One of the "holes" in real-world Haskell is you never know if a library/function is calling unsafePerformIO and you have to trust the library author. I recognize the necessity of the function, but should it announce itself? unsafePerformIO has this type: unsafePerformIO :: IO a -> a Would there be any value to making it have a type that can be stripped off, like some other monads? For example, providing a "runUnsafe" or similar: data UnsafePerformIO a = Unsafe a runUnsafe :: UnsafePerformIO a -> a runUnsafe (Unsafe o) = o and changing unsafePerformIO to have the type: unsafePerformIO :: IO a -> UnsafePerformIO a It seems it would be valuable to have functions announce when they use unsafePerformIO, but additionally allow it to be stripped off. So the classic launchMissiles :: a -- Uses unsafePerfomIO! Would become launchMissiles :: UnsafePerformIO a Which could be stripped off it you wanted: evilDictatator :: a evilDictator = runUnsafe $ launchMissiles But doesn't have to be: incompetentDictator :: a incompetentDictator = launchMissiles -- Doesn't type check! I doubt this is original - does it buy anything? Justin