Redux uses a state reducer pattern where essentially you create a pure function that looks like:
function reducer (previousState, action) {
//...
return newState;
}
This looks similar to JavaScript's Array.reduce function, so I don't think the concept of a 'reducer' is something original to Redux.
However, when I google terms like 'reducer function' or 'reducer pattern' I only get results that are about Redux. (Although down the list is NgRx documentation about reducers).
Can someone give me definitive reference/answer the explains the concept of reducer functions in functional programming generally?