April 2020 - Haskell-Cafe

Where is Show for GHC AST?
by Daneel Yaitskov 22 Apr '20

22 Apr '20

Hi, I am trying to modify LiquidHaskell and want to see how source code is represented in AST format. I think I have AST i.e. HsExpr value, but there is no Show instance for that. I noticed that GHC classes implement similar class Outputable, but it doesn't do what I expected. It just reconstruct AST back to source code. I could probably write a TH function generating Show instances for all types which HsExpr depends on, but I hope there is more straight forward way to do that. And after all I curious what is the reason for not having Show for GHC AST types? It would be so convenient having Show. -- Daneel S. Yaitskov Java Developer

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Re: [Haskell-cafe] Where is Show for GHC AST?
by Michal J Gajda 22 Apr '20

22 Apr '20

Hi Daneel, Did you check the `Outputable` class? http://hackage.haskell.org/package/ghc-8.6.5/docs/Outputable.html#t:Outputa… -- Cheers Michał

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FMBC 2020: 2nd Workshop on Formal Methods for Blockchains (CfP, Deadline Extension)
by Bruno Bernardo 21 Apr '20

21 Apr '20

[ Please distribute, apologies for multiple postings. ] ======================================================================== 2nd Workshop on Formal Methods for Blockchains (FMBC) 2020 - Second Call https://fmbc.gitlab.io/2020 July 19, 2020, Los Angeles, USA Co-located with the 32nd International Conference on Computer-Aided Verification (CAV 2020) http://i-cav.org/2020/ ------------------------------------------------------------- IMPORTANT DATES -------------------------------- Abstract submission: May 5, 2020 (extended) Full paper submission: May 12, 2020 (extended) Notification: June 16, 2020 (extended) Camera-ready: July 7, 2020 Conference: July 19, 2020 -------------------------------- -------------------------------- TOPICS OF INTEREST -------------------------------- Blockchains are decentralized transactional ledgers that rely on cryptographic hash functions for guaranteeing the integrity of the stored data. Participants on the network reach agreement on what valid transactions are through consensus algorithms. Blockchains may also provide support for Smart Contracts. Smart Contracts are scripts of an ad-hoc programming language that are stored in the Blockchain and that run on the network. They can interact with the ledger’s data and update its state. These scripts can express the logic of possibly complex contracts between users of the Blockchain. Thus, Smart Contracts can facilitate the economic activity of Blockchain participants. With the emergence and increasing popularity of cryptocurrencies such as Bitcoin and Ethereum, it is now of utmost importance to have strong guarantees of the behavior of Blockchain software. These guarantees can be brought by using Formal Methods. Indeed, Blockchain software encompasses many topics of computer science where using Formal Methods techniques and tools are relevant: consensus algorithms to ensure the liveness and the security of the data on the chain, programming languages specifically designed to write Smart Contracts, cryptographic protocols, such as zero-knowledge proofs, used to ensure privacy, etc. This workshop is a forum to identify theoretical and practical approaches of formal methods for Blockchain technology. Topics include, but are not limited to: * Formal models of Blockchain applications or concepts * Formal methods for consensus protocols * Formal methods for Blockchain-specific cryptographic primitives or protocols * Design and implementation of Smart Contract languages * Verification of Smart Contracts -------------------------------- -------------------------------- SUBMISSION -------------------------------- Submit original manuscripts (not published or considered elsewhere) with a maximum of twelve pages (full papers), six pages (short papers), and two pages (extended abstract) describing new and emerging ideas or summarizing existing work). Each paper should include a title and the name and affiliation of each author. Authors of selected extended-abstracts are invited to give a short lightning talk. At least one author of an accepted paper is expected to present the paper at the workshop as a registered participant. Submission link: https://easychair.org/conferences/?conf=fmbc2020 The authors are encouraged to use LaTeX and the EasyChair style files: https://easychair.org/publications/for_authors -------------------------------- -------------------------------- PROCEEDINGS -------------------------------- All submissions will be peer-reviewed by at least three members of the program committee for quality and relevance. Accepted regular papers (full and short papers) will be included in the workshop proceedings. -------------------------------- -------------------------------- INVITED SPEAKER -------------------------------- Grigore Rosu, Professor at University of Illinois at Urbana-Champaign, USA and Founder of Runtime Verification http://fsl.cs.illinois.edu/index.php/Grigore_Rosu https://runtimeverification.com/ -------------------------------- -------------------------------- PROGRAM COMMITTEE -------------------------------- PC CO-CHAIRS * Bruno Bernardo (Nomadic Labs, France) (bruno(a)nomadic-labs.com) * Diego Marmsoler (University of Exeter, UK) (D.Marmsoler(a)exeter.ac.uk) PC MEMBERS * Wolfgang Ahrendt (Chalmers University of Technology, Sweden) * Lacramioara Astefanoei (Nomadic Labs, France) * Massimo Bartoletti (University of Cagliari, Italy) * Bernhard Beckert (Karlsruhe Institute of Technology, Germany) * Achim Brucker (University of Exeter, UK) * Silvia Crafa (Universita di Padova, Italy) * Zaynah Dargaye (Nomadic Labs, France) * Jérémie Decouchant (University of Luxembourg, Luxembourg) * Ansgar Fehnker (University of Twente, Netherlands) * Georges Gonthier (Inria, France) * Florian Kammueller (Middlesex University London, UK) * Maurice Herlihy (Brown University, USA) * Igor Konnov (Informal, Austria) * Andreas Lochbihler (Digital Asset, Switzerland) * Anastasia Mavridou (NASA Ames, USA) * Simão Melo de Sousa (Universidade da Beira Interior, Portugal) * Andrew Miller (University of Illinois at Urbana-Champaign, USA) * Karl Palmskog (KTH, Sweden) * Vincent Rahli (University of Birmingham, UK) * Andreas Rossberg (Dfinity Foundation, Germany) * Claudio Russo (Dfinity Foundation, USA) * César Sanchez (Imdea, Spain) * Clara Schneidewind (TU Wien, Austria) * Ilya Sergey (Yale-NUS College/NUS, Singapore) * Bas Spitters (Aarhus University/Concordium, Denmark) * Mark Staples (CSIRO Data61, Australia) * Meng Sun (Peking University, China) * Simon Thompson (University of Kent, UK) * Philip Wadler (University of Edinburgh / IOHK, UK)

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[ANN] Haskell Beginners WT.Social Community: "Haskell: The Haskell-Beginners Community"
by Benjamin L. Russell 18 Apr '20

18 Apr '20

Twenty-eight days ago (on March 23, 2020 JST), I created a new Haskell beginners WT.Social community, "Haskell: The Haskell-Beginners Community" (see https://pashpost.com/group/haskell-the-haskell-beginners-community) and migrated a substantial portion of the posts originally from my former corresponding pashPOST (since renamed to "theTUNDRA") community of the same name thereto (sansposts with missing links or irrelevant content). Feel free to join and contribute! -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Computer Science Document Translator/Editor "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

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GHC Dockerimage
by Alexander Ben Nasrallah 18 Apr '20

18 Apr '20

Hi fellow Haskellers, since I was missing a Dockerimage for GHC built with musl and integer-simple for static linking, which is kept up to date, I created my own. I use it to test compatibility with different GHC versions and provide a full statically linked binary for download with GitLab CI/CD. Maybe someone will find it useful, too. Or maybe there already is another more sophisticated project someone can point me to. https://registry.hub.docker.com/r/neosimsim/ghc

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Attoparsec: match many, skipping rest
by amindfv＠gmail.com 17 Apr '20

17 Apr '20

Say I've got an Attoparsec parser like: p = string "prio:" *> digit And some text, e.g. s = "this is just a prio:5 example, I'd prio:6 very much like to prio:4 parse" What's the most idiomatic way to apply p to s so that I get out a list ['5', '6', '4']? Thanks, Tom

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streaming package: How to demux a stream properly?
by ☂Josh Chia (謝任中) 15 Apr '20

15 Apr '20

I have a streaming package question. Suppose I have a: Stream (Of (Int, a)) m () I would like to demultiplex it into Vector (Stream (Of a) m ()) using the Int as the index of an item into the Vector of output streams. How can I do this efficiently (constant memory and linear time)? Does the following work? import qualified Streaming.Prelude as SP import qualified Data.Vector as V type StreamOf a m r = Stream (Of a) m r demuxStream :: forall a m. MonadIO m => Int -> StreamOf (Int, a) m () -> m (Vector (StreamOf a m ())) demuxStream numSyms stream = let emptyStreams = V.replicate numSyms (pure ()) processItem v (iD, x) = V.modify (\vm -> VM.modify vm (>> SP.yield x) iD) v in SP.fold_ processItem emptyStreams id stream My guess is that it takes more than constant memory as it goes through the entire input stream before returning. Josh

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Haskell Symposium 2020 -- Call for Papers: Regular track & demos
by Tom Schrijvers 14 Apr '20

14 Apr '20

================================================================================ ACM SIGPLAN CALL FOR SUBMISSIONS Haskell Symposium 2020 New Jersey, United States 27--28 August, 2020 http://www.haskell.org/haskell-symposium/2020/ ================================================================================ The ACM SIGPLAN Haskell Symposium 2020 will be co-located with the 2020 International Conference on Functional Programming (ICFP). Like last 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 2020 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: 20 March 2020 (Fri) Notification: 24 April 2020 (Fri) Regular track and demos: Submission deadline: 15 May 2020 (Fri) Notification: 26 June 2020 (Fri) 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://haskell20.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. 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 permssion-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 ================= Arthur Azevedo de Amorim Carnegie Mellon University Manuel Chakravarty Tweag I/O / IOHK Jan Christiansen Flensburg University of Applied Sciences Youyou Cong Tokyo Institute of Technology Pierre-Evariste Dagand CNRS Anton Ekblad Chalmers University of Technology Jurriaan Hage Universiteit Utrecht Graham Hutton University of Nottingham José Pedro Magalhães Standard Chartered Clare Martin Oxford Brookes University Andrey Mokhov Jane Street Shin-Cheng Mu Academia Sinica Nikolaos Papaspyrou National Technical University of Athens Simon Peyton Jones Microsoft Research Cambridge Norman Ramsey Tufts University Exequiel Rivas INRIA Tom Schrijvers (chair) KU Leuven Martin Sulzmann Karlsruhe University of Applied Sciences If you have questions, please contact the chair at: tom.schrijvers(a)kuleuven.be ================================================================================

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Re: [Haskell-cafe] Eff verbose/ambiguous/type safety
by Anthony Clayden 13 Apr '20

13 Apr '20

Hi Daneel, welcome > Recently I discovered for my self an alternative for monad > transformers - extensible effects. > > http://okmij.org/ftp/Haskell/extensible/ > So straight away a word of warning: the 'ok' there is Oleg Kiselyov, who has produced many wonderful demonstrations of the power of Haskell's type system. (HList is anoher inspiration.) Many would say he has warped the type system beyond what it could reasonably be expected to achieve. So we measure the brain power needed to understand type signatures and messages in milli-Olegs. > Overall it is really cool and Eff1.hs started working right away, > but I noticed a problem with mixing several effects in 1 function. > Type checker requires pretty verbose type signature, which looks > unreasonable plus the error reported to a beginner developer > is not intuitive. Extensible effects/all of Oleg's work is not aimed at beginners. I advise beginners to stay well clear. You can expect enormous, inscrutable type errors. I agree with Georgi you should give type signatures everywhere you can. And your code should be used only by type experts. AntC

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Eff verbose/ambiguous/type safety
by Daneel Yaitskov 13 Apr '20

13 Apr '20

Hello Group, Recently I discovered for my self an alternative for monad transformers - extensible effects. http://okmij.org/ftp/Haskell/extensible/ Overall it is really cool and Eff1.hs started working right away, but I noticed a problem with mixing several effects in 1 function. Type checker requires pretty verbose type signature, which looks unreasonable plus the error reported to a beginner developer is not intuitive. So my questions are: - why it happens? - what could I do to get more friendly error message? - is there a workaround enforcing GHC make an extra mile and work without these "extra hints"? - any more maintainable Eff implementations? Here it an example I wish should working. $ stack gchi Eff1.hs *Eff1 > doLift = lift (putStrLn "EFF!") *Eff1 > doWrite = tell "HELLO" *Eff1 > doLiftAndWrite = doLift >> doWrite *Eff1 > runLift (runWriter doLiftAndWrite) <interactive>:82:20: error: * Couldn't match type `Writer [Char]' with `Lift IO' arising from a use of `doLiftAndWrite' * In the first argument of `runWriter', namely `doLiftAndWrite' In the first argument of `runLift', namely `(runWriter doLiftAndWrite)' In the expression: runLift (runWriter doLiftAndWrite) The error message looks unclear, because documentation makes me think that Writer and Lift are members of same Eff monad and they are composable and doLiftAndWrite has been evaluated successfully. And my workaround: *Eff1 > runLift $ do { x :: ((), [String]) <- runWriter doLiftAndWrite; return x; } EFF! ((),["HELLO"]) Plus GHCi swallows a type error: *Eff1 > badCast = do { x :: ((), [Int]) <- runWriter doLiftAndWrite; return x; } *Eff1 > :t badCast badCast :: (MemberU2 Lift (Lift IO) r, OpenUnion52.FindElem (Writer [Char]) r) => Eff r ((), [Int]) Definitely Extensible Effects are more flexible that MTL, but compile type safety looks jeopardized. Type verbosity overhead is kind of acceptable, but having possibility of run-time errors is too big price for flexibility. -- Daneel S. Yaitskov

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