- Haskell-Cafe - Haskell.org

Promoted data types
by coot＠coot.me 03 May '21

03 May '21

Hello, Currently with `DataKind` extension, Haskell allows to promote terms / types to types / kinds. Currently, one cannot write: ``` data K a where K0 :: forall (x :: a). x -> K a ``` Because `K0` is both a term and a type constructor, and as a term and one cannot represent `x` of kind `a`. Is there a proposal or an issue to allow such declaration and error at use sites of `K0` as a term, rather than at declaration site? Best regards, Marcin Szamotulski

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[Announcement] ZuriHac 2021 (18-20 June) - Registration now open
by Jasper Van der Jeugt 02 May '21

02 May '21

Hey Haskell friends, We are happy to announce that you can now register for ZuriHac 2021. It will take place from Friday 18th to Sunday 20th of June. Like last year, we are holding the event online. While we are sad that we don't yet get to see each other in person, this also allowed ~1000 people to join in 2021, instead of the usual 400-500 in Zurich. We have a couple of exciting things lined up for you this year. Here is a peek preview, but you can always check out https://zurihac.com for up-to-date information. This year, we are honoured to have talks by: - Emily Pillmore - Gabriele Keller - John Hughes - Veronika Romashkina And we have a couple of tutorials and teaching tracks in the works, as well as one more talk. We put a special focus on covering the whole beginner, intermediate, advanced spectrum: - There will be an advanced track held by our friends at Well-Typed. - digitally induced will teach you IHP, a new batteries-included web framework that has been gaining a lot of traction. Check it out at https://ihp.digitallyinduced.com/. - There will be a workshop on Unison, an exciting programming language that shares a lot of Haskell's syntax and semantics. Have a look at https://unisonweb.org/. We are working on more talks and tutorials, so expect further details to be communicated in the coming weeks. Keep an eye on our website! Apart from this, there will be the usual stuff that makes ZuriHac so much fun. There will be projects to hack on with other people, and the possibility to bring your own. There will be plenty of socialising, some impromptu hallway tracks, friendly fellow Haskellers to help you out, and an overall welcoming vibe. A quick note on how the online event works: - The main hub for the event will be on our Discord server. It worked really well for us last year, since it provided a sense of togetherness. It's easy to use, and it has chats, voice, and video. You will get a link when you register. - The talks will be streamed (and recorded) on YouTube. Q&A will be held on Discord. Check out last year's excellent talks: https://youtube.com/playlist?list=PLiU7KJ5_df6aZbNfh_TUJt-6w9N3rYkTX Registration is free and open as of right now: https://zureg.zfoh.ch/register/ Looking forward to seeing you in June! The Zurich Friends of Haskell - https://zfoh.ch

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Free online intro/advanced Haskell courses [YouTube]
by Graham Hutton 01 May '21

01 May '21

Hi all, For the last few months, I've been preparing YouTube videos for the introductory and advanced Haskell courses that I teach to students at the University of Nottingham. The courses have now finished, and the full sets of videos are now available: Intro course: http://www.tinyurl.com/haskell-notts Advanced course: http://www.tinyurl.com/haskell-notts2 There’s also a 25% discount for the textbook on which both of the courses are based, Programming in Haskell: Discount link: http://tinyurl.com/25pct-off Best wishes, Graham — Professor Graham Hutton School of Computer Science University of Nottingham, UK http://www.cs.nott.ac.uk/~pszgmh This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please contact the sender and delete the email and attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. Email communications with the University of Nottingham may be monitored where permitted by law.

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ANN: second release candidate for stack-2.7
by Emanuel Borsboom 30 Apr '21

30 Apr '21

You can download binaries for this pre-release from https://github.com/commercialhaskell/stack/releases/tag/rc%2Fv2.7.0.3 Please test it and let us know if you run into any trouble. If all goes well, we expect to release the final version in X weeks. Release notes: * Stack's bindists are now built with GHC 8.10.4, and our `stack.yaml` has moved to lts-17.10. This means Stack can now be built on macOS 11.0 (Big Sur) without ugly workarounds. GHC 8.8 is now the minimum GHC version supported for building Stack itself (but this does not effect _users_ of Stack, which still supports using much older GHC versions). **Changes since v2.7.0.1:** (no changes)

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[ANNOUNCE] Experimental Windows GHC 8.10.5 binary release. Supports Haskell DLLs.
by kyra 29 Apr '21

29 Apr '21

An experimental Windows GHC 8.10.5 64-bit Visual C/Native Windows SDK binary compatible distribution is released. Features: Supports Haskell DLLs. Both static and dynamic compilers are shipped. Uses LLVM tools exclusively, hence linking is blazing fast compared to the stock distro. Is position-independent (can be loaded to any address, not only the lower 2GBs) and generates position-independent code. Based on and targets Microsoft Visual C runtime and native Windows SDK. The "full" variant of distro contains 438 extra prebuilt packages and a set utilities, including not only the mandatory cabal, stack, Happy and Alex, but also linters, formatters, preprocessors, and even beasts like pandoc, haskell-language-server and even Agda compiler. Distribution site: https://awson.github.io/ghc-nw/. Cheers, K. Briantsev (aka awson)

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Munich Virtual Haskell Meeting, 2021-04-29 @ 19:30
by Leah Neukirchen 28 Apr '21

28 Apr '21

Dear all, This week, our monthly Munich Haskell Meeting will take place again tomorrow(!) Thursday, April 29 on Google Meet at 19:30 CEST. **Due to meetup limitations in Bavaria, this meeting will take place online!** For details see here: https://muenchen.haskell.bayern/dates.html A Google Meet link to join the room is provided on the page. Everybody is welcome, especially the Haskellers from Bavaria that do not usually come to our Munich meetings due to travel distance! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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Template Haskell question
by Kai-Oliver Prott 28 Apr '21

28 Apr '21

Dear Cafe, what is the reasoning behind the behavior of the following two Haskell expressions: ghci> :set -XTemplateHaskell ghci> let f x ($([p| x |])) = x in f 1 2 2 ghci> let f ($([p| x |])) x = x in f 1 2 2 I'd have guessed that they should both fail compilation with "Conflicting definitions for ‘x’" like the following expression. ghci> let f x x = x in f 1 2 error: ... Moreover, it seems odd that the "x" on the right side always refers to the rightmost pattern variable "x" (regardless if quoted or not). Cheers, Kai

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Haskell translation and transformation
by Dušan Kolář 27 Apr '21

27 Apr '21

Dear Café, I've tried to make my code more compact and faster in runtime and I tried to use primitive types, e.g. Int#. To omit all influences, I ended with Ackermann function: acker :: Int# -> Int# -> Int# acker 0# n = n +# 1# acker m 0# = acker (m -# 1#) 1# acker m n = acker (m -# 1#) (acker m (n -# 1#)) I was quite surprised, that the result was the same as for function without primitive types when it was compiled with -XStrict option. Both memory and time consumption was the same (small difference under 0.5%). Of course, -O2 option was used. :-) I compared with the same C implementation: int acker(int m, int n) { if (m==0) return n+1; if (n==0) return acker(m-1, 1); return acker(m-1, acker(m,n-1)); } with -O2 option used for gcc, the C code is 7 times faster, for no -O options provided both for ghc and gcc, the C code is also 7 times faster. Thus, no difference. My question is: does the ghc use primitive types automatically when possible? Otherwise, I cannot explain the same times... Or, to my big surprise, using primitives does not save memory and computation time, really? And the other question is about reasoning during translation and code generation, what is the reason the code is so slow? I would guess that forcing primitive types and strict evaluation would produce a code with comparable time to C code... The difference seems to be like the one between compiled code to executable and to low level virtual machine code, which is interpreted then. Versions I used: ghc: 8.10.3 gcc: 10.2.0 Dušan P.S. I definitely don't want to make someone upset with the content, I'm simply wondering... D.

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FMBC 2021 - 3rd Call for Papers (Deadline extensions)
by Bruno Bernardo 27 Apr '21

27 Apr '21

[ Please distribute, apologies for multiple postings. ] ======================================================================== 3rd International Workshop on Formal Methods for Blockchains (FMBC) - Third 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 6, 2021 (extended) Paper submission: May 13, 2021 (extended) Notification: June 24, 2021 (extended) Camera-ready: July 8, 2021 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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Re: [Haskell-cafe] [Haskell] [ANNOUNCE] GHC 9.2.1-alpha2 released
by Henning Thielemann 26 Apr '21

26 Apr '21

On Thu, 22 Apr 2021, Ben Gamari wrote: > The GHC developers are very happy to announce the availability of the > second alpha release in the 9.2.1 series. Binary distributions, source > distributions, and documentation are available at > > https://downloads.haskell.org/ghc/9.2.1-alpha2 When I try a GHC installed from the Debian tarball I get a permission error on the package.cache because of $ ll /usr/local/ghc-9.2.0.20210422/lib/ghc-9.2.0.20210422/package.conf.d/package.cache -rw------- 1 root root 188641 23. Apr 16:56 /usr/local/ghc-9.2.0.20210422/lib/ghc-9.2.0.20210422/package.conf.d/package.cache I can solve the problem with $ sudo chmod a+r /usr/local/ghc-9.2.0.20210422/lib/ghc-9.2.0.20210422/package.conf.d/package.cache

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