How are your functions pure if inside them you call `useEffect`, `useState` ? Where is pureness when at first look they generate side effects, or am I missing something ?

> not all hooks break pureness

Sure, if you define a function called useWhatever that doesn't actually call any hooks, that might be a pure function. But the restrictions described in https://reactjs.org/docs/hooks-rules.html are not restrictions that pure functions have.

But functions that use hooks aren't pure because hooks break referential transparency.

Simplicity does not necessarily imply clarity.