Hi Isaac, <Moving to Haskell-cafe>
How does or might this relate to the typeclass-based Restricted IO monad http://article.gmane.org/gmane.comp.lang.haskell.general/14526 ? RIO's technique has the advantage that multiple capabilities can be easily combined in one use of the monad - but this manner of using typeclasses might interfere with how testable it is? (I think that should be okay... Also that this is a really neat project - incremental progress on taming Haskell IO in practice!)
Stefan is absolutely right. The RIO, as far as I remember, restricts which parts of the IO monad you use. The same could be said for the Test.IOSpec modules. However, the Test.IOSpec also give you a pure specification of the functions you are using. This is very important if you want to trace/debug an execution of you code - you can see how the state of your machine changes at every step. There's also a bit finer control over how you test your functions: concurrent code is parameterised over the scheduler, for instance. Both these aren't possible with the RIO approach.
P.S. why
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