Simplified Redux Reducers

Simplified-Redux-Reducers.js

import Maybe from 'folktale/maybe';

const Inc = 'Inc';
const Dec = 'Dec';
const IncBy = 'IncBy';

const IncFn = state => state + 1;
const DecFn = state => state - 1;
const IncByFn = (state, action) => state + action.incBy;

const Actions = { [Inc]: IncFn, [Dec]: DecFn, [IncBy]: IncByFn };

const CounterReducer = (state = 0, action) =>
	Maybe.fromNullable(Actions[action.type]).matchWith({
		Just: ({ value }) => value(state, action),
		Nothing: () => state
	});

CounterReducer(4, { type: Inc }); //=> 5
CounterReducer(undefined, { type: Inc }); //=> 1
CounterReducer(4, { type: Dec }); //=> 3
CounterReducer(undefined, { type: Dec }); // => -1
CounterReducer(4, { type: IncBy, incBy: 5 }); // => 9