- Beginners - Haskell.org

Re: Haskell Weekly News: Issue 134 - October 10, 2009
by Benjamin L.Russell 13 Oct '09

13 Oct '09

Either way is fine with me. Since HWN also contains beginner-related topics, personally, I don't think that posting it to Haskell-Beginners takes the group any more off-topic than posting it to Haskell-Cafe (although I can see the argument against cross-posting it to mailing lists in addition to the main Haskell mailing list). If it winds up getting posted to Haskell-Beginners, I'll gladly read it there, but if it just gets posted to the main Haskell mailing list, I'll read it there, also. -- Benjamin L. Russell On Sun, 11 Oct 2009 14:31:22 +0200, Max Rabkin <max.rabkin(a)gmail.com> wrote: >Why don't you subscribe to haskell? It's much lower volume, and I >think it's a better option than taking -beginners off-topic. > >--Max > >On Sun, Oct 11, 2009 at 2:10 PM, Patrick LeBoutillier ><patrick.leboutillier(a)gmail.com> wrote: >> Hi, >> >> Could/should the Haskell Weekly News be posted to the beginners list as >> well? >> >> I normally don't follow haskell-cafe (too much traffic and generally above >> my level I must admit...), but I like to follow what's going on in the >> Haskell community. >> >> >> Patrick -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

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Re: [Haskell-cafe] Haskell Weekly News: Issue 134 - October 10, 2009
by Patrick LeBoutillier 11 Oct '09

11 Oct '09

Hi, Could/should the Haskell Weekly News be posted to the beginners list as well? I normally don't follow haskell-cafe (too much traffic and generally above my level I must admit...), but I like to follow what's going on in the Haskell community. Patrick On Sat, Oct 10, 2009 at 3:47 AM, <jfredett(a)gmail.com> wrote: > > --------------------------------------------------------------------------- > Haskell Weekly News > http://sequence.complete.org/hwn/20091010 > Issue 134 - October 10, 2009 > --------------------------------------------------------------------------- > Welcome to issue 134 of HWN, a newsletter covering developments in the > [1]Haskell community. > > What with Don Stewart's [2]call to [3]arms to lead Haskell to conquest > over (E)DSL-land, I've once again tried to highlight discussion of > EDSL's this week. Fortunately, it was actually more difficult choosing > what _not_ to include this week, since there was so much discussion > about DSLs and Syntax extensions (a related notion, in my opinion). > Also, this week Bryan O'Sullivan put his Criterion Library to good use > on the `text` package, leading to [4]code which is more than ten times > faster than before! With all this fantastic news, I won't hold you up > any longer, Haskellers, the Haskell Weekly News! > > Announcements > > CfPart: FMICS 2009, 2-3 November 2009, Final Call. FMICS 2009 workshop > chair [5]announced the final call for particpaction for FMICS 2009 > > ICFP videos now available. Wouter Swierstra [6]announced the > availablity of videos from the International Conference on Functional > Programming (ICFP) > > GPipe-1.0.0: A functional graphics API for programmable GPUs. Tobias > Bexelius [7]announced the first release of GPie, a functional graphics > API for programmable GPUs. > > text 0.5, a major revision of the Unicode text library. Bryan > O'Sullivan [8]announced a new, major version of the text package. New > API features, and huge improvments in speed, as Bryan says, 'Get it > while it's fresh on Hackage, folks!' > > vty-ui 0.2. Jonathan Daugherty [9]announced a new version of the vty-ui > package, with fewer bugs, more widgets, and cleaner code due to new > more powerful abstractions. > > htzaar-0.0.1. Tom Hawkins [10]announced HTZAAR, a Haskell > implementation of TZAAR > > Graphalyze-0.8.0.0 and SourceGraph-0.5.5.0. Ivan Lazar Miljenovic > [11]announced To keep this editor happy, Ivan released two new packaged > in one announcement. This time, he's added Legend support to > Graphalyze, but also many new changes to SourceGraph, including a > legend so you can see what all the symbols mean, Better color support, > and much more. > > TxtSushi 0.4.0. Keith Sheppard [12]announced a new version of TxtSushi, > a set of command line utilities for processing CSV and TSV files. > > Discussion > > Applicative do? Philippa Cowderoy [13]asked about a `do` like syntax > for Applicative functors. > > How to add use custom preprocessor in cabal. Bernd Brassel [14]asked > how to add a custom preprocessor to the build chain of a cabal file. > > On DSLs - one last time. Gunther Schmidt [15]summarized his impressions > on al the recent discussion of DSLs > > What is a DSL? Oleg [16]offered some insight into different > [17]properties that can be part of a single tagless framework. He also > pointed to some slides and other materials such as a website [18]here > and slides [19]here about DSL implementations and definitions. > > What is a DSL? Gunther Schmidt [20]posed the question, 'What is a DSL', > and with some further questions added by yours truly, a lively > discussion about the definition of a DSL ensued. > > Finally tagless - stuck with implementation of 'lam'. Gunther Schmidt > [21]asked another question about Finally Tagless DSLs and resolving an > issue with the implementation of 'lam' > > Blog noise > > [22]Haskell news from the [23]blogosphere. Blog posts from people new > to the Haskell community are marked with >>>, be sure to welcome them! > * Darcs: [24]darcs weekly news #43. > * JP Moresmau: [25]What client for an Haskell Multi Player Game?. > * Mikael Vejdemo Johansson (Syzygy-): [26][MATH198] Third lecture is > up. > * Bryan O'Sullivan: [27]Announcing a major revision of the Haskell > text library. > * Eric Kow (kowey): [28]darcs hashed-storage work merged (woo!). > * David Amos: [29]Symmetries of PG(n,Fq). > * The GHC Team: [30]Parallelism /= Concurrency. > * >>> Nefigah: [31]Fake World Haskell. Nefigah, a recent addition to > the community, has been working through RWH, and is providing some > excellent examples. Though, This editor prefers the title 'Real > Life Haskell' as opposed to his choice. > * Tom Schrijvers: [32]Release 0.6 of Monadic Constraint Programming. > * Neil Brown: [33]Concurrency Can Be Deterministic (But The Type > System Doesn't Know It). > * Clint Moore: [34]Curiously Parallel. > * Galois, Inc: [35]Tech Talk: Constructing A Universal Domain for > Reasoning About Haskell Datatypes. > * Neil Brown: [36]Terminal Concurrency: The Printing Process. > * Sean Leather: [37]'Upwards and downwards accumulations on trees' > translated into Haskell. > * Mikael Vejdemo Johansson (Syzygy-): [38][MATH 198] Second lecture. > * Chris Smith: [39]View Patterns as Pattern Matching for Records. > * Chris Smith: [40]Playing With Records. > * FP Lunch: [41]Left Kan extensions of containers. > > Quotes of the Week > > * Baughn: Blum Blum Shub, a PRNG derived from poking around R'Lyeh. > * ksf: * lambdabot locks up ksf in a Monad <ksf> mmmmh it's warm and > fuzzy in here. > * monochrom: Don't wrap your head around Haskell. Immerse! Wrap > Haskell around your head. > * chak: ... In other words, FP is inevitable. > * robreim: I'm in your base hacking all your lambdas > * gwern: RAM is overrated, swap is where it's at ;) > * idnar: [to gwern] swap to a ramdisk! ;P > > About the Haskell Weekly News > > New editions are posted to [42]the Haskell mailing list as well as to > [43]the Haskell Sequence and [44]Planet Haskell. [45]RSS is also > available, and headlines appear on [46]haskell.org. > > To help create new editions of this newsletter, please see the > information on [47]how to contribute. Send stories to jfredett . at . > gmail . dot . com. The darcs repository is available at darcs get > [48]http://patch-tag.com/r/jfredett/HWN2/pullrepo HWN2 . > > References > > 1. http://haskell.org/ > 2. > http://www.haskell.org/pipermail/haskell-cafe/2009-October/067203.html > 3. > http://www.reddit.com/r/haskell/comments/9qk54/haskell_should_own_the_edsl_… > 4. > http://www.serpentine.com/blog/2009/10/09/announcing-a-major-revision-of-th… > 5. http://article.gmane.org/gmane.comp.lang.haskell.general/17555 > 6. http://article.gmane.org/gmane.comp.lang.haskell.general/17552 > 7. http://article.gmane.org/gmane.comp.lang.haskell.general/17546 > 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64591 > 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64529 > 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64516 > 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64399 > 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64301 > 13. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64616 > 14. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64558 > 15. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64552 > 16. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64533 > 17. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/ > 18. http://dsl09.blogspot.com/ > 19. http://dsl09.blogspot.com/2009/07/panel.html > 20. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64474 > 21. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64343 > 22. http://planet.haskell.org/ > 23. http://haskell.org/haskellwiki/Blog_articles > 24. http://blog.darcs.net/2009/10/darcs-weekly-news-43.html > 25. > http://jpmoresmau.blogspot.com/2009/10/what-client-for-haskell-multi-player… > 26. > http://blog.mikael.johanssons.org/archive/2009/10/math198-third-lecture-is-… > 27. > http://www.serpentine.com/blog/2009/10/09/announcing-a-major-revision-of-th… > 28. > http://koweycode.blogspot.com/2009/10/darcs-hashed-storage-work-merged-woo.… > 29. http://haskellformaths.blogspot.com/2009/10/symmetries-of-pgnfq.html > 30. > http://ghcmutterings.wordpress.com/2009/10/06/parallelism-concurrency/ > 31. http://my.life-is-virtual.com/2009/10/07/fake-world-haskell-part-1/ > 32. > http://tomschrijvers.blogspot.com/2009/10/release-06-of-monadic-constraint.… > 33. > http://chplib.wordpress.com/2009/10/07/concurrency-can-be-deterministic/ > 34. http://www.l2mlogistics.com/2009/10/curiously-parallel.html > 35. http://www.galois.com/blog/2009/10/06/huffman-universal/ > 36. http://chplib.wordpress.com/2009/10/06/the-printing-process/ > 37. > http://feedproxy.google.com/~r/splonderzoek/~3/4E8TZPDZ-aM/upwards-and-down…<http://feedproxy.google.com/%7Er/splonderzoek/%7E3/4E8TZPDZ-aM/upwards-and-…> > 38. > http://blog.mikael.johanssons.org/archive/2009/10/math-198-second-lecture/ > 39. > http://cdsmith.wordpress.com/2009/10/04/view-patterns-as-pattern-matching-f… > 40. http://cdsmith.wordpress.com/2009/10/03/playing-with-records/ > 41. http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=237 > 42. http://www.haskell.org/mailman/listinfo/haskell > 43. http://sequence.complete.org/ > 44. http://planet.haskell.org/ > 45. http://sequence.complete.org/node/feed > 46. http://haskell.org/ > 47. http://haskell.org/haskellwiki/HWN > 48. http://patch-tag.com/r/jfredett/HWN2/pullrepo%20HWN2 > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- ===================== Patrick LeBoutillier Rosemère, Québec, Canada

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questions about randomness
by Michael Mossey 10 Oct '09

10 Oct '09

I would like to know if this is a good way to do this job, both from the point of view of elegance and efficiency. Maybe it needs to be more strict? I may create lists of 100,000 elements and don't want to run into space/time problems. I want to create an infinite list of Floats (for purposes of lazily zipping or writing later), with the following form: a random number of zeros, followed by a single random non-zero value, repeat the pattern. I call it a "break series" for reasons I won't go into here, but in practice, I want to choose the number of zeros in each section from a range of integers, and I want the non-zero values to have a particular frequency distribution. Here's some code I wrote: import System.Random import Control.Monad import Control.Monad.Random breakSeries :: Rand StdGen [Float] breakSeries = do x <- getRandomR (0.0::Float, 1.0) -- Hacking a simple frequency distribution of values of d. d <- if x < 0.6 then getRandomR (5.0::Float, 8.0) else if x < 0.8 then getRandomR (12.0::Float , 24.0) else getRandomR (60.0::Float , 90.0) n <- getRandomR (4::Int, 6) let bits = replicate n 0.0 ++ [d] liftM (bits++) breakSeries test = print . take 20 . evalRand breakSeries =<< newStdGen

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Re: (ab)use compiler optimization
by Martin Hofmann 09 Oct '09

09 Oct '09

Thanks apfelmus this worked fine.

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(ab)use compiler optimization
by Martin Hofmann 09 Oct '09

09 Oct '09

Hello, To analyse, test, and debug my system I use a WriterT for logging. The log file created can be quite large and a lot of 'Log' is created in memory, too. I thought, that maybe I can (ab)use the compiler to switch logging on and off as needed before compiling. I tried to either always return an empty Log when running the WriterT, or just always ignore logging depending on a constant and hoped GHC to optimize the logging away. _NOLOGGING = True runWT :: (Monad m) => (WriterT Log m a) -> m (a, Log) runWT m | _NOLOGGING = runWriterT m empty >>= \(a,_) -> return (a,emptyLog ) | otherwise = runWriterT m emptyLog logging :: Message -> WriterT Log m () logging msg = if _NOLOGGING then return () else tell msg However, according to the heap profile there is still a lot of 'Log' in the memory. So, is this possible this way at all and if not, is there another (apart from removing all logging by hand). Thanks

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Compiling C that calls Haskell with GCC
by John Velman 05 Oct '09

05 Oct '09

More specifically, I want to link a haskell .o file into a project I create on OS X using Xcode, but the answer to the gcc question should do it. I've followed the simple "calling haskell from C" example from HaskellWiki, and it works as advertised when compiled as advertised with gcc. However, I'm looking toward writing OS X programs with Xcode and the standard Mac interface, calling some functions written in Haskell. Consequently, I want to compile and link using the mac Xcode IDE, which uses gcc. Seems like the thing that GHC puts in must be include .h files and libraries. But which ones? I think I ran across the answer to this in my browsing, but can't find it again. Can someone point me in the right direction? Thanks, John Velman

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string instead of char
by John Moore 05 Oct '09

05 Oct '09

Hi, I am now writing a function that replaces vowels with the letter x. eg.put in a string "help" and out comes hxlp. I tried this: f x = case x of {'a' -> 'x';'e' -> 'x';'i' -> 'x';'o' -> 'x';'u' -> 'x';_ -> x} but this wont work on strings, only on the individual letters. Any direction would be very welcome. Yours john

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Advantage to installing Hugs with GHC?
by John Velman 05 Oct '09

05 Oct '09

My machine is an iMac running Leopard, 10.5.8. I've installed GHC from the haskell-platform-..(Leopard/x86) disk image. Ghci works fine as far as I can tell. Is there any particular advantage to also installing Hugs? Thanks, John Velman

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parse error
by John Moore 04 Oct '09

04 Oct '09

Hi, This is a function that returns true if divisible by 2. But it keeps telling me parse error on input | . What is wrong here. is_even n | mod n 2 == 0 | True Not sure if I need another statement for false John

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redirect stdout to /dev/null
by Hong Yang 04 Oct '09

04 Oct '09

On UNIX, we can easily redirect stdout to /dev/null in a Shell. How is this realized in Haskell on both UNIX and Windows? I used a library which gave me unwanted stdout display. I tried to find any function to hide the stdout output, but could not. Can someone help me out? Otherwise I have to modify the code in the library to comment out some print commands. Thanks, Hong

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