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Haskell in Web Browser: draft tutorial
by Dimitry Golubovsky 26 Mar '08

26 Mar '08

Hi, I have written a draft of the tutorial on Haskell programming for client side of Web applications (related to Yhc/Javascript backend): http://www.haskell.org/haskellwiki/Haskell_in_web_browser Any feedback, suggestions, and additions (like your own code examples) are welcome. Thanks. PS This part of the Tutorial does not cover XMLHTTP programming; this is yet to be written, but there is Haddock documentation under http://www.golubovsky.org:5984/_utils/yhcws/index.html Yhc web service online (where you may experiment with your code): http://www.golubovsky.org:5984/static/yhcws/MainGUI.html Users guide: http://www.haskell.org/haskellwiki/Yhc_web_service -- Dimitry Golubovsky Anywhere on the Web

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Gtk2hs on GHC6.8.2?
by Ryan Ingram 26 Mar '08

26 Mar '08

The WinXP binary release of Gtk2hs won't install for me; it seems to expect GHC6.8.1 and refuses to install on 6.8.2. Is there any significant difference in the compilers that would cause it not to work on 6.8.2? Is there a way I can trick it into installing? I really don't want to have to build from source. I've had nothing but trouble trying to get large projects to build within cygwin/mingw/msys. -- ryan

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Parsec (Zero or One of)
by Paul Keir 25 Mar '08

25 Mar '08

Hi, I'm having some difficulty using the Parsec library, perhaps you could help. I've reduced my problem as shown below. I would like the 'only_prod' parser to require the reserved string "only", _optionally_ followed by an identifier. As part of 'mytest', this should then be followed by the reserved string "end". mytest = do { only_prod; end } only_prod = do { reserved "only"; try identifier } end = reserved "end" i.e. I'd like both > parseTest mytest "only end" and >parseTest mytest "only green end" to parse successfully. As it stands, only the second is successful. The first fails with: parse error at (line 1, column 9): unexpected end of input expecting letter or digit or "end" Does anyone have an idea how I could repair the situation? Thanks in advance, Paul

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True parallelism missing :-(
by Dusan Kolar 25 Mar '08

25 Mar '08

Dear all, I've thought the following three (dummy) programs would run some of their parts in parallel (on dual core) if compiled with option threaded (smp). The truth is that only the first one exploits multicore CPU. Why? Moreover, using RTS option -sstderr makes runtime not to evaluate in parallel even for the first program. Why? Thanks for tips Dusan My arch: Linux pcx 2.6.24-ARCH #1 SMP PREEMPT Sun Feb 10 15:44:59 CET 2008 x86_64 Intel(R) Core(TM)2 CPU 6600 @ 2.40GHz GenuineIntel GNU/Linux My ghc: The Glorious Glasgow Haskell Compilation System, version 6.8.2 /64bit, binary distro for FC/ ---------------------------------------------------- Prog 1: module Main() where import Control.Parallel import Control.Parallel.Strategies fibs :: Integer -> Integer fibs n | n > 1 = fibs (n-1) + fibs (n-2) | n == 1 = 1 | True = 0 fib n = if n<0 then error "Negative input to fib!" else f1+f2 where [f1,f2] = parMap rnf fibs [(n-1),(n-2)] main = do putStrLn "Starting..." putStrLn $ "Fib 43: " ++ show (fib 43) putStrLn "Done!" ---------------------------------------------------- Prog 2: module Main() where import Control.Concurrent import Control.Concurrent.MVar fibs :: Integer -> Integer fibs n | n > 1 = fibs (n-1) + fibs (n-2) | n == 1 = 1 | True = 0 fib n = if n<0 then error "Negative input to fib!" else do v1 <- newEmptyMVar v2 <- newEmptyMVar h1 <- forkIO $ putMVar v1 $ fibs (n-1) h2 <- forkIO $ putMVar v2 $ fibs (n-2) f1 <- takeMVar v1 f2 <- takeMVar v2 killThread h1 killThread h2 return (f1+f2) main = do putStrLn "Starting..." f <- fib 43 putStrLn $ "Fib 43: " ++ show f putStrLn "Done!" ---------------------------------------------------- Prog 3: module Main() where import Control.Concurrent import Control.Concurrent.MVar fibs :: Integer -> Integer fibs n | n > 1 = fibs (n-1) + fibs (n-2) | n == 1 = 1 | True = 0 fib n = if n<0 then error "Negative input to fib!" else do v1 <- newEmptyMVar v2 <- newEmptyMVar h1 <- forkOS $ putMVar v1 $ fibs (n-1) h2 <- forkOS $ putMVar v2 $ fibs (n-2) f1 <- takeMVar v1 f2 <- takeMVar v2 killThread h1 killThread h2 return (f1+f2) main = do putStrLn "Starting..." f <- fib 43 putStrLn $ "Fib 43: " ++ show f putStrLn "Done!"

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ANNOUNCE: Haskell Server Pages v 0.4
by Niklas Broberg 25 Mar '08

25 Mar '08

Greetings fellow Haskelleers, I am very pleased to announce a new chapter in the Haskell Server Pages saga. After a two-year long hiatus, while we in the team have been busy with Other Stuff, we have resumed work on Project HSP, and this release marks the first milestone. ================= === Project HSP === ================= Haskell Server Pages (HSP) is a programming model for writing dynamic web pages in Haskell, both server-side and client-side. One of its core features is the use of literal XML syntax mixed with ordinary Haskell code. * Project HSP home (with bug/feature tracker): http://code.google.com/p/hsp * Project HSP mailing list: haskell-server-pages(a)googlegroups.com * Project HSP darcs repos: http://code.haskell.org/HSP For flavor, here is a simple Hello World application written in HSP: ----- module HelloWorld where import HSP import HSP.HJScript import HJScript import HJScript.DOM -- A simple HTML page holding a button with onClick action. page :: HSP XML page = <html> <head> <title>Hello World</title> </head> <body> <% <button>click</button> `onClick` (window # alert (string "Hello World !")) %> </body> </html> ----- Note that literal XML elements are first class expressions in HSP, unlike languages like PHP. Also note that using literal XML syntax is by no means required, if you don't feel like writing the XML manually (I sure don't!). There are combinators for building XHTML pages (although they are currently missing from version 0.4, will be added shortly, but release early and all that...). The most interesting new feature in version 0.4 is that literal XML syntax (or the equivalent combinators) can now be used to create XML elements both server-side and client-side, with the same code. Here is another short example script showing this feature: ------------------ module AddParagraph where import HJScript hiding (test) import HJScript.DOM import HSP import HSP.HJScript makeP x = <p><b><% x %></b></p> page :: HSP XML page = <html> <head><title>Add paragraph</title></head> <% do (r,b) <- ref <body><% makeP "Paragraph created Server-side!" %></body> let fun = do let x = document # getElementById (string r) x <: makeP "Paragraph created Client-side!" return () b <: (<button>Click Me!</button> `onClick` fun) %> </html> -------------------- Project HSP v 0.4 consists of a set of packages with related functionality: == package hsx == Haskell Source with XML (HSX, hsx) is a package that contains everything pertaining to literal XML syntax. In particular it contains a) the trhsx preprocessor that translates hsx source files into vanilla Haskell, and b) modules defining the functions that are injected by trhsx. It also nominally contains generic combinators for creating values of the same types as the literal XML syntax, though these modules are not present in 0.4. darcs get --partial http://code.haskell.org/HSP/hsx http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsx-0.4 == package hsp == The core HSP package defines the datatypes and functions for writing server-side dynamic web pages. Also defines how to use the HJScript functionality in HSP pages, to allow for client-side dynamics as well. darcs get --partial http://code.haskell.org/HSP/hsp http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsp-0.4 == package HJavaScript == This package defines an abstract syntax and (not-so-)pretty printer for a large subset of JavaScript, as Language.HJavaScript. However, a significant difference from JavaScript is that HJavaScript is typed, even on the abstract syntax level using GADTs. The subset of JavaScript that is supported is those parts that lend themself to typing (i.e. no prototyping of classes). darcs get --partial http://code.haskell.org/HSP/hjavascript http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HJavaScript-0.4 == package HJScript == HJScript is a DSL built on top of HJavaScript, for writing client-side dynamic web pages. The programming model is fairly low-level, resembling the actual JavaScript code quite a lot, but should be easy to extend with higher-level functionality. Notable is that HJScript supports the use of literal XML syntax for creating DOM ElementNodes. Also notable is that HJScript supports Ajax functionality. HJScript and HJavaScript can be used independently of HSP, for creating JavaScript code. darcs get --partial http://code.haskell.org/HSP/hjscript http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HJScript-0.4 == package hsp-cgi == Run HSP pages as CGI scripts. darcs get --partial http://code.haskell.org/HSP/hsp-cgi http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsp-cgi-0.4 (Note: Earlier versions of HSP have come with a server application, hspr, providing the runtime environment for HSP. As of 0.4, this server has been discontinued and should be considered deprecated.) ===================== Notable items on the TODO list for Project HSP: - More functionality, allowing for higher-level programming models. - Writing larger applications, in order to stress test, and serve as inspiration for higher-level functionality. - Integrate with HAppS, to allow stateful computation (among other things). - A home on the web for HSP, with a web page written in HSP. We welcome both users (of course) and contributors to the project. There is much work to be done, and we welcome all help we can get. If you think this is interesting stuff, drop by our mailing list (haskell-server-pages(a)googlegroups.com) Like to do web programming in Haskell? Want to do a GSoC project? We in the project would be happy to see applications for HSP projects, and the list above is a good starting place. See for instance (http://hackage.haskell.org/trac/summer-of-code/ticket/1538) and (http://hackage.haskell.org/trac/summer-of-code/ticket/1539) Cheers, /Niklas on behalf of the Project HSP team

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separate input calculation output
by Thomas Engel 25 Mar '08

25 Mar '08

Hello, I'm new to haskell and want to write a small program for some winder calcucations. I want to input 10-15 values and based on this input doing some calculations. After this calculations I want to print out the results. My problem is: How can I get the input values into the calculations and back the result to the output. In an other language I would use global variables for this. So what should I use in haskell? An other point is that I want to separate the input from the calculations and the output. How can I achieve this with haskell? Modules? Data types? See some pseudo code below. inputvalues :: IO() inputvalues = do hSetBuffering stdout NoBuffering putStr "Berechnung Bremsgenerator \n\n" ve <- readNum "Bitte Maschinengeschwindigkeit (m/min) angeben: " de <- readNum "Bitte Durchmesser der vollen Rolle eingeben (mm): " dewalze <- readNum "Bitte Durchmesser der Walze eingeben (mm): " dewand <- readNum "Bitte Wandstaerke der Walze eingeben (mm): " and so on .............. readNum :: String -> IO Float readNum text = do putStrLn text readLn -- calculations nvr :: Float-> Float-> Float nvr ve de = ve / de /pi *1000 pzugmin :: Float-> Float-> Float->Float pzugmin ve femin be = 1.666 * ve * femin * be * 0.00000001 pzugmax :: Float-> Float-> Float->Float pzugmax ve femax be = 1.666 * ve * femax * be * 0.00000001 and so on .............. outputvalues = do putStr "\n\nErgebnisse Bremsgenerator \n\n" putStr "Drehzahl leere Trommel: " putStr(show(round(nvr))) putStr " U/min \n" putStr "Drehzahl volle Trommel: " putStr(show(round(drehbgmax))) putStr " U/min \n" and so on ...................... Thanks Thomas

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getChar
by Cetin Sert 25 Mar '08

25 Mar '08

Hi, is there a version of getChar that doesn't buffer keyboard input until enter is pressed? specialReadln :: IO String specialReadln = do c ← getChar if c == '#' then do return [] else do cs ← specialReadln return (c:cs) I want the input process to terminate when '#' or any other specific key has been pressed. Best Regards, Cetin Sert

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Problem with OpenAL
by George Giorgidze 25 Mar '08

25 Mar '08

I tried OpenAL binding (the one which is on the Hackage), but with no luck. I can not hear anything from speakers and also according to generated output on console it seems that "AL.play" never completes playback of a buffer as buffer remains registered as "unprocessed" in OpenAL context. Here is the piece of code. I am not getting any error messages from OpenAL library functions. playOpenAL :: Int -> IO () playOpenAL sr = do mDevice <- AL.openDevice Nothing when (isNothing mDevice) $ error "opening OpenAL device" let device = fromJust mDevice mContext <- AL.createContext device [ AL.Frequency (fromIntegral sr) , AL.Refresh (fromIntegral sr) ] when (isNothing mContext) $ error "creating OpenAL context" let context = fromJust mContext AL.currentContext AL.$= (Just context) let sampleNumber = 256 bufSize = sampleNumber * (sizeOf (undefined :: CShort)) buf2 <- mallocBytes bufSize -- here I am filling buf2 with noise .... [source] <- AL.genObjectNames 1 [buffer] <- AL.genObjectNames 1 let region = AL.MemoryRegion buf2 (fromIntegral bufSize) AL.bufferData buffer AL.$= (AL.BufferData region AL.Mono16 (fromIntegral sr)) AL.queueBuffers source [buffer] AL.loopingMode source AL.$= AL.OneShot let waitForSource = do putStrLn "waiting" s <- AL.get (AL.buffersProcessed source) putStrLn $ show s s <- AL.get (AL.buffersQueued source) putStrLn $ show s state <- AL.get (AL.sourceState source) case state of AL.Playing -> do threadDelay 1024 waitForSource _ -> return () putStrLn "Start Playing ... " AL.play [source] waitForSource AL.currentContext AL.$= Nothing AL.destroyContext context b <- AL.closeDevice device when (not b) $ error "closing device" Is this library still maintained? Best, George

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How to program with sqlite?
by Deng Chao 25 Mar '08

25 Mar '08

Hi all, I'm learning sqlite, and as I know haskell has some libraries like HDBC or HSQL can access sqlite DB. Can anybody give me a small example to show how to use it? It will be very appreciate? Thanks! Best Regards, Deng Chao

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Random Monad
by Matthew Pocock 24 Mar '08

24 Mar '08

Hi, Who currently maintains the Random monad code? I have some patches to contribute. Matthew

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