April 2011 - Haskell-Cafe

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

4 7

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

2 1

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

2 1

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); } }

9 11

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

2 2

ghc7 bug? associated type + implicit parameters
by Michal Konečný 14 Apr '11

14 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

2 1

Experimental 64 bit installer fails
by Andrew Pennebaker 14 Apr '11

14 Apr '11

I downloaded the experimental 64 bit installer for from Haskell Platform<http://hackage.haskell.org/platform/mac.html>. It fails with the message "The installation failed." In case Haskell Platform i386 was interfering, I uninstalled it. But the 64 bit installer still yields "The installation failed." Specs - Haskell Platform 2011.2.0.0-x86_64 installer - Haskell Platform 2011.2.0.0-i386 present - Mac OS X 10.6.7 - MacBook Pro 5,1 /var/log/install.log Apr 14 17:58:38 wonko Installer[18657]: Haskell Platform Installation Log Apr 14 17:58:38 wonko Installer[18657]: Opened from: /Users/andrew/Downloads/Haskell Platform 2011.2.0.0-x86_64.pkg Apr 14 17:58:46 wonko runner[18669]: Administrator authorization granted. Apr 14 17:58:46 wonko Installer[18657]: ================================================================================ Apr 14 17:58:46 wonko Installer[18657]: User picked Standard Install Apr 14 17:58:46 wonko Installer[18657]: Choices selected for installation: Apr 14 17:58:46 wonko Installer[18657]: Upgrade: "Haskell Platform" Apr 14 17:58:46 wonko Installer[18657]: Upgrade: "Glasgow Haskell Compiler" Apr 14 17:58:46 wonko Installer[18657]: Haskell Platform 2011.2.0.0-x86_64.pkg#ghc.pkg : org.haskell.HaskellPlatform.GHC.pkg : 1 Apr 14 17:58:46 wonko Installer[18657]: Upgrade: "Haskell Platform Libraries" Apr 14 17:58:46 wonko Installer[18657]: Haskell Platform 2011.2.0.0-x86_64.pkg#haskell.pkg : org.haskell.HaskellPlatform.Libraries.pkg : 1 Apr 14 17:58:46 wonko Installer[18657]: Haskell Platform 2011.2.0.0-x86_64.pkg#haskellPlatformPostflight.pkg : org.haskell.haskellPlatform.postflight.pkg : 1.0 Apr 14 17:58:46 wonko Installer[18657]: ================================================================================ Apr 14 17:58:46 wonko Installer[18657]: It took 0.00 seconds to summarize the package selections. Apr 14 17:58:46 wonko Installer[18657]: -[IFDInstallController(Private) _buildInstallPlan]: location = file://localhost Apr 14 17:58:46 wonko Installer[18657]: -[IFDInstallController(Private) _buildInstallPlan]: file://localhost/Users/andrew/Downloads/Haskell%20Platform%202011.2.0.0-x86_64.pkg#ghc.pkg Apr 14 17:58:46 wonko Installer[18657]: -[IFDInstallController(Private) _buildInstallPlan]: file://localhost/Users/andrew/Downloads/Haskell%20Platform%202011.2.0.0-x86_64.pkg#haskell.pkg Apr 14 17:58:46 wonko Installer[18657]: -[IFDInstallController(Private) _buildInstallPlan]: file://localhost/Users/andrew/Downloads/Haskell%20Platform%202011.2.0.0-x86_64.pkg#haskellPlatformPostflight.pkg Apr 14 17:58:46 wonko Installer[18657]: Will use PK session Apr 14 17:58:46 wonko Installer[18657]: Starting installation: Apr 14 17:58:46 wonko Installer[18657]: Configuring volume "Wonko" Apr 14 17:58:46 wonko Installer[18657]: Preparing disk for local booted install. Apr 14 17:58:46 wonko Installer[18657]: Free space on "Wonko": 52.51 GB (52508946432 bytes). Apr 14 17:58:46 wonko Installer[18657]: Create temporary directory "/var/folders/N-/N-IxaaKuFae5ik1WKxV6wE+++TI/-Tmp-//Install.18657bWOdda" Apr 14 17:58:46 wonko Installer[18657]: IFPKInstallElement (3 packages) Apr 14 17:58:46 wonko installd[18673]: PackageKit: ----- Begin install ----- Apr 14 17:58:46 wonko installd[18673]: PackageKit: request=PKInstallRequest <3 packages, destination=/> Apr 14 17:58:46 wonko installd[18673]: PackageKit: packages=(\n "PKLeopardPackage <file://localhost/Users/andrew/Downloads/Haskell%20Platform%202011.2.0.0-x86_64.pkg#ghc.pkg>",\n "PKLeopardPackage <file://localhost/Users/andrew/Downloads/Haskell%20Platform%202011.2.0.0-x86_64.pkg#haskell.pkg>",\n "PKLeopardPackage <file://localhost/Users/andrew/Downloads/Haskell%20Platform%202011.2.0.0-x86_64.pkg#haskellPlatformPostflight.pkg>"\n) Apr 14 17:58:47 wonko installd[18673]: PackageKit: Extracting file://localhost/Users/andrew/Downloads/Haskell%20Platform%202011.2.0.0-x86_64.pkg#ghc.pkg (destination=/var/folders/zz/zzzivhrRnAmviuee+++++++++++/Cleanup At Startup/PKInstallSandbox-tmp/Root/Library/Frameworks, uid=0) Apr 14 17:59:06 wonko installd[18673]: PackageKit: Extracting file://localhost/Users/andrew/Downloads/Haskell%20Platform%202011.2.0.0-x86_64.pkg#haskell.pkg (destination=/var/folders/zz/zzzivhrRnAmviuee+++++++++++/Cleanup At Startup/PKInstallSandbox-tmp/Root/Library, uid=0) Apr 14 17:59:12 wonko installd[18673]: PackageKit: Extracting file://localhost/Users/andrew/Downloads/Haskell%20Platform%202011.2.0.0-x86_64.pkg#haskellPlatformPostflight.pkg (destination=/var/folders/zz/zzzivhrRnAmviuee+++++++++++/Cleanup At Startup/PKInstallSandbox-tmp/Root, uid=0) Apr 14 17:59:14 wonko installd[18673]: PackageKit: Shoving /var/folders/zz/zzzivhrRnAmviuee+++++++++++/Cleanup At Startup/PKInstallSandbox-tmp/Root (1 items) to / Apr 14 17:59:16 wonko installd[18673]: PackageKit: Executing script "./postinstall" in /private/tmp/PKInstallSandbox.e59JtF/Scripts/org.haskell.HaskellPlatform.GHC.pkg.k6SuIR Apr 14 17:59:16 wonko installd[18673]: PackageKit: Executing script "./postinstall" in /private/tmp/PKInstallSandbox.e59JtF/Scripts/org.haskell.HaskellPlatform.Libraries.pkg.dWwJo8 Apr 14 17:59:17 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/GLUT-2.1.2.1.conf" ... done. Apr 14 17:59:17 wonko installd[18673]: ./postinstall: GLUT-2.1.2.1: dependency "OpenGL-2.2.3.0-f260c686098842b872fcd761a1de8b56" doesn't exist (ignoring) Apr 14 17:59:17 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/HTTP-4000.1.1.conf" ... done. Apr 14 17:59:17 wonko installd[18673]: ./postinstall: HTTP-4000.1.1: dependency "mtl-2.0.1.0-5b7a9cce5565d8cc8721ba4f95becf1b" doesn't exist (ignoring) Apr 14 17:59:17 wonko installd[18673]: ./postinstall: HTTP-4000.1.1: dependency "network-2.3.0.2-980e23d4d2855583b05d6ed337c0eaed" doesn't exist (ignoring) Apr 14 17:59:17 wonko installd[18673]: ./postinstall: HTTP-4000.1.1: dependency "parsec-3.1.1-d6e895e0dfa7aa6990c069c9c9c706bb" doesn't exist (ignoring) Apr 14 17:59:17 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/HUnit-1.2.2.3.conf" ... done. Apr 14 17:59:17 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/OpenGL-2.2.3.0.conf" ... done. Apr 14 17:59:17 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/QuickCheck-2.4.0.1.conf" ... done. Apr 14 17:59:17 wonko installd[18673]: ./postinstall: QuickCheck-2.4.0.1: dependency "mtl-2.0.1.0-5b7a9cce5565d8cc8721ba4f95becf1b" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/cgi-3001.1.7.4.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: cgi-3001.1.7.4: dependency "mtl-2.0.1.0-5b7a9cce5565d8cc8721ba4f95becf1b" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: cgi-3001.1.7.4: dependency "network-2.3.0.2-980e23d4d2855583b05d6ed337c0eaed" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: cgi-3001.1.7.4: dependency "parsec-3.1.1-d6e895e0dfa7aa6990c069c9c9c706bb" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: cgi-3001.1.7.4: dependency "xhtml-3000.2.0.1-fa3c2d95250480afb9bfb787b25e7398" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/deepseq-1.1.0.2.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/fgl-5.4.2.3.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: fgl-5.4.2.3: dependency "mtl-2.0.1.0-5b7a9cce5565d8cc8721ba4f95becf1b" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/haskell-platform-2011.2.0.0.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "haskell-src-1.0.1.4-1aa2c7df30199d039aa020a6edd80791" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "html-1.0.1.2-0cdd616c514cf10f5323f121a96991b6" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "mtl-2.0.1.0-5b7a9cce5565d8cc8721ba4f95becf1b" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "network-2.3.0.2-980e23d4d2855583b05d6ed337c0eaed" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "parallel-3.1.0.1-cecd6f84e9c097c6abc356ad52b80887" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "parsec-3.1.1-d6e895e0dfa7aa6990c069c9c9c706bb" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "regex-base-0.93.2-ea22834f5565d6f16b2cec3e7a63917a" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "regex-compat-0.93.1-bfb1854d3b8f7b71bdd9d0efc565110d" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "regex-posix-0.94.4-d6abc61e1702c884e7bba4f3e318dda9" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "stm-2.2.0.1-88d46817e31bfcb31467cd8ca2c7850b" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "syb-0.3-00d8c06f799942b01364e795b2a54d70" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "text-0.11.0.5-efa21e4f4b045cc91adb4295f85c7319" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "transformers-0.2.2.0-4bbbfde1fb5c4eb17cdb1963dda698f3" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "xhtml-3000.2.0.1-fa3c2d95250480afb9bfb787b25e7398" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-platform-2011.2.0.0: dependency "zlib-0.5.3.1-7e19941cbd00147a79723e25160ffc8b" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/haskell-src-1.0.1.4.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: haskell-src-1.0.1.4: dependency "syb-0.3-00d8c06f799942b01364e795b2a54d70" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/html-1.0.1.2.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/mtl-2.0.1.0.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: mtl-2.0.1.0: dependency "transformers-0.2.2.0-4bbbfde1fb5c4eb17cdb1963dda698f3" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/network-2.3.0.2.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: network-2.3.0.2: dependency "parsec-3.1.1-d6e895e0dfa7aa6990c069c9c9c706bb" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/parallel-3.1.0.1.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/parsec-3.1.1.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/regex-base-0.93.2.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/regex-compat-0.93.1.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: regex-compat-0.93.1: dependency "regex-posix-0.94.4-d6abc61e1702c884e7bba4f3e318dda9" doesn't exist (ignoring) Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/regex-posix-0.94.4.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/stm-2.2.0.1.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/syb-0.3.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/text-0.11.0.5.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/transformers-0.2.2.0.conf" ... done. Apr 14 17:59:18 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/xhtml-3000.2.0.1.conf" ... done. Apr 14 17:59:19 wonko installd[18673]: ./postinstall: Reading package info from "/Library/Haskell/ghc-7.0.2/lib/registrations/zlib-0.5.3.1.conf" ... done. Apr 14 17:59:19 wonko installd[18673]: ./postinstall: ln: /Library/Haskell/ghc-7.0.2/doc/ghc-doc: File exists Apr 14 17:59:19 wonko installd[18673]: ./postinstall: ln: /Library/Haskell/ghc-7.0.2/doc/ghc-api: File exists Apr 14 17:59:19 wonko installd[18673]: PackageKit: Install Failed: PKG: post-install scripts for "org.haskell.HaskellPlatform.Libraries.pkg"\nError Domain=PKInstallErrorDomain Code=112 UserInfo=0x102f52820 "An error occurred while running scripts from the package “Haskell Platform 2011.2.0.0-x86_64.pkg”." {\n NSFilePath = "./postinstall";\n NSLocalizedDescription = "An error occurred while running scripts from the package \U201cHaskell Platform 2011.2.0.0-x86_64.pkg\U201d.";\n NSURL = "#haskell.pkg -- file://localhost/Users/andrew/Downloads/Haskell%20Platform%202011.2.0.0-x86_64.pkg";\n PKInstallPackageIdentifier = "org.haskell.HaskellPlatform.Libraries.pkg";\n} Apr 14 17:59:19 wonko Installer[18657]: install:didFailWithError:Error Domain=PKInstallErrorDomain Code=112 UserInfo=0x1002af810 "An error occurred while running scripts from the package “Haskell Platform 2011.2.0.0-x86_64.pkg”." Apr 14 17:59:19 wonko Installer[18657]: Install failed: The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance. Apr 14 17:59:19 wonko Installer[18657]: IFDInstallController 23DC40 state = 7 Apr 14 17:59:19 wonko Installer[18657]: Displaying 'Install Failed' UI. Apr 14 17:59:19 wonko Installer[18657]: 'Install Failed' UI displayed message:'The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.'. Apr 14 18:02:50 wonko Installer[24606]: @(#)PROGRAM:Install PROJECT:Install-595.1 Apr 14 18:02:50 wonko Installer[24606]: @(#)PROGRAM:Installer PROJECT:Installer-430.1 Apr 14 18:02:50 wonko Installer[24606]: Hardware: MacBookPro5,5 @ 2.53 GHz (x 2), 4096 MB RAM Apr 14 18:02:50 wonko Installer[24606]: Running OS Build: Mac OS X 10.6.7 (10J869) Apr 14 18:02:50 wonko Installer[24606]: Env: PATH=/usr/bin:/bin:/usr/sbin:/sbin Apr 14 18:02:50 wonko Installer[24606]: Env: TMPDIR=/var/folders/N-/N-IxaaKuFae5ik1WKxV6wE+++TI/-Tmp-/ Apr 14 18:02:50 wonko Installer[24606]: Env: SHELL=/bin/bash Apr 14 18:02:50 wonko Installer[24606]: Env: HOME=/Users/andrew Apr 14 18:02:50 wonko Installer[24606]: Env: USER=andrew Apr 14 18:02:50 wonko Installer[24606]: Env: LOGNAME=andrew Apr 14 18:02:50 wonko Installer[24606]: Env: DISPLAY=/tmp/launch-IvsorY/org.x:0 Apr 14 18:02:50 wonko Installer[24606]: Env: SSH_AUTH_SOCK=/tmp/launch-kqVUwk/Listeners Apr 14 18:02:50 wonko Installer[24606]: Env: Apple_PubSub_Socket_Render=/tmp/launch-dpKpq2/Render Apr 14 18:02:50 wonko Installer[24606]: Env: COMMAND_MODE=unix2003 Apr 14 18:02:50 wonko Installer[24606]: Env: __CF_USER_TEXT_ENCODING=0x1F5:0:0 Cheers, Andrew Pennebaker www.yellosoft.us

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Questioning seq
by Andrew Coppin 14 Apr '11

14 Apr '11

A couple of questions: 1. Why is the existence of polymorphic seq bad? 2. Why would the existence of polymorphic rnf be worse? 3. How is pseq different from seq? That is all...

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Type Classes in Haskell - how can I make GHC make a choice of types, when the type chosen doesn't matter?
by Chris Dew 14 Apr '11

14 Apr '11

This is a question about the use of type classes in Haskell. I get an error (below) when trying to compile the code (below and at https://github.com/chrisdew/haskell-sandbox/blob/master/not_working_but_cle… ). As someone just learning Haskell, I have tried following GHC's advice, but I think the cause is different. I believe the problem is that either of the types 'IO String' or plain 'String' could be the type of 'lhello ->> lbracket', but GHC doesn't know which. The problem is that it doesn't matter, either type would work fine. I have posted a working version of the code at https://github.com/chrisdew/haskell-sandbox/blob/master/working_but_ugly.hs . This replaces one of the ->> operators with a new (non type class) operator '->>>' which forces 'lhello ->> lbracket' to be of type 'IO String'. * Is my analysis correct? Or is there something else going on here? * Is there any way of informing GHC what the type of 'lhello ->> lbracket' doen't matter and that is should just chose either of the two possibilities. Or perhaps theres a LANGUAGE option which will let me specify that 'lastest declared matching instance of the class wins' if anything is undecided. Thanks, Chris. Error: chris@chris-linux-desktop:~/nonworkspace/haskell-sandbox$ ghc not_working_but_clean.hs not_working_but_clean.hs:40:16: No instance for (Stream (IO String) (IO String) (IO String) d) arising from a use of `->>' at not_working_but_clean.hs:40:16-34 Possible fix: add an instance declaration for (Stream (IO String) (IO String) (IO String) d) In the first argument of `(->>)', namely `lhello ->> lbracket' In the second argument of `($)', namely `lhello ->> lbracket ->> putStrLn' In a stmt of a 'do' expression: forkIO $ lhello ->> lbracket ->> putStrLn not_working_but_clean.hs:40:16: No instance for (Stream d String (IO ()) (IO ())) arising from a use of `->>' at not_working_but_clean.hs:40:16-47 Possible fix: add an instance declaration for (Stream d String (IO ()) (IO ())) In the second argument of `($)', namely `lhello ->> lbracket ->> putStrLn' In a stmt of a 'do' expression: forkIO $ lhello ->> lbracket ->> putStrLn In the expression: do { forkIO $ (bracket $ hello) ->> putStrLn; forkIO $ lhello ->> lbracket ->> putStrLn; forkIO $ bracket hello ->> putStrLn; forkIO $ lbracket lhello ->> putStrLn; .... } not_working_but_clean.hs: {-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, TypeSynonymInstances, OverlappingInstances #-} {-# OPTIONS_GHC #-} module Main ( main ) where import Control.Concurrent (forkIO, MVar, newEmptyMVar, putMVar, takeMVar, ThreadId, threadDelay) import Control.Monad (forever, liftM) class Stream a b c d where (->>) :: a -> (b -> c) -> d instance Stream (IO d) d (IO c) (IO c) where f ->> g = f >>= g instance Stream d d (IO c) (IO c) where f ->> g = g f instance Stream d d c c where x ->> y = y $ x -- This simply wraps a string in brackets. bracket :: String -> String bracket x = "(" ++ x ++ ")" lbracket :: IO String -> IO String lbracket x = liftM bracket x hello :: String hello = "Hello World!" lhello :: IO String lhello = do return hello main :: IO () main = do forkIO $ (bracket $ hello) ->> putStrLn forkIO $ lhello ->> lbracket ->> putStrLn forkIO $ bracket hello ->> putStrLn forkIO $ lbracket lhello ->> putStrLn threadDelay 10000000 -- Sleep for at least 10 seconds before exiting. working_but_ugly.hs: {-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, TypeSynonymInstances, OverlappingInstances #-} {-# OPTIONS_GHC #-} module Main ( main ) where import Control.Concurrent (forkIO, MVar, newEmptyMVar, putMVar, takeMVar, ThreadId, threadDelay) import Control.Monad (forever, liftM) class Stream a b c d where (->>) :: a -> (b -> c) -> d instance Stream (IO d) d (IO c) (IO c) where f ->> g = f >>= g instance Stream d d (IO c) (IO c) where f ->> g = g f instance Stream d d c c where x ->> y = y $ x x ->>> y = y $ x -- This simply wraps a string in brackets. bracket :: String -> String bracket x = "(" ++ x ++ ")" lbracket :: IO String -> IO String lbracket x = liftM bracket x hello :: String hello = "Hello World!" lhello :: IO String lhello = do return hello main :: IO () main = do forkIO $ (bracket $ hello) ->> putStrLn forkIO $ lhello ->>> lbracket ->> putStrLn forkIO $ bracket hello ->> putStrLn forkIO $ lbracket lhello ->> putStrLn threadDelay 10000000 -- Sleep for at least 10 seconds before exiting.

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Re: [Haskell-cafe] Questioning seq
by Janis Voigtländer 14 Apr '11

14 Apr '11

Am 14.04.2011 18:57:35 schrieb Andrew Coppin<andrewcoppin(a)btinternet.com>: > A couple of questions: > > 1. Why is the existence of polymorphic seq bad? See http://www.iai.uni-bonn.de/~jv/acta.pdf, Sections 1 and 2 and pointers therein. Also, numerous discussions on this list over the years. Best, Janis. > 2. Why would the existence of polymorphic rnf be worse? > > 3. How is pseq different from seq? > > That is all... > -- Jun.-Prof. Dr. Janis Voigtländer http://www.iai.uni-bonn.de/~jv/ mailto:jv@iai.uni-bonn.de

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