April 2012 - Haskell-Cafe

I am having trouble with the type declaration for creating an identity matrix.
by KC 24 Apr '12

24 Apr '12

initIdentityMat :: Int -> ST s (STUArray s (Int,Int) ((Int, Int), Double)) initIdentityMat m = newListArray ((1,m),(1,m)) ([((i,j), if i == j then 1.0 else 0.0) | i <- [1..m], j <- [1..m]] :: [((Int,Int), Double)]) Doesn't seem to compile, nor do minor variations of the type declaration. -- -- Regards, KC

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Is protocol-buffers package maintainer reachable?
by Paul Graphov 24 Apr '12

24 Apr '12

Hello Cafe! I am using protocol-buffers and hprotoc packages but they fail to compile with recent GHC due to trivial errors. Hackage names Christopher Edward Kuklewicz as their maintainer. I've sent him patches more than a month ago but neiter they were applied nor I got any response. It's quite inconvenient to keep patched versions all the time. Does anybody know if he is still interested in maintaining those packages? Is it possible to contact him? And what should I do if he is unreachable? Thanks! Links: http://hackage.haskell.org/package/protocol-buffers http://hackage.haskell.org/package/hprotoc

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Offer to mirror Hackage
by Dan Knapp 24 Apr '12

24 Apr '12

With Hackage down, now seemed like a good time to push this issue again. It's such an important site to us that it's really rather a shame there are no mirrors of it. I have a personal-and-business server in a data center in Newark, with a fair chunk of bandwidth, which I'd like to offer for a permanent mirror. Is there interest in this? Who do I need to talk to for it to happen? Strategy-wise, I think the best approach is round-robin DNS, since that's transparent to the end user - everything would still appear at the URL it's at now, but behind-the-scenes magic would let things keep working when one or the other site is down. I haven't personally set up such a system before but I'm willing to take on the burden of figuring it out. So I have a better idea of what I'm signing up for, can anyone tell me how much disk space and how much bandwidth per month Hackage uses? I have a fair chunk of both, as I say, but I'd like to know in advance to ensure that things go smoothly. As for what I'd want in return for this, really nothing. I wouldn't say no to an unobtrusive mention somewhere on the site, but I'd be happy just knowing I'd given something back to the Haskell community, which has given a lot to me. -- Dan Knapp "An infallible method of conciliating a tiger is to allow oneself to be devoured." (Konrad Adenauer)

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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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