State changes with vary — Discover and trace

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.

Recall note

A rough note is enough. You can revise it after the example.

PART II

Instruction & guided example

Carry the current value into the next update

A sequence of state changes uses the most recent stored value each time. The second update does not restart from the declaration. Trace statement by statement and keep the old value visible until you have calculated the new one.

stock starts at 10. The delivery update += 4 reads 10 and stores 14. The correction += -2 then reads 14 and stores 12. Return reads 12. A four-column ledger can record statement, before, adjustment and after: delivery | 10 | +4 | 14; correction | 14 | -2 | 12.

If you calculate both updates from the initial 10, you might incorrectly record the correction as 8 and lose the delivery. Another mistake is counting the return as another update; it reads the value and sends it to the caller without adding anything.

Worked reasoning and supplied artifact

fnc stockAfterChanges() -> i32 {
    vary stock: i32 = 10;
    stock += 4;
    stock += -2;
    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 stockAfterChanges() -> 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 = 10;
Introduce a binding intended to change. Identify its initial value now so later updates can be traced rather than guessed.
stock += 4;
Read the current value, add the right-hand amount and store the new value. A before/after trace makes the state change visible.
stock += -2;
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

Reproduce the two transition rows, then trace an additional += 3 update after the correction.

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.

Prediction or guided notes

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.

Your drafts remain here. Continue whenever you are ready.

PART IV

Independent practice

Project context: Workshop stock counter. Build a small, understandable change around state changes with vary.

Model 18 supplies, a delivery of 7, then a signed correction of -4. Record every transition and show the exact value the return reads.

What to produce

A ledger 18 → 25 → 21, a helper and a sentence explaining the second update’s input value.

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.

Your .ws practice draft

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?

Original learning-path task and reference

In a rhythm-game audio editor, demonstrate state changes with vary. Read the source-grounded example and predict its observable behavior before making changes. 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.

What value does the second worked update read?14 from the first update10 from the declaration12 from the future return

Explain a normal or boundary case

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.

Carry the current value into the next update
A sequence of state changes uses the most recent stored value each time. The second update does not restart from the declaration. Trace statement by statement and keep the old value visible until you have calculated the new one.
Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Explain why the return is a read rather than another state transition.

Your recap

This marks your personal practice record only. It is not a certification or an official workspace assessment.