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## Background information
For this assignment, we will use immutable lists. You should look at the following docs to learn more about them:https://immutable-js.com/docs/latest@main/List/
You don't need to understand this library in detail, but do need to understand how to create lists and manipulate them. We are using this library instead of JavaScript's built-in arrays because they are conceptually simpler. You will not mutate lists, all functions on lists that return lists will return new lists.
## Getting started
First download and install [Node.js](https://nodejs.org/en/).
Either the LTS or Current versions are fine for this course.
You will need to install the immutable library (see above). To do this you should run `npm install` in the top-level assignment directory. This will install the dependency.
## Assignments
- Quicksort (`quick.js`): implement quicksort in a functional programming style. This problem asks that you implement various helper functions that do most of the heavy lifting (`fold_left`, `map`, etc.) for the actual quicksort implementation.
To solve this problem: read and modify `quick.js` as instructed there.
- Extra credit (`extra.js`): various short exercises. The point of the short exercises is to get you more familiar with immutable lists and high-order functions. We strongly recommend that you do these exercises, if only to test some of the things you implemented for the quicksort problem.
This problem is optional, but any extra credits can be used as points towards mistakes you make in the other 2 problems.
To solve this problem: read and modify `extra.js` as instructed there.
In all both files, we have removed the solutions and included a comment `/**
<FILL-IN> **/` where you are expected to fill in your answers. (You'll want to remove the `undefined` values appropriately.) You should not need to add code anywhere outside these comment blocks.
### Testing your solution
We have included simple tests in the test.js file and the extra.js file.
You can run the code by with the Node.js CLI tool:
For example:
```bash
node test.js
```
Node will raise an exception due to the `assert` at the bottom of the file.
This is how we are testing your code locally. Once you work through the assignment, you will stop receiving assertion errors.
If you don't get an assertion error, you are likely done. You may, of course, want to add more tests.
#### No-nos
- In all cases we are exporting the answers (e.g., `exports.fold_left = ...`), please do not remove any of this code. If we can't test your code, you lose points.
- We will be loading your modules with `require()`. Please make sure that your modules can be loaded -- test them by loading them and checking to make sure `require()` doesn't fail (by throwing an exception). This is especially important if you don't solve everything. We will not be fixing your files to ensure they can be loaded.
#### Grading
The quicksort is worth 50 points. Each extra credit question is worth 2 points.
#### Submission
You must submit the assignment via gradescope.
Submit your assignment by uploading the following files:
- quick.js
- extra.js
**NOTE:** Upload only these .js files, not a zip file containing your whole project directry, not fewer files, not more files.