[Haskell-cafe] Cabal: Retrieve directory in which binaries get installed

Hello cafe, I'd like to retrieve the path in which binaries get installed when I `cabal install` a package. Normally, this would be ~/.cabal/bin on my Linux, but since I share my home folder on two architectures, in ~/.cabal/config I set the user-install prefix to ~/.cabal/$arch, so binaries get installed to ~/.cabal/$arch/bin. I have the feeling that it should be rather simple to retrieve the FilePath from the Cabal API, does anyone know how to do this? Thanks in advance, Björn