August 2006 - Haskell

AutoForms release 0.2
by Mads Lindstrøm 27 Aug '06

27 Aug '06

Hi all Haskeleers I am pleased to announce AutoForms release 0.2. AutoForms is a library to ease the creation of Graphical User Interfaces (GUI). It does this by using generic programming (SYB) to construct GUI components. See the full description at http://autoforms.sourceforge.net/ . Any comments will be much appreciated. Greetings, Mads Lindstrøm

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Re: [Haskell] [Haskell - I/O] Problem with 'readFile'
by L. J. 27 Aug '06

27 Aug '06

On 8/27/06, John Hughes <rjmh(a)cs.chalmers.se> wrote: > > > > Hi, I use the operation 'readFile' for obtain information locates on > > a file. When I try to write another information on the same file, I > > obtain this error message: "openFile: permision denied". I found this: > > "The readFile operation holds a semi-closed handle on the file until > > the entire contents of the file have been consumed. It follows that an > > attempt to write to a file (using writeFile, for example) that was > > earlier opened by readFile will usually result in failure with > > isAlreadyInUseError." in this web > > http://www.haskell.org/onlinereport/io.html. > > > > How can I break that semi-closed handle for to write in the > > preaviously readed file? Thank you. > > readFile returns an *unevaluated* list of characters from the file--as your > program needs those characters, so they will be read from the file. Once > they have all been read, then the file is closed. So to ensure that the > file is closed, you just have to make sure your program reads all the > characters. One way is to count them. So here's a function that reads a > file, then rewrites it with "hello" added at the beginning: > > addHello f = do > s <- readFile f > length s `seq` writeFile f ("hello"++s) > > length s counts the characters in the file (forcing it all to be read), and > the `seq` is like a semicolon in C: it forces length s to be computed before > the writeFile is performed. > > John Thanks you for your code. I try with it and it works well, but I can not use it in my aplication because I read the file in one function, I compute the results with the readed information and, finally, I wrote this results in another function (in this moment I do not have the readed string, I have my structured data). How can I use this `seq` with different functions?

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Re: [Haskell] [Haskell - I/O] Problem with 'readFile'
by L. J. 27 Aug '06

27 Aug '06

On 8/27/06, Donald Bruce Stewart <dons(a)cse.unsw.edu.au> wrote: > djsenda: > > Hi, I use the operation 'readFile' for obtain information locates on > > a file. When I try to write another information on the same file, I > > obtain this error message: "openFile: permision denied". I found this: > > "The readFile operation holds a semi-closed handle on the file until > > the entire contents of the file have been consumed. It follows that an > > attempt to write to a file (using writeFile, for example) that was > > earlier opened by readFile will usually result in failure with > > isAlreadyInUseError." in this web > > http://www.haskell.org/onlinereport/io.html. > > > > How can I break that semi-closed handle for to write in the > > preaviously readed file? Thank you. > > Due to lazy IO, you'll need to either read the entire file first, before > you can safely write to that file, (or explicitly close the Handle): > > import Control.Exception > > main = do > s <- readFile "x" > evaluate $ length s -- evaluate the list, reading it in > writeFil e "x" (reverse s) GHCi says me that: evaluate is not in scope > Here we use 'evaluate (length s)' to explictily force the entire file to > be read, which will close the Handle, and allows us to safely write back > to the same file. > > -- Don > > P.S. Learning Haskell questions are better addressed to haskell-cafe(a)haskell.org Ok, for another question I will write in this mailing list.

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Re: [Haskell] Exists any null instruction in Haskell?
by L. J. 27 Aug '06

27 Aug '06

On 8/27/06, Neil Mitchell <ndmitchell(a)gmail.com> wrote: > [Moving to haskell-cafe] > > Hi, > > > I want to know if it exists a null instruction (a instruction > > that do anything > > Not really, since instructions don't "do anything" anyway - they only > compute values. > > If you are in the IO monad then "return ()" is the do nothing. I need this answer. This is my case. Thanks you very much. > In the function world, "id" is the do nothing. > > In recursive list processing, then something like [] is probably the > "base case" in a recursive function, so stops the recursivity. > > If you give a more concrete example, then maybe we can give you a better answer. > > Thanks > > Neil >

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[Haskell - I/O] Problem with 'readFile'
by L. J. 27 Aug '06

27 Aug '06

Hi, I use the operation 'readFile' for obtain information locates on a file. When I try to write another information on the same file, I obtain this error message: "openFile: permision denied". I found this: "The readFile operation holds a semi-closed handle on the file until the entire contents of the file have been consumed. It follows that an attempt to write to a file (using writeFile, for example) that was earlier opened by readFile will usually result in failure with isAlreadyInUseError." in this web http://www.haskell.org/onlinereport/io.html. How can I break that semi-closed handle for to write in the preaviously readed file? Thank you.

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Exists any null instruction in Haskell?
by L. J. 26 Aug '06

26 Aug '06

Hi, I want to know if it exists a null instruction (a instruction that do anything, for stop the recursivity of a function, for exemple) in Haskell. Thanks you.

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Re: [Haskell] Haskell / Full-fledge verified OS
by William DUCK 26 Aug '06

26 Aug '06

Hello all, Linus Torvalds said in 2000 : "Talk is cheap. Show me the code." (2000) I would want to say : "Talk is cheap. Show me the formal verification." (2006) Best Regards, Will

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Haskell / Full-fledge verified OS
by William DUCK 26 Aug '06

26 Aug '06

Hello Misters, As you are iin functional programming, I am asking your help. I am attempting to build up a team. I believe it's time for a full-fledge verified OS. http://www.ertos.nicta.com.au/publications/papers/Tuch_KH_05.pdf Here are my guidelines : http://www.cse.ogi.edu/~hallgren/House/ *OS-design : http://www.ertos.nicta.com.au/publications/papers/Leslie_06.pdf ( for transition ) http://www.marcus-brinkmann.org/hurd-ng.pdf http://www.eecg.toronto.edu/~tornado/ ( scalability / hot swapping ) *kernel : http://os.inf.tu-dresden.de/L4/L4.Sec/ http://www.doclsf.de/papers/vstte06.pdf#search=%22formalising%20high%20perf… *network stack : http://www.cl.cam.ac.uk/~pes20/Netsem/ *programming : http://fling-l.seas.upenn.edu/~plclub/cgi-bin/poplmark/index.php?title=The_… http://www.informatik.uni-bonn.de/~loeh/GFP.html http://maude.cs.uiuc.edu/tools/scc/ *proving environment : http://isabelle.in.tum.de/ http://www.cl.cam.ac.uk/Research/HVG/HOL/ *compiler : http://pauillac.inria.fr/~xleroy/compcert-backend/ http://www.score.is.tsukuba.ac.jp/~okuma/vc/ Any suggestions ? Thank you for your answer, If you want to contact me, my mail is guillaume_dot_fortaine_at_wanadoo_dot_fr I will set up a mailing-list, a web server, a wiki and an IRC Best Regards, Best Regards, Guillaume FORTAINE

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ANNOUNCE : HSPClientside 0.2
by Joel Björnson 25 Aug '06

25 Aug '06

I'm pleased to announce a new version of HSPClientside (0.2) ,developed as a GSoC project during this summer. HSPClientside is a Haskell Server Pages library for generating JavaScript code. Some features include. * An embedding of (typed) JavaScript language in Haskell. * Implementation of an interface to (parts of) XML/HTML DOM. * An embedded language (HJScript) , with combinatiors for producing blocks of JavaScript. * High-level interface to Ajax functionality. My desire is that it should be easily extendable with all sorts of more special purposed JavaScript functionality. Even though the GSoC is now officially over, I will continue working on the project as time occurs. I would also like to invite as many of you as possible to join ! At last, a big thank you to all (Google, Haskell.org, Niklas Broberg etc..) who made this project possible (and turned my summer into a Haskell coding session :-) ) . For more information see www.dtek.chalmers.se/~bjornson/soc/<http://www.dtek.chalmers.se/%7Ebjornson/soc/> Darcs repository is available at darcs.haskell.org/SoC/hsp.clientside/ /Joel

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Graphics.SOE.Gtk
by Duncan Coutts 23 Aug '06

23 Aug '06

Due to popular demand, the new SOE implementation based on Gtk2Hs is now available separately: http://haskell.org/~duncan/soegtk-0.9.10.tar.gz http://haskell.org/~duncan/soegtk-0.9.10.zip or darcs get http://haskell.org/~duncan/soegtk/ It works with the latest released version of Gtk2Hs, ie version 0.9.10 It works at least on Linux and Windows. It's packaged with Cabal. The rendering quality is better than the original HGL version. Here's a side-by-side comparison: http://haskell.org/~duncan/gtk2hs/SOE-cairo.png and it works with GHC on Windows, which the original doesn't. Sadly it doesn't work with Hugs98 (but I hear that the HGL version does work with Hugs98). There may be some slight differences in the semantics from the original. Please test it with any SOE examples you've got. If you find any mismatches, then report them as bugs here: http://hackage.haskell.org/trac/gtk2hs/newticket Enjoy. Duncan

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