ghc-pkg-clean, ghc-pkg-reset

gistfile1.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; \
        # echo 'erasing ~/.cabal/packages'; rm -rf ~/.cabal/packages; \                                                                                                                                                                     
        # echo 'erasing ~/.cabal/share'; rm -rf ~/.cabal/share; \                                                                                                                                                                           
        )
}

alias cabalupgrades="cabal list --installed  | egrep -iv '(synopsis|homepage|license)'"

I modified your ghc-pkg-reset shell function to work on zsh as well as bash if you're interested:

https://gist.github.com/timmytofu/7417408

@timmytofu, read build-in in zsh doesn't accept -p flag.
Then /proc is Linux virtual fs. FreeBSD - and other too - doesn't use it.
Here an other attempt to get rid of OS specifics
https://gist.github.com/p-alik/4f8cc64ace8a20a8bebcb8e8e1cba2a4