> No. As you say the world1 value is immutable, but that's not > contradictory. If between 'getLine' and 'print' something was done by a > concurrent thread, then that change to the world is captured by 'print'. Well, that's technically true, but it basically amounts to saying that the 'model' of IO is itself. If I see 'print x', I don't really think of an action that performs arbitrary side effects and prints x in the process (unless some error prevents even that). Some notion of compositionality is required, which would allow me to state how 'print x' contributes to the changes of the world in a way that doesn't depend on any context. Actions in the state monad are composable in that sense, while the same doesn't apply to the IO monad when explained in terms of state passing.
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