Hi, I want to use something like (Control.Monad.StateT (Data.Map.Map String Dynamic) m). So I wrote VarStateT datatype and corresponding classes (Control/Monad/VarState.hs in [1]). Then I tried to use it in my program (Math/Eigenvalues.hs in [1]). But compiler refused to compile it with many type errors. I thought that it would be sufficient to use ScopedTypeVariables and write all type annotations. It helped slightly, many messages were gone, but now compiler throws an error I don't know how to solve. ghc --make -o out/eigenvalues -outputdir build Main.hs [3 of 4] Compiling Math.Eigenvalues ( Math/Eigenvalues.hs, build/Math/Eigenvalues.o ) Math/Eigenvalues.hs:14:30: Could not deduce (MutableMatrix a e m) from the context (MutableMatrix a2 e2 m, Typeable a2, Typeable e2, Floating e2, Ord e2) arising from a use of `getPhi' at Math/Eigenvalues.hs:14:30-35 Possible fix: add (MutableMatrix a e m) to the context of the type signature for `compute' In the second argument of `(>>)', namely `getPhi' In the first argument of `(>>)', namely `maxElem a >> getPhi' In the first argument of `(>>)', namely `maxElem a >> getPhi >> buildB' Math/Eigenvalues.hs:14:40: Could not deduce (MutableMatrix a1 e1 m) from the context (MutableMatrix a2 e2 m, Typeable a2, Typeable e2, Floating e2, Ord e2) arising from a use of `buildB' at Math/Eigenvalues.hs:14:40-45 Possible fix: add (MutableMatrix a1 e1 m) to the context of the type signature for `compute' In the second argument of `(>>)', namely `buildB' In the first argument of `(>>)', namely `maxElem a >> getPhi >> buildB' In the first argument of `(>>=)', namely `maxElem a >> getPhi >> buildB >> buildA' How to sort this out? [1] http://dl.dropbox.com/u/1415321/prog/eigenvalues.tar.gz