April 2011 - Haskell-Cafe

DSL for task dependencies
by Serge Le Huitouze 07 Apr '11

07 Apr '11

Hi Haskellers! I think I remember reading a blog post or web page describing a EDSL to describe tasks and their dependencies "a la" make. Can anyone point me to such published material? Thanks in advance. --serge

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'Progress bar' enumeratee
by David Hotham 07 Apr '11

07 Apr '11

Hello, I've spent some time over the last couple of days trying to write an enumeratee that prints a "." every n bytes (with obvious intended use as a progress tracker). Seems like it oughtn't be hard, but it has been a steep learning curve... I have come up with something that seems to do the job but I don't know that I'm completely happy with it (or even that I completely understand it, to be honest). If anyone more expert would be kind enough either to reassure me that I'm doing it right or - more likely - to offer improvements / suggestions on what obvious simplifications I have overlooked, I'd be grateful. Thanks David import qualified Data.ByteString.Char8 as B import qualified Data.ByteString.Lazy.Char8 as BL import qualified Data.Enumerator as E import qualified Data.Enumerator.Binary as EB import Control.Monad.IO.Class (liftIO, MonadIO) import System.IO (hFlush, stdout) dotEvery :: MonadIO m => Integer -> E.Enumeratee B.ByteString B.ByteString m b dotEvery count = E.checkDone $ E.continue . dotIn count where dotIn need k E.EOF = E.yield (E.Continue k) E.EOF dotIn need k (E.Chunks []) = E.continue (dotIn need k) dotIn need k (E.Chunks xs) = iter where lazy = BL.fromChunks xs len = toInteger $ BL.length lazy iter = if len < need then k (E.Chunks xs) E.>>== E.checkDone (E.continue . dotIn (count - len)) else let (x1, x2) = BL.splitAt (fromInteger need) lazy s1 = E.Chunks $ BL.toChunks x1 s2 = E.Chunks $ BL.toChunks x2 enumee = E.checkDoneEx s2 (\k' -> dotIn count k' s2) in E.Iteratee $ do newStep <- E.runIteratee $ k s1 liftIO $ putStr "." >> hFlush stdout E.runIteratee $ enumee newStep PS Implementations which involve "EB.take count" seem to me unsatisfactory; one surely oughtn't need to have a large buffer to solve this problem PPS I did find an implementation via mapAccumM which I consider pleasing enough from an aesthetic point of view - but which runs 30x slower dotAt :: MonadIO m => Integer -> Integer -> Word8 -> m (Integer, Word8) dotAt n s w | s >= n = do liftIO $ putStr "." >> hFlush stdout return (1, w) | otherwise = return (s+1, w) dotEvery' :: MonadIO m => Integer -> E.Enumeratee B.ByteString B.ByteString m b dotEvery' n = EB.mapAccumM (dotAt n) 1

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parsec - source position information
by Ozgur Akgun 07 Apr '11

07 Apr '11

Hi, Is there a way to get source position[1] information from parsec while defining a parser? It surely knows about source positions, as they are used while reporting a parsing error. data Identifier = Identifier String SourcePos pIdentifier :: Parser Identifier pIdentifier = do pos <- ?? s <- pString return (Identifier s pos) [1] http://hackage.haskell.org/packages/archive/parsec/3.0.0/doc/html/Text-Pars… Thanks in advance, Ozgur

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Local copy of hackageDB
by José Pedro Magalhães 07 Apr '11

07 Apr '11

Hi all, I want to use cabal-install on a machine without internet access. I tried downloading http://hackage.haskell.org/cgi-bin/hackage-scripts/archive.tar, unpacking it and setting the local-repo field in the config file to this location but that doesn't work, as cabal-install says that it is missing the package list for the local repo. What should I do? Thanks, Pedro

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ANNOUNCE: swish 0.3.0.0
by Doug Burke 07 Apr '11

07 Apr '11

I am pleased to announce an update of the swish package to version 0.3.0.0 [1]. It is mainly meant to be a maintenance upgrade over the existing version on Hackage [2] by Vasili I. Galchin, but does add additional functionality in that it now supports the NTriples format and the N3 parser and formatter has been updated to better match the current specification. For those not aware of what Swish actually is, it is an experiment by Graham Klyne in writing a "Semantic Web" framework in Haskell [3]. I note that the wonderful machinery behind Hackage has already processed the documentation so you can read more about it at [1] as well as the very-sparsely-documented Wiki at [4]. [1] http://hackage.haskell.org/package/swish-0.3.0.0 [2] http://hackage.haskell.org/package/swish-0.2.1 [3] http://www.ninebynine.org/Software/swish-0.2.1.html [4] https://bitbucket.org/doug_burke/swish/wiki/Home Thanks for reading this far, Doug

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ANNOUNCE: DocTest-0.2.0
by Simon Hengel 07 Apr '11

07 Apr '11

I just uploaded a new version of DocTest[1] to Hackage. WHAT IS DocTest? ================ DocTest is a port of Python's doctest[2] to Haskell. It can be used to verify, that examples in Haddock comments[3] do still work. This also provides you with a simple mechanism to write unit test, without the burden of maintaining a dedicated test suite. A basic example of usage is at [4]. WHAT'S NEW IN THIS VERSION? =========================== Support for blank lines in the result of an expression (analogous to the <BLANKLINE>-feature of Python's doctest). Here is an example of usage: -- | -- Some example: -- -- >>> putStrLn "foo\n\nbar" -- foo -- <BLANKLINE> -- bar Currently this is implemented in DocTest, but we will move it to Haddock with the next release. Cheers, Simon [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/DocTest [2] http://docs.python.org/library/doctest.html [3] http://www.haskell.org/haddock/doc/html/ch03s08.html#id566093 [4] http://haskell.org/haskellwiki/DocTest _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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mtlx has a nice design but is slow
by Sean Leather 07 Apr '11

07 Apr '11

I just refactored my type and transform system prototype (introduced in [1] but changed since then) from using mtlx [2] (type-indexed monad transformers described in [3]) to mtl using RWST. mtlx allowed me to cleanly separate the various monadic components in a convenient way. Unfortunately, I found it to be too slow. The refactoring was an experiment to see how slow. I was rather surprised: Running time of a compiled main with a list of tests: mtlx (7 transformers): 2 min 52 sec mtl (RWST): 0 min 13 sec It's frustrating to see such a huge performance gap for a better design. Regards, Sean [1] http://splonderzoek.blogspot.com/2011/03/draft-type-changing-program-improv… [2] http://hackage.haskell.org/package/mtlx [3] http://www.ittc.ku.edu/~marks/cgi-bin/pubs/monadfactory.pdf

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Haskell Weekly News: Issue 176
by Daniel Santa Cruz 06 Apr '11

06 Apr '11

Welcome to issue 176 of the HWN, a newsletter covering developments in the [1]Haskell community. This release covers the week of March 27 to April 02, 2011. You can find the HTML version at: http://bit.ly/fEdQka Announcements Wren Ng Thornton [2]announced the release of version 0.3.4 of unix-bytestring. Ian Lynagh and the GHC team [3]announced version 7.0.3 of GHC, containing a handful of bugfixes. Jose A. Ortega Ruiz [4]annouced the release of version 0.13 of xmobar. Might want to check it out specially if you are using xmonad! Jason Dagit [5]annouced release 0.2.0 of the nehe-tuts package, tutorials for using OpenGL. David Sorokin [6]annouced the release of his new library aivika: a multi-paradigm simulation library. Tom Hawkins [7]annouced version 0.3.1 of ImProve: an imperative DSL for hard realtime embedded applications. Eric Y. Kow [8]introduced the first issue of Parallel Haskell Digest, "a newsletter aiming to show off all the work that's going on using parallelism and concurrency in the Haskell community." Here is to hoping we get more of these! George Giorgidze [9]announced version 0.5.5 of DSH (Database Supported Haskell). Jasper Van der Jeugt [10]annouced the 7th Ghent Functional Programming Group meeting on Tuesday, April 26, in celebration of the group's first year of existance. The meetup will be at the Technicum building of Ghent University at 19:30. Quotes of the Week * lispy: [in response to "C++ is a huge language, the type system is complex"] real and imaginary components :) the imaginary bits are the type safety * gwern: amazing `catch` (how sweet the type), that saved an exception like me! I once was thrown, but now am caught; was impure, but now pure be * hpc: appEndo sounds like a harry potter spell * monochrom: yeah, get out of Turing tarpit, provable termination, only to get into Godel tarpit * xplat: to me, the great thing about pointfree programming is you don't have to let variable names get in the way of your logic. and the great thing about pointful programming is you don't have to let '(flip .) . (.) . (flip flip . join)' get in the way of your logic. it's nice to have multiple tools in your toolbox * lispy: I've never looked at the gtk2hs source. I'm not sure I can muster the intestinal fortitude * kmc: time to play "transfinite ordinal or asian emoticon" * killing-joke: rip oop. "Object-oriented programming is eliminated entirely from the introductory curriculum, because it is both anti-modular and anti-parallel by its very nature, and hence unsuitable for a modern CS curriculum." Top Reddit Stories * Promo code to get Learn You a Haskell 40% off + e- book for free + swag From (learnyouahaskell.com) scored 68 with 25 comments. Read on [11]reddit. Read the [12]original post. * Real Time Edge Detection in Parallel Haskell From (disciple-devel.blogspot.com) scored 39 with 9 comments. Read on [13]reddit. Read the [14]original post. * Modern OpenGL with Haskell From (arcadianvisions.com) scored 39 with 10 comments. Read on [15]reddit. Read the [16]original post. * GHC migration to Git complete From (haskell.org) scored 37 with 15 comments. Read on [17]reddit. Read the [18]original post. * Haskell is 21 years old today! From (twitter.com) scored 37 with 8 comments. Read on [19]reddit. Read the [20]original post. * Re-implementing XMonad's core in Coq : Wouter Swiestra :: PDF From (cs.ru.nl), scored 34 with 13 comments. Read on [21]reddit. Read the [22]original post. * GHC 7.0.3 released From (haskell.org) scored 33 with 9 comments. Read on [23]reddit. Read the [24]original post. * "Reactive-banana and the essence of FRP". I implemented a small FRP library that can be mixed freely with imperative code. From (apfelmus.nfshost.com) scored 30 with 7 comments. Read on [25]reddit. Read the [26]original post. * New release of OpenGL NeHe tutorials in Haskell From (self.haskell), scored 27 with 22 comments. Read on [27]reddit. * Do you read academic papers on a Kindle? From (dmwit.com) scored 26 with 27 comments. Read on [28]reddit. Read the [29]original post. Top StackOverflow Questions * [30]Implementing lazy functional languages votes: 19, answers: 3 * [31]Is it possible to roll your own syntax sugar (like do-notation, or arrow-notation) in Haskell? votes: 12, answers: 2 * [32]Are there any LL Parser Generators for Functional Languages such as Haskell or Scala? votes: 11, answers: 4 * [33]Programming language for functional parallelism: F# vs Haskell votes: 10, answers: 6 * [34]easy "undo" in functional data structures votes: 8, answers: 2 About the Haskell Weekly News If you have any comments/thoughts on the newsletter, don't hesitate to contact me at dstcruz(a)gmail.com. Happy coding! Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.libraries/15521 3. http://article.gmane.org/gmane.comp.lang.haskell.general/18607 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/87583 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/87584 6. http://article.gmane.org/gmane.comp.lang.haskell.general/18612 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/87628 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/87709 9. http://article.gmane.org/gmane.comp.lang.haskell.general/18635 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/87752 11. http://www.reddit.com/r/haskell/comments/ge10y/promo_code_to_get_learn_you_… 12. http://learnyouahaskell.com/ 13. http://www.reddit.com/r/haskell/comments/gdudz/real_time_edge_detection_in_… 14. http://disciple-devel.blogspot.com/2011/03/real-time-edge-detection-in-hask… 15. http://www.reddit.com/r/haskell/comments/gepfm/modern_opengl_with_haskell/ 16. http://www.arcadianvisions.com/blog/?p=224 17. http://www.reddit.com/r/haskell/comments/ggu2r/ghc_migrati%C3%B6n_t%C3%B6_g… 18. http://www.haskell.org/pipermail/cvs-ghc/2011-April/060798.html 19. http://www.reddit.com/r/haskell/comments/ggwv3/haskell_is_21_years_old_toda… 20. http://twitter.com/donsbot/status/54026417721188352 21. http://www.reddit.com/r/haskell/comments/gf3sb/reimplementing_xmonads_core_… 22. http://www.cs.ru.nl/~wouters/Talks/BrouwerExtraction.pdf 23. http://www.reddit.com/r/haskell/comments/gcmsz/ghc_703_released/ 24. http://www.haskell.org/pipermail/haskell/2011-March/022673.html 25. http://www.reddit.com/r/haskell/comments/gd46d/reactivebanana_and_the_essen… 26. http://apfelmus.nfshost.com/blog/2011/03/28-essence-frp.html 27. http://www.reddit.com/r/haskell/comments/gcsi1/new_release_of_opengl_nehe_t… 28. http://www.reddit.com/r/haskell/comments/gfz5k/do_you_read_academic_papers_… 29. http://dmwit.com/pdfsplit 30. http://stackoverflow.com/questions/5451645/implementing-lazy-functional-lan… 31. http://stackoverflow.com/questions/5450003/is-it-possible-to-roll-your-own-… 32. http://stackoverflow.com/questions/5507665/are-there-any-ll-parser-generato… 33. http://stackoverflow.com/questions/5492930/programming-language-for-functio… 34. http://stackoverflow.com/questions/5447054/easy-undo-in-functional-data-str…

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Re: [Haskell-cafe] mtlx has a nice design but is slow
by Mark Snyder 06 Apr '11

06 Apr '11

I'm the author for mtlx, and admittedly I didn't do anything about efficiency when I implemented it. Is there any initial place I ought to look for tips on inlining? I'll start with the pragmas page (http://www.haskell.org/ghc/docs/7.0.3/html/users_guide/pragmas.html) I suppose. I'm happy for any suggestions--optimizing hasn't been one of my focuses, so it's time for me to learn I suppose! I did switch to newtype definitions in the most recent version (0.1.5), which probably helped a lot compared to data definitions, but there are no inline pragmas in use, so perhaps there are some good opportunities for optimization. ~Mark Snyder > >Is the package missing some obvious inlining in the instances? > >> I just refactored my type and transform system prototype (introduced in [1] >> but changed since then) from using mtlx [2] (type-indexed monad transformers >> described in [3]) to mtl using RWST. mtlx allowed me to cleanly separate the >> various monadic components in a convenient way. Unfortunately, I found it to >> be too slow. The refactoring was an experiment to see how slow. I was rather >> surprised: >> >> Running time of a compiled main with a list of tests: >> ? mtlx (7 transformers): 2 min 52 sec >> ? mtl (RWST): 0 min 13 sec >> >> It's frustrating to see such a huge performance gap for a better design. >> >> Regards, >> Sean >>

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Re: [Haskell-cafe] How to contact OpenGL package maintainer (where is Sven?)
by Jason Dagit 06 Apr '11

06 Apr '11

No response yet from Sven after about a month and no one seems to have heard from him in over a year. I'm going to take over for now under the assumption that Sven is missing. == My plans for moving forward == * Assemble an opengl taskforce, a few people have already mentioned an interest in being on the team * clean up the current cabal files (I already wrote patches for that) * put the repos on github to make team collaboration easier * add the RULES that Andy Gill suggested for realToFrac * look at adding instances for MArray so that GLfloat et al can be stored in IOUArrays * add support for opengl 4.x * look at adding deprecation pragmas for deprecated opengl calls * new hackage releases * anything else that comes up Thanks, Jason On Sun, Mar 27, 2011 at 2:11 PM, Jason Dagit <dagitj(a)gmail.com> wrote: > I sent the message below to Haskell-Cafe about a week ago. I got one > response saying that Sven has disappeared in the past but reappeared when > updates were necessary. I still haven't heard from Sven. Now I'm widening > my search. My original email to Sven was on March 11th. > > It looks like the OpenGL packages on hackage[1,2,3,4] have not been > updated in some time. No updates later than Oct 2009. I tried to email > Sven directly using the email address listed on hackage but after over two > weeks I still haven't heard from him. I sent some patches to the opengl list > about a week ago but I noticed that Sven hasn't posted on that list since > Oct 2009 when he released the current version of OpenGLRaw. None of the > public darcs repos have patches newer than Oct 2009. Also, the homepage url > listed in the packages is a 404: > http://www.haskell.org/HOpenGL/ > > My concern is that Sven has disappeared for some reason. I hope he's well. > He has always done top notch work in the past maintaining these libraries. > Perhaps he's simply busy or lost interest? > > Does anyone know if he was looking for a new maintainer? Perhaps you've > heard from him more recently than Oct 2009? > > If a new maintainer is needed, I would consider nominating myself :) > > Thanks, > Jason > > [1] http://hackage.haskell.org/package/OpenGLRaw > [2] http://hackage.haskell.org/package/OpenGL > [3] http://hackage.haskell.org/package/GLURaw > [4] http://hackage.haskell.org/package/GLUT >

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