80 lines
1.5 KiB
Markdown
80 lines
1.5 KiB
Markdown
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---
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id: 594810f028c0303b75339ace
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title: Accumulator factory
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challengeType: 5
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forumTopicId: 302222
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dashedName: accumulator-factory
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---
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# --description--
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A problem posed by [Paul Graham](https://en.wikipedia.org/wiki/Paul_Graham_(programmer)) is that of creating a function that takes a single (numeric) argument and which returns another function that is an accumulator. The returned accumulator function in turn also takes a single numeric argument, and returns the sum of all the numeric values passed in so far to that accumulator (including the initial value passed when the accumulator was created).
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# --instructions--
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Create a function that takes a number $n$ and generates accumulator functions that return the sum of every number ever passed to them.
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**Rules:**
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Do not use global variables.
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**Hint:**
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Closures save outer state.
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# --hints--
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`accumulator` should be a function.
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```js
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assert(typeof accumulator === 'function');
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```
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`accumulator(0)` should return a function.
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```js
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assert(typeof accumulator(0) === 'function');
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```
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`accumulator(0)(2)` should return a number.
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```js
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assert(typeof accumulator(0)(2) === 'number');
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```
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Passing in the values 3, -4, 1.5, and 5 should return 5.5.
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```js
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assert(testFn(5) === 5.5);
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```
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# --seed--
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## --after-user-code--
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```js
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const testFn = typeof accumulator(3) === 'function' && accumulator(3);
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if (testFn) {
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testFn(-4);
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testFn(1.5);
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}
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```
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## --seed-contents--
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```js
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function accumulator(sum) {
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}
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```
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# --solutions--
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```js
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function accumulator(sum) {
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return function(n) {
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return sum += n;
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};
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}
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```
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