PART I
Warm-up
Reconnect with a useful idea before starting state changes with vary. In one or two sentences, describe the input, output or host boundary from the previous exercise that this lesson builds on. If you are arriving directly, skim the worked example first; there is no locked prerequisite.
A rough note is enough. You can revise it after the example.
PART II
Instruction & guided example
Review an update sequence with invariants
An invariant is a statement intended to remain true at chosen points in a calculation. For a simple stock ledger, one arithmetic invariant is final = initial + sum of adjustments. A stricter feature policy may also require nonnegative stock after each transition. State which one you are reviewing.
For initial 10, delivery 6 and correction -3, the sequence is 10 → 16 → 13. The arithmetic cross-check gives 10 + 6 - 3 = 13. Every intermediate value is nonnegative in this case. If the correction were -20, the arithmetic still has a prediction, -4, while the nonnegative policy would be violated.
The cross-check should be derived independently from the source sequence, not copied from its final value. A duplicated delivery would end at 19 and fail the intended adjustment sum even though all states remain nonnegative. Different checks catch different defects.
Worked reasoning and supplied artifact
fnc countedStock(initial: i32, delivery: i32, correction: i32) -> i32 {
vary stock: i32 = initial;
stock += delivery;
stock += correction;
return stock;
}Illustrative example from the proposed WillowScript design. The language and WUIX/WMATH/WDB/WAUDIO/WTMP services are not implemented in the supplied source. This site has no interpreter, VM or native host and does not execute or certify the snippet.
Walk through the example, one line at a time
fnc countedStock(initial: i32, delivery: i32, correction: i32) -> i32 {Read the function name, its parameter names/types and the result type after ->. This is the contract the body must satisfy.
vary stock: i32 = initial;Introduce a binding intended to change. Identify its initial value now so later updates can be traced rather than guessed.
stock += delivery;Read the current value, add the right-hand amount and store the new value. A before/after trace makes the state change visible.
stock += correction;Read the current value, add the right-hand amount and store the new value. A before/after trace makes the state change visible.
return stock;Evaluate the following expression using the current values, then send its result to the caller. Explain the value; do not confuse it with printed output.
}Close the nested block or value begun earlier. Match it to its opening boundary to keep the structure readable.
Try the guided change
Build the worked ledger and the independent adjustment-sum check. Then simulate a duplicated delivery and identify which invariant reveals it.
- Write the supplied inputs and initial state before following the example.
- Reconstruct each intermediate calculation or host decision, then compare with the worked artifact.
- Explain why the contrasting alternative fails before attempting the changed inputs in Part IV.
PART III
Take a breather
Step back after the guided example. Look away from the screen, stretch, or reread your prediction. This is an optional learning pause, not a timer or an assessment gate.
When you return, try to name the lesson’s key idea without copying its wording. If that feels difficult, return to Part II and trace one line rather than restarting the entire lesson.
PART IV
Independent practice
Project context: Workshop stock counter. Build a small, understandable change around state changes with vary.
Review starting stock 25 with deliveries 4 and 7 and a correction -6. Supply a complete ledger, an independent final-sum prediction and one deliberately duplicated-update countertrace.
What to produce
Ledger 25 → 29 → 36 → 30, arithmetic cross-check 30, and a duplicate-event result distinguished from the intended rule.
- State the intended behavior in a sentence before editing.
- Use only source-backed syntax and the host services whose contract you have been given.
- Record a normal case and a boundary or unavailable-resource case.
- Label hand predictions separately from anything actually measured in a supplied toolchain.
Syntax colors are a reading aid, not a compiler. The line you are editing stays uncolored until you move to a different line; capitalization is never changed. Drafts stay on this browser and code is not executed.
Need a hint?
For initial 10, delivery 6 and correction -3, the sequence is 10 → 16 → 13. The arithmetic cross-check gives 10 + 6 - 3 = 13. Every intermediate value is nonnegative in this case. If the correction were -20, the arithmetic still has a prediction, -4, while the nonnegative policy would be violated.
The cross-check should be derived independently from the source sequence, not copied from its final value. A duplicated delivery would end at 19 and fail the intended adjustment sum even though all states remain nonnegative. Different checks catch different defects.
Original learning-path task and reference
In a small-shop operations tool, demonstrate state changes with vary. Submit source, acceptance cases, and an explanation proving the section objective. Include .ws source and a host-resource contract; compare at least one normal case and one edge case.
fnc total() -> i32 {
vary count: i32 = 1;
const bonus: i32 = 2;
count += bonus;
return count;
}Where the original task needs a host API that is not supplied here, write the contract and predictions. Do not invent a runtime result.
PART V
Self-check
Use this check to notice what to revisit. It does not award a private course grade, block another page or claim to verify compiled code. Every answer has a learning explanation.
You may keep exploring even if you are unsure. Use the hint, compare the trace, and revise your explanation.
PART VI
Recap & small task
Bring the idea back to the mod feature you are building. A useful recap connects the mechanism to a decision you can make in your own code.
- Review an update sequence with invariants
- An invariant is a statement intended to remain true at chosen points in a calculation. For a simple stock ledger, one arithmetic invariant is final = initial + sum of adjustments. A stricter feature policy may also require nonnegative stock after each transition. State which one you are reviewing.
- Separate source-backed behavior, host requirements and untested predictions.
One small recap task
Choose one arithmetic invariant and one feature-policy invariant for your own stock counter.
This marks your personal practice record only. It is not a certification or an official workspace assessment.