Spanda

Chapter 6 — Oops: common mistakes

Back to index

Everyone hits these once. Here’s the fix.

---

“ActionProposal cannot be used where SafeAction is expected”

You did: wheels.execute(proposal);

Fix:

let action = safety.validate(proposal);
wheels.execute(action);

Example: examples/showcase/ai_safety_violation.sd (broken) vs rover_navigation.sd (fixed)

---

“Expected unit” / unit mismatch

You did: wheels.drive(linear: 0.5, ...) without m/s

Fix: Always attach units to physical quantities:

wheels.drive(linear: 0.5 m/s, angular: 0.1 rad/s);

Distances: m. Angles: rad. Time: ms, s.

---

spanda: command not found

Fix:

export PATH="$PWD/target/release:$PATH"
# or
./target/release/spanda check examples/hello_world.sd

Build first: npm run build:rust

---

check passes but run does nothing visible

Simulation often stops or drives slowly by design. Try:

spanda sim file.sd
spanda run file.sd --trace-scheduler

Or increase loop visibility in examples/basics/02_sensors_and_safety.sd.

---

verify fails — sensor not on hardware profile

You declared sensor camera: Camera but hardware only lists Lidar.

Fix: Add Camera to the hardware block’s sensors [ ... ] list, or remove the sensor from the robot.

spanda verify file.sd --target RoverV1 --json

Read the JSON report — it names the mismatch.

---

Forgot deploy line

verify needs to know which robot maps to which hardware:

deploy MyRobot to RoverV1;

---

Module / import not found

You did: import foo.bar; without a module foo.bar; file in the project.

Fix: Match module names to file paths, or start with single-file examples in examples/basics/.

---

Infinite loop in simulation

Symptom: run hangs or runs forever.

Fix: Behaviors with loop every run until the simulator hits maxLoopIterations. For tests, golden fixtures pass "run": { "maxLoopIterations": 5 }. This is normal for control loops.

---

“I copied Python syntax”

Python habit	Spanda habit
def foo():	behavior foo() { } or export fn foo() { }
True / False	true / false
None	None() for Option, or language-specific patterns
No units	Always m/s, rad, ms
import rospy	sensor / topic declarations in the robot block

---

Still stuck?

1. Run spanda check file.sd --json and read the first diagnostic
2. Find a working example in examples/basics/ for the same feature
3. Read the matching Spanda 101 lesson
4. See the full troubleshooting guide for fleet, ROS2, packages, CI, and ops issues
5. Open an issue on GitHub

---

Next: Glossary

This site is open source. Improve this page.