106 lines
2.6 KiB
Markdown
106 lines
2.6 KiB
Markdown
---
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id: 587d7dab367417b2b2512b70
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title: Introduction to Currying and Partial Application
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challengeType: 1
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forumTopicId: 301232
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---
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## Description
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<section id='description'>
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The <code>arity</code> of a function is the number of arguments it requires. <code>Currying</code> a function means to convert a function of N <code>arity</code> into N functions of <code>arity</code> 1.
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In other words, it restructures a function so it takes one argument, then returns another function that takes the next argument, and so on.
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Here's an example:
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```js
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//Un-curried function
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function unCurried(x, y) {
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return x + y;
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}
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//Curried function
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function curried(x) {
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return function(y) {
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return x + y;
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}
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}
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//Alternative using ES6
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const curried = x => y => x + y
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curried(1)(2) // Returns 3
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```
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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 <code>curried</code> function in the example above:
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```js
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// Call a curried function in parts:
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var funcForY = curried(1);
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console.log(funcForY(2)); // Prints 3
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```
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Similarly, <code>partial application</code> can be described as applying a few arguments to a function at a time and returning another function that is applied to more arguments.
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Here's an example:
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```js
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//Impartial function
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function impartial(x, y, z) {
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return x + y + z;
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}
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var partialFn = impartial.bind(this, 1, 2);
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partialFn(10); // Returns 13
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```
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</section>
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## Instructions
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<section id='instructions'>
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Fill in the body of the <code>add</code> function so it uses currying to add parameters <code>x</code>, <code>y</code>, and <code>z</code>.
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: <code>add(10)(20)(30)</code> should return <code>60</code>.
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testString: assert(add(10)(20)(30) === 60);
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- text: <code>add(1)(2)(3)</code> should return <code>6</code>.
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testString: assert(add(1)(2)(3) === 6);
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- text: <code>add(11)(22)(33)</code> should return <code>66</code>.
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testString: assert(add(11)(22)(33) === 66);
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- text: Your code should include a final statement that returns <code>x + y + z</code>.
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testString: assert(code.match(/[xyz]\s*?\+\s*?[xyz]\s*?\+\s*?[xyz]/g));
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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function add(x) {
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// Add your code below this line
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// Add your code above this line
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}
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add(10)(20)(30);
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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const add = x => y => z => x + y + z
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```
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</section>
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