Where objects can hide state or I/O in a program, types and functional type driven development make each function very clear as to what it has for input and out

Where objects can hide state or I/O in a program, types and functional type driven development make each function very clear as to what it has for input and outputs and part of that is not hiding state anywhere that doesn’t make sense. You might still have a global logger because that makes sense, but generally you know the things you have access to because they’re in the function signature. It can break down if you aren’t careful, and there’s some nuance where you might still store a configuration data as an object property, but it’s a clearly typed property that’s assigned at initialization rather than hidden state that magically appears due to some hidden program flow.