---
layout: reference
title: Modules
subhead: Inspired by ES2015
---

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Cream & Sugar takes inspiration from module syntax introduced in ES2015 and also supports C&S' new [data types](/reference/data-types/).

At a high level, any C&S file can import other modules and export functions of its own. The compiled code uses `require` syntax so that it can work with as many types of transpiled/compiled code in as many environments as possible. With that in mind, you are not limited to importing only C&S modules. C&S simply sits on top of JavaScript so you are free to import as many JavaScript modules as you like.

```
import '/path/to/filename'
```

To import a module that does not actually export any particular values, simply `import` a filename. This will cause the module to be executed if it hasn't been already.

```
import x from '/path/to/filename'
```

To assign a module's exported value to a variable, drop a variable name into the expression. This example will create a value called `x` that references whatever it is that your module exported.

```
import {x, y} from '/path/to/filename'
```

To destructure values from a module that exports an object, place your variable names between curly braces. This will find values in the export associated with keys named `x` and `y`, and turn those into variables
in the module importing them.

```
import {
  keyname1: x,
  keyname2: y
} from '/path/to/filename'
```

Use full object syntax in order to import keys under different variable names. This will assign the value at `keyname1` to the variable name `x` and the value at `keyname2`, to the variable name `y`.

When you export, you can export any type of value you want. As such, you can use destructuring of any object type in your imports. More options are shown here.

```
# Import the first 2 items of an exported tuple.
import {{ x, y }} from '/path/to/filename'

# Import the first two items from an exported array.
import [ x, y ] from '/path/to/filename'

# Assign the first item in an array to `hd`
# and all the rest of them to `tl`.
import [ hd | tl ] from '/path/to/filename'
```


When it comes to exports, ES2015 and C&S begin to differ. Whereas JavaScript allows using the `export` keyword multiple times per module, exporting items in C&S is akin to assigning a value to `module.exports` every time you invoke the `export` function. As such, you'll want to make sure you only call it once.

Since you can only call `export` once per module, it's likely that you will want to export an object.

Exports are also a good place to lock down the allowed arities that may be used with your functions. For example, if you have defined a function called `funA` and you export it as `aritize funA, 2`, then when a user imports your function, they will only be allowed to call it with 2 arguments. If they try to call it with any other number of arguments, they'll get an error. Following is a great example of where that would be useful.

```
map list, fun => map list, fun, []
map [], fun, acc => acc
map [h|t], fun, acc =>
  map t, fun, acc << (fun h, acc.length)

export aritize map, 2
```

In this example, we created a function called `map` that essentially mimics JavaScript's `Array.map` method. It assumes the user will call it with two arguments (an array and a function) and, when that happens, it will recur with a third argument – an array that accumulates all of the values as iterations occur.

In this case, we don't want users of our module to be able to pass in 3 arguments to this function as they could pretty easily mess things up. So when we export it, we call the `aritize` function and lock it down to an arity of 2. This way, if a user tries to call it with a third argument, they'll get an error. However, this does not inhibit the function's own ability to recurse with 3 arguments.

```
import { Component } from 'react'

App = React.createClass {

  render: fn =>
    <div>"Hello"</div>

}

export App
```

Of course, you don't always want to lock down everything you export in this way. Leaving arity open can be important when working with certain libraries, for example React.js. If you export a react class, you'll need to leave the arity open so that you don't end up with a console error:

Remember that you can export any type of data from a C&S module including atoms and tuples.


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