December 2019 - Haskell-Cafe

Request for Nominations to the GHC Steering Committee
by Joachim Breitner 11 Dec '19

11 Dec '19

Dear Haskell community, the GHC Steering committee is seeking nominations for one new member. The committee scrutinizes, nitpicks, improves, weights and eventually accepts or rejects proposals that extend or change the language supported by GHC and other (public-facing) aspects of GHC. Our processes are described at https://github.com/ghc-proposals/ghc-proposals which is also the GitHub repository where proposals are proposed. We are looking for a member who has the ability * to understand such language extension proposals, * to find holes and missing corner cases in the specifications, * foresee the interaction with other language features and specifications, * comment constructively and improve the proposals, * judge the cost/benefit ratio and * finally come to a justifiable conclusion. We look for committee members who have some of these properties: * have substantial experience in writing Haskell applications or libraries, which they can use to inform judgements about the utility or otherwise of proposed features, * have made active contributions to the Haskell community, for some time, * have expertise in language design and implementation, in either Haskell or related languages, which they can share with us. The committee’s work requires a small, but non-trivial amount of time, especially when you are assigned a proposal for shepherding. We estimate the workload to be around 2 hours per week, and our process works best if members usually respond to technical emails within 1-2 weeks (within days is even better). Please keep that in mind if your email inbox is already overflowing. The GHC developers themselves are already well represented already. We seek Haskell _users_ more than GHC hackers. There is no shortage of people who are eager to get fancy new features into the language, both in the committee and the wider community. But each new feature imposes a cost, to implement, to learn, (particularly) through its unexpected interaction with other features. We need to strike a balance, one that encourages innovation (as GHC always has) while still making Haskell attractive for real-world production use and for teaching. We therefore explicitly invite “conservative” members of the community to join the committee. To make a nomination, please send an email to me (as the committee secretary) at mail(a)joachim-breitner.de until January 2nd. I will distribute the nominations among the committee, and we will keep the nominations and our deliberations private. We explicitly encourage self-nominations. You can nominate others, but please obtain their explicit consent to do so. (We don’t want to choose someone who turns out to be unable to serve.) On behalf of the committee, Joachim Breitner -- Joachim Breitner mail(a)joachim-breitner.de http://www.joachim-breitner.de/

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Call for Haskell.org Committee Nominations
by Jasper Van der Jeugt 08 Dec '19

08 Dec '19

Dear Haskellers, It is time to put out a call for new nominations (typically but not necessarily self-nominations) to the Haskell.org committee. We have three members of our committee due for retirement -- Jasper Van der Jeugt, Niki Vazou, and Mitsutoshi Aoe. To nominate yourself, please send an email to committee at haskell.org by the 7th of January, 2020. The retiring members are eligible to re-nominate themselves. Please feel free to include any information about yourself that you think will help us to make a decision. The Haskell.org committee serves as a board of directors for Haskell.org, a 501(c)3 nonprofit which oversees technical and financial resources related to Haskell community infrastructure. Being a member of the committee does not necessarily require a significant amount of time, but committee members should aim to be responsive during discussions when the committee is called upon to make a decision. Strong leadership, communication, and judgement are very important characteristics for committee members. The role is about setting policy, providing direction/guidance for Haskell.org infrastructure, planning for the long term, and being fiscally responsible with the Haskell.org funds (and donations). As overseers for policy regarding the open source side of Haskell, committee members must also be able to set aside personal or business related bias and make decisions with the good of the open source Haskell community in mind. We seek a broad representation from different segments of the Haskell world -- including but not limited to those focused on education, those focused on industrial applications, those with background in organizing users-groups, and those focused directly on our technical infrastructure. More details about the committee's roles and responsibilities are on https://wiki.haskell.org/Haskell.org_committee If you have any questions about the process, please feel free to e-mail us at committee at haskell.org, or contact one of us individually. Warm regards, Jasper Van der Jeugt

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ZuriHac 2020 (12-14 June) registration is now open
by Jasper Van der Jeugt 06 Dec '19

06 Dec '19

Hi Haskell friends! We are happy to announce that ZuriHac 2020 will take place from Friday the 12th to Sunday the 14th of June, hosted again at the HSR (https://www.hsr.ch/) on the shores of beautiful Lake Zurich. You can find all the information on: https://zurihac.com The Zurich Haskell Hackathon is a free, international, grassroots, and collaborative coding festival. Our goal is to nourish the Haskell community, learn exciting new things, and to have fun working on projects together. This year, we are already excited to announce talks by: - Alexis King - Rob Rix More speakers will be announced later. In addition to talks, we will offer beginner, intermediate, and advanced tracks, similar to last year. The details of this will also be communicated in the coming months. The event is open to any experience level, from beginners to gurus. If you are completely new to Haskell, rest assured that there will be tutorials for you to take, and a bunch of friendly advanced Haskellers to answer your questions and help you along. We will have space for 500 attendees, making this the largest Haskell gathering that we know of! Registration is free and open as of right now: https://zurihac.com/#registration We would also like to thank the Hochschule für Technik Rapperswil for their amazing support and for hosting us again this year. Without them, an event of this scale and quality would be extremely difficult to pull off. We can't wait to see you in June, The Zurich Friends of Haskell (https://zfoh.ch/)

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[RFC] Constraint based arrow notation (GHC proposal)
by Alexis King 06 Dec '19

06 Dec '19

Hello all, I have recently written a GHC proposal to change the typechecking rules for arrow notation (aka `proc`) to better support custom control operators. Specifically, it reverses a change made in GHC 7.8 due to technical limitations that requires control operators to have significantly uglier types. Although arrows have fallen out of favor with the Haskell community in recent years, presumably there are still at least a few users. If you use `proc` notation, and especially if you use its support for custom control operators (i.e. (| banana brackets |)), your feedback would be highly valued. To read or comment on the proposal, follow this link: https://github.com/ghc-proposals/ghc-proposals/pull/303 Thanks, Alexis

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ANN: hledger 1.16
by Simon Michael 03 Dec '19

03 Dec '19

I'm pleased to announce hledger 1.16.1 ! hledger 1.16 was released on schedule on 2019-12-01, but only to hackage and github, since I was travelling and behind a rain-disrupted microwave link. Today brings the release notes & docs updates on hledger.org, and a 1.16.1 point release with some packaging updates. Thanks to release contributors Dmitry Astapov, Mykola Orliuk, Brian Wignall, Alejandro García Montoro, Timofey ZAKREVSKIY, Amitai Burstein, and Michael Kainer. hledger is a robust, cross-platform, multicurrency, plain text accounting tool, with command-line, terminal and web UIs. It is one of the leading implementations of plain text accounting, and is a modern and largely compatible reimplementation of Ledger. Use it for tracking money, time, stocks, cryptocurrencies or any other commodity, Learn more at http://hledger.org and http://plaintextaccounting.org . WHAT'S NEW: GHC 8.8 support, much more powerful CSV conversion rules, percentage balance reports, misc improvements. https://hledger.org/release-notes#hledger-1-16 . GETTING STARTED: Many install methods are described at http://hledger.org/download . Some of these might take a few days to become up to date; look for the green badges. You can build the latest by doing: stack update; stack install --resolver=lts hledger-lib-1.16.1 hledger-1.16.1 hledger-ui-1.16.1 hledger-web-1.16.1 --silent or: cabal v2-update; cabal v2-install hledger-1.16.1 hledger-web-1.16.1 hledger-ui-1.16.1 To start recording transactions: "hledger add". To list more commands: "hledger". See http://hledger.org for docs and support, or join #hledger on Freenode (http://irc.hledger.org) or join via Matrix (http://riot.hledger.org) New and old users, contributors, sponsors, and all feedback are most welcome! Best, -Simon

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Open Position: Lecturer in Cybersecurity - University of Exeter
by Achim D. Brucker 03 Dec '19

03 Dec '19

Dear all, As part of the expansion of the Department of Computer Science [1] at the University of Exeter, we are recruiting for a Lecturer in Cybersecurity. The lecturer will be part of the newly formed Security and Trust of Advanced Systems Group [2]. This is a *unique* opportunity to join a new group and to influence its future research and teaching. We are looking for a candidate with an outstanding research record in any area of cybersecurity such as (but not limited to): language-based security, access control, usable security, software security, formal methods for security, security analytics, security protocols, human aspects of security, security economics, security by design, applied cryptography, security testing. We are particularly keen on research areas that either extend the current strength in software security and formal methods in security or that complement these existing focus area. Please apply by 12th of December 2019! See the full announcement and application details at https://jobs.exeter.ac.uk/hrpr_webrecruitment/wrd/run/ETREC107GF.open?VACAN… Feel free to contact me for informal inquires about the post. Best, Achim [1] https://www.exeter.ac.uk/computer-science/ [2] https://emps.exeter.ac.uk/computer-science/research/cyber-security/ -- Prof. Achim Brucker | Chair in Cybersecurity & Head of Group | University of Exeter https://www.brucker.ch | https://logicalhacking.com/blog @adbrucker | @logicalhacking

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ANN: reflex-libtelnet-0.1.0.0
by Jack Kelly 02 Dec '19

02 Dec '19

I have just pushed an initial release of reflex-libtelnet[1] to Hackage. reflex-libtelnet wraps libtelnet[2] in a Reflex interface, so that you can describe data flows through a telnet state tracker using Reflex Events. Even if you're not using Telnet in 2019, you might find it interesting as a study in binding Reflex to a callback-oriented library. A telnet echo server is provided as an example[3]. Bug reports[4] and questions/patches[5] are welcome on Sourcehut. Best, -- Jack [1]: https://hackage.haskell.org/package/reflex-libtelnet-0.1.0.0 [2]: https://hackage.haskell.org/package/libtelnet [3]: https://git.sr.ht/~jack/reflex-libtelnet/tree/master/reflex-libtelnet-examp… [4]: https://todo.sr.ht/~jack/reflex-libtelnet [5]: https://lists.sr.ht/~jack/reflex-libtelnet-discuss

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Re: [Haskell-cafe] Is UndecidableInstances unavoidable in heterogenous Show derivation?
by Anthony Clayden 30 Nov '19

30 Nov '19

> ... was mildly surprised by the need for -XUndecidableInstances > when deriving the 'Show' instance for the heterogenous N-ary product 'NP': Hi Viktor, yes 'Undecidable' sounds scary, but it isn't. There's been much debate: should we find a less scary name? Presumably your program compiles and runs OK with that switched on(?) Providing your program compiles, it is type-safe. The risk with -XUndecidableInstances is that you might throw the compiler into a loop, in which case you'll get a stack depth check, with an unhelpful error message. See the Users Guide on UndecidableInstances, also this is a faq on StackOverflow. > deriving instance All (Compose Show f) xs => Show (NP f xs) Yes the constraint on that instance violates the Paterson Conditions (see Users Guide), the constraint is no smaller than the instance head. The P Conditions aim to make each step of instance resolution smaller, by strictly decreasing "constructors and variables (taken together ...". But that constraint has a count of 4, same as the head. > I guess I should also ask whether there's a way to define something equivalent > to 'Compose' without 'UndecidableSuperClasses', and perhaps the two are not unrelated. Not exactly related, but again superclass instance resolution wants to make the problem smaller at each step. The definition for class Compose has a constraint no smaller than the class head (3 variables). > [ Perhaps I should be more blasé about enabling these extensions, but I prefer > to leave sanity checks enabled when possible. ] Yes that's a sensible policy. The trouble with -XUndecidableInstances is that it's a module-wide setting, so lifts the check for all instances of all classes. There are/were several proposals to make this a per-instance or per-class pragma. But they got no support in the proposals process. AntC

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