February 2012 - Haskell-Cafe

Haskell compilers targeting VMs
by ARJANEN Loïc Jean David 23 Feb '12

23 Feb '12

Hello, Does any one knows of an Haskell compiler targeting the JVM ? And of one targeting the .Net virtual machine ? Regards, ARJANEN Loïc

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ANN: cabal-file-th-0.2.2
by Simon Michael 23 Feb '12

23 Feb '12

I have uploaded a new version of cabal-file-th which bumps the Cabal upper bound to avoid difficulties with GHC 7.4. Best - Simon

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getAddrInfo: does not exist
by Alexander Vasiliev 23 Feb '12

23 Feb '12

Hi. I use FreeBsd and get the following error during execution. "mvz_server: getAddrInfo: does not exist (servname not supported for ai_socktype)" System: FreeBsd 7.1; amd64. Haskell: ghc-7.0.3; network-2.3.0.5. The programm works well on Ubuntu and on Windows XP. The piece of code is: bindit :: String -> ServData -> IO() bindit port sd@(mvzs, clnts) = withSocketsDo $ do addrinfos <- getAddrInfo (Just (defaultHints {addrFlags = [AI_PASSIVE]})) Nothing (Just port) I googled that this error was solved in ghc 6.8. But i use ghc 7.0.3. Can anyone help me? Best Regards, Alexander

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Re: [Haskell-cafe] Clarifying a mis-understanding about regions (and iteratees)
by John Lato 23 Feb '12

23 Feb '12

ResourceT really addresses a different problem. Specifically, the issue of how to guarantee that finalizers will run in the context of short-circuiting monadic effects. It does this by providing a single region (not nested regions as Oleg describes) as the base of the monad stack, ensuring that any short-circuiting effects still need to go through the ResourceT layer's finalization steps. Same implementation strategy, different goal. It doesn't provide nested regions, although you may be able to stack multiple ResourceT's on top of each other (I have no idea if this works or not) to do so. The "regions" package (http://hackage.haskell.org/package/regions) is another implementation predating ResourceT. I don't know why it never caught on, except perhaps that at announcement time it was a solution without a problem. John L. > From: Yves Par?s <yves.pares(a)gmail.com> > > Hi, so there are different regions libraries? > Is there a shootout comparing them, possibly also with ResourceT from > conduit (which has also been implemented in a stand-alone package > http://hackage.haskell.org/package/resource-simple-0.1 by Robin Banks), for > I take it it tries to respond to the same problem? > > 2012/2/23 <oleg(a)okmij.org> > >> >> I have just come across the reddit discussion about regions and >> iteratees. >> >> http://www.reddit.com/r/haskell/comments/orh4f/combining_regions_and_iterat… >> >> There is an unfortunate misunderstanding about regions which I'd like to >> correct. I'm posting in Cafe in hope that some of the participants of >> that discussion read Haskell-Cafe (I'm not a redditor). >> >> The user Faucelme wrote: >> > Would it be possible to implement a region-based iteratee which opened >> some >> > file "A" and wrote to it, then opened some file "B" and wrote to it, >> while >> > ensuring that file A is closed before file B is opened? >> >> To which the user tibbe replied >> > You can typically explicitly close the files as well. >> >> and the user dobryak commented >> >> > Regions that Oleg refers to started out with region-based memory >> allocation, >> > which is effectively a stack allocation strategy, in which resource >> > deallocation is in LIFO order. So I think your assumption is correct. >> >> Regretfully, these comments are incorrect. First of all, memory >> regions were invented to get around the stack allocation, LIFO >> strategy. If the stack allocation sufficed, why do we need heap? We >> have heap specifically because the memory allocation patterns are >> complex: a function may allocate memory that outlives it. Regions >> let the programmer create arbitrarily many nested regions; everything >> in a parent region is available to a child. Crucially, a child may >> request any of its ancestors to allocate memory in their >> regions. Therefore, although regions are nested, memory does not have >> to be allocated and freed in LIFO order. >> >> The Lightweight monadic regions implement all these patterns for files >> or other resources (plus the dynamic bequest). >> http://okmij.org/ftp/Computation/resource-aware-prog/region-io.pdf >> >> The running example of the Haskell Symposium 08 paper was the >> following (see sec 1.1) >> >> 1. open two files for reading, one of them a configuration file; >> 2. read the name of an output file (such as the log file) from the >> configuration file; >> 3. open the output file and zip the contents of both input files into >> the output file; >> 4. close the configuration file; >> 5. copy the rest, if any, of the other input file to the output file. >> >> As you can see, the pattern of opening and closing is non-LIFO: the >> output file has to be opened after the configuration file and is >> closed also after the configuration file. Therefore, the user Faucelme >> can find the solution to his question in the code accompanying the >> Monadic Regions paper. >> >> Section 5 of the paper describes even more complex example: >> >> 1. open a configuration file; >> 2. read the names of two log files from the configuration file; >> 3. open the two log files and read a dated entry from each; >> 4. close the configuration file and the newer log file; >> 5. continue processing the older log file; >> 6. close the older log file. >> >> where the pattern of opening and closing is not statically known: >> it is decided on values read from the files. >> >> So, Faucelme's question can be answered in affirmative using the >> existing RegionIO library (which, as has been shown, well integrates >> with Iteratees). There is already a region library with the desired >> functionality. >> >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >

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Haskell Meeting in Munich
by Heinrich Hördegen 23 Feb '12

23 Feb '12

Dear all, it's time again for our monthly Haskell meeting in Munich. If you plan to join us on Tuesday, 28th of February at Cafe Puck in Munich at 19h30, please go to: http://www.haskell-munich.de/dates and hit the button. This will help us to reserve tables. With hope to meet many of you, Heinrich -- -- hoerdegen(a)funktional.info www.funktional.info --

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Clarifying a mis-understanding about regions (and iteratees)
by oleg＠okmij.org 23 Feb '12

23 Feb '12

I have just come across the reddit discussion about regions and iteratees. http://www.reddit.com/r/haskell/comments/orh4f/combining_regions_and_iterat… There is an unfortunate misunderstanding about regions which I'd like to correct. I'm posting in Cafe in hope that some of the participants of that discussion read Haskell-Cafe (I'm not a redditor). The user Faucelme wrote: > Would it be possible to implement a region-based iteratee which opened some > file "A" and wrote to it, then opened some file "B" and wrote to it, while > ensuring that file A is closed before file B is opened? To which the user tibbe replied > You can typically explicitly close the files as well. and the user dobryak commented > Regions that Oleg refers to started out with region-based memory allocation, > which is effectively a stack allocation strategy, in which resource > deallocation is in LIFO order. So I think your assumption is correct. Regretfully, these comments are incorrect. First of all, memory regions were invented to get around the stack allocation, LIFO strategy. If the stack allocation sufficed, why do we need heap? We have heap specifically because the memory allocation patterns are complex: a function may allocate memory that outlives it. Regions let the programmer create arbitrarily many nested regions; everything in a parent region is available to a child. Crucially, a child may request any of its ancestors to allocate memory in their regions. Therefore, although regions are nested, memory does not have to be allocated and freed in LIFO order. The Lightweight monadic regions implement all these patterns for files or other resources (plus the dynamic bequest). http://okmij.org/ftp/Computation/resource-aware-prog/region-io.pdf The running example of the Haskell Symposium 08 paper was the following (see sec 1.1) 1. open two files for reading, one of them a configuration file; 2. read the name of an output file (such as the log file) from the configuration file; 3. open the output file and zip the contents of both input files into the output file; 4. close the configuration file; 5. copy the rest, if any, of the other input file to the output file. As you can see, the pattern of opening and closing is non-LIFO: the output file has to be opened after the configuration file and is closed also after the configuration file. Therefore, the user Faucelme can find the solution to his question in the code accompanying the Monadic Regions paper. Section 5 of the paper describes even more complex example: 1. open a configuration file; 2. read the names of two log files from the configuration file; 3. open the two log files and read a dated entry from each; 4. close the configuration file and the newer log file; 5. continue processing the older log file; 6. close the older log file. where the pattern of opening and closing is not statically known: it is decided on values read from the files. So, Faucelme's question can be answered in affirmative using the existing RegionIO library (which, as has been shown, well integrates with Iteratees). There is already a region library with the desired functionality.

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Where to get kansas-lava version 2.5
by dilawar rajput 23 Feb '12

23 Feb '12

Hello Cafe, Greetings from Mumbai. Does anyone know where to get kansas-lava version 2.5? On their github repository (as well as on Hackage), they have not posteed version 2.5. However their kansas-lava-cores requires version kansas-lava 2.5. Currently I am working with kansas-lava 2.4 but I can not use their latest kansas-lava-core with it. -- Dilawar

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Preventing leaked open file descriptors when catching exceptions
by Ryan Newton 22 Feb '12

22 Feb '12

Hi all, I'm trying to run a loop that repeatedly attempts to open a file until it succeeds. The file is a named pipe in nonblocking mode, so the writer can only connect after the reader has connected. (Perhaps there is some way to determine this by stat'ing the pipe, but I don't know it yet.) Thus I do something like the following: tryUntilNoIOErr $ do performGC -- The reader must connect first, the writer here spins with backoff. PIO.openFd filename PIO.WriteOnly Nothing fileFlags I'm running GC between iterations to try to make sure I get rid of open files. Also, in the "tryUntilNoIOErr" code below I have some debugging messages which indicate that ioeGetHandle reports no handles associated with the exceptions I'm getting back. (If there were handles provided I could close them explicitly.) In spite of these attempted precautions I'm seeing "too many open files" exceptions in simple benchmarks that should only have a maximum of ONE file open. Any hints / pointers? Thanks, -Ryan mkBackoff :: IO (IO ()) mkBackoff = do tref <- newIORef 1 return$ do t <- readIORef tref writeIORef tref (min maxwait (2 * t)) threadDelay t where maxwait = 50 * 1000 tryUntilNoIOErr :: IO a -> IO a tryUntilNoIOErr action = mkBackoff >>= loop where loop bkoff = handle (\ (e :: IOException) -> do bkoff BSS.hPutStr stderr$ BSS.pack$ " got IO err: " ++ show e case ioeGetHandle e of Nothing -> BSS.hPutStrLn stderr$ BSS.pack$ " no hndl io err." Just x -> BSS.hPutStrLn stderr$ BSS.pack$ " HNDL on io err!" ++ show x loop bkoff) $ action

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Re: [Haskell-cafe] Data.Array.Accelerate initialization timings
by Paul Sujkov 22 Feb '12

22 Feb '12

Ah, it seems that I see now what's going wrong way. I'm not using the 'run' function from the CUDA backend, and so by default I guess the code is interpreted (the test backend used for semantics check). However, it's not perfectly clear how to use CUDA backend explicitly. If you have any suggestions, it would be a great help! On 20 February 2012 16:06, Alex Gremm <algremm(a)googlemail.com> wrote: > Hi Paul, > > even though I just started reading about Accelerate, it seems to me that > you didn't use the "use" method which according to [1] initiates > asynchronous data transfer from host to GPU. > > > Cheers, > Alex > > [1]: http://www.cse.unsw.edu.au/%7Echak/papers/acc-cuda.pdf > On 20/02/12 14:46, Paul Sujkov wrote: > > Hi everyone, > > > > since accelerate mail list seems to be defunct, I'm trying to ask > > specific questions here. The problem is: array initialization in > > Data.Array.Accelerate takes a 10x amount of time in contrast to both > > Data.Array and bare C++ CUDA array initialization. This can be due to > > Data.Array.Accelerate having two backends (however, it's own tests show > > that my nVidia card is CUDA-capable), but I'm not aware of how can I > > profile GPU to check whether it is used or not. Anyway, here's code: > > > > http://hpaste.org/64036 > > > > both generateArray (DIM3) and generateArray1 (DIM1) take the same amount > > of time to initialize array. I'd say the problem is in GPU memory > > copying time, but here's bare C++ code: > > > > http://hpaste.org/64037 > > > > which does exactly the same, but 10 times faster. I'm wandering what am > > I doing wrong and how to check if I really am. Thanks in advance if > > anyone can point me on my mistakes! > > > > -- > > Regards, Paul Sujkov > > > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -- Regards, Paul Sujkov

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Haskell Weekly News: Issue 216
by Daniel Santa Cruz 22 Feb '12

22 Feb '12

Welcome to issue 216 of the HWN, a newsletter covering crowdsourced links for the Haskell community. This release covers the week of February 12 to 18, 2012. You can find the HTML version at: http://contemplatecode.blogspot.com/2012/02/haskell-weekly-news-issue-216.h… Quotes of the Week * monochrom: the selfish program's motive is to fool the programmer * WilliamByrd: Oleg is an emissary from some advanced alien race. Working with him is both exhausting and enlightening. * CodeWeaverX: do-block, or do-not-block. There is no try-catch-block. Top Reddit Stories * Where is Hackage 2.0? Domain: self.haskell, Score: 66, Comments: 42 On Reddit: [1] http://goo.gl/uXq10 Original: [2] http://goo.gl/uXq10 * Haskell Performance Patters [HTML slideshow] Domain: blog.johantibell.com, Score: 52, Comments: 13 On Reddit: [3] http://goo.gl/Y5tCb Original: [4] http://goo.gl/T9zZI * Concatenative, Row-Polymorphic Programming in Haskell (re: Why Concatenative Programming Matters) Domain: github.com, Score: 41, Comments: 21 On Reddit: [5] http://goo.gl/0w83b Original: [6] http://goo.gl/aw22p * Neil Mitchell - Shake: A Better Make Domain: neilmitchell.blogspot.com, Score: 37, Comments: 7 On Reddit: [7] http://goo.gl/MeFQ1 Original: [8] http://goo.gl/4HM0d * Why concatenative programming matters. Domain: evincarofautumn.blogspot.com, Score: 37, Comments: 23 On Reddit: [9] http://goo.gl/Udpdt Original: [10] http://goo.gl/VvUvt * GSOC 2012 Project Proposal - GHCi in the web browser Domain: apfelmus.nfshost.com, Score: 36, Comments: 34 On Reddit: [11] http://goo.gl/KS6d8 Original: [12] http://goo.gl/epgTZ * Yesod Blog :: Call for GSoC: expand the reach of Haskell with interactive websites and good persistence Domain: yesodweb.com, Score: 31, Comments: 20 On Reddit: [13] http://goo.gl/1HQ9d Original: [14] http://goo.gl/bxKIC * hxournal - A pen notetaking program written in Haskell Domain: ianwookim.org, Score: 25, Comments: 16 On Reddit: [15] http://goo.gl/4UG5E Original: [16] http://goo.gl/kQOMh * Type checking by theorem proving in IDRIS: Brady [pdf, 29 slides] Domain: cs.st-andrews.ac.uk, Score: 25, Comments: 33 On Reddit: [17] http://goo.gl/qAD5L Original: [18] http://goo.gl/mhdlC * Using Lawvere theories to combine effects Domain: blog.sigfpe.com, Score: 24, Comments: 0 On Reddit: [19] http://goo.gl/4IHq7 Original: [20] http://goo.gl/QS1aO * BayHac '12 Domain: haskell.org, Score: 23, Comments: 0 On Reddit: [21] http://goo.gl/nuxUm Original: [22] http://goo.gl/NCQGy * Hope for Haskell: making Hackage and cabal-install more awesome Domain: github.com, Score: 22, Comments: 23 On Reddit: [23] http://goo.gl/E9MmZ Original: [24] http://goo.gl/sLpkp * Thoughts on Haskell Development Domain: self.haskell, Score: 21, Comments: 77 On Reddit: [25] http://goo.gl/Qdt4b Original: [26] http://goo.gl/Qdt4b * Relating Category Theory to Programming Language Theory - MathOverflow Domain: mathoverflow.net, Score: 21, Comments: 1 On Reddit: [27] http://goo.gl/wA9E2 Original: [28] http://goo.gl/6Ox5n * The Other Prelude — any activity here? It seems like a worthwhile project. Domain: haskell.org, Score: 18, Comments: 13 On Reddit: [29] http://goo.gl/j94fj Original: [30] http://goo.gl/kwGCm Top StackOverflow Questions * Covariance / Contravariance in Haskell? votes: 24, answers: 2 Read on SO: [31] http://goo.gl/wBjaP * Haskell for someone who already knows some category theory votes: 17, answers: 1 Read on SO: [32] http://goo.gl/ms4dE * Haskell libraries overview and their quality [closed] votes: 16, answers: 1 Read on SO: [33] http://goo.gl/H3Rwg * Haskell existential quantification in detail votes: 12, answers: 1 Read on SO: [34] http://goo.gl/uiJZG * Derivative Towers and how to use the vector-space package (haskell) votes: 11, answers: 1 Read on SO: [35] http://goo.gl/lkPEl * Why doesn't Scala have an IO Monad? votes: 10, answers: 1 Read on SO: [36] http://goo.gl/dyTte * How to let a function [a] -> [a] operate on [(a,Int)]? votes: 9, answers: 2 Read on SO: [37] http://goo.gl/Js3As * Speed up runhaskell votes: 9, answers: 4 Read on SO: [38] http://goo.gl/yc3qo * Unnecessary type juggling to define Data.Void (package “void” on Hackage)? votes: 8, answers: 1 Read on SO: [39] http://goo.gl/FCmyv * Lazy vs eager evaluation and double linked list building votes: 8, answers: 3 Read on SO: [40] http://goo.gl/Z55Og Until next time, Daniel Santa Cruz References 1. http://www.reddit.com/r/haskell/comments/pn2oh/where_is_hackage_20/ 2. http://www.reddit.com/r/haskell/comments/pn2oh/where_is_hackage_20/ 3. http://blog.johantibell.com/2012/02/slides-from-haskell-performance.html 4. http://www.reddit.com/r/haskell/comments/pry5h/haskell_performance_patters_… 5. https://github.com/leonidas/codeblog/blob/master/2012/2012-02-17-concatenat… 6. http://www.reddit.com/r/haskell/comments/ptji8/concatenative_rowpolymorphic… 7. http://neilmitchell.blogspot.com/2012/02/shake-better-make.html 8. http://www.reddit.com/r/haskell/comments/plv2b/neil_mitchell_shake_a_better… 9. http://evincarofautumn.blogspot.com/2012/02/why-concatenative-programming-m… 10. http://www.reddit.com/r/haskell/comments/pmcav/why_concatenative_programmin… 11. http://apfelmus.nfshost.com/blog/2012/02/14-summer-of-code-proposal.html 12. http://www.reddit.com/r/haskell/comments/ppdgq/gsoc_2012_project_proposal_g… 13. http://www.yesodweb.com/blog/2012/02/call-for-gsoc-2012 14. http://www.reddit.com/r/haskell/comments/pqudh/yesod_blog_call_for_gsoc_exp… 15. http://ianwookim.org/hxournal 16. http://www.reddit.com/r/haskell/comments/por66/hxournal_a_pen_notetaking_pr… 17. http://www.cs.st-andrews.ac.uk/~eb/writings/idris-stp.pdf 18. http://www.reddit.com/r/haskell/comments/pp6i3/type_checking_by_theorem_pro… 19. http://blog.sigfpe.com/2012/02/using-lawvere-theories-to-combine.html 20. http://www.reddit.com/r/haskell/comments/pm46y/using_lawvere_theories_to_co… 21. http://www.haskell.org/haskellwiki/BayHac2012 22. http://www.reddit.com/r/haskell/comments/puzxx/bayhac_12/ 23. https://github.com/DanBurton/Blog/blob/master/Markdown/Hope.md 24. http://www.reddit.com/r/haskell/comments/pswbp/hope_for_haskell_making_hack… 25. http://www.reddit.com/r/haskell/comments/ppf7p/thoughts_on_haskell_developm… 26. http://www.reddit.com/r/haskell/comments/ppf7p/thoughts_on_haskell_developm… 27. http://mathoverflow.net/questions/4235/relating-category-theory-to-programm… 28. http://www.reddit.com/r/haskell/comments/put1g/relating_category_theory_to_… 29. http://www.haskell.org/haskellwiki/The_Other_Prelude 30. http://www.reddit.com/r/haskell/comments/ppwst/the_other_prelude_any_activi… 31. http://stackoverflow.com/questions/9302739/covariance-contravariance-in-has… 32. http://stackoverflow.com/questions/9252488/haskell-for-someone-who-already-… 33. http://stackoverflow.com/questions/9286799/haskell-libraries-overview-and-t… 34. http://stackoverflow.com/questions/9259921/haskell-existential-quantificati… 35. http://stackoverflow.com/questions/9313994/derivative-towers-and-how-to-use… 36. http://stackoverflow.com/questions/9345008/why-doesnt-scala-have-an-io-monad 37. http://stackoverflow.com/questions/9324862/how-to-let-a-function-a-a-operat… 38. http://stackoverflow.com/questions/9326097/speed-up-runhaskell 39. http://stackoverflow.com/questions/9261490/unnecessary-type-juggling-to-def… 40. http://stackoverflow.com/questions/9277176/lazy-vs-eager-evaluation-and-dou…

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