In `fastn`, the `list` keyword can be used to create an array or list of values. The `list` keyword is followed by the data type of the values that the list will contain.

Declaring a `list`

To declare a new list variable, you can use the following syntax:

Declaring a `list`

-- <data-type> list <list-name>:

-- <value>
-- <value>
-- <value>
-- ...

-- end: <list-name>

Lang:

ftd

Also make sure to use the end syntax `-- end: ` to mark the end of the list during initialization. For example, to create a list of strings called `weekdays`, you would use the following syntax:

a list of string

-- string list weekdays:

-- string: Sunday
-- string: Monday
-- string: Tuesday
-- string: Wednesday
-- string: Thursday
-- string: Friday
-- string: Saturday

-- end: weekdays

Lang:

ftd

This creates a new variable called `weekdays`, which is a list of `string`s. The list is initialized with seven strings representing the days of the week. By default, lists in `fastn` are immutable, which means that their contents cannot be changed after they are initialized. However, you can make a list mutable by prefixing it with a `$` symbol, like this:

Mutable Variable

-- string list $weekdays:
-- end: $weekdays

Lang:

ftd

Let's checkout the list declaration for the more complex type data like record.

Record list

-- record person:
caption name:
body bio:

-- person list people:

-- person: Amit Upadhyay

Amit is CEO of FifthTry.

-- person: Shobhit Sharma

Shobhit is a developer at FifthTry.

-- end: people

Lang:

ftd

Here we have created a `list` of `person` objects, called it `people`, and created two `person` objects and inserted them the `people` list.

`ftd.ui` type as a list

You can use [`ftd.ui list`](ftd/built-in-types/#ftd-ui) type or [`children`](ftd/built-in-types/#children) type to pass a UI component in a list.

Using `ftd.ui list` type

-- ftd.ui list uis:

-- ftd.text: Hello World!
color: $inherited.colors.text-strong

-- ftd.text: I love `fastn`.
color: $inherited.colors.text-strong

-- end: uis

Lang:

ftd

Using `children` type

-- foo:

-- ftd.text: Hello World!
color: $inherited.colors.text-strong

-- ftd.text: I love `fastn`.
color: $inherited.colors.text-strong

-- end: foo

-- component foo:
children uis:

... some code here

-- end: foo

Lang:

ftd

Accessing list items

Once you have created a list, you can access its elements using indexing or looping. Once you have created a list, you can access its items using their index. In `fastn`, indexing starts at 0. Or you can use

Using `loop`

You can also access the elements of a list using a loop. In `fastn`, you can use the `$loop$` keyword to iterate over a list. Here's an example:

-- ftd.text: $obj
$loop$: $weekdays as $obj

Lang:

ftd

Output

Sunday

Monday

Tuesday

Wednesday

Thursday

Friday

Saturday

This code will output each element of the `weekdays` list on a separate line. Similarly, To iterate over a `uis` list, you would use the following syntax:

-- obj:
$loop$: $uis as $obj

Lang:

ftd

Output

Hello World!

I love `fastn`.

Using index

You can access an element of a list by its index. In `fastn`, list indexing is zero-based, which means the first element of a list has an index of 0, the second element has an index of 1, and so on. You can use the `.` operator to access an element of a list by its index. For example, to access the first item in the `weekdays` list, you would use the following syntax:

-- ftd.text: $weekdays.0
color: $inherited.colors.text-strong

Lang:

ftd

Output

Sunday

Similarly, To access the first component in the `uis` list, you would use the following syntax:

-- uis.0:

Lang:

ftd

Output

Hello World!

`$processor$`

A list can be created using platform provided processors:

Using `$processor$`

-- string list foo:
$processor$: some-list

Lang:

ftd

Here the value of the list will be provided by the `some-list` processor. If we already have a list we can insert values to it using `$processor$` as well:

-- string list $foo:
-- end: $foo

-- $foo:
$processor$: some-list

Lang:

ftd

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[⭐️](https://github.com/fastn-stack/fastn)

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[💻️](/community/)

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Quick links:

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