addIceCream.js

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

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

/*
  The action to add the icecream flavor looks like this:
  const action = {
    type: 'ICE_CREAM_FLAVOR',
    data: {
      id: 'developer2',
      prop: 'iceCreamFlavor',
      flavor: 'wasabi'
    }
  }
*/