Sontag language specification

Introduction

This is an informal specification for version 0.1 of the Sontag language, last updated Jul 8, 2024. Sontag is a template language for JavaScript static site generators that borrows concepts from Twig, Liquid, Jinja, and Nunjucks.

Basic concepts

Expressions are enclosed by {{ … }}. The result of an expression gets interpolated into the surrounding text.

Tags enclosed by {% … %} provide structure and composition to templates. Some are single tags expressed as {% mytag %}, others are paired, such as {% mytag %} some content {% endmytag %}. Some tags support both styles.

Endtags can contain arbitrary text after the tag name.

The language comes with some built-in tags.

Comments marked with {# … #} are used for documentation and won’t be included in the output.

Built-in tags

set

Assign the result of an expression to an identifier.

Can be used as a single tag:

{% set <identifier> = <expression> %}

Or as a paired tag, in which case the tag’s content gets assigned to the identifier:

{% set <identifier> %}
Content 
{% endset %}

if

for

extend

block

include

raw

Process the tag’s content literally, as if it were plain text:

{% raw %}
<p>The syntax for expressions is <code>{{ expression }}</code></p>.
{% endraw %}

Aliased to verbatim for compatibility with Twig.

Built-in filters

Note: Lots of filters can be readily expressed in JavaScript, but we may want to add some for compatibility with other languages.