The Last Reducer You'll Ever Need

universal-reducer.ts

interface UniversalAction<TState> {
	type: "UNIVERSAL";
	map: (previous: TState) => TState;
}

function universalAction<TState>(map: (previous: TState) => TState): UniversalAction<TState> {
	return { type: "UNIVERSAL", map };
}

// all other reducers are now redundant
function universalReducer<TState>(previous: TState, action: UniversalAction<TState>) {
	switch (action.type) {
		case "UNIVERSAL": return action.map(previous);
		default: throw "Obsolete action type detected";
	}
}