{- From: http://en.wikibooks.org/wiki/Haskell/Monad_transformers if for instance we apply StateT to the List monad, a function that returns a list (i.e., a computation in the List monad) can be lifted into StateT s [], where it becomes a function that returns a StateT (s -> [(a,s)]). That is, the lifted computation produces multiple (value,state) pairs from its input state. -} import Control.Monad.Trans.State.Lazy type GeneratorState = StateT Int -- a function in the list monad f :: Int -> [Int] f n = [0..n] Will someone please demonstrate the above comment from the wiki page. Michael