Embedded code

Typst formulas can contain code, and Typlet evaluates it as Typst does: # expressions, the arguments of math calls, content blocks, and statements. The supported features list every function.

Values and calls

Literals, operators, arrays and dictionaries, colors and alignments, and calls to the math functions and to h, rgb and luma:

mat(delim: "[", augment: #1, 1, 2; 3, 4) quad x #h(-1em/6) y

$$\left[\begin{array}{cc}1& 2\\ 3& 4\end{array}\right]𝑥𝑦$$1324𝑥𝑦

Styled content

Content blocks with markup, and the functions text, strong, emph, highlight, hide, box and link:

#text(fill: blue)[blue] + #box(stroke: 0.5pt, inset: 2pt, $x^2$) + #highlight[$y$]

$$\text{blue}+$$${𝑥}^2$+$𝑦$ #text(fill: blue)[blue] + #box(stroke: 0.5pt, inset: 2pt, $x^2$) + #highlight[$y$] blue+𝑥+𝑦

Definitions and set rules

let bindings, functions with named parameters and defaults, if, code blocks, and set rules. In a formula, a set rule goes in a content or code block, and styles the rest of the block:

#{ let sq(x) = $#x^2$; set math.mat(delim: "["); $mat(sq(a), sq(b))$ }

$$\left[\begin{array}{cc}{𝑎}^2& {𝑏}^2\end{array}\right]$$𝑎𝑏

Show-set rules for equations work too, most usefully in a preamble: #show math.equation: set text(fill: blue) styles every formula, and #show math.equation.where(block: true): set text(size: 1.2em) only display formulas. Their styles apply inside each equation, over the set rules around it, as in Typst. Other show rules are refused.

Preambles

The preamble option holds code that comes before every formula, like the start of a document: definitions and set rules that formulas share. It replaces KaTeX's macros. Typlet evaluates a preamble once for each set of options.

const options = { preamble: '#let RR = $bb(R)$\n#let norm(x) = $lr(|| #x ||)$' };
renderToString('f: RR^n -> RR, quad norm(v) <= 1', options);

Numbered equations

A preamble's set rule numbers display equations. They take their numbers from the equationCounter option, an object whose value each numbered equation increments, so a page numbers its equations in order. Auto-render and the Markdown plugins keep one counter per page or document.

const options = { displayMode: true, preamble: '#set math.equation(numbering: "(1)")', equationCounter: { value: 0 } };
renderToString('a^2 + b^2 = c^2', options); // numbered (1)
renderToString('e^(i pi) + 1 = 0', options); // numbered (2)

Numbering patterns such as "(1)", "1.a" and "i" work, and so do numbering functions such as n => [Eq. #n].

Links

#link draws a link only where the trust option allows it: true, or a function of the URL and its protocol. Without trust, the link's text shows without the link, and a warning names the URL.

renderToString('#link("https://typst.app")[Typst]', { trust: ({ protocol }) => protocol === 'https' });

What Typlet refuses

Code that needs Typst's document engine raises a TypletError of kind unsupported: show rules other than show math.equation: set …, loops, introspection such as context and counter, imports and file access, and document elements such as headings. The fallback option can render those formulas another way, for example with Typst compiled to WebAssembly, loaded only when a formula needs it:

render(source, element, { fallback: (source, error) => renderWithTypst(source) });

render shows the formula's source until a promise from the fallback resolves.

Budgets

Formulas can compute, so every formula runs under budgets: function calls, collection sizes, string lengths, content elements, sizes and output length. Abuse stops quickly with a TypletError of kind limit. See security for the defaults and the options that change them.