- Haskell-Cafe - Haskell.org

advancePtr for ForeignPtr
by Henning Thielemann 23 Feb '09

23 Feb '09

Is still someone on haskell.org ? ---------- Forwarded message ---------- Date: Thu, 19 Feb 2009 21:40:08 +0100 (CET) From: Henning Thielemann <lemming(a)henning-thielemann.de> To: ffi(a)haskell.org Subject: advancePtr for ForeignPtr I want to have an advancePtr on ForeignPtr in order create a subarray. Is this reasonable and possible? Do I have to use 'touchForeignPtr' as finalizer of the subarray's ForeignPtr in order to assert that the superarray lives at least as long as the subarray? Anyway I'd prefer a function in the standard modules than doing such things by myself.

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looking for a 2d graphics package
by Martin DeMello 23 Feb '09

23 Feb '09

What 2d graphics library would be the best fit for this sort of thing? http://www.superliminal.com/geometry/tyler/gallery/circular/tiles060.html I took a look at diagrams but it seemed more geared towards things that fit on a rectangular layout. martin

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Semantic web
by gregg reynolds 23 Feb '09

23 Feb '09

Anybody implementing rdf or owl stuff in haskell? Seems like a natural fit. G

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Fwd: [plt-scheme] Vancouver Lisp Users Group meeting for March 2009 - Haskell for Lisp Programmers
by Tim Wawrzynczak 23 Feb '09

23 Feb '09

I thought you guys might find this interesting: Haskell for Lisp programmers ---------- Forwarded message ---------- From: Bill Clementson <billclem(a)gmail.com> Date: Mon, Feb 23, 2009 at 11:12 AM Subject: [plt-scheme] Vancouver Lisp Users Group meeting for March 2009 - Haskell for Lisp Programmers To: undisclosed-recipients Hi all, Haskell is a polymorphically statically typed, lazy, purely functional language based on the lambda calculus. As such, it shares some things in common with some dialects of Lisp but differs in other regards. Our March lispvan speaker will present an introduction to Haskell geared towards Lisp programmers. If you want to read up about Haskell before the meeting, a good starting point is the Haskell Wiki. Here's the "official" meeting notice: Topic: Haskell for Lisp Programmers Presenter: Erik Charlebois Date: Wednesday, March 4th, 2009 Time: 7pm - 10pm (or whenever) Venue: The Hackery, 304 Victoria Dr (entrance off Franklin), Vancouver (see map) Summary: Haskell is a lazy, pure, statically-typed functional programming language enjoying a lot of attention these days. Its strict approach to side effects is seen as one of the viable approaches to making parallel programming tractable. Erik will talk about the core differences between Haskell and Lisp, the actions the Haskell community is taking to manage this growth, and some neat applications of the language already in the wild. * Differences between Haskell and Lisp * Syntax * Static typing * Side effects with monads * The Haskell Platform * Build, Package, Distribute * Community * Haskell Dog and Pony Show Bio: Erik was a compiler developer for 3 years at IBM working on the XL Fortran and C/C++ compilers for the Cell processor. He is currently employed at Slant Six Games doing gameplay programming. For the past 2 years, he has been studying programming languages and databases in a search for smarter ways to build soft real-time applications like games. If possible, I will record the presentation and post it on my blog after the meeting for those who are unable to attend. Join us for a beer (bring your own - there's a fridge) and a chance to learn what static typing and monads are all about! Any updates will be posted on my blog entry for the meeting: http://bc.tech.coop/blog/090223.html -- Bill Clementson _________________________________________________ For list-related administrative tasks: http://list.cs.brown.edu/mailman/listinfo/plt-scheme

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Online GHC documentation
by Maurício 23 Feb '09

23 Feb '09

Just a small tip: I think it would be nice if GHC online documentation were built with links to the source code, like in hackage. Best, Maurício

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Fwd: cabal-install and bash scripts in windows- Was: Re: pkgenv - disposable, isolated pkg environments
by Alberto G. Corona 23 Feb '09

23 Feb '09

Forwarded to the list: By the way, there are important packages such are haskell plugins, that have also this same single obstacle for workining under Windows. Many have basically the same bash script that test the type of c compiler, which fails miserably under windows: example output: checking for C compiler default output file name... configure: error: C compiler cannot create executables See `config.log' for more details. cabal: Error: some packages failed to install: plugins-1.4.0 failed during the configure step. The exception was: exit: ExitFailure 77 Could be possible to check if this problem can be solved with cabal-install?. 2009/2/22 Duncan Coutts <duncan.coutts(a)worc.ox.ac.uk> > On Sun, 2009-02-22 at 18:38 +0100, Paolo Losi wrote: > > Duncan Coutts wrote: > > > > > Would it be useful to have cabal-install check a env var for its config > > > file? > > > > Definitely yes. > > This would allow dropping the dependency on bash aliasing and > > make porting to Windows fairly easy. > > Ok, I've filed a ticket so hopefully someone will pick it up. It should > be pretty easy. Just a few lines of code. > > http://hackage.haskell.org/trac/hackage/ticket/505 > > Duncan > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Practise of hiding contsructors and serialization
by Marc Weber 23 Feb '09

23 Feb '09

While working on extending scion I got some trouble and wonder which is the best way to do this? I have to pass a compilation result from a scion process instance to the scion daemon process. Of course I'd just like to use a simple Read Show for that. However I can't because two datatypes are NominalDiffTime and Bag ErrMsg: newtype NominalDiffTime = MkNominalDiffTime Pico deriving (Eq,Ord) data ErrMsg = ErrMsg { errMsgSpans :: [SrcSpan], errMsgContext :: PrintUnqualified, errMsgShortDoc :: Message, errMsgExtraInfo :: Message } Both are fine and both don't export all contstructors so you can't just let ghc derive instances for it? So the only way is to duplicate those datatypes in order to derive some Show, Read instances? On the one hand I do understand that you don't want users to access constructors directly. On the other hand it would be desirable to derive Read, Show instances here. Is there a way to get all? a) hiding constructors so that you don't have to expose implementation details to the user. b) still allow deriving serialization instances? Is there a better way than using toRational to get a type which can be serialzied quickly? I don't like Rational because the unit information 1e-12[s] is no longer included in the type.. Sincerly Marc Weber

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Error on instance of Control.Exception.Exception
by Maurício 23 Feb '09

23 Feb '09

Hi, I read here: www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Exception.html that this is declared: --- class (Typeable e, Show e) => Exception e where toException :: e -> SomeException fromException :: SomeException -> Maybe e --- I understand this means Excepton is a class. But after I try: --- instance Exception DbError where --- GHC says: Type constructor `Exception' used as a class In the instance declaration for `Exception DbError' Isn't Exception a class? If it is, what is the proper way to have an Exception instance for my type? Thanks, Maurício

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ANNOUNCE: X Haskell Bindings 0.2
by Antoine Latter 22 Feb '09

22 Feb '09

I'd like to announce the 0.2.* series release of the X Haskell Bindings. This release, like the prior 0.1.* series focuses on making the API prettier. This does mean that there's a good chance this is a breaking release. Also, 0.2.* is based on the just-released version 1.4 of the XML descriptions of the X protocol. The goal of XHB is to provide a Haskell implementation of the X11 wire protocol, similar in spirit to the X protocol C-language Binding (XCB). On Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xhb New this release: In the core protocol, a lot of the fields which previously were of type 'Word8' or 'Word16' now have appropriate higher-level types. For example, in the type GetWindowAttributesReply, the 'class' field was previously of type 'Word16', and is now of type 'WindowClass,' and the 'all_event_masks' field was of type 'Word32' and is now of type '[EventMask]'. These improvements haven't made their way out to the extensions yet, but the code-generation machinery is now in place for this to happen as the information makes its way into the XML protocol description. Related projects: X C Bindings: http://xcb.freedesktop.org/ -Antoine

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pkgenv - disposable, isolated pkg environments
by Paolo Losi 22 Feb '09

22 Feb '09

Hi all, I've been recently toying with a small tool inspired by the Python tool virtualenv [1]. What it basically allows to do is to setup isolated, disposable package environments. You can find a small session example in: http://www.haskell.org/haskellwiki/PkgEnv The main benefits should be: 1. allowing experimenting with package installations without "polluting" or breaking the default user package DB. When you're done you can simply remove the pkgenv directory => disposable 2. starting from a clean, fresh pkg "configuration" containing only system packages. This make cabal-install dependency analysis job much easier and predictable => isolated pkgenv now only runs on unix, even if it could be possible to port it to windows... To test it, download it from http://bitbucket.org/pao/pkgenv/raw/488bfe8e58dd/pkgenv chmod a+x and drop to an executable directory. Any feedback would be really appreciated. Is this useful at all? Are there better ways to reach the same goals? Pao 1. http://pypi.python.org/pypi/virtualenv

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