- Beginners - Haskell.org

Loading QuickCheck in GHCi.
by Kwanghoon Choi 16 Feb '10

16 Feb '10

Dear All, Whenever I tried to load QuickCheck in GHCi, I met the following problem: Prelude> :l Test.QuickCheck <no location info>: module `Test.QuickCheck' is a package module Failed, modules loaded: none. Test.QuickCheck seems to be a module anyway, bit it couldn't be loaded directly by issuing the command. I don't understand why. Thanks in advance. Kwanghoon PS. Of course, I installed QuickCheck-2.1.0.3, and I can use it when I load it by loading some haskell program having "import Test.QuickCheck".

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Equivalent of FOOLANGUAGEPATH environment variable?
by Tom Tobin 16 Feb '10

16 Feb '10

Is there an easy way to declare a particular directory as a location for finding Haskell modules, similar to PYTHONPATH and similar environment variables for other languages? The GHC_PACKAGE_PATH doesn't seem to be quite the same thing. There's the option of setting -iSOMEPATH in one's .ghci file, but that doesn't seem to allow declaring a relative path via ~ or $HOME, making it a bit of a pain to maintain separate versions of one's .ghci across different machines.

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space leak
by Uchida Yasuo 15 Feb '10

15 Feb '10

Hello, I came across the following space leak problem today. How can I fix this? (Tested on Mac OS X 10.5.8, GHC 6.10.3) -- test.hs module Main where import System import qualified Data.ByteString.Lazy.Char8 as L main = do args <- getArgs let n = read $ args !! 0 cs <- L.getContents let !a = L.take n cs mapM_ (print . L.length) $ L.lines cs print a -- gen.hs module Main where main = do putStrLn $ take 1000000 $ cycle "foo" main These are compiled with the following options: $ ghc --make -O2 test $ ghc --make -O2 gen The memory usage seems to depend on the argument(=17000) passed. On my MacBook(Core2 Duo 2.0GHz), 16000 works fine. $ ./gen | head -1000 | ./test 17000 +RTS -sstderr ... 3,793,673,564 bytes allocated in the heap 9,901,516 bytes copied during GC 635,576,092 bytes maximum residency (11 sample(s)) 248,725,136 bytes maximum slop 1759 MB total memory in use (562 MB lost due to fragmentation) Generation 0: 6941 collections, 0 parallel, 16.91s, 18.15s elapsed Generation 1: 11 collections, 0 parallel, 0.03s, 0.03s elapsed INIT time 0.00s ( 0.00s elapsed) MUT time 3.04s ( 27.64s elapsed) GC time 16.94s ( 18.18s elapsed) EXIT time 0.00s ( 0.01s elapsed) Total time 19.99s ( 45.82s elapsed) %GC time 84.8% (39.7% elapsed) Alloc rate 1,245,766,300 bytes per MUT second Productivity 15.2% of total user, 6.6% of total elapsed $ ./gen | head -1000 | ./test 16000 +RTS -sstderr ... 4,000,652,128 bytes allocated in the heap 7,428,180 bytes copied during GC 1,057,588 bytes maximum residency (1001 sample(s)) 525,092 bytes maximum slop 5 MB total memory in use (1 MB lost due to fragmentation) Generation 0: 6362 collections, 0 parallel, 0.10s, 0.12s elapsed Generation 1: 1001 collections, 0 parallel, 0.09s, 0.09s elapsed INIT time 0.00s ( 0.00s elapsed) MUT time 2.59s ( 23.26s elapsed) GC time 0.18s ( 0.22s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 2.77s ( 23.47s elapsed) %GC time 6.6% (0.9% elapsed) Alloc rate 1,545,246,968 bytes per MUT second Productivity 93.4% of total user, 11.0% of total elapsed -- Regards, Yasuo Uchida

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indentation
by Gabi 15 Feb '10

15 Feb '10

BTW, is there some indent tool for Haskell. Something like "indent" command line tool for c? -- Regards, Gabi http://bugspy.net

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indentation
by John Moore 15 Feb '10

15 Feb '10

Hi all, I must be doing something wrong with my tabs. Because this keeps telling me parse error. Can some one see if it is indentation. I'm sending a file so as you'll be able to see what going on. If I copy it here it can appear wrong the difference is with the Var expression. John

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Calculating SHA1 hashes?
by Tom Tobin 14 Feb '10

14 Feb '10

I'm trying to figure out the best way to calculate SHA1 hashes for files using Haskell. There are several libraries I tried from Hackage, but they all seem to end up computing the hash far too slowly vs. OpenSSL. Some of the libraries seem to be FFI bindings to OpenSSL, but I haven't figured out how to efficiently feed these. (For instance, hopenssl consumes a [Word8], but I haven't figured out how to lazily produce that from a file; using "unpack" on a ByteString seems to end up much too slow.) I also tried mimicking nano-md5 by writing a "nano-sha1" that was largely a "replace the name of the digest function" hack job, but I couldn't manage to get that working. Is there a particular accepted way to generate hashes that I'm missing?

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getting memory usage to be constant when mixing wav files
by Renick Bell 14 Feb '10

14 Feb '10

I've written a program that mixes wav files read in by hsndfile, and it does so with reasonably satisfactory performance using RTS options -A and -K. Unfortunately, it does not have constant memory usage. Profiling the program shows that almost all of the memory allocation comes down to the following two functions: the first which calculates and writes the values of individual indexes to the target array (longer), and the second which runs the first for all the indexes in the shorter array. addInBase :: IOCArray Int Double -> IOCArray Int Double -> (Int, Int) -> IO () addInBase longer shorter (!li,!si) = do x <- readArray longer li y <- readArray shorter si let result = x + y writeArray longer li result addIn :: IOCArray Int Double -> IOCArray Int Double -> Int -> Int -> Int -> IO () addIn longer shorter shorterBounds !li !si | si > shorterBounds = return () | si <= shorterBounds = addInBase longer shorter (li,si) >> addIn longer shorter shorterBounds (li+1) (si+1) Basically, the addIn function is called by mapM_ across a list of all of the occurrences of the input wav files. I've tried ! and seq in many different places and combinations, but I cannot get the memory usage constant. How can I achieve that? What technique or principle will show me more specifically what is not being evaluated so that I can avoid this trouble in the future? I have read the wiki pages on Strictness, Laziness, and Performance, but maybe I have not fully understood how to apply what is written there to this code. Any help is greatly appreciated. If you notice any other glaring mistakes or bad ideas in the code above, I'm interested in that as well. -- Renick Bell http://the3rd2nd.com

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running HGL on OSX
by Vojtěch Knyttl 14 Feb '10

14 Feb '10

Hello, I am having difficulties running HGL on Mac OSX, Snow Leopard. Here is what I've done: –– 1. Installed X11 for OSX ("About" dialog says: The X Window System, XQuartz 2.3.4 (xorg-server 1.4.2-apple45)) –– 2. Got X11 from Hackage – configured, built and installed – however, there where quite a lot of warnings: … [ 8 of 25] Compiling Graphics.X11.Xlib.Color ( Graphics/X11/Xlib/Color.hs, dist/build/Graphics/X11/Xlib/Color.o ) Graphics/X11/Xlib/Color.hs:38:0: Warning: The import of `Foreign.C.Types' is redundant except perhaps to import instances from `Foreign.C.Types' To import instances alone, use: import Foreign.C.Types() [ 9 of 25] Compiling Graphics.X11.Xlib.Font ( dist/build/Graphics/X11/Xlib/Font.hs, dist/build/Graphics/X11/Xlib/Font.o ) Graphics/X11/Xlib/Font.hsc:167:1: Warning: A do-notation statement discarded a result of type CInt. Suppress this warning by saying "_ <- xTextExtents font_struct c_string (fromIntegral nchars) direction_return font_ascent_return font_descent_return overall_return", or by using the flag -fno-warn-unused-do-bind … and so on. –– 3. Got HGL package, built and installed with some warnings like: … [ 1 of 27] Compiling Graphics.HGL.Internals.Flag ( Graphics/HGL/Internals/Flag.hs, dist/build/Graphics/HGL/Internals/Flag.o ) Graphics/HGL/Internals/Flag.hs:1:0: Warning: Module `Prelude' is deprecated: You are using the old package `base' version 3.x. Future GHC versions will not support base version 3.x. You should update your code to use the new base version 4.x. … –– Now, when I try to run simple program like: main = runGraphics $ withWindow_ "Hello World Window" (300, 200) $ \ w -> do drawInWindow w $ text (100, 100) "Hello World" drawInWindow w $ ellipse (100, 80) (200, 180) getKey w it says: $ ghci graphics.hs GHCi, version 6.12.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. Ok, modules loaded: Main. Prelude Main> main Loading package syb-0.1.0.2 ... linking ... done. Loading package X11-1.5.0.0 ... can't load .so/.DLL for: X11 (dlopen(libX11.dylib, 9): image not found) Prelude Main> Just to precise, I have X11 running (it can be seen in the OSX dock) Thanks

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Draft paper submission deadline is extended: MULTICONF-10, Orlando, USA
by John Edward 13 Feb '10

13 Feb '10

It would be highly appreciated if you could share this announcement with your colleagues, students and individuals whose research is in computer science, computer engineering, information science and related areas. Draft paper submission deadline is extended: MULTICONF-10, Orlando, USA The 2010 multi-conference (MULTICONF-10) (website: http://www.promoteresearch.org) will be held during July 12-14, 2010 in Orlando, Florida, USA. The primary goal of MULTICONF is to promote research and developmental activities in computer science, information technology, control engineering, and related fields. Another goal is to promote the dissemination of research to a multidisciplinary audience and to facilitate communication among researchers, developers, practitioners in different fields.The following conferences are planned to be organized as part of MULTICONF-10. * International Conference on Artificial Intelligence and Pattern Recognition (AIPR-10) * International Conference on Automation, Robotics and Control Systems (ARCS-10) * International Conference on Bioinformatics, Computational Biology, Genomics and Chemoinformatics (BCBGC-10) * International Conference on Computer Communications and Networks (CCN-10) * International Conference on Enterprise Information Systems and Web Technologies (EISWT-10) * International Conference on High Performance Computing Systems (HPCS-10) * International Conference on Information Security and Privacy (ISP-10) * International Conference on Image and Video Processing and Computer Vision (IVPCV-10) * International Conference on Software Engineering Theory and Practice (SETP-10) * International Conference on Theoretical and Mathematical Foundations of Computer Science (TMFCS-10) MULTICONF-10 will be held at Imperial Swan Hotel and Suites. It is a full-service resort that puts you in the middle of the fun! Located 1/2 block south of the famed International Drive, the hotel is just minutes from great entertainment like Walt Disney World® Resort, Universal Studios and Sea World Orlando. Guests can enjoy free scheduled transportation to these theme parks, as well as spacious accommodations, outdoor pools and on-site dining — all situated on 10 tropically landscaped acres. Here, guests can experience a full-service resort with discount hotel pricing in Orlando. Please see the website http://www.promoteresearch.org for more details. Sincerely John Edward

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distinguished types
by Rick Murphy 13 Feb '10

13 Feb '10

Greetings and thanks in advance for all the great work on this list. Being new Haskell I hope someone could help me clarify the use of the term *distinguished type* in relation to Haskell 98 as well as confirm my understanding of the construction of a distinguished type in GHC. I understand from [1] that a distinguised type is defined as a type with only one non-bottom value and that value is in fact identical to the name of the type. [1] provides the unit type () as an example of a Haskell distinguished type. Would it be accurate to say that an approach to creating distinguished types in Haskell is to create data types with a single constructor whose name is identical to the data type name? More specifically, would > data F = F deriving (Show) create a distinguished type F in Haskell? I've searched the Haskell Report, but there's no indication that the report recognizes distinguished types. Is that true and if so why ? 1. http://okmij.org/ftp/Scheme/misc.html -- Rick cell: 703-201-9129 web: http://www.rickmurphy.org blog: http://phaneron.rickmurphy.org

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