Hi, i got a little problem and don't know how to solve that. Hope you can help me. code: ---------- module Test where {-# LANGUAGE Rank2Types, RankNTypes #-} import Control.Monad.Trans data TestType = TestType {tst :: (Conf a, MonadIO m) => m a} class Conf a where get :: MonadIO m => m a testFunc :: (forall a. Conf a, MonadIO m => m a) -> TestType testFunc = TestType -------------- error: -------------- Test.hs:11:23 Class `Conf' used as a type In the type signature for `testFunc': testFunc :: (forall a. Conf a, (MonadIO m) => m a) -> TestType -------------- explanation: I need a data type that creates a record with a member that has no fixed type, because its not known at compile-time. The Rank2Types language extension fits that need, but i figured out that i ll need to make that time monadic to avoid the use of unsafePerformIO in the program that uses this lib. Thanks and greetings, Alex