[Haskell-cafe] QuickChecking IO

I'd like to use QuickCheck on IO code. For instance, I'd like to check a property of type String -> IO Bool. Using unsafePerformIO seems straightforward (though I haven't written the code, so I may be wrong about that) and it might be possible to make a solution involving unsafeInterleaveIO work. Short of rewriting QuickCheck, is there any way to check IO code "safely"? Barring that, I suspect it's possible modify QuickCheck to accommodate IO code (or perhaps, general monadic code). Has anyone done this? thanks -m