I upgraded ghc from 7.0.4 to 7.4.1 yesterday. After I ran haskell-updater --upgrade to migrate the haskell packages. Sadly I don't have the exact errors anymore, but it was easy enough to figure out that 2 packages needed additional rebuild: dev-haskell/syb and dev-haskell/random. Among the failed packages were from dev-haskell: happy, x11, x11-xft from x11-wm: xmonad and xmonad-contrib. I apologize if this is insufficient information. Reproducible: Always
Yeah, it's a bit too little info.