Since I'm very new to Haskell I have what is probably a simple question yet I'm having trouble finding a clear example of how it works. The basic question is: how do I pass state through existing code without the intermediate code knowing about it. If I have, for example, several layers of function calls and the innermost function needs to access some state that is only "seeded" by the outermost function, how do I do that without the functions in between knowing about the additional state being threaded through them? I have a simple example (that may *not* be good idiomatic Haskell): -- process :: Integer -> Integer -> Integer process x y = 2 * x * y doit :: IO () doit = do printf "f x y = %d\n" $ process 42 43 main :: IO () main = do doit putStrLn "done" -- (I'm not totally sure about the type of "doit" but the code compiles and runs as expected) What I want to do is add some state handing to "process" to have it, say, count the number of times it's been called (putting threading/thread-local concerns aside for the moment). I'm trying to understand how to add state to "process" along the lines of: -- process :: Integer -> Integer -> State Integer Integer process x y = do s <- get put $ s + 1 return $ 2 * x * y -- but I want to only seed the state from "main" without "doit" having to change -- I can call "process" from "doit" like "(execState (process 42 43) 0)" but I want the initial state to be determined at the top level, from main. I have a feeling there's some kind of "ah ha" moment that I'm just not seeing yet. Any help or pointers to where I can look for myself would be greatly appreciated. Thanks in advance, -thor