- Haskell-Cafe - Haskell.org

Experimental 64 bit installer fails
by Andrew Pennebaker 15 Apr '11

15 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

2 2

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...

3 2

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.

3 6

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

1 0

parallel-haskell mailing list
by Eric Y. Kow 14 Apr '11

14 Apr '11

Hi everybody, I thought I should point out that there is a mailing list dedicated to parallelism and concurrency in Haskell. The group exists to bring together the various groups in the Haskell community that are working on parallelism. It is intended to provide some visibility into the various efforts and to encourage collaboration. So if you want to know what's going on in the parallel Haskell world, this is the place to hang out. You can join the list by sending an email to parallel-haskell%2Bsubscribe(a)googlegroups.com You can also visit the group on the web at http://groups.google.com/group/parallel-haskell Or for those of you who prefer GMane http://dir.gmane.org/gmane.comp.lang.haskell.parallel Enjoy! Eric -- Got news for the Parallel Haskell Digest? Send a mail to eric(a)well-typed.com!

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Munich functional programmers' UG
by "Dr. Heinrich Hördegen" 14 Apr '11

14 Apr '11

Dear all, last week, there have been thoughts to create a user group for functional programmers in Munich, Germany. People who are interessted can join the new mailing list: http://www.fs.lmu.de/cgi-bin/mailman/listinfo/high-order-munich The idea is to have meetings every now and then with talks on aspects of functional programming. However, it's not restricted to Haskell. Please spread the word to anyone who could be interested. Thank you, Heinrich -- hoerdegen(a)funktional.info www.funktional.info --

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Haskell on-line judge for Programming Challenges / Contests ?
by Dmitri O.Kondratiev 14 Apr '11

14 Apr '11

Hello, I am looking for a site providing on-line automatic judge for Programming Challenges that can be coded in Haskell. For example this site: http://www.programming-challenges.com provides lots of interesting programming provlems: http://www.programming-challenges.com/pg.php?page=index Yet, unfortunately only C, C++ and Java code can be submitted, judge on that site can't compile and run Haskell code. Is there any similar online judge for Haskell? Thanks, Dmitri

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IO and Cont as monads
by Burak Ekici 14 Apr '11

14 Apr '11

Dear List, I am quite new in Haskell's categorical manner of programming. However I have enough knowledge in Category Theory. I want to ask a question, maybe very well-known one by some of you, about monads of Haskell. For the type constructors like Maybe and [], I managed to prove that together with 2 natural transformations (bind + return), both of these triples construct a monad. But when I try to prove that IO and Cont type constructors with the same natural transformations (bind + return) are monads as well, it was failed. Here my question is: Is there anyone who knows how to prove that IO and Cont are monads with satisfing following properties: join . fmap join = join . joinjoin . fmap return = join . return = idreturn . f = fmap f . returnjoin . fmap (fmap f) = fmap f . join Thanks already now, Burak Ekici.

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Template Haskell tutorials?
by Kenneth Hoste 14 Apr '11

14 Apr '11

Hi, The links to the supposedly brilliant Template Haskell tutorials by Bulat are broken. http://www.haskell.org/bz/thdoc.htm http://www.haskell.org/bz/th3.htm Does anyone know if these tutorials moved to somewhere else? greetings, Kenneth

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Haskell Weekly News: Issue 177
by Daniel Santa Cruz 14 Apr '11

14 Apr '11

Welcome to issue 177 of the HWN, a newsletter covering developments in the [1]Haskell community. This release covers the week of April 3 to 9, 2011. You can find a HTML rendition of this issue at: http://bit.ly/hR2sMB Announcements Brent Yorgey [2]sent out a call for contributions for the second edition of Typeclassopedia. Roel van Dijk started what became a popular[3]thread on the mailing list about encodings of Haskell source files. What would you like to see here? I have gotten mixed feedback on what constitutes interesting items for the "announcements" section of the mailing list. Some have pointed out that package announcements tend to be noisy and not all that interesting to the community at large, or that have a bias towards only pointing out packages where the maintainer decides to send an email to the mailing list. What do *you* think? How about the "calls for papers"? Do those catch your attention? Let me hear what you think. Quotes of the Week * ion: Itâs a well-known historical fact cave men writing Haskell hated the ASCII pseudoglyphs. * shapr: I persuaded academics to show up and hang out. [...] I told the academics that there were academics worth chatting with on #haskell :-) * pjscott: If you really want to see something ridiculous, try looking at the auto-generated library documentation for anything involving regular expressions. The type declarations in Text.Regex.TDFA are like something H. P. Lovecraft might write about. * monochrom: the road to haskell is paved with good abstractions Top Reddit Stories * Typeclassopedia second edition: call for contributions From (byorgey.wordpress.com) scored 53 with 1 comments. Read on [4]reddit. Read the [5]original post. * High-Performance Web Applications In Haskell : Gregory Collins : QCon London :: PDF From (qconlondon.com) scored 45 with 8 comments. Read on [6]reddit. Read the [7]original post. * Haskell For the Cloud (new paper by Jeff Epstein, Andrew Black, and and Simon Peyton Jones) From (research.microsoft.com) scored 41 with 23 comments. Read on [8]reddit. Read the [9]original post. * Yhc is dead !? From (yhc06.blogspot.com) scored 32 with 27 comments. Read on [10]reddit. Read the [11]original post. * What is a functional language? :: Robert Harper From (existentialtype.wordpress.com) scored 29 with 35 comments. Read on [12]reddit. Read the [13]original post. * Functions are values From (existentialtype.wordpress.com) scored 27 with 16 comments. Read on [14]reddit. Read the [15]original post. * Understanding practical API design, static typing and functional programming. From (blog.tmorris.net) scored 27 with 2 comments. Read on [16]reddit. Read the [17]original post. * Platform Robots in Nikki and the Robots: a Haskell platform game From (joyridelabs.de), scored 22 with 3 comments. Read on [18]reddit. Read the [19]original post. * A Model for Denotative Continuous-Time Programming (AKA: FRP) From (creativelad.wordpress.com) scored 21 with 1 comments. Read on [20]reddit. Read the [21]original post. * Type Kata: Local data type From (blog.ezyang.com) scored 19 with 3 comments. Read on [22]reddit. Read the [23]original post. Top StackOverflow Questions * [24]Difference between State, ST, IORef, and MVar votes: 16, answers: 3 * [25]Duality approaches in functional programming votes: 11, answers: 1 * [26]What are the main differences of language features between Haskell and the functional part of F#? [closed] votes: 9, answers: 5 * [27]Using the Maybe Monad in "reverse" in Haskell votes: 9, answers: 3 * [28]How to reason about space complexity in Haskell votes: 8, answers: 1 About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. I'm in dire need of finding good "quotes of the week". If you happen to come across any, please don't hesitate to send it along. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.general/18636 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/87815 4. http://www.reddit.com/r/haskell/comments/ghs1x/typeclassopedia_second_editi… 5. http://byorgey.wordpress.com/2011/04/03/call-for-contributions-second-editi… 6. http://www.reddit.com/r/haskell/comments/gj7ud/highperformance_web_applicat… 7. http://qconlondon.com/dl/qcon-london-2011/slides/GregoryCollins_HighPerform… 8. http://www.reddit.com/r/haskell/comments/gjb52/haskell_for_the_cloud_new_pa… 9. http://research.microsoft.com/en-us/um/people/simonpj/papers/parallel/ 10. http://www.reddit.com/r/haskell/comments/ghtlf/yhc_is_dead/ 11. http://yhc06.blogspot.com/2011/04/yhc-is-dead.html 12. http://www.reddit.com/r/haskell/comments/gk1tp/what_is_a_functional_languag… 13. http://existentialtype.wordpress.com/2011/03/16/what-is-a-functional-langua… 14. http://www.reddit.com/r/haskell/comments/ghdvn/functions_are_values/ 15. http://existentialtype.wordpress.com/2011/04/02/functions-are-values/ 16. http://www.reddit.com/r/haskell/comments/gir70/understanding_practical_api_… 17. http://blog.tmorris.net/understanding-practical-api-design-static-typing-an… 18. http://www.reddit.com/r/haskell/comments/ghs81/platform_robots_in_nikki_and… 19. http://joyridelabs.de/blog/?p=612 20. http://www.reddit.com/r/haskell/comments/ghrmv/a_model_for_denotative_conti… 21. http://creativelad.wordpress.com/2011/04/03/dctp-model/ 22. http://www.reddit.com/r/haskell/comments/gk1w4/type_kata_local_data_type/ 23. http://blog.ezyang.com/2011/04/type-kata-local-data-type/ 24. http://stackoverflow.com/questions/5545517/difference-between-state-st-iore… 25. http://stackoverflow.com/questions/5557810/duality-approaches-in-functional… 26. http://stackoverflow.com/questions/5541487/what-are-the-main-differences-of… 27. http://stackoverflow.com/questions/5606228/using-the-maybe-monad-in-reverse… 28. http://stackoverflow.com/questions/5552433/how-to-reason-about-space-comple…

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