freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/introduction-to-currying-and-partial-application.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
587d7dab367417b2b2512b70	Introduction to Currying and Partial Application	1	301232	introduction-to-currying-and-partial-application

--description--

The arity of a function is the number of arguments it requires. Currying a function means to convert a function of N arity into N functions of arity 1.

In other words, it restructures a function so it takes one argument, then returns another function that takes the next argument, and so on.

Here's an example:

function unCurried(x, y) {
  return x + y;
}

function curried(x) {
  return function(y) {
    return x + y;
  }
}

const curried = x => y => x + y

curried(1)(2)

curried(1)(2) would return 3.

This is useful in your program if you can't supply all the arguments to a function at one time. You can save each function call into a variable, which will hold the returned function reference that takes the next argument when it's available. Here's an example using the curried function in the example above:

const funcForY = curried(1);
console.log(funcForY(2)); // 3

Similarly, partial application can be described as applying a few arguments to a function at a time and returning another function that is applied to more arguments. Here's an example:

function impartial(x, y, z) {
  return x + y + z;
}

const partialFn = impartial.bind(this, 1, 2);
partialFn(10); // 13

--instructions--

Fill in the body of the add function so it uses currying to add parameters x, y, and z.

--hints--

add(10)(20)(30) should return 60.

assert(add(10)(20)(30) === 60);

add(1)(2)(3) should return 6.

assert(add(1)(2)(3) === 6);

add(11)(22)(33) should return 66.

assert(add(11)(22)(33) === 66);

Your code should include a final statement that returns x + y + z.

assert(code.match(/[xyz]\s*?\+\s*?[xyz]\s*?\+\s*?[xyz]/g));

--seed--

--seed-contents--

function add(x) {
  // Only change code below this line


  // Only change code above this line
}

add(10)(20)(30);

--solutions--

const add = x => y => z => x + y + z