Spanda

Lesson 5 — Modules and traits

Goal: Split code across files and define agent interfaces with traits.

Examples:

Modules

module navigation.path_planning;

export fn plan_path(from: Pose, to: Pose) -> Path {
  return trajectory(from: from, to: to, steps: 8);
}

Keyword	Purpose
`module name;`	Identifies this compilation unit
`export fn`	Visible to importers
`private fn`	Internal to the module
`import other.module;`	Pull exported symbols into scope

Cross-file example:

spanda check examples/modules/navigation.sd

Traits and implementations

Traits define interfaces agents can implement:

trait PathPlanner {
  fn plan(goal: NavGoal) -> Path;
}

agent Navigator {
  tools [wheels];
  goal "Plan safe paths";
  plan { wheels.stop(); }
}

impl PathPlanner for Navigator {
  fn plan(goal: NavGoal) -> Path {
    wheels.stop();
  }
}

Call the trait method from a behavior:

let route = Navigator.plan(goal);

This separates what planning means (trait) from who does it (agent).

Agents vs behaviors

Construct	Role
`behavior`	Direct robot logic, often the main loop
`agent`	AI-facing entity with goals, tools, and optional trait impls
`ai_model`	LLM, vision, or other model (Lesson 6)

Try it

spanda check examples/basics/05_traits_and_impl.sd
spanda run examples/basics/05_traits_and_impl.sd
spanda check examples/modules/path_planning.sd
spanda check examples/modules/navigation.sd

Exercise

Create examples/modules/my_planner.sd with module my.planner and an exported plan_path function
Import it from a robot file and call plan_path inside a behavior
Add a trait Planner and impl Planner for an agent that wraps the call

Next: Lesson 6 — AI and the safety gate

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