Re: [Haskell-cafe] Monadic style with Streams (as in Data.Array.Parallel.Stream)
Roman Leshchinskiy wrote: On 16/05/2010, at 11:54, Mark Wassell wrote: Hi, This possibly might go against the spirit of what Stream programming is about but I having difficulties converting an imperative algorithm [1] into Haskell and think it would be easier if I was able to write it in a monadic style with operations to read and write from and to the streams. I first tried to approach it by delving into the innards of other Stream functions to devise what I needed. I only got so far and the sticking point was defining the Monad. I then approached it from the Monad side and although what I have is workable, it probably isn't going to perform (for one it uses fromStream and tailS on each read off the front of the stream). Data.Array.Parallel.Stream serves only one purpose: to represent loops produced by DPH in such a way that the compiler is able to optimise them well. Putting a monad on top of that will very very likely break this. To be honest, I'm not sure why you need the monad anyway. I would expect compression/decompression to be pure functions of type Stream Word8 - Stream Word8. In any case, I would urgently recommend not to use Data.Array.Parallel.Stream for anything at this point. This whole subsystem will soon die of old age and be replaced by the much nicer stuff from package vector, specifically Data.Vector.Fusion.Stream and Data.Vector.Fusion.Stream.Monadic. Note that the latter implements monadic streams as described in http://www.cse.unsw.edu.au/~rl/publications/recycling.html. Perhaps those can be useful for you if you really need a monad. Roman Thanks. No, I don't need a Monad and I suspected it was a bad idea. It was really needed for convenience as all I had to go on was a C implementaiton of arithmetic coding (which included a getc part-way through the code block which I hoped to map to something like a get from the stream). However thanks to Stephen I have something better to work from. I will also take a look at Data.Vector.Fusion.Stream. Cheers Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Monadic style with Streams (as in Data.Array.Parallel.Stream)
Hi, This possibly might go against the spirit of what Stream programming is about but I having difficulties converting an imperative algorithm [1] into Haskell and think it would be easier if I was able to write it in a monadic style with operations to read and write from and to the streams. I first tried to approach it by delving into the innards of other Stream functions to devise what I needed. I only got so far and the sticking point was defining the Monad. I then approached it from the Monad side and although what I have is workable, it probably isn't going to perform (for one it uses fromStream and tailS on each read off the front of the stream). So: 1. Is this monadic style within the spirit of what Stream programming is about? 2. Is there anyway to do this more elegantly and without the user of fromStream and tailS, for example. This is the workable solution I have: module StreamMonad where import Data.Array.Parallel.Stream import Data.Monoid import Control.Monad.Writer import Control.Monad.State instance Monoid (Stream a) where mempty = emptyS mappend = (+++) type SM a b c = StateT (Stream a) (Writer (Stream b)) c readS :: SM a b a readS = do s - get let a = head $ fromStream s put $ tailS s return a writeS :: b - SM a b () writeS x = tell $ singletonS x t1' :: SM (Int,Int) Int () t1' = mapM_ (\_ - do (x,y) - readS writeS x writeS y) [1..2] t1 = fromStream $ snd $ runWriter $ runStateT t1' $ toStream [(1,2),(3,4)] -- At least this works .. t2 = fromStream $ snd $ runWriter $ runStateT t1' $ toStream [(2*x-1,2*x) | x - [1..] ] Cheers Mark [1] The arithmentic coding and decoding algorithms given in http://mattmahoney.net/dc/dce.html#Section_32 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] MonadPlus or Alternative or ...?
Check the laws that instances of MonadPlus and Alternative should comply with to help you make your decision. Cheers Mark Sean Leather wrote: I want to generalize a set of functions from lists to some functor type. I require the following three operation types. f a a - f a f a - f a - f a Should I choose MonadPlus and use these? mzero return mplus Or should I choose Alternative and use these? empty pure (|) Or should I make my own class? Or is there another option? Thanks, Sean ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] games of chance
Take a look at: http://hackage.haskell.org/package/probability and http://web.engr.oregonstate.edu/~erwig/pfp/ Mark Dupont Corentin wrote: Hello, are you aware of a framework to find probabilities in a given game of chance, in Haskell? l would like to compute probabilities like: roll 3 dices, sum the result, then roll 3 other dices, sum the result, what is the probability to obtain the same sum? Cheers, Corentin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Collection of sets containing no sets which are a subset of another in the collection
Hi, I am looking for a data structure that will represent a collection of sets such that no element in the collection is a subset of another set. In other words, inserting an element that is already a subset of another element will return the original collection, and inserting an element that is a superset of any elements will result in a collection with the superset added and the subsets removed. What I have so far is the below but I am wondering if there has been any prior work on this (particularly using Haskell but also conceptual work). Inserting a set that is a subset is easy to handle, inserting a superset and remove subsets of it is a little tricker. Cheers Mark module SetTrie where -- -- A set of sets which does not contain elements which are subsets of any other element. -- ie insert a element which is a proper subset of another set returns the same set of sets --insert a element which is a proper superset of one or more elements causes those elements to be removed -- (and the first element to be added) -- import Data.Set hiding (toList,singleton,map,insert) import Data.Map hiding (fromList,showTreeWith,toAscList,toList,singleton,map,insert) import qualified Data.Map as M (toList,fromList,lookup,insert) import qualified Data.Set as S (toList,fromList) -- Normally we would have a flag at a node to indicate a subset is there, but we -- don't store subsets. data SetTrie a = Leaf [a] | Node (Map a (SetTrie a)) deriving (Show,Eq) singleton :: Ord a = Set a - SetTrie a singleton = Leaf . S.toList toList' :: Ord a = SetTrie a - [[a]] toList' (Leaf xs) = [xs] toList' (Node m) = concatMap (\(x,y) - map (x:) (toList' y)) $ M.toList m toList :: Ord a = SetTrie a - [Set a] toList x = map S.fromList $ toList' x insert :: Ord a = SetTrie a - Set a - SetTrie a insert t s = insert' t $ toAscList s insert':: Ord a = SetTrie a - [a] - SetTrie a insert' (Leaf (y:ys)) (x:xs) = Node (M.fromList [(y,Leaf ys),(x,Leaf xs)]) insert' (Node m) (x:xs) = case M.lookup x m of Nothing - case xs of [] - Node $ M.insert x (Leaf xs) m _ - Node $ M.insert x (Leaf xs) m Just t' - case xs of [] - Node m _ - Node $ M.insert x (insert' t' xs) m -- removeSubsets :: -- terminate (Node m) = Node mTrue m -- terminate (Leaf (x:xs)) = Node True (M.fromList [(x,Leaf xs)]) s1 = fromList [1,2,3,5,2] s2 = fromList [2,3,5] t1 = Node (M.fromList [(1,Leaf [2]),(3,Leaf [5]),(2,Node (M.fromList [(4,Leaf [6])]))]) t2 = insert (singleton (S.fromList [1])) $ S.fromList [1,2,3] t3 = insert t1 $ S.fromList [2,4,7] t4 = insert t2 $ S.fromList [1] t5 = insert t3 $ S.fromList [2,5] t6 = insert t5 $ S.fromList [2,4] -- Now add a superset of everything t7 = insert (singleton (S.fromList [8])) $ S.fromList [1,2,3,4,5,6,7,8,9] Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Converting typeset mathematics into Haskell ?
Does anyone know of any papers or projects, either for Haskell or any other language, that relate to what I am going to attempt to describe in the following: Go to any paper or book that includes some amount of calculation type mathematics. An example is the formula in the Description section of http://en.wikipedia.org/wiki/K-means_clustering. Think about how you would convert this into Haskell. You might then find yourself wondering why you have to convert it into Haskell at all. Given that most mathematics online is typeset using something like latex or mathml, why can't we parse this typesetting and convert it into Haskell code? In all likelyhood the conversion might be ambiguous so some rules might be needed to guide the conversion. Furthermore, if there are editors that allow you to edit these sorts of equations in a wysiwyg style, why not leverage these to edit the Haskell+Math code also in a wysiwyg style. I think this goes to the larger question of why are most programming languages (or to be more exact the way we write programs in those languages) is still based around a linear sequence of tokens rather than something that is more 2D (there is still some linearity as even in math formula there is still a top down and left to right flow). Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Using -Nx Option with GHC
Hi, I am trying to compile and run my program so that it utilises more than one core on my machine. I have looked at http://haskell.org/haskellwiki/Shootout/Parallel/BinaryTrees and am using parMap at a point in my code. I compile with ghc --make -O2 -threaded and run with the options +RTS -N5 The runtime complains that it doesn't understand the N option. I am running 6.10.4 on Windows XP. Cheers Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Using -Nx Option with GHC
That did it, thanks. Neil Mitchell wrote: Hi Mark, I compile with ghc --make -O2 -threaded That should work - try deleting all .o/.obj files and the executable and trying to compile again. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hsmagick crash
Have you tried http://hackage.haskell.org/cgi-bin/hackage-scripts/package/pngload ? Mark Ron de Bruijn wrote: Hi, I am trying to extract the image data from various file formats and it appeared that hsmagick would be the right package to use. However, it doesn't actually work or I use it incorrectly. If you have installed hsmagick and change the value of some_png_file to some existing png file, you should see that it crashes at some random pixel. For the particular 256*256 image I had, it crashed on pixel_nr `elem` [54,56,57]. I am open to suggestions for better ways to get a Array (Int,Int) RGB from e.g. a png file. import Graphics.Transform.Magick.Images import Graphics.Transform.Magick.Types import Foreign.Storable import Control.Monad image_file_name_to_2d_array file = do himage - readImage file let ptr_to_image = image himage himage_ - peekElemOff ptr_to_image 0 let bounds@(_rows, _cols) = (rows himage_,columns himage_) number_of_pixels = fromIntegral _rows * fromIntegral _cols mapM (\pixel_nr - do putStrLn (Pixel: ++ show pixel_nr) pixel_packet - liftM background_color_ $ peekElemOff ptr_to_image pixel_nr let red_component = red pixel_packet putStrLn (Pixel packet: ++ show red_component) return red_component) [0.. number_of_pixels - 1] some_png_file = foo.png t = do initialize_image_library image_file_name_to_2d_array some_png_file initialize_image_library = initializeMagick Best regards, Ron de Bruijn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Function Returning Type?
To the original poster: next time, just leave the function definition without the signature and query GHCi for the correct type: Remember that the type checker is your friend; let it work for you :) Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: vacuum-cairo: a cairo frontend to vacuum for live Haskell data visualization
Great work. However I am have a problem running on windows - it needs librsvg: Prelude System.Vacuum.Cairo view [1] Loading package mtl-1.1.0.2 ... linking ... done. Loading package parallel-1.1.0.0 ... linking ... done. Loading package glib-0.10.0 ... linking ... done. Loading package cairo-0.10.0 ... linking ... done. Loading package svgcairo-0.10.0 ... can't load .so/.DLL for: librsvg-2-2 (addDLL: could not load DLL) Prelude System.Vacuum.Cairo Anyone know where I can get this? I have googled around and whilst there is the librsvg development site, there is no sign of a windows DLL. All I can find is some generic site which seems to provide DLLs. I don't trust it. Cheers Mark Don Stewart wrote: I am pleased to announce the release of vacuum-cairo, a Haskell library for interactive rendering and display of values on the GHC heap using Matt Morrow's vacuum library. This library takes vacuum's output, generates dot graph format from it, renders it to SVG with graphviz, and displays the resulting structure using the gtk2hs Cairo vector graphics bindings ... all at the GHCi command line. This tool is useful for examining Haskell data structures as they are represented directly in the heap. In particular, it makes sharing visible for the first time, as well as unboxed values. It should be useful for teaching Haskell, or for library authors debugging the design of their data structures. You can see pictures of the rendered display here: http://code.haskell.org/~dons/images/vacuum/intmap.png And youtube screencasts of vacuum-cairo in action: http://www.youtube.com/watch?v=oujaqo9GAmA Get it: cabal install vacuum-cairo And on Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/vacuum-cairo -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Problem with cabal-install where package requires* mutually exclusive versions of another package
I am trying install a package using cabal-install however the package requies an older version of QuickCheck and one of the required packages requires the latest version: $ cabal fetch Reactive Resolving dependencies... cabal.exe: cannot configure Stream-0.3.1. It requires QuickCheck =2.0 For the dependency on QuickCheck =2.0 there are these packages: QuickCheck-2.1 and QuickCheck-2.1.0.1. However none of them are available. QuickCheck-2.1 was excluded because checkers-0.1.3 requires QuickCheck 2.0 QuickCheck-2.1 was excluded because reactive-0.10.5 requires QuickCheck 2.0 QuickCheck-2.1.0.1 was excluded because checkers-0.1.3 requires QuickCheck 2.0 QuickCheck-2.1.0.1 was excluded because reactive-0.10.5 requires QuickCheck 2.0 How can I get around this? I could work around this and install the packages individually. Can I have two versions of a package installed (ie QuickCheck) and will everything get resolved correctly? Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Physics engines purely in Haskell?
Has anyone thought about or embarked on the task of developing a 2D or 3D physics engine purely in Haskell? There is Hipmunk but I'm wondering about a purely Haskell implementation; possibly a port of Chipmunk to Haskell. Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ghc-6.11 + OpenGL/GLUT crashes on WinXP
Hi, Works here: Windows XP SP 3 ghc-6.10.20081007 glut32 from http://www.xmission.com/~nate/glut.html Don't know if this will help: DLLS loaded glut32.dll0x10000x38000C:\WINDOWS\glut32.dll opengl32.dll0x5ed00xcc000C:\WINDOWS\system32\opengl32.dll glu32.dll0x68b20x2C:\WINDOWS\system32\glu32.dll ddraw.dll0x73760x4b000C:\WINDOWS\system32\ddraw.dll dciman32.dll0x73bc0x6000C:\WINDOWS\system32\dciman32.dll msvcrt.dll0x77c10x58000C:\WINDOWS\system32\msvcrt.dll advapi32.dll0x77dd0x9b000C:\WINDOWS\system32\advapi32.dll rpcrt4.dll0x77e70x92000C:\WINDOWS\system32\rpcrt4.dll gdi32.dll0x77f10x49000C:\WINDOWS\system32\gdi32.dll secur32.dll0x77fe0x11000C:\WINDOWS\system32\secur32.dll kernel32.dll0x7c800xf6000C:\WINDOWS\system32\kernel32.dll ntdll.dll0x7c900xaf000C:\WINDOWS\system32\ntdll.dll user32.dll0x7e410x91000C:\WINDOWS\system32\user32.dll Some of the versions opengl32.dll OpenGL DLL (Microsoft) Version 5.01.2600.5512 glu32.dll OpenGL Utility Library DLL (Microsoft) Version 5.01.2600.5512 ddraw.dll - DirectDraw (Microsoft) 5.03.2600.5512 dciman32.dll - DCI Manage (Microsft) 5.01.2600.5512. glut32 had no version info. DirectX 9.0c (always thought OpenGL and DirectX were orthogonal but ddraw.dll is being used). Mark Conal Elliott wrote: No display lists. The crash happens during the GLUT call initialize. I can trigger it from ghci with the following simple incantation: Prelude import Graphics.UI.GLUT Prelude Graphics.UI.GLUT initialize foo [] And no trouble under ghc 6.9.20080622. Stumped. :( - Conal On Tue, Oct 28, 2008 at 3:14 PM, Jefferson Heard [EMAIL PROTECTED] mailto:[EMAIL PROTECTED] wrote: Conal, are you using display lists at all? I've had problems with allocating lists, but you seem to be able to leave off the allocation step in Windows on nVidia cards so long as you're careful not to conflict names yourself. On Tue, Oct 28, 2008 at 4:03 PM, Matti Niemenmaa [EMAIL PROTECTED] mailto:[EMAIL PROTECTED] wrote: Conal Elliott wrote: I am using glut32 rather than freeglut (and no need for patching the darcs GLUT). I wonder if glut32-vs-freeglut could account for crash-vs-nocrash on 6.10 and 6.11 but not 6.9. I'd love to hear from someone on Windows and glut32. Windows XP with SP3 ghc-6.10.20081007 glut32 Works fine for me. Taking a look at my GL headers, I did have to mess with at least glut.h to get something to work---whether it was to build HOpenGL, to make programs linkable, or to make them runnable, I'm not sure. In any case, what I did was force GLUTAPIENTRY to be #defined as __stdcall. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org mailto:Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- I try to take things like a crow; war and chaos don't always ruin a picnic, they just mean you have to be careful what you swallow. -- Jessica Edwards ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org mailto:Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Minim interpreter
Hugh Perkins wrote: That works just fine as long as the only thing eval has to cope with is print statements (so eval has type IO ()), but I'm guessing the clean solution is to thread a Map.Map through that somehow? You could do that but your code starts to become messy and you'll hit other limitations. The standard approach to this problem is to use a State monad. Since you are already using one monad, IO, you can can stack the monads using Monad transformers which makes them both available (although you will need to use liftIO, see below) import Control.Monad import Control.Monad.State import Data.Map type Env = Map String String type InterpM = StateT Env IO eval :: a - InterpM t instance Eval Print where eval (Print value) = liftIO $ putStrLn value You access and store the state using get and put. For example: eval (Variable s) = do s - get lookup the value and return it. There is a paper on using Monads with interpreters (http://web.cecs.pdx.edu/~mpj/pubs/modinterp.html) and an example described at http://www.haskell.org/haskellwiki/Libraries_and_tools/HJS. Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Frag
Donald Bruce Stewart wrote: jon: I just stumbled upon this fast action 3D shooter written entirely in Haskell: http://haskell.org/haskellwiki/Frag After 15 minutes trying to build it I find that it segfaults. Can anyone else get this to work? Likely depends on your OpenGL version, and possibly even graphics card. It's not been updated in about a year and half, but last time I tried it, it worked fine. Anyone with a bit more OpenGL-fu able to test it against current HOpenGL? Builds easily and works for me with GHC 6.6.1 on widows (though). You need to specify a level when running it and you will get a series of messages about loading textures before the window appears. Does it get this far? Cheers Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] SWIG with Haskell ?
Hello, Has anyone got any pointers on using SWIG with Haskell to integrate a C++ library? For the library there other language bindings, so I am in a position to leverage off these. In general what are the particular issues with C++ and Haskell. One obvious one is management of object lifecycle - making sure the object stays around long enough but doesn't out stay its welcome. Is using ForeignPtr sufficient? Cheers Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Happy outputs parE - ideas on what to change in my .y file?
Sometimes happy outputs 'parE' when I run it on my .y file? I believe it is coming from a part of Grammer.lhs which has the comment line This bit is a real mess, mainly because of the error message support. Are there any suggestions on what to change in my .y file to get over this? Thanks Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Composing monads (sort of)
Hi, I have a set of functions: f1 :: DBRecord - Maybe Int f2 :: Int - IO Maybe DBRecord f3 :: DBRecord - Maybe Int The odd numbered functions are field accessors, accessing a field that might hold an identifier for another record. The even numbered functions are record fetch functions that get records from the database. I want to compose these so that I can navigate structures of joined records in the database. How can I concisely compose these functions without having to write a cascade of case statements such as: case f1 rec1 of Nothing - return Nothing Just id1 - do rec2 - f2 id2 return $ case rec2 of Nothing - return Nothing Just rec2' - case f3 rec2' of I understand that if I was just dealing with Maybe I could use the fact that Maybe is a monad. I am also not sure if composing the IO and the Maybe will get me what I want (some of the functions only return Maybe Int). Cheers Mark PS Heard this on the 'West Wing' and thought it was appropriate in a way: A coach goes up to a player and asks Are you ignorant or apathetic?. The player replies I don't know and I don't care. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I'd like start with Haskell, but...
Hi, Take a look at http://www.haskell.org/haskellwiki/HGene which uses HSQL and Gtk2hs. I don't have any code to release yet - only parts work and the code is in an extreme state of flux; I am currently refactoring (see my post on monads). More generally you might be interested in the other page that I have started http://www.haskell.org/haskellwiki/Enterprise_Haskell Mark Duncan Coutts wrote: On Sat, 2006-12-16 at 19:50 +0100, Waldemar Biernacki wrote: Hello! I'd like to start programming in Haskell. But as an industry programmer I have a hope to use Haskell in my every-day work. Big part of my every-day work are GUI applications (in MS-Windows) working with SQL databases (PostgreSQL on Linux servers). My question: Is there a TRUE possibility to use Haskell for such applications? Is anybody there who have ANY experience in the field? If answer would be positive what GUI+database libraries could be used in such a case? I don't actually know of anyone using one of the GUI libs in combination with one of the DB libs. It's an obvious thing to do but you'll not find a lot of pre-existing examples or infrastructure to help you. That's certainly one of the use cases that we're aiming for in the Gtk2Hs project with our new api for the list/tree widget system. We can now more easily implement the data model in Haskell so the obvious thing to try would be a model based on a DB query. We're aiming for a Gtk2Hs release with this new api before xmas. For databases there are three major libs you could use, HDBC, HSQL, and HaskellDB. HSQL and HDBC are in essentially the same niche, they provide a common medium level api to a bunch of different db backends. They work at the level of taking SQL strings and returning result sets. HaskellDB is a higher level library (that can use HDBC or HSQL). It provides a type safe way of constructing queries (and internally generates SQL). So personally what I'd try would be Gtk2Hs+HDBC or Gtk2Hs+HDBC+HaskellDB. I've seen some GUI libraries web pages, but they seem to be NOT maintenanced any more. There are several GUI libs that were started but not maintained. The main ones that are maintained are Gtk2Hs and wxHaskell. For platform support you're fine, all those DB libs support PostgreSQL and both GUI libs support Windows, Linux and others. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
