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Re: [Haskell-cafe] Are there arithmetic composition of functions?
by oleg＠okmij.org 22 Mar '12

22 Mar '12

> At present we can easily express different flavors of conjunction, but > expressing disjunction is hard. Disjunction is not particularly difficult. See, for example, http://okmij.org/ftp/Haskell/TTypeable/TTypeable.hs and search for ORELSE. The code demonstrates higher-order type-level programming (for example, higher-order function Member with the equality predicate as the argument). The file implements closed-world negation for type predicates. See http://okmij.org/ftp/Haskell/typeEQ.html for explanations. Incidentally, one application of that machinery is precisely your original problem. The code http://okmij.org/ftp/Haskell/TTypeable/NotAFunctionT.hs implements vector spaces as function spaces, so you can use the same operation <+> :: Vspace v => v -> v -> v to add arguments of the type (Num n =>n), Num n => a -> n, Num n => a -> b -> n, etc. (there is also a scalar-vector multiplication).

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GSoC and Data Parallel Haskell
by Dmitry Dzhus 22 Mar '12

22 Mar '12

How are you gentlemen. I'm interested about what additions to DPH would really benefit the community. The only ticket on DPH in GSoC Trac seems a bit stale: http://hackage.haskell.org/trac/summer-of-code/ticket/1537. Any new tips? My field is currently molecular simulation. (I'm doing a Direct Simulation Monte-Carlo implementation for rarefied gas dynamics with application to space satellites&stuffs aerodynamics in Haskell for my Master's thesis, I believe using DPH as well would be my final goal as molecular simulations vectorize nicely. Simulation domain is partitioned into cells and stochastic collision sampling (as in DSMC) may be performed in every cell in parallel.)

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Haskell Weekly News: Issue 219
by Daniel Santa Cruz 22 Mar '12

22 Mar '12

Welcome to issue 218 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of March 11 to 17, 2012. Quotes of the Week * cmccann: * cmccann needs to hurry up and get his stream processing library finished before all the possible synonyms for "thing that other things flow through" are taken * shergill: silver bullets don't respect eta equivalency. it needs to be made of silver, and not simply *act* like one :P Top Reddit Stories * Shelly: Write your shell scripts in Haskell Domain: yesodweb.com, Score: 65, Comments: 34 On Reddit: [1] http://goo.gl/lZdyV Original: [2] http://goo.gl/HHIU0 * The Glasgow Haskell Compiler (draft chapter for "The Architecture of Open Source Applications, Volume 2") Domain: community.haskell.org, Score: 53, Comments: 28 On Reddit: [3] http://goo.gl/qVoFj Original: [4] http://goo.gl/Rc42A * Announcing the Yesod Platform Domain: yesodweb.com, Score: 52, Comments: 13 On Reddit: [5] http://goo.gl/TzW0w Original: [6] http://goo.gl/z3fwC * The Cabal of my dreams Domain: blog.johantibell.com, Score: 42, Comments: 19 On Reddit: [7] http://goo.gl/VTpJu Original: [8] http://goo.gl/wrrNP * Announcing: Snap Framework v0.8 Domain: snapframework.com, Score: 39, Comments: 6 On Reddit: [9] http://goo.gl/19EyG Original: [10] http://goo.gl/USfny * Leksah 0.12 Domain: haskell.org, Score: 32, Comments: 9 On Reddit: [11] http://goo.gl/5Ft8w Original: [12] http://goo.gl/K6OEx * uncurryWith and concatenative programming Domain: self.haskell, Score: 30, Comments: 4 On Reddit: [13] http://goo.gl/dzzXH Original: [14] http://goo.gl/dzzXH * New course on parallel functional programming at Chalmers Domain: cse.chalmers.se, Score: 29, Comments: 2 On Reddit: [15] http://goo.gl/vwH6F Original: [16] http://goo.gl/zKQjh * Announcing Haskell project support on travis-ci.org Domain: about.travis-ci.org, Score: 28, Comments: 8 On Reddit: [17] http://goo.gl/uH7g3 Original: [18] http://goo.gl/KbE7I * Anyone in the Toronto area looking for a job? Domain: self.haskell, Score: 28, Comments: 22 On Reddit: [19] http://goo.gl/NHdwz Original: [20] http://goo.gl/NHdwz * Building a Concurrent Web Scraper With Haskell Domain: adit.io, Score: 26, Comments: 1 On Reddit: [21] http://goo.gl/G7QXM Original: [22] http://goo.gl/FV2LO * Using Text.Parsec.Indent to parse an indentation-sensitive language with Haskell’s Parsec library. Domain: spin.atomicobject.com, Score: 26, Comments: 7 On Reddit: [23] http://goo.gl/dXkzO Original: [24] http://goo.gl/9BFa3 * Coapplicative Functor? Domain: self.haskell, Score: 21, Comments: 37 On Reddit: [25] http://goo.gl/4eluT Original: [26] http://goo.gl/4eluT * HalVM: Easy install on Fedora 16 + 64bit support Domain: community.galois.com, Score: 21, Comments: 2 On Reddit: [27] http://goo.gl/goN4p Original: [28] http://goo.gl/6EQAu Top StackOverflow Questions * How do you represent a graph in Haskell? votes: 18, answers: 4 Read on SO: [29] http://goo.gl/t5vij * Impredicative types vs. plain old subtyping votes: 16, answers: 0 Read on SO: [30] http://goo.gl/3cmCj * Can GHC really never inline map, scanl, foldr, etc.? votes: 14, answers: 3 Read on SO: [31] http://goo.gl/se91V * Redefine IO to simplify debugging? votes: 11, answers: 1 Read on SO: [32] http://goo.gl/s62s9 * Quadratic programming in Haskell votes: 11, answers: 1 Read on SO: [33] http://goo.gl/jYWEP * How can I test a higher-order function using QuickCheck? votes: 11, answers: 2 Read on SO: [34] http://goo.gl/1YHql * Haskell: how to map a tuple? votes: 10, answers: 7 Read on SO: [35] http://goo.gl/fk7LE * Repacking monads — any generic way? votes: 9, answers: 4 Read on SO: [36] http://goo.gl/QklWI * Is there any reason not to use the INLINABLE pragma for a function? votes: 9, answers: 1 Read on SO: [37] http://goo.gl/t75CV * Repa 3 performance and correct usage of 'now' votes: 9, answers: 1 Read on SO: [38] http://goo.gl/PbyzK Until next time, Daniel Santa Cruz References 1. http://www.yesodweb.com/blog/2012/03/shelly-for-shell-scripts 2. http://www.reddit.com/r/haskell/comments/qt17p/shelly_write_your_shell_scri… 3. http://community.haskell.org/~simonmar/papers/aos.pdf 4. http://www.reddit.com/r/haskell/comments/qvyup/the_glasgow_haskell_compiler… 5. http://www.yesodweb.com/blog/2012/03/announcing-yesod-platform 6. http://www.reddit.com/r/haskell/comments/qxopq/announcing_the_yesod_platfor… 7. http://blog.johantibell.com/2012/03/cabal-of-my-dreams.html 8. http://www.reddit.com/r/haskell/comments/qwj5j/the_cabal_of_my_dreams/ 9. http://snapframework.com/blog/2012/03/16/snap-0.8-released 10. http://www.reddit.com/r/haskell/comments/qzzfe/announcing_snap_framework_v0… 11. http://www.haskell.org/pipermail/haskell-cafe/2012-March/100023.html 12. http://www.reddit.com/r/haskell/comments/qro91/leksah_012/ 13. http://www.reddit.com/r/haskell/comments/qy8h2/uncurrywith_and_concatenativ… 14. http://www.reddit.com/r/haskell/comments/qy8h2/uncurrywith_and_concatenativ… 15. http://www.cse.chalmers.se/edu/course/pfp/ 16. http://www.reddit.com/r/haskell/comments/quc64/new_course_on_parallel_funct… 17. http://about.travis-ci.org/blog/announcing_support_for_haskell_on_travis_ci/ 18. http://www.reddit.com/r/haskell/comments/qsyr5/announcing_haskell_project_s… 19. http://www.reddit.com/r/haskell/comments/qw99e/anyone_in_the_toronto_area_l… 20. http://www.reddit.com/r/haskell/comments/qw99e/anyone_in_the_toronto_area_l… 21. http://adit.io/posts/2012-03-10-building_a_concurrent_web_scraper_with_hask… 22. http://www.reddit.com/r/haskell/comments/qvp1u/building_a_concurrent_web_sc… 23. http://spin.atomicobject.com/2012/03/16/using-text-parsec-indent-to-parse-a… 24. http://www.reddit.com/r/haskell/comments/qzeyk/using_textparsecindent_to_pa… 25. http://www.reddit.com/r/haskell/comments/qsrmq/coapplicative_functor/ 26. http://www.reddit.com/r/haskell/comments/qsrmq/coapplicative_functor/ 27. http://community.galois.com/pipermail/halvm-devel/2012-March/000022.html 28. http://www.reddit.com/r/haskell/comments/qynuq/halvm_easy_install_on_fedora… 29. http://stackoverflow.com/questions/9732084/how-do-you-represent-a-graph-in-… 30. http://stackoverflow.com/questions/9732766/impredicative-types-vs-plain-old… 31. http://stackoverflow.com/questions/9658438/can-ghc-really-never-inline-map-… 32. http://stackoverflow.com/questions/9656734/redefine-io-to-simplify-debugging 33. http://stackoverflow.com/questions/9672686/quadratic-programming-in-haskell 34. http://stackoverflow.com/questions/9686665/how-can-i-test-a-higher-order-fu… 35. http://stackoverflow.com/questions/9722689/haskell-how-to-map-a-tuple 36. http://stackoverflow.com/questions/9684252/repacking-monads-any-generic-way 37. http://stackoverflow.com/questions/9709823/is-there-any-reason-not-to-use-t… 38. http://stackoverflow.com/questions/9713378/repa-3-performance-and-correct-u…

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Rewrite rules not firing for rules matching multiple instance methods
by Acshi Haggenmiller 22 Mar '12

22 Mar '12

Hi, I have some rewrite rules set up and am finding that in the case where my rule pattern matches to instance methods and there are more than one of them, my rules do not fire. If they are simply taken out from being instance methods, they match just fine. I have posted more details and a code example to http://stackoverflow.com/questions/9811294/rewrite-rules-not-firing-for-rul… I appreciate the help, Acshi

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MSIL manipulation libraries
by ARJANEN Loïc Jean David 21 Mar '12

21 Mar '12

Hello, Someone knows of a good MSIL library, to manipulate and output MSIL ? Regards, ARJANEN Loïc

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Quickest way to pass Text to C code
by Yves Parès 21 Mar '12

21 Mar '12

Hello, I have to interact with a C++ library that accepts as string types (putting c++ strings aside) pointers of wchar_t (CWString in Haskell) or unsigned 32-bit int (Ptr Word32 for UTF-32 codepoints). I have read what text, bytestring and base provide, but Text can only be directly converted to (Ptr Word16), and if I use encodeUTF32 to get a ByteString, then I only get useAsCString, no direct conversion to CWString or Ptr WordXX is possible. Not to mention the extra memory allocations due to intermediate conversions. base provides Foreign.C.String.useAsCWString, but it requires that either I use simple Strings at the first place or (same thing than before) I convert from Text to String before passing to C. Is there something I'm missing or isn't this kind of conversion that easy?

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ANN: Haskell Platform Versions Comparison Chart
by Simon Hengel 21 Mar '12

21 Mar '12

Hi, I compiled a chart that gives a side-by-side comparison of package versions in various Haskell Platform releases. http://sol.github.com/haskell-platform-versions-comparison-chart/ This includes both, packages that come with ghc and platform packages. Source is on GitHub[1]. Cheers, Simon [1] https://github.com/sol/haskell-platform-versions-comparison-chart

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Are there arithmetic composition of functions?
by sdiyazg＠sjtu.edu.cn 21 Mar '12

21 Mar '12

By arithmetic I mean the everyday arithmetic operations used in engineering. In signal processing for example, we write a lot of expressions like f(t)=g(t)+h(t)+g'(t) or f(t)=g(t)*h(t). I feel it would be very natural to have in haskell something like g::Float->Float --define g here h::Float->Float --define h here f::Float->Float f = g+h --instead of f t = g t+h t --Of course, f = g+h is defined as f t = g t+h t I guess as long as all operands have the same number of arrows in there types then they should have the potential to be composed like this. Or g::Float->Float->Float --define g here h::Float->Float->Float --define h here f::Float->Float->Float f = g+h --means f x y = g x y + h x y -- f = g+h is defined as f x = g x+h x which in turn is defined as f x y = g x y+h x y This should be easy to implement, with TH perhaps. And I thought there would be a library (not in the language itself, of course) for this, but I haven't find one. Can someone tell me whether there is some implementation of such composition? If there isn't then I may build one.

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good lightweight web-framework like sinatra?
by Greg Weber 21 Mar '12

21 Mar '12

WAI has CGI handlers, so you should be able to deploy a WAI-based framework like Yesod to CGI. If you want a simple framework, you can just use WAI directly. Scotty is a WAI framework that mimics Sinatra. Greg Weber

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ANN: doctest-0.6.0 (support for ghc-7.4, please test)
by Simon Hengel 21 Mar '12

21 Mar '12

Hi, I just uploaded a new version of Doctest that adds support for ghc-7.4. http://hackage.haskell.org/package/doctest Doctest now comes with it's own parser and does not depend on Haddock anymore. This is a quite involved change, and it may still have issues. So pleases test, and do not be shy in reporting any bugs (either as a reply to this post or on [1]). Cheers, Simon [1] https://github.com/sol/doctest-haskell/issues

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