- Haskell-Cafe - Haskell.org

Haskell Weekly News
by Kim-Ee Yeoh 15 May '15

15 May '15

*Top Picks:* - Is Servant <http://haskell-servant.github.io/>the most type-safe HTTP server library ever? Are the type signatures hard to read <https://news.ycombinator.com/item?id=9519782#up_9520750>? In addition to its utmost relevance as a web library, Servant is also an awesome case study in the type safety vs type readability trade-off spectrum, brought to you by Alp Mestanogullari and Julian Arni. HN <https://news.ycombinator.com/item?id=9519782> and /r/haskell <http://www.reddit.com/r/haskell/comments/35hiie/servant_04_released/> - Ozan Sener compiles Pandoc into JS via GHCJS and creates a web interface to it using the Reflex FRP library <https://github.com/ryantrinkle/reflex>. Markup.Rocks <https://github.com/osener/markup.rocks> is much loved on /r/haskell <http://www.reddit.com/r/haskell/comments/35ax22/ive_compiled_pandoc_with_gh…>. See also HN <https://news.ycombinator.com/item?id=9512293>. - Is Haskell a "Startup Secret Weapon"? Alexandr Kurilin reveals adoption challenges <https://github.com/commercialhaskell/commercialhaskell/blob/master/usage/fr…> at Front Row Education <https://www.crunchbase.com/organization/front-row>. Among them, slow build times. Also, "senior developers [that] get very frustrated when something wouldn't compile for hours and they couldn't find any help to move forward." Comments on HN <https://news.ycombinator.com/item?id=9519924> and /r/haskell <http://www.reddit.com/r/haskell/comments/35h8vh/how_front_row_education_use…> . - At Facebook, Bryan O'Sullivan debugs aeson's gigabyte space leak <http://www.serpentine.com/blog/2015/05/13/sometimes-the-old-ways-are-the-be…> on decoding a JSON megabyte of non-stop backslashes. Culprit? The streaming interface didn't match the use case. In place of streaming, Bryan now blasts bytes into a single big buffer, gaining 27x speed and 42x memory reduction. Comments on HN <https://news.ycombinator.com/item?id=9540389>, Proggit <http://www.reddit.com/r/programming/comments/35udjh/fixing_a_haskell_perfor…>, /r/haskell <http://www.reddit.com/r/haskell/comments/35udfy/fixing_an_aeson_performance…> . - Paul Chiusano's Unison programming platform <http://unisonweb.org/2015-05-07/about.html> hits the HN <https://news.ycombinator.com/item?id=9512955> and /r/haskell <http://www.reddit.com/r/haskell/comments/35cop9/unison_a_nextgeneration_pro…> headlines. Features include a browser-based UI that constrains edits to those that are well-typed. Also, DRY-ness up the wazoo: every type and term is uniquely identified by a hash a la Git. - Joey Hess reports <http://www.reddit.com/r/haskell/comments/35bw0b/at_last_debian_unstable_has…> that Debian unstable now has a working GHCi for ARM. The Template Haskell challenges have been surmounted. - Garrison Jensen blows the whistle <http://www.garrisonjensen.com/2015/05/13/haskell-programs-are-lies.html> on the impostor sieve on the front page of Haskell.org. In jest. A festive one-upmanship of fondly treasured code ensues on /r/haskell <http://www.reddit.com/r/haskell/comments/35vc31/the_real_way_to_generate_a_…>. And since bad publicity is better than no publicity, we owe kudos to Garrison. HN-worthy <https://news.ycombinator.com/item?id=9541478>. - Michael Snoyman decries use of ExceptT IO <https://www.fpcomplete.com/user/commercial/content/exceptions-best-practices> for exception handling because the user exception data type creates misleading expectations of comprehensiveness. The gotcha is that it doesn't cover IO exceptions! Furthermore, distinct exception types mean that the corresponding code can't compose. Instead? Use MonadThrow. /r/haskell <http://www.reddit.com/r/haskell/comments/35sk6w/best_practices_for_using_ex…> - JP Moresmau steps down as chief of EclipseFP <http://jpmoresmau.blogspot.com/2015/05/eclipsefp-end-of-life-from-me-at-lea…> and the companion Haskell packages BuildWrapper, ghc-pkg-lib, and scion-browser. Without anyone to take his place, the sun sets on EclipseFP. But the sun continues to shine on ide-backend (previously reported <http://haskell.1045720.n5.nabble.com/Haskell-Weekly-News-td5768107.html>), a GHC API wrapper akin to BuildWrapper. JP spitballs <http://haskell.1045720.n5.nabble.com/IDE-backend-Atom-editor-td5809240.html> on how he might move on to the Atom editor, jiggering it to use ide-backend-client. /r/haskell <http://www.reddit.com/r/haskell/comments/35y5v1/jp_moresmaus_blog_eclipsefp…> - Tatsuya Hirose translates Go By Example into Haskell. GBE <https://gobyexample.com/> comprises code samples annotated for an experienced programmer new to Go. For this first cut <http://lotz84.github.io/haskellbyexample/>, Tatsuya stays close to the original and creates Go-ish, imperative Haskell. Already good for Go-to-Haskell crossovers. Potentially excellent when done in idiomatic Haskell. /r/haskell <http://www.reddit.com/r/haskell/comments/3586e3/haskell_by_example/> - Tomas Petricek observes <http://tomasp.net/blog/2015/against-types/> the diversity of type theories and type systems and posits harm in any attempt at a single all-encompassing capture of the meaning of 'types'. What about unsound types? He doesn't offer a way out for those stuck with the appellation. Comments on HN <https://news.ycombinator.com/item?id=9545540> and /r/haskell <http://www.reddit.com/r/haskell/comments/35zzvu/against_the_definition_of_t…> . - John De Goes launches a crowdfund <https://www.indiegogo.com/projects/record-all-lambdaconf-2015-talks> to solicit $15,000 for video-recording 70 talks at LambdaConf 2015, which features many known Haskell programmers. /r/haskell <http://www.reddit.com/r/haskell/comments/35n14p/indiegogo_record_all_lambda…> - A redditor asks ex-Lispers what it's like moving to Haskell <http://www.reddit.com/r/haskell/comments/35bybo/lispers_of_haskell_whats_yo…>. "I miss Lisp parens" is a frequent answer. Also, Lisp has a better REPL experience. A biggie upside? The refactoring afforded by Haskell's type system. *Tip of the Week:* - When programming fractals, use the LLVM backend <https://ghc.haskell.org/trac/ghc/ticket/10400#comment:3> because it's "usually good at optimizing this kind of non-allocating code" as Reid Barton advises. -- Kim-Ee

1 0

Equality Contstraint?
by Michael Jones 15 May '15

15 May '15

I am poking around in Arrow to understand it better. There is the following definition: second :: a b c -> a (d,b) (d,c) second f = arr swap >>> first f >>> arr swap where swap :: (x,y) -> (y,x) swap ~(x,y) = (y,x) Can someone explain what the ~ is? Searching the net resulted in frustration. I kind of think it is some kind of equality constraint but can’t find documentation. Perhaps if I knew what it was called I might succeed in finding something. If it is an equality constraint, please provide a reference if you have one. I did not find anything in a search including GHC, etc. Thanks

6 5

trying to go from FFT type to Vector.Storable
by briand＠aracnet.com 15 May '15

15 May '15

Hi, I'm using the FFT package (the FFTW bindings), and for a complex FFT I get back : (FFTWReal r, Ix i, Shapable i) => CArray i (Complex r) -> CArray i (Complex r) at first I thought I could use elems to get to a list and then do Vector.Storable.fromList to get back to a Vector.Storable. Unfortunately r is FFTWReal so i need to map over the returned list and get a haskell Double back from that. FFTWReal maps to RealFloat which i found, but i haven't found anything that will take a RealFloat and give me a Double. Was hoping someone might know how to do that, or maybe have a little cleaner way to get from the FFT data type over to Vector. Thanks. Brian

4 7

evaluate arbitrary code + mutable variables
by Jeffrey Brown 14 May '15

14 May '15

I wrote a graph-like data type, with some functions for adding statements and relationships between statements. (It's different from a graph in that there's no edge/vertex distinction; there are only statements, but a statement might refer to other statements.) Currently I'm using them in GHCI. Because it does not allow one to change a variable, I keep having to do things like this: let g0 = emptyDocument let s1 = newStatement ... let g1 = addStatement s1 g0 let s2 = newStatement ... let g2 = addStatement s2 g1 ... If I wrote a standalone application, I could use mutable variables, so I would not have to define a new object every time I want to modify an existing one. However I like being able to type in arbitrary code into GHCI. Can one have both of those at once? That is, could I either (1) use MVars from within GHCI, or (2) write a standalone app that lets the user evaluate arbitrary Haskell?

3 3

Suggestion: "Sizable" super class for Storable
by jones.noamle＠gmail.com 14 May '15

14 May '15

Storable instances have a size, given by sizeOf. In many cases, we're not interested in peeking/poking data but only passing it opaquely via the FFI. A common use case is when the C API offers an "init" function such as: void mycontext_init(mycontext *context); For these cases it would be useful to know the size of "mycontext", so we could malloc it and pass a pointer to mycontext_init. Also, it allows Haskell-side code to decide how it wants to allocate the data, perhaps using some other (external) mechanism not related to the specific API that the FFI bindings are wrapping. c2hs would benefit by allowing users to use the '+' notation in function parameters (which generate malloc-and-pass style code), without having to guess the size of the structure. Instead, it could simply use the Sizable (TM) instance to get the size, and the user will define Sizable in any way they want (for example, using the {#sizeof#} macro, which is somewhat unreliable, or by hard-coding or manually entering the size or by some other method). Your thoughts are much appreciated!

3 2

IDE-backend + Atom editor
by JP Moresmau 14 May '15

14 May '15

Hello, when the open sourcing of IDE-backend was announced ( https://www.fpcomplete.com/blog/2015/03/announce-ide-backend) one thing mentioned was Atom support, and indeed the home page for the client ( https://github.com/chrisdone/ide-backend-client) mentions Atom. But is there a project out there I can use that brings the two together? The ide-haskell (https://atom.io/packages/ide-haskell) Atom plugin still relies on ghc-mod as far as I can tell. I saw edsko tutorial on writing Atom plugin in Haskell ( http://edsko.net/2015/02/14/atom-haskell/) so it seem we are tentalizingly close to have Atom + Haskell implemented in Haskell, and I'd like to give it a go if there's anything available out there (and maybe help if needed). Thanks! JP -- JP Moresmau http://jpmoresmau.blogspot.com/

2 1

CFP: Extended Deadline: Functional High-Performance Computing (held with ICFP)
by Geoffrey Mainland 14 May '15

14 May '15

====================================================================== CALL FOR PAPERS FHPC 2015 The 4th ACM SIGPLAN Workshop on Functional High-Performance Computing Vancouver, British Columbia, Canada, Canada September 3, 2015 https://sites.google.com/site/fhpcworkshops/ Co-located with the International Conference on Functional Programming (ICFP 2015) EXTENDED Submission Deadline: Friday, 22 May, 2015 (anywhere on earth) ====================================================================== The FHPC workshop aims at bringing together researchers exploring uses of functional (or more generally, declarative or high-level) programming technology in application domains where high performance is essential. The aim of the meeting is to enable sharing of results, experiences, and novel ideas about how high-level, declarative specifications of computationally challenging problems can serve as maintainable and portable code that approaches (or even exceeds) the performance of machine-oriented imperative implementations. All aspects of performance critical programming and parallel programming are in-scope for the workshop, irrespective of hardware target. This includes both traditional large-scale scientific computing (HPC), as well as work targeting single node systems with SMPs, GPUs, FPGAs, or embedded processors. It is becoming apparent that radically new and well founded methodologies for programming such systems are required to address their inherent complexity and to reconcile execution performance with programming productivity. Proceedings: ============ Accepted papers will be published by the ACM and will appear in the ACM Digital Library. * Submissions due: Friday, 22 May, 2015 (anywhere on earth) * Author notification: Friday, 26 June, 2015 * Final copy due: Sunday, 19 July, 2015 Submitted papers must be in portable document format (PDF), formatted according to the ACM SIGPLAN style guidelines (2 column, 9pt format). See http://www.sigplan.org/authorInformation.htm for more information and style files. Typical papers are expected to be 8 pages (but up to four additional pages are permitted). Contributions to FHPC 2015 should be submitted via Easychair, at the following URL: * https://www.easychair.org/conferences/?conf=fhpc15 The submission site is now open. The FHPC workshops adhere to the ACM SIGPLAN policies regarding programme committee contributions and republication. Any paper submitted must adhere to ACM SIGPLAN's republication policy. PC member submissions are welcome, but will be reviewed to a higher standard. http://www.sigplan.org/Resources/Policies/Review http://www.sigplan.org/Resources/Policies/Republication Travel Support: =============== Student attendees with accepted papers can apply for a SIGPLAN PAC grant to help cover travel expenses. PAC also offers other support, such as for child-care expenses during the meeting or for travel costs for companions of SIGPLAN members with physical disabilities, as well as for travel from locations outside of North America and Europe. For details on the PAC programme, see its web page (http://www.sigplan.org/PAC.htm) Programme Committee: ==================== Tiark Rompf (co-chair), Purdue University, USA Geoffrey Mainland (co-chair), Drexel University, USA Kevin Brown Stanford University, USA James Cheney University of Edinburgh, UK Albert Cohen INRIA, France David Duke University of Leeds, UK Yukiyoshi Kameyama University of Tsukuba, Japan Gabriele Keller University of New South Wales, Australia Paul H J Kelly Imperial College London, UK Trevor L. Mcdonell Indiana University, USA Greg Michaelson Heriot-Watt University, UK Cosmin E. Oancea University of Copenhagen, Denmark Markus Pueschel ETH Zurich, Switzerland Sukyoung Ryu KAIST, Korea Alexander Slesarenko Huawei, Russia Josef Svenningsson Chalmers University of Technology, Sweden

1 0

all for Contributions - Haskell Communities and Activities Report, May 2015 edition (28th edition)
by Mihai Maruseac 14 May '15

14 May '15

Dear all, We would like to collect contributions for the 28th edition of the ============================================================ Haskell Communities & Activities Report http://www.haskell.org/haskellwiki/Haskell_Communities_and_Activities_Report Submission deadline: 17 May 2015 (please send your contributions to hcar at haskell.org, in plain text or LaTeX format) ============================================================ This is the short story (one extra point to the story added from previous editions): * If you are working on any project that is in some way related to Haskell, please write a short entry and submit it. Even if the project is very small or unfinished or you think it is not important enough --- please reconsider and submit an entry anyway! * If you are interested in an existing project related to Haskell that has not previously been mentioned in the HCAR, please tell us, so that we can contact the project leaders and ask them to submit an entry. * **NEW**: If you are working on a project that is looking for contributors, please write a short entry and submit it, mentioning that your are looking for contributors. The final report might have an index with such projects, provided we get enough such submissions. * Feel free to pass on this call for contributions to others that might be interested. More detailed information: The Haskell Communities & Activities Report is a bi-annual overview of the state of Haskell as well as Haskell-related projects over the last, and possibly the upcoming six months. If you have only recently been exposed to Haskell, it might be a good idea to browse the previous edition --- you will find interesting projects described as well as several starting points and links that may provide answers to many questions. Contributions will be collected until the submission deadline. They will then be compiled into a coherent report that is published online as soon as it is ready. As always, this is a great opportunity to update your webpages, make new releases, announce or even start new projects, or to talk about developments you want every Haskeller to know about! Looking forward to your contributions, Mihai Maruseac and Alejandro Serrano Mena FAQ: Q: What format should I write in? A: The required format is a LaTeX source file, adhering to the template that is available at: http://haskell.org/communities/05-2015/template.tex There is also a LaTeX style file at http://haskell.org/communities/05-2015/hcar.sty that you can use to preview your entry. If you do not know LaTeX, then use plain text. If you modify an old entry that you have written for an earlier edition of the report, you should soon receive your old entry as a template (provided we have your valid email address). Please modify that template, rather than using your own version of the old entry as a template. Q: Can I include Haskell code? A: Yes. Please use lhs2tex syntax (http://www.andres-loeh.de/lhs2tex/) The report is compiled in mode polycode.fmt. Q: Can I include images? A: Yes, you are even encouraged to do so. Please use .jpg or .png format, then, PNG being preferred for simplicity. Q: Should I send files in .zip archives or similar? A: No, plain file attachements are the way. Q: How much should I write? A: Authors are asked to limit entries to about one column of text. A general introduction is helpful. Apart from that, you should focus on recent or upcoming developments. Pointers to online content can be given for more comprehensive or "historic" overviews of a project. Images do not count towards the length limit, so you may want to use this opportunity to pep up entries. There is no minimum length of an entry! The report aims for being as complete as possible, so please consider writing an entry, even if it is only a few lines long. Q: Which topics are relevant? A: All topics which are related to Haskell in some way are relevant. We usually had reports from users of Haskell (private, academic, or commercial), from authors or contributors to projects related to Haskell, from people working on the Haskell language, libraries, on language extensions or variants. We also like reports about distributions of Haskell software, Haskell infrastructure, books and tutorials on Haskell. Reports on past and upcoming events related to Haskell are also relevant. Finally, there might be new topics we do not even think about. As a rule of thumb: if in doubt, then it probably is relevant and has a place in the HCAR. You can also simply ask us. Q: Is unfinished work relevant? Are ideas for projects relevant? A: Yes! You can use the HCAR to talk about projects you are currently working on. You can use it to look for other developers that might help you. You can use HCAR to ask for more contributors to your project, it is a good way to gain visibility and traction. Q: If I do not update my entry, but want to keep it in the report, what should I do? A: Tell us that there are no changes. The old entry will typically be reused in this case, but it might be dropped if it is older than a year, to give more room and more attention to projects that change a lot. Do not resend complete entries if you have not changed them. Q: Will I get confirmation if I send an entry? How do I know whether my email has even reached its destination, and not ended up in a spam folder? A: Prior to publication of the final report, we will send a draft to all contributors, for possible corrections. So if you do not hear from us within two weeks after the deadline, it is safer to send another mail and check whether your first one was received. -- Mihai Maruseac (MM) "If you don't know, the thing to do is not to get scared, but to learn." -- Atlas Shrugged.

1 1

Job openings for Haskell, O'Caml programmers at Swedish spin-off startup
by Johan Glimming 14 May '15

14 May '15

Hi Haskell people, and beyond, Summary: Openings for software developers <https://goo.gl/vdu1d4> highly trained in functional programming, six developer or more entangled in our "teams", three with considerable Haskell, O'Caml experience, talents, entrepreneurial mind-set, and three for Scala, spear-edge Functor Consulting branch, with out-standing industrial track-records, as the new constructive programming paradigm is gradually unleashed to the software industry from Functor Group AB, Sweden. Keywords: type theory, dependent type, new programming paradigm, static analysis with dependent types, DDD-like development with solid Scandinavian-style Martin-Löf type theory operational semantics in the VM above LLVM, Haskell, O’Caml, embedded systems is one submarket. Official call with the details here: https://goo.gl/vdu1d4 <https://goo.gl/vdu1d4> <https://goo.gl/vdu1d4> We will always work closely with academia and internships, MSc theses and research collaborations are always interesting though right now we are focused on delivering to customers and building up the business meaning larger research projects are not yet possible, a large-scale EU project planned but not for this year. You’re most welcome to apply via jobs(a)functor.se <mailto:jobs@functor.se>. See the call for details! Yours Sincerely, Johan Glimming — Dr Johan Glimming Chief Technical Officer and Co-Founder at Functor AB and Functor Group AB LinkedIn profile: www.linkedin.com/in/glimming <http://www.linkedin.com/in/glimming> Mobile: +46-76-7646000 (direct) Main: +46-8-55005500 Functor AB, Box 7070, 164 07 Kista, SWEDEN Web: www.functorgroup.com <http://www.functorgroup.com/> Twitter: @functors <https://www.twitter.com/functors/>

1 0

Start GHCI with a static library
by aditya siram 13 May '15

13 May '15

Hi all, I have a Haskell library I'd like to load up in GHCI along with a statically linked C library (libblah.a) . Is there any way to do this? My Googling only turns up instructions on loading a shared library (libblah.so). Thanks! -deech

3 3