What libraries are Haskell programs linked against? In particular, is the mtl library in there? (Check with "ghc-pkg list mtl".) I got a compilation error like "Couldn't find module Control.Monad.State", which surprised me a lot. (Actually, I'm a bit surprised it even got that far, since the previous line imports Control.Monad.Reader, which is in the same library, and the line before that asks for Control.Arrow, which comes from a less common library.)
If the mtl isn't available, can it be made available? The monad library is a very common tool in Haskell programming.
~d