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PhD studentships at Leeds
by David Duke 12 Dec '16

12 Dec '16

The School of Computing at the University of Leeds is advertising a number of PhD studentships open to UK, EU and international applicants. Two of the projects are at the overlap between functional programming and visualization, one on performance analysis, one on explaining type inference. Please see the following URL for further information including how to apply: https://engineering.leeds.ac.uk/research-opportunity/201323/research-degree… Closing date: 06/01/2017 --- David Duke T: +44 113 3436800 Professor of Computer Science E: D.J.Duke(a)leeds.ac.uk Head, School of Computing W: www.comp.leeds.ac.uk/scsdjd/

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[Ann] Haskell Ecosystem Proposals
by Alan & Kim Zimmerman 12 Dec '16

12 Dec '16

Earlier this year Simon Peyton Jones wrote about respect [1], and said "It's worth separating two things 1. Publicly debating an issue where judgements differ 2. Using offensive or adversarial language in that debate" There is now a repository[2] for us as a community to have the first kind of discussion about issues that affect the community as a whole. The intention is that this becomes a neutral place where discussion can take place about coordinating the various services offered to the haskell community. This is partly to expose the thinking and constraints on a particular approach, so proponents of other approaches can have a better understanding of how things can evolve. The idea is that through an honest understanding of the various parts we can achieve consensus on how to improve things. If this all sounds a bit handwavy, the first concrete example of this approach is a pull request [3] discussing the management of implicit or speculative version bounds between cabal-install/hackage and stack/stackage. This has reached a point where there is a clearer understanding of the actual problem, and a viable solution must be agreed. The structure of the repository is shamelessly copied from the one for GHC proposals, so the actual process description is way off. It should probably just state that we discuss until consensus is reached if possible, but that we are always open for further discussion. It is up to all of us to make this work. Regards Alan [1] https://mail.haskell.org/pipermail/haskell/2016-September/024995.html [2] https://github.com/haskell/ecosystem-proposals [3] https://github.com/haskell/ecosystem-proposals/pull/1

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what is lens-based parsing?
by Ruben Astudillo 10 Dec '16

10 Dec '16

Dear Cafe I've reading the tutorial for pipes-parse, and I got some references that it supports lens-based parsing. I know lens, yet I don't really know what is that about. Also looking in google doesn't get any detailed blogpost. Can anybody help me out on what is this? -- -- Ruben

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Partial Evaluation & Program Manipulation (PEPM'17): Call for Participation
by Jeremy Yallop 10 Dec '16

10 Dec '16

CALL FOR PARTICIPATION Workshop on PARTIAL EVALUATION AND PROGRAM MANIPULATION (PEPM 2017) http://conf.researchr.org/home/PEPM-2017 Paris, France, January 16th - 17th, 2017 (co-located with POPL 2017) Registration ------------ http://popl17.sigplan.org/attending/registration Early registration deadline: Saturday 17th Dec 2016 Programme --------- Monday 16th January 09:00-10:00: Keynote Compiling Untyped Lambda Calculus to Lower-Level Code by Game Semantics and Partial Evaluation Neil D. Jones (with Daniil Berezun) 10:30-12:00: Programming languages Lightweight Soundness for Towers of Language Extensions Alejandro Serrano, Jurriaan Hage Detecting code clones with gaps by function applications Tsubasa Matsushita, Isao Sasano PEG Parsing in Less Space Using Progressive Tabling and Dynamic Analysis Fritz Henglein, Ulrik Terp Rasmussen 14:00-15:30: Tutorial and Poster Session Idris, Inside-Out: A Tutorial on Extending Idris in Idris David Christiansen Language-integrated Query with Ordering, Grouping and Outer Joins (poster) Tatsuya Katsushima, Oleg Kiselyov 16:00-17:00: Transformation (part I) Verification of Code Generators via Higher-Order Model Checking Takashi Suwa, Takeshi Tsukada, Naoki Kobayashi, Atsushi Igarashi Interactive data representation migration: Exploiting program dependence to aid program transformation Krishna Narasimhan, Julia Lawall, Christoph Reichenbach Tue 17th January 09:00-10:00: Tutorial Reversible computing from a programming language perspective Robert Glück 10:30-12:00: Types Cost versus Precision for Approximate Typing for Python Levin Fritz, Jurriaan Hage Refining types using type guards in TypeScript Ivo Gabe de Wolff, Jurriaan Hage Predicting Resource Consumption of Higher-Order Workflows Markus Klinik, Jurriaan Hage, Jan Martin Jansen, Rinus Plasmeijer 14:00-15:30: Tutorial Practical Partial Evaluation for Language Implementation with Graal & Truffle Gilles Duboscq 16:00-17:00: Transformation (part II) Functional Parallels of Sequential Imperatives Tiark Rompf, Kevin J. Brown A Functional Reformulation of UnCAL Graph-Transformations: Or, Graph Transformation as Graph Reduction Kazutaka Matsuda, Kazuyuki Asada

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Dockerfile for building ghc8.0 with ubuntu 16.04LTS
by Takenobu Tani 09 Dec '16

09 Dec '16

Hi cafe, I pushed Dockerfile for building ghc8.0 with ubuntu 16.04LTS. (If you need Debian and Arcanist, please use Greg's Dockerfile[1].) Dockerfile for Haskell GHC building https://github.com/takenobu-hs/ghc-build-docker Let's get familiar with ghc building and validating :) [1]: https://github.com/gregwebs/ghc-docker-dev [2]: https://ghc.haskell.org/trac/ghc/wiki/Building Enjoy, Takenobu

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Summer of Haskell 2016 Wrap-Up
by Gershom B 09 Dec '16

09 Dec '16

We wanted to let folks know what happened with all our Summer of Haskell projects, and thank again all those who donated as individuals or sponsored students to make this possible. As a reminder, the accepted projects were announced on reddit at: https://www.reddit.com/r/haskell/comments/4kp6zg/summer_of_haskell_2016_acc… * * * 1) Native Metaprogramming in Haskell This very ambitious project made significant progress, though is not yet ready for a full merge into GHC. A talk and paper on work relating to it were presented at the Haskell Implementors Workshop at ICFP, and a page on the GHC wiki describes the current status. - https://www.youtube.com/watch?v=DSWoGdfYt68 - https://arxiv.org/abs/1610.04799 - https://ghc.haskell.org/trac/ghc/wiki/NativeMetaprogramming 2) GHCVM - A JVM Backend for GHC Again, significant progress made on a very ambitious project, which has now been renamed to “eta”. A talk on the work done was given at the HIW, and the project is considered ready for “hobbyist use”. - https://www.youtube.com/watch?v=G4m7xFVzd50 - https://github.com/typelead/eta 3) Completing the LLVM backend for Accelerate All operators of the LLVM backend are now implemented, and we’re told that the accelerate-llvm project, already usable, will be get a more proper announcement as ready for widespread use real soon now (tm). - https://github.com/AccelerateHS/accelerate-llvm - https://github.com/AccelerateHS/accelerate-llvm/commits?author=ZihengJiang 4) Hackage Improvements A whole raft of usability improvements to hackage (including the long-awaited rollout of reverse dependency tracking, and a very usable package browser interface) are undergoing final code review and polish in a PR before being rolled out. The student’s blog contains more information about what’s on the way. - http://sooryanarayan.me/blog/hsoc-testimonial/ 5) Derivable Storable and Prim instances This work resulted in both a package (usable today) and a plugin to improve the performance of the derived code. Updates on the decisions made and work done were posted to the numerical-haskell group - https://hackage.haskell.org/package/derive-storable - http://hackage.haskell.org/package/derive-storable-plugin - https://groups.google.com/forum/#!forum/numericalhaskell 6) Visual functional block-based programming language for CodeWorld This work went well and is described on the student’s blog. It is usable today at https://code.world/blocks and apparently has already begun to be integrated into CodeWorld lesson plans. - http://stefanj.me/funblocks/ - https://code.world/blocks 7) Jupyter for GHCJS Apparently this ran into a far amount of difficulties and didn’t make significant progress, though not for lack of effort. The student is anticipated to write up an experience report describing some of the problems encountered and how others might work around them in the future. 8) Live Profiling and Performance Monitoring Server A lot of work was accomplished on various fronts here. A number of changes to the GHC RTS are in review and pending merge. A tool has been written to take advantage of the newly available information. And various other small packages that met needs along the way were extracted and contributed to hackage. A fuller write-up of progress and future work is available at the student’s blog. - https://phabricator.haskell.org/D2522 - https://github.com/NCrashed/live-profile-monitor - http://ncrashed.github.io/blog/posts/2016-09-11-hsoc-results.html * * * Apologies for the delays in assembling this information -- as they say, man plans, the fates laugh. Thanks to all our students for their dedicated work and contributions to the ecosystem. We hope to see much more from all of you in the future. And thanks to all our mentors for donating their time to guide, teach, and make this possible. And a very special thanks to Edward Kmett for co-ordinating much of the administrative work here, as well as fundraising towards this great Summer of Haskell. * * * Sponsors (listed on summer.haskell.org) - haskell.org kicked things off this year by funding a student and organizing the Summer of Haskell. - Awake Networks is building a next generation network security and analytics platform. They are a proud sponsor of the Summer of Haskell and contribute broadly to the Haskell community. - Haskell Book is a proud sponsor of the Summer of Haskell and provides a complete and up-to-date resource for learning Haskell, suitable whether you're completely new to Haskell or are at an intermediate level and want to deepen your understanding. - YOW! Australia is a proud sponsor of the Summer of Haskell and organizes conferences throughout Australia. - Chris Smith volunteered to fund two students to work on CodeWorld in particular. - Edward Kmett and Gershom Bazerman volunteered to personally fund a student project. Best, Gershom Bazerman Haskell.org Committee

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Bits.bitSize
by ALeX Kazik 08 Dec '16

08 Dec '16

Hi, I think it would be a good idea to provide a default implementation for bitSize, example: bitSize b = fromMaybe (error "bitSize is undefined") (bitSizeMaybe b) The advantage is that from now on new instances of Bits no longer need to define bitSize. And once bitSize has been removed there will be no errors about it not being a method of class Bits. ALeX.

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ANN: Free hands-on Haskell workshop in Augsburg, Germany on 2012-12-17 [with German videos]
by Ingo Blechschmidt 08 Dec '16

08 Dec '16

Dear lovers of generalized abstract nonsense, this mail is directed at Haskell neophytes, novices, and advanced learners living near Augsburg, Germany; and at Haskell aficionados living all over the world but speaking German. On 2012-12-17, we -- the Curry Club Augsburg -- will organize a free all-day hands-on workshop on Haskell. Join us in the morning without having seen a single line of Haskell code and leave with working knowledge of Haskell's basics. If you already know a bit of Haskell, then learn your ways with Haskell's vast library ecosystem, how to structure bigger programs, how to check your code for correctness, and how to write parsers/websites/numerical simulations/user interfaces/two- and three-dimensional games. So that we don't exceed our capacity for individual mentoring during the workshop, a mandatory but nonbinding registration is necessary. [1] In case that you want to dive deeper into Haskell and other functional languages after having participated in the workshop, you are invited to join us at our monthly meetings. There are typically two to three talks on a wide range of topics of interest to Haskell programmers, such as latest news from the Kmettiverse, glimpses into formal logic and proof assistants like Isabelle, and introductions to the category-theoretic background of freer monads or to infinite-time Turing machines and the effective topos. All of our talks are recorded [2]. Our workshop documents are CC-licensed [3]. Feel free to copy them, modify them, and host Haskell workshops at other places! Cheers, Ingo of Augsburg's Curry Club [1] http://curry-club-augsburg.de/posts/2016-12-06-dritter-workshop.html [2] https://www.youtube.com/channel/UCKV6TVS9DWaEix6l3_l457Q [3] https://rawgit.com/curry-club-aux/haskell-workshop/gh-pages/uebung.pdf https://rawgit.com/curry-club-aux/haskell-workshop/gh-pages/uebung2.pdf http://curry-club-augsburg.de/posts/2015-10-27-monaden-in-haskell.html (All hail the monad tutorial fallacy. English translation by Harry Garrood at https://gist.github.com/iblech/429652a31b05e408262b.)

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Injective type family on a sub domain
by Guillaume Bouchard 08 Dec '16

08 Dec '16

Hi. I have the following GADT : ----------------------------- type family Or a b where Or 'False 'False = 'False Or _ _ = 'True data Expr t where Add :: Expr t -> Expr t' -> Expr (Or t t') Lit :: Int -> Expr 'False Var :: Expr 'True ---------------------- The idea is that if the `Expr` contains a sub `Var`, its type is `Expr 'True`, else it is `Expr 'False`. I now want to evaluate my expression, something like that : -------------- eval :: Expr t -> Int eval (Lit i) = i eval (Add a b) = eval a + eval b eval Var = error "Cannot evaluate expression with variable" ---------------- Using the GADT I previously defined, I'm tempted to remove the impossible "Var" case with : --------------- eval' :: Expr 'False -> Int eval' (Lit i) = i eval' (Add a b) = eval' a + eval' b ---------------- However this does not typecheck because GHC cannot deduce that `a` and `b` are `~ Expr 'False`. Because the type family `Or` is not injective. The wiki https://ghc.haskell.org/trac/ghc/wiki/InjectiveTypeFamilies classifies injectives types families in three categories, but I don't think my `Or` appears in any of them. Actually `Or` is injective only if `Or t t' ~ 'False` and in this case, we can deduce that `t ~ 'False` and `t' ~ 'False`. I qualify it as a "partialy injective type family". The type checker does not know that, hence my code does not compile. Is there a solution, other than writing a custom type checker plugin? Is there a way to provide the inverse type family function, something such as: type family InverseOr a where InverseOr 'False = ('False, 'False) Thank you. -- G.

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Re: [Haskell-cafe] Gitter Haskell Community
by Ben Spencer 08 Dec '16

08 Dec '16

I think it's important to recognize that users have different tastes and needs. Additionally, Gitter allows you to view the chat channel if you wish. It's also something that's publicly viewable and searchable from Gitter explore. It doesn't require the odd signup process that Slack has implemented. I can actually see my chat history for more than 2 days! But beyond that if you like Slack and its community then more power to you. We can certainly have a difference of opinion and preferences. -Ben On Dec 07, 2016, at 12:09 PM, Michael Walker <mike(a)barrucadu.co.uk> wrote: The Haskell slack seems to be working well, so regardless of the suitability of slack to open communities or not, I don't really see the advantage of fragmenting the community even further. Why would someone pick gitter over the two existing platforms that have thousands of users? They would be intentionally limiting the help they can get. On 7 December 2016 at 17:07, Ben Spencer <ben.richard.spencer(a)me.com> wrote: Hey Chris, As I've mentioned Slack isn't a good choice for open communities. It's really designed for businesses. On Dec 07, 2016, at 11:52 AM, Christopher Allen <cma(a)bitemyapp.com> wrote: For that, there's http://fpchat.com/ which is an established Slack community. The #haskell channel alone has 1,208 people in it right now. On Wed, Dec 7, 2016 at 10:50 AM, Tomas Carnecky <tomas.carnecky(a)gmail.com> wrote: Usability matters. It's easier to tell people to open a browser window and point them at a URL than tell them to download an IRC chat client and how to connect to the server and... On Wed, Dec 7, 2016 at 5:41 PM William Yager <will.yager(a)gmail.com> wrote: What are the advantages of this over the #haskell IRC on freenode? It's very active, usually with over 1500 nicks at any given time. I generally prefer IRC to any of these hip web chat solutions because IRC is client-agnostic and very rugged against companies folding or deciding they don't want to host a project any more. Basically the only way to kill an IRC channel is through social attrition, whereas any social value built up in hosted chat services might disappear overnight. The one major advantage of hosted chats over IRC is that they work better with mobile users, but I don't think that's very relevant for haskell dev. Will On Wed, Dec 7, 2016 at 7:34 AM, Ben Spencer <ben.richard.spencer(a)me.com> wrote: Why Gitter you might ask? _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post. _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post. -- Chris Allen Currently working on http://haskellbook.com _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post. -- Michael Walker (http://www.barrucadu.co.uk)

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