effect.ts

export type Effect = { type: string; value?: any }
export type State<T> = T

const get: Effect = { type: 'GET' }
const put = (value: any): Effect => ({ type: 'PUT', value })

const runState = <T>(
  genFn: () => Generator<Effect, void, State<T>>,
  initialState: State<T>,
) => {
  const gen = genFn()
  let state = { ...initialState }
  let curr = gen.next()

  while (!curr.done) {
    switch (curr.value.type) {
      case 'GET':
        curr = gen.next(state)
        break
      case 'PUT':
        state = curr.value.value
        curr = gen.next()
        break
    }
  }
}

function* increment() {
    const state = yield get
    yield put(state + 1)
  }
  
  runState(increment, 0)


export { runState, get, put }