post_install() {
   echo '==> It may be necessary to run `ghc-pkg recache` as root.'
   # or this error might occur when trying to use GHC(I):
   #/usr/lib/ghc/package.conf.d/package.cache: openBinaryFile: does not exist (No such file or directory)
   #(solution from http://jonathan.bergknoff.com/journal/installing-ghc-haskell-slitaz)
}

pre_upgrade() {
   echo '==> Unregistering cabalized packages...'
   [[ -d /usr/share/haskell ]] && find /usr/share/haskell -maxdepth 2 -name 'unregister.sh' -exec {} \;
   echo '==> Done.'
}

post_upgrade() {
   echo '==> All cabalized packages need to be reinstalled now.'
   echo '==> See /usr/share/haskell/ for a tentative list of affected packages.'
   post_install
}