October 2007 - Haskell-Cafe

newbie question about list performance
by John Lato 29 Oct '07

29 Oct '07

Hello, I've been following the list optimization thread with great interest, as it pertains to something I'm working on at the moment. I'm working with moderate-sized files (tens to hundreds of MBs) that have some ascii header data followed by a bunch of 32-bit ints. I can read the files into a lazy ByteString (and parse the header), but I'd like some advice as to the best data type to convert the ints into. Ideally, I'd have some functions like this: decode :: ByteString -> (FileFormat, [Int32]) encode :: FileFormat -> [Int32] -> ByteString but I don't know if Int32 is actually the best choice. It seems to me that something like a lazy list of strict arrays (analogous to a lazy bytestring) would be better. Is there a library like this already? Or is this a case of premature optimization, and I should just try the list and see if it's good enough? Any suggestions would be appreciated. Also, I'd like to let the maintainers and implementors know that I really appreciate the work that's been done on optimizing Haskell. I haven't used Haskell much yet, but I've fallen in love with the language and it's great to see that performance even for heavy I/O tasks can be comparable to or exceed C. Thank you, John Lato

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ANNOUNCE / POST MORTEM: hswm, version ()
by Remi Turk 28 Oct '07

28 Oct '07

Hi everyone, HSWM was my attempt at a Haskell Window Manager, mostly written during the first half of 2006 as a personal research project, and out of frustration with some not to be named other window managers. Although I have been running it myself for almost two years, I never got around to polishing it into something releasable due to lack of time. [1] Since, as of today, its number of users is officially back to zero [2], this seems like a good moment to release version () of HSWM: The first and last version of my own window manager. Features are: - includes a lambda mouse cursor - multiple desktops - sticky windows - about 2300 lines, about half of which is X boilerplate and user configuration - somewhat based on evilwm - still regularly dies due to unhandled X errors, so a script to automatically restart in that case is included - my first Xlib program ever The basic idea is an event loop inside an X monad providing three services to "plugins": - registering X Event handlers - registering X Error handlers - registering/requesting "services", to be used by other "plugins" (a global registry of named Dynamics, basically) Compared to XMonad: - no tiling - much less stable - no extensions - needs no external libs So you might want to look at it, but even _I_ don't use it anymore. HSWM only was its working name, so if anybody ever feels like writing another window manager and calling it HSWM, I certainly won't mind. The BSD-licensed code: darcs get http://student.science.uva.nl/~rturk/hswm/ `make' compiles, and that's it. Greetings, Remi [1] Technical detail: The one feature I really wanted before releasing it, but never got around to implementing, is having the WM add a frame for each managed window and reparenting the window below that frame. This way, focusing windows can go right even when the WM dies, among others. [2] It once had 3 users: Me at home, me at the University of Amsterdam and me at Utrecht University. Utrecht now runs KDE and the rest xmonad.

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Re: [Haskell-cafe] viewing HS files in Firefox
by Richard Kelsall 28 Oct '07

28 Oct '07

Shachaf Ben-Kiki wrote: > Richard Kelsall wrote: >> Thomas Schilling wrote: >>> On Sat, 2007-10-27 at 18:48 -0400, Isaac Dupree wrote: >>>> When I try to go to one of the Module.hs files, e.g. on >>>> darcs.haskell.org, it now has type HS and Firefox refuses to display >>>> it (and only lets me download it). Does anyone know how to make >>>> Firefox treat certain file types as others (HS as plain text, >>>> in particular)? so that I can browse them with any convenience >>> I believe those kinds of problem have to do with the MIME-encoding on >>> the server side: The server uses text/x-haskell. For Firefox to >>> display the document inline it probably has to be text/plain. Not sure >>> what the proper fix is, though. >> It should probably be fixed in one of the Apache config files. In the >> HTTP headers from darcs.haskell.org (viewed with the Live HTTP headers >> extension in FireFox) I'm getting > > Fixed? It's already fixed. text/x-haskell is the right Content-Type to > send; this is Haskell after all, not just plaintext. It's your > browser's responsibility to display it any way it likes. People have > had this discussion in #xmonad, and it seems that MIME edit > (<https://addons.mozilla.org/en-US/firefox/addon/4498>) is a workable > solution (I don't use it myself, though). Of course, Sterling Clover's > suggestion (Open in Browser) would also work well. Hello Shachaf, I hope you intended this for the list, as I haven't seen it come through, if not my apologies for posting it. Ah, yes I see what you mean, text/x-haskell is the best media-type, however I think it ought to be possible to use 'content negotiation' http://httpd.apache.org/docs/2.2/content-negotiation.html with more than one representation to supply the same file as text/plain to non-Haskell-capable browsers. I haven't actually done this though so can't be certain of it or provide configuration details. If somebody really wanted to get clever with it it could also supply pretty coloured Haskell for a text/html representation. Sorry, I couldn't find the #xmonad discussion, is this published somewhere? Richard.

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Recipes for organizing HUnit tests
by Mushfeq Khan 28 Oct '07

28 Oct '07

I'm new to Haskell and am trying to find a good way to organize my HUnit tests. Having used some of the other XUnit frameworks, I tended towards trying to organize them all in a parallel "test" folder structure, but this seems to be a bad fit for Haskell, since the test modules cannot see the source modules unless they are either in the same folder or a folder above it. That's without modifying the module search path when I run the tests, which I would like to avoid. So I tried looking for examples of HUnit-tested source code out there and found that the cryptographic library Crypto has some unit tests. However, Crypto seems to place all its test code at the top of the folder hierarchy for the reasons I mentioned above. This turns out to be fine for Crypto since there are few tests. But I can foresee the tests for my project multiplying to the point where it would become very unsightly to put them all in the top-level folder. My questions to you are: how do you organize your HUnit/QuickCheck tests? Is there a convention? Is there some library out there that embodies this convention? Mushfeq.

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Problem with PDF/PS backend in GTK2HS
by Peter Verswyvelen 28 Oct '07

28 Oct '07

I have a strange problem, which is so elementary that I think I must be missing something... In GTK2HS, when I draw text using using textPath, the text is located at different locations depending on which backend is used. I'm not talking about a difference of a couple of pixels , but in my case it's half a page off. The PNG and Win32 backend work fine, but the PDF/PS backends get it wrong. For example, I modified the Text.hs demo in the demos/Cairo subdirectory so it also outputs PDF. Here the text is also at different locations, so I guess it's not just my code. Code is pasted below. I'm using Windows, and GTK2HS version 0.9.12 from http://www.haskell.org/gtk2hs Maybe someone could give this a quick test on Linux? I guess this is most likely a Cairo problem, and has nothing to do with the Haskell wrapper? Still this is hard to believe, since these kinds of bugs would be quickly found. Thanks, Peter ---------------------------------------- import Graphics.Rendering.Cairo import qualified Graphics.Rendering.Cairo.Matrix as M boxText :: String -> Double -> Double -> Render () boxText text x y = do save lineWidth <- getLineWidth (TextExtents xb yb w h _ _) <- textExtents text rectangle (x + xb - lineWidth) (y + yb - lineWidth) (w + 2 * lineWidth) (h + 2 * lineWidth) stroke moveTo x y textPath text fillPreserve setSourceRGBA 0 0 1 0.5 setLineWidth 3.0 stroke restore transpSurface :: Double -> Double -> Render () transpSurface w h = do save rectangle 0 0 w h setSourceRGBA 0 0 0 0 setOperator OperatorSource fill restore width = 400 height = 300 main :: IO () main = withImageSurface FormatARGB32 width height $ \surface -> do let render = do setSourceRGB 0.0 0.0 0.0 setLineWidth 2.0 transpSurface (fromIntegral width) (fromIntegral height) selectFontFace "sans" FontSlantNormal FontWeightNormal setFontSize 40 extents <- fontExtents let fontHeight = fontExtentsHeight extents boxText "Howdy, world!" 10 fontHeight translate 0 fontHeight save translate 10 fontHeight rotate (10.0 * pi / 180.0) boxText "Yay for Haskell!" 0 0 restore translate 0 (3 * fontHeight) save setFontMatrix $ M.rotate ((-10.0) * pi / 180.0) $ M.scale 40.0 40.0 M.identity boxText "...and Cairo!" 10 fontHeight restore renderWith surface render surfaceWriteToPNG surface "Text.png" withPDFSurface "Text.pdf" (realToFrac width) (realToFrac height) (flip renderWith $ render >> showPage) return ()

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Good news for Windows developers?
by Peter Verswyvelen 28 Oct '07

28 Oct '07

If I understand this blog correctly, F# leaves the research lab and becomes an "official" Visual Studio language? http://blogs.msdn.com/somasegar/archive/2007/10/17/f-a-functional-programmi… Okay it's not Haskell, but I think it's good news anyway... Cheers, Peter PS: Shouldn't the Super Simons do some more PR at Microsoft so this also happens to Haskell? ;-) ;-)

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lazily traversing a foreign data structure
by Graham Fawcett 26 Oct '07

26 Oct '07

Hi folks, I'm writing a Gnu DBM module as an exercise for learning Haskell and its FFI. I'm wondering how I might write a function that returns the database keys as a lazy list. I've wrapped the two relevant foreign functions: firstKey :: Ptr Db -> IO (Maybe String) nextKey :: Ptr Db -> String -> IO (Maybe String) NextKey takes a key, and returns the next one. Either function could return Nothing, since the db may have 0 or 1 keys. Given these, is it possible to write a (simple) function allKeys :: Ptr Db -> IO [String] that lazily fetches the keys? (Or, an idiomatic way of achieving the same end?) Thanks, Graham

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Linking problems with a fresh gtk2hs build
by Olivier Boudry 26 Oct '07

26 Oct '07

Hello, I just built gtk2hs 0.9.12 using MinGW, GTK_2.0 and ghc-6.8.0.20071016. I just changed some EXTERNALDEPS in the Makefile based on info found in the following page http://haskell.org/haskellwiki/Grapefruit 25a126,128 > if HAVE_SPLIT_BASE > tools_c2hs_c2hsLocal_EXTERNALDEPS += pretty containers array > endif 358a362,364 > if HAVE_SPLIT_BASE > libHSgtk_a_EXTERNALDEPS += containers array > endif 1578a1585,1587 > if HAVE_SPLIT_BASE > libHSsoegtk_a_EXTERNALDEPS += old-time > endif I had no problem building and installing the library but when trying to compile the HelloWorld example to check the installation I get this error: C:\Temp>ghc --make HelloGtk.hs Linking HelloGtk.exe ... C:/Progra~1/Haskell/lib/gtk2hs/libHSgtk.a(Gtk__1.o)(.text+0x419):fake: undefined reference to `__stginit_gtkzm0zi9zi12_GraphicsziUIziGtkziLayoutziHPaned_' collect2: ld returned 1 exit status I found an irc log talking of using nm to track the problem. Tried nm and got this (different from the problem specified in the irc log). nm libHSgtk.a | grep __stginit_gtkzm0zi9zi12_GraphicsziUIziGtkziLayoutziHPaned_ U ___stginit_gtkzm0zi9zi12_GraphicsziUIziGtkziLayoutziHPaned_ c:\MinGW\bin\nm.exe: HPaned__4.o: File format not recognized c:\MinGW\bin\nm.exe: MenuBar__48.o: File format not recognized The "missing symbol" is found but I have a problem with the HPaned__4.o and MenuBar__48.o of the libHSgtk.a file. Any idea of what could have gone wrong? Thanks, Olivier.

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latest hdbc-odbc
by jeff p 26 Oct '07

26 Oct '07

Hello, When building the latest hdbc-odbc (1.1.2.0) on a linux box with ghc6.6.1, I get the following warnings: [7 of 7] Compiling Database.HDBC.ODBC ( Database/HDBC/ODBC.hs, dist/build/Database/HDBC/ODBC.o ) hdbc-odbc-helper.c: In function â: hdbc-odbc-helper.c:131:0: warning: pointer targets in passing argument 6 of â differ in signedness hdbc-odbc-helper.c:131:0: warning: pointer targets in passing argument 8 of â differ in signedness hdbc-odbc-helper.c: In function â: hdbc-odbc-helper.c:136:0: warning: pointer targets in passing argument 8 of â differ in signedness /usr/bin/ar: creating dist/build/libHSHDBC-odbc-1.1.2.0.a then, after installing the package I get the following error/strange behavior: Prelude> :t Database.HDBC.ODBC.connectODBC /usr/local/lib/HDBC-odbc-1.1.2.0/ghc-6.6.1/Database/HDBC/ODBC/Connection.hi Declaration for connectODBC: Failed to load interface for `Database.HDBC.ODBC.ConnectionImpl': Use -v to see a list of the files searched for. Cannot continue after interface file error Can anyone shed light on what is going wrong? Is it something I can fix, or is the distribution buggy? thanks, Jeff

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Re: [Haskell-cafe] Haskell to math
by Peter Verswyvelen 26 Oct '07

26 Oct '07

Jerzy K wrote >wants. He wants a specific pretty-printer *in Haskell*. This was most >probably a subject of many students' exercices... Yes Jerzy, exactly. I wrote some Haskell code to create plots of binary relations and functions on the Cartesian plane, using GTK2HS (Cairo). I have to pretty print the math formulas used in these plots. Now I'm retyping the math formulas in Word, but being a really lazy programmer, I want to automate this task. So I wanted to write some code that renders math formulas (maybe using GTK, or to MathML; I must admit I don't know LaTex at all, sorry...), but since this feels like a lot of work to get right, I was wandering if it existed allready. Okay, I could have skipped all the above and just use Maple or whatever other tool, but I'm trying to use Haskell whenever possible, because I'm kind of addicated to it. Also I still feel a bit stuck in newbie land (although I think I'm approaching escape velocity ;-), so I grab every opportunity to practice in Haskell... Thanks, Peter

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