I'm pretty sure you can move black boxes around in the real world too :) There are definitely sensible things to do with "general IO operations." For example,

I'm pretty sure you can move black boxes around in the real world too :) There are definitely sensible things to do with "general IO operations." For example, consider `withArgs`, which replaces argv for the duration of an action. A natural approach is to pick through the received action, and replace all calls to `getArgs` with `return tempArgs`. But `withArgs` doesn't work this way because Haskell can't pick apart IO actions. Instead it uses a nasty FFI to modify a global. (It doesn't even look thread-safe: I'll bet withArgs "leaks" into other threads.) It's also overbroad: IO encapsulates "real world" computations like deleting files, but also basic operations like getting argv! I'd argue it's a failure of Haskell that the type system does not distinguish between a function that erases your hard drive and a function that gets your command line arguments.