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Thank you for the explanation. Haskell's not as bad as I thought in this respect. My understanding was IO streams were a single input function (ie the stream).

Thank you for the explanation. Haskell's not as bad as I thought in this respect. My understanding was IO streams were a single input function (ie the stream). As a result the destructiveness would be less obvious. Can you replay a get from stream by passing in an older token?

solidsnack9000 11y ago
Because the token is passed only within the implementation of `>>=`, which is private to the IO module, you never have access to it. So no need for the runtime to keep snapshots lying around. Monads provide a way to combine them and a way to inject values into them; but not all monads provide the inspection interface that would allow you to examine that state token. The definition of a monad guarantees only the injection and the combination (the "unit" and "multiply").