Modeling Agents with Probabilistic Programs

Source for agentmodels.org, an interactive online book on modeling rational and biased agents for (PO)MDPs and reinforcement learning using probabilistic programs. Code examples run directly in the browser via WebPPL.

By Owain Evans, Andreas Stuhlmüller, John Salvatier, and Daniel Filan.

Local development

With Docker (no Ruby setup needed):

docker compose up

Or with a local Ruby (3.x):

bundle install
bundle exec jekyll serve

Either way, the site is served at http://localhost:4000.

How the site works

Chapters live in chapters/*.md (Jekyll/kramdown Markdown, front matter sets title, description, and chapter order via filename). Pages with status: stub appear unlinked in the table of contents.
Code boxes: every ~~~~ fenced block is turned into an editable, runnable WebPPL editor in the browser (wpEditor.setup in assets/js/main.js).
Math is written as kramdown $$...$$ and rendered client-side with KaTeX (auto-render finds the $...$ / \[...\] delimiters kramdown emits).
Citations: markers like refp:key, reft:key, and cite:key in the text are resolved client-side against bibliography.bib.
Vendored assets: all third-party JS/CSS/fonts (jQuery, KaTeX, Pure, Merriweather, the WebPPL editor and viz bundles) are checked in under assets/vendor/ — the site has no runtime dependencies on external CDNs.

The WebPPL bundle (intentionally frozen)

assets/js/webppl.min.js is a 2019 build of WebPPL bundled with the packages the book uses (webppl-agents, webppl-dp, webppl-timeit, webppl-nn). WebPPL is no longer actively maintained, so the bundle is frozen on purpose: the goal is keeping the book's examples working, not tracking upstream.

If you ever need to regenerate it, the historical recipe is in scripts/update-webppl (uses the dependencies pinned in package.json); expect to need an old Node version.

Deployment

The site is published with GitHub Pages from the gh-pages branch — pushing to gh-pages deploys. The Gemfile pins the github-pages gem so local builds match production. CI (GitHub Actions) builds the site and checks internal links on every push.

Repo layout

chapters/        Book chapters (Markdown)
index.md         Landing page and table of contents
bibliography.bib Citations, rendered client-side
assets/css       Site stylesheet
assets/js        Site JS + frozen WebPPL bundle
assets/vendor    Vendored third-party assets
assets/img       Figures
assets/tex       LaTeX sources for some figures
_layouts, _includes  Jekyll templates
notes/, scratch/ Old planning notes (not published)
scripts/         Historical build scripts for the WebPPL bundle