Organize related declarations with domain — Connect the previous skills

PART I

Warm-up

Reconnect with a useful idea before starting organize related declarations with domain. 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

Connect domain boundaries to error ownership

A domain groups related declarations under a meaningful boundary. The shared domain vocabulary expresses organization. Group declarations because they share a coherent responsibility and contract, not because they happen to be called from the same screen. A namespace is not automatically a resource permission boundary, an ownership transfer or a runtime isolation guarantee.

Pricing receives a negative quantity, violating its contract. Screen receives a valid price but its display target is unavailable. These are different failures with different responsible layers.

Draw the declarations and their dependencies. Follow one call across a domain boundary and write the input and result contract on that edge. If two domains depend on each other, inspect whether a shared rule or an explicit orchestration layer would make the direction understandable. Worked case: The caller must correct or reject invalid pricing input before claiming a price. Display unavailability belongs to the host-facing screen layer and does not mean the valid calculation was numerically wrong. Distinct contracts support distinct user responses.

Compare the tempting alternative: Reporting every error as “Pricing failed” hides where the promise was broken and sends the learner toward the wrong repair.

Worked reasoning and supplied artifact

// Paper trace / supplied exercise-host contract; no execution claimed.
// Pricing receives a negative quantity, violating its contract. Screen receives a valid price but its display target is unavailable. These are different failures with different responsible layers.
// The caller must correct or reject invalid pricing input before claiming a price. Display unavailability belongs to the host-facing screen layer and does not mean the valid calculation was numerically wrong. Distinct contracts support distinct user responses.

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

Reconstruct the supplied worked case first: list its inputs, intermediate decisions and final artifact. Compare each row with the explanation and identify exactly where the rejected alternative fails. Then use the changed inputs in Part IV for independent work.

• 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 organize related declarations with domain.

Write input/result/error cards for Pricing and Screen, then trace invalid quantity and unavailable display independently.

What to produce

Two domain contracts and two failure attribution ledgers.

• 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.

• Connect domain boundaries to error ownership
• Write input/result/error cards for Pricing and Screen, then trace invalid quantity and unavailable display independently.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Name the precondition violation that belongs to Pricing.

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