March 2018 - Haskell-Cafe

vim syntax file
by Marcin Szamotulski 19 Mar '18

19 Mar '18

Hello, I am looking for the maintainer of the haskell vim syntax script. The header points to the haskell-cafe mailing lists. I added @Spell and @NoSpell groups so it's easier to spell check haskell in vim. I hope others will find it useful :) Best regards, Marcin Szamotulski

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S-REPLS 9: Call for talks
by Martin Berger 19 Mar '18

19 Mar '18

============================================================================ S-REPLS 9 (#srepls) South of England Regional Programming Language Seminar series Friday 25 May 2018, 10:00 - 19:00 University of Sussex, Brighton, Fulton building, Room A (FUL-A) http://users.sussex.ac.uk/~mfb21/srepls9 Call for talks ============================================================================ Overview S-REPLS is a regular, informal and friendly meeting for those based in the South of England with a professional interest - whether it be academic or commercial - in the semantics, implementation, and use of programming languages, and related areas. Attendance is free! Lunch and refreshments will be provided. Submitting a talk S-REPLS talks are typically 20-30 minutes long on any topic related to programming languages. We are currently requesting talk suggestions for S-REPLS 9 at the University of Sussex in Brighton. Submissions from industrial professionals and junior researchers (postdocs and students), as well as descriptions of work in progress, are especially welcome. Please email <M.F.Berger(a)sussex.ac.uk> with the title "S-REPLS 9 talk suggestion", a draft title, and an abstract by 17:00 on April 25th 2018.

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Scala: Type synonyms for implicits?
by Thomas Jakway 18 Mar '18

18 Mar '18

Posting this here since some of you are Scala programmers:https://stackoverflow.com/questions/49353695/type-synonyms-for-… A type-level question you won't encounter in Haskell.

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Call for Tutorial Proposals: ICFP 2018
by Lindsey Kuper 18 Mar '18

18 Mar '18

CALL FOR TUTORIAL PROPOSALS ICFP 2018 23rd ACM SIGPLAN International Conference on Functional Programming September 23-29, 2018 St. Louis, Missouri, United States http://conf.researchr.org/home/icfp-2018 The 23rd ACM SIGPLAN International Conference on Functional Programming will be held in St. Louis, Missouri, United States on September 23-29, 2018. ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. Proposals are invited for tutorials to be presented during ICFP and its co-located workshops and other events. These tutorials are the successor to the CUFP tutorials from previous years, but we also welcome tutorials whose primary audience is researchers rather than practitioners. Tutorials may focus either on a concrete technology or on a theoretical or mathematical tool. Ideally, tutorials will have a concrete result, such as "Learn to do X with Y" rather than "Learn language Y". Tutorials may occur in parallel to both ICFP and its co-located workshops, from September 23 through September 29. Additionally, ICFP is co-located with Strange Loop this year, and this will be taken into account when scheduling tutorials. ---------------------------------------------------------------------- Submission details Deadline for submission: April 9, 2018 Notification of acceptance: April 16, 2018 Prospective organizers of tutorials are invited to submit a completed tutorial proposal form in plain text format to the ICFP 2018 workshop co-chairs (Christophe Scholliers and David Christiansen), via email to icfp-workshops-2018(a)googlegroups.com by April 9, 2018. Please note that this is a firm deadline. Organizers will be notified if their event proposal is accepted by April 16, 2018. The proposal form is available at: http://www.icfpconference.org/icfp2018-files/icfp18-tutorials-form.txt ---------------------------------------------------------------------- Selection committee The proposals will be evaluated by a committee comprising the following members of the ICFP 2018 organizing committee. Workshop Co-Chair: Christophe Scholliers (University of Ghent) Workshop Co-Chair: David Christiansen (Galois, Inc.) General Chair: Robby Findler (Northwestern University) Program Chair: Matthew Flatt (University of Utah) ---------------------------------------------------------------------- Further information Any queries should be addressed to the workshop co-chairs (Christophe Scholliers and David Christiansen), via email to icfp-workshops-2018(a)googlegroups.com

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[Announcement]: New release of ppTable: Pretty Print containers in a tabular format
by Guru Devanla 17 Mar '18

17 Mar '18

Hello Haskell-Cafe, I am happy to announce a new release of the ppTable library that lets you print records in list/vectors/maps in a pretty tabular format. https://hackage.haskell.org/package/pptable The new release also handles nested record structures by displaying the headers in a multi-hierarchical fashion. As they say in Python 'Flat is better than nested'. But for now, nested works too! I am willing and happy to get any feedback and suggestions on the library API and implementation itself. Thank you very much Guru

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Documenting Examples for a library
by Guru Devanla 17 Mar '18

17 Mar '18

Hello, I am close to releasing a new version of the https://hackage.haskell.org/package/pptable library I have been working on off late. I am a little confused on what approach I need to take regarding providing good documentation and working examples. Please, note that I am not referring to the API documentation attached to the code. For API documentation I will continue to use haddock and generate documentation as I build. The approaches I have in mind to provide clear examples are as follows: 1. Provide a README.md and document all usage examples in markdown format. Allow github to produce the HTML. 2. Create and ship an Example.hs file along with library. Using a .hs file allows haddock to build the documentation as part of the package. I took this approach for the previous release. Here is an example: https://hackage.haskell.org/package/pptable-0.2.0.0/docs/Text-PrettyPrint-T…. 3. Using Example.lhs. I like this approach since it lets me load the code in ghci and test out the examples seamlessly. But, I am hitting roadblocks with this, since I am not able to include this file as part of my stack project. `stack haddock` fails too. When I include .lhs file in a stack project, I get the following error File name does not match module name: Saw: ‘Main’ Expected: ‘Text.PrettyPrint.Tabulate.Example’ I like (3) because I can make sure my examples run successfully, (using stack ghci Example.lhs), before I publish them. With options (1) and (2), I need to manually copy/past code into ghci to make sure there are no errors. Is there a better way to do this? Please could the group provide any recommendations and guidance on what approach I should be taking and why. Thanks

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[Google Summer of Code 2018] Student Applications are now open
by Jasper Van der Jeugt 15 Mar '18

15 Mar '18

Hey all, As we've previously announced through different channels, Haskell.org was accepted into Google Summer of Code 2018 [1]. Students application have now opened. Students can submit their proposal at the Summer of Code Dashboard [2]. We are also seeking mentors for possible projects. This year, we would like to assign a back-up mentor for each student. If you are interested in mentoring, please contact us [3] so we can add you to the mentor list directly. Having good mentors is an important factor in making the students feel welcome and guiding them to a succesful completion of their projects. If you would like to apply but you don't know how to start your proposal, have a look at our ideas list [4] and this great guide [5]. Lastly, we recognize that inclusion is an important part of our mission to promote Haskell. Therefore, we strongly encourage applications from people in communities that are underrepresented in functional programming, including but not limited to women; people of color; people in gender, sexual and romantic minorities; people with disabilities; people residing in Asia, Africa, or Latin America; and people who have never taken part in similar programs before. Kind regards, Jasper Van der Jeugt & George Wilson on behalf of the Haskell.org Committee [1]: https://summerofcode.withgoogle.com/organizations/5706672807346176/ [2]: https://summerofcode.withgoogle.com/ [3]: https://summer.haskell.org/contact.html [4]: https://summer.haskell.org/ideas.html [5]: http://write.flossmanuals.net/gsocstudentguide/writing-a-proposal/

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Using Backpack for initial and final encodings
by David Laing 15 Mar '18

15 Mar '18

Hi everyone, Ed Kmett recently pointed me towards his usage of Backpack to write some code in the tagless final style, and I've been playing with it and riffing on it for a while. There's a solution to the expression problem in there involving classy Prisms (and now Backpacky Prisms) that seems pretty neat. I've written it up here: https://qfpl.io/posts/backpack-for-initial-and-final-encodings/ Hopefully some of you find it interesting. Cheers, Dave

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[ANNOUNCE] GHC 8.4.1 released
by Ben Gamari 14 Mar '18

14 Mar '18

The GHC developers are very happy to announce the 8.4.1 release of Glasgow Haskell Compiler. Binary and source distributions can be found at https://downloads.haskell.org/~ghc/8.4.1/ This is the third major release in the GHC 8 series. As such, the focus of this release is performance, stability, and consolidation. Consequently numerous cleanups can be seen throughout the compiler including, * Further refinement of TypeInType, including significant improvements in error messages. * Improvements in code generation resulting in noticable performance improvements in some types of programs. * Core library improvements, including phase 2 of the Semigroup/Monoid proposal * Many improvements to instance deriving * The resolution of nearly 300 other tickets A more thorough list of the changes in this release can be found in the release notes, https://downloads.haskell.org/~ghc/8.4.1/docs/html/users_guide/8.4.1-notes.… There are a few changes in release-engineering matters that should be noted, * This is GHC's first release on it's new, accelerated release schedule. From now on GHC will produce one release every six months. * While we typically strive to produce OpenBSD builds, the gcc shipped with OpenBSD 6.1 is unfortunately too old to compile this release. * FreeBSD builds are still in progress This release has been the result of approximately six months of work by over one hundred code contributors. Thanks to everyone who has helped in writing patches, testing, reporting bugs, and offering feedback over the last year. As always, let us know if you encounter trouble. How to get it ~~~~~~~~~~~~~ The easy way is to go to the web page, which should be self-explanatory: http://www.haskell.org/ghc/ We supply binary builds in the native package format for many platforms, and the source distribution is available from the same place. Packages will appear as they are built - if the package for your system isn't available yet, please try again later. Background ~~~~~~~~~~ Haskell is a standard lazy functional programming language. GHC is a state-of-the-art programming suite for Haskell. Included is an optimising compiler generating efficient code for a variety of platforms, together with an interactive system for convenient, quick development. The distribution includes space and time profiling facilities, a large collection of libraries, and support for various language extensions, including concurrency, exceptions, and foreign language interfaces. GHC is distributed under a BSD-style open source license. A wide variety of Haskell related resources (tutorials, libraries, specifications, documentation, compilers, interpreters, references, contact information, links to research groups) are available from the Haskell home page (see below). On-line GHC-related resources ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Relevant URLs on the World-Wide Web: GHC home page http://www.haskell.org/ghc/ GHC developers' home page http://ghc.haskell.org/trac/ghc/ Haskell home page http://www.haskell.org/ Supported Platforms ~~~~~~~~~~~~~~~~~~~ The list of platforms we support, and the people responsible for them, is here: http://ghc.haskell.org/trac/ghc/wiki/Contributors Ports to other platforms are possible with varying degrees of difficulty. The Building Guide describes how to go about porting to a new platform: http://ghc.haskell.org/trac/ghc/wiki/Building Developers ~~~~~~~~~~ We welcome new contributors. Instructions on accessing our source code repository, and getting started with hacking on GHC, are available from the GHC's developer's site run by Trac: http://ghc.haskell.org/trac/ghc/ Mailing lists ~~~~~~~~~~~~~ We run mailing lists for GHC users and bug reports; to subscribe, use the web interfaces at http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-tickets There are several other haskell and ghc-related mailing lists on www.haskell.org; for the full list, see https://mail.haskell.org/cgi-bin/mailman/listinfo Some GHC developers hang out on #haskell on IRC, too: http://www.haskell.org/haskellwiki/IRC_channel Please report bugs using our bug tracking system. Instructions on reporting bugs can be found here: http://www.haskell.org/ghc/reportabug

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Append after index and update items after inserted item with lens
by Cody Goodman 13 Mar '18

13 Mar '18

Hello, I'm trying to insert a new elemnt into a list after a given index and increment the orderId accordingly with the lens library. I'm a bit confused at why this code isn't working: ``` import Control.Lens data A = A { _customOrderId :: Int } deriving Show things = [ A {_customOrderId = 0} , A {_customOrderId = 1} , A {_customOrderId = 2} , A {_customOrderId = 3} ] main = print $ things & ( (_drop 2 %~ ((A 22)<|)) . ((traversed . indices (> 2) . customerOrderIdLens) %~ (+ 1)) ) ``` The first portion works to insert where desired, but the second portion `((traversed . indices (> 2) . customerOrderIdLens) %~ (+ 1))` only increments the order id in indices 4. Any idea why this is happening? Thanks, Cody Goodman

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