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On Oct 27, 2008, at 7:25 PM, Rodney D Price wrote:
Perhaps my mental picture is a little less flawed,
now, but this brings up something about the IO
monad that has always bothered me. Papers on the
IO monad say things like "A term of type IO ()
denotes an action, but does not necessarily perform
the action." (Wadler, "How to Declare an Imperative")
Or, "putc '!' denotes the command that, if it is ever
performed, will print an exclamation mark."
I like to think of the IO monad as a lazy imperative program
generator. That is, the runtime lazily evaluates actions as they are
needed, perhaps as though main is a (potentially infinite) lazy list
of actions. In my mental model, runtime basically works like:
What should I do first? *evaluate first action* *perform action*
What should I do next? *evaluate next action* *perform action*
What should I do next? *evaluate next action* *perform action*
What should I do next? *evaluate next action* *perform action*
...
- - Jake
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