Newbie alert: I have some superficial familiarity with continuations as they occur in traditional denotational semantics, but certainly not a deep understanding. I also have a special interest in distributed and/or concurrent processing, so it only seemed natural to me that the monad concept was one I'd want to confront head on. Now, I warn you: I am quite new to Haskell (though I have some prior exposure to Scheme and a background in mathematics). Now, I've just started reading through Thompson's text and came across this example: goUntilEmpty :: IO () goUntilEmpty = do line <- getLine if (line == []) then return () else (do putStrLn line goUntilEmpty) Okay, this seems sensible enough. Loosely speaking, I see this code as getting a line, checking to see if it's empty. If it is, it just quits (returning the "empty" value). Otherwise, it prints line, and invokes itself through a *new* do statement. That seems awfully like using a continuation to track the input stream as part of the environment. But it seems obvious to me that here is something I'm not understanding here. I think of the do as providing an appropriate continuation (one in which the line just read is gone) to pass to the next call. Okay, maybe I'm taking things a bit too literally here, but I seem to recall that a monad is an algebraic object with right and left identity and an associative composition. I understand the monad here takes a value (()) and returns an object IO (), and do becomes a functor of sorts, taking ordinary functions and mapping them to new functions having their codomain in a new category (an instance of a monad?) This is where it seems to me that I must be getting the terminology wrong. Can someone help me out here? === Gregory Woodhouse gregory.woodhouse@sbcglobal.net "The most incomprehensible thing about the world is that it is at all comprehensible." --Albert Einstein (1879-1955)