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Haskell Weekly News: Issue 271
by Daniel Santa Cruz 27 Jun '13

27 Jun '13

Welcome to issue 271 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of June 9 to 11, 2013. Quotes of the Week * cmccann: also please note that "malign" remains one of my best function names ever * dolio: Peak file descriptors is a myth. * mami: i think my brain rewired for higher typesystem compatibility in my sleep * elliott: it's impure but only depending on the environment! which is to say it is impure. * johnw: lens makes one into a mutating ninja * applicativ: een my language we say Z for one * DavidJacobs: Code is like poetry; most of it shouldn't have been written. * merijn: If I could program with arbitrary real world side effects I'd use "unsafeStabComputerUser" if someone attempted that * shachaf: Hackage going down regularly is part of the rustic charm of Haskell! * shachaf: JavaScript is the best example of a domain-specific language. Because of the same-origin policy. * chrisdone: [on being invited to help with idris development] dude i've already got 20 yaks lined up waiting to be shaved, don't send me a whole truck full * shachaf: edwardk isn't benevolent or malevolent. edwardk is more of a simple mechanical process tending toward maximal complexity. * AndrejBauer: When have you ever heard a category theorist say: I want to prove this diagram commutesâLet's suppose it doesn't. Top Reddit Stories * Applicative => Monad is coming. Domain: haskell.org, Score: 122, Comments: 62 On Reddit: [1] http://goo.gl/JCvQ4 Original: [2] http://goo.gl/fJxeX * The Homotopy Type Theory Book is now available for free online and in print at Lulu.com Domain: homotopytypetheory.org, Score: 86, Comments: 16 On Reddit: [3] http://goo.gl/x8nLW Original: [4] http://goo.gl/DR9gf * Three useful monads Domain: adit.io, Score: 71, Comments: 25 On Reddit: [5] http://goo.gl/WHqPr Original: [6] http://goo.gl/1r8nC * Beta sign up for FP Complete new IDE Domain: fpcomplete.com, Score: 63, Comments: 11 On Reddit: [7] http://goo.gl/RPV0P Original: [8] http://goo.gl/c03Od * HLearn implements more with 6 trivial lines of Haskell than Weka implements with over 100 complex lines of Java Domain: izbicki.me, Score: 47, Comments: 9 On Reddit: [9] http://goo.gl/EEqwS Original: [10] http://goo.gl/Ukk4E * Top secret School of Haskell articles leaked Domain: self.haskell, Score: 47, Comments: 17 On Reddit: [11] http://goo.gl/zhhYm Original: [12] http://goo.gl/zhhYm * F-algebra tutorial Domain: fpcomplete.com, Score: 41, Comments: 35 On Reddit: [13] http://goo.gl/Ybmbs Original: [14] http://goo.gl/szfGk * John Carmack on haskell today. Domain: self.haskell, Score: 40, Comments: 79 On Reddit: [15] http://goo.gl/8qHkt Original: [16] http://goo.gl/8qHkt * Data Flow Fusion with Series Expressions in Haskell Domain: justtesting.org, Score: 40, Comments: 19 On Reddit: [17] http://goo.gl/ZNeIP Original: [18] http://goo.gl/JAjjy * So you still don't understand Hindley-Milner? Part 1 Domain: akgupta.ca, Score: 38, Comments: 0 On Reddit: [19] http://goo.gl/OOk43 Original: [20] http://goo.gl/SZ1Gb * Ask HN: Any downsides of programming in Haskell? Domain: news.ycombinator.com, Score: 36, Comments: 104 On Reddit: [21] http://goo.gl/vRuHW Original: [22] http://goo.gl/fcleS * FP Complete - Haskell Introduction Domain: youtube.com, Score: 36, Comments: 12 On Reddit: [23] http://goo.gl/GqgC5 Original: [24] http://goo.gl/KoVYs * Fix your posture with haskell Domain: github.com, Score: 35, Comments: 2 On Reddit: [25] http://goo.gl/lznTr Original: [26] http://goo.gl/x21Ax * preprint list for ICFP'13 papers (additional links welcome) Domain: github.com, Score: 34, Comments: 9 On Reddit: [27] http://goo.gl/mZsTn Original: [28] http://goo.gl/bhbC9 * GHC: now with closed type families Domain: github.com, Score: 34, Comments: 15 On Reddit: [29] http://goo.gl/JJSSv Original: [30] http://goo.gl/QlV4s Top StackOverflow Questions * How to compare two functions for equivalence, as in (λx.2*x) == (λx.x+x)? votes: 15, answers: 2 Read on SO: [31] http://goo.gl/A6YDd * Should I use typeclasses or not? votes: 15, answers: 2 Read on SO: [32] http://goo.gl/EOV1M * Is there something like `map2 :: (i -> a) -> (i -> b) -> [i] -> [(a,b)]`? votes: 11, answers: 2 Read on SO: [33] http://goo.gl/WZyEy * Why isn't GeneralizedNewtypeDeriving a Safe Haskell? votes: 11, answers: 1 Read on SO: [34] http://goo.gl/on6Fc * It's not a monad, but what is it? votes: 10, answers: 0 Read on SO: [35] http://goo.gl/sm9gR * Writing efficient iterative loop for ST monad votes: 10, answers: 0 Read on SO: [36] http://goo.gl/WAAwA * Getting multiple results from map with “lens” votes: 10, answers: 2 Read on SO: [37] http://goo.gl/zqX8E * How to run Frege programs on Android? votes: 10, answers: 2 Read on SO: [38] http://goo.gl/XlSCN * Are there problems that can't be solved efficiently without arrays? [duplicate] votes: 9, answers: 0 Read on SO: [39] http://goo.gl/Z5j9a * Haskell: How to organize a group of functions that all take the same arguments votes: 9, answers: 4 Read on SO: [40] http://goo.gl/z64H7 Until next time, [41]+Daniel Santa Cruz References 1. http://www.haskell.org/haskellwiki/Functor-Applicative-Monad_Proposal 2. http://www.reddit.com/r/haskell/comments/1gsejt/applicative_monad_is_coming/ 3. http://homotopytypetheory.org/book/ 4. http://www.reddit.com/r/haskell/comments/1gr3uw/the_homotopy_type_theory_bo… 5. http://adit.io/posts/2013-06-10-three-useful-monads.html 6. http://www.reddit.com/r/haskell/comments/1g3a7e/three_useful_monads/ 7. https://www.fpcomplete.com/blog/2013/06/beta-sign-up 8. http://www.reddit.com/r/haskell/comments/1giy7l/beta_sign_up_for_fp_complet… 9. http://izbicki.me/blog/hlearns-code-is-shorter-and-clearer-than-wekas 10. http://www.reddit.com/r/haskell/comments/1g4v7u/hlearn_implements_more_with… 11. http://www.reddit.com/r/haskell/comments/1g5k80/top_secret_school_of_haskel… 12. http://www.reddit.com/r/haskell/comments/1g5k80/top_secret_school_of_haskel… 13. https://www.fpcomplete.com/user/bartosz/understanding-algebras 14. http://www.reddit.com/r/haskell/comments/1g2g3s/falgebra_tutorial/ 15. http://www.reddit.com/r/haskell/comments/1g1mvx/john_carmack_on_haskell_tod… 16. http://www.reddit.com/r/haskell/comments/1g1mvx/john_carmack_on_haskell_tod… 17. http://justtesting.org/post/53175916852/data-flow-fusion-with-series-expres… 18. http://www.reddit.com/r/haskell/comments/1gi5m1/data_flow_fusion_with_serie… 19. http://akgupta.ca/blog/2013/05/14/so-you-still-dont-understand-hindley-miln… 20. http://www.reddit.com/r/haskell/comments/1g0ueo/so_you_still_dont_understan… 21. https://news.ycombinator.com/item?id=5893442 22. http://www.reddit.com/r/haskell/comments/1gknfs/ask_hn_any_downsides_of_pro… 23. https://www.youtube.com/watch?v=Fqi0Xu2Enaw 24. http://www.reddit.com/r/haskell/comments/1glw2o/fp_complete_haskell_introdu… 25. https://github.com/keera-studios/keera-posture 26. http://www.reddit.com/r/haskell/comments/1gr044/fix_your_posture_with_haske… 27. https://github.com/gasche/icfp2013-papers#readme 28. http://www.reddit.com/r/haskell/comments/1gg2xf/preprint_list_for_icfp13_pa… 29. https://github.com/ghc/ghc/commit/569b26526403df4d88fe2a6d64c7dade09d003ad 30. http://www.reddit.com/r/haskell/comments/1gu2yl/ghc_now_with_closed_type_fa… 31. http://stackoverflow.com/questions/17045941/how-to-compare-two-functions-fo… 32. http://stackoverflow.com/questions/17100036/should-i-use-typeclasses-or-not 33. http://stackoverflow.com/questions/17074424/is-there-something-like-map2-i-… 34. http://stackoverflow.com/questions/17137111/why-isnt-generalizednewtypederi… 35. http://stackoverflow.com/questions/17034427/its-not-a-monad-but-what-is-it 36. http://stackoverflow.com/questions/17126923/writing-efficient-iterative-loo… 37. http://stackoverflow.com/questions/17144334/getting-multiple-results-from-m… 38. http://stackoverflow.com/questions/17222383/how-to-run-frege-programs-on-an… 39. http://stackoverflow.com/questions/17128103/are-there-problems-that-cant-be… 40. http://stackoverflow.com/questions/17176829/haskell-how-to-organize-a-group… 41. https://plus.google.com/105107667630152149014/about

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homotopy type theory for amateurs
by Ben 26 Jun '13

26 Jun '13

hello cafe -- by now i'm sure you have heard that the homotopy type theory folks have just written up a free introductory book on their project. http://homotopytypetheory.org/2013/06/20/the-hott-book/ gabriel gonzalez and i are starting up a small reading group for the book. the level of study will be "amateur", though i have high hopes for rigor and thoroughness. personally, i know hardly any type theory or logic, and the last time i thought about homotopy theory in any seriousness was years ago. thankfully the book looks very accessible. being time-constrained we were going to do it mostly over email, maybe starting a google group or other mailing list, but we might meet as well, say once a month in san francisco (where we both are.) if you're interested in joining us, send me an email (midfield at gmail) and i'll try to keep you informed of any developments. best, ben

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Geometric Algebra [Was: writing a function to make a correspondance between type-level integers and value-level integers]
by oleg＠okmij.org 26 Jun '13

26 Jun '13

> It seems very interesting, but I have not currently the time to make a > detailed comparison with vector/tensor algebra. Moreover I have not I would suggest the freely available Oersted Medal Lecture 2002 by David Hestenes http://geocalc.clas.asu.edu/pdf/OerstedMedalLecture.pdf the person who discovered and developed the Geometric Algebra. In particular, see Section V of the above paper. It talks about vectors, geometric products, the coordinate-free representation for `vector product' and the geometric meaning of the imaginary unit i. Section 1 gives a good motivation for the Geometric Algebra. Other sections of the paper develop physical applications, from classical mechanics to electrodynamics to non-relativistic and relativistic quantum mechanics. Computer Scientists might then like http://www.geometricalgebra.net/ see the good and free introduction http://www.geometricalgebra.net/downloads/ga4cs_chapter1.pdf Incidentally, David Hestenes said in the lecture that he has applied for an NSF grant to work on Geometric Algebra TWELVE times in a row, and was rejected every single time.

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writing a function to make a correspondance between type-level integers and value-level integers
by oleg＠okmij.org 26 Jun '13

26 Jun '13

Well, I guess you might be interested in geometric algebra then http://dl.acm.org/citation.cfm?id=1173728 because Geometric Algebra is a quite more principled way of doing component-free calculations. See also the web page of the author http://staff.science.uva.nl/~fontijne/ Geigen seems like a nice DSL that could well be embedded in Haskell. Anyway, the reason I pointed out Vectro is that it answers your question about reifying and reflecting type-level integers (by means of a type class).

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Roman Numeral Problem
by Christopher Howard 26 Jun '13

26 Jun '13

Hi. I am working on some practice programming problems, and one is the Roman numeral problem: write a program that converts Roman numerals into their (arabic) numeral equivalent. I imagine I could hack something together, but I was trying to think about the problem a bit more deeply. I don't know much about parsing, but I was wondering if this problem matched up with some kind of parsing or grammar or other generic approach to thinking about the problem. (I once read something about Context Free Grammars, which was rather interesting.) I can do more of my own research if I can get some initial guidance. -- frigidcode.com

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ANNOUNCE: haskell-names-0.1
by Roman Cheplyaka 26 Jun '13

26 Jun '13

I am pleased to announce the first public release of haskell-names, a name resolution library for haskell-src-exts AST. Namely, it can do the following: * for a module, compute its interface, i.e. the set of entities exported by the module, together with their original names. * for each name in the module, figure out what it refers to — whether it's bound locally (say, by a where clause) or globally (and then give its origin). Thanks to haskell-packages, this library is fully integrated with Cabal, so that you can easily generate name interfaces for any Cabalized package. See more details in the README: http://documentup.com/haskell-suite/haskell-names This library is based on the code written by Lennart Augustsson in 2010. Little of that code survived, but nevertheless it's been a great help. Roman

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tangential request...
by Mark Lentczner 26 Jun '13

26 Jun '13

As you may know, I've been writing a shell in Haskell called Plush<https://code.google.com/p/plush/> . I'm working on the look of the terminal input and output, and I want to do a little data gathering. I want to know what your terminal looks like! You can help me by: 1) Download this file: http://www.ozonehouse.com/mark/plush/TerminalDisplay.txt 2) Open a new terminal window 3) Do not resize the terminal window 4) cat the file 5) Take a screen shot of the whole terminal window 6) E-mail it to me: mark.lentczner%2Bterm(a)gmail.com The file contains some sample text, including some screen codes to change colors and bold. This looks like: - in my terminal program <http://www.ozonehouse.com/mark/plush/term.png> - in Plush <http://www.ozonehouse.com/mark/plush/term-plush.png> (bleeding edge, not checked in yet) Thanks!

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[OT]Help with translating Error Monads to C++
by Larry Evans 25 Jun '13

25 Jun '13

Currently in the c++ developers ml, there's a discussion of a proposed Expected<T> or an Either<L,R> template: http://article.gmane.org/gmane.comp.lib.boost.devel/242496 A lot of the discussion appears, at least to me, to not be aware of how haskell handles similar situations. The above link was to my post suggesting they try to emulate the way haskell solves the problem using Monads. However, I've only briefly dabbled in haskell; hence, my responses on that thread are probably missing something. I invite anyone on this list to please provide insights on this particular thread in the boost.devel mailing list. -kind regards, Larry

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Munich Haskell Meeting
by Heinrich Hördegen 24 Jun '13

24 Jun '13

Dear all, if you plan to join our monthly Munich Haskell Meeting on Wed, 26th of June, please go to http://www.haskell-munich.de/dates and hit the button. See you soon, Heinrich -- -- Funktionale Programmierung Dr. Heinrich Hördegen Gutenbergstr. 26 80638 München FON: +49 (89) 12 59 79 49 FAX: +49 (89) 12 59 79 50 hoerdegen(a)funktional.info www.funktional.info --

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A friendly reminder: Ghent-FPG meeting on 26 June, 2013
by Andy Georges 24 Jun '13

24 Jun '13

Hello, This is to remind you that you are kindly invited to attend our next meeting. The original email follows below. The "Functional Programming Group Ghent" (GhentFPG) [1] is a friendly group for all people interested in functional programming, with a tendency towards Haskell. It is organised as part of Zeus WPI [2]. We are pleased to announce that we will hold a next meeting on Wednesday, 26th of June, starting at 19h00! There will be three talks. The main presentation, by Adam Bergmark from Silk [3] is about Fay [4]: Fay is a proper subset of Haskell that compiles to JavaScript. There is a compiler with the same name written in Haskell. Web browsers only speak JavaScript but more and more people find that they want to compile to JavaScript instead. Why do we want to compile Haskell to JavaScript, and what advantages does Fay have compared to other compilers? What are the challenges in compiling Haskell and supporting a language ecosystem, and how do we do it? What can Fay currently do, and what is planned for the future? This will be a broad overview about Fay for prospective users, followed by an in-depth look at interesting parts of the compiler internals. Additionally, there will be two short talks by two students who did an Msc. Thesis about functional programming languages: "Genetic Algorithms in Haskell" by Matthias Delbar "Automatic Detection of Recursion Patterns" by Jasper Van der Jeugt The meeting will take place in the Jozef Plateauzaal at the following address, Faculteit Ingenieurswetenschappen Universiteit Gent Plateaustraat 22 9000 Gent As mentioned above, we aim to start at 19:00. After the meeting we can go for drinks in a nearby pub (this latter part is, of course, completely optional) We hope to see you all there! Regards, On behalf of the GhentFPG organising committee. [1]: http://groups.google.com/group/ghent-fpg [2]: http://zeus.ugent.be/ [3]: http://www.silkapp.com/ [4]: http://www.fay-lang.org/

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