- Haskell-Cafe - Haskell.org

ANNOUNCE: attoparsec-iteratee v0.1
by Gregory Collins 13 Mar '10

13 Mar '10

Hi all, I've just uploaded the first version of the attoparsec-iteratee library to Hackage: http://hackage.haskell.org/package/attoparsec-iteratee It takes applicative parsers written using attoparsec and automagically converts them to iteratees that can parse things from streams in O(1) space. ....and the combination is fast: a prototype HTTP server I'm working on uses this library and can handle as many as 13k reqs/sec on my Macbook. G -- Gregory Collins <greg(a)gregorycollins.net>

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mirroring patch tag
by Thomas Hartman 13 Mar '10

13 Mar '10

http://blog.patch-tag.com/2010/03/13/mirroring-patch-tag/ cheers, thomas.

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generalized newtype deriving allows the definition of otherwise undefinable functions
by Wolfgang Jeltsch 13 Mar '10

13 Mar '10

Hello, some time ago, it was pointed out that generalized newtype deriving could be used to circumvent module borders. Now, I found out that generalized newtype deriving can even be used to define functions that would be impossible to define otherwise. To me, this is surprising since I thought that generalized newtype deriving was only intended to save the programmer from writing boilerplate code, not to extend expressiveness. Have a look at the following code: > {-# LANGUAGE > GeneralizedNewtypeDeriving, > MultiParamTypeClasses, > FlexibleInstances > #-} > > class Iso a b where > > conv :: item a -> item b > > instance Iso a a where > > conv = id > > newtype Wrapped a = Wrap a deriving (Iso a, Show) Now any value whose type contains some type t can be converted into a value of the type that you get if you replace t by Wrap t. Here is some code to demonstrate this for binary operations: > newtype BinOp a = BinOp (a -> a -> a) > > convBinOp :: (a -> a -> a) -> (Wrapped a -> Wrapped a -> Wrapped a) > convBinOp op = let BinOp op' = conv (BinOp op) in op' Now, you can enter convBinOp (*) (Wrap 5) (Wrap 3) into GHCi, and you will get Wrap 15 as the result. The point is, of course, that such conversions are not only possible for binary operations but for arbitrary values and that these conversions are done by a single generic function conv. I don’t think it would be possible to implement conv without generalized newtype deriving. Any thoughts? Best wishes, Wolfgang

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Hackaton: A roof to stay
by Hugo Gomes 12 Mar '10

12 Mar '10

Hello, im planing on going to the hackaton, but the prices in Zurich are unusually high for my tight budget, so i was wondering if there is anyone here that lives there and would allow me to sleep on their couch or on the floor during the hackaton. Is there ? Thanks.

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Google Summer of Code 2010.
by Edward Kmett 12 Mar '10

12 Mar '10

It is that time of year again; the Google Summer of Code is upon us! *Sign Up Information* If you are a student and want to sign up to make $4,500 for hacking on the code you love over the summer or are willing to help out as a mentor, now is the time to act. Please sign up by adding your name to the list at: http://hackage.haskell.org/trac/summer-of-code/wiki/People2010 I have extracted an initial list of interested mentors from Malcolm's earlier inquiry to the cafe and have submitted our initial application to Google. A strong list of potential mentors and students will help bolster our case. Our main wiki entry for the Summer of Code 2010 is now online: http://hackage.haskell.org/trac/summer-of-code/wiki/Soc2010 If you are interested in applying as a student, here are some guidelines: http://hackage.haskell.org/trac/summer-of-code/wiki/StudApply2010 The official deadline for student applications with Google is April 7th, but if you are interested please add your name to the People2010 page above, as soon as possible. *Interested in helping out, but not sure how? * There are a number of ideas that we've been collecting for projects available through the trac http://hackage.haskell.org/trac/summer-of-code/report/1 and which have been collecting over time in a reddit: http://www.reddit.com/r/haskell_proposals/top/ While the reddit is a great place to discuss proposals, we had to choose one mechanism to supply Google with our ideas officially, so please submit proposals <http://hackage.haskell.org/trac/summer-of-code/newticket> to the trac if you can think of something you like to work on, or which would be an appropriately beneficial project for a summer worth of work. *Helping Out Darcs * Haskell.org is going to continue to act as an umbrella organization covering darcs <http://darcs.net/> for the Summer of Code once more. If you are interested in helping them out, they also have a page full of project ideas as well: http://wiki.darcs.net/GoogleSummerOfCode Again, please submit proposals<http://hackage.haskell.org/trac/summer-of-code/newticket>as tickets to the trac if you can think of something you'd like to work on. *More Information* Here are a bunch of relevant links that may be able to answer your questions: Google's Summer of Code Homepage <http://socghop.appspot.com/> Google's Summer of Code 2010 FAQ<http://socghop.appspot.com/document/show/gsoc_program/google/gsoc2010/faqs> Google's Summer of Code 2010 Timeline<http://socghop.appspot.com/document/show/gsoc_program/google/gsoc2010/timel…> Google's Summer of Code Wiki Knowledge Base<http://code.google.com/p/google-summer-of-code/wiki/WikiStart> Of course, you can always feel free to email me <ekmett(a)gmail.com> or inquire on irc.freenode.net #haskell-soc or with the darcs folks over on #darcs for more information. If you don't have an IRC client, you can get there from: http://webchat.freenode.net Thank you all very much and we look forward to another successful Summer of Code! -Edward Kmett

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Cabal and LLVM bindings
by Ville Tirronen 12 Mar '10

12 Mar '10

Hi! I'm trying to get cabal build my toy compiler, which is based on llvm bindings on hackage. Everything is fine with ghc --make, but with cabal install I get: Loading package llvm-0.7.1.1 ... <command line>: can't load .so/.DLL for: LLVMSystem (dlopen(libLLVMSystem.dylib, 9): image not found) cabal: Error: some packages failed to install: QV-0.1 failed during the building phase. The exception was: ExitFailure 1 This is done on os x 10.5.8, if that has any relevance. Anyone got any hints on how to proceed with this? Ville Tirronen

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3rd party widgets with qtHaskell (Marble)
by Philip Beadling 12 Mar '10

12 Mar '10

Hi, I know this isn't a qtHaskell list, but I don't think there is one. Was wondering if anyone has any ideas on the below. Basically I'm trying to control a Marble (Map software) Qt widget from qtHaskell. So I've mocked up a very simple user interface in Qt Designer (1 form, 1 Marble widget). I can load this up and display it fine in Haskell, but as soon as I try to interrogate the widget I get a seg fault (eg qObjectProperty) My guess is that the call to findChild, although it executes OK it is not producing a valid QObject - probably casting to Marble::MarbleWidget* it crux of the problem. I can get this working using standard Qt Widgets (just like the examples show from qtHaskell), so I know the method is sound - although calling 3rd party widgets like this may be ambitious or impossible. I recognise this is a fairly broad query! Has anyone tried anything similar? Is it even possible to do this in qtHaskell as I'm proposing? I'm a Qt novice, so it may well be that I've misunderstood qtHaskell. Cheers, Phil. Using: GHC 6.12.1 / QT4.5 / Marble 0.8 / Ubuntu 9.04 module Main where import Qtc main :: IO () main = do app <- qApplication () rok <- registerResource "marble.rcc" loader <- qUiLoader () uiFile <- qFile ":/marble.ui" open uiFile fReadOnly ui <- load loader uiFile close uiFile () ui_map <- findChild ui ("<Marble::MarbleWidget*>", "MarbleWidget") sc <- qObjectProperty ui_map "showCompass" qshow ui () ok <- qApplicationExec () return ()

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If the local variable can be changed ...
by zaxis 11 Mar '10

11 Mar '10

In FP the variable can not be changed once created. Yes, it has much advantage . However, i feel it is too strict. As we know, the local variable is allocated on stack which is thread safe. So if the local variable can be changed, then we can use loop, etc. same as imperative languages. For example, for (i=0; i<100; i++) where `i` is a local variable in function. Any suggestion is appreciated! ----- fac n = let { f = foldr (*) 1 [1..n] } in f -- View this message in context: http://old.nabble.com/If-the-local-variable-can-be-changed-...-tp27844016p2… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Re: Anyone up for Google SoC 2010?
by Yakov Zaytsev 11 Mar '10

11 Mar '10

I've got N900 recently and saw that according to this page http://hackage.haskell.org/trac/ghc/wiki/Platforms it's not possible to run GHC and GHCi easily on ARM. This sucks. I want to propose a project "bring GHC back to life on arm-linux". It is supposed that the outcome will be a package for Maemo 5. Actually, I want to apply for this project as a student. I hope to make NCG for ARM working in some sense. Dear list, what do you think about it? -- Yakov

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ANN: HaskellTorrent v0.1.1
by Jesper Louis Andersen 11 Mar '10

11 Mar '10

Hello Cafe, I am pleased to announce yet another release of the HaskellTorrent project. In this release, focus has been on improving upon the work laid in v0.0. Highlights include: * Certain data structures have changed from Data.List to Data.IntSet, yielding much improved performance. * Addition of a GetOpt option parser. * Use of test-framework to run unit-tests. * Assertion optimization, cutting down CPU usage by quite a margin. * Change SHA1 checksumming to use Peter Simons hopenssl package. This plugged some serious memory leaks. * Support for listen() on port 1579 so incoming connections get handled correctly. * Support for more graceful stopping. The supervisor tree is now terminated in the opposite order of creation. * When closing down, tell the tracker we are stopping. * Add KeepAlive messages on idle socket connections. * Improve the console interface a bit so it is quasi-usable. * Change the logging framework from my own to hslogger by John Goerzen. It is better than my attempts and it shaves 150 lines of code from the project not having to maintain a logging framework. This also makes the client BEP003 compliant, so we can now claim to be a full BitTorrent client. Looking forward, I'd like to get less CPU usage, and support for more BitTorrent extensions. -- There are still bugs in the code, so watch out for spinning processes. Also, performance is still far from optimal. From a profiler run, we get the following: total time = 64.26 secs (3213 ticks @ 20 ms) total alloc = 6,712,153,496 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc MAIN MAIN 58.0 3.7 assertPieceDB Process.PieceMgr 13.4 29.6 logP Process 3.7 6.0 syncP Process 2.8 12.1 download Main 2.1 0.0 updateBS Digest 2.1 0.0 recvP Process 2.0 4.3 chooseP Process 1.9 7.0 receiverP Process.Peer 1.8 1.5 peerP Process.Peer 1.2 0.6 grabBlocks' Process.PieceMgr 1.0 3.1 senderP Process.Peer 1.0 1.4 sendP Process 0.9 3.1 checkPiece FS 0.7 6.1 msgPeer Process.ChokeMgr 0.6 2.4 registerL Process.Timer 0.2 1.9 getByteString Data.Serialize.Get 0.2 1.0 newBuffer Data.Serialize.Builder 0.0 10.1 which tells us we are still allocating far too much memory. I wonder what the 58.0% on MAIN means (this is with -prof -auto-all -caf-all). The code is heavily concurrent, using the cml package. My guess is that we have somewhere between 500 and 1000 threads when running. I ponder if that has something to do with it. The price of assertPieceDB can easily be removed by running the assertions at a rarer pace. -- J.

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