It's an outstandingly well-written introduction, but it only goes so far; a more formal treatment (an inevitably longer one, off topic in a discussion of I/O) w

It's an outstandingly well-written introduction, but it only goes so far; a more formal treatment (an inevitably longer one, off topic in a discussion of I/O) would be needed to understand what, exactly, can be done with monads and how they differ from other types.