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SOE code on Mac OS X Lion
by N. Raghavendra 24 Apr '12

24 Apr '12

I am trying to use code from the book `The Haskell School of Expression' on an iMac with Mac OS X Lion. I have installed the latest version of Haskell Platform (2011.4.0.0 64bit). I then followed step 1 on the Web page http://www.cs.yale.edu/homes/hudak/SOE/software1.htm, and did `cabal install GLFW'. There were no errors in the installation. Regarding step 2 in the instructions, I have downloaded SOE-20120121.zip, but don't know how to proceed further. The Web page says, "Note for OS X users: running graphics applications from GHCi is no longer supported. Instead, one has to compile a graphics program using GHC in order to run it (see example/GMIExamples.lhs for an example)." Also, SOE/src/Code.html says, "For MacOS X, unfortunately SOE cannot be run from under GHCi interactively due to problems with the Graphics library it uses. SOE programs must be compiled in order to run OS X. This means you have to export the main function from a particular module (by adding it to the module export list) and compile with command line: ghc -main-is=...." I am only trying to learn Haskell from SOE, and don't understand how to compile the SOE software with GHC. What precisely is the command that I should invoke in the Terminal for the compilation? I'd appreciate any help on compiling and using the SOE code. Thanks and regards, Raghavendra. -- N. Raghavendra <raghu(a)mri.ernet.in> | http://www.retrotexts.net/ Harish-Chandra Research Institute | http://www.mri.ernet.in/

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Announce: Hackager - new version of hackage-test
by David Terei 23 Apr '12

23 Apr '12

Hi all, I've updated the old hackage-test tool and renamed to hackager. http://hackage.haskell.org/package/hackager Hackager is a tool to automate the compiling of all packages on Hackage. It builds each package on hackage in isolation and records the results. The purpose being to catch regressions caused by changes to GHC (and Cabal although this was not the motivation). Two runs of Hackager can be compared, so the first run is done with a known version of GHC and the next run with a new, experimental version of GHC... ect. The improvements to Hackager over hackage-test are: * Parallelized the build process. Can now specify how many packages to build in parallel, which cuts total run time down greatly (e.g 2 days -> 5 hours) * hackage-test and hackage-report are now one tool, 'hackager' that works as a mutli-command tool. * Proper option handling * Fixed some stability issues The new homepage for development can be found here: https://github.com/dterei/Hackager Cheers, David

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The last statement in a 'do' construct must be an expression: a <- readArray arr (1, 1)
by KC 23 Apr '12

23 Apr '12

I'm getting the above error message and I cannot figure out why? buildPair = do arr <- newArray ((1,1),(1,10)) 37 :: ST s (STArray s (Int,Int) Int) a <- readArray arr (1,1) writeArray arr (1,1) 64 b <- readArray arr (1,1) return (a,b) main = print $ runST buildPair -- -- Regards, KC

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HaL-7, 2012-07-13, Call for submissions
by Henning Thielemann 23 Apr '12

23 Apr '12

Call for submissions and Save the date for our local Haskell Workshop in Halle/Saale, Germany. Tutorials, talks, demonstrations ... everything welcome. Workshop language is German (mainly), and English (by request). Submission deadline: May, 21, Workshop date: July, 13 Workshop homepage: http://iba-cg.de/hal7.html The complete call in German: ------------------------------------------------- Aufruf zum Einreichen von Beiträgen und Hinweis zum Vormerken des Termins Was: Haskell-Treffen HaL-7 Wann: Freitag, 13.07.2012 Wo: Institut für Informatik an der Martin-Luther-Universität in Halle an der Saale Wir suchen Vorträge zu Haskell im Besonderen und der funktionalen Programmierung im Allgemeinen, zum Beispiel zu den Themen * Neues von Sprache, Bibliotheken, Werkzeugen, * Anwendungen von Kunst bis Industrie, * Lehre an Schulen und Hochschulen, gerne aber auch zu anderen Themen. Die Beiträge können präsentiert werden als * Tutorium (60 .. 90 min) * Vortrag (30 min) * Demonstration, künstlerische Aufführung Die Veranstaltungssprache ist Deutsch, in begründeten Ausnahmen Englisch. Presentations will be given in German but we can switch to English if requested. Bitte reichen Sie Kurzfassungen der Beiträge ein (2 bis 4 Seiten), die dem Programmkomitee eine Einschätzung ermöglichen. Die Kurzfassung soll mit einer Zusammenfassung (10 Zeilen) beginnen und einem Literaturverzeichnis enden. Teilnehmer des Workshops sind Interessenten (keine Erfahrung mit Haskell/FP), Anfänger (wenig Erfahrung) und Experten. Wir bitten die Vortragenden, die Zielgruppe des Beitrags anzugeben und die nötigen Vorkenntnisse zu beschreiben. Bei Tutorien sollen Teilnehmer auf eigenen Rechnern arbeiten. Bitte beschreiben Sie dazu die vorher zu installierende Software. Schicken Sie Beitragsvorschläge als PDF-Dokument bis zum 21.05.2012 per Mail an hal-committee at iba-cg punkt de oder an ein Mitglied des Programmkomitees. Programmkomitee * Henning Thielemann - Univ. Halle (Vorsitzender), * Petra Hofstedt - BTU Cottbus, * Alf Richter - iba CG Leipzig, * Uwe Schmidt - FH Wedel, * Janis Voigtländer - Univ. Bonn, * Johannes Waldmann - HTWK Leipzig. Mit besten Grüßen Henning Thielemann

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(no subject)
by KC 23 Apr '12

23 Apr '12

buildPair = do arr <- newArray ((1,1),(1,10)) 37 :: ST s (STArray s (Int,Int) Int) a <- readArray arr (1,1) writeArray arr (1,1) 64 b <- readArray arr (1,1) return (a,b) main = print $ runST buildPair -- -- Regards, KC

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Is it only one data structure per ST monad?
by KC 23 Apr '12

23 Apr '12

Is it only one data structure per ST monad? -- -- Regards, KC

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Need feedback on my EDSL attempt for writing test scripts
by C K Kashyap 23 Apr '12

23 Apr '12

Dear cafe, Recently, I decided to use Haskell to drive the testing of a C++ DLL that we develop. After getting the FFI etc working, I thought it might be a good idea to expose an EDSL for the testers to alter the flow of invocations of the functions in the DLL. I've tried to demonstrate the approach I am contemplating here - http://hpaste.org/67495 The outcome is that I'll have a set of "Instructions" for the testers can arrange to create a sequence of calls. > data Command = Void | Init | Get3Numbers Int Int Int| GetName String | PrintName | PrintSum | Close | PrintMessage String > deriving (Show) > mainloop :: StateT (ScriptState Command) IO () > mainloop = do > liftIO $ putStrLn "Hello World" > executeCommand Init > executeCommand Init > executeCommand $ PrintMessage "Enter name" > executeCommand $ GetName "abcd" > return () I'd like to ensure that some level of validation done. For example, if Init is called twice, the tester should get to know about it. Similarly, GeName should not be called unless PrintMessage has been called. > executeCommand :: Command -> StateT (ScriptState Command) IO () > executeCommand Init = do > (ScriptState c) <- get > case c of > Void -> liftIO $ putStrLn (show c) > _ -> liftIO $ putStrLn "Init already called" > put (ScriptState Init) > return () > executeCommand (GetName x) = do > (ScriptState c) <- get > case c of > PrintMessage _ -> do { str <- liftIO $ getLine; put (ScriptState (GetName str)); return ()} > _ -> liftIO $ putStrLn "PrintMessage not called" > executeCommand (PrintMessage m) = do > liftIO $ putStrLn m > put (ScriptState (PrintMessage m)) I'd appreciate it very much if you could give me some feedback on my approach. I get this feeling that I am wrapping up the whole program inside a State monad - does this mean that I am giving up the functional goodies. Regards, Kashyap

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No email verification token from trac.haskell.org
by Niklas Broberg 23 Apr '12

23 Apr '12

Hi all, I have problems with my trac for haskell-src-exts. When I log in, I am asked to verify my email address, but no verification token is ever sent to my email address. And before I verify my address, I'm not allowed to do anything on the trac. Help? :-) /Niklas

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ANNOUNCE: hsx-0.10.1, hjscript-0.6.0, hsp-0.7.0
by Niklas Broberg 23 Apr '12

23 Apr '12

Hi all, I'm pleased to announce the release of the latest versions of the libraries in the Haskell Server Pages suite. Haskell Server Pages enables literal XML syntax to be used mixed with Haskell code (like e.g. PHP), in a sane way (unlike said PHP). In principle the functionality could be used together with any Haskell web framework, but is (currently) best integrated in and supported by Happstack. For this release I owe much to Jeremy Shaw, both for inspiration and for actual patches. There are some grand plans in the pipeline for some more extensive changes to the suite, to shape it up to be worthy of the current exciting state-of-the-art of Haskell web development. Stay tuned! Cheers, /Niklas Specific changes in this release: * In the XMLGen class, the following associated types have been renamed to avoid frequent name clashes, and to better match the intention of those types: XML => XMLType, Child => ChildType, Attribute => AttributeType. * Literal CDATA strings are now given an explicit type signature in the post-processed code. This to avoid ambiguities when OverloadedStrings is enabled. * class XMLGenerator m now has EmbedAsChild m () as another premise. * HSX.Transform now exports a method transformExp :: Exp -> Exp, intended to be used with quasi-quotation. * trhsx no longer performs fixity resolution before transforming, allowing the tool to be used on files using operators with (locally) unknown fixity. * hsp and hjscript updated to work with hsx-0.10.

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Data-Type Serialization
by Lyndon Maydwell 23 Apr '12

23 Apr '12

Hi Café. I'm pondering over an old chestnut that I'd forgotten about until recently. I'd like to be able to express schemas for general recursive datatypes (excluding functions and possibly encoding bounds) and have an interactive constructor for that datatype generated automatically. Originally this idea came about as an XML/JS framework for creating advanced form inputs on the client-side, however, I'm interested in how this could be implemented idiomatically in Haskell. I'm guessing that the best way to go about this would be to capture the declaration in template Haskell, having a passthrough for the declaration itself, and also generating a representation that can be used for introspection and the creation of the interactive component. Ideally I'd like to integrate this concept into one of the web-frameworks such as Yesod so that complicated data-types can be constructed interactively on the client-side using (generated) javascript in order to get instantaneous feedback about validity of fields, etc, and avoid page reloads and even ajax communication. The details of the web-side of things would probably be quite messy, but if the Haskell side can be made general enough then this can be considered a separate problem :-) Has anyone had experience with trying to solve this, or a similar issue? What approach did you take? Did you use Template-Haskell, or something else? Thanks!

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