Forest

Forest (forestdb.org) is a community repository for generative models written in probabilistic programming languages, mainly Church and WebPPL. Most code boxes are editable and run directly in the browser. Forest is maintained as a teaching resource and archive; it has long served as the home for class projects from courses such as Probabilistic Languages Understanding.

Adding models

To add a new model, create a markdown file in the models directory. You can do this directly on GitHub: add model.

For an example of the file format, see example.md. A minimal model file looks like this:

---
layout: model
title: My Model
model-language: webppl
model-status: code
model-category: Probabilistic Language Understanding
model-tags: concepts, program induction
---

Prose describing the model.

~~~~
flip(0.5)
~~~~

Frontmatter fields:

• model-language (required to make code boxes runnable): webppl or church.
• model-language-version (optional, webppl only): pins a webppl version. Available: pre-v0.7, v0.9.6, v0.9.7, v0.9.9, v0.9.13, v0.9.15 (default).
• model-status (optional): code (code runs), static (code shown as a non-runnable listing; add a model-status-verbose explanation), link (page links to external code), or hidden (not listed on the front page).
• model-category (optional but encouraged): one of Concept Learning, Reasoning about Reasoning, Probabilistic Language Understanding, Counterfactuals and Explanations, Machine Learning, Nonparametric Models, Bayesian Data Analysis, Undirected Constraints, Inverse Dynamics, PPAML Challenge Problems, Miscellaneous. Models without a category are listed under "Uncategorized" on the front page.
• model-tags (optional): arbitrary comma-separated words or phrases.

To display a code box without making it runnable (e.g. to show a model fragment), mark the fence with norun:

~~~~ norun
// this box renders as static code
~~~~

Machine-readable index

forestdb.org/models.json lists every model with title, URL, markdown source URL, language, version, status, category, and tags.

Local development

The site is plain Jekyll, built by GitHub Pages from the gh-pages branch. To preview locally:

docker run --rm -v "$PWD":/site -p 4000:4000 -w /site jekyll/jekyll \
  jekyll serve --host 0.0.0.0

then open localhost:4000.

All JavaScript and CSS (jQuery, Bootstrap, the webppl runtimes, webchurch) is vendored under assets/, so the site has no runtime dependencies on external CDNs. To support a new webppl version, build or download the browser bundle, add it as assets/webppl/webppl-<version>.js, and add the version to the list in this README and to scripts/test-models/package.json.

Continuous checks

Two scheduled GitHub Actions keep the site healthy (see .github/workflows/):

• Test models runs every webppl model headless against its declared webppl version (scripts/test-models/runner.js) and files a report issue. Run locally with cd scripts/test-models && npm install --install-strategy=nested && node runner.js (nested install needed for webppl 0.6.1's hardcoded module paths).
• Check links runs lychee over all model pages and files a report issue when links break.

License

Site code is MIT-licensed; models belong to their authors, with new contributions accepted under CC-BY 4.0 (prose) and MIT (code). See LICENSE.md.