Mutable and stable bindings — Build the smallest useful slice

PART I

Warm-up

Reconnect with a useful idea before starting mutable and stable bindings. 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

Build a one-update counter

Start a stateful feature with one known starting value and one explicit transition. For an attendance counter, the input is the current count and the change is one arrival. A small helper can demonstrate the transition without pretending to subscribe to real events.

The example copies starting into a local mutable count, adds one, then returns the new value. For starting 6, the rows are count = 6, count = 7, return 7. The parameter starting retains its role as the supplied input; the trace distinguishes it from the working local binding.

The helper does not continue counting after it returns, and no persistent attendance store is shown. Calling it once with 6 predicts 7; a second independent call with 6 also predicts 7. Persistent behavior needs an explicit owner or host storage contract.

Worked reasoning and supplied artifact

fnc afterArrival(starting: i32) -> i32 {
    vary count: i32 = starting;
    count += 1;
    return count;
}

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 afterArrival(starting: i32) -> i32 {
Read the function name, its parameter names/types and the result type after ->. This is the contract the body must satisfy.
vary count: i32 = starting;
Introduce a binding intended to change. Identify its initial value now so later updates can be traced rather than guessed.
count += 1;
Read the current value, add the right-hand amount and store the new value. A before/after trace makes the state change visible.
return count;
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

Trace afterArrival(6) and afterArrival(0), labelling the parameter and local count separately.

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 mutable and stable bindings.

Build a local counter for one newly placed checkpoint, starting from 9. Show the declaration and one update. Explain what would have to supply the result as a later call’s input to count a second checkpoint.

What to produce

A one-update helper, predicted result 10, and a second-call description using input 10 to obtain 11.

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 puzzle-level authoring tool, demonstrate mutable and stable bindings. Create the smallest .ws integration that demonstrates the section contract. 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 does a second independent afterArrival(6) call predict?7 again8 because the previous local count persists automaticallyAn app-ready event

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.

Build a one-update counter
Start a stateful feature with one known starting value and one explicit transition. For an attendance counter, the input is the current count and the change is one arrival. A small helper can demonstrate the transition without pretending to subscribe to real events.
Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Name who must carry the first returned count into a later call.

Your recap

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