Folks, I've been reading RWH and this http://www.haskell.org/haskellwiki/IO_inside#Haskell_is_a_pure_language I think I understand monads. I think I understand how IO is much different from, e.g. Maybe, State, etc. However there are some turns of phrase with respect to IO that have me baffled. I am giving a presentation on monads next week, and hope you can help. (I'm not quite as lost as this might imply!) Q1: The web page mentions that normal Haskell functions cannot cause side-effects, yet later talks about side-effects with putStrLn. I assume the key point here that IO actions are, by definition, _not_ normal functions? Q2: Is it true to say that *any* monadic action *could *cause side-effects, depending on the design of that monad? i.e. Does one generalize from the IO monad to (possibly) an arbitrary monad? *Musing* This must be true as using State must surely be considered a side-effect. Q3: The web page mentions IO as being a baton, or token, that is used to thread/order the actions. Is true that this is merely one simple perspective, with respect to order of evaluation? This is hard to articulate, but it seems to me that "in the IO monad" there is a large subsystem of (inaccessible) state, machinery, etc. Is it really a token? Q4: Is the following idea accurate: a Haskell program is partitioned into 2 spaces. One is a sequence of IO actions; the other is a space of pure functions and 'normal' Haskell operations. The execution of a program begins with the main :: IO () action and, effectively, crosses from one space to the other. In the pure space, the math-like functions can be highly optimized but only insofar as they do not disrupt the implied order of the IO actions. Because of the type system, the program recognizes when it enters "back" into the IO space and follows different, less optimized rules. My concern is that the above is *not* accurate, but I don't know why. thanks so much for your help Michael Easter -- ---------------------- Michael Easter http://codetojoy.blogspot.com: Putting the thrill back in blog http://youtube.com/ocitv -> Fun people doing serious software engineering