November 2008 - Haskell-Cafe

generalized list comprehensions
by Johannes Waldmann 10 Nov '08

10 Nov '08

Looking at this funny new feature http://haskell.org/ghc/docs/6.10.1/html/users_guide/syntax-extns.html#gener… I have just one question - why doesn't this work with the do-notation? I avoid list comprehensions because I feel that "return" belongs at the end, not in front. If I recall correctly, "putting the SQL-select where it belongs" is a slogan used by Hijlsberg to justify the LINQ syntax for C#, and of course he is right. Now ghc copies LINQ (syntactically), but stops halfway? Just wondering - J.W.

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Are arbitrary rank types and existentials equivalent?
by Loup Vaillant 10 Nov '08

10 Nov '08

Maybe one subsumes the other? What I want to know is if there is an easy way to emulate one with the other, and how much convenience is lost in doing so. For instance, is it possible to implement stream fusion with rank2 types, or the ST monad with existantials? Is there any paper discussing this kind of things? Thanks, Loup

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ANN (sorta): OpenGL with extra type safety
by Neal Alexander 10 Nov '08

10 Nov '08

I recently modified the hOpenGL (and GLFW) source tree to force extra type checking on its various IO actions using the -XGeneralizedNewtypeDeriving extension (see http://hackage.haskell.org/trac/ghc/ticket/736) The main motivation was for writing concurrent OpenGL applications. Here its important to know what functions contain OpenGL commands so they can be directed to the proper threads (ones with active rendering contexts). Plus it aids in partitioning work that can be offloaded or done asynchronously. The second motivation was to enforce static type checking on commands that can only be executed in certain OpenGL contexts (sending vertex data for example). As it is now, there are 3 new monads (their names will probably change): OpenGLM: the basic opengl command PrimitiveM: commands that can only be issued between begin/end() class MonadGL: commands that can be issued in any GL context Now for the big question: Does anyone care? If so, should i make it a new hackageDB package, or try to merge it into the official GL package. Ideally, it'd be nice to get some more input on the API changes, since they're more or less a rough draft as is. Also, the GLU modules were all placed in the OpenGLM monad, which is probably wrong, assuming some commands can be called between begin/end. I'll post the code later if anyone is interested. ---------------- class MonadIO m => MonadGL m instance MonadGL OpenGLM instance MonadGL PrimitiveM newtype OpenGLM a = OpenGLM (IO a) deriving (Functor, Monad, MonadIO) newtype PrimitiveM a = PrimitiveM (IO a) deriving (Functor, Monad, MonadIO)

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Announce: FieldTrip library (functional 3D) and mailing list
by Conal Elliott 10 Nov '08

10 Nov '08

FieldTrip [1] is a library for functional 3D graphics. It is intended for building static, animated, and interactive 3D geometry, efficient enough for real-time synthesis and display. Since FieldTrip is functional, one describes what models are, not how to render them (being rather than doing). Surfaces are described as functions from 2D space to 3D space. As such, they are intrinsically curved rather than faceted. Surface rendering tessellates adaptively, caching tessellations in an efficient, infinite data structure (from the MemoTrie library) for reuse. Surface normals are computed automatically and exactly, using the derivative tools in the vector-space library. For animation or interaction, FieldTrip can be used with the Reactive [2] library for functional reactive programming (and possibly other animation frameworks). By design, FieldTrip is completely orthogonal to any formulation or implementation of FRP. The reactive-fieldtrip [3] library links Reactive and FieldTrip. FieldTrip now has a mailing list [4] and a feature/bug tracker [5]. [1] http://haskell.org/haskellwiki/FieldTrip [2] http://haskell.org/haskellwiki/reactive [3] http://haskell.org/haskellwiki/reactive-fieldtrip [4] http://www.haskell.org/mailman/listinfo/FieldTrip [5] http://trac.haskell.org/FieldTrip

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FFI documentation?
by Nun Aurbiz 10 Nov '08

10 Nov '08

Where do I find the documentation for the FFI for GHC? I've read the FFI report, the GHC user guide and scoured haskell.org but they all gloss over what commands you actually need to give GHC and how to give them. "foreign import blah blah" just gives me undefined references.

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Re: [Haskell-cafe] A video of Frag
by Hugo Pacheco 10 Nov '08

10 Nov '08

Yes, I installed it via cabal-install.I am using GHC 6.10.1 now, but it had > the same results in 6.6 (if I remember well) before. It may be a Mac issue. > > On Mon, Nov 10, 2008 at 1:39 PM, Korcan Hussein <korcan_h(a)hotmail.com>wrote: > >> Sorry I have no idea, which version of GHC are you using? did you try >> using cabal-install? ( >> http://hackage.haskell.org/trac/hackage/wiki/CabalInstall) >> >> ------------------------------ >> Date: Mon, 10 Nov 2008 10:46:45 +0000 >> >> From: hpacheco(a)gmail.com >> To: korcan_h(a)hotmail.com >> Subject: Re: [Haskell-cafe] A video of Frag >> >> Oh, sorry I haven't noticed.Trying to compile in my OS X machine, all >> compiles ok via cabal, but then I get >> >> $ ./frag ../share/frag-1.1.2/leveleg >> Bus error >> >> I remember compiling frag 1/2 years ago and getting the same result. >> It is not windows, but do you have any hint? >> >> On Mon, Nov 10, 2008 at 10:12 AM, Korcan Hussein <korcan_h(a)hotmail.com>wrote: >> >> Actually such a package already exists, it's quite a simple procedure as >> long as you have the right tools and and setup but for windows platform >> this information is a bit scattered/dispersed and there is no central >> information about getting such a thing up and running from complete scratch. >> This is what i'm referring to in my comment. >> >> ------------------------------ >> Date: Mon, 10 Nov 2008 09:15:14 +0000 >> From: hpacheco(a)gmail.com >> To: korcan_h(a)hotmail.com >> Subject: Re: [Haskell-cafe] A video of Frag >> CC: haskell-cafe(a)haskell.org >> >> >> I read on your youtube post that you are planning to write a >> build-it-yourself tutorial. Perhaps this effort could be targeted at >> creating a cabal package in Hackage (I do not know the implications of that, >> just speaking out loud). >> >> Cheers, >> hugo >> >> 2008/11/10 Korcan Hussein <korcan_h(a)hotmail.com> >> >> I don't understand why there is no video of Frag online so I made one >> here: http://uk.youtube.com/watch?v=0jYdu2u8gAU >> >> ------------------------------ >> Click here for FREE customisable desktop wallpapers. Get them Now!<http://wallpapers.msn.com/?ocid=%5BB001MSN42A0716B%5D> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> >> >> >> -- >> www.di.uminho.pt/~hpacheco <http://www.di.uminho.pt/%7Ehpacheco> >> >> ------------------------------ >> Click here for FREE customisable desktop wallpapers. Get them Now!<http://wallpapers.msn.com/?ocid=%5BB001MSN42A0716B%5D> >> >> >> >> >> -- >> www.di.uminho.pt/~hpacheco <http://www.di.uminho.pt/%7Ehpacheco> >> >> ------------------------------ >> Get the best wallpapers on the Web - FREE. Click here!<http://wallpapers.msn.com/?ocid=[B001MSN42A0716B]> >> > > > > -- > www.di.uminho.pt/~hpacheco >

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announcing darcs 2.1.1rc2
by Eric Kow 10 Nov '08

10 Nov '08

Hi everybody, The release candidate for darcs 2.1.1 is now available at http://darcs.net/darcs-2.1.1rc2.tar.gz This release is very much intended to be darcs 2.1.0 plus GHC 6.10.1 support. We have also thrown in some simplifications to the regression testing suite and a Windows bugfix (which we pulled in because of a dependency and retained because it was a small and useful). Please give this a try, especially those of you on GHC 6.10 or Windows, and let us know how things work out. Because we have only selected a very small subset of changes to include (using darcs's cherry-picking abilities, of course!), I am confident that we can get by on a reduced release cycle. If all goes well, the official release date for darcs 2.1.1 will be 2008-11-17. Thanks! Eric darcs (2.1.1rc2) * Portability: Removed accidental QuickCheck 2.1 configure check. Note that it may be required in a future version of darcs. -- Eric Kow <kowey(a)darcs.net> Mon, 10 Nov 2008 11:17:00 GMT darcs (2.1.1rc1) * Portability: GHC 6.10.1 support (Petr Ročkai, Eric Kow) * Bug Fix: Fix file handle leak and check for exceptions on process running on Windows (issue784, Salvatore Insalaco) * Quality Assurance: Consolidated regression test suites using shell scripts only (Eric Kow, Tommy Petterson, Matthias Kilian) -- Eric Kow <kowey(a)darcs.net> Mon, 10 Nov 2008 09:49:00 GMT -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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How to getCh on MS Windows command line?
by Ahn, Ki Yung 10 Nov '08

10 Nov '08

What I mean by getCh is the non-buffered non-echoed version of getChar, which Hugs used to provided as an extension but not any more. Is there any way to have a non-buffered non-echoed single character input function on MS Windows command line using only the libraries in the MS Windows distribution packages of either GHC or Hugs? The reason to why this is important for me is because I am translating Graham Hutton's "Programming in Haskell" into Korean (soon to be published), which illustrates interactive programming with the example of a calculator that responds instantly for every keystroke of numbers and arithmetic operations running on text mode. It is very important to consider the readers who only have access to MS Windows systems, because Korean OS market share is completely skewed towards MS Windows for very embarrassing reasons that I do not even want to mention. And, isn't GHC developed in MSR anyway? :-) I remember that this is an old problem for both of the two most widely used Haskell implementation, Hugs and GHC. In ghc 6.8 getChar had a bit strange behavior. As far as I remember it always worked as if it were NoBuffering. Fortunately, in the recently released ghc 6.10, this has been fixed. We now actually have to set the buffering mode to NoBuffering with hSetBufferring to get the non-buffered behavior of getChar. But, it still isn't working on MS Windows. In Hugs, hSetBuffering neither works on Unix terminal nor on MS Windows command line. Surprisingly, it works in WinHugs. However, I cannot use WinHugs for my purpose because the interactive calculator example in the book also uses beep characters and ANSI codes which do not work in WinHugs. Thanks for any hacks or suggestions, -- Ahn, Ki Yung

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foldl vs foldl'
by Daryoush Mehrtash 09 Nov '08

09 Nov '08

Are there cases (function or list) where the result of foldl (or foldr)would be different that foldl' (or foldr')? thanks, daryoush

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Announce: Reactive library (FRP) and mailing list
by Conal Elliott 09 Nov '08

09 Nov '08

Reactive [1] is a library for functional reactive programming (FRP), similar to the original Fran [2] but with a more modern interface (using standard type classes) and a hybrid push/pull implementation. It is designed to be used in a variety of contexts, such as interactive 2D and 3D graphics, graphical user interfaces, web services, and automatic recompilation/re-execution. It has a simple and precise semantics based on continuous time and is built on a notion of functional future values. The semantics and implementation are described in the paper "Simply efficient functional reactivity" [3]. Reactive now has a mailing list [4] and a feature/bug tracker [5]. [1] http://haskell.org/haskellwiki/Reactive [2] http://conal.net/Fran [3] http://conal.net/papers/simply-reactive [4] http://www.haskell.org/mailman/listinfo/reactive [5] http://trac.haskell.org/reactive

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