Hallo Thomas, when compiling your sources in our context I get an "Overlapping instances" error (below). However, first compiling the offending file (base/TI/OrigTiMonad.hs) and then compiling the rest works (but I don't want adapt our Makefile for this to do). Could you adjust your sources? We're using ghc-6.4.2. Or is there a further compiler switch that would get this right? I don't know if both instances are identical. Cheers Christian ../programatica/tools/base/TI/OrigTiMonad.hs:61:36: Overlapping instances for Functor (Either (Error (HsIdentI i))) arising from use of `fmap' at ../programatica/tools/base/TI/OrigTiMonad.hs :61:36-39 Matching instances: Imported from Control.Monad.Error: instance Functor (Either e) ../programatica/tools/base/lib/Monads/ExceptM.hs:26:0: instance Functor (Either x) In a lambda abstraction: \ env ids -> fmap (fmap f) (m env ids) In the second argument of `($)', namely `\ env ids -> fmap (fmap f) (m env i ds)' In the definition of `fmap': fmap f (IM m) = IM $ (\ env ids -> ...)