Hi all, Am very new to Haskell, apologies in advance. Suppose I have a transformer A of type State s a. Suppose I have other state transformers of type StateT s m a. These are similar to the first kind but e.g. might throw errors or perform IO or whatever. I can manually convert A to be of the second kind as follows: -- | Used to invoke a "pure" state transformer -- from a context in which other effects may occur. pure :: (Monad m) => State s a -> StateT s m a pure func = StateT (\arg -> (return (runState func arg))) This seems like something one might want to do often. For instance, I might have a state type that I want to operate on, call it System. Then type PureSystemTransformer a = State System a defines a type for "pure" System transformers that return results of type a. However, other system transformers might need to throw errors. So I might define type SystemTransformer a e = StateT System (Either e) a for the type of system transformers that return results of type a or throw errors of type e. 'pure' is then used to convert a PureSystemTransformer to a SystemTransformer. I wonder whether there is something in the standard libraries that achieves the same thing as 'pure' above. i.e. Is there a more standard way to do this? Cheers Toby