- Haskell-Cafe - Haskell.org

[C Binding] Turning the mutable to immutable?
by Yves Parès 08 Jul '10

08 Jul '10

Hello, I don't know if some of you are familiar with the SFML library (stands for Simple and Fast Multimedia Library) --> http://sfml-dev.org As SDL, SFML is a 2D graphics library, but conversely to SDL it provides a hardware-accelerated drawing, through OpenGL. Well, I'm currently writing its Haskell binding, and I'm stuck with design issues. What I'm heading to is a full IO binding, and that's what I'd like to avoid. I particularly like the way HGL works, with the Draw monad which (IMO) enables powerful composability of the drawings. But HGL is simpler in the way that, for instance, it doesn't deal with images/sprites. So that's why I would like to pick up advice concerning the design of such a binding. First, this is how SFML (in C/C++) works: The main types are RenderWindow, Drawable, Image, Sprite, Shape, Font and Text. An Image basically represents an array of pixels. It is just a resource, and is not directly drawable. An image is loaded from a file, and provides methods for accessing/altering its pixels. Its main purpose is to be bound as an OpenGL texture. A RenderWindow is the window on which the Drawables are... well... drawn. A Sprite, now, is a Drawable. One Sprite is linked to one Image. A Sprite NEVER alters its Image, it just provides positionning/rotation/resizing/colorizing methods that will be translated, when drawing on the RenderWindow, to glTranslate/glRotate/glScale/glColor, etc. So we can see a Sprite as an instance of an Image, since if a same Image is to be drawn 3 times on the same frame, we are advised to create three Sprites of it, which will differ by their position. A Font is loaded from a file, it is a simple resource, just like Image. Text and Shape are Drawables. So, now, questions: 1) For those who know HGL, can the monad Draw principle be adapted to my case? Or am I heading for disaster? 2) How would I handle images? SFML API enables the user to alter the pixels of the image, and I obviously don't wanna copy the entire Image each time a pixel is changed. 3) Is there another library on hackage that handles images in a functional way? (I mean not *all in IO*)

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monadic design patterns for the web -- a 2 day, hands-on workshop
by Greg Meredith 07 Jul '10

07 Jul '10

Dear Haskellians, Biosimilarity and Stellar Scala Consulting will be running a 2 day workshop in Seattle in September on monadic design patterns for the web. You can get the details here <http://monadic.eventbrite.com/>. Best wishes, --greg -- L.G. Meredith Managing Partner Biosimilarity LLC 1219 NW 83rd St Seattle, WA 98117 +1 206.650.3740 http://biosimilarity.blogspot.com

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Adding new entry to list
by Mrwibbly 07 Jul '10

07 Jul '10

Hi all I'm having a problem trying to add a new record to a list. I need to be able to add a new record to the database. My code is below, I also need to work out the total sales for everything in the Sales list. As you can see, I've tried to do it but I can't seem to work it out. type Title = String type Artist = String type Sold = Int --type Record = (Title, (Artist, Sold)) type Sales = [(Title, Artist, Sold)] testDatabase :: Sales testDatabase = [("Kids", "MGMT", 3), ("This Charming Man", "The Smiths", 5), ("Gimme Shelter", "The Rolling Stones", 7)] totalSales :: Sales -> Title -> Artist -> Sold totalSales [] title artist = 0 --totalSales ((t,a,n):testDatabase) title artist = title artist --addSale :: Sales -> Sales --addSale (Title, Artist, sold) = (title, artist, sold + 1) --newRecord :: String -> String -> Sales -> Sales --newRecord testDatabase title artist = (title, artist) ++ testDatabase --newRecordAction :: Sales -> IO() --newRecordAction testDatabase = do --putStrLn "Enter a new title: " --title <- getLine --putStrLn "Enter an artist: " --artist <- getLine --return $ newRecord title artist testDatabase getTitle :: Sales -> Title getTitle (title,_) = title printNames :: Sales -> IO() printNames testDatabase = mapM_ print testDatabase mainLoop :: Sales -> IO() mainLoop testDatabase = do putStrLn "1 - Show all tracks in database" putStrLn "2 - Exit" putStrLn "" putStrLn "Please select an option:" input <- getLine case read input of 1 -> do putStrLn "------------------" putStrLn "Show All Tracks" putStrLn "------------------" printNames testDatabase putStrLn "" mainLoop testDatabase 2 -> do return () main :: IO() main = mainLoop testDatabase Thank you, Jack -- View this message in context: http://old.nabble.com/Adding-new-entry-to-list-tp29099032p29099032.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Re: [Haskell-cafe] Re: [Haskell] analogous functions in Sound.File.Sndfile
by John Lato 07 Jul '10

07 Jul '10

> From: stefan kersten <sk(a)k-hornz.de> > > following up on haskell-cafe ... > > > i just noticed though that the lazy versions don't work correctly because they > don't take closing the file handle into account properly. i think they should be > removed from the API, for incremental processing an iteratee interface would > probably be more appropriate. Incidentally I've been meaning to write an iteratee interface to hsndfile for some time. It would be an excellent fit, and it should be quite simple to implement. This would be a good small project for someone interested in audio and iteratees. John

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reading and playing music openAL
by Maria Gabriela Valdes 07 Jul '10

07 Jul '10

Hi ! We have a question about about openAL. We would like to know if anybody knows how to read a WAV file by chunks of a determined size, and after doing some processing with a specific chunk send that same chunk back to the sound card so we can play the whole WAV continiously (just like a music player). Thanks in advance, -- Maria Gabriela Valdes G. Linux Registered User #485743

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Re: [Haskell-cafe] finding the right mathematical model
by John Lato 07 Jul '10

07 Jul '10

If you ignore the identity mappings (which all technically create trivial loops), these mappings would form a directed acyclic graph (DAG). I would look at some of the graph libraries, e.g. fgl, to see if they have anything appropriate. John > From: G?nther Schmidt <gue.schmidt(a)web.de> > Hi list, > > the problem I have stems from the app I had developed. What my app does > is to split the money a hospital receives for a case to the departments > involved in a fair way. > > An additional requirement however was to allow the users of the app to > re-map any revenue shares credited to certain departments to other > departments. Such cases are sometimes due to politics within the > hospital and also have more legitimate reasons, like saying the > radiology should not receive shares for surgical procedures but those > shares should be redirected to the "General surgery" department. > > The feature is already implemented, but I'm not pleased with it, > especially since I did not develop a mathematical model for it. > > Details: > > It boils down to model mappings, or rather what sort of data structure > would be suited for this kind of thing. > > Dept A is "mapped" to itself > A -> A > > Dept B is mapped to Dept C > B -> C > > Dept C is mapped to Dept C > C -> C > > Dept D is mapped to Dept A > D -> A > > It should not be possible to construct looping mappings, ie. > > 1. A -> B > 2. B -> C > 3. C -> A > > ...... > > > What sort of model would be suitable to describe this, some sort of matrix? > > Günther

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analogous functions in Sound.File.Sndfile
by Maria Gabriela Valdes 07 Jul '10

07 Jul '10

Does anybody know what are the analogous functions and data types in the haskell library "Sound.File.Sndfile" of the libsndfile library in C ? data type : SNDFILE function: sf_open function : sf_read_short Thanks in advance, -- Maria Gabriela Valdes G. Linux Registered User #485743

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finding the right mathematical model
by Günther Schmidt 07 Jul '10

07 Jul '10

Hi list, the problem I have stems from the app I had developed. What my app does is to split the money a hospital receives for a case to the departments involved in a fair way. An additional requirement however was to allow the users of the app to re-map any revenue shares credited to certain departments to other departments. Such cases are sometimes due to politics within the hospital and also have more legitimate reasons, like saying the radiology should not receive shares for surgical procedures but those shares should be redirected to the "General surgery" department. The feature is already implemented, but I'm not pleased with it, especially since I did not develop a mathematical model for it. Details: It boils down to model mappings, or rather what sort of data structure would be suited for this kind of thing. Dept A is "mapped" to itself A -> A Dept B is mapped to Dept C B -> C Dept C is mapped to Dept C C -> C Dept D is mapped to Dept A D -> A It should not be possible to construct looping mappings, ie. 1. A -> B 2. B -> C 3. C -> A ...... What sort of model would be suitable to describe this, some sort of matrix? Günther

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Re: [Haskell-cafe] reading and playing music openAL
by Patai Gergely 07 Jul '10

07 Jul '10

Hello, > Hi ! We have a question about about openAL. We would like to know if anybody > knows how to read a WAV file by chunks of a determined size, and after doing > some processing with a specific chunk send that same chunk back to the sound > card so we can play the whole WAV continiously (just like a music player). The basic idea is that you have to define a source and repeatedly call queueBuffers on it. I wrote an OpenAL version of the Hemkay module player (example code without comments, with some horrible way to achieve double buffering can be found at [1]), which can be compiled if you have installed the hemkay-core package. Also, you might want to ask sound related questions on the Haskell art list [2]. Gergely [1] http://hpaste.org/fastcgi/hpaste.fcgi/view?id=27083 [2] http://lists.lurk.org/mailman/listinfo/haskell-art -- http://www.fastmail.fm - Does exactly what it says on the tin

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Debugging cause of indefinite thread blocking
by Ben Lever 07 Jul '10

07 Jul '10

Hi all, I am making use of the Data.Array.Repa module to achieve data-parallelism. On running my program I get the error: "thread blocked indefinitely on an MVar operation" Two questions: 1. What could be some of the potential causes for the above error when the only use of parallelism is Repa arrays? 2. What are the best strategies for debugging he cause(s) of such an error? Cheers, Ben. The information in this e-mail may be confidential and subject to legal professional privilege and/or copyright. National ICT Australia Limited accepts no liability for any damage caused by this email or its attachments.

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