Lennart Augustsson wrote:
And yes, somewhere there's some global mutable state in the OS. I've never claimed that it should be totally forbidden. Various circumstances forces it upon us. What I've been claiming is that it should be avoided where possible. Which is almost always.
Thus there seems to be agreement that whereas this should be avoided where possible, it is still needed in some cases.
Therefore the question arises as to how to safely incorporate this into the language. As everyone knows, use of unsafePerformIO could break the type system without a programmer knowing it, but I think I am right in saying that if only monomorphic refs were allowed at the top level, type safety would be ensured (so there would be no need for the truly horrible value restriction that infects the whole of SML for example)
Therefore I propose a new keyword to define monomorphic top level IORefs, something like:
augment ref = monomorphicvalue -- just a plain value not a monadic computation
where "augment" refers to the augmentation of the RealWorld state by the state of ref as in John's suggestion to use "augmented IO" in preference to "global mutable state"
The use of a plain value to initialize the ref rather than a monadic computation would ensure that there would be no problems with trying to work out which order to initialize top level refs that are dependent on values of refs in other modules since there could be no dependencies.
Regards, Brian.
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