103 lines
2.3 KiB
Markdown
103 lines
2.3 KiB
Markdown
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---
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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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dashedName: introduction-to-currying-and-partial-application
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---
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# --description--
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The <dfn>arity</dfn> of a function is the number of arguments it requires. <dfn>Currying</dfn> a function means to convert a function of N arity into N functions of arity 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 curried 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, <dfn>partial application</dfn> 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:
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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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# --instructions--
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Fill in the body of the `add` function so it uses currying to add parameters `x`, `y`, and `z`.
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# --hints--
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`add(10)(20)(30)` should return `60`.
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```js
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assert(add(10)(20)(30) === 60);
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```
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`add(1)(2)(3)` should return `6`.
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```js
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assert(add(1)(2)(3) === 6);
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```
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`add(11)(22)(33)` should return `66`.
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```js
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assert(add(11)(22)(33) === 66);
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```
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Your code should include a final statement that returns `x + y + z`.
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```js
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assert(code.match(/[xyz]\s*?\+\s*?[xyz]\s*?\+\s*?[xyz]/g));
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```
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# --seed--
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## --seed-contents--
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```js
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function add(x) {
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// Only change code below this line
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// Only change code above this line
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}
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add(10)(20)(30);
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```
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# --solutions--
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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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