October 2008 - Haskell-Cafe

ANNOUNCE: Salsa: A .NET Bridge for Haskell
by Andrew Appleyard 15 Oct '08

15 Oct '08

I'd like to announce the first release of Salsa, an experimental Haskell library that allows Haskell programs to access .NET libraries. Here's a taste: > type Hello.hs import Foreign.Salsa import Bindings main = withCLR $ do _Console # _writeLine ("Hello .NET World!") > type Hello.imports System.Console: WriteLine > msbuild > .\hello Hello .NET World! Salsa operates by loading the .NET runtime into your Haskell process and using the FFI (and run-time code generation) to marshall calls between the .NET and Haskell runtimes. It includes a code generator and a type-level library (which uses type families) to provide type-safe access to .NET libraries in Haskell with C#-style method overload resolution and implicit conversions. The adventurous can find version 0.1.0.1 of Salsa on Hackage [1], the darcs repository on code.haskell.org [2], and some (limited) documentation on the Haskell wiki [3]. The library is experimental and by no means complete (refer to the wiki page [3] for some of its limitations). Be prepared to end up with incomprehensible error messages and/or a broken compiler! :-) At the moment you'll need Windows, GHC 6.8, and version 3.5 of the .NET Framework to use it. Have fun! [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Salsa [2] http://code.haskell.org/Salsa [3] http://haskell.org/haskellwiki/Salsa -- Andrew

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How to specify multiple fonts for xmobar?
by Magicloud 15 Oct '08

15 Oct '08

Hi, I am using xmonad + xmobar. And I am using sgi screen font. But sometimes I need to display CJK characters, which need another font. In gtk2 software, this is OK. I just specify the screen font for ascii. It can auto-choose a CJK font. Everything looks fine, maybe not pretty. While, xmobar does not auto-choose a CJK font, if I just specify screen font for ascii, it displays CJK characters in blank. How to fix this?

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Foreign.Marshal.Error.void
by Mauricio 15 Oct '08

15 Oct '08

Hi, Wouldn't it be nice if we had something like 'void' in Foreign.Marshal.Error in standard monad functions, so that we could use it instead of, for instance, mapM_ or sequence_? Best, Maurício

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There is something wrong with hprotoc-0.3.1 package.
by Magicloud 14 Oct '08

14 Oct '08

Hi, I wanted to install this package. Well, Building hprotoc-0.3.1... ... [3 of 7] Compiling Text.ProtocolBuffers.ProtoCompile.Parser ... Text/ProtocolBuffers/ProtoCompile/Parser.hs:48:0: Type synonym `GenParser' should have 2 arguments, but has been given 1 In the type synonym declaration for `P' And it just stopped here.

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There is something wrong in derive-0.1.2 package.
by Magicloud 14 Oct '08

14 Oct '08

Hi, I wanted to install it with cabal. Well $ cabal install derive Resolving dependencies... cabal: Couldn't read cabal file "./derive/0.1.2/derive.cabal" As I traced a little, it seemed that line: 'build-depends: base == 4.*, syb' was wrong.

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[ANN] Haskell Cheatsheet v1.0
by Justin Bailey 14 Oct '08

14 Oct '08

All, I've created a "cheat sheet" for Haskell. It's a PDF that tries to summarize Haskell 98's syntax, keywords and other language elements. It's currently available on hackage[1]. Once downloaded, unpack the archive and you'll see the PDF. A literate source file is also included. If you install with "cabal install cheatsheet", run "cheatsheet" afterwards and the program will tell you where the PDF is located. The audience for this document is beginning to intermediate Haskell programmers. I found it difficult to look up some of the less-used syntax and other language stumbling blocks as I learned Haskell over the last few years, so I hope this document can help others in the future. This is a beta release (which is why I've limited the audience by using hackage) to get feedback before distributing the PDF to a wider audience. With that in mind, I welcome your comments or patches[2]. Justin [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/CheatSheet [2] git://github.com/m4dc4p/cheatsheet.git

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gtk2hs and GTK+OSX
by Jeroen Baekelandt 14 Oct '08

14 Oct '08

Hi, I was wondering if anybody managed to get gtk2hs working with GTK+OSX from http://www.gtk-osx.org/ I'm trying but there seems to be a quite long dependency list that keeps on building up. So I was wondering if it ends and if it works in the end. Thanks, Jeroen

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Re: What I wish someone had told me...
by John Lato 14 Oct '08

14 Oct '08

While this may be true, it's missing the point. The claim that type classes are like interfaces (the usual argument is that they define an interface, but not an implementation) misleads OO-grounded programmers into thinking of type classes in terms of an already-familiar concept. This is bad because said programmers then attempt to apply familiar OO-styles, when they would be better off abandoning most of what they already know about design. I don't mean in the sense of "abstraction good, separation of processing good, repetition bad", but rather how to develop a useful/stable API, how to divide up the different processing the module should do, etc. In short, how to approach API design, which is very different in Haskell than the practice that most OO disciples are familiar with. IMHO, stating that type classes act like interfaces in argument types, but not return types, is too complicated a relationship to be useful to somebody's first introduction to FP. Better to avoid the whole issue completely. John Lato Alexey Romanov wrote: > > Well, they act like interfaces in argument types, just not variable or > return types. > > Yours, Alexey Romanov >

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Congrats. to wxHaskell
by Don Stewart 14 Oct '08

14 Oct '08

I just want to congratulate the wxHaskell team on their new release. With GHC 6.10 RC, cabal 1.6, and cabal-install 0.6, I was able to simply, cabal install wxcore wx And it all worked. Well done! -- Don

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hackage warning: Exposed modules use unallocated top-level names: ... what am I doing wrong?
by Thomas Hartman 14 Oct '08

14 Oct '08

However the package generated the following warnings: * A 'license-file' is not specified. * Exposed modules use unallocated top-level names: Algorithms everything fetchable with darcs get http://code.haskell.org/external-sort external-sort is on hackage and seems to work (you can run demo.hs after cabal installing) but I'd still like to understand if this warning is something I should pay attention to anyway.

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