December 2010 - Haskell-Cafe

cpphs is missing from new Haskell.org server
by Dimitry Golubovsky 17 Dec '10

17 Dec '10

Hi, One more thing is missing after migration. The link found on the cpphs package page at Hackage, http://haskell.org/cpphs/ points to non-existing page. Thanks. -- Dimitry Golubovsky Anywhere on the Web

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Monadic Design Patterns for the Web C9 Video Series -- Part 2 is live!
by Greg Meredith 17 Dec '10

17 Dec '10

Dear Haskellians, Just in time for the Holidays! Best wishes, --greg ---------- Forwarded message ---------- From: Charles Torre <ctorre(a)microsoft.com> Date: Tue, Dec 14, 2010 at 11:31 AM Subject: Part 2 is live! To: Meredith Gregory <lgreg.meredith(a)gmail.com> Hi Greg! Part 2 is now live on 9. Front and center: http://channel9.msdn.com/Shows/Going+Deep/C9-Lectures-Greg-Meredith-Monadic… Thank you! See you in the new year to continue with this great series. Best, C -- L.G. Meredith Managing Partner Biosimilarity LLC 1219 NW 83rd St Seattle, WA 98117 +1 206.650.3740 http://biosimilarity.blogspot.com

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Infinite lists in real world programs
by Yves Parès 17 Dec '10

17 Dec '10

Hello Café, I was wondering if using infinite lists was a viable and efficient solution in haskell programs (I mean not simple prototypes) : I was considering using them to model agents in a hierarchical multi-agent application for school. A list would representate the state of an agent at a step of the program. Let's say we have two simple agents, one multiplying its input by 2 and the other dividing it by 4 : agent1 = fmap (*2) agent2 = fmap (/4) allValues = xs where ys = agent1 xs xs = 100:agen2 ys main = do mapM_ print $ take 100 allValues Of course, in a real program, an agent would rather take a list of multiple agents (i.e. a list of lists) in input, so that its ouput could depend on what several agents feed him. Some could state what I'm trying to do is FRP, and I agree. But it remains a simple goal so I'd like to keep the program simple, and not go into the whole complexity of a FRP framework (and I'm working with a non-haskeller). For instance, with my solution, I cannot dynamically connect or disconnect agents during the runtime, but I'll will not need to do that in my program. Besides, I'd like to try to implement this myself, not use an already existing framework. So is it viable or would the use of multiple infinite lists kill the performances?

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cannot install regex-posix using cabal ?
by z_axis 16 Dec '10

16 Dec '10

%ghc-pkg list|grep -i regex regex-base-0.93.2 %cabal install regex-posix Resolving dependencies... Configuring regex-posix-0.94.4... Preprocessing library regex-posix-0.94.4... running dist/build/Text/Regex/Posix/Wrap_hsc_make failed command was: dist/build/Text/Regex/Posix/Wrap_hsc_make >dist/build/Text/Regex/Posix/Wrap.hs cabal: Error: some packages failed to install: regex-posix-0.94.4 failed during the building phase. The exception was: ExitFailure 1 How can i fix such a problem ? ----- e^(π.i) + 1 = 0 -- View this message in context: http://haskell.1045720.n5.nabble.com/cannot-install-regex-posix-using-cabal… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Re: [Haskell-cafe] Iteratee-like
by John Lato 16 Dec '10

16 Dec '10

> > From: Permjacov Evgeniy <permeakra(a)gmail.com> > > current links > > https://github.com/permeakra/Rank2Iteratee > https://github.com/permeakra/PassiveIteratee > > The main difference from 'original' iteratees I read about is that both > do not use 'chunks' and pass data one-by-one. So, what I wrote may be > slower, but should be easier to maintain and more transparent for ghc > optimising facilities. I wanted as clean and simple code as possible, > but it is still very, very messy at some places and I want it cleaner. > Any suggestions? I also want to check, how good ghc does its work with > this messy modules. They may become interesting benchmarks. > Have you tried comparing it to either iteratee or enumerator (which had mostly comparable performance last time I checked, with a slight edge to iteratee)? Or to Oleg's library? Try writing test cases, a simple byte-counting application, or similar, so you can compare the performance with the other versions. Both enumerator and iteratee include demo programs that you could use as a starting point. I agree that iteratees which work on a per-element level are very clean and should be amenable to optimization by GHC. It also shows a very clear relationship with stream-fusion techniques. Unfortunately when I last tried it I couldn't get acceptable performance. I was using ghc-6.12.1 IIRC, so it could be different now. John

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Strong version of 'local' for reader monad
by Brent Yorgey 16 Dec '10

16 Dec '10

Hi all, Today I wanted this function strongLocal :: (MonadReader r1 m1, MonadReader r2 m2) => (r2 -> r1) -> m1 a -> m2 a Of course, after staring at this type for ten seconds I realized that it cannot be implemented. But I wondered whether anyone has any pointers to anything related, or if anyone has good ideas for a reasonable interface that would allow this. -Brent

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typesetting with lhs2tex
by Permjacov Evgeniy 16 Dec '10

16 Dec '10

I write docs for my iteratee-like library and I have problem with lhs2tex. When I execute lhs2tex and then latex, I get a document with long typesignatures and expressions expanded beyound page margins. I attached a sourcefile I have problem with. Can someone give me an advise how to force long signatures and expressions to be broken into multible lines ?

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ghc/dph
by Johannes Waldmann 16 Dec '10

16 Dec '10

Hi, I want to use dph (data parallel haskell) for a presentation. (Nothing fancy, just compile and run some demos.) What ghc version should I use and where do I get it? I read the advice "use HEAD" but when I build from the 7.1.20101213 source snapshot, dph is not installed (should it be?) Best - J.W.

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Re: [Haskell-cafe] Beginners help
by z_axis 16 Dec '10

16 Dec '10

According to map's definition, we know the 'fs' should be a list of function. so 'p' need a [a->b] as its parameter. And the result of 'p' should be a list of function which accepts [a] and return [b]. So the type of 'p' is [a->b] -> [[a] -> [b]] hope i make it clear. ----- e^(π.i) + 1 = 0 -- View this message in context: http://haskell.1045720.n5.nabble.com/Beginners-help-tp3306796p3307470.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Haskell Weekly News: Issue 162 - December 15, 2010
by Daniel Santa Cruz 16 Dec '10

16 Dec '10

Welcome to issue 162 of the HWN, a newsletter covering developments in the [1]Haskell community in the week of December 05 - 11. Wouter Swierstra [2]sent a call for papers for the ICFP 2011 to be held in Tokyo, Japan between September 19 - 21. The announcement contains all relevant dates of importance Dmitry Astapov [3]announced the realease of haskell-mpi, "a suite of Haskell bindings to the C MPI [Message Passing Interface] and convenience APIs on top of it." David Waern [4]annouced a new version of the venerable Haddock. "This version is compatible with .haddock files produced by the version of Haddock that comes with GHC 7.0.1." Michael Snoyman [5]announced the first release of his library and executable packdeps. "This is a library and executable containing the same functionality as the original packdeps website, namely letting you know when your version bounds exclude the use of the newest version of a library available." Michael also [6]announced the second major release of the mime-mail library. This "is a package providing support for rendering multipart emails." Jasper Van der Jeugt [7]announced the 0.0.2.0 release of the digestive functors library. "The library provides a general API to input consumption, and is an upgrade of formlets." So, what went on this week? Top Reddit Stories * Cartesian Closed Comic: Résumé Domain: ro-che.info, Score: 35, Comments: 1 On Reddit: http://www.reddit.com/r/haskell/comments/ekiao/cartesian_closed_comic_résum… Original: http://ro-che.info/ccc/11.html * GHC blog: An overhaul of stack management, and some performance improvements Domain: hackage.haskell.org, Score: 32, Comments: 2 On Reddit: http://www.reddit.com/r/haskell/comments/emabe/ghc_blog_an_overhaul_of_stac… Original: http://hackage.haskell.org/trac/ghc/blog/stack-chunks * How do You use Emacs for Haskell Development? Domain: self.haskell, Score: 29, Comments: 10 On Reddit: http://www.reddit.com/r/haskell/comments/ehl99/how_do_you_use_emacs_for_has… Original: /r/haskell/comments/ehl99/how_do_you_use_emacs_for_haskell_development/ * Library versus Framework: Yesod's Own World Domain: docs.yesodweb.com, Score: 26, Comments: 22 On Reddit: http://www.reddit.com/r/haskell/comments/ejgen/library_versus_framework_yes… Original: http://docs.yesodweb.com/blog/yesods-own-world/ * Visualizing Haskell types part II, Gin and monotonic : Inside T5 Domain: blog.ezyang.com, Score: 24, Comments: 2 On Reddit: http://www.reddit.com/r/haskell/comments/eiaef/visualizing_haskell_types_pa… Original: http://blog.ezyang.com/2010/12/gin-and-monotonic/ * Package of the day: parallel-io: combinators for sequencing IO actions onto a thread pool Domain: hackage.haskell.org, Score: 21, Comments: 15 On Reddit: http://www.reddit.com/r/haskell/comments/ehsqo/package_of_the_day_paralleli… Original: http://hackage.haskell.org/package/parallel-io-0.2.2 * Package of the day: haskell-mpi: Control.Parallel.MPI for high performance parallel (cluster) computations in Haskell Domain: hackage.haskell.org, Score: 19, Comments: 5 On Reddit: http://www.reddit.com/r/haskell/comments/ej5av/package_of_the_day_haskellmp… Original: http://hackage.haskell.org/package/haskell-mpi-1.0.0 * From Polymorphism To Polytypism Domain: zenzike.com, Score: 19, Comments: On Reddit: http://www.reddit.com/r/haskell/comments/ejleb/from_polymorphism_to_polytyp… Original: http://zenzike.com/posts/2010-12-10-from-polymorphic-to-polytypic/ * Hussling Haskell types into Hasse diagrams : Inside T5 Domain: blog.ezyang.com, Score: 18, Comments: On Reddit: http://www.reddit.com/r/haskell/comments/eh2zw/hussling_haskell_types_into_… Original: http://blog.ezyang.com/2010/12/hussling-haskell-types-into-hasse-diagrams/ * Building a business with Haskell: Case Studies: Cryptol, HaLVM and Copilot Domain: corp.galois.com, Score: 17, Comments: 1 On Reddit: http://www.reddit.com/r/haskell/comments/ejmwq/building_a_business_with_has… Original: http://corp.galois.com/blog/2010/12/10/building-a-business-with-haskell-cas… Top StackOverflow Questions * What is the benefit of purely functional data structure? votes: 15, answers: 4 Read on SO: http://stackoverflow.com/questions/4399837/what-is-the-benefit-of-purely-fu… * Haskell: Equation Expander 1+(1+(1+(1+(…))))=∞ votes: 9, answers: 2 Read on SO: http://stackoverflow.com/questions/4404663/haskell-equation-expander-1111 * Pure Functional Language: Haskell votes: 7, answers: 6 Read on SO: http://stackoverflow.com/questions/4382223/pure-functional-language-haskell * How does a haskell compiler works? votes: 7, answers: 4 Read on SO: http://stackoverflow.com/questions/4385160/how-does-a-haskell-compiler-works * Haskell typeclasses and C++ template classes votes: 7, answers: 6 Read on SO: http://stackoverflow.com/questions/4411279/haskell-typeclasses-and-c-templa… * Are there any special challenges for functional programming in an embedded environment? votes: 7, answers: 1 Read on SO: http://stackoverflow.com/questions/4418617/are-there-any-special-challenges… * Haskell: Where vs. Let votes: 6, answers: 3 Read on SO: http://stackoverflow.com/questions/4362328/haskell-where-vs-let * What are some good example haskell projects? votes: 6, answers: 2 Read on SO: http://stackoverflow.com/questions/4369962/what-are-some-good-example-haske… * Program Structure — Simple Commandline To Do List App — What's the Haskell way? votes: 6, answers: 2 Read on SO: http://stackoverflow.com/questions/4383512/program-structure-simple-command… * Learning to read haskell in english votes: 6, answers: 4 Read on SO: http://stackoverflow.com/questions/4393908/learning-to-read-haskell-in-engl… Quotes of the Week * kmc: it's great how laziness lets you ignore the order of evaluation except all the times when it doesn't * tg_: I can't wait until 100 years from now when 'eating food' will be deprecated from our lexicon in favor of 'oming noms' * kmc: maybe the 9,639,482nd time we argue about C++ we will finally resolve the issue * Berengal: * ddarius liked xmonad better when it was 90 lines... * Berengal liked xmonad better when it was on vinyl About the Haskell Weekly News New editions are posted to [8]the Haskell mailing list as well as to [9]the Haskell Sequence and [10]Planet Haskell. [11]RSS is also available, and headlines appear on [12]haskell.org. To help create new editions of this newsletter, please send stories to dstcruz * at * gmail * dot * com. The code used to produce this version of the newsletter is not yet publicly available, as it is a complete hack designed to get things started again. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.general/18355 3. http://article.gmane.org/gmane.comp.lang.haskell.general/18357 4. http://groups.google.com/group/fa.haskell/browse_thread/thread/b0c838a2249f… 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/84141 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/84142 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/84201 8. http://www.haskell.org/mailman/listinfo/haskell 9. http://sequence.complete.org/ 10. http://planet.haskell.org/ 11. http://sequence.complete.org/node/feed 12. http://haskell.org/

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