August 2010 - Haskell-Cafe

Infinite types should be optionally allowed
by Job Vranish 22 Feb '11

22 Feb '11

There are good reasons against allowing infinite types by default (mostly, that a lot of things type check that are normally not what we want). An old haskell cafe conversation on the topic is here: http://www.nabble.com/There%27s-nothing-wrong-with-infinite-types!-td771373… However, I think infinite types should be allowed, but only with an explicit type signature. In other words, don't allow infinite types to be inferred, but if they are specified, let them pass. I think it would be very hard to shoot yourself in the foot this way. Newtype is the standard solution to situations where you really need an infinite type, but in some cases this can be a big annoyance. Using newtype sacrifices data type abstraction and very useful type classes like Functor. You can use multiparameter type classes and functional dependencies to recover some of the lost abstraction, but then type checking becomes harder to reason about and the code gets way more ugly (If you doubt, let me know, I have some examples). Allowing infinite types would fix this. I'm imagining a syntax something like this: someFunctionThatCreatesInfiniteType :: a -> b | b = [(a, b)] Thoughts? Opinions? Am I missing anything obvious? - Job

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trouble with HDBC-mysql on Mac OS X
by Mark Lentczner 21 Nov '10

21 Nov '10

I'm having trouble with HDBC-mysql on Mac OS X (10.6, Snow Leopard). It compiles and builds fine, but when loaded (into ghci), the dynamic loader complains about not being able to find libmygcc.dylib. The issue is, MySQL's libmygcc is a static lib, not a dynamic one, so of course it won't find it. I've checked the build sequence that HDBC-mysql uses, and it calls upon mysql_config to generate the lib options. I've checked those and they are correct, expressly listing libmygcc statically (!). I've tried building against both the 64bit and 32bit versions of MySQL libs. (Suspect that only the 32bit should work.) Anyone have HDBC-mysql running on 10.6? Any ideas for me to try would be appreciated. - Mark Mark Lentczner http://www.ozonehouse.com/mark/ IRC: mtnviewmark

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IORef memory leak
by Jim Snow 15 Oct '10

15 Oct '10

I'm having some trouble with excessive memory use in a program that uses a lot of IORefs. I was able to write a much simpler program which exhibits the same sort of behavior. It appears that "modifyIORef" and "writeIORef" leak memory; perhaps they keep a reference to the old value. I tried both ghc-6.8.3 and ghc-6.10.1. Is this a known limitation, or is this a ghc bug, or am I using IORefs in the wrong way? -jim module Main where import Data.IORef import Control.Monad -- Leaks memory leakcheck1 ior = do go 1000000000 where go 0 = return () go n = do modifyIORef ior (+1) go (n-1) -- Leaks memory leakcheck2 ior = do go 1000000000 where go 0 = return () go n = do x <- readIORef ior writeIORef ior (x+1) go (n-1) -- Runs in constant memory leakcheck3 ior = do go 1000000000 where go 0 = return () go n = do x <- readIORef ior go (n-1) main :: IO () main = do ior <- newIORef 0 leakcheck2 ior compiled with: ghc -O2 --make Leak.hs -o Leak

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BelHac: A Hackaton in Belgium, 5-7 November
by Jasper Van der Jeugt 27 Sep '10

27 Sep '10

Hello all, We are very pleased to officially announce an international Hackaton/Get-together in Ghent, Belgium, on 5, 6 and 7 November 2010. If you are interested in attending, we have put some information on the wiki [1]. We will soon put up more details about transportation, accommodation and food. (And Belgian beer, of course!) You can register here [2]. WHEN Friday November 5: 2pm - 7pm Saturday November 6: 10am - 6pm Sunday November 7: 10am - 6pm WHERE In “The Therminal”, in Ghent, Belgium. Please see the wiki [1] for more details. We hope to see you in Belgium! [1]: http://www.haskell.org/haskellwiki/Ghent_Functional_Programming_Group/BelHac [2]: http://www.haskell.org/haskellwiki/Ghent_Functional_Programming_Group/BelHa… On behalf of the GhentFPG organizing committee, Kind regards, Jasper Van der Jeugt

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OpenGL Speed!
by Eitan Goldshtrom 20 Sep '10

20 Sep '10

I'm having an unusual problem with OpenGL. To be honest I probably shouldn't be using OpenGL for this, as I'm just doing 2D and only drawing Points, but I don't know about any other display packages, so I'm making due. If this is a problem because of OpenGL however, then I'll have to learn another package. The problem is speed. I have a list of points representing the color of 800x600 pixels. All I'm trying to do is display the pixels on the screen. I use the following: renderPrimitive Points $ mapM_ display list flush where display [] = return () display ((x,y,i):n) = do color $ Color3 i i i vertex $ Vertex2 x y display n But, for some reason this takes FOREVER. I don't know how to use debugging hooks yet without an IDE -- and I don't use an IDE -- but I used a cleverly placed putStrLn to see that it was actually working, just really really slowly. Is there a solution to this speed problem or should I use a package that's more suited to 2D applications like this? Also, if I should use another package, are there any suggestions for which to use? Thanks for any help. -Eitan

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cabal problem on OS X
by Bill Atkins 20 Sep '10

20 Sep '10

When I run "cabal update" on my Mac (Snow Leopard, Intel), I get: % cabal update Downloading the latest package list from hackage.haskell.org cabal: Codec.Compression.Zlib: incompatible zlib version Anyone else seeing this? Reinstalling the Haskell Platform hasn't helped. Thanks!

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Trying to compile Glade Gtk2Hs demo / cabal install glade problem
by Peter Schmitz 11 Sep '10

11 Sep '10

(I am posting this to Cafe and Gtk2Hs Users; if you subscribe to both, please reply to Cafe; but I will see your replies either place; thanks much.) I am trying to compile the Gtk2Hs demo program GladeTest.hs (located in the ...\demo\glade dir), under MS Windows XP. The error I get is: H:\proc\tools\Gtk2Hs\demo\glade>ghc --make GladeTest.hs GladeTest.hs:4:7: Could not find module `Graphics.UI.Gtk.Glade': (--Note:-- I am using H: instead of C: for reasons described later.) I did these okay: cabal install cabal-install cabal update cabal install gtk2hs-buildtools cabal install gtk and I can compile and run some other Gtk2Hs demos (that do not use Glade) okay. In general, I am assuming that I need to "cabal install foo" when Haskell module foo cannot be found during compile. (Please correct me if I am wrong.) I get an error during the glade install: H:\proc\dev\cmd>cabal install glade ... Configuring glade-0.11.1... setup.exe: The pkg-config package libglade-2.0 version >=2.0.0 is required but it could not be found. ... (the full output is listed below) I think I have package libglade-2.0 installed, because I installed the GTK+ and Glade bundle from: http://ftp.gnome.org/pub/GNOME/binaries/win32/glade3/3.6/glade3-3.6.7-with-… at: http://ftp.gnome.org/pub/GNOME/binaries/win32/glade3/3.6/ at: http://glade.gnome.org/ That install created tree: H:\proc\tools\Gtk+\ which includes these: H:\proc\tools\Gtk+\include\libglade-2.0\ and H:\proc\tools\Gtk+\glade-3.exe H:\proc\tools\Gtk+\bin\libglade-2.0-0.dll H:\proc\tools\Gtk+\lib\libglade-2.0.a H:\proc\tools\Gtk+\lib\pkgconfig\libglade-2.0.pc So, I'm thinking maybe my install of Gtk+ (just running glade3-3.6.7-with-GTK+.exe) was lacking somehow, or cabal somehow doesn't see my Gtk+ dir (during "cabal install glade") ? So, I tried editing my cabal config so it would see my Gtk+ tree. I uncommented and edited these lines in the main, un-indented section: extra-include-dirs: H:\proc\tools\Gtk+\include extra-lib-dirs: H:\proc\tools\Gtk+\lib but it doesn't seem to help. (my full cabal config listing is below) Regarding my use of H: instead of C:, I have a non-standard configuration of the Haskell Platform and cabal. I need to develop (Haskell code that uses Gtk2Hs, Glade, etc.) in a MS Windows network, from any of several PCs (one at a time), each of which uses a common tools tree. So, instead of installing the Haskell Platform, cabal, Gtk+, etc. to C:, I have installed them to a network drive (H:). So, I have: H:\proc\tools\Haskell Platform H:\proc\tools\Gtk+ H:\proc\tools\cabal etc. Any help or pointers would be appreciated. Thanks very much, -- Peter --- Following is various config and output info --- My PATH is: ++++++++++++++ SET P_TOOLS=H:\proc\tools SET HASK_PLAT=%P_TOOLS%\Haskell Platform\2010.1.0.0 PATH %HASK_PLAT%\bin; %P_TOOLS%\cabal\bin; %P_TOOLS%\gtk\bin; %HASK_PLAT%\lib\extralibs\bin; %HASK_PLAT%\mingw\bin ++++++++++++++ Some of my environment vars are: ============== REM This is so Cabal will get its config from the Haskell Platform, REM rather than C:\Documents and Settings\pschmitz\Application Data\cabal SET CABAL_CONFIG=%P_TOOLS%\cabal\config CABAL_CONFIG=H:\proc\tools\cabal\config PKG_CONFIG_PATH=H:\proc\tools\Gtk+\lib\pkgconfig GTK_HOME=\\fbpxfile01\users$\pschmitz\proc\tools\Gtk+ HASK_PLAT=H:\proc\tools\Haskell Platform\2010.1.0.0 INCLUDE=\\fbpxfile01\users$\pschmitz\proc\tools\Gtk+\include LIB=\\fbpxfile01\users$\pschmitz\proc\tools\Gtk+\lib Path=H:\proc\tools\Haskell Platform\2010.1.0.0\bin;H:\proc\tools\cabal\bin;H:\proc\tools\Gtk+\bin; H:\proc\tools\Haskell Platform\2010.1.0.0\lib\extralibs\bin;H:\proc\tools\Haskell Platform\2010.1. 0.0\mingw\bin; ============== The full output from "cabal install glade" is: ----------------------------- H:\proc\dev\cmd>cabal --version cabal-install version 0.8.2 using version 1.8.0.2 of the Cabal library H:\proc\dev\cmd>cabal list glade * glade Synopsis: Binding to the glade library. Latest version available: 0.11.1 Latest version installed: [ Not installed ] Homepage: http://www.haskell.org/gtk2hs/ License: LGPL-2.1 ... H:\proc\dev\cmd>cabal info glade * glade (library) Synopsis: Binding to the glade library. Latest version available: 0.11.1 Latest version installed: [ Not installed ] Homepage: http://www.haskell.org/gtk2hs/ Bug reports: http://hackage.haskell.org/trac/gtk2hs/ Description: This library allows to load externally stored user interfaces into programs. This allows alteration of the interface without recompilation of the program. Category: Graphics License: LGPL-2.1 Author: Manuel M T Chakravarty Maintainer: gtk2hs-users(a)sourceforge.net Source repo: http://code.haskell.org/glade/ Dependencies: base >=4 && <5, array -any, containers -any, haskell98 -any, mtl -any, glib >=0.11 && <0.12, pango >=0.11 && <0.12, cairo >=0.11 && <0.12, gtk >=0.11 && <0.12 Cached: Yes Modules: Graphics.UI.Gtk.Glade H:\proc\dev\cmd>cabal install glade Resolving dependencies... C:\DOCUME~1\pschmitz\LOCALS~1\Temp\glade-0.11.13100\glade-0.11.1\Gtk2HsSetup.hs:25: warning: #warning Setup.hs is guessing the version of Cabal. If compilation of Setup.hs fails use -DCABAL_VERSION_MINOR=x for Cabal version 1.x.0 when building (prefixed by --ghc-option= when using the 'cabal' command) [1 of 2] Compiling Gtk2HsSetup ( C:\DOCUME~1\pschmitz\LOCALS~1\Temp\glade-0.11.13100\glade-0.11.1\Gtk2HsSetup.hs, C:\DOCUME~1\pschmitz\LOCALS~1\Temp\glade-0.11.13100\glade-0.11.1\dist\setup\Gtk2HsSetup.o ) [2 of 2] Compiling Main ( C:\DOCUME~1\pschmitz\LOCALS~1\Temp\glade-0.11.13100\glade-0.11.1\Setup.hs, C:\DOCUME~1\pschmitz\LOCALS~1\Temp\glade-0.11.13100\glade-0.11.1\dist\setup\Main.o ) Linking C:\DOCUME~1\pschmitz\LOCALS~1\Temp\glade-0.11.13100\glade-0.11.1\dist\setup\setup.exe ... Configuring glade-0.11.1... setup.exe: The pkg-config package libglade-2.0 version >=2.0.0 is required but it could not be found. cabal: Error: some packages failed to install: glade-0.11.1 failed during the configure step. The exception was: ExitFailure 1 ----------------------------- My complete Cabal config follows. The email may alter the indentation, but I was careful to maintain the original indentation when editing. -- ---------------------------------------------------------------------------------------------- -- This is the configuration file for the 'cabal' command line tool. -- The available configuration options are listed below. -- Some of them have default values listed. -- Lines (like this one) beginning with '--' are comments. -- Be careful with spaces and indentation because they are -- used to indicate layout for nested sections. remote-repo: hackage.haskell.org:http://hackage.haskell.org/packages/archive remote-repo-cache: H:\proc\tools\cabal\packages -- local-repo: -- verbose: 1 -- compiler: ghc -- with-compiler: -- with-hc-pkg: -- scratchdir: -- program-prefix: -- program-suffix: -- library-vanilla: True -- library-profiling: False -- shared: False -- executable-profiling: False -- optimization: True -- library-for-ghci: True -- split-objs: False -- executable-stripping: True -- user-install: True -- package-db: -- flags: -- -- -------------------------------- -- extra-include-dirs: -- extra-lib-dirs: extra-include-dirs: H:\proc\tools\Gtk+\include extra-lib-dirs: H:\proc\tools\Gtk+\lib -- -------------------------------- -- -- constraint: -- cabal-lib-version: -- preference: -- documentation: False -- doc-index-file: $datadir\doc\index.html -- root-cmd: -- symlink-bindir: build-summary: H:\proc\tools\cabal\logs\build.log -- build-log: remote-build-reporting: anonymous -- username: -- password: install-dirs user prefix: "H:\\proc\\tools\\cabal" -- bindir: $prefix\bin -- libdir: $prefix -- libsubdir: $pkgid\$compiler -- libexecdir: $prefix\$pkgid datadir: "H:\\proc\\tools\\Haskell Platform\\2010.1.0.0" -- datasubdir: $pkgid -- docdir: $prefix\doc\$pkgid -- htmldir: $docdir\html -- haddockdir: $htmldir install-dirs global prefix: "H:\\proc\\tools\\Haskell Platform\\2010.1.0.0" -- bindir: $prefix\bin -- libdir: $prefix -- libsubdir: $pkgid\$compiler -- libexecdir: $prefix\$pkgid datadir: "H:\\proc\\tools\\Haskell Platform\\2010.1.0.0" -- datasubdir: $pkgid -- docdir: $prefix\doc\$pkgid -- htmldir: $docdir\html -- haddockdir: $htmldir -- ---------------------------------------------------------------------------------------------- -- end of post: Trying to compile Glade Gtk2Hs demo / cabal install glade problem --

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ANNOUNCE: DSTM 0.1.1
by Frank Kupke 10 Sep '10

10 Sep '10

Hi, DSTM is an implementation of a robust distributed Software Transactional Memory (STM) library for Haskell. Many real-life applications are distributed by nature. Concurrent applications may profit from robustness added by re-implementation as distributed applications. DSTM extends the STM abstraction to distributed systems and presents an implementation efficient enough to be used in soft real-time applications. Further, the implemented library is robust in itself, offering the application developer a high abstraction level to realize robustness, hence, significantly simplifying this, in general, complex task. The DSTM package consists of the DSTM library, a name server application, and three sample distributed programs using the library. Provided are a simple Dining Philosophers, a Chat, and a soft real-time Bomberman game application. Distributed communication is transparent to the application programmer. The application designer uses a very simple name server mechanism to set up the system. The DSTM library includes the management of unavailable process nodes and provides the application with abstract error information thus facilitating the implementation of robust distributed application programs. For usage please look into the documentation file: DSTMManual.pdf. The package including the documentation can be found on: http://hackage.haskell.org/package/DSTM-0.1.1 Best regards, Frank Kupke

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CnC Haskell
by Vasili I. Galchin 08 Sep '10

08 Sep '10

Hello, I have been reading work done at Rice University: http://habanero.rice.edu/cnc. Some work has been done by http://www.cs.rice.edu/~dmp4866/ on CnC for .Net. One component that David wrote a CnC translator that translates CnC textual form to the underlying language, e.g. F#. Is anybody working on a CnC textual form translator for Haskell so a Haskell user of CnC Haskell can write in a higher level?? Thanks, Vasili

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Re: [Haskell-cafe] Re: Fwd: Semantics of iteratees, enumerators, enumeratees?
by John Lato 07 Sep '10

07 Sep '10

> > From: Heinrich Apfelmus <apfelmus(a)quantentunnel.de> > > Jason Dagit wrote: > > Heinrich Apfelmus wrote: > >> > >> I'm curious, can you give an example where you want to be explicit about > >> chunking? I have a hard time imagining an example where chunking is > >> beneficial compared to getting each character in sequence. Chunking > >> seems to be common in C for reasons of performance, but how does that > >> apply to Haskell? > > > > [...] > > I think it basically comes down to this: We replace lazy io with explicit > > chunking because lazy io is unsafe, but explicit chunking can be safe. > > Ah, I mean to compare Iteratees with chunking to Iteratees with single > character access, not to lazy IO. > > In C, this would be a comparison between read and getchar . If I > remember correctly, the former is faster for copying a file simply > because copying one character at a time with getchar is too granular > (you have to make an expensive system call every time). Of course, this > reasoning only applies to C and not necessarily to Haskell. > > Do you have an example where you want chunking instead of single > character access? > I am unable to think of any examples where you want chunking for any reason other than efficiency. Yesterday I spent some time on an element-wise iteratee implementation, and unfortunately it's significantly slower than any of the chunked implementations. I'm certain there's room for optimization, but I don't know if it's possible to make up the whole difference. I'd need to make some examination of the core to figure out where it could be improved. It's also possible that certain other implementations, such as your ProgramT version or the simplified implementation John Millikin recently posted to this list, would be more amenable to compiler magic for this purpose. John

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