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Data.StorableVector vs Data.Vector.Storable
by Roman Cheplyaka 24 Mar '13

24 Mar '13

What is the relationship between these two modules? Do we really need both? (Data.Vector.Storable is part of vector, Data.StorableVector is from a separate package, storablevector.) Roman

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Need some advice around lazy IO
by C K Kashyap 24 Mar '13

24 Mar '13

Hi, I am working on an automation that periodically fetches bug data from our bug tracking system and creates static HTML reports. Things worked fine when the bugs were in the order of 200 or so. Now I am trying to run it against 3000 bugs and suddenly I see things like - too many open handles, out of memory etc ... Here's the code snippet - http://hpaste.org/84197 It's a small snippet and I've put in the comments stating how I run into "out of file handles" or simply file not getting read due to lazy IO. I realize that putting ($!) using a trial/error approach is going to be futile. I'd appreciate some pointers into the tools I could use to get some idea of which expressions are building up huge thunks. Regards, Kashyap

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hsc2hs fails?
by Henk-Jan van Tuyl 24 Mar '13

24 Mar '13

L.S., I am trying to install SDL-ttf: SDL-ttf-0.6.2>cabal install : : Preprocessing library SDL-ttf-0.6.2... dist\build\Graphics\UI\SDL\TTF\Version.hs:1:1: File name does not match module name: Saw: `Main' Expected: `Graphics.UI.SDL.TTF.Version' Failed to install SDL-ttf-0.6.2 : The error message is caused by the fact that Version.hs is empty; there is however a file dist\build\Graphics\UI\SDL\TTF\stdout.txt that contains the contents of Version.hs; there is also a file dist\build\Graphics\UI\SDL\TTF\Types.hs that is empty. These files are generated from Version.hsc and Types.hsc, in directory Graphics\UI\SDL\TTF How can this occur? Any way to debug this? Regards, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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Announcement - HGamer3D - 0.2.1 - featuring FRP based GUI and more
by Peter Althainz 24 Mar '13

24 Mar '13

Dear All, I'm happy to announce release 0.2.1 of HGamer3D, the game engine with Haskell API, featuring FRP based API and FRP based GUI. The new FRP API is based on the netwire package. Currently only available on Windows: http://www.hgamer3d.org. Peter

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A question about data declaration
by C K Kashyap 23 Mar '13

23 Mar '13

Hi, I have a situation where I need to define a data type T such that data T = C1 Int | C2 Char | C3 T However, I want to enforce a constraint that C3 only allows (C2 Char) and not (C1 Int). That is x = C3 (C1 10) -- should not compile - but my above definition will let it compile I was thinking of this - data C1 = C1 Int data C2 = C2 Char data T = TC1 C1 | TC1 C2 | TC3 C2 Is there a better way to do it? Regards, Kashyap

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ANN: pdf-toolbox
by Yuras Shumovich 23 Mar '13

23 Mar '13

Hello, I have uploaded the first release of my pdf toolbox, a collection of tools for processing PDF files. It supports both parsing and generating of pdf files. It consists of two libraries: - core ( http://hackage.haskell.org/package/pdf-toolbox-core ) contains low level tools. - document ( http://hackage.haskell.org/package/pdf-toolbox-document ) contains pretty limited set of middle level tools. (Also there is the 3d library, pdf-toolbox-content. It contains tools for processing pdf page content, e.g. text extraction. It is not released yet, but you can find it on github.) The initial plan was to create higher level tools before releasing on hackage, but I found it hard to design good high level API without wide rage on use cases. So I decided to release it earlier in order to receive feedback. You can find few examples here: https://github.com/Yuras/pdf-toolbox/tree/master/examples Thanks, Yuras

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Ticking time bomb
by Edward Z. Yang 23 Mar '13

23 Mar '13

https://status.heroku.com/incidents/489 Unsigned Hackage packages are a ticking time bomb. Cheers, Edward

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Compiled code
by MigMit 23 Mar '13

23 Mar '13

Suppose I compiled some module and kept it's .hi and .o files. Is it possible to use this module in my program if the source code was deleted for some reason? Seems like the answer is "yes" — by creating a fake .hs file (with no real content) and touch-in .hi and .o files I tricked ghc so that it didn't attempt to recompile the module, so the information in .hi and .o files is sufficient. But ghc insists on having the .hs file around, and I didn't find a way to turn it off. Is there any? Or there is a specific reason not to allow this?

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question about PutM patterns
by Alexander V Vershilov 23 Mar '13

23 Mar '13

Hello, cafe. I have a big problem using builders, so currently I'm using own builder based on Nettle one [1]. It uses Strict bytestring to build into and unchecked writes, thus it's very unsafe, plus other builders/PutM, developed rapidly so I like to switch to another one. However I use some patterns that seems not implemented in other builders, so I'd like to hear advices how to implement it there or how I can write code without using them. All of the patterns is done in order to have more performance and gives a way to build complex data without additional allocations. 1). Delayed input: This unsafe pattern can be implemented in any PutM monad for any constant sized value, the idea is that we write a plaseholder and returns a funtion that will write correct value to the address when applied. This pattern is needed when we need to update length or CRC sum after content is written: > test1 put = delayedWord16be >>= \ph -> someOtherStuff >> undelay ph calculateCRC 2). LookAhead: Sometimes I need to know the length of the content to be written, possibly I can write content to ByteString, and calculate length and write it, however if resulting type is not LBS it leads to additional allocations and memory move. For PutM a special wrapper can be written withLength :: a {- length type -} -> PutM () -> PutM (). Or special data structure and delayed input can be used, special data structure is Marker, it marks a place in datastructure allowing to calculate distances, it works very efficiently with ByteString, but I have no idea how to implement it with LBS: > test1 put = delayedWord32be >>= \ph -> marker -> \m -> put >> distance m >>= undelay . fromIntegral 3). LookBehind Returning back to crc calculation I had to use additional pattern, it's a lookback: I need to inspect unfinished data, that I've already have written, I have not done correct wrappers so I've used markers and fromForeignPtr from ByteString.Internal: > test3 = do > m <- marker > somestuff > d <- distance marker > let crc = (unsafePerformIO $ BS.unsafePackAddressLen hlen' (toAddr m)) -- Alexander

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Tutorials at Commercial Users of Functional Programming 2013
by Simon Thompson 22 Mar '13

22 Mar '13

There's still time to submit a tutorial proposal for Commercial Users of Functional Programming in Boston … http://cufp.org/cufp2013-call-tutorials Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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