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Functional Programming Patterns With RamdaJS!

Spicy Exercises

Exercises with problem, solution, and explanation.

We'll cover the following...

Time for some exercises! While doing them take a look at Ramda’s docs to see what functions can help you.

Remember point-free means your data’s not visible.

Javascript (babel-node)
// sum is NOT point-free...
// nums parameter is showing
const sum = (nums) => nums.reduce((x, y) => x + y, 0);
// sum is point-free
import { add, reduce } from 'ramda';
const sum = reduce(add, 0);
// This is okay too,
// but inner function (x, y) => {} isn't point-free
import { reduce } from 'ramda';
const sum = reduce((x, y) => x + y, 0);

Exercise 1

This code tells you if a given sentence contains “Bobo”, regardless of case. Refactor it to be point-free.

https://ramdajs.com/docs/#test

Javascript (babel-node)
// Uncommenting this import may help :D
// import R from 'ramda';
const countBobos = (sentence) => /bobo/ig.test(sentence);

Exercise 2

This code tells you if someone should consider a tech career. Refactor it to be point-free.

https://ramdajs.com/docs/#ifElse
https://ramdajs.com/docs/#where

Javascript (babel-node)
// import R from 'ramda';
const shouldCode = (person) => (
  person.lovesTech && person.worksHard ?
    `${person.name} may enjoy a tech career!` :
    `${person.name} wouldn't enjoy a tech career.`
);

Exercise 3

This code returns everyone’s age. Refactor it to be point-free.

https://ramdajs.com/docs/#map
https://ramdajs.com/docs/#prop
https://ramdajs.com/docs/#pluck

Javascript (babel-node)
// import R from 'ramda';
const getAges = (people) => people.map((person) => person.age);

Exercise 4

This code rejects everyone under 18, and over 25. Refactor it to be point-free.

https://ramdajs.com/docs/#filter
https://ramdajs.com/docs/#propSatisfies

Javascript (babel-node)
// import R from 'ramda';
const keepYoungAdults = (people) => people.filter((p) => (
  p.age >= 18 && p.age <= 25
));

Exercise 5

Create a function called defaultTo. It takes two parameters:

  • defaultVal: A default value
  • val: The value to return

If val is null or undefined, return defaultVal.
Else, return val.

Curry it to allow preloading arguments.

const defaultToBobo = defaultTo('Bobo');

defaultToBobo(null); // 'Bobo'
defaultToBobo('Patrick'); // 'Patrick'
Javascript (babel-node)
// your code here