On Tuesday 30 Nov 2004 9:19 pm, Benjamin Franksen wrote:
I don't get it: How can they be top-level without scoping over an entire module? I mean, the proposal was to have
x <- action
at the top-level, right? Then how can it not be visible in the whole module? What scope *does* it have, in your opinion?
x scopes over an entire module, and may be reasonably described as "global" if x is exported. But in this example.. userInit <- oneShot realInit oneShot creates a top level MVar which is only accessible via userInit and no other function, so it doesn't even scope over an entire module and is certainly not exportable. With the ACIO monad the type of oneShot would be.. oneShot :: IO a -> ACIO(IO a) If userInit is exported, it could reasonably be described as "global", but this doesn't matter because as far as users are concerned it's just a perfectly ordinary side-effectful, state manipulating IO function that works it's magic by unknown means. There's no reason for them to know or care that the some of the state it manipulates is top-level Haskell state rather than "real world" state, and there's no possibility of anybody getting at the underlying MVar and accidently corrupting it. The only way it can be got at is by executing userInit. Regards -- Adrian Hey