- Haskell-Cafe - Haskell.org

ANN: prelude-safeenum
by wren ng thornton 30 May '13

30 May '13

-------------------------------------------- -- prelude-safeenum 0.1.0 -------------------------------------------- The prelude-safeenum package offers a safe alternative to the Prelude's Enum class in order to render it safe. While we're at it, we also generalize the notion of enumeration to support types which can only be enumerated in one direction. -------------------------------------------- -- Description -------------------------------------------- The prelude-safeenum package offers an alternative to the notion of enumeration provided by the Prelude. For now it is just a package, but the eventual goal is to be incorporated into haskell prime. Some salient characteristics of the new type-class hierarchy are: * Removes partial functions: The Haskell Language Report defines pred, succ, fromEnum, and toEnum to be partial functions when the type is Bounded[1], but this is unacceptable. The new classes remove this problem by correcting the type signatures for these functions. * Generalizes the notion of enumeration: Rather than requiring that the type is linearly enumerable, we distinguish between forward enumeration (which allows for multiple predecessors) and backward enumeration (which allows for multiple successors). * Adds new functions: enumDownFrom, enumDownFromTo One of the big problems with the partiality of pred is that there is no safe way to enumerate downwards since in the border case (enumFromThen x (pred x)) will throw an error rather than evaluating to [x] as desired. These new functions remove this problem. * Removes the requirement that the enumeration order coincides with the Ord ordering (if one exists). Though, of course, it's advisable to keep them in sync if possible, for your sanity. * Ensures that the notion of enumeration is well-defined: This much-needed rigor clarifies the meaning of enumeration. In addition, it rules out instances for Float and Double which are highly problematic and often confuse newcomers to Haskell. Unfortunately, this rigor does render the instance for Ratio problematic. However, Ratio instances /can/ be provided so long as the base type is enumerable (and Integral, naturally); but they must be done in an obscure order that does not coincide with Ord. * The obscure order required for well-defined enumeration of Ratio is provided. [1] <http://www.haskell.org/onlinereport/haskell2010/haskellch6.html#x13-1310006…> -------------------------------------------- -- Links -------------------------------------------- Homepage: http://code.haskell.org/~wren/ Hackage: http://hackage.haskell.org/package/prelude-safeenum Darcs: http://community.haskell.org/~wren/prelude-safeenum Haddock (Darcs version): http://community.haskell.org/~wren/prelude-safeenum/dist/doc/html/prelude-s… -- Live well, ~wren

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Ghent FPG meeting on 26 June, 2013
by Jasper Van der Jeugt 30 May '13

30 May '13

Hello, The "Functional Programming Group Ghent" (GhentFPG) [1] is a friendly group for all people interested in functional programming, with a tendency towards Haskell. It is organised as part of Zeus WPI [2]. We are pleased to announce that we will hold a next meeting on Wednesday, 26th of June, starting at 19h00! There will be three talks. The main presentation, by Adam Bergmark from Silk [3] is about Fay [4]: Fay is a proper subset of Haskell that compiles to JavaScript. There is a compiler with the same name written in Haskell. Web browsers only speak JavaScript but more and more people find that they want to compile to JavaScript instead. Why do we want to compile Haskell to JavaScript, and what advantages does Fay have compared to other compilers? What are the challenges in compiling Haskell and supporting a language ecosystem, and how do we do it? What can Fay currently do, and what is planned for the future? This will be a broad overview about Fay for prospective users, followed by an in-depth look at interesting parts of the compiler internals. Additionally, there will be two short talks by two students who did an Msc. Thesis about functional programming languages: "Genetic Algorithms in Haskell" by Matthias Delbar "Automatic Detection of Recursion Patterns" by Jasper Van der Jeugt The meeting will take place in the Jozef Plateauzaal at the following address, Faculteit Ingenieurswetenschappen Universiteit Gent Plateaustraat 22 9000 Gent As mentioned above, we aim to start at 19:00. After the meeting we can go for drinks in a nearby pub (this latter part is, of course, completely optional) We hope to see you all there! Regards, On behalf of the GhentFPG organising committee. [1]: http://groups.google.com/group/ghent-fpg [2]: http://zeus.ugent.be/ [3]: http://www.silkapp.com/ [4]: http://www.fay-lang.org/

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[haskell.org Google Summer of Code 2013] Approved Projects
by Edward Kmett 30 May '13

30 May '13

We've worked our way through the project approval process for another year. This year we accepted 9 projects for haskell.org in general and are hosting 2 additional projects for darcs as an umbrella organization. haskell.org: * Parallelise 'cabal build' by Mikhail Glushenkov, mentored by Johan Tibell * Extending GHC to support building modules in parallel by Patrick Palka, mentored by Thomas Schilling * Communicating with mobile devices by Marcos Pividori, mentored by Michael Snoyman * Improve Haddock Markup and Capabilities by Fūzetsu, mentored by Simon Hengel * Haskell Qt Binding Generator by Zhengliang Feng, mentored by Carter Schonwald with help from Ian-Woo Kim * Improve the feedback of the cabal-install dependency solver by Martin Ruderer, mentored by Andres Löh * Interactive-diagrams and a paste site with the ability for dynamic rendering of diagrams by Dan Frumin, mentored by Luite Stegeman * Overloaded record fields for GHC by Adam Gundry, mentored by Simon Peyton-Jones * Port Charts to use Diagrams by Jan Bracker, mentored by Tim Docker darcs: * Better record command for darcs by José Neder, mentored by Gillaume Hoffmann * Enhancing Darcsden by BSRK Aditya, mentored by Ganesh Sittampalam Students have from now through Jun 16th to get up to speed and get to know their mentors. And while the summer of code officially starts on Jun 17th, keep in mind that the mid-term evaluations aren't that much farther behind, starting July 29th, so you'll want to hit the ground running. If you put in a project proposal and it wasn't accepted and/or you would like feedback, please feel free to email me or contact me on the #haskell-gsoc channel on irc.freenode.net. We received more proposals than slots this year, and so we were forced to make a few hard decisions. Shachaf Ben-Kiki is helping out as this year's backup administrator and he should also be able to help out with administrivia or questions as well. I'd like to thank everyone for participating in the selection process and I think we can look forward to another excellent summer of code! Edward Kmett haskell.org Google Summer of Code Administrator

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Re: [Haskell-cafe] using a win32 dll (Happy too soon)
by Robert Jakob 29 May '13

29 May '13

> If I compile with ghc --make testGlasPng.hs -lglasPng I > get: ..\ld.exe: cannot find -lglasPng. Collect 2: ld returned 1 exit > status. > > Ld can't find lglasPng (with the l in front, does it trim the l?). > Why? Okay I try > > ghc --make testGlasPng.hs -L<path to glasPng.dll> I get: > > testGlasPng.o: fake: (.text + 0x82) :undefined reference to > 'getPngVersion@0'. I think it has found the dll, but it complains the > function is not in the dll. But TDump and Dll export viewer say > getPngVersion is in the dll. I think you should use both -L and -l. ghc --make testGlasPng.hs -L/path/to/folder/where/glasPng/is -lglasPng -L should point to the folder, NOT the dll itself. Hope this helps. R.

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using a win32 dll (Happy too soon)
by Kees Bleijenberg 29 May '13

29 May '13

Unfortunatly the proposed solutions didn't work after all (It worked once, I think, but.) Here again the problem: glasPng.dll is a Delphi dll with the function getPngVersion in it. Calling convention is stdCall. I want to use this dll. The code: {-# LANGUAGE ForeignFunctionInterface #-} module Main( main ) where import Control.Monad import Foreign.C import Foreign.Marshal.Alloc import Foreign.Marshal.Array import System.Win32.Types foreign import stdcall "getPngVersion" getPngDllVersion :: IO CString main :: IO () main = do s <- getPngDllVersion putStrLn (show s) glasPng.dll is in the Windows path (I've checked it). If I compile with ghc --make testGlasPng.hs -lglasPng I get: ..\ld.exe: cannot find -lglasPng. Collect 2: ld returned 1 exit status. Ld can't find lglasPng (with the l in front, does it trim the l?). Why? Okay I try ghc --make testGlasPng.hs -L<path to glasPng.dll> I get: testGlasPng.o: fake: (.text + 0x82) :undefined reference to 'getPngVersion@0'. I think it has found the dll, but it complains the function is not in the dll. But TDump and Dll export viewer say getPngVersion is in the dll. I run ghc on a 64 bits computer. The dll is 32 bits. Is that the problem? What can I do? Kees

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Re: [Haskell-cafe] using a win32 dll
by Kees Bleijenberg 29 May '13

29 May '13

Thank you Krzystof! This did the trick. Now I also have a better understanding what is going on. Great. Kees Van: Krzysztof Skrzętnicki [mailto:gtener@gmail.com] Verzonden: woensdag 29 mei 2013 11:58 Aan: Kees Bleijenberg Onderwerp: Re: [Haskell-cafe] using a win32 dll Oh, I didn't mean kernel32. And -L provides search path not the actual library. The idea was to use -l<yourLibrary.dll> , so it would be -lpngDLL.dll, provided it is in library search path. If not use -Ldirectory-with-dll -lpngDLL.dll On Wed, May 29, 2013 at 11:49 AM, Kees Bleijenberg <k.bleijenberg(a)lijbrandt.nl> wrote: I’ve tried to compile it with –l kernel32, but nothing changed. I’ve also tried -LpngDll.dll but that didn’t work either. Kees My first guess would be missing -l parameter. The examples you have linked read: ghc --make compname.hs -lkernel32 Best regards, Krzysztof Skrzętnicki On Wed, May 29, 2013 at 9:13 AM, Kees Bleijenberg <k.bleijenberg(a)lijbrandt.nl> wrote: I made a Delphi dll (32 bits windows). This dll exports a function named getPngVersion. This is a function with no arguments that returns a pointer to a array of chars. If I examine the dll with a tools like tdump, I can see the function getPngVersion on index 1. Now I want to use this dll in Haskell: {-# LANGUAGE ForeignFunctionInterface #-} module Main( main ) where import Control.Monad import Foreign.C import Foreign.Marshal.Alloc import Foreign.Marshal.Array import System.Win32.Types foreign import stdcall "glasPng getPngVersion" getPngDllVersion :: IO CString main :: IO () main = do s <- getPngDllVersion putStrLn (show s) Compiling this with ghc --make glasPng.hs gives: GlasPng.o: fake: (.text +0x82): undefined reference to ‘getPngVersion@0’ collect2 : Id returned 1 exit status I wonder what went wrong. In the foreign import line I use “glasPng…. “ to tell ghc, it has to searh in glasPng.dll (changing glasPng to glasPng.dll doesn’t help). I’ve changed the name of the function in the dll to getPngVersion@0 but no luck. I’ve read and tested the last example at http://stackoverflow.com/questions/1027246/haskell-foreign-import-stdcall-o… (win32_getComputername, this works!). I wonder how haskell knows which dll to use in this example?) Probably I’am doing something wrong with the way I tell ghc which dll to link or…. Any ideas? Kees _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Install wx on Windows XP
by Eric Wong 29 May '13

29 May '13

Hi Haskellers, I'm trying to install wxHaskell on Windows XP. I have already installed Haskell Platform 2012.04.0.0, MinGW and wxWidgets. When I try to install wx, I got the following error when cabal is installing wxcore: $ cabal install wx Resolving dependencies... [1 of 1] Compiling Main ( C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\wxcore- 0.90.0.3-896\wxcore-0.90.0.3\Setup.hs, C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\wxcore -0.90.0.3-896\wxcore-0.90.0.3\dist\setup\Main.o ) Linking C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\wxcore-0.90.0.3-896\wxcore-0.90.0.3\d ist\setup\setup.exe ... Configuring wxcore-0.90.0.3... Generating class type definitions from .h files generating: src/haskell/Graphics/UI/WXCore/WxcClassTypes.hs reading class definitions: parsing: C:\Documents/include/wxc.h wxdirect: C:\Documents/include/wxc.h: openFile: does not exist (No such file or directory) Generating class info definitions generating: src/haskell/Graphics/UI/WXCore/WxcClassInfo.hs reading class definitions: parsing: C:\Documents/include/wxc.h wxdirect: C:\Documents/include/wxc.h: openFile: does not exist (No such file or directory) Generating class method definitions from .h files parsing: Data\cabal\wxc-0.90.0.4\ghc-7.4.2\include/wxc.h wxdirect: Data\cabal\wxc-0.90.0.4\ghc-7.4.2\include/wxc.h: openFile: does not ex ist (No such file or directory) Building wxcore-0.90.0.3... Preprocessing library wxcore-0.90.0.3... src\haskell\Graphics\UI\WXCore\WxcClassTypes.hs:1:1: File name does not match module name: Saw: `Main' Expected: `Graphics.UI.WXCore.WxcClassTypes' cabal.exe: Error: some packages failed to install: wx-0.90.0.1 depends on wxcore-0.90.0.3 which failed to install. wxcore-0.90.0.3 failed during the building phase. The exception was: ExitFailure 1 It looks like it's confused by the spaces in the path and can't find the wxc.h file. I tried to configure cabal to install all user packages into a simpler directory. But cabal always install to the C:\Documents and Settings\Administrator\Application Data\cabal directory no matter how I change the config file there. Anyone knows how to fix this problem or change cabal directory on Windows? Thanks. p.s. I'm using the user Administrator.

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Re: [Haskell-cafe] using a win32 dll
by Robert Jakob 29 May '13

29 May '13

On Wed, 29 May 2013 09:13:09 +0200 "Kees Bleijenberg" <k.bleijenberg(a)lijbrandt.nl> wrote: > I made a Delphi dll (32 bits windows). This dll exports a function > named getPngVersion. This is a function with no arguments that > returns a pointer to a array of chars. Did you annotate the exported function with stdcall? The calling conventions of Delphi are different to that of C. I had problems with that sometimes (not with Haskell, but with C) R.

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Re: [Haskell-cafe] using a win32 dll
by Krzysztof Skrzętnicki 29 May '13

29 May '13

My first guess would be missing -l parameter. The examples you have linked read: ghc --make compname.hs -lkernel32 Best regards, Krzysztof Skrzętnicki On Wed, May 29, 2013 at 9:13 AM, Kees Bleijenberg < k.bleijenberg(a)lijbrandt.nl> wrote: > I made a Delphi dll (32 bits windows). This dll exports a function named > getPngVersion. This is a function with no arguments that returns a pointer > to a array of chars.**** > > If I examine the dll with a tools like tdump, I can see the function > getPngVersion on index 1.**** > > Now I want to use this dll in Haskell:**** > > ** ** > > {-# LANGUAGE ForeignFunctionInterface #-}**** > > module Main(**** > > main**** > > )**** > > ** ** > > where**** > > import Control.Monad**** > > import Foreign.C**** > > import Foreign.Marshal.Alloc**** > > import Foreign.Marshal.Array**** > > import System.Win32.Types**** > > ** ** > > foreign import stdcall "glasPng getPngVersion" getPngDllVersion :: IO > CString**** > > ** ** > > main :: IO ()**** > > main = do **** > > s <- getPngDllVersion**** > > putStrLn (show s)**** > > ** ** > > Compiling this with ghc --make glasPng.hs gives:**** > > GlasPng.o: fake: (.text +0x82): undefined reference to ‘getPngVersion@0’ > collect2 : Id returned 1 exit status **** > > ** ** > > I wonder what went wrong. In the foreign import line I use “glasPng…. “ to > tell ghc, it has to searh in glasPng.dll (changing glasPng to glasPng.dll > doesn’t help). I’ve changed the name of the function in the dll to > getPngVersion@0 but no luck. I’ve read and tested the last example at > http://stackoverflow.com/questions/1027246/haskell-foreign-import-stdcall-o… > (win32_getComputername, this works!). I wonder how haskell knows which > dll to use in this example?)**** > > Probably I’am doing something wrong with the way I tell ghc which dll to > link or….**** > > ** ** > > Any ideas?**** > > ** ** > > Kees**** > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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using a win32 dll
by Kees Bleijenberg 29 May '13

29 May '13

I made a Delphi dll (32 bits windows). This dll exports a function named getPngVersion. This is a function with no arguments that returns a pointer to a array of chars. If I examine the dll with a tools like tdump, I can see the function getPngVersion on index 1. Now I want to use this dll in Haskell: {-# LANGUAGE ForeignFunctionInterface #-} module Main( main ) where import Control.Monad import Foreign.C import Foreign.Marshal.Alloc import Foreign.Marshal.Array import System.Win32.Types foreign import stdcall "glasPng getPngVersion" getPngDllVersion :: IO CString main :: IO () main = do s <- getPngDllVersion putStrLn (show s) Compiling this with ghc --make glasPng.hs gives: GlasPng.o: fake: (.text +0x82): undefined reference to 'getPngVersion@0' collect2 : Id returned 1 exit status I wonder what went wrong. In the foreign import line I use "glasPng.. " to tell ghc, it has to searh in glasPng.dll (changing glasPng to glasPng.dll doesn't help). I've changed the name of the function in the dll to getPngVersion@0 but no luck. I've read and tested the last example at http://stackoverflow.com/questions/1027246/haskell-foreign-import-stdcall-on -dll-function (win32_getComputername, this works!). I wonder how haskell knows which dll to use in this example?) Probably I'am doing something wrong with the way I tell ghc which dll to link or.. Any ideas? Kees

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