squiggle/packages/website/docs/Api/List.md
2022-07-29 08:07:11 -07:00

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---
sidebar_position: 7
title: List
---
Squiggle lists are a lot like Python lists or Ruby arrays. They accept all types.
```javascript
myList = [3, normal(5, 2), "random"];
```
### make
```
List.make: (number, 'a) => list<'a>
```
Returns an array of size `n` filled with the value.
```js
List.make(4, 1); // creates the list [1, 1, 1, 1]
```
See [Rescript implementation](https://rescript-lang.org/docs/manual/latest/api/belt/array#make)
### toString
```
toString: (list<'a>) => string
```
### length
```
length: (list<'a>) => number
```
### upTo
```
List.upTo: (low:number, high:number) => list<number>
```
```js
List.upTo(0, 5); // creates the list [0, 1, 2, 3, 4, 5]
```
Syntax taken from [Ruby](https://apidock.com/ruby/v2_5_5/Integer/upto).
### first
```
first: (list<'a>) => 'a
```
### last
```
last: (list<'a>) => 'a
```
### reverse
```
reverse: (list<'a>) => list<'a>
```
### map
```
map: (list<'a>, a => b) => list<'b>
```
See [Rescript implementation](https://rescript-lang.org/docs/manual/latest/api/belt/array#map).
### filter
```
filter: (list<'a>, 'a => bool) => list<'a>
```
See [Rescript implementation of keep](https://rescript-lang.org/docs/manual/latest/api/belt/array#keep), which is functionally equivalent.
### reduce
```
reduce: (list<'b>, 'a, ('a, 'b) => 'a) => 'a
```
`reduce(arr, init, f)`
Applies `f` to each element of `arr`. The function `f` has two paramaters, an accumulator and the next value from the array.
```js
reduce([2, 3, 4], 1, {|acc, value| acc + value}) == 10
```
See [Rescript implementation](https://rescript-lang.org/docs/manual/latest/api/belt/array#reduce).
### reduce reverse
```
reduceReverse: (list<'b>, 'a, ('a, 'b) => 'a) => 'a
```
Works like `reduce`, but the function is applied to each item from the last back to the first.
See [Rescript implementation](https://rescript-lang.org/docs/manual/latest/api/belt/array#reducereverse).