Don't sudo cabal install whatever. Actually, avoid cabal install without sudo too, unless you're working with software using dynamic recompilation like xmonad. Use cabal-dev instead, this will save you a world of pain.
I'm confused by your comments relating to sudo ..?
That said it seems that cabal-dev is not packaged for Debian. Come the wheezy release of Debian the hakyll project I wished to try out will be available as a .deb, so I'll try it again then.
What I mean is, "cabal install" is usually a bad idea, with or without sudo.
However, you can do "cabal install cabal-dev" and rely on cabal-dev for the rest. It means you don't have a global package cache, but in this case it's really for the best. Don't forget to add .cabal/bin to your $PATH if you want access to cabal-dev.
