function* main() {
    while( yield take('START_BACKGROUND_SYNC') ) {
      // starts the task in the background
      const bgSyncTask = yield fork(bgSync)

      // wait for the user stop action
      yield take('STOP_BACKGROUND_SYNC')
      // user clicked stop. cancel the background task
      // this will throw a SagaCancellationException into the forked bgSync
      // task
      yield cancel(bgSyncTask)
    }
  }

  const fetchPostsWithTimeout:Saga = function* fetchPostsWithTimeout() {
    while( yield take('FETCH_POSTS') ) {
      // starts a race between 2 effects
      const {posts, timeout} = yield race({
        posts   : call(fetchApi, '/posts'),
        timeout : call(delay, 1000)
      })

      if(posts)
        put( {type: 'RECEIVE_POSTS', posts} )
      else
        put( {type: 'TIMEOUT_ERROR'} )
    }
  }

  const incrementAsync:Saga = function* incrementAsync() {

    while(true) {

      // wait for each INCREMENT_ASYNC action
      const nextAction = yield take('INCREMENT_ASYNC')

      // delay is a sample function
      // return a Promise that resolves after (ms) milliseconds
      yield delay(1000)

      // dispatch INCREMENT_COUNTER
      yield put( {type: 'INCREMENT_COUNTER'} )
    }

  }

 function* watchFetch() {
   while ( yield take('FETCH_POSTS') ) {
     yield fork(fetchPosts) // non blocking call
   }
 }