example of using curried functions

learn-curry.js

/** Store Data */
const prices = {
  game: 59.95,
  nintendo: 399.99,
  controller: 49.99,
  xbox: 299.99,
  ps1: 349.99
}

const basket = [
  { name: 'nintendo', qty: 1 },
  { name: 'controller', qty: 3 },
  { name: 'game', qty: 4 },
]

const TAX_RATE = 0.075

/** Utils */
function curry(fn) {
  return (...args) => {
    if (args.length >= fn.length) {
      return fn.apply(null, args)
    }

    return curry(fn.bind(null, ...args))
  }
}

const trace = curry((label, val) => {
  console.log(label, val)
  return val
})
const sum = (a, b) => a + b;
const multi = curry((m, n) => m * n);
const isObj = (mixed) => !!mixed && typeof mixed === 'object';
const get = curry((obj, name) => isObj(obj) ? obj[name] : undefined)
const prop = curry((name, obj) => get(obj, name))
const zip = (...arrays) => {
  return new Array(arrays[0].length).fill([])
    .map((acc, index) => {
      return arrays.map(item => item[index])
    })
}
const _apply = curry((fn, items) => fn.apply(null, items))

// console.log(zip([1,2,3], ['a','b','c']));
// [1,2,3] [a, b, c] ---> [[1, a], [2, b], [3, c]]

/** APP */
const getPrice = get(prices)
const getTax = multi(TAX_RATE)

const items = basket.map(prop('name'))//.map(trace('item --> '))
const priceOfItems = items.map(getPrice)//.map(trace('price --> '))
const quantities = basket.map(prop('qty'))//.map(trace('qty --> '))
const pricesQuantities = zip(priceOfItems, quantities)
const subtotals = zip(priceOfItems, quantities).map(_apply(multi))

const subtotal = subtotals.reduce(sum, 0)
const tax = getTax(subtotal)
const total = sum(subtotal, tax)

trace('subtotal: ', subtotal)
trace('tax: ', tax)
trace('total: ', total)

// pricesQuantities.map(_apply(multi)).map(trace('subtotals -->')
// console.log(pricesQuantities)
// this is ugly
// pricesQuantities
//   .map(items => multi.apply(null, items))
//   .map(trace('subtotal --> '))

// console.log(getPrice('banana'))// undefined
// console.log(getPrice('game')) // 399.99
// console.log(priceOfItems)// [399.99, 49.99, 59.95]

This is still not as pure in the functional paradigm as we can go because I am doing things one line at a time instead of composing the functions together.