Jane Street Releases Bonsai, an OCaml UI Library for Reactive Web Applications

Introduction to Bonsai

Bonsai is a new UI library developed by Jane Street for creating performant and reactive web applications. It is written in OCaml and draws inspiration from the Elm programming language. Jane Street has utilized Bonsai internally for a range of its web applications, including corporate directories and tools for monitoring trading systems.

Core Architecture and Features

Bonsai components are implemented as purely functional state machines, which are designed for easy composability. A key feature is its incrementalization framework, which ensures that values are recomputed only when necessary, applying this principle beyond just the view layer to all values within the application.

Unlike other web frameworks that often combine state, incrementality, and rendering into a single UI component abstraction, Bonsai allows for the a la carte composition of state and incrementality primitives. This design enables the same mechanisms that prevent full page re-rendering during user interaction to also incrementalize complex business logic computations on live-updating datasets.

State Management and OCaml Integration

Bonsai provides an extensive API for managing the lifecycle and scoping of state, as state is not directly associated with explicit components. This simplifies embedding collections of stateful UI components within other components, as Bonsai handles state management automatically, removing the need to manually hoist internal component state to a top-level model.

The use of OCaml for Bonsai means developers can use a single language and type system across both the backend and frontend. This unified language approach is intended to improve legibility and maintainability for large web application codebases.