Forester Syntax Overview

The syntax of the .tree language is declarative, strongly typed, and modular. A Forester script consists of six primary elements:

1. Imports: Module references to include external .tree files or built-in stdlib actions.
2. Root Declarations: The entry point of the behavior tree (root main ...).
3. Tree Definitions: Named sub-trees (sequence, fallback, parallel) with typed parameters.
4. Action Implementations (impl): Contract definitions for native or remote actions executed by the runtime.
5. Invocations & Decorators: Calls to sub-trees and actions, wrapped with built-in decorators (e.g. retry, inverter, timeout).
6. Higher-Order Tree Delegates (..): Invoking sub-trees passed as parameters.

Comprehensive Syntax Example

// 1. Imports
import "std::actions"
import "sensors/battery.tree" {
    check_battery => is_battery_ok,
}

// 2. Root Entry Point
root main sequence {
    // Check battery or charge
    fallback {
        is_battery_ok()
        charge_robot()
    }
    
    // Execute target action with retry decorator
    retry(3) execute_task(
        target = {"x": 10, "y": 20},
        sub_action = place_item([100])
    )
}

// 3. Higher-Order Tree Definition
sequence execute_task(target: object, sub_action: tree) {
    fallback {
        is_target_reachable(target)
        approach_target(target)
    }
    sequence {
        savepoint()
        sub_action(..) // Delegate invocation of passed sub_action
    }
}

// 4. Sub-tree Definition
sequence place_item(location: array) {
    validate_location(location)
    info_wrapper(drop_payload({"speed": "slow"}))
}

// 5. Decorator Wrapper Pattern
sequence info_wrapper(action: tree) {
    log("Starting action execution")
    action(..)
    log("Action execution completed")
}

// 6. Action Signatures (linking to runtime implementation)
impl charge_robot();
impl approach_target(pos: object);
impl validate_location(coords: array);
impl drop_payload(config: object);
impl log(message: string);

Core Constructs Quick Reference