however true the statement may be, it's not therefore an abandonment of pure functional programming. You don't have to program in `IO` or `MonadIO m => m`. Exp

however true the statement may be, it's not therefore an abandonment of pure functional programming. You don't have to program in `IO` or `MonadIO m => m`. Expressing your state in terms of pure functions of input events, as can be done with an FRP like Reflex, means you can test all your logic purely. You can be confident that you'll only request to launch the nukes when the nukes need to be launched. Then you have to make yourself confident that, when the system asks the nukes to launch, it sends the right signal. But that's mockable by running the system attached to device that reads the signal and reports its correctness. And making sure the nukes take off, aim correctly, and land on their target is not my department (says Werner von Braun).