interface Fruit {
  isRotten: boolean
}

interface Apple extends Fruit {
  apple: true
}

interface Banana extends Fruit {
  banana: true
}

interface State {
  apples: Apple[]
  bananas: Banana[]
  selected: Set<'Apples' | 'Bananas'>
}

const isRotten = <F extends Fruit>(fruit: F) => fruit.isRotten
const edibleFruits = <F extends Fruit>(fruits: F[]) => fruits.filter(fruit => !isRotten(fruit))

const apples$ = (state: State) => state.apples
const bananas$ = (state: State) => state.bananas
const selectedFruits$ = (state: State) => state.selected

const edibleApples$ = map(apples$)(edibleFruits)
const edibleBananas$ = map(bananas$)(edibleFruits)
const selectedFruitsArray$ = map(selectedFruits$)(selected => Array.from(selected))

const fruitBasket$ = flatMap(selectedFruitsArray$)(fruits => {
  const selectors$: Selector<State, Fruit[]>[] = fruits.map(fruit => {
    switch (fruit) {
      case 'Apples':
        return apples$
      case 'Bananas':
        return bananas$
    }
  })

  return createSelector(selectors$, (...allFruits) => ([] as Fruit[]).concat(...allFruits))
})