Probability trees n×p, growing left-to-right (the standard reading direction for probability trees). This module is built on CeTZ (@preview/cetz:0.5.2). The sources are available on GitHub.

Features

• Probability trees n×p, growing left-to-right.
• Local overrides for every node and probability (sn / sp).
• Global and local text styles (weight, italic, small caps, highlight, custom function…).
• Probability labels above, below or on top of the edge (above, below, on, hybrid), optionally sloped along the edge.
• In on mode, the edge is cut under the label, with transparency preserved.
• Improved error messages for malformed tree data.
• Exact node positions exposed for precise custom labels or annotations (extra callback).
• Quick list-based syntax (proba-tree-short) to write the tree with Typst lists instead of nested tuples.

Table of contents

• Installation
• Quick start
• Data structure
• Quick tree syntax (proba-tree-short)
• API
• Node positions (extra)
• Text styles
• Probability positions
• Default tree
• Error handling
• Dependencies
• License
• Authors

Installation

#import "@preview/probabilitree:0.1.3": proba-tree, sn, sp, proba-tree-short

If the package is installed locally:

#import "@local/probabilitree:0.1.3": proba-tree, sn, sp, proba-tree-short

Quick start

#proba-tree(data: (
  $Omega$,
  (sn($A$, style: (fill: green)), $p$, ($B$, $q$), ($overline(B)$, $1-q$)),
  ($overline(A)$, $1-p$, ($B$, $q$), ($overline(B)$, $1-q$)),
))

data structure

Each node is an array (label, proba, ..children):

• label: node content (e.g. $A$, [A], "A") or a local setting sn(...).
• proba: probability shown on the branch (e.g. $p$, $1-p$) or a local setting sp(...).
• ..children: zero or more child nodes, with the same structure.

The root has no probability: $Omega$ is just the label.

#proba-tree(data: (
  $Omega$,
  (sn($A$, style: (fill: green)), sp($p$, style: (fill: red, weight: "bold")), ($B$, $q$)),
  ($overline(A)$, $1-p$, ($B$, $q$)),
))

Quick tree syntax (proba-tree-short)

Writing nested tuples can get verbose. proba-tree-short lets you write the same tree with Typst lists — - for a node, + for the probability of the branch leading to it, alternating and nested:

#proba-tree-short[
  - $Omega$
    + $p$
    - $A$
      + $q$
      - $B$
      + $1-q$
      - $overline(B)$
    + $1-p$
    - $overline(A)$
      + $q$
      - $B$
      + $1-q$
      - $overline(B)$
]

All the proba-tree options (h, v, proba-position, node-style, extra, …) remain available — only the construction of data changes. Per-node fine styles (sn / sp) are not expressible in this syntax: use proba-tree directly if you need them.

proba-tree-short-data returns the data array alone, so you can reuse it in proba-tree:

#let data = proba-tree-short-data[
  - $Omega$
    + $p$
    - $A$
]
#proba-tree(data: data)

API

proba-tree(...)

proba-tree-short(..options, markup) — quick list-based syntax

Writes a tree with Typst lists instead of nested tuples (- for a node, + for the probability of the branch leading to it, alternating and nested). All the proba-tree options are forwarded; only data is built from the markup.

#proba-tree-short[
  - $Omega$
    + $p$
    - $A$
]

sp(content, ...) — local probability settings

Returns a dictionary usable as a probability in data. Any omitted parameter falls back to the global settings.

#proba-tree(data: (
  $Omega$,
  ($A$, sp($p$, style: (fill: red, weight: "bold")), ($B$, $q$)),
  ($overline(A)$, $1-p$),
))

sn(content, ...) — local node settings

#proba-tree(data: (
  $Omega$,
  (sn($A$, style: (fill: green, weight: "bold")), $p$, ($B$, $q$)),
  ($overline(A)$, $1-p$),
))

Node positions (extra)

proba-tree exposes the exact canvas position of every node, so you can overlay labels, annotations or lines that align perfectly with the tree — without importing CeTZ yourself.

#proba-tree(
  data: (
    $Omega$,
    ($F$, $$, ($F$, $$, ($F$, $$), ($P$, $$)), ($P$, $$, ($F$, $$), ($P$, $$))),
    ($P$, $$, ($F$, $$, ($F$, $$), ($P$, $$)), ($P$, $$, ($F$, $$), ($P$, $$))),
  ),
  extra: (pos, draw) => {
    let issues = ("FFF", "FFP", "FPF", "FPP", "PFF", "PFP", "PPF", "PPP")
    for i in range(0, 8) {
      let p = pos.at("N4" + str(i + 1))
      draw.content((p.at(0) + 0.35, p.at(1)), anchor: "west", [$space arrow.long.r space #issues.at(i)$])
    }
  },
)

The callback receives two arguments:

• pos: a dictionary keyed N<level><index> (1-indexed) → (x, y) in canvas units. N11 is the root, N41 the 1st leaf of a 4-level tree, etc. Indices follow the visual top-to-bottom order, whatever the value of first-child-top.
• draw: the CeTZ draw namespace, usable directly (draw.content, draw.line, …).

Text styles

Styles apply globally (proba-style / node-style) or locally (sp(style:) / sn(style:)). Local keys override global ones; the others are preserved.

Accepted keys:

• All #text parameters: size, fill, weight, style (italic), background, font, features, …
• smallcaps (bool): small caps (via the OpenType smcp feature).
• highlight (color): highlighting (background box) — works with text and equations.
• function (content -> content): custom function applied last.

#proba-tree(
  proba-style: (fill: blue),
  node-style: (size: 11pt, fill: blue),
  data: (
    $Omega$,
    ($A$, $p$, ($B$, sp($q$, style: (highlight: yellow)))),
    ($overline(A)$, $1-p$),
  ),
)

Probability positions

Constants: above, below, on, hybrid.

• above / below: above / below the edge.
• on: the probability sits on the edge, which is cut under the label (no colored background, transparency preserved). The gap between the cut line and the probability is set with proba-padding.
• hybrid (default): above if the branch goes up, below if it goes down.

#proba-tree(proba-position: "on", proba-padding: 5pt)

Default tree

If data is omitted, the following tree is drawn: root Ω, with A/Ā (probabilities p/1-p), each leading to B/B̄ (q/1-q).

Error handling

If a non-root node is missing a probability (i.e., the tuple is malformed), the package now provides a clear error message:

proba-tree: non-root node without probability — expected format is (label, proba, ..children). Received: ...

This replaces the generic Typst index error, making debugging easier.

Dependencies

• CeTZ @preview/cetz:0.5.2

License

Distributed under the MIT License.

Copyright (c) 2026 Mikaël MAUNIER and DeepSeek

Authors

• Mikaël MAUNIER
• DeepSeek
• Claude