sagas.js

// ------------------
// SomeComponent.js
// ------------------
function SomeComponent() {
    ...
    const getUser = id => {
      dispatch({ type: '@user/FETCH_REQUESTED', id })
    }
    ...
}

// ------------------
// sagas.js
// ------------------
import { takeEvery } from 'redux-saga/effects'

// Exemplo anterior
export function* fetchUser(action) {
    const { data } = yield call(api.get, `/user/${action.id}`)
    yield put({ type: "@user/FETCH_SUCCEEDED", data })
}

// Opa! Código novo!
function* watchFetchData() {
  yield takeEvery('@user/FETCH_REQUESTED', fetchUser)
}

// ------------------
// reducer.js
// ------------------
export default function users(state = [], action) {
    switch (action.type) {
        case '@user/FETCH_SUCCEEDED':
            return {
                ...state,
                users: [...users, action.data]
            }

        default: 
            return state;
    }
}