iceCreamReducer.js

// addProps :: {k: v} -> {k: v}
const addProps = props => Object.assign({}, {iceCreamFlavor: '', favoriteFood: []}, props)

function addFood (state, action) {
  // food :: Food
  const food = addProps(Object.assign({}, state[action.data.id], {
    [action.data.prop]: state[action.data.id].favoriteFood.concat(action.data.food)
  }))
  // assocPath :: [String] -> {k: v} -> {k: v} -> {k: v}
  return R.assocPath([action.data.id])(food)(state)
}

function iceCreamFlavor (state, action) {
  // flavor :: Flavor
  const flavor = addProps(Object.assign({}, state[action.data.id], {
    [action.data.prop]: action.data.flavor
  }))
  // assocPath :: [String] -> {k: v} -> {k: v} -> {k: v}
  return R.assocPath([action.data.id])(flavor)(state)
}

export default function reducer (state = devs, action) {
  switch (action.type) {
    case 'ADD_FOOD':
      return addFood(state, action)
    case 'ICE_CREAM_FLAVOR':
      return iceCreamFlavor(state, action)
    default:
      return state
  }
}