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Intergalactic Telefunctors
by Gregg Reynolds 15 Feb '09

15 Feb '09

Came up with an alternative to the container metaphor for functors that you might find amusing: http://syntax.wikidot.com/blog:9

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Race condition possible?
by Peter Verswyvelen 15 Feb '09

15 Feb '09

Consider the following code stamp v x = do t <- getCurrentTime putMVar v (x,t) Is it possible - with GHC - that a thread switch happens after the t <- getCurrentTime and the putMVar v (x,t)? If so, how would it be possible to make sure that the operation of reading the current time and writing the pair to the MVar is an "atomic" operation, in the sense that no thread switch can happen between the two? Would this require STM? Thanks again for sharing your wisdom with me :) Peter

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Telnet handshaking
by Martijn van Steenbergen 15 Feb '09

15 Feb '09

Hello, Are there any Haskell libraries out there that implement telnet? Bare sockets are a good approximation, but I'm looking for a library that understands the escape sequences specific to telnet. Thanks, Martijn.

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Help with Menu item handlers in gtk2hs with glade
by Lakshmi Narasimhan 15 Feb '09

15 Feb '09

I designed a basic GUI with Menu bar and menu items in glade. I use the glade bindings in haskell to get the menu item using xmlGetWidget and castToMenuItem function. I set a *onActivateItem* handler for this menuitem. However this is not working. I saw the glade file and it has a signal function in the xml. I tried to use the same function name, but it doesn't work either. Any suggestions on what I might be doing wrong here and how to get menu item handlers working.

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Delimited continuations: please comment
by Cristiano Paris 15 Feb '09

15 Feb '09

Hi, I'm experimenting with delimited continuations in the effort to understand how they work and when it's convenient to use them. Consider this piece of code (install the CC-delcont before running it): ---- {-# LANGUAGE NoMonomorphismRestriction #-} import Control.Monad.CC import Control.Monad.Trans -- why do I have to import this? data Monad m => Susp m a b = Stop | Susp (a -> m (Susp m a b)) job = reset $ \p -> let askMsg = shift p $ \k -> return $ Susp $ k . return in do x <- askMsg liftIO $ putStrLn $ "x was " ++ show x y <- askMsg liftIO $ putStrLn $ "y was " ++ show y return Stop scheduler j = do Susp nj <- j Susp nj <- nj "Hello!" nj "World!" return undefined main = runCCT $ scheduler job ---- which produces the output: ---- [paris@bagend haskell]$ runhaskell dc.hs x was "Hello!" y was "World!" [paris@bagend haskell]$ ---- The goal of this is to have a test-case implementation of the system call mechanism found in operating systems, like the one described by Oleg in (see page 3): http://okmij.org/ftp/papers/context-OS.pdf In effect, this is a bit different from the syscall service routine described by Oleg, as the scheduler function reacts in different ways for subsequent calls (the first time feeds "Hello!", the second one "World!", in a nice monad style). Yet, I liked the separation between the scheduler and the job, which are two completely different values and which I tried to keep. As this is (almost) my first time using delconts, could you provide feedback, comments, opinions about my piece of code and the topic in general (convenience, performances, alternatives and so on)? Thank you, Cristiano

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Feynman on Mathematics and Physics
by Daryoush Mehrtash 15 Feb '09

15 Feb '09

Just came across this 6 part video of Feynman lecture on relationship of mathematics and physics. http://www.youtube.com/watch?v=W1jIPzjFU_U&e Enjoy, Daryoush

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A day with xmonad
by Colin Paul Adams 15 Feb '09

15 Feb '09

I have blogged my experience of trying out xmonad with Fedora 10 at http://colina.demon.co.uk/?q=node/534 . -- Colin Adams Preston Lancashire

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ANNOUNCE: haha-0.1 - Animated ascii lambda
by Sebastiaan Visser 15 Feb '09

15 Feb '09

Always wanted to have an full-color rotating vector based ascii art lambda on your terminal? This is your chance, installing `haha' will do the trick! This is very minimal vector based ascii art library written just for fun. There is a sample program called `rotating-lambda' which does exactly what is says. Make sure your terminal window is at least 80x40 and supports the most basic ANSI escape sequences before trying the demo. -- Sebastiaan

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Iteratee-based IO and lightweight monadic regions in the wild
by Artyom Shalkhakov 15 Feb '09

15 Feb '09

Hello, Is anybody planning to use these shiny new ways for doing IO? I'm also interested in a fair comparison of ByteString/Binary with iteratee-based IO. Has anybody done this? Regards, Artyom Shalkhakov.

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Re: [Haskell-beginners] Re: permuting a list
by Daniel Fischer 15 Feb '09

15 Feb '09

Am Samstag, 14. Februar 2009 16:37 schrieb Heinrich Apfelmus: > > That of course begs the question whether there is a faster but purely No, it didn't beg any question. (Sorry for being a humourless pedant here) > functional algorithm for generating random permutations without indexes > and arrays? > > The answer is a resounding "yes" and the main idea is that shuffling a > list is *essentially the same* as sorting a list; the minor difference > being that the former chooses a permutation at random while the latter > chooses a very particular permutation, namely the one that sorts the input. > > For the full exposition, see > > http://apfelmus.nfshost.com/random-permutations.html Excellent work, thanks. > > > Regards, > apfelmus Cheers, Daniel

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