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Announcing AusHac 2011 - The second annual Australian Haskell Hackathon (July 8-10)
by Alex Mason 17 Apr '11

17 Apr '11

Attention all Australasian Haskellers! After last year’s fantastic turnout for the first Australian Haskell Hackathon - AusHac 2010 - we’ve decided to organise another. As it’s rather boring to have a Hackathon with only two people, we encourage and welcome anyone interested in Haskell in Australia, New Zealand and surrounding areas (or further afield if you want!) to come and join us. Last year we had more than 25 Haskellers come from Brisbane, Canberra, Melbourne, Sydney and even two from as far away as New Zealand. AusHac 2011 will be held from Friday July 8th until Sunday July 10th, again at UNSW’s Computer Science building in Sydney. There’s no need to come for the entire weekend, just for whenever you’re able to. Last year, people worked on several projects including: • Accelerate: a high performance library for array computations using various backends (CUDA, LLVM, etc.) being written at UNSW. • Leksah: the Haskell IDE written in Haskell • DDC: the compiler for the Haskell-like language Disciple, which has strict evaluation by default, region, effect and closure typing and other interesting language features. • Hubris: the Haskell/Ruby bridge for calling Haskell from Ruby and vice-versa. • haskell-mpi: bindings to MPI, the message passing interface used frequently on high performance super-computers to allow programs to run on many nodes in parallel with easy communication. • There was even some work on LLVM to produce HTML output showing register allocations (as an aid to those writing new code generators etc.), which has now been included upstream. This work did not use Haskell, but it did happen at AusHac 2010. • And much more! This is a great chance to collaborate with others and get feedback on your work, while having heaps of fun and meeting other Haskellers, to verify they do actually exist! And don’t worry if you can’t think of a project to work on; just come along and pitch in with whatever strikes your fancy! If you’re interested in coming and have a project you’d like to work on, check out the wikipage http://www.haskell.org/haskellwiki/AusHac2011 where you can add your project ideas, or just take a look and see what others will be working on that you can help out with. People of all skill levels are welcome, from complete beginners to Oleg-level sage masters. We’re more than happy to help you learn Haskell if you’re just starting out or help you solve that little niggly bit in your code. If you’re interested in coming along, fill out our registration form http://axman6.wufoo.com/forms/aushac-2011-sign-up/. Registration is required so we know numbers and for you to get access to the university Wifi. Even if you’re not sure, fill it in to express your interest, obligation free. We’d rather know we have room for too many people than not enough. So come along! And if for some reason you don’t enjoy yourself, registration comes with a money-back guarantee! Hope to see you there, -- Alex Mason and Ivan Miljenovic, AusHac organisers P.S: If you have received this email directly, it is because you have shown previous interest in AusHac by signing up via the previous signup. If you do not wish to receive any more email regarding AusHac, please email me (axman6(a)gmail.com) and I'll be sure to take you off the list of interested people.

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Re: [Haskell-cafe] Cairo and Haskell
by Hans van Thiel 16 Apr '11

16 Apr '11

Hello Paulo, << I guess that would be using Cairo so I can have a 2d canvas to draw in and maybe even preview before exporting to PDF. However, I can't find any documentation on Cairo with Haskell or any code examples related to what I want to do. >> With regard to export to pdf and other formats this might be useful: http://muitovar.com/gtk2hs/app1.html (There's a Spanish translation too.) However, this tutorial is a few years old now, and I don't know if it's still up to date for the later Gtk2Hs versions. Best Regards, Hans van Thiel

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64 bit generic link warning on every compile
by Andrew Pennebaker 16 Apr '11

16 Apr '11

GHC 7 compiles fine, but there's an additional warning during linking. $ system_profiler SPSoftwareDataType | grep "System Version" System Version: Mac OS X 10.6.7 (10J869) $ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.0.2 $ cat hello.hs #!/usr/bin/env runhaskell module Main where main :: IO () main = putStrLn "Hello World" $ ghc --make hello.hs [1 of 1] Compiling Main ( hello.hs, hello.o ) Linking hello ... ld: warning: -read_only_relocs cannot be used with x86_64 $ ./hello Hello World Cheers, Andrew Pennebaker www.yellosoft.us

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ANN: bindings to xfconf-4.8.0.0
by John Obbele 15 Apr '11

15 Apr '11

Hi all, I'm very happy to announce my first hackageDB package: xfconf[0], a Haskell binding to the XFCE xfconfd configuration dæmon. It's mainly a pet project I have done to learn Haskell using the FFI and QuickCheck but if someone can find it useful or instructive I would be happy. This package allows easy access to your favorite XFCE desktop settings (wallpaper, colors, police, etc.) and easier synchronisations between the configuration backend and your own Gtk+2 widget properties (a feature missing in gconf but now part of gsettings). A practical use of this binding can be found in hThemes[1], a quick&dirty front-end to switch between pre-defined desktop themes (eg. switching from a light-white theme for daytime to a dark-black one for your nightly hack sessions). [0.a]: http://hackage.haskell.org/package/xfconf [0.b]: http://patch-tag.com/r/obbele/xfconf/home [1]: http://patch-tag.com/r/obbele/hThemes/home Thanks to Andy Stewart and Axel Simon for their help in integrating xfconf to the gtk2hs stack. Any comments on this first work are welcomed ,-) regards, /John

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Cairo and Haskell
by Paulo J. Matos 15 Apr '11

15 Apr '11

Hi, I would like to use Haskell to generate automatically a poster. I guess that would be using Cairo so I can have a 2d canvas to draw in and maybe even preview before exporting to PDF. However, I can't find any documentation on Cairo with Haskell or any code examples related to what I want to do. Any suggestions? Cheers, -- PMatos

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timsort
by Ben 15 Apr '11

15 Apr '11

hello -- has anyone every implemented (and benchmarked) timsort in haskell? http://bugs.python.org/file4451/timsort.txt it is a stable mergesort-like algorithm, seems like a good fit for haskell. best, ben

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build fails due to sem_close...
by Jiri Skala 15 Apr '11

15 Apr '11

Hi all, I've got error listed below when I've tried to build ghc-7.0.2 on ppc64 arch. I 've tested patch from Debian (-pthread option) but this didn't fix the issue. Any idea what's wrong? Thanks for any tip/help. Jiri used packages: glibc: 2.12.90, 2.13.90 (tested for both) gcc: 4.6.0 I use these options for ppc64 arch in build.mk %ifarch ppc64 GhcUnregisterised=YES GhcWithNativeCodeGen=NO SplitObjs=NO GhcWithInterpreter=NO GhcNotThreaded=YES SRC_HC_OPTS+=-optc-mminimal-toc SRC_CC_OPTS+=-mminimal-toc -Wa,--noexecstack %endif error log: configure: Building in-tree ghc-pwd /usr/bin/ld: /usr/lib64/ghc-7.0.2/unix-2.4.2.0/libHSunix-2.4.2.0.a(Semaphore.o): undefined reference to symbol 'sem_close@@GLIBC_2.3' /usr/bin/ld: note: 'sem_close@@GLIBC_2.3' is defined in DSO /lib64/libpthread.so.0 so try adding it to the linker command line /lib64/libpthread.so.0: could not read symbols: Invalid operation collect2: ld returned 1 exit status configure: error: Building ghc-pwd failed

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Programming Chalenges: The 3n+1 problem
by Dmitri O.Kondratiev 15 Apr '11

15 Apr '11

3n+1 is the first, "warm-up" problem at Programming Chalenges site: http://www.programming-challenges.com/pg.php?page=downloadproblem&probid=11… (This problem illustrates Collatz conjecture: http://en.wikipedia.org/wiki/3n_%2B_1#Program_to_calculate_Collatz_sequences ) As long as the judge on this site takes only C and Java solutions, I submitted in Java some add-hock code (see at the end of this message) where I used recursion and a cache of computed cycles. Judge accepted my code and measured 0.292 sec with best overall submissions of 0.008 sec to solve the problem. *** Question: I wonder how to implement cache for this problem in Haskell? At the moment, I am not so much interested in the speed of the code, as in nice implementation. To illustrate my question I add the problem description and my Java solution at the end of this message. Thanks! *** Problem Consider the following algorithm to generate a sequence of numbers. Start with an integer *n*. If *n* is even, divide by 2. If *n* is odd, multiply by 3 and add 1. Repeat this process with the new value of *n*, terminating when *n* = 1. For example, the following sequence of numbers will be generated for *n* = 22: 22 11 34 17 52 26 13 40 20 10 5 16 8 4 2 1 It is *conjectured* (but not yet proven) that this algorithm will terminate at *n* = 1 for every integer *n*. Still, the conjecture holds for all integers up to at least 1, 000, 000. For an input *n*, the *cycle-length* of *n* is the number of numbers generated up to and *including* the 1. In the example above, the cycle length of 22 is 16. Given any two numbers *i* and *j*, you are to determine the maximum cycle length over all numbers between *i* and *j*, *including* both endpoints. InputThe input will consist of a series of pairs of integers *i* and *j*, one pair of integers per line. All integers will be less than 1,000,000 and greater than 0. OutputFor each pair of input integers *i* and *j*, output *i*, *j* in the same order in which they appeared in the input and then the maximum cycle length for integers between and including *i* and *j*. These three numbers should be separated by one space, with all three numbers on one line and with one line of output for each line of input. Sample Input 1 10 100 200 201 210 900 1000 Sample Output 1 10 20 100 200 125 201 210 89 900 1000 174 *** my Java solution import java.io.BufferedReader; import java.io.InputStreamReader; public class Main { final static BufferedReader reader_ = new BufferedReader(new InputStreamReader(System.in)); /** * @param args */ public static void main(String[] args) { new Problem().run(); } static String[] ReadLn() { String[] tokens = null; try { String line = reader_.readLine(); String REGEX_WHITESPACE = "\\s+"; String cleanLine = line.trim().replaceAll(REGEX_WHITESPACE, " "); tokens = cleanLine.split(REGEX_WHITESPACE); } catch (Exception e) {} return tokens; } } class Problem implements Runnable { long CACHE_SIZE = 65536; private final long[] cache_ = new long[(int) CACHE_SIZE]; /** * Compute cycle length for a single number * * @param n number for which we find cycle length * @return cycle length */ long cycleLen(long n) { long len = 1; if (n != 1) { len = getFromCache(n); if (len == 0) { //not yet in cache // Recursively compute and store all intermediate values of cycle length if ((n & 1) == 0) { len = 1 + cycleLen(n >> 1); } else { len = 1 + cycleLen(n * 3 + 1); } putInCache(n, len); } } return len; } void putInCache(long n, long len) { if(n < CACHE_SIZE) { cache_[(int)n] = len; } } long getFromCache(long n) { long result = 0; if(n < CACHE_SIZE) { result = cache_[(int)n]; } return result; } /** * Find max cycle on interval * * @param from interval start * @param to interval end * @return max cycle */ Long maxCycle(Long from, Long to) { Long result = 0L; Long cycle = 0L; // Get all values of cycle length on the interval and put these values into a sorted set for (long i = from; i <= to; i++) { cycle = cycleLen(i); if (cycle > result) result = cycle; } return result; } public void run() { String[] tokens = null; long from, to, result = 0; long arg1, arg2 = 0; while ((tokens = Main.ReadLn()) != null) { if (tokens.length == 2) { arg1 = new Long(tokens[0]).longValue(); arg2 = new Long(tokens[1]).longValue(); from = (arg1 <= arg2) ? arg1 : arg2; to = (arg2 >= arg1 ) ? arg2 : arg1; result = maxCycle(from, to); out(arg1+" "+arg2+" "+result); } } } static void out(String msg) { System.out.println(msg); } }

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Problem building qtHaskell
by Øystein Kolsrud 15 Apr '11

15 Apr '11

Hi! I am trying to install qtHaskell on a Windows 7 machine, but I am running into some problems while running the build script. I believe I have followed all the steps stated in the installation instructions, but get errors of this type: Creating library file: ..\bin\libqtc_core.a c:\Prog\Qt\2010.05\qt\lib/libQtUiTools.a(quiloader.o):quiloader.cpp:(.text+0x3c3): undefined reference to `_Unwind_Resume' Can anyone help me figure out what is missing? I have the following versions installed which should meet the requirements: C:\Prog\QTHASK~1.4>g++ --version g++ (GCC) 4.4.3 C:\Prog\QTHASK~1.4>gmake --version GNU Make 3.81 This program built for Windows32 C:\Prog\QTHASK~1.4>ghc --version The Glorious Glasgow Haskell Compilation System, version 7.0.2 Thanks! Best regards, Øystein Kolsrud

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ghc7 bug? associated type + implicit parameters
by Michal Konečný 15 Apr '11

15 Apr '11

Hi, I have stumbled across some strange behaviour in ghc7. The following compiles fine with ghc 6.12.3: {-# LANGUAGE ImplicitParams #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE NoMonomorphismRestriction #-} module Test where class C t where type TF t ttt :: TF t -> t b :: (C t, ?x :: TF t) => t b = ttt ?x but ghc7 says: Could not deduce (?x::TF t) arising from a use of implicit parameter `?x' from the context (C t, ?x::TF t) bound by the type signature for b :: (C t, ?x::TF t) => t at Test.hs:13:1-10 In the first argument of `ttt', namely `?x' In the expression: ttt ?x In an equation for `b': b = ttt ?x Moreover, when I comment out the type declaration for b, it compiles and the inferred type for b is identical to the one in the above program: *Test> :t b b :: (C t, ?x::TF t) => t It feels to me like a bug but I am not entirely confident. Any ideas? Michal -- |o| Michal Konecny <mikkonecny(a)gmail.com> |o| http://www-users.aston.ac.uk/~konecnym/ |o| office: (+42) (0)121 204 3462 |o| PGP key http://www-users.aston.ac.uk/~konecnym/ki.aston -- |o| Michal Konecny <mikkonecny(a)gmail.com> |o| http://www-users.aston.ac.uk/~konecnym/ |o| office: (+42) (0)121 204 3462 |o| PGP key http://www-users.aston.ac.uk/~konecnym/ki.aston -- |o| Michal Konecny <mikkonecny(a)gmail.com> |o| http://www-users.aston.ac.uk/~konecnym/ |o| office: (+42) (0)121 204 3462 |o| PGP key http://www-users.aston.ac.uk/~konecnym/ki.aston

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