function
A mapping from argument values to a return value.
You can call a function by writing a comma-separated list of function
arguments enclosed in parentheses directly after the function name.
Additionally, you can pass any number of trailing content blocks arguments to a
function after the normal argument list. If the normal argument list would
become empty, it can be omitted. Typst supports positional and named arguments.
The former are identified by position and type, while the later are written as
name: value
.
Within math mode, function calls have special behaviour. See the math documentation for more details.
Example
// Call a function.
#list([A], [B])
// Named arguments and trailing
// content blocks.
#enum(start: 2)[A][B]
// Version without parentheses.
#list[A][B]

Functions are a fundamental building block of Typst. Typst provides functions for a variety of typesetting tasks. Moreover, the markup you write is backed by functions and all styling happens through functions. This reference lists all available functions and how you can use them. Please also refer to the documentation about set and show rules to learn about additional ways you can work with functions in Typst.
Defining functions
You can define your own function with a let binding that has a parameter list after the binding's name. The parameter list can contain positional parameters, named parameters with default values and argument sinks. The right-hand side of the binding can be a block or any other expression. It defines the function's return value and can depend on the parameters.
#let alert(body, fill: red) = {
set text(white)
set align(center)
rect(
fill: fill,
inset: 8pt,
radius: 4pt,
[*Warning:\ #body*],
)
}
#alert[
Danger is imminent!
]
#alert(fill: blue)[
KEEP OFF TRACKS
]

Unnamed functions
You can also created an unnamed function without creating a binding by
specifying a parameter list followed by =>
and the function body. If your
function has just one parameter, the parentheses around the parameter list are
optional. Unnamed functions are mainly useful for show rules, but also for
settable properties that take functions like the page function's
footer
property.
#show "once?": it => [#it #it]
once?

Notable fact
In Typst, all functions are pure. This means that for the same arguments, they always return the same result. They cannot "remember" things to produce another value when they are called a second time.
MethodsMethods are functions that are available on values of a type. They can be called for a value using the .
operator.
.
operator.with
method
Returns a new function that has the given arguments pre-applied.
arguments
anyVariadicVariadic parameters can be specified multiple times.
The named and positional arguments to apply.
where
method
Returns a selector that filters for elements belonging to this function whose fields have the values of the given arguments.
fields
anyVariadicVariadic parameters can be specified multiple times.
The field values to filter by.