Spanda

Typed handler I/O

Return type annotations on behaviors, tasks, triggers, events, and agent plans — validated at compile time in Rust and the TypeScript mirror (Phases 28–34).

Example: examples/features/typed_handler_returns.sd

---

Syntax

Behavior

behavior status() -> Bool {
    return true;
}

Task

task Monitor every 50ms -> Bool {
    return battery_ok;
}

Triggers

every 100ms -> Bool {
    return true;
}

when lidar.nearest_distance > 1.0 m -> Bool {
    return true;
}

while operating -> Bool {
    return true;
}

Event handlers

event Alert;

on Alert -> Bool {
    return true;
}

Mismatching return types are compile errors:

behavior bad() -> Bool {
    return 1;  // error: expected Bool, found Number
}

---

Agent plan returns

When an agent is granted propose_motion or execute, the plan block must return SafeAction (not raw ActionProposal):

agent Navigator {
    uses planner;
    can [ propose_motion ];

    plan {
        let proposal = planner.reason(prompt: "...", input: scan);
        let action = safety.validate(proposal);
        return action;  // SafeAction required
    }
}

See agentic-programming.md for capability enforcement.

---

Agent can[] default deny

An empty can [] denies high-risk actions at runtime (Phase 32):

agent Restricted {
    can [];
    plan { /* propose_motion denied at runtime */ }
}

Example: examples/features/agent_can_deny.sd

---

Debugger

Typed handlers participate in DAP stepping. Debug sessions enter from behavior, task every, or top-level every trigger bodies.

Example: examples/integration/debugger_every.sd · debugging.md

---

Related

• health-checks.md — health-specific triggers (on health … becomes)
• triggers.md — trigger execution model
• verification-diagnostics.md — compile-time verification output

This site is open source. Improve this page.