- Beginners - Haskell.org

Working With TVars
by aditya siram 28 Apr '09

28 Apr '09

Hi all, I have a tuple inside a TVar : > type MySTM = TVar (Int,Int) Whenever I want to edit/read 'a' or 'b' I find myself writing : > editFunction mySTM = do (a',b') <- readTVar mySTM dostuff a' ... This is boilerplate stuff, so I decided to write some accessors. So far I have : > getA , getB :: MySTM -> STM Int > getA mySTM = do > (a',b') <- readTVar mySTM > return a' > > getB mySTM = do > (a',b') <- readTVar mySTM > return b' I want to be able to use these accessors like so: > doSomethingWithA mySTM = do > case (getA mySTM) of > 1 -> doStuff > 0 -> doSomethingElse But getA returns an STM Int, so I still have to do a : > doSomethingWithA = do > a' <- (getA mySTM) > case a' of > 1 -> doStuff > 0 -> doSomethingElse This doesn't really save me a lot of boilerplate. What is the best way of writing a function that just returns my values do I can work with them in the STM monad without unpacking them all the time? Thanks , Deech

3 2

Problem install ghc 6.10.2
by aditya siram 28 Apr '09

28 Apr '09

Hi all, I am trying to install the Linux GHC 6.10.2 binary, but when I fire up ghci I get the following error: GHCi, version 6.10.2: http://www.haskell.org/ghc/ :? for help Glasgow Haskell Compiler, Version 6.10.2, for Haskell 98, stage 2 booted by GHC version 6.10.1 Using package config file: /usr/local/lib/ghc-6.10.2/./package.conf wired-in package ghc-prim[""] not found. wired-in package integer[""] not found. wired-in package base[""] not found. wired-in package rts mapped to rts-1.0 wired-in package haskell98[""] not found. wired-in package syb[""] not found. wired-in package template-haskell[""] not found. wired-in package dph-seq[""] not found. wired-in package dph-par[""] not found. package haddock-2.4.2 will be ignored due to missing or recursive dependencies: Cabal-1.6.0.3 array-0.2.0.0 base-4.1.0.0 containers-0.2.0.1 directory-1.0.0.3 filepath-1.1.0.2 ghc-6.10.2 haskell98-1.0.1.0 pretty-1.0.1.0 package ghc-6.10.2 will be ignored due to missing or recursive dependencies: Cabal-1.6.0.3 array-0.2.0.0 base-4.1.0.0 bytestring-0.9.1.4 containers-0.2.0.1 directory-1.0.0.3 editline-0.2.1.0 filepath-1.1.0.2 haskell98-1.0.1.0 hpc-0.5.0.3 old-time-1.0.0.2 process-1.0.1.1 template-haskell-2.3.0.1 unix-2.3.2.0 Hsc static flags: -static *** Deleting temp files: Deleting: *** Deleting temp dirs: Deleting: ghc: panic! (the 'impossible' happened) (GHC version 6.10.2 for i386-unknown-linux): interactiveUI:setBuffering2 Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Running ghc-pkg check gave me : There are problems in package haddock-2.4.2: dependency Cabal-1.6.0.3 doesn't exist dependency array-0.2.0.0 doesn't exist dependency base-4.1.0.0 doesn't exist dependency containers-0.2.0.1 doesn't exist dependency directory-1.0.0.3 doesn't exist dependency filepath-1.1.0.2 doesn't exist dependency haskell98-1.0.1.0 doesn't exist dependency pretty-1.0.1.0 doesn't exist There are problems in package ghc-6.10.2: dependency Cabal-1.6.0.3 doesn't exist dependency array-0.2.0.0 doesn't exist dependency base-4.1.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.1 doesn't exist dependency directory-1.0.0.3 doesn't exist dependency editline-0.2.1.0 doesn't exist dependency filepath-1.1.0.2 doesn't exist dependency haskell98-1.0.1.0 doesn't exist dependency hpc-0.5.0.3 doesn't exist dependency old-time-1.0.0.2 doesn't exist dependency process-1.0.1.1 doesn't exist dependency template-haskell-2.3.0.1 doesn't exist dependency unix-2.3.2.0 doesn't exist The following packages are broken, either because they have a problem listed above, or because they depend on a broken package. haddock-2.4.2 ghc-6.10.2 Listing user packages ( ghc-pkg list --user ) shows that ghc-pkg is looking for a package.conf in ~/.ghc/i386-linux-6.10.2/package.conf which doesn't exist:. So I created it and copied over the package.conf file from ~/.ghc/i386-linux-6.10.1/ and ran ghc-pkg check again with the following error : There are problems in package CC-delcont-0.2: dependency base-3.0.3.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist There are problems in package terminfo-0.2.2.1: dependency base-3.0.3.0 doesn't exist There are problems in package darcs-2.2.0: dependency array-0.2.0.0 doesn't exist dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency html-1.0.1.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency parsec-2.1.0.1 doesn't exist dependency process-1.0.1.0 doesn't exist dependency random-1.0.0.1 doesn't exist dependency regex-compat-0.71.0.1 doesn't exist dependency unix-2.3.1.0 doesn't exist There are problems in package extensible-exceptions-0.1.1.0: dependency base-4.0.0.0 doesn't exist There are problems in package binary-0.4.4: dependency array-0.2.0.0 doesn't exist dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist There are problems in package syb-with-class-0.4: dependency array-0.2.0.0 doesn't exist dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package hspread-0.3.1: dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist There are problems in package happstack-state-0.1: dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency random-1.0.0.1 doesn't exist dependency stm-2.1.1.2 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist dependency unix-2.3.1.0 doesn't exist There are problems in package happstack-ixset-0.1: dependency base-4.0.0.0 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package happstack-server-0.1: dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency html-1.0.1.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-locale-1.0.0.1 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency parsec-2.1.0.1 doesn't exist dependency process-1.0.1.0 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist dependency unix-2.3.1.0 doesn't exist dependency xhtml-3000.2.0.1 doesn't exist There are problems in package happstack-contrib-0.1: dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency unix-2.3.1.0 doesn't exist There are problems in package X11-1.4.5: dependency base-3.0.3.0 doesn't exist There are problems in package xmonad-0.8.1: dependency base-3.0.3.0 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency process-1.0.1.0 doesn't exist dependency unix-2.3.1.0 doesn't exist There are problems in package utf8-string-0.3.4: dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist There are problems in package X11-xft-0.3: dependency base-3.0.3.0 doesn't exist There are problems in package ghc-paths-0.1.0.5: dependency base-3.0.3.0 doesn't exist There are problems in package haddock-2.4.1: dependency Cabal-1.6.0.1 doesn't exist dependency array-0.2.0.0 doesn't exist dependency base-4.0.0.0 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency ghc-6.10.1 doesn't exist dependency pretty-1.0.1.0 doesn't exist There are problems in package regex-base-0.93.1: dependency array-0.2.0.0 doesn't exist dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist There are problems in package regex-posix-0.94.1: dependency array-0.2.0.0 doesn't exist dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist There are problems in package regex-compat-0.92: dependency array-0.2.0.0 doesn't exist dependency base-3.0.3.0 doesn't exist There are problems in package syb-with-class-0.5.1: dependency array-0.2.0.0 doesn't exist dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package terminfo-0.3: dependency base-3.0.3.0 doesn't exist There are problems in package time-1.1.2.3: dependency base-3.0.3.0 doesn't exist dependency old-locale-1.0.0.1 doesn't exist There are problems in package xmonad-contrib-0.8.1: dependency base-3.0.3.0 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-locale-1.0.0.1 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency process-1.0.1.0 doesn't exist dependency random-1.0.0.1 doesn't exist dependency unix-2.3.1.0 doesn't exist There are problems in package wxcore-0.11.0: dependency base-4.0.0.0 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency stm-2.1.1.2 doesn't exist There are problems in package process-1.0.1.1: dependency base-4.0.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency unix-2.3.1.0 doesn't exist There are problems in package darcs-2.2.1: dependency array-0.2.0.0 doesn't exist dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency html-1.0.1.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency parsec-2.1.0.1 doesn't exist dependency random-1.0.0.1 doesn't exist dependency unix-2.3.1.0 doesn't exist There are problems in package haskell98-1.0.1.0: dependency array-0.2.0.0 doesn't exist dependency base-4.0.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency old-locale-1.0.0.1 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency random-1.0.0.1 doesn't exist There are problems in package HaXml-1.13.3: dependency base-3.0.3.0 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency pretty-1.0.1.0 doesn't exist There are problems in package terminfo-0.3.0.1: dependency base-3.0.3.0 doesn't exist There are problems in package hslogger-1.0.7: dependency base-3.0.3.0 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-locale-1.0.0.1 doesn't exist dependency unix-2.3.1.0 doesn't exist There are problems in package happstack-util-0.1: dependency HUnit-1.2.0.3 doesn't exist dependency QuickCheck-1.2.0.0 doesn't exist dependency array-0.2.0.0 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency random-1.0.0.1 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package happstack-data-0.1: dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency pretty-1.0.1.0 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package happstack-util-0.1.9: dependency HUnit-1.2.0.3 doesn't exist dependency QuickCheck-1.2.0.0 doesn't exist dependency array-0.2.0.0 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency random-1.0.0.1 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package happstack-data-0.1.9: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency pretty-1.0.1.0 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package happstack-state-0.1.9: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency random-1.0.0.1 doesn't exist dependency stm-2.1.1.2 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist dependency unix-2.3.1.0 doesn't exist There are problems in package happstack-ixset-0.1.9: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package MaybeT-0.1.2: dependency base-3.0.3.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist There are problems in package zlib-0.5.0.0: dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist There are problems in package happstack-server-0.1.9: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency html-1.0.1.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-locale-1.0.0.1 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency parsec-2.1.0.1 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist dependency unix-2.3.1.0 doesn't exist dependency xhtml-3000.2.0.1 doesn't exist There are problems in package happstack-contrib-0.1.9: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency unix-2.3.1.0 doesn't exist There are problems in package HJavaScript-0.4.4: dependency base-3.0.3.0 doesn't exist There are problems in package cpphs-1.6: dependency base-3.0.3.0 doesn't exist There are problems in package harp-0.4: dependency base-3.0.3.0 doesn't exist There are problems in package haskell-src-exts-0.4.8: dependency array-0.2.0.0 doesn't exist dependency base-4.0.0.0 doesn't exist dependency pretty-1.0.1.0 doesn't exist There are problems in package hsx-0.4.8: dependency base-3.0.3.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist There are problems in package HJScript-0.4.4: dependency base-3.0.3.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist There are problems in package hsp-0.4.5: dependency base-3.0.3.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist There are problems in package happstack-0.1.9: dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency syb-0.1.0.0 doesn't exist There are problems in package Xauth-0.1: dependency base-3.0.3.0 doesn't exist There are problems in package byteorder-1.0.0: dependency base-3.0.3.0 doesn't exist There are problems in package xhb-0.2.2009.2.21: dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency parsec-2.1.0.1 doesn't exist dependency stm-2.1.1.2 doesn't exist There are problems in package HStringTemplate-0.4.3: dependency array-0.2.0.0 doesn't exist dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency old-locale-1.0.0.1 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency parsec-2.1.0.1 doesn't exist dependency pretty-1.0.1.0 doesn't exist There are problems in package happstack-util-0.2.1: dependency HUnit-1.2.0.3 doesn't exist dependency QuickCheck-1.2.0.0 doesn't exist dependency array-0.2.0.0 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-locale-1.0.0.1 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency parsec-2.1.0.1 doesn't exist dependency random-1.0.0.1 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package happstack-data-0.2.1: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency pretty-1.0.1.0 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package happstack-ixset-0.2.1: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package happstack-server-0.2.1: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency html-1.0.1.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-locale-1.0.0.1 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency parsec-2.1.0.1 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist dependency unix-2.3.1.0 doesn't exist dependency xhtml-3000.2.0.1 doesn't exist There are problems in package happstack-state-0.2.1: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency random-1.0.0.1 doesn't exist dependency stm-2.1.1.2 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist dependency unix-2.3.1.0 doesn't exist There are problems in package happstack-0.2.1: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency syb-0.1.0.0 doesn't exist There are problems in package uniplate-1.2.0.3: dependency base-4.0.0.0 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency syb-0.1.0.0 doesn't exist There are problems in package wx-0.11.0: dependency base-4.0.0.0 doesn't exist dependency stm-2.1.1.2 doesn't exist There are problems in package wx-0.11.1.2: dependency base-4.0.0.0 doesn't exist dependency stm-2.1.1.2 doesn't exist dependency wxcore-0.11.1.2 doesn't exist There are problems in package bimap-0.2.4: dependency base-3.0.3.0 doesn't exist dependency containers-0.2.0.0 doesn't exist There are problems in package encoding-0.5.1: dependency array-0.2.0.0 doesn't exist dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package fclabels-0.1: dependency base-3.0.3.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package hscolour-1.11: dependency base-3.0.3.0 doesn't exist There are problems in package parsec-3.0.0: dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency mtl-1.1.0.2 doesn't exist There are problems in package pureMD5-0.2.4: dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist There are problems in package salvia-0.1.1: dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-locale-1.0.0.1 doesn't exist dependency random-1.0.0.1 doesn't exist dependency stm-2.1.1.2 doesn't exist There are problems in package salvia-extras-0.1.1: dependency base-3.0.3.0 doesn't exist There are problems in package Diff-0.1.2: dependency array-0.2.0.0 doesn't exist dependency base-3.0.3.0 doesn't exist There are problems in package clevercss-0.1.1: dependency base-3.0.3.0 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency parsec-2.1.0.1 doesn't exist There are problems in package datetime-0.1: dependency QuickCheck-1.2.0.0 doesn't exist dependency base-3.0.3.0 doesn't exist dependency old-locale-1.0.0.1 doesn't exist dependency old-time-1.0.0.1 doesn't exist There are problems in package nano-md5-0.1.2: dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist There are problems in package network-2.2.0.1: dependency base-4.0.0.0 doesn't exist dependency parsec-2.1.0.1 doesn't exist There are problems in package split-0.1.1: dependency base-3.0.3.0 doesn't exist There are problems in package xml-1.3.4: dependency base-3.0.3.0 doesn't exist There are problems in package filestore-0.2: dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency parsec-2.1.0.1 doesn't exist There are problems in package hsemail-1.3: dependency base-3.0.3.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency parsec-2.1.0.1 doesn't exist There are problems in package SMTPClient-1.0.1: dependency base-3.0.3.0 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency old-locale-1.0.0.1 doesn't exist dependency old-time-1.0.0.1 doesn't exist There are problems in package HTTP-4000.0.4: dependency array-0.2.0.0 doesn't exist dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency parsec-2.1.0.1 doesn't exist There are problems in package happstack-util-0.3: dependency HUnit-1.2.0.3 doesn't exist dependency QuickCheck-1.2.0.0 doesn't exist dependency array-0.2.0.0 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-locale-1.0.0.1 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency parsec-2.1.0.1 doesn't exist dependency random-1.0.0.1 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package happstack-data-0.3: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency pretty-1.0.1.0 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package happstack-state-0.3: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency random-1.0.0.1 doesn't exist dependency stm-2.1.1.2 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist dependency unix-2.3.1.0 doesn't exist There are problems in package happstack-ixset-0.3: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist There are problems in package happstack-server-0.3: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.0 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency html-1.0.1.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-locale-1.0.0.1 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency parsec-2.1.0.1 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency template-haskell-2.3.0.0 doesn't exist dependency unix-2.3.1.0 doesn't exist dependency xhtml-3000.2.0.1 doesn't exist There are problems in package happstack-contrib-0.3: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency syb-0.1.0.0 doesn't exist dependency unix-2.3.1.0 doesn't exist There are problems in package FileManip-0.3.2: dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency unix-2.3.1.0 doesn't exist There are problems in package happstack-0.3: dependency HUnit-1.2.0.3 doesn't exist dependency base-4.0.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency directory-1.0.0.2 doesn't exist dependency filepath-1.1.0.1 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency syb-0.1.0.0 doesn't exist There are problems in package HTTP-4000.0.5: dependency array-0.2.0.0 doesn't exist dependency base-3.0.3.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency mtl-1.1.0.2 doesn't exist dependency old-time-1.0.0.1 doesn't exist dependency parsec-2.1.0.1 doesn't exist There are problems in package haddock-2.4.2: dependency Cabal-1.6.0.3 doesn't exist dependency array-0.2.0.0 doesn't exist dependency base-4.1.0.0 doesn't exist dependency containers-0.2.0.1 doesn't exist dependency directory-1.0.0.3 doesn't exist dependency filepath-1.1.0.2 doesn't exist dependency pretty-1.0.1.0 doesn't exist There are problems in package ghc-6.10.2: dependency Cabal-1.6.0.3 doesn't exist dependency array-0.2.0.0 doesn't exist dependency base-4.1.0.0 doesn't exist dependency bytestring-0.9.1.4 doesn't exist dependency containers-0.2.0.1 doesn't exist dependency directory-1.0.0.3 doesn't exist dependency editline-0.2.1.0 doesn't exist dependency filepath-1.1.0.2 doesn't exist dependency hpc-0.5.0.3 doesn't exist dependency old-time-1.0.0.2 doesn't exist dependency template-haskell-2.3.0.1 doesn't exist dependency unix-2.3.2.0 doesn't exist The following packages are broken, either because they have a problem listed above, or because they depend on a broken package. CC-delcont-0.2 terminfo-0.2.2.1 darcs-2.2.0 extensible-exceptions-0.1.1.0 binary-0.4.4 syb-with-class-0.4 hspread-0.3.1 happstack-state-0.1 happstack-ixset-0.1 happstack-server-0.1 happstack-contrib-0.1 X11-1.4.5 xmonad-0.8.1 utf8-string-0.3.4 X11-xft-0.3 ghc-paths-0.1.0.5 haddock-2.4.1 regex-base-0.93.1 regex-posix-0.94.1 regex-compat-0.92 syb-with-class-0.5.1 terminfo-0.3 time-1.1.2.3 xmonad-contrib-0.8.1 wxcore-0.11.0 process-1.0.1.1 darcs-2.2.1 haskell98-1.0.1.0 HaXml-1.13.3 terminfo-0.3.0.1 hslogger-1.0.7 happstack-util-0.1 happstack-data-0.1 happstack-util-0.1.9 happstack-data-0.1.9 happstack-state-0.1.9 happstack-ixset-0.1.9 MaybeT-0.1.2 zlib-0.5.0.0 happstack-server-0.1.9 happstack-contrib-0.1.9 HJavaScript-0.4.4 cpphs-1.6 harp-0.4 haskell-src-exts-0.4.8 hsx-0.4.8 HJScript-0.4.4 hsp-0.4.5 happstack-0.1.9 Xauth-0.1 byteorder-1.0.0 xhb-0.2.2009.2.21 HStringTemplate-0.4.3 happstack-util-0.2.1 happstack-data-0.2.1 happstack-ixset-0.2.1 happstack-server-0.2.1 happstack-state-0.2.1 happstack-0.2.1 uniplate-1.2.0.3 wx-0.11.0 wx-0.11.1.2 bimap-0.2.4 encoding-0.5.1 fclabels-0.1 hscolour-1.11 parsec-3.0.0 pureMD5-0.2.4 salvia-0.1.1 salvia-extras-0.1.1 Diff-0.1.2 clevercss-0.1.1 datetime-0.1 nano-md5-0.1.2 network-2.2.0.1 split-0.1.1 xml-1.3.4 filestore-0.2 hsemail-1.3 SMTPClient-1.0.1 HTTP-4000.0.4 happstack-util-0.3 happstack-data-0.3 happstack-state-0.3 happstack-ixset-0.3 happstack-server-0.3 happstack-contrib-0.3 FileManip-0.3.2 happstack-0.3 HTTP-4000.0.5 haddock-2.4.2 ghc-6.10.2 Did I do something wrong in the installation step? thanks ... -deech

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Re: [Haskell-beginners] generating the set of all finite-valued ...
by Erik Quaeghebeur 28 Apr '09

28 Apr '09

> On Thu, Apr 23, 2009 at 03:45:27PM +0200, Erik Quaeghebeur wrote: >> >> I'd like to lazily generate the set of all {-1,0,1}-valued functions on >> {'a','b','c'}? How should I best approach this. I was thinking about >> generalizing the power set definition On Thu, 23 Apr 2009, Jan Jakubuv wrote: > > Try to start with this: > > mapM (\x -> [(x,-1),(x,0),(x,1)]) ['a','b','c'] Aha. Great. Thanks, Jan. And now I realized that I don't really care about the domain, so I said: Prelude> let m = mapM (\x -> [(x,-1),(x,0),(x,1)]) ['a','b','c'] Prelude> map (\x -> snd $ unzip x) m [[-1,-1,-1],[-1,-1,0],[-1,-1,1],[-1,0,-1],[-1,0,0],[-1,0,1],[-1,1,-1],[-1,1,0],[-1,1,1],[0,-1,-1],[0,-1,0],[0,-1,1],[0,0,-1],[0,0,0],[0,0,1],[0,1,-1],[0,1,0],[0,1,1],[1,-1,-1],[1,-1,0],[1,-1,1],[1,0,-1],[1,0,0],[1,0,1],[1,1,-1],[1,1,0],[1,1,1]] Any more direct way of doing this? (Still trying to understand how the mapM works... I've found it's sequence.map, but that doesn't really help.) The next step will be to choose a good data format for what I'm trying to achieve. The functions (now represented as lists) would more naturally be represented as column matrices, e.g., from Numeric.LinearAlgebra of hmatrix, as I'll be needing some linear system solver. I can do the transition from lists to that, but I'm afraid they don't give me the necessary flexibility; I'd need to filter them based on (maximum/minimum) component values and sum them and such. Any thoughts on that? Erik

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Re: [Haskell-beginners] problem cabal install'ing hmatrix
by Alberto Ruiz 27 Apr '09

27 Apr '09

Hi Erik, Probably a dependency not mentionend in extra-libraries is missing. There is not a standard way to link -llapack. For instance, in Ubuntu/Debian we only need gsl and lapack: $ ld -lgsl -llapack ld: warning: cannot find entry symbol _start; not setting start address This means that everything is ok, but in other systems we may also need some of -l[gsl]cblas, -lgfortran, or -lf77blas, -latlas, -lgcc_s, etc. Try to find the correct libraries with $ ld -lgsl -llapack -lgslcblas or other combinations, and modify the extra-libraries field in hmatrix.cabal. In any case, I will try to add cabal flags to cover common situations. (There is also a possible issue with ghc-6.8 that must be fixed, but the library should work ok with 6.10). Alberto PS: I CC the list for reference. Erik Quaeghebeur wrote: > Alberto, > > Original message: >>> >>> $ cabal install hmatrix >>> Resolving dependencies... >>> Configuring hmatrix-0.5.1.1... >>> Preprocessing library hmatrix-0.5.1.1... >>> running dist/build/Numeric/GSL/Special/Internal_hsc_make failed >>> command was: dist/build/Numeric/GSL/Special/Internal_hsc_make >>> > dist/build/Numeric/GSL/Special/Internal.hs >>> cabal: Error: some packages failed to install: >>> hmatrix-0.5.1.1 failed during the building phase. The exception was: >>> exit: ExitFailure 1 >>> >>> What should I do to diagnose/resolve this problem? > > On Tue, 21 Apr 2009, Alberto Ruiz wrote: >> >> Erik, do you have the same problem with a previous version? >> >> cabal install hmatrix-0.5.0.1 > > Thanks for your (speedy) reply. Yes it gives the same problem: > > $ cabal install hmatrix-0.5.0.1 > Resolving dependencies... > Configuring hmatrix-0.5.0.1... > Preprocessing library hmatrix-0.5.0.1... > running dist/build/Numeric/GSL/Special/Internal_hsc_make failed > command was: dist/build/Numeric/GSL/Special/Internal_hsc_make >> dist/build/Numeric/GSL/Special/Internal.hs > cabal: Error: some packages failed to install: > hmatrix-0.5.0.1 failed during the building phase. The exception was: > exit: ExitFailure 1 > > Also, suggested by Heinrich Apfelmus: > > $ cabal install hmatrix --verbose > /usr/bin/ghc --numeric-version > looking for package tool: ghc-pkg near compiler in /usr/bin > found package tool in /usr/bin/ghc-pkg > /usr/bin/ghc-pkg --version > /usr/bin/ghc --supported-languages > Reading installed packages... > /usr/bin/ghc-pkg list > Reading available packages... > Resolving dependencies... > selecting hmatrix-0.5.1.1 (hackage) and discarding hmatrix-0.1.0.0, > 0.1.1.0, > 0.2.0.0, 0.2.1.0, 0.3.0.0, 0.4.0.0 and 0.5.0.1 > selecting base-3.0.1.0 (installed) > selecting rts-1.0 (installed) > selecting storable-complex-0.2 (installed or hackage) and discarding > storable-complex-0.1 > selecting haskell98-1.0.1.0 (installed or hackage) and discarding > haskell98-1.0 > selecting process-1.0.0.0 (installed or hackage) and discarding > process-1.0.1.1 > selecting unix-2.3.0.0 (installed or hackage) and discarding unix-2.0, > 2.2.0.0, 2.3.1.0 and 2.3.2.0 > selecting directory-1.0.0.0 (installed or hackage) and discarding > directory-1.0.0.3 > selecting filepath-1.1.0.0 (installed or hackage) and discarding > filepath-1.0, > 1.1.0.1 and 1.1.0.2 > selecting array-0.1.0.0 (installed or hackage) and discarding array-0.2.0.0 > selecting QuickCheck-1.2.0.0 (installed or hackage) and discarding > QuickCheck-1.0, 1.1.0.0, 2.1 and 2.1.0.1 > selecting random-1.0.0.0 (installed or hackage) and discarding > random-1.0.0.1 > selecting old-time-1.0.0.0 (installed or hackage) and discarding > old-time-1.0.0.2 > selecting old-locale-1.0.0.0 (installed or hackage) and discarding > old-locale-1.0.0.1 > selecting HUnit-1.2.0.3 (installed or hackage) and discarding HUnit-1.1, > 1.2.0.0, 1.2.0.1 and 1.2.0.2 > In order, the following would be installed: > hmatrix-0.5.1.1 (new package) > hmatrix-0.5.1.1 has already been downloaded. > Extracting > /home/equaeghe/.cabal/packages/hackage.haskell.org/hmatrix/0.5.1.1/hmatrix-0.5.1.1.tar.gz > > to /tmp/hmatrix-0.5.1.16320... > Configuring hmatrix-0.5.1.1... > Flags chosen: unsafe=False, accelerate=False, mkl=False, splitbase=True > Dependency HUnit -any && ==1.2.0.3: using HUnit-1.2.0.3 > Dependency QuickCheck -any && ==1.2.0.0: using QuickCheck-1.2.0.0 > Dependency array -any && ==0.1.0.0: using array-0.1.0.0 > Dependency base >=3 && ==3.0.1.0: using base-3.0.1.0 > Dependency haskell98 -any && ==1.0.1.0: using haskell98-1.0.1.0 > Dependency storable-complex -any && ==0.2: using storable-complex-0.2 > Using Cabal-1.6.0.3 compiled by ghc-6.8 > Using compiler: ghc-6.8.2 > Using install prefix: /home/equaeghe/.cabal > Binaries installed in: /home/equaeghe/.cabal/bin > Libraries installed in: /home/equaeghe/.cabal/lib/hmatrix-0.5.1.1/ghc-6.8.2 > Private binaries installed in: /home/equaeghe/.cabal/libexec > Data files installed in: /home/equaeghe/.cabal/share/hmatrix-0.5.1.1 > Documentation installed in: /home/equaeghe/.cabal/share/doc/hmatrix-0.5.1.1 > No alex found > Using ar found on system at: /usr/bin/ar > No c2hs found > No cpphs found > No ffihugs found > Using gcc version 4.3.2 found on system at: /usr/bin/gcc > Using ghc version 6.8.2 found on system at: /usr/bin/ghc > Using ghc-pkg version 6.8.2 found on system at: /usr/bin/ghc-pkg > No greencard found > No haddock found > No happy found > No hmake found > Using hsc2hs version 0.66 found on system at: /usr/bin/hsc2hs > No hscolour found > No hugs found > No jhc found > Using ld found on system at: /usr/bin/ld > No nhc98 found > Using pkg-config version 0.23 found on system at: /usr/bin/pkg-config > Using ranlib found on system at: /usr/bin/ranlib > Using strip found on system at: /usr/bin/strip > Using tar found on system at: /bin/tar > /usr/bin/gcc /tmp/6320.c -o /tmp/6320 -D__GLASGOW_HASKELL__=608 -I. > -DFINIT -I/usr/lib64/ghc-6.8.2/lib/process-1.0.0.0/include > -I/usr/lib64/ghc-6.8.2/lib/unix-2.3.0.0/include > -I/usr/lib64/ghc-6.8.2/lib/directory-1.0.0.0/include > -I/usr/lib64/ghc-6.8.2/lib/old-time-1.0.0.0/include > -I/usr/lib64/ghc-6.8.2/lib/base-3.0.1.0/include > -I/usr/lib64/ghc-6.8.2/include -lgsl -llapack > Creating dist/build (and its parents) > Creating dist/build/autogen (and its parents) > Preprocessing library hmatrix-0.5.1.1... > Creating dist/build/Numeric/GSL/Special (and its parents) > /usr/bin/hsc2hs --cc=/usr/bin/gcc --ld=/usr/bin/gcc > --cflag=-D__GLASGOW_HASKELL__=608 --cflag=-DFINIT --lflag=-lgsl > --lflag=-llapack > --cflag=-I/usr/lib64/ghc-6.8.2/lib/process-1.0.0.0/include > --cflag=-I/usr/lib64/ghc-6.8.2/lib/unix-2.3.0.0/include > --cflag=-I/usr/lib64/ghc-6.8.2/lib/directory-1.0.0.0/include > --cflag=-I/usr/lib64/ghc-6.8.2/lib/old-time-1.0.0.0/include > --cflag=-I/usr/lib64/ghc-6.8.2/lib/base-3.0.1.0/include > --cflag=-I/usr/lib64/ghc-6.8.2/include > --lflag=-L/home/equaeghe/.cabal/lib/storable-complex-0.2/ghc-6.8.2 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/haskell98-1.0.1.0 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/process-1.0.0.0 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/unix-2.3.0.0 --lflag=-lutil > --lflag=-ldl --lflag=-L/usr/lib64/ghc-6.8.2/lib/directory-1.0.0.0 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/filepath-1.1.0.0 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/array-0.1.0.0 > --lflag=-L/home/equaeghe/.cabal/lib/QuickCheck-1.2.0.0/ghc-6.8.2 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/random-1.0.0.0 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/old-time-1.0.0.0 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/old-locale-1.0.0.0 > --lflag=-L/home/equaeghe/.cabal/lib/HUnit-1.2.0.3/ghc-6.8.2 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/base-3.0.1.0 > --lflag=-L/usr/lib64/ghc-6.8.2 --lflag=-lm --lflag=-lgmp --lflag=-ldl > --lflag=-lrt -o dist/build/Numeric/GSL/Special/Internal.hs > lib/Numeric/GSL/Special/Internal.hsc > running dist/build/Numeric/GSL/Special/Internal_hsc_make failed > command was: dist/build/Numeric/GSL/Special/Internal_hsc_make >> dist/build/Numeric/GSL/Special/Internal.hs > cabal: Error: some packages failed to install: > hmatrix-0.5.1.1 failed during the building phase. The exception was: > exit: ExitFailure 1 > > I still have to test the version in the Gentoo Haskell overlay. That > should work (but then I wouldn't use cabal install). > > Regards, > > Erik >

2 3

Re: [Haskell-beginners] generating the set of all finite-valued [...]
by Erik Quaeghebeur 27 Apr '09

27 Apr '09

> 2009/4/23 Erik Quaeghebeur <equaeghe(a)nospammail.net> > >> I'd like to lazily generate the set of all {-1,0,1}-valued functions on >> {'a','b','c'}? How should I best approach this. I was thinking about >> generalizing the power set definition >> >> powerset :: [a] -> [[a]] >> powerset = filterM (const [True, False]) >> >> but clearly don't know enough about filterM and the like to do it this way. >> >> Erik On Mon, 27 Apr 2009, Haroldo Stenger wrote: > > i got curious about this one. Can you elaborate ? Well, elaborate about my ultimate goal, or about the powerset definition? The latter I can tell little about, I found it on-line and recognized it as a starting point. The former: generalizing http://users.ugent.be/~equaeghe/constraints.php to previsions from probabilities; C++ is a little too heavy, so I thought I'd try out Haskell. Erik

1 0

data constructors
by Michael Mossey 27 Apr '09

27 Apr '09

This is probably a side-effect of coming from OO land, but I'm confused about how to organize my data. Let's say I want to model musical information that occurs on a single staff. A staff consists of a list of StaffItem which occurs at specific times. type Time = Double type Staff = [(Time,StaffItem)] A StaffItem can be one of several things. Let's say it can be a "chord" or a "control". I might like to define Chord and Control first: data Chord = Chord { duration :: Double, notes :: [Note] } data Control = DynamicMark Int | TempoMark Int Okay, so now I want to express the idea a StaffItem can be a Chord or a Control. data StaffItem = StaffItemChord Chord | StaffItemControl Control My problem is the awkward need for separately named constructors "StaffItemChord" and "StaffItemControl". Is there a better way? (Is this even right?) Thanks, Mike

4 10

music layout problem
by Michael Mossey 25 Apr '09

25 Apr '09

I'm continuing to work on this music layout problem, and I'm trying another angle. A page of music is made of many individual symbols and graphical items like lines and arcs. I decided to call a drawable symbol/item a Grapheme. so type MusicPage = [Grapheme] The program also maintains the more fundamental description of music in conceptual form---that is, notes, chords, time signatures, tempo indications, etc. I decided to call bits of information about music Datemes. type MusicScore = [Dateme] A function to lay out a musical page would have this signature: layoutPage :: [Dateme] -> [Grapheme] Now let's think about the structure of a page of music for a moment. It's made of *systems*, which are groups of notes read from left to right. A page consists of a number of systems stacked vertically (like a page of text has lines of text stacked vertically). The layout algorithm will fit as many systems as it can into a page. When it runs out of space, it will stop (even if there are Dateme left). A layout algorithm in imperative pseudocode would look something like: - initialize the list remainingDateme to the input list of Dateme - loop - looking at the list of remainingDateme, make a system - try to fit the system to the page - if the system doesn't fit, break out of the loop - add the system to the page - drop the used Dateme from remainingDateme - if remainingDateme is empty, break out of the loop - go to top of loop I tried to write this in Haskell, and it seem awkward. It would be something like: -- layout page, produce list of Grapheme and also list of -- unused Dateme layoutPage :: PageDimensions -> [Dateme] -> ( [Grapheme], [Dateme] ) layoutPage dim dateme = layoutPage' dim [] dateme layoutPage' :: PageDimensions -> [Grapheme] -> [Dateme] -> ( [Grapheme], [Dateme] ) layoutPage' dim graphemeSoFar [] = ( graphemeSoFar, [] ) layoutPage' dim graphemeSoFar remainingDateme = let ( newGrapheme, remainingDateme', dim' ) = layoutSystem dim remainingDateme in if null newGrapheme then ( graphemeSoFar, remainingDateme ) else layoutPage' dim' (graphemeSoFar ++ newGrapheme) remainingDateme' We assume this is defined elsewhere: -- layoutSystem takes as input the current page dimensions (think of -- the "current page dimensions" as the room *remaining* on the page), -- and a list of Dateme, and returns the triple: -- ( [Grapheme] for the new system, or null list if no additional system -- can fit on the page, -- remaining [Dateme] that are not consumed, -- new page dimensions ) layoutSystem :: PageDimensions -> [Dateme] -> ( [Grapheme], [Dateme], PageDimensions )

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parser comparison question
by Walck, Scott 25 Apr '09

25 Apr '09

I've been comparing Graham Hutton's simple parser with Parsec. Here is some example code. -- Comparison of Hutton's simple parser with Parsec -- Hutton's simple parser is available at -- http://www.cs.nott.ac.uk/~gmh/Parsing.lhs -- Hutton simple parser called H -- Parsec called P import qualified Parsing as H import qualified Text.ParserCombinators.Parsec as P exH = H.parse (H.string "hi") "hiho" exP = P.parse (P.string "hi") "" "hiho" charH = H.parse (H.char 'a' H.+++ H.char 'b') "bbb" charP = P.parse (P.char 'a' P.<|> P.char 'b') "" "bbb" choiceH = H.parse (H.string "hoo" H.+++ H.string "ho") "hono" choiceP1 = P.parse (P.string "bb" P.<|> P.string "ba") "" "bbb" choiceP2 = P.parse (P.string "ba" P.<|> P.string "bb") "" "bbb" choiceP22 = P.parse (P.try (P.string "ba") P.<|> P.string "bb") "" "bbc" I am interested if anyone could comment on the design of the Parsec 'try' function. For example, choiceP2 fails and returns Left error, while choiceP22 succeeds. Hutton's simple parser doesn't need try. It seems so simple and elegant. I'm wondering why Parsec requires me to use 'try' for a string parse that might fail. Thanks, Scott Scott N. Walck Associate Professor of Physics Lebanon Valley College

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WWAAA... I hate monads
by Daniel Carrera 25 Apr '09

25 Apr '09

I hate monads. I love 90% of Haskell. The functional stuff is beautiful, easy to understand, crystal clear, elegant, etc. But I'm having a mighty hard time getting my head around monads. Consider the following explanation of a monad: "A monad is represented as a type constructor (call it m), a function that builds values of that type (a -> m a), and a function that combines values of that type with computations that produce values of that type to produce a new computation for values of that type". 1) I know what a type is, but not a "type constructor". I don't normally think of an Int or even a complex type as being "constructed" except in the sense of OOP which I know is not what the author means. 2) Just *read* the paragraph... "a type constructor, a function that builds value of that type, and a function that combines values of that type with computations that produce values of that type to produce a computation of values of that type" Ugh.... Can anyone recommend a simple and clear explanation of monads? You can assume that I know basic math and basic Haskell syntax. So, for example, "a -> b" is much more clear than "a function that takes input of one type and has an output of a different type". Any help would be appreciated. Daniel.

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doing state right
by Floptical Logic 24 Apr '09

24 Apr '09

I am using a PPM library to generate a square image where each white pixel represents a prime number. The PPM library takes a function (Int -> Int -> Colour) to create the image. This interface isn't ideal but it is what I have to work with. I am convinced that using a sieve is faster than testing every pixel in the image for primality, but the (Int -> Int -> Colour) interface makes this awkward. The code below attempts to treat the list of prime numbers as a stack via global mutable state, popping the head whenever the pixel is prime. Obviously this is not idiomatic Haskell. What is the correct approach of dealing with state here? Thanks for reading. import ONeillPrimes import PPM6 import Colour import Data.IORef import System.IO.Unsafe limit = 2000 slimit = limit*limit primeList = takeWhile (<=slimit) primes p :: IORef [Int] p = unsafePerformIO (newIORef primeList) pcol n = unsafePerformIO $ do xs <- readIORef p if null xs then return black else if n == head xs then do writeIORef p (tail xs) return white else return black main = quick_ppm "foo.ppm" (\i j -> pcol ((i-1)*limit+j)) limit limit -- quick_ppm :: FilePath -> (Int -> Int -> Colour.Colour) -> Int -> Int -> IO ()

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