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Hal Daume III's NewBinary now ghc6ized, cabalized, debianize, darcsized.
by Jeremy Shaw 08 Nov '04

08 Nov '04

Hello, I am quite interested in having better Binary support in Haskell -- especially support for reading and writing binary files and protocols that have fields smaller than 8-bits and non-byte alignment. As a first step, I have republished Hal Daume III's NewBinary package in hopes that it will inspire some forward movement on it. I have made the following 'improvements': ~ ghc6ized cd /tmp/NewBinary/ diff /tmp/Binary.hs /tmp/NewBinary/NewBinary/Binary.hs 81c81,82 < import GHC.Handle ( openFileEx, IOModeEx(..) ) --- > import GHC.Handle > import IOExts ( openFileEx, IOModeEx(..) ) (hrm, I probably don't need to import GHC.Handle anymore either...) ~ cabalized To build, you need the Cabal libraries installed. Then do something like this: ghc -package Setup.lhs -o setup ./setup configure ./setup build ./setup install ./setup register (? maybe not needed ?) ~ debianized You should be able to build and install it like any other debian package: dpkg-buildpackage && debi ~ darcsized darcs get http://www.n-heptane.com/nhlab/repos/NewBinary I hope I am not stepping on anyone's toes or duplicating efforts. Jeremy Shaw. ps. The original is available at: http://www.isi.edu/~hdaume/haskell/NewBinary/ -- This message contains information which may be confidential and privileged. Unless you are the addressee (or authorized to receive for the addressee), you may not use, copy or disclose to anyone the message or any information contained in the message. If you have received the message in error, please advise the sender and delete the message. Thank you.

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Re: [Haskell-cafe] Re: Double -> CDouble, realToFrac doesn't work
by MR K P SCHUPKE 08 Nov '04

08 Nov '04

>I would be very careful of adding non-rationals to the Rational type. Why is there no Irrational class. This would make more sense for Floats and Doubles than the fraction based Rational class. We could also add an implementation of infinite precision irrationals using a pair of Integers for exponent and mantissa. Keean.

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Dynamic Type Contruction
by Vitor Rodrigues 08 Nov '04

08 Nov '04

I'm trying to create a library to querying XML data using Strafunski. I'm also using DrIFT to generate the instances of Typeable and Term of my Datatypes to be used inside Strafunski. Supose i've this datatypes: data Shape = Circle Float (Float,Float) | Triangle (Float, Float) (Float, Float) (Float, Float) then DrIFT, among other things, creates the functions: isCircle (Circle _ _ ) = True isCircle _ = False isTriangle (Triangle _ _ _) = True isTriangle _ = False what i'd like to have "is" as a generic "isFoo" function, with the type: is :: String -> DataType -> Bool that when running will act like this: is "Circle" (Circle 3.4 (3.0,3.1)) = True is "Triangle" (Circle 3.4 (3.0,3.1)) = False is "Circle" 2 = False I was looking on TyCon constructor and mkTyCon function, but i didn't understood it well. Can anyone tell me how can i create this "is Foo" function? I was thinking about create a dynamic type with mkTyCon and then see if it matches with the DataType receiveid as function parameter. Regards, Vitor Rodrigues

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RE: [Haskell-cafe] Making MVar and Chan Instances of Typeable
by Simon Peyton-Jones 08 Nov '04

08 Nov '04

| instance Typeable a => Typeable (MVar a) where | typeOf x = | mkAppTy (mkTyCon "Control.Concurrent.MVar.MVar") [typeOf (undefined::a)] As I think you now know, the above declaration is fine if you use -fglasgow-exts. Haskell 98 does not support lexically scoped type variables, but GHC -fglasgow-exts does. You can read about it in the GHC user manual. Type variables are bound by instance declarations, as above, but you can also bind them in patterns. So as others have said an alternative is | instance Typeable a => Typeable (MVar a) where | typeOf (x::MVar b) = | mkAppTy (mkTyCon "Control.Concurrent.MVar.MVar") [typeOf (undefined::b)] But that's not legal in Haskell 98 either, and since 'a' is already in scope with -fglasgow-exts, the extra binding for 'b' seems less nice. The best Haskell 98 solution is the one Remi gives: instance Typeable a => Typeable (MVar a) where typeOf v = mkAppTy (mkTyCon "Control.Concurrent.MVar.MVar") [typeOf (t v)] where t :: a b -> b t = undefined Simon

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Lnear algebra library for game programming.
by Serguey Zefirov 08 Nov '04

08 Nov '04

Right now I explore the possibilities of building the prototype for game physics library in Haskell. This is a purely hobby approach to gain more knowledge on Haskell and library design in general. One of intermediate steps is to build linear algebra library for further utilisation. But, here I face some difficulties. In C++ I could define needed operators on per-type basis, and define universal operators for, say, Vec3 * Mat3x3, Vec3 * Mat3x4, etc. In Haskell I should define different operators, something like `v3mulm3x3`, `v3mulm3x4`. This is somewhat inconvenient, given that I expect to utilize Vec2,3,4 and Mat(3,4)x(3,4) parametrized by Double and Float. So the question is: what other people do in situation like this and is there any paper(s) on linear algebra library design? -- Yours truly, Serguey Zefirov, theszATmail.ru.

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Re: [Haskell-cafe] (Re arrows and Haskell) ...
by Andy Elvey 07 Nov '04

07 Nov '04

On Saturday 06 November 2004 08:36 am, you wrote: < snip > > > It might be an immense project, but I also think it would be interesting. > I wonder if Haskell would be much faster after being restructured around > arrows. > If an arrow-based version of Haskell existed, I'd love to try it. > > I think it's entirely possible that it would have significant benefits in > speed, elegance, and structural simplicity. > -- > Shae Matijs Erisson - Programmer Hi Shae! Thanks for your comments, and i agree totally! It would indeed be very interesting, and I tend to agree too that speed might be helped if this were done. ( and yes - I'd love to try an arrow-based Haskell too! ). While I was mulling this over this morning, I was thinking how (or even "if" ) an EBNF grammar (Haskell's in this case) could be represented in terms or arrows. I stopped pretty quickly as it made my head hurt just thinking about it ... :-)) - Andy

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(Re arrows and Haskell) ...
by Andy Elvey 06 Nov '04

06 Nov '04

Hi again - Apologies for another post from me so soon (and for replying to my own post). Regarding my post about arrows and Haskell (and the idea of trying to define Haskell's grammar in terms of arrows) - upon thinking about that, I'm pretty much of the opinion that it'd be an immense task ... I also think that although maybe some of the grammar might be possible to define using arrows, it wouldn't be possible to do all of it :-) . So, I'll politely "withdraw to a corner" for a little while, resolving to think a bit more before I post! ;-) - Andy

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Defining Haskell using "arrows"
by Andy Elvey 06 Nov '04

06 Nov '04

Hi all - I'm a first-timer here, and am *very* much attracted by Haskell's elegance and power ... :-) I have only poked around briefly with Haskell so far (at the "hello world" level). One thing that I have come across, and which really got me thinking, was the page on the Haskell website about "arrows". They really seem to take elegance and the "generic-ness" of algorithms to a new level. I was thinking - arrows are a relatively recent concept. Haskell's grammar (as defined in the Haskell report) has now been around for quite some time. So - I thought "what if?" What if Haskell were to be defined (er, *re*-defined) in terms of arrows? In other words, what if it were possible to start totally "from scratch", re-defining Haskell's grammar using arrows? (and preferably, *only* arrows ... ). This would presumably involve somehow coding up the arrows first, and then (haivng got them), using them to create/define the rest of the language. My reason for suggesting this - simply to see if it were possible to do a very small (but still quite comprehensive) Haskell implementation. Small meaning maybe 2-3 MB or so ... As an interesting "benchmark" of this, the Rebol language (though proprietary - sigh!) - comes in at 0.5 Mb or so, including a GUI. So, "very small but very powerful" is possible (although undoubtedly pretty difficult ... ) As a Haskell newbie, I have to defer to everyone else on this list (in terms of my Haskell ability), but just thought I'd post this idea anyway. I was thinking " I wonder if anyone has thought of this? ....... " . Arrows seem to be a recent "add-on", as it were, so I thought -given their power and flexibility, why not turn things totally around, and put them at the *very core* of the language, using them to define the language itself. Anyway, I'm keen to hear people's thoughts on this! Very many thanks in advance ... :-) - Andy

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mkEmptyWeakPtr?
by David Roundy 06 Nov '04

06 Nov '04

I was wondering whether there might be any sort of trick one could use to create an empty "Weak a", i.e. one that has already been GCed? It should be possible to create such a pointer without having an object of type a. mkEmptyWeakPtr :: IO (Weak a) I know I could get this effect by using instead a "Maybe (Weak a)", but that's ugly and adds an additional layer of redirection. The point is that the weak pointer is being used to cache a value, but I'd like to not fill the cache until I actually need to read it. i.e. I have a data type AntiMemo (IO a) (IORef (Weak a)) where the second term is a cache of the result of the first, which is really a pure function, but I'm using the IO monad to force reevaluation, so the result, which is large, can be discarded and recomputed. So I could change this to AntiMemo (IO a) (IORef (Maybe (Weak a))) but it just seems a shame when Weak already effectively has a "Nothing" value type. I suppose one could also make it a "Weak (Maybe a)", but in any case, I'd rather be able to just initialize the IORef to an empty weak pointer, so there wouldn't need to be any extra code when reading the value. -- David Roundy http://www.abridgegame.org

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Making MVar and Chan Instances of Typeable
by Benjamin Franksen 06 Nov '04

06 Nov '04

Hello Experts, I need MVar and Chan to be instances of Typeable. Any hint on how this is most easily done would be greatly appreciated. I could change the libraries and add 'deriving Typeable' but I hesitate to do so. Cheers, Ben

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