- Haskell-Cafe - Haskell.org

scotty: call for maintainers
by Ryan Scott 13 May '21

13 May '21

Hello, The scotty web framework [1] is looking for additional maintainers to help keep it a thriving project. The core functionality of scotty has been stable for a while, but there are a number of open issues [2] which concern the design of the framework. Although I have been keeping scotty compiling for a while (as I have code which transitively depends on it), I am not a web developer by trade, and as a result, I don't feel like I have the keenest sense for broad design changes. If you feel like you would be able to step up and fill this role, please let me know! Related issue: https://github.com/scotty-web/scotty/issues/274 [1] https://github.com/scotty-web/scotty [2] https://github.com/scotty-web/scotty/issues

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Second call for the *regular* round of Papers for the Haskell Symposium 2021
by Hage, J. (Jurriaan) 12 May '21

12 May '21

Dear all, First, some * BREAKING NEWS *: Jean-Philippe Bernardy has accepted the invitation to speak at the symposium. He will be talking about Linear Haskell. This is the second 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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[Ann] A new Haskell crypto lib: Z-Botan 0.1.1
by Dong Han 11 May '21

11 May '21

Dear Haskellers: After hundreds of days working. I'm happy to announce that the very first version of [Z-Botan](http://hackage.haskell.org/package/Z-Botan) is published, It's a new crypto lib built around the versatile [botan]( http://botan.randombit.net/) C++ crypto lib. Currently, all crypto stuff exported by Botan FFI is implemented, i.e.: * Random number generators. * Block Cipher and symmetric cipher. * Hash. * MAC. * Key derivation functions. * Password hash. * Constant time multiple precision integers. * Public key creation, import and export. * Public key encryption/decryption * Diffie-Hellman key exchange. * Signature generation & signature verification. * X.509 certificates & X.509 certificate revocation lists. * One time password. * AES Key Wrapping * Format Preserving Encryption. We will continue to polish this work, e.g. build TLS upon it. If you have any crypto usage, please give it a try. as usual, we wish you happy hacking! Cheers~ Dong 2021.05.11

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FMBC 2021 - Final Call for Papers (Deadline extension)
by Bruno Bernardo 10 May '21

10 May '21

[ Please distribute, apologies for multiple postings. ] ======================================================================== 3rd International Workshop on Formal Methods for Blockchains (FMBC) - Final Call https://fmbc.gitlab.io/2021 July 18 or 19 (TBA), 2021, *online* Co-located with the 33nd International Conference on Computer-Aided Verification (CAV 2021) http://i-cav.org/2021/ ------------------------------------------------------------- IMPORTANT DATES -------------------------------- Abstract submission: May 16, 2021 (extended) Paper submission: May 23, 2021 (extended) Notification: June 30, 2021 (extended) Camera-ready: July 14, 2021 (extended) Workshop: July 18 or 19 (TBA), 2021 Deadlines are Anywhere on Earth: https://en.wikipedia.org/wiki/Anywhere_on_Earth -------------------------------- -------------------------------- 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 page limit of 12 pages for full papers and 6 pages for short papers (excluding bibliography and short appendix of up to 5 additional pages). Alternatively you may also submit an extended abstract of up to 3 pages (including bibliography) summarizing your ongoing work in the area of formal methods and blockchain. Authors of selected extended-abstracts are invited to give a short lightning talk. Submission link: https://easychair.org/conferences/?conf=fmbc2021 Authors are encouraged to use LaTeX and prepare their submissions according to the instructions and styling guides for OASIcs provided by Dagstuhl. Instructions for authors: https://submission.dagstuhl.de/documentation/authors#oasics At least one author of an accepted paper is expected to present the paper at the workshop as a registered participant. -------------------------------- -------------------------------- 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, published as a volume of the OpenAccess Series in Informatics (OASIcs) by Dagstuhl. -------------------------------- -------------------------------- INVITED SPEAKER -------------------------------- David Dill, Lead Researcher, Blockchain, Novi/Facebook, USA https://research.fb.com/people/dill-david/ -------------------------------- -------------------------------- 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) * Joachim Breitner (Dfinity Foundation, Germany) * Achim Brucker (University of Exeter, UK) * Zaynah Dargaye (Nomadic Labs, France) * Jérémie Decouchant (TU Delft, Netherlands) * Dana Drachsler Cohen (Technion, Israel) * Ansgar Fehnker (University of Twente, Netherlands) * Maurice Herlihy (Brown University, USA) * Lars Hupel (INNOQ, Germany) * Florian Kammueller (Middlesex University London, UK) * Igor Konnov (Informal Systems, Austria) * Andreas Lochbihler (Digital Asset, Switzerland) * Simão Melo de Sousa (Universidade da Beira Interior, Portugal) * Karl Palmskog (KTH, Sweden) * Maria Potop-Butucaru (Sorbonne Université, France) * Andreas Rossberg (Dfinity Foundation, Germany) * Albert Rubio (Complutense University of Madrid, Spain) * César Sanchez (Imdea, Spain) * Clara Schneidewind (TU Wien, Austria) * Ilya Sergey (Yale-NUS College/NUS, Singapore) * Mark Staples (CSIRO Data61, Australia) * Meng Sun (Peking University, China) * Simon Thompson (University of Kent, UK) * Josef Widder (Informal Systems, Austria)

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ANN: stack-2.7.1
by Emanuel Borsboom 07 May '21

07 May '21

See https://haskellstack.org/ for installation and upgrade instructions. **Changes since v2.5.1.1:** Behavior changes: * `stack repl` now always warns about GHCi problems with loading multiple packages. It also sets now proper working directory when invoked with one package. See [#5421](https://github.com/commercialhaskell/stack/issues/5421) * `custom-setup` dependencies are now properly initialized for `stack dist`. This makes `explicit-setup-deps` no longer required and that option was removed. See [#4006](https://github.com/commercialhaskell/stack/issues/4006) Other enhancements: * Nix integration now passes `ghcVersion` (in addition to existing `ghc`) to `shell-file` as an identifier that can be looked up in a compiler attribute set. * Nix integration now allows Nix integration if the user is ready in nix-shell. This gets rid of "In Nix shell but reExecL is False" error. * `stack list` is a new command to list package versions in a snapshot. See [#5431](https://github.com/commercialhaskell/stack/pull/5431) * Consider GHC 9.0 a tested compiler and remove warnings. * `custom-preprocessor-extensions` is a new configuration option for allowing stack to be aware of any custom preprocessors you have added to `Setup.hs`. See [#3491](https://github.com/commercialhaskell/stack/issues/3491) * Added `--candidate` flag to `upload` command to upload a package candidate rather than publishing the package. * Error output using `--no-interleaved-output` no longer prepends indentating whitespace. This allows emacs compilation-mode and vim quickfix to locate and track errors. See [#5523](https://github.com/commercialhaskell/stack/pull/5523) Bug fixes: * `stack new` now suppports branches other than `master` as default for GitHub repositories. See [#5422](https://github.com/commercialhaskell/stack/issues/5422) * Ignore all errors from `hi-file-parser`. See [#5445](https://github.com/commercialhaskell/stack/issues/5445) and [#5486](https://github.com/commercialhaskell/stack/issues/5486). * Support basic auth in package-indices. See [#5509](https://github.com/commercialhaskell/stack/issues/5509). * Add support for parsing `.hi`. files from GHC 8.10 and 9.0. See [hi-file-parser#2](https://github.com/commercialhaskell/hi-file-parser/pull/…. **Thanks to all our contributors for this release:** * Aaron Allen * Alexey Kuleshevich * Andreas Källberg * Domen Kožar * Emanuel Borsboom * Felix Yan * Jens Petersen * Kirill Zaborsky * Marcin Tolysz * Matt Audesse * Matthew Wraith * Michael Snoyman * Mike Pilgrem * Simon Michael

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Re: [Haskell-cafe] (Online) Utrecht Summer School on Advanced functional programming
by Olaf Klinke 07 May '21

07 May '21

> The lectures will cover several more advanced topics regarding > programming with types in Haskell, including topics such as: > > * monads and applicative functors; > * lambda calculus; > * generalized algebraic datatypes; > * datatype generic programming > * type families and type-level programming; Even if the schedule is yet to be finalized, a definitive list of topics covered would be nice. Thanks, Olaf

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wai-middleware-validation
by Kenzo Yotsuya 07 May '21

07 May '21

Dear Haskell-Cafe, I've uploaded a new package named wai-middleware-validation to Hackage. This is a WAI middleware to automate the validation of request and response bodies according to the schema defined in OpenAPI. I hope Web API developers using OpenAPI will give it a try. https://hackage.haskell.org/package/wai-middleware-validation https://iij-ii.github.io/wai-middleware-validation/ Thanks, Kenzo Yotsuya

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Repeating type variables in MultiParamTypeClasses instance heads
by Leif-Erik Krüger 07 May '21

07 May '21

Hello Haskell-Cafe, I have a question regarding the rules on type class instances with the MultiParamTypeClasses extension. For single-parameter type classes, there is the restriction that an instance head must have the form `C (T a1 ... an)`, where `C` is a type class, `T` is a data type constructor and `a1 ... an` are distinct type variables ( https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/instances.html ). To my knowledge, this restriction ensures the impossibility of potential overlap between instances (except for the case where two instance heads are equivalent, but this case is caught by an error message). This restriction can be lifted with the FlexibleInstances extension, so that instances like `instance C (a, a, b)` and `instance C (a, b, b)` are allowed. As can be seen in this example, FlexibleInstances introduces the potential of overlap with single-parameter type classes. When using MultiParamTypeClasses without FlexibleInstances, the current restrictions on instance heads are similiar to those for single-parameter classes. For each parameter, the instance type must have the form `(T a1 ... an)` with `a1 ... an` being distinct from one another, but type variables can be shared between instance types. Therefore, instances like `instance D [a] [a] [b]` and `instance D [a] [b] [b]` are allowed and do cause potential overlap. If there was the restriction of all type variables in the instance head being different from one another however, I think there would be no potential for overlap, just like with single-parameter type classes. To me, these instances allowed by MultiParamTypeClasses seem similar to the single-parameter class instances that are only possible with FlexibleInstances. And just like FlexibleInstances for single-parameter class instances, they introduce potential overlap, so that the MultiParamTypeClasses extension by itself becomes less "safe" than it otherwise would be. Therefore, it seems reasonable to me to only allow these repeated type variables in instance heads with the FlexibleInstances extension. So, is there a good reason for the design choice of allowing these kinds of overlap without FlexibleInstances? Am I missing something here? Or are the current rules the way they are because of historic reasons? Best regards, Leif-Erik Krüger

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bootstrapping a monad via continuations
by Olaf Klinke 06 May '21

06 May '21

Dear Café, I've been scratching my head over a monad instance. I wonder whether there is a deeper theory behind this. Suppose you have a functor T and you happen to find a special type r such that there is a natural embedding into the continuation monad Cont r. More precisely, if there are natural transformations trans :: forall x. T x -> Cont r x trans' :: forall x. Cont r x -> T x with trans' . trans = id and trans . trans' . return = return trans . trans' . (=<<) (trans . f) = (=<<) (trans . f) then you can define monad operations for T so that trans becomes a monad morphism. Once that T is a monad, one can invoke a theorem from a 1970 paper by Anders Kock and obtain Eilenberg-Moore T-algebra structure on r, and the entire monad structure of T can be recovered from this single T-algebra. Examples of this scheme in the mathematical literature are the Riesz representation theorem, which identifies measures on X with a subset of the space of real functionals (X -> R) -> R. Ultimately, the monad structure of the functor of measures is encoded in the operation that sends a measure on R to its mean. Anders Kock's theorem says: (1) There is a bijecitive correspondence between natural transformations T -> Cont r and functions T r -> r. (2) In particular if T is a monad, (1) restricts to a bijection between monad morphisms and Eilenberg-Moore algebra structures. (Incidentally, this is what underlies the continuation monad transformer: Apply to the structure join :: m (m r) -> m r.) It thus seems that my observation is a kind of converse to part (2), namely if a function T r -> r is an Eilenberg-Moore algebra structure, then T is a monad. The preceding sentence is self-referential though, because the property of being an Eilenberg-Moore algebra depends on monad structure already present. As usual I suspect the answer in one of Edward Kmett's packages, but my Category-Fu is not strong enough to identify the matching concept. Olaf

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Safe Haskell?
by Richard Eisenberg 04 May '21

04 May '21

Hi café, Do you use Safe Haskell? Do you know someone who does? If you do, which of Safe Haskell's guarantees do you rely on? Here, a user of Safe Haskell is someone who relies on any guarantees that Safe Haskell provides, not someone who makes sure to have the right pragmas, etc., in your library so that users can import it Safely. Context: Safe Haskell is not lightweight to support within GHC and the ecosystem. Despite being a formidable research project with a (in my opinion) quite worthwhile goal, it's unclear which of Safe Haskell's purported guarantees are actually guaranteed by GHC. (The lack of unsafeCoerce is not actually guaranteed: https://gitlab.haskell.org/ghc/ghc/-/issues/9562 <https://gitlab.haskell.org/ghc/ghc/-/issues/9562>.) Recent design questions about what should be Safe and what shouldn't be (somehow cannot find the discussion after a few minutes of searching; perhaps fill this in) have been answered only by stabs in the dark. The status quo is causing pain: https://gitlab.haskell.org/ghc/ghc/-/issues/19590 <https://gitlab.haskell.org/ghc/ghc/-/issues/19590>. There are hundreds (maybe thousands) of lines of delicate logic within GHC to support Safe Haskell. These parts of GHC have to be read, understood, and maintained by people with limited time. I thus wonder about deprecating and eventually removing Safe Haskell. I don't have a concrete plan for how to do this yet, but I'm confident we could come up with a migration strategy. The set of people who would win by removing Safe Haskell is easy enough to discover. But this email is intended to discover who would be harmed by doing so. If you know, speak up. Otherwise, I expect I will write up a GHC proposal to remove the feature. Thanks, Richard

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