May 2016 - Haskell-Cafe

[Final CFP] Haskell 2016
by Geoffrey Mainland 16 May '16

16 May '16

======================================================================== ACM SIGPLAN CALL FOR SUBMISSIONS Haskell Symposium 2016 Nara, Japan, 22-23 September 2016, directly after ICFP http://www.haskell.org/haskell-symposium/2016 ======================================================================== The ACM SIGPLAN Haskell Symposium 2016 will be co-located with the International Conference on Functional Programming (ICFP 2016) in Nara, Japan. The Haskell Symposium aims to present original research on Haskell, discuss practical experience and future development of the language, and to promote other forms of denotative programming. Topics of interest include: * Language Design, with a focus on possible extensions and modifications of Haskell as well as critical discussions of the status quo; * Theory, such as formal semantics of the present language or future extensions, type systems, effects, metatheory, and foundations for program analysis and transformation; * Implementations, including program analysis and transformation, static and dynamic compilation for sequential, parallel, and distributed architectures, memory management, as well as foreign function and component interfaces; * Libraries, that demonstrate new ideas or techniques for functional programming in Haskell; * Tools, such as profilers, tracers, debuggers, preprocessors, and testing tools; * Applications, to scientific and symbolic computing, databases, multimedia, telecommunication, the web, and so forth; * Functional Pearls, being elegant and instructive programming examples; * Experience Reports, to document general practice and experience in education, industry, or other contexts. Papers in the latter three categories need not necessarily report original academic research results. For example, they may instead report reusable programming idioms, elegant ways to approach a problem, or practical experience that will be useful to other users, implementors, or researchers. The key criterion for such a paper is that it makes a contribution from which other Haskellers can benefit. It is not enough simply to describe a standard solution to a standard programming problem, or report on experience where you used Haskell in the standard way and achieved the result you were expecting. More advice is available via the Haskell wiki: (http://wiki.haskell.org/HaskellSymposium/ExperienceReports) Regular papers should explain their research contributions in both general and technical terms, identifying what has been accomplished, explaining why it is significant, and relating it to previous work, and to other languages where appropriate. In addition, we solicit proposals for: * System Demonstrations, based on running software rather than novel research results. These proposals should summarize the system capabilities that would be demonstrated. The proposals will be judged on whether the ensuing session is likely to be important and interesting to the Haskell community at large, whether on grounds academic or industrial, theoretical or practical, technical, social or artistic. Please contact the program chair with any questions about the relevance of a proposal. 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 program, see its web page (http://pac.sigplan.org) Proceedings: ============ Accepted papers will be included in the ACM Digital Library. Authors must grant ACM publication rights upon acceptance (http://authors.acm.org/main.html) Authors are encouraged to publish auxiliary material with their paper (source code, test data, etc.); they retain copyright of auxiliary material. Accepted proposals for system demonstrations will be posted on the symposium website but not formally published in the proceedings. All accepted papers and proposals will be posted on the conference website one week before the meeting. Publication date: The official publication date of accepted papers is the date the proceedings are made available in the ACM Digital Library. This date may be up to two weeks prior to the first day of the conference. The official publication date affects the deadline for any patent filings related to published work. Submission Details: =================== Submitted papers should be in portable document format (PDF), formatted using the ACM SIGPLAN style guidelines (http://www.acm.org/sigs/sigplan/authorInformation.htm) The text should be in a 9-point font in two columns. The length is restricted to 12 pages, except for "Experience Report" papers, which are restricted to 6 pages. Papers need not fill the page limit---for example, a Functional Pearl may be much shorter than 12 pages. Each paper submission must adhere to SIGPLAN's republication policy, as explained on the web. Demo proposals are limited to 2-page abstracts, in the same ACM format as papers. "Functional Pearls", "Experience Reports", and "Demo Proposals" should be marked as such with those words in the title at time of submission. The paper submission deadline and length limitations are firm. There will be no extensions, and papers violating the length limitations will be summarily rejected. Papers may be submitted at: https://icfp-haskell2016.hotcrp.com/ Submission Timetable: ===================== Early Track Regular Track System Demos ---------------- ------------------- --------------- 1st April Paper Submission 20th May Notification 6th June Abstract Submission 10th June Paper Submission 17th June Resubmission Demo Submission 8th July Notification Notification Notification 31st July Camera ready due Camera ready due Deadlines stated are valid anywhere on earth. The Haskell Symposium uses a two-track submission process so that some papers can gain early feedback. Papers can be submitted to the early track on 1st April. On 20th May, strong papers are accepted outright, and the others will be given their reviews and invited to resubmit. On 17th June, early track papers may be resubmitted and are sent back to the same reviewers. The Haskell Symposium regular track operates as in previous years. Papers accepted via the early and regular tracks are considered of equal value and will not be distinguished in the proceedings. Although all papers may be submitted to the early track, authors of functional pearls and experience reports are particularly encouraged to use this mechanism. The success of these papers depends heavily on the way they are presented, and submitting early will give the program committee a chance to provide feedback and help draw out the key ideas. Program Committee: =================== James Cheney University of Edinburgh Iavor Diatchki Galois David Duke University of Leeds Richard Eisenberg University of Pennsylvania Ken Friis Larsen University of Copenhagen Andy Gill University of Kansas Zhenjiang Hu National Institute of Informatics Ranjit Jhala UC San Diego Yukiyoshi Kameyama University of Tsukuba Geoffrey Mainland (chair) Drexel University Mary Sheeran Chalmers University of Technology David Terei Stanford Niki Vazou UC San Diego Dimitrios Vytiniotis Microsoft Research =====================================================================

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Confirmation Email for Hackage Account?
by Christopher Howard 15 May '16

15 May '16

Hi. How long does it usually take to receive the confirmation email for a hackage account registration? -- http://justonemoremathproblem.com To protect my privacy, please use PGP encryption. It's free and easy to use! My public key ID is 0x340EA95A (pgp.mit.edu)

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[ANN] process-extras-0.4.1
by David Fox 14 May '16

14 May '16

I thought I should announce the process-extras package, available from hackage <https://hackage.haskell.org/package/process-extras>. It extends the process reading functions in System.Process to allow output types ByteString and Text, both strict and lazy. It also provides a function readCreateProcessLazy that can read from processes whose output is infinite - the regular readProcess functions block until they find EOF. There are also some new usage examples in the README.md file. This package has a long history, so if you are familiar with an older version you may want to take another look. Best, David Fox

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Yesos forms and types with foreign keys
by fr33domlover 14 May '16

14 May '16

Hello, I have a question about RESTful web apps in Haskell. I'm using Yesod but I suppose the same question can apply to any other framework with type safety features. Suppose I have entities A and B defined in my Persistent model file. One of A's fields is a foreign key referring to B. Each A has its own unique B. The process of creating a new A would be: 1. Set the user a web form via GET 2. Receive for field data via POST 3. Validate the input 4. Insert a new B value to the DB, and get its ID 5. Define an A value which includes that ID as a foreign key, and insert the new A value to the DB In Yesod, If I use a form of type 'AForm A', running the form must return a complete A value. But when I runFormPost, I don't have the B entity yet so I don't have an ID for the foreign key! Ideas what I can do: - Set that field to some dummy value, and override it later when I insert the B value and get its ID - Define a 'NewA' type which has the same fields as A except for that foreign key field - Insert to the DB in the form itself. Define my form as an MForm so that I have access to Handler monad and use runDB to insert to the DB right in the form itself, i.e. form success means the DB has been updated I know little about REST common practice but afaik to allow alternative representations, e.g. a JSON API, my forms need to return entity types, e.g. A and not some partial NewA. Also my forms so far are all simple AForms which just do validation, sometimes against the DB, and never insert or delete anything. Insertion and deletetion I always do in the handlers. The dummy value may work, I already have one case where I use it, but it's ugly and requires that I rely on the specific underlying type of the key, e.g. Int64 for postgresql but could be ByteString for other backends if I ever want to change. Maybe some 'dummyKey' function could make it prettier, if at all this is a good approach. What should I do here? --fr33

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Re: [Haskell-cafe] Haskell-Cafe Digest, Vol 153, Issue 17
by Julian Leviston 14 May '16

14 May '16

If you’re on the mac, Haskell for Mac is very good to start with. http://haskellformac.com http://www.happylearnjavascripttutorial.com/ <http://www.happylearnjavascripttutorial.com/> - begin programming with JavaScript today using our awesome new method! http://www.happylearnhaskelltutorial.com/ <http://www.happylearnhaskelltutorial.com/> - begin programming with Haskell today using our awesome new method! > On 14 May 2016, at 10:00 PM, haskell-cafe-request(a)haskell.org wrote: > > Date: Fri, 13 May 2016 15:47:29 -0300 > From: Henson <jfsihenson(a)gmail.com <mailto:jfsihenson@gmail.com>> > To: haskell-cafe(a)haskell.org <mailto:haskell-cafe@haskell.org> > Subject: [Haskell-cafe] Haskell Better Editor > Message-ID: <57362141.7070205(a)gmail.com <mailto:57362141.7070205@gmail.com>> > Content-Type: text/plain; charset=windows-1252; format=flowed > > Friends, > > What's the better text editor for Haskell development? > More productive and more rapid learning curve? > Any trick for initiating in haskell and rapid advance? > Please let your comments. > > Thank you, > Josenildo

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Problems with function recursion in Haskell
by Henson 13 May '16

13 May '16

Hi, I'm new in Haskell and I need help in recursion. That function below is returning "*** Exception: Prelude.head: empty list" and I need resolve that: execNTimes 0 [] = return() execNTimes n xs = if n<=0 || null xs then return() else do si <- getLine let s = words si l = read (s !! 1) :: Int r = read (s !! 2) :: Int if head s=="Q" then do let z = slice l r xs m = foldl lcm 1 z print (m `mod` (toInteger 1000000007)) else do let s1 = update l r xs execNTimes (n-1) s1 execNTimes (n-1) xs Anybody can me help? Thank you, Josenildo Silva

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Using parallels for fibonacci
by Michael Litchard 11 May '16

11 May '16

I am trying to efficiently use multicores for my fizzbuzz <https://github.com/mlitchard/swiftfizz> project. My fizzbuzz uses a Fibonacci generator as input, and this is where it can get computationally heavy. I believe I have picked the best algorithm for my project (please correct this if wrong), and now I am trying to use the parallel package <https://hackage.haskell.org/package/parallel-3.2.1.0>. I am not getting any better performance in the sense that if I try to compute the 100th Fibonacci number, it is still computing , using 4 cores, several minutes later. Here is my attempt. Please show me how to use this library right. from src/FizzBuzz.hs fizzBuzzFib :: Integer -> [Text] fizzBuzzFib ub = parMap rdeepseq fizzbuzz $! fibSeq ub from src/FizzFub.hs fibSeq :: Integer -> [Integer] fibSeq ub = withStrategy (parBuffer buffer rdeepseq) $ genericTake ub fibbwhere buffer = 100 fibb :: [Integer] fibb = 0 : 1 : zipWith (+) fibb (tail fibb)

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Template Haskell Tutorial
by Dominik Bollmann 11 May '16

11 May '16

Hi, I've been diving into Template Haskell recently and thought to write down what I've learned. The result hopes to be a practical, example-driven introduction to Template Haskell's main features: https://wiki.haskell.org/A_practical_Template_Haskell_Tutorial I hope it serves others new to Template Haskell. It's all on the Haskell wiki, so feedback and improvements are welcome! Cheers, Dominik.

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Applying a Constraint to a Proxy'd type
by Ivan Lazar Miljenovic 11 May '16

11 May '16

I'm not sure if it's possible (and I have an alternate method of doing this so it isn't strictly speaking _necessary_, but would make the code cleaner if I can), but I would like to convert a "value" of kind (k -> Constraint) into one of kind (Proxy k -> Constraint). I can achieve this using a type family (note: I've also made this polymorphic in terms of the Proxy type used, but that isn't necessary): > type family LiftConstraint_ c pa :: Constraint where > LiftConstraint_ c (proxy a) = c a > LiftConstraint_ c pa = () ~ Bool -- A nonsensical failing Constraint value which has the problem that it can't be partially applied (which I also need). This can be wrapped up in a typeclass: > class (LiftConstraint_ c pa) => LiftConstraint c pa > instance (LiftConstraint_ c pa) => LiftConstraint c pa The problem with this is that if I try and use it somewhere that - having already a type of kind (c :: * -> Constraint) from the environment - that expects a function of type (forall a. (c a) => a -> b) with a fixed "b" value, then trying to use something like this function prevents it from working (for the purposes of argument, assume the old specification of Num that had an Eq superclass; this is the way I can produce the smallest example): > fn :: forall pn. (LiftConstraint Num (Proxy n)) => Proxy n -> Bool > fn = join (==) . asProxyTypeOf 0 The resulting error message is: "Could not deduce (a ~ Proxy n0) ..." This occurs even if I make the type of fn polymorphic in terms of the proxy type or if I make LiftConstraint_ specific. Note that the error goes away if I make the definition to be "fn = const True"; it's only if I try and _use_ the proxy value. I've tried defining and using an IsProxy type family + class but that fails to the same basic problem: it can't tell that the provided value can be pulled apart to get what's in the Proxy. Any ideas? -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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Haskell Weekly News
by Kim-Ee Yeoh 11 May '16

11 May '16

*Top Picks:* - Oskar Wickström rewrites the Oden-to-Go transpiler from Racket to Haskell <http://oden-lang.org/blog/compiler/2016/01/18/the-haskell-rewrite.html>. Oden is an FP language comprising an ML type system and LISP syntax. Oskar explains that he made the migration because of several advantages that Haskell offered over Racket: exhaustive pattern-match checking, type-guided refactoring, monad transformers, and faster execution times. Apropos, the convo over at lobste.rs <https://lobste.rs/s/8hidko/the_haskell_rewrite_the_motivation_for_moving_aw…> links to this claim by Gabriel Gonzalez: "Haskell is an amazing language for writing your own compiler. If you are writing a compiler in another language you should genuinely consider switching." - Reviewing 2015 work month-by-month, Gracjan Polak tells the story of how he decided to lead the development of Haskell Mode <https://github.com/haskell/haskell-mode/wiki/Haskell-Mode-2015-retrospective>, "a bunch of Emacs major and minor modes put together in a single package." Discussion over at /r/haskell <https://www.reddit.com/r/haskell/comments/425gn4/haskell_mode_2015_retrospe…> . - Jared Tobin presents monadic versions of five recursion-schemas <http://jtobin.ca/monadic-recursion-schemes/>, namely: cata-, ana-, para-, apo-, and hylomorphisms. *Quotes of the Week:* - Tim Kellogg: <https://lobste.rs/s/erxkun/redundancy_vs_dependencies_which_is_worse/commen…> I’ve known a few old programmers nearing retirement that have a long list of very impressive accomplishments. The older and more accomplished they get, the more they prefer redundancy over dependency. The oldest and most accomplished will write their own load balancers, TCP stacks, loggers, everything if need be. Are they on to something? - From HN: <https://news.ycombinator.com/item?id=10972051#up_10979314> If you have the time, I'd advise you to learn Haskell, in order to stretch your mind and become an excellent OCaml developer, the way learning Latin makes you a better French or Italian writer. - HN markov chain parody site headline: <http://news.ycombniator.com/comments/comments_419.html> $690 for an hour minimum wage for state management in haskell *Recorded Talk of the Week:* - On Dec 17 last year <http://www.meetup.com/haskellhackersathackerdojo/events/226870399/>, Andrew Gibiansky demoed IHaskell, a Mathematica-like "capable graphical alternative" to the ghci REPL at the NorCal Hacker Dojo. Thanks go to Joe "begriffs" Nelson who recorded the talk and summarized it into bullet points <http://begriffs.com/posts/2016-01-20-ihaskell-notebook.html>. Joe's page was well-received at both Hacker News <https://news.ycombinator.com/item?id=10942969> and Haskell Reddit <https://www.reddit.com/r/haskell/comments/41xnhw/demo_of_ihaskell_notebook_…> . p.s. There will be no News next week. HWN will resume the week after. -- Kim-Ee

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