sources/docs/reference/language/scripting.md

---
description: Automate your document with Typst's scripting capabilities.
---

# Scripting
Typst embeds a powerful scripting language. You can automate your documents and
create more sophisticated styles with code. Below is an overview over the
scripting concepts.

## Expressions
In Typst, markup and code are fused into one. All but the most common elements
are created with _functions._ To make this as convenient as possible, Typst
provides compact syntax to embed a code expression into markup: An expression is
introduced with a hash (`#`) and normal markup parsing resumes after the
expression is finished. If a character would continue the expression but should
be interpreted as text, the expression can forcibly be ended with a semicolon
(`;`).

```example
#emph[Hello] \
#emoji.face \
#"hello".len()
```

The example above shows a few of the available expressions, including
[function calls]($function), [field accesses]($scripting/#fields), and
[method calls]($scripting/#methods). More kinds of expressions are
discussed in the remainder of this chapter. A few kinds of expressions are not
compatible with the hash syntax (e.g. binary operator expressions). To embed
these into markup, you can use parentheses, as in `[#(1 + 2)]`.

## Blocks
To structure your code and embed markup into it, Typst provides two kinds of
_blocks:_

- **Code block:** `{{ let x = 1; x + 2 }}` \
  When writing code, you'll probably want to split up your computation into
  multiple statements, create some intermediate variables and so on. Code blocks
  let you write multiple expressions where one is expected. The individual
  expressions in a code block should be separated by line breaks or semicolons.
  The output values of the individual expressions in a code block are joined to
  determine the block's value. Expressions without useful output, like `{let}`
  bindings yield `{none}`, which can be joined with any value without effect.

- **Content block:** `{[*Hey* there!]}` \
  With content blocks, you can handle markup/content as a programmatic value,
  store it in variables and pass it to [functions]($function). Content
  blocks are delimited by square brackets and can contain arbitrary markup. A
  content block results in a value of type [content]. An arbitrary number of
  content blocks can be passed as trailing arguments to functions. That is,
  `{list([A], [B])}` is equivalent to `{list[A][B]}`.

Content and code blocks can be nested arbitrarily. In the example below,
`{[hello ]}` is joined with the output of  `{a + [ the ] + b}` yielding
`{[hello from the *world*]}`.

```example
#{
  let a = [from]
  let b = [*world*]
  [hello ]
  a + [ the ] + b
}
```

## Bindings and Destructuring { #bindings }
As already demonstrated above, variables can be defined with `{let}` bindings.
The variable is assigned the value of the expression that follows the `=` sign.
The assignment of a value is optional, if no value is assigned, the variable
will be initialized as `{none}`. The `{let}` keyword can also be used to create
a [custom named function]($function/#defining-functions). Variables can be
accessed for the rest of the containing block (or the rest of the file if there
is no containing block).

```example
#let name = "Typst"
This is #name's documentation.
It explains #name.

#let add(x, y) = x + y
Sum is #add(2, 3).
```

Let bindings can also be used to destructure [arrays]($array) and
[dictionaries]($dictionary). In this case, the left-hand side of the
assignment should mirror an array or dictionary. The `..` operator can be used
once in the pattern to collect the remainder of the array's or dictionary's
items.

```example
#let (x, y) = (1, 2)
The coordinates are #x, #y.

#let (a, .., b) = (1, 2, 3, 4)
The first element is #a.
The last element is #b.

#let books = (
  Shakespeare: "Hamlet",
  Homer: "The Odyssey",
  Austen: "Persuasion",
)

#let (Austen,) = books
Austen wrote #Austen.

#let (Homer: h) = books
Homer wrote #h.

#let (Homer, ..other) = books
#for (author, title) in other [
  #author wrote #title.
]
```

You can use the underscore to discard elements in a destructuring pattern:

```example
#let (_, y, _) = (1, 2, 3)
The y coordinate is #y.
```

Destructuring also works in argument lists of functions ...

```example
#let left = (2, 4, 5)
#let right = (3, 2, 6)
#left.zip(right).map(
  ((a,b)) => a + b
)
```

... and on the left-hand side of normal assignments. This can be useful to
swap variables among other things.

```example
#{
  let a = 1
  let b = 2
  (a, b) = (b, a)
  [a = #a, b = #b]
}
```

## Conditionals
With a conditional, you can display or compute different things depending on
whether some condition is fulfilled. Typst supports `{if}`, `{else if}` and
`{else}` expressions. When the condition evaluates to `{true}`, the conditional
yields the value resulting from the if's body, otherwise yields the value
resulting from the else's body.

```example
#if 1 < 2 [
  This is shown
] else [
  This is not.
]
```

Each branch can have a code or content block as its body.

- `{if condition {..}}`
- `{if condition [..]}`
- `{if condition [..] else {..}}`
- `{if condition [..] else if condition {..} else [..]}`

## Loops
With loops, you can repeat content or compute something iteratively. Typst
supports two types of loops: `{for}` and `{while}` loops. The former iterate
over a specified collection whereas the latter iterate as long as a condition
stays fulfilled. Just like blocks, loops _join_ the results from each iteration
into one value.

In the example below, the three sentences created by the for loop join together
into a single content value and the length-1 arrays in the while loop join
together into one larger array.

```example
#for c in "ABC" [
  #c is a letter.
]

#let n = 2
#while n < 10 {
  n = (n * 2) - 1
  (n,)
}
```

For loops can iterate over a variety of collections:

- `{for value in array {..}}` \
  Iterates over the items in the [array]. The destructuring syntax described in
  [Let binding]($scripting/#bindings) can also be used here.

- `{for pair in dict {..}}` \
  Iterates over the key-value pairs of the [dictionary]. The pairs can also be
  destructured by using `{for (key, value) in dict {..}}`. It is more efficient
  than `{for pair in dict.pairs() {..}}` because it doesn't create a temporary
  array of all key-value pairs.

- `{for letter in "abc" {..}}` \
  Iterates over the characters of the [string]($str). Technically, it iterates
  over the grapheme clusters of the string. Most of the time, a grapheme cluster
  is just a single codepoint. However, a grapheme cluster could contain multiple
  codepoints, like a flag emoji.

- `{for byte in bytes("😀") {..}}` \
  Iterates over the [bytes], which can be converted from a [string]($str) or
  [read] from a file without encoding. Each byte value is an [integer]($int)
  between `{0}` and `{255}`.

To control the execution of the loop, Typst provides the `{break}` and
`{continue}` statements. The former performs an early exit from the loop while
the latter skips ahead to the next iteration of the loop.

```example
#for letter in "abc nope" {
  if letter == " " {
    break
  }

  letter
}
```

The body of a loop can be a code or content block:

- `{for .. in collection {..}}`
- `{for .. in collection [..]}`
- `{while condition {..}}`
- `{while condition [..]}`

## Fields
You can use _dot notation_ to access fields on a value. For values of type
[`content`], you can also use the [`fields`]($content.fields) function to list
the fields.

The value in question can be either:
- a [dictionary] that has the specified key,
- a [symbol] that has the specified modifier,
- a [module] containing the specified definition,
- [content] consisting of an element that has the specified field. The
  available fields match the arguments of the
  [element function]($function/#element-functions) that were given when the
  element was constructed.

```example
#let it = [= Heading]
#it.body \
#it.depth \
#it.fields()

#let dict = (greet: "Hello")
#dict.greet \
#emoji.face

```

## Methods
A _method call_ is a convenient way to call a function that is scoped to a
value's [type]. For example, we can call the [`str.len`]($str.len) function in
the following two equivalent ways:

```example
#str.len("abc") is the same as
#"abc".len()
```

The structure of a method call is `{value.method(..args)}` and its equivalent
full function call is `{type(value).method(value, ..args)}`. The documentation
of each type lists its scoped functions. You cannot currently define your own
methods.

```example
#let values = (1, 2, 3, 4)
#values.pop() \
#values.len() \

#("a, b, c"
    .split(", ")
    .join[ --- ])

#"abc".len() is the same as
#str.len("abc")
```

There are a few special functions that modify the value they are called on (e.g.
[`array.push`]($array.push)). These functions _must_ be called in method form.
In some cases, when the method is only called for its side effect, its return
value should be ignored (and not participate in joining). The canonical way to
discard a value is with a let binding: `{let _ = array.remove(1)}`.

## Modules
You can split up your Typst projects into multiple files called _modules._ A
module can refer to the content and definitions of another module in multiple
ways:

- **Including:** `{include "bar.typ"}` \
  Evaluates the file at the path `bar.typ` and returns the resulting [content].

- **Import:** `{import "bar.typ"}` \
  Evaluates the file at the path `bar.typ` and inserts the resulting [module]
  into the current scope as `bar` (filename without extension). You can use the
  `as` keyword to rename the imported module: `{import "bar.typ" as baz}`. You
  can import nested items using dot notation: `{import "bar.typ": baz.a}`.

- **Import items:** `{import "bar.typ": a, b}` \
  Evaluates the file at the path `bar.typ`, extracts the values of the variables
  `a` and `b` (that need to be defined in `bar.typ`, e.g. through `{let}`
  bindings) and defines them in the current file. Replacing `a, b` with `*`
  loads all variables defined in a module. You can use the `as` keyword to
  rename the individual items: `{import "bar.typ": a as one, b as two}`

Instead of a path, you can also use a [module value]($module), as shown in the
following example:

```example
#import emoji: face
#face.grin
```

## Packages
To reuse building blocks across projects, you can also create and import Typst
_packages._ A package import is specified as a triple of a namespace, a name,
and a version.

```example
>>> #let add(x, y) = x + y
<<< #import "@preview/example:0.1.0": add
#add(2, 7)
```

The `preview` namespace contains packages shared by the community. You can find
all available community packages on [Typst Universe]($universe).

If you are using Typst locally, you can also create your own system-local
packages. For more details on this, see the
[package repository](https://github.com/typst/packages).

## Operators
The following table lists all available unary and binary operators with effect,
arity (unary, binary) and precedence level (higher binds stronger). Some
operations, such as [modulus]($calc.rem-euclid), do not have a special syntax
and can be achieved using functions from the
[`calc`]($category/foundations/calc) module.

| Operator   | Effect                          | Arity  | Precedence |
|:----------:|---------------------------------|:------:|:----------:|
|  `{-}`     | Negation                        | Unary  |     7      |
|  `{+}`     | No effect (exists for symmetry) | Unary  |     7      |
|  `{*}`     | Multiplication                  | Binary |     6      |
|  `{/}`     | Division                        | Binary |     6      |
|  `{+}`     | Addition                        | Binary |     5      |
|  `{-}`     | Subtraction                     | Binary |     5      |
|  `{==}`    | Check equality                  | Binary |     4      |
|  `{!=}`    | Check inequality                | Binary |     4      |
|  `{<}`     | Check less-than                 | Binary |     4      |
|  `{<=}`    | Check less-than or equal        | Binary |     4      |
|  `{>}`     | Check greater-than              | Binary |     4      |
|  `{>=}`    | Check greater-than or equal     | Binary |     4      |
|  `{in}`    | Check if in collection          | Binary |     4      |
| `{not in}` | Check if not in collection      | Binary |     4      |
|  `{not}`   | Logical "not"                   | Unary  |     3      |
|  `{and}`   | Short-circuiting logical "and"  | Binary |     3      |
|  `{or}`    | Short-circuiting logical "or"   | Binary |     2      |
|  `{=}`     | Assignment                      | Binary |     1      |
|  `{+=}`    | Add-Assignment                  | Binary |     1      |
|  `{-=}`    | Subtraction-Assignment          | Binary |     1      |
|  `{*=}`    | Multiplication-Assignment       | Binary |     1      |
|  `{/=}`    | Division-Assignment             | Binary |     1      |

[semver]: https://semver.org/