on GitHub[3]; bug reports and pull requests are welcome. Best, -- Jack [1]: https://hackage.haskell.org/package/wai-handler-hal-0.1.0.0 [2]: https://aws.amazon.com/cdk/ [3]: https://github.com/bellroy/wai-handler-hal

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Re: [Haskell-cafe] Haskell function composition commutivity?
by Dominic Steinitz 15 Apr '21

15 Apr '21

I’d recommend *not* reading Categories for the Working Mathematician unless you are a mathematician (lots of background assumed) and even then it’s a bit of a dull read. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.org Twitter: @idontgetoutmuch > From: Viktor Dukhovni <ietf-dane(a)dukhovni.org> > To: haskell-cafe(a)haskell.org > Subject: Re: [Haskell-cafe] Haskell function composition commutivity? > Message-ID: <YHYPMnJcYzdEolzl(a)straasha.imrryr.org> > Content-Type: text/plain; charset=us-ascii > > On Tue, Apr 13, 2021 at 02:19:46PM -0500, Galaxy Being wrote: > >> Your answers seem to originate outside of normal Haskell tutorials. Where >> can I start with this higher superset theory? > > There's a reason why the tutorials don't cover this, the categorical > foundations of Haskell types are not beginner material. It is perhaps > best to defer going down this rabbit hole until you're more comfortable > with the Haskell generally. > > You could start with: > > https://bartoszmilewski.com/2014/10/28/category-theory-for-programmers-the-… > https://bartoszmilewski.com/2015/04/07/natural-transformations/ > > For the Yoneda Lemma specifically, I'd recommend: > > http://blog.sigfpe.com/2006/11/yoneda-lemma.html > > Parametricity is covered in "Theorems for free": > > https://www2.cs.sfu.ca/CourseCentral/831/burton/Notes/July14/free.pdf > > but it is by no means elementary, though skimming it for the essential > facts and skipping the gory details is not too difficult. > > You could also read "Categories for the Working Mathematician" by > Saunders Mac Lane.

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