- Haskell-Cafe - Haskell.org

GC'ing file handles and other resources
by Conal Elliott 18 Apr '08

18 Apr '08

Are Haskell folks satisfied with the practical necessity of imperatively & explicitly reclaiming resources such as file handles, fonts & brushes, video memory chunks, etc? Doesn't explicit freeing of these resources have the same modularity and correctness problems as explicit freeing of system memory (C/C++ programming)? I wrote a lovely purely functional graphics library that used video memory to lazily compute and cache infinite-resolution images, and I found that I don't know how to get my finalizers to run anytime soon after video memory chunks become inaccessible. Explicit freeing isn't an option, since the interface is functional, not imperative (IO). I guess I'm wondering a few things: * Are Haskell programmers generally content with imperative and bug-friendly interfaces involving explicit freeing/closing of resources? * Do people assume that these resources (or handling them frugally) aren't useful in purely functional interfaces? * Are there fundamental reasons why GC algorithms cannot usefully apply to resources like video memory, file descriptors, etc? * Are there resource management techniques that have the flexibility, efficiency, and accuracy of GC that I could be using for these other resources? Thanks, - Conal 2008/4/14 Abhay Parvate <abhay.parvate(a)gmail.com>: > Hello, > > In describing the Handle type, the GHC documentation says (in the > System.IO documentation): > > GHC note: a Handle will be automatically closed when the garbage collector > detects that it has become unreferenced by the program. However, relying on > this behaviour is not generally recommended: the garbage collector is > unpredictable. If possible, use explicit an explicit hClose to close Handles > when they are no longer required. GHC does not currently attempt to free up > file descriptors when they have run out, it is your responsibility to ensure > that this doesn't happen. > > But one cannot call hClose on Handles on which something like hGetContents > has been called; it just terminates the character list at the point till > which it has already read. Further the manual says that hGetContents puts > the handle in the semi-closed state, and further, > > A semi-closed handle becomes closed: > > - if hClose is applied to it; > - if an I/O error occurs when reading an item from the handle; > - or once the entire contents of the handle has been read. > > So do I safely assume here, according to the third point above, that it's > fine if I do not call hClose explicitly as far as I am consuming all the > contents returned by hGetContents? > > Thanks, > Abhay > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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Separate a string into a list of strings
by Sara Kenedy 18 Apr '08

18 Apr '08

Hi all, I want to write a function to separate a string into a list of strings separated by commas. Example: separate :: String -> [String] separate "Haskell, Haskell, and Haskell" = ["Haskell", "Haskell", "and Haskell"] If anyone has some ideas, please share with me. Thanks. S.

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incompatibility issues in installing wxHaskell 0.10.3 with GHCi 6.8.2 on Windows XP Pro
by Benjamin L. Russell 18 Apr '08

18 Apr '08

Perhaps this is not the best mailing list for this issue, but since this problem involves a library for Haskell and is not a bug of GHC proper, I thought this would be a better place than the Glasgow-haskell-bugs mailing list.... I tried installing wxHaskell 0.10.3 with GHCi 6.8.2 already installed on Windows XP Professional Service Pack 2, but every time I run the wxhaskell-register.bat script to install the library, the following error message appears (I am installing on the Japanese version of Windows XP at work, so some of the error messages are in Japanese, which I shall translate accordingly below): ----- error message begins immediately after this line ----- 1 ÂÌt@CðRs[µÜµ½B R}hÌ\¶ªëÁÄ¢Ü·B R}hÌ\¶ªëÁÄ¢Ü·B - register packages Reading package info from "C:\\Documents and Settings\\Benjamin\\My Documents\\H askell\\Libraries\\wxHaskell\\wxhaskell-0.10.3\\bin\\wxcore.pkg" ... done. WARNING: unversioned dependencies are deprecated, and will NOT be accepted by GH C 6.10: base haskell98 ghc-pkg: C:\Documents doesn't exist or isn't a directory (use --force to overrid e) Reading package info from "C:\\Documents and Settings\\Benjamin\\My Documents\\H askell\\Libraries\\wxHaskell\\wxhaskell-0.10.3\\bin\\wx.pkg" ... done. ghc-pkg: dependency wxcore-0.10.3 doesn't exist (use --force to override) error: Unable to register the package using "ghc-pkg". Maybe you have an incompatible version of ghc installed? ±s·éÉÍ½©L[ðµÄ¾³¢ . . . ----- error message ends immediately before this line ----- The first paragraph above means the following: " 1 file copied. Syntax error in command. Syntax error in command." The final line above means the following: "Press any key to continue...." However, there do not seem to be any errors in my unmodified wxhaskell-register.bat file, quoted below: ----- text of wxhaskell-register.bat file begins immediately after this line ----- @SET wxclibname=wxc-msw2.6.4-0.10.3 @SET generate=yes @ECHO OFF IF "%1"=="" GOTO noarg IF "%1"=="--help" GOTO help IF "%1"=="-?" GOTO help IF "%1"=="/?" GOTO help GOTO installarg :installarg SET installdir=%1 GOTO check :noarg COPY /B /Y setcd setcd.bat CD .. CD >> bin\setcd.bat CD bin CALL setcd.bat DEL setcd.bat SET installdir=%CURDIR% GOTO check :check IF "%generate%"=="yes" GOTO generate GOTO checkfile :generate IF NOT EXIST %installdir%\bin\wx-partial.pkg GOTO notfound COPY /Y %installdir%\bin\wx-partial.pkg %installdir%\bin\wx.pkg ECHO import-dirs:%installdir%\lib\imports >> %installdir%\bin\wx.pkg ECHO library-dirs:%installdir%\lib >> %installdir%\bin\wx.pkg COPY /Y %installdir%\bin\wxcore-partial.pkg %installdir%\bin\wxcore.pkg ECHO import-dirs:%installdir%\lib\imports >> %installdir%\bin\wxcore.pkg ECHO library-dirs:%installdir%\lib >> %installdir%\bin\wxcore.pkg GOTO checkfile :checkfile IF NOT EXIST "%installdir%\bin\wx.pkg" GOTO notfound :install ECHO - register packages SET wxhlibdir=%installdir%\lib ghc-pkg update "%installdir%\bin\wxcore.pkg" ghc-pkg update "%installdir%\bin\wx.pkg" IF ERRORLEVEL 1 GOTO regerror ECHO. IF "%OS%"=="Windows_NT" GOTO copyNT ECHO - copy %wxclibname%.dll to the windows system directory (%WINDIR%\system) COPY %installdir%\lib\%wxclibname%.dll %WINDIR%\system\%wxclibname%.dll GOTO checkcopy :copyNT ECHO - copy %wxclibname%.dll to the windows system directory (%WINDIR%\system32) COPY %installdir%\lib\%wxclibname%.dll %WINDIR%\system32\%wxclibname%.dll :checkcopy IF ERRORLEVEL 1 GOTO copyerror ECHO - done! GOTO end :regerror ECHO error: ECHO Unable to register the package using "ghc-pkg". ECHO Maybe you have an incompatible version of ghc installed? ECHO. goto end :copyerror ECHO error: ECHO Unable to copy dynamic link libraries to the system folder. ECHO This is not a real problem but you will have to add the wxHaskell ECHO library directory to your PATH environment variable. ECHO. ECHO The library directory is: %installdir%\lib ECHO. goto end :notfound ECHO error: ECHO Unable to find the wxHaskell packages (bin\wx.pkg) ECHO Maybe the installation directory is not properly specified? ECHO. GOTO help :help ECHO usage: ECHO wxhaskell-register [installdir] ECHO. ECHO (or just double click on the batch file from the explorer) ECHO. GOTO end :end PAUSE ----- text of wxhaskell-register.bat file ends immediately before this line ----- Any ideas? Has anybody else encountered this bug? Benjamin L. Russell

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Shim: finding modules
by Graham Fawcett 17 Apr '08

17 Apr '08

Hi folks, I'm a newbie, so please forgive any terminological mistakes. I've been using Shim in Emacs with great success, but there's one issue I've encountered, and I don't know if it's configuration problem or something fundamental. Consider a module 'App' and submodules 'App.Front' and 'App.Back'. When editing code in App that depends on the submodules, Shim works well at resolving the location of the submodules, and validates my code. But when editing App.Front, which depends on App.Back, Shim fails to validate -- my working directory is App.Front, and Shim doesn't seem able to find the location of App.Back. I'd like to be able to tell Shim that 'App' is the root of my project, and to locate modules from that root. Is this possible? On a related note, it seems that Shim is moribund (though others have forked it, mostly for Vim support?). Given its utility, I'm surprised by this. Do you have other support tools that serve a similar role? (I know of haskell-mode, but the GHC API integration seems to be the feature that sets Shim apart.) Thanks, Graham

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Announcing DarcsWatch (with link)
by Joachim Breitner 17 Apr '08

17 Apr '08

Hi, sorry for the spam, but what I forgot in the first mail: You can find DarcsWatch at: http://darcswatch.nomeata.de/ A lot of haskell-related projects use the darcs version control system. Darcs has the nice feature that you can easily submit a patch by e-mail, usually sent to the project maintainer or a mailing list. What has bothered me in the past was that I had to manually check whether my patch was applied yet. So this week, I wrote DarcsWatch. DarcsWatch receives submitted patches and compares them to the repositories it knows about, whether the patch is missing there or not. You either send your patches to DarcsWeb directly when submitting them, using CC, or DarcsWatch is subscribed to the project mailing list itself, which is the case for the darcs-devel and xmonad lists. Other than that, not much is to do, and you’ll find a nice overview of your patches with diffs and download links. For an example, see: http://darcswatch.nomeata.de/user_mail@joachim-breitner.de.html If you want to use DarcsWatch for your contributions to other projects, or for your own projects, have a look the documentation at http://darcs.nomeata.de/darcswatch/documentation.html There are probably still bugs around, and the problem of marking patches as obsolete is not really solved yet, so if you have ideas about it, mail me or come to #darcs on freenode. Patches are always welcome, you can get the source from DarcsWatch’s repository, found at http://darcs.nomeata.de/darcswatch/ Enjoy, Joachim -- Joachim Breitner e-Mail: mail(a)joachim-breitner.de Homepage: http://www.joachim-breitner.de ICQ#: 74513189 Jabber-ID: nomeata(a)joachim-breitner.de

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Ann: Emping 0.5 in Hackage
by Hans van Thiel 17 Apr '08

17 Apr '08

Emping is a utility which derives the shortest rules from a table of rules. For example, in a list of 8000 different mushrooms, it finds 21 single predicates that determine the mushroom is poisonous, and 23 that it is edible. But it also finds all combinations of two, three and more predicates that determine this property. Each shorter rule is a generalization of an original one. So, if r1 covers {a,b,c} and r2 {a,b}, then r2 implies r1 (r1 entails r2). The shorter rules are partially ordered. Thanks to the functional graphs library, which comes with ghc, the reduced rules are now displayed as graphs which can be viewed with a Graphviz viewer. Also new in 0.5 is that the reduced rules, and the reduced rules in an equivalence class, are ordered by length. Lastly, the GUI has been improved. Testing has also shown some bugs and issues, most importantly when the data contains ambiguous rules. Ambiguities are rules with the same antecedent, but a different consequent. You can test for them, but if the user turns the checks off and run Emping without correcting the data, the program could hang, in a special case. See http://home.telfort.nl/sp969709/emp/empug.html for more info and a few screenshots. Thank you all, Hans van Thiel

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export question (GHC.Handle)
by Graham Fawcett 17 Apr '08

17 Apr '08

I notice in the source for GHC.Handle that certain functions (e.g. fdToHandle_stat) are in the export list, but are not actually exported (at least, it seems you cannot import them). What mechanism causes these functions to be "hidden", and are they still accessible in some way? Graham

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Announcing DarcsWatch
by Joachim Breitner 17 Apr '08

17 Apr '08

Hi, (Hi again to those on haskell-cafe, but things have changed since the other announcement) A lot of haskell-related projects use the darcs version control system. Darcs has the nice feature that you can easily submit a patch by e-mail, usually sent to the project maintainer or a mailing list. What has bothered me in the past was that I had to manually check whether my patch was applied yet. So this week, I wrote DarcsWatch. DarcsWatch receives submitted patches and compares them to the repositories it knows about, whether the patch is missing there or not. You either send your patches to DarcsWeb directly when submitting them, using CC, or DarcsWatch is subscribed to the project mailing list itself, which is the case for the darcs-devel and xmonad lists. Other than that, not much is to do, and you’ll find a nice overview of your patches with diffs and download links. For an example, see: http://darcswatch.nomeata.de/user_mail@joachim-breitner.de.html If you want to use DarcsWatch for your contributions to other projects, or for your own projects, have a look the documentation at http://darcs.nomeata.de/darcswatch/documentation.html There are probably still bugs around, and the problem of marking patches as obsolete is not really solved yet, so if you have ideas about it, mail me or come to #darcs on freenode. Patches are always welcome, you can get the source from DarcsWatch’s repository, found at http://darcs.nomeata.de/darcswatch/ Enjoy, Joachim -- Joachim Breitner e-Mail: mail(a)joachim-breitner.de Homepage: http://www.joachim-breitner.de ICQ#: 74513189 Jabber-ID: nomeata(a)joachim-breitner.de

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Fwd: [Haskell-cafe] Hackage Haddock fails where local succeeds
by David Waern 17 Apr '08

17 Apr '08

2008/4/17, John Goerzen <jgoerzen(a)complete.org>: > On Thu April 17 2008 7:01:18 am Ross Paterson wrote: > > On Thu, Apr 17, 2008 at 06:45:40AM -0500, John Goerzen wrote: > > > My local haddock, 0.8, parses this file fine. Is Hackage running and > > > older version? Could it be upgraded? Or is there something else going > > > on here? > > > > No, it's running haddock 2.1.0, which understands all the GHC > > extensions, but is more picky about comments. > > > OK. I have been able to replicate this behavior with Haddock 2.0.0.0, which > is the latest according to www.haskell.org/haddock. Where did 2.1.0 come > from? > > Although I can replicate the behavior, I can't explain it. My reading of the > Haddock docs leads me to believe I have done the correct thing. Is this a > bug in Haddock or am I missing something? It's a bug. Comments on type synonyms were missed when Haddock support was added to the GHC parser. This might be fixed in future versions of GHC. David

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Hackage Haddock fails where local succeeds
by John Goerzen 17 Apr '08

17 Apr '08

Hi folks, Over at http://hackage.haskell.org/packages/archive/MissingH/1.0.1.2/logs/failure/g… the build has failed in the Hackage step with this output: src/Data/BinPacking.hs:78:32: parse error on input `-- ^ The sizes of bins' haddock: Failed to check module: Data.BinPacking That section of code looks like this: {- | The primary type for bin-packing functions. These functions take a list of size of bins. If every bin is the same size, you can pass @(repeat binSize)@ to pass an infinite list of bins if the same size. Any surplus bins will simply be ignored. -} type BinPacker = (Num size, Ord size, Show size, Show obj) => [size] -- ^ The sizes of bins -> [(size, obj)] -- ^ The sizes and objects -> Either (BinPackerError size obj) [[(size, obj)]] -- ^ Either error or results (the last line got artificially wrapped in my mail client) My local haddock, 0.8, parses this file fine. Is Hackage running and older version? Could it be upgraded? Or is there something else going on here? -- John

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