Stefan, What version of ghc are you using? Mine is 6.6. Data/Derive/Play.hs:9:7: Could not find module `Control.Monad.State': it is a member of package mtl-1.0, which is hidden I commented out that import line. Preprocessing library derive-0.1... Preprocessing executables for derive-0.1... Building derive-0.1... [1 of 9] Compiling Data.Derive.FixedPpr ( Data/Derive/FixedPpr.hs, dist/build/Data/Derive/FixedPpr.o ) [2 of 9] Compiling Data.Derive ( Data/Derive.hs, dist/build/Data/ Derive.o ) [3 of 9] Compiling Data.Derive.SYB ( Data/Derive/SYB.hs, dist/build/ Data/Derive/SYB.o ) [4 of 9] Compiling Data.Derive.TH ( Data/Derive/TH.hs, dist/build/ Data/Derive/TH.o ) Data/Derive/TH.hs:25:26: No instance for (Functor Q) arising from use of `fmap' at Data/Derive/TH.hs:25:26-31 Possible fix: add an instance declaration for (Functor Q) In the first argument of `(.)', namely `fmap f' In the expression: (fmap f) . deriveOne In the definition of `derive': derive (Derivation f _) = (fmap f) . deriveOne This I don't know how to deal with. Thanks, Joel -- http://wagerlabs.com/