Professor Frisby's functional programming exercises (Part 1: currying)

fp.exercises_1.js

const expect = require('expect')
const { curry, split, map, filter, reduce } = require('ramda')

// Exercise 1
//==============
// Refactor to remove all arguments by partially applying the function.

const words = split(' ')

expect(words('Jingle bells Batman smells')).toEqual([
  'Jingle',
  'bells',
  'Batman',
  'smells',
])

// Exercise 1a
//==============
// Use map to make a new words fn that works on an array of strings.

const sentences = map(words)

expect(sentences(['Jingle bells Batman smells', 'Robin laid an egg'])).toEqual([
  ['Jingle', 'bells', 'Batman', 'smells'],
  ['Robin', 'laid', 'an', 'egg'],
])

// Exercise 2
//==============
// Refactor to remove all arguments by partially applying the functions.

const match = curry((reg, str) => reg.test(str))
const filterQs = filter(match(/q/i))

expect(filterQs(['quick', 'camels', 'quarry', 'over', 'quails'])).toEqual([
  'quick',
  'quarry',
  'quails',
])

// Exercise 3
//==============
// Use the helper function _keepHighest to refactor max to not reference any
// arguments.

// LEAVE BE:
const _keepHighest = (x, y) => (x >= y ? x : y)

// REFACTOR THIS ONE:
const max = reduce(_keepHighest, -Infinity)

expect(max([323, 523, 554, 123, 5234])).toBe(5234)

// Bonus 1:
// ============
// Wrap array's slice to be functional and curried.
// [1, 2, 3].slice(0, 2)
const slice = curry((x, y, z) => z.slice(x, y))

expect(slice(1)(3)(['a', 'b', 'c'])).toEqual(['b', 'c'])

// Bonus 2:
// ============
// Use slice to define a function "take" that returns n elements from the beginning of an array.
// Make it curried. For ['a', 'b', 'c'] with n=2 it should return ['a', 'b'].
const take = slice(0)

expect(take(2)(['a', 'b', 'c'])).toEqual(['a', 'b'])

console.info('You are now a CURRY genius!!! 🍛 👏🏼 👏🏼 👏🏼')