July 2011 - Haskell-Cafe

Re: [Haskell-cafe] NLP libraries and tools?
by wren ng thornton 09 Jul '11

09 Jul '11

On 7/7/11 3:50 AM, Aleksandar Dimitrov wrote: > It's actually a shame we're discussing this on -cafe and not on -nlp. Then > again, maybe it's going to prompt somebody to join -nlp, and I'm gonna CC it > there, because some folks over there might be interested, but not read -cafe. Quite :) > When you mentioned Arabic for producing sentences that go on for ages > you don't really need to go that far. I have had the doubtful pleasure of > reading Kant and Hegel in their original versions. In German, it is sometimes > still considered good style to write huge sentences. I once made it a point, > just to stick it to a Kant-loving-person, to produce a sentence that spanned 2 > whole pages (A4.) It wasn't even difficult. The Romans were big fans of that too (though there's only a small group of folks interested in doing NLP on Latin these days). I've only read Hegel et al. in translation, but the Latin I've read falls nicely into the notion of "span". It doesn't, however, always fall nicely into a clause-based approach like Japanese does. Then again, that could be due to the poetic/rhetorical nature of the texts in question. I wonder if there's been any computational attempt to make the notion of span or discourse atoms rigorous enough for pragmatic use... > I'm very much a "works for me" person in these matters. Mostly because I'm tired > of linguists fighting each other over trivial matters. Give me something I can > work with already! I can't help but be a (meta)theorist. But then, I'm of the firm opinion that theory must be grounded in actual practice, else it belongs more to the realm of theology than science. -- Live well, ~wren

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video for linux two (v4l2) bindings
by Claude Heiland-Allen 09 Jul '11

09 Jul '11

Greetings all, I uploaded 4 new packages that may be of interest: bindings-linux-videodev2 0.1 - bindings to Video For Linux Two (v4l2) kernel interfaces http://hackage.haskell.org/package/bindings-linux-videodev2-0.1 bindings-mmap 0.1 - bindings to mmap for POSIX http://hackage.haskell.org/package/bindings-mmap-0.1 bindings-libv4l2 0.1 - bindings to libv4l2 for Linux http://hackage.haskell.org/package/bindings-libv4l2-0.1 v4l2-examples 0.1 - video for linux two examples http://hackage.haskell.org/package/v4l2-examples-0.1 The first wraps the low-level structures and ioctls of the V4L2 API. The second wraps the raw mmap/munmap functions and constants (which I couldn't seem to find on hackage, only higher level wrappers which I couldn't use for various reasons). It would make more sense for this to be folded into bindings-posix at some point. The third wraps libv4l2, which provides an interface very similar to the use of V4L2 ioctls, but the library adds extra capabilities behind the scenes (I'm led to believe colour space conversion is one of them) which is hopefully useful. And the last is a crude example dumping frames from a video device (like a webcam) to stdout in YUV4MPEG2 format. The code is *very* low-level and imperative (almost a direct translation from the C example provided on the linuxtv API reference), there is plenty of room for a much nicer layer to (for example) get video data into RePa arrays or OpenGL textures. As these are raw bindings, documentation is best found upstream. Thanks to Maurício C. Antunes's package for making this possible, I recommend it: http://hackage.haskell.org/package/bindings-DSL Claude -- http://claudiusmaximus.goto10.org

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Re: [Haskell-cafe] Call for GUI examples - Functional Reactive Programming
by Daniel Patterson 08 Jul '11

08 Jul '11

Forgot to cc the list On Jul 8, 2011, at 11:20 AM, Daniel Patterson wrote: > On Jul 8, 2011, at 3:51 AM, Heinrich Apfelmus wrote: >> Jason Dagit wrote: >>> Heinrich Apfelmus wrote: >>>> Do you know any *small GUI programs* that you would *like* to see >>>> *implemented with Functional Reactive Programming?* >>>> >>>> I would love to hear your examples, so that I can try to convert them to FRP >>>> style and test my library against them! >>> How about a GUI for darcs? >> >> This would involve a lot of functionality unrelated to GUIs. Could you break it down to a minimal "GUI-only" example that still gets the point across? > > > What about something that just showed the list of patches for a given repository, which would update when the repository changed? That is deadly simple, but could still be somewhat useful (ie, have it track a relatively central repo, and running on a screen somewhere in the metaphorical office). It would also be wonderful to start on a GUI for darcs, and I could say it might interest _me_ in taking a stab at improving it :) And it might be an example of the kind of open system that was mentioned earlier > > Daniel

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Using Acid-State for IPC?
by Dmitri O.Kondratiev 08 Jul '11

08 Jul '11

Hi, I am wondering if Acid-State (http://hackage.haskell.org/package/acid-state) can be used to share data between processes running in different address spaces? For example, one demon system process (not thread!) periodically collects data from Web and stores it in a list. On regular intervals this process checkpoints the list to a disk file. Another independent process randomly starts and reads this list from the checkpoint file. Can this simple scenario be done with Acid-State? Any conflicts accessing checkpoint file from two system processes simultaneously? What other Haskell libs can be used for such a task? Thanks!

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CfP: Haskell Workshop in Leipzig, Germany, October 7
by Johannes Waldmann 08 Jul '11

08 Jul '11

Call for submissions for our local Haskell Workshop in Leipzig, Germany. Tutorials, talks, demonstrations ... everything welcome. Workshop language is German (mainly), and English (by request). Submission deadline: August 20, Workshop date: October 7 http://portal.imn.htwk-leipzig.de/events/hal6-haskell-workshop Best regards, Johannes Waldmann.

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Diagnose stack space overflow
by Logo Logo 08 Jul '11

08 Jul '11

Hi, For the following error: Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize -RTS' to increase it. I want to find out the culprit function and rewrite it tail-recursively. Is there a way to find out which function is causing this error other than reviewing the code manually? Thanks, Loganathan

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ANNOUNCE: hacphi satellite in berlin july 29-31
by Matthias Fischmann 08 Jul '11

08 Jul '11

yet another hackathon: in case you wanted to join the philadelphia haskell hackathon but decided it's too far away (or in case you happen to be anywhere near and think this is a great opportunity), please join us in berlin: http://haskell.org/haskellwiki/Hac_%CF%86#Berlin_satellite admission is free. we have limited seats, so don't wait too long! hope to see you there, cheers, matthias

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Re: [Haskell-cafe] Diagnose stack space overflow
by John Lato 08 Jul '11

08 Jul '11

> From: Logo Logo <saraslogo(a)gmail.com> > > Hi, > > For the following error: > > Stack space overflow: current size 8388608 bytes. > Use `+RTS -Ksize -RTS' to increase it. > > I want to find out the culprit function and rewrite it tail-recursively. Is > there a way to find out which function is causing this error other > than reviewing the code manually? > I'd like to point out that a stack-space overflow in Haskell isn't quite the same thing as in other functional languages. In particular, it's possible for tail-recursive functions to overflow the stack because of laziness. Consider this tail-recursive sum function: > trSum :: [Int] -> Int > trSum l = go 0 l > where > go acc [] = acc > go acc (x:xs) = go (acc+x) xs It's tail-recursive. But if you enter this in ghci and run it, you'll find that it uses increasing stack space, and will likely cause a stack overflow for large enough inputs. The problem is that the accumulator 'acc' isn't strict and builds up a thunk of the form: 0+n1+n2+...+nn The solution is to add strictness. For this example, a '!' on the accumulator will do. GHC will sometimes spot cases where extra strictness is helpful (it'll figure this one out when compiled with -O), but it often needs help. I'd recommend Edward Yang's series of blog posts about debugging, space leaks, and the Haskell heap. One useful article is http://blog.ezyang.com/2011/05/anatomy-of-a-thunk-leak/ , but you may want to start at the beginning of the heap series. John L.

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Re: [Haskell-cafe] NLP libraries and tools?
by wren ng thornton 07 Jul '11

07 Jul '11

On 7/7/11 3:38 AM, Aleksandar Dimitrov wrote: > On Wed, Jul 06, 2011 at 07:27:10PM -0700, wren ng thornton wrote: >> I definitely agree with the iteratees comment, but I'm curious about the >> leaks you mention. I haven't run into leakiness issues (that I'm aware of) >> in my use of ByteStrings for NLP. > > The issue is this: strict ByteStrings retain pointers to the original chunk. The > chunk is probably bigger than you'd want to keep in memory, if you, say, wanted > to just keep one or two words. In my case, the chunk was some 65K (that was my > Iteratee chunk size.) Oh, that issue. Yeah, I maintain an intern table and make sure that the copy in the table is a trimmed copy instead of keeping the whole string alive. I guess I should factor that part of my tagger out into a separate package :) I didn't know if you meant there was a technical issue, e.g. something about the fact that ByteStrings uses pinned memory (whereas Text doesn't IIRC). -- Live well, ~wren

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NVIDIA's CUDA and Haskell
by Vasili I. Galchin 07 Jul '11

07 Jul '11

Hi, NVIDIA's CUDA library seems to be really hot in the massively parallel world: http://www.nvidia.com/object/cuda_home_new.html. I realize that given CUDA seems to be implemented in an extension of ANSI C that it is pervaded by statefulness. However, is there any effort to build "a bridge" between Haskell and CUDA, foreign language bindings or maybe better yet a monad to encapsulate state?? Kind regards, Vasili

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