Functions as reusable contracts — Flash-check repair

PART I

Warm-up

Reconnect with a useful idea before starting functions as reusable contracts. 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

Repair a formula while preserving the helper promise

The shared fnc/parameter/return grammar can make a Willow learner feel immediately at home, but familiar arithmetic does not establish that a proposed .ws program has a runtime. Treat each helper as a typed input/result contract and keep the caller’s units and role assumptions explicit. This bridge separates portable reasoning from unverified execution.

A fee helper promises price+fee but its body returns price-fee. With (160,20), the intended result is 180 and the broken paper result is 140. Sample repair card names one operator change, retains both typed parameters and retraces a nonzero-fee case. The zero-fee case agrees under both bodies and cannot establish the repair alone.

Changing the example price to 200 so the subtraction happens to reach 180 conceals the defect. Hardcoding return 180 discards the reusable contract. Repair the responsible operation rather than tuning inputs to a preferred result.

Worked reasoning and supplied artifact

// Worked contract artifact:
// A fee helper promises price+fee but its body returns price-fee. With (160,20), the intended result is 180 and the broken paper result is 140. Sample repair card names one operator change, retains both typed parameters and retraces a nonzero-fee case. The zero-fee case agrees under both bodies and cannot establish the repair alone.

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.

Try the guided change

Build expected/broken/repaired columns for (160,20) and (160,0).

• 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: Shared pricing rules. Build a small, understandable change around functions as reusable contracts.

Repair a points helper that should add a fixed bonus but subtracts it. Use starting 45, bonus 8 and a zero-bonus case; explain why the latter is a regression case but a weak diagnosis case.

What to produce

A one-operator repair, predictions 53 versus broken 37, and the masking zero-bonus explanation.

• 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.

fnc add(a: i32, b: i32) -> i32 {
    return a + b;
}
fnc main() -> i32 {
    return add(2, 3);
}

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.

• Repair a formula while preserving the helper promise
• Build expected/broken/repaired columns for (160,20) and (160,0).
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Build expected/broken/repaired columns for (160,20) and (160,0).

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