Forester Tree Language (.tree)

The Forester Tree Language is a strongly-typed, functional domain-specific language (DSL) designed to describe behavior tree architecture cleanly without verbosity or repetition.

Unlike traditional XML-based or JSON-based behavior tree formats, Forester treats behavior trees as first-class, composable abstractions.

Why a Dedicated DSL?

Standard behavior tree formats (such as XML trees used in ROS) often suffer from extreme duplication and verbosity. Forester’s DSL solves this by introducing functional primitives:

• Higher-Order Trees (HOT): Pass trees as parameters to other trees to create reusable patterns (e.g., generic retry loops, fallback wrappers, logging decorators).
• Strong Type System: Built-in support for strings, numbers, booleans, arrays, objects, and subtrees, validated at compile time.
• Blackboard Pointers: Pass live references to Blackboard memory into actions, allowing nodes to operate on dynamically updated state (essential for AI agent context).
• Lambdas: Write inline, anonymous subtrees without declaring throwaway named definitions.

Project Structure & File Conventions

Forester projects consist of one or more .tree files organized within a root project directory:

my_project/
├── main.tree           # Entry point containing the root tree
├── agent_tools.tree    # Custom actions and tool definitions
├── navigation/
│   ├── move.tree       # Sub-tree definitions
│   └── recovery.tree   # Recovery patterns

Key Conventions

1. File Extension: All Forester source files use the .tree extension.
2. Root Entry Point: A project must define at least one root node (e.g., root main sequence { ... }).
3. Module Imports: Imports resolve relative to the root directory (e.g., import "navigation::move").

Language Roadmap & Tooling

To ensure a seamless developer experience, Forester provides language tooling across popular editors:

• Syntax Highlighting & Linting: Editor support for .tree files.
• Language Server Protocol (LSP): Autocompletion, inline type errors, and navigation support for VS Code, Neovim, and IntelliJ.