pseudocode Extension For Quarto

This extension provides a filter to render pseudocode blocks in Typst output documents. It uses the lovelace Typst package to typeset algorithms with automatic indentation and bold keywords.

Installing

From a directory with an existing Quarto file or project, run:

quarto add christopherkenny/pseudocode

This will install the extension under the _extensions subdirectory. If you're using version control, you will want to check in this directory.

Using

Add the following to your document metadata after installing as above.

filters:
  - quarto
  - pseudocode

Placing quarto before pseudocode ensures Quarto's built-in processing (including cross-reference resolution) runs before this filter, which is required for @alg-* references to resolve correctly.

Then write pseudocode in a fenced code block with the pseudocode class:

```pseudocode
+ initialize parameters θ randomly
+ *while* not converged
  + *for* each data point $x_i$
    + compute posterior $Q(z_i) = P(z_i \mid x_i, \theta)$
  + *end*
+ *end*
+ return $\theta$
```

Each + item becomes one line of pseudocode. Nested lists create indented blocks. Bold keywords like *while*, *for*, *if*, *then*, *else*, and *end* are written with *...*. Inline math uses standard LaTeX notation with $...$. Line comments use //.

The filter only activates for format: typst output and does nothing for other formats.

Options

Options are passed as code block attributes. All options are optional.

Option	Type	Default	Description
title	string	—	Title shown in the algorithm header
line-numbering	string or none	—	Line number format, e.g. "1" or "a"
booktabs	true/false	false	Decorative top/bottom rules
stroke	Typst stroke	1pt + gray	Indentation guide style
hooks	Typst length	0pt	Indentation guide hook length
indentation	Typst length	1em	Width of each indentation level
line-gap	Typst length	.8em	Vertical space between lines
booktabs-stroke	Typst stroke	2pt + text.fill	Style for booktabs rules
title-inset	Typst length	0.8em	Padding around the title
line-number-supplement	string	"Line"	Label used in line references
line-number-alignment	Typst alignment	horizon + right	Position of line numbers

For example:

```{.pseudocode title="EM Algorithm" line-numbering="1" booktabs="true"}
+ initialize parameters θ randomly
+ *while* not converged
  + ...
+ *end*
```

Length and stroke values (e.g. stroke, indentation) are passed directly as raw Typst, so write them in Typst syntax: stroke="0.5pt + blue", indentation="1.5em".

Cross-references

To make an algorithm referenceable, add a #alg-* identifier and a cap attribute. The filter wraps the block in a Typst #figure(kind: "algorithm", ...), which gives it an "Algorithm N" counter. Add a crossref block to your document metadata and use filters: [quarto, pseudocode] so the filter runs after Quarto's crossref pass and can rewrite unresolved @alg-* references to native Typst #ref().

crossref:
  custom:
    - kind: float
      key: alg
      reference-prefix: Algorithm

```{.pseudocode #alg-sort title="Bubble Sort" cap="Bubble sort in-place."}
+ *for* $i = 1$ *to* $n - 1$
  + ...
+ *end*
```

Then reference it with standard Quarto syntax:

@alg-sort shows bubble sort.

Note: Quarto will emit a WARNING: Unable to resolve crossref @alg-* message during rendering. This is a false positive. The algorithm label lives inside a raw Typst block, Quarto's crossref pass cannot see it. The filter intercepts the resulting broken reference and rewrites it to a native Typst #ref() call, so the output is correct.

Example

Here is the source code for a minimal example: example.qmd.

Licensing

MIT License. See the license file for further details.