Safer cabal --upgrade-dependencies. Easy detection of non-optimal upper bounds. Unregister broken packages with ghc. Reset ghc pkg db.

peace.sh

# unregister broken GHC packages. Run this a few times to resolve
# dependency rot in installed packages.  ghc-pkg-clean -f
# cabal/dev/packages*.conf also works.
function ghc-pkg-clean() {
    for p in `ghc-pkg check $* 2>&1  | grep problems | awk '{print $6}' | sed -e 's/:$//'`
    do
        echo unregistering $p; ghc-pkg $* unregister $p
    done
}
 
# remove all installed GHC/cabal packages, leaving ~/.cabal binaries
# and docs in place.  When all else fails, use this to get out of
# dependency hell and start over.
function ghc-pkg-reset() {
    read -p 'erasing all your user ghc and cabal packages - are you sure (y/n) ? ' ans
    test x$ans == xy && ( \
        echo 'erasing directories under ~/.ghc'; rm -rf `find ~/.ghc -maxdepth 1 -type d`; \
        echo 'erasing ~/.cabal/lib'; rm -rf ~/.cabal/lib; \
    )
}

# Utility to constrain cabal from messing with global packages.  If you install
# packages distributed with ghc as global packages and optionally the haskell 
# platform as global packages, then the following command line will save you from 
# messing up:
# $ cabal install `echo eval $(ghc-global-constraints)`
# or
# $ cabal install --upgrade-dependencies `echo eval $(ghc-global-constraints)`
function ghc-global-constraints() {
    ghc-pkg list --global | tail -n+2  | head -n-1 | grep -v '(' | while read a; do
        VER=${a##*-}
        PKG=${a%-*}
        echo -n "--constraint='$PKG==$VER' "
    done
}

# Quick check to see which upper bounds are probably in need of an upgrade.  Example usage:
# $ cabal-check-upper-bounds ./iproute.cabal 
# Package Build-Depends:, upper bound base  5
#
# Package doctest, upper bound >= 0.9.3
# pkg: doctest 0.9.7
# From that output we can see that doctest could potentially be upgraded to version 0.9.7
function cabal-check-upper-bounds() {
    grep '>=' $1 |
    grep -v 'if ' |
    grep -vi cabal-version |
    perl -p -e 's,>=.*<,,;s/,//;' | while read a b; do
        echo "Package $a, upper bound $b";
        BEST_PKG=$(egrep "pkg: $a " ~/.cabal/packages/hackage.haskell.org/00-index.cache |
            sort -r|
            head -n 1 |
            cut -d ' ' -f1,2,3);
        echo $BEST_PKG;
    done
}