created: 20221009124003601
modified: 20221009163124867
tags: Concepts Reference
title: Functions
type: text/vnd.tiddlywiki

!! Introduction

<<.from-version "5.3.0">> A <<.def function>> is a named snippet of text containing a [[Filter Expression]]. Functions can have named parameters which are available within the function as variables.

Functions are usually defined with the [[Pragma: \function]]:

```
\function my-function(parameter:"2")
[<parameter>multiply[1.5]]
\end
```

Functions can be invoked in several ways:

* Directly transclude functions with the syntax `<<myfn param:"value">>`
* Assign functions to widget attributes with the syntax `<div class=<<myfn param:"value">>>`
* Invoke functions via the [[function Operator]] with the syntax `[function[myfn],[value],...]`
* Directly invoke functions whose names start with a period as custom filter operators with the syntax `[.myfn[value]]`

!! How Functions Work

Functions are implemented as a special kind of [[variable|Variables]]. The only thing that distinguishes them from ordinary variables is the way that the parameters are handled.