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Grouping - Map / Reduce
by Gü?nther Schmidt 26 Mar '09

26 Mar '09

Hi, let say I got an unordered lazy list of key/value pairs like [('a', 99), ('x', 42), ('a', 33) ... ] and I need to sum up all the values with the same keys. So far I wrote a naive implementation, using Data.Map, foldl and insertWith. The result of this grouping operation, which is effectively another list of key/value pairs, just sums this time, needs to be further processed. The building of this map is of course a bottleneck, the successive processing needs to wait until the entire list is eventually consumed the Map is built and flattened again. Is there another way of doing this, something more "streaming architecture" like? Is Googles "Map - Reduce" related to this? Günther

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an OS-independent executeFile??
by Vasili I. Galchin 26 Mar '09

26 Mar '09

Hello, I have been looking through Hackage and using Hoogle to "fork and execute" a program in an OS-independent way, i.e. neutral from POSIX and Win32 APIs. Does such a library function exist? Regards, Vasili

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Language.Haskell.Parser question
by Vasyl Pasternak 26 Mar '09

26 Mar '09

Hi, I want to parse haskell file to find all calls to function 'foo' and gathers a create a list of all argumets, which passed to it. E.g. from the following code: f1 = foo 5 f2 = foo 8 f3 = foo 9 I want to extract a list [5, 8, 9] (suppouse function takes only one argument) The most obvious way is to use Language.Haskell for this task. The parser works pretty good, but its output data type is terrible. As I understand, I need to extract all objects that looks like HsApp (HsVar (UnQual (HsIdent "foo"))) .... The question is, is there a method to do it quickly or I have to process each object of different type separately ? Maybe it is a work for a template Haskell ? Thanks. -- Best regards, Vasyl Pasternak

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Compile OpenGL for jhc
by Csaba Hruska 26 Mar '09

26 Mar '09

Hi! As OpenGL haskell binding depends only on base, it would be great to compile it with jhc. I've tried to do that, but I had some problems with preprocessor directives. It would be also great to add jhc support for OpenGL bindings build scripts. Or, it would be better to add jhc support for cabal-install. :) Is there anyone who has any idea any of this things? (for soulution)

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ANN: io-capture-0.2 capturing std(out|err) in IO action
by Yusaku Hashimoto 26 Mar '09

26 Mar '09

Hi, I announce the release of io-capture package of version 0.2 io-capture is a Library to capturing stdout and stderr in IO action. It exports a function named `capture', It takes an IO and an String, the action to run and the given whole stdin, and returns whole stdout and stderr in the action as String. For example: ghci> :m +System.IO.Capture ghci> :m +System.IO ghci> capture (getLine >>= putStr >> getLine >>= hPutStr stderr) "foo \nbar\n" ("foo","bar") io-capture is available on hackage, repository is on patch-tag. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/io- capture-0.2 http://patch-tag.com/repo/io-capture/browse It behaves almost fine, but It's still experimental, I know some trouble about when given lazy reading action such as getContents. And there may be unknown bugs. If you find it, feel free to report it and any feedbacks are welcome. Thanks for reading, Yusaku Hashimoto

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Re: Exception handling in numeric computations
by John Lato 26 Mar '09

26 Mar '09

> Message: 15 > From: Xiao-Yong Jin <xj2106(a)columbia.edu> > John Lato <jwlato(a)gmail.com> writes: > > So I have another question. Is the following function safe > and legitimate? > >> safeDiv :: (Exception e, Integral a) => >> a -> a -> Either e a >> safeDiv x y = unsafePerformIO . try . evaluate $ div x y > > I believe it should be okay to use this 'safeDiv'. What do > you think? Your question is unclear. Are you asking if this function can be safely used with current Haskell standards and implementations or are you asking should the Haskell specification make a guarantee that this function will do what you want? I would answer "no" either way, but for different reasons. Common to both is: Don't use unsafe* functions unless you can prove that your usage is safe. That is proof as in mathematical usage; it must be rigorous and complete. John Lato

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Copying data files when installing, using Cabal
by Henk-Jan van Tuyl 26 Mar '09

26 Mar '09

L.S., I am trying to install an application with data files (I am developing that application). These data files are mentioned in the .cabal file, after the "Data-files:" keyword. When I give command "runhaskell setup install", the data files are not copied; how can I correct this? -- Regards, Henk-Jan van Tuyl -- http://functor.bamikanarie.com http://Van.Tuyl.eu/ --

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[ANN] I/O library for Windows
by Felix Martini 26 Mar '09

26 Mar '09

Hi all, winio is an I/O library for Windows using Windows API functions and has I/O completion port support. The main goal of this library is to support Simon Marlow's new Handle API once he has added that to GHC. The library also has a compatibility module for socket functions from the network-bytestring package. Because the library uses IOCP instead of select it is not limited to 1024 open sockets. Try for example the thread-ring program where each Haskell thread passes a UDP message around (Change the MaxUserPort field in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters to 65534 to enable all ports). The winio package is available on Hackage. Notice that it uses a development version of the network package which is available at http://darcs.haskell.org/packages/network/. The library has not been tested much and should be considered experimental so please try it if you use Windows and notify me of any issue or corner case. Kind Regards, Felix

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Fwd: [Haskell-cafe] Re: ANNOUNCE: WinGhci, a GUI for GHCI on Windows
by Pepe Gallardo 26 Mar '09

26 Mar '09

2009/3/23 Andrew Butterfield <Andrew.Butterfield(a)cs.tcd.ie> > Benjamin L.Russell wrote: > >> This is wonderful--just what I was waiting for! The application looks >> beautiful, and I'm very happy that GHCi now has a matching GUI >> application along the lines of WinHugs. >> >> > Indeed - me too ! > >> It would be even better if you could provide some >> installation/uninstallation information. I unzipped the contents of >> WinGhci-1.0-bin.zip into the "C:\Documents and Settings\<username>\My >> Documents\" folder, but there was no README file. >> >> > And version information - I tried it with GHC 6.4 and it died (Not > Responding) > > What version of GHCi does it require? > > And no, I won't upgrade GHC just yet (this is the latest GHC/wxHaskell > combo that works for me with GHCi...) > >> >> >> > I have tested it with GHC 6.10.1. The latest GHC version that I have currently installed is GHC 6.6, and it seems to work too. Do you have GHC bin directory on your path? > > -- > -------------------------------------------------------------------- > Andrew Butterfield Tel: +353-1-896-2517 Fax: +353-1-677-2204 > Foundations and Methods Research Group Director. > School of Computer Science and Statistics, > Room F.13, O'Reilly Institute, Trinity College, University of Dublin > http://www.cs.tcd.ie/Andrew.Butterfield/ > -------------------------------------------------------------------- > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Fwd: [Haskell-cafe] Re: ANNOUNCE: WinGhci, a GUI for GHCI on Windows
by Pepe Gallardo 26 Mar '09

26 Mar '09

---------- Forwarded message ---------- From: Pepe Gallardo <pepe.haskell(a)gmail.com> Date: 2009/3/25 Subject: Re: [Haskell-cafe] Re: ANNOUNCE: WinGhci, a GUI for GHCI on Windows To: "Benjamin L.Russell" <DekuDekuplex(a)yahoo.com> Hi Benjamin*,* ** The only requirement to run WinGhci is to have GHC installed and to have GHC bin directory on your path. The way to start the application is by executing winghci.exe. Install.exe is an small program that associates .hs files with WinGhci (it should be run from the same directory where WinGhci is installed). Note that this association is optional. I have added a wiki page on this. 2009/3/23 Benjamin L.Russell <DekuDekuplex(a)yahoo.com> > Just another couple of thoughts for possible additional improvement: > > 1. It would be even nicer if WinGhci added a menu entry to the > "Start" menu automatically, as WinHugs does. > > 2. For the proposed menu entry, it would also probably be a good idea > if WinGhci added a folder for that menu entry, and included a link to > a "README" file in there, as WinHugs does also. > > 3. In order to distinguish WinGhci from GHCi, it might also be > helpful if WinGhci had a different icon; the current WinGhci icon is > identical to the one for GHCi (perhaps use the forthcoming official > Haskell logo here?). > WinGhci icon is different (although quite similar) from GHCi icon, at least for medium to large icon sizes. > > Just my two cents for now.... > > -- Benjamin L. Russell > -- > Benjamin L. Russell / DekuDekuplex at Yahoo dot com > http://dekudekuplex.wordpress.com/ > Translator/Interpreter / Mobile: +011 81 80-3603-6725 > "Furuike ya, kawazu tobikomu mizu no oto." > -- Matsuo Basho^ > > _______________________________________________ > Haskell-Cafe mailing list > Haskell <Haskell-Cafe(a)haskell.org>-Cafe(a)haskell.org<Haskell-Cafe(a)haskell.org> > http://www.haskell.org/mailman/listinfo/haskell-cafe > <Haskell-Cafe(a)haskell.org> >

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