Bonsai: Janestreet's UI Library
Bonsai is an OCaml UI library used by Jane Street for building reactive web applications. It separates state, incrementality, and rendering, allowing composable functional components and efficient incremental updates. The framework also provides a templating system and automated testing capabilities.
- ▪Bonsai components are implemented as purely functional state machines with incremental rendering.
- ▪The library enables composition of state and incrementality primitives without tying them to specific UI components.
- ▪Using OCaml for both backend and frontend allows shared types and reduces errors across Jane Street’s internal tools.
- ▪Bonsai includes a templating language, component-specific stylesheets, and supports realistic automated tests that manipulate the DOM programmatically.
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Story provenance
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Record
| Original publisher | GitHub |
| Canonical URL | https://github.com/janestreet/bonsai |
| Publication time | Mon, 03 Aug 2026 08:29:57 +0000 |
| Retrieval time | 2026-08-03T08:55:46.622Z |
| Last seen | 2026-08-03T08:55:46.622Z |
| Headline source | Publisher (no WeSearch rewrite) |
| Excerpt source | publisher body |
| Excerpt method | First ~120 words (~800 chars) of extracted publisher body, fair-use limited. |
| Summary | WeSearch · cerebras-chat (WeSearch summarizer) |
| Summary source text | contentText |
| Citation coverage | Summary is a WeSearch-generated derivative; primary citation is the original publisher URL. |
| Cluster | da8LwKWEd-SD · 1 stories |
| Cluster logic | Grouped by semantic title/content similarity across sources within a rolling window. Same-publisher template collisions are excluded from coverage comparison. |
| Ranking reason | Story pages are not engagement-ranked. Hub feeds use recency, with optional source-diversified chronological ordering (cap consecutive stories per source). No personalized ranking. |
| Publisher visit | Yes — open original |
| Substitutes article? | No — link-out required for full text |
Rights status (four layers)
WeSearch handling by dimension
| Indexing | May the item be indexed (stored, ranked, made findable)? | Allowed |
| Snippet | May a short excerpt of the publisher's text be shown? | Allowed |
| AI summary | May WeSearch generate its own short summary of the article? | Limited |
| Retrieval / RAG | May the content be exposed for third-party retrieval-augmented generation? | Not asserted |
| Model training | May the content be used to train AI models? | Not asserted |
| Commercial reuse | May the content be reused commercially? | Not permitted |
Basis: Derived from the published RSS/Atom feed. Contact: [email protected]. Reviewed: 2026-07-24.
Opening excerpt (first ~120 words) tap to expand
Bonsai Bonsai Bonsai is a UI library for building performant, reactive web applications in OCaml, partly inspired by Elm. It is used to build almost all web applications inside Jane Street, everything from the corporate directory to tools that monitor and interact with our trading systems. A simple Bonsai component with a little interactivity looks like this: module Dice = struct let faces = [ "⚀"; "⚁"; "⚂"; "⚃"; "⚄"; "⚅" ] ;; let component (graph @ local) = (* Components are implemented as purely functional state machines. *) let face, set_face = Bonsai.state (List.hd_exn faces) graph in (* Components are incrementally rendered, only when the relevant parts of the state change.
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Excerpt limited to ~120 words for fair-use compliance. The full article is at GitHub.