Propose a host-neutral application contract — Boundary detective

PART I

Warm-up

Reconnect with a useful idea before starting propose a host-neutral application contract. 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

Specify invalid input without a sentinel collision

The planner accepts zero quantity as a valid empty request producing subtotal0. A proposed design also returns0 for negative quantity.

The same scalar now conflates success and rejection. Preserve typed failure or a separately documented status/data contract so callers can distinguish the cases. The exact error representation belongs to the language/host boundary; do not invent a result object syntax and call it implemented. State the information requirement before selecting representation.

This is a supplied exercise-host design contract. WillowScript and these cross-library integrations remain proposed and unimplemented here. The trace is a hand prediction or supplied observation for analysis, never a claimed script run. No cancellation method, WDB transaction API, permission manifest or native lifetime mechanism is invented.

Worked reasoning and supplied artifact

// Design artifact; not executable WillowScript.
// The planner accepts zero quantity as a valid empty request producing subtotal0. A proposed design also returns0 for negative quantity.
// 1. Quantity0 -> normal subtotal0.
// 2. Quantity-1 -> documented rejection category.
// 3. Quantity3 -> normal36; caller can distinguish all outcomes.

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: Independent WillowScript application. Build a small, understandable change around propose a host-neutral application contract.

Create outcome cards forquantity0,-1 and3 atprice12; identify normal payload versus failure category.

What to produce

Create outcome cards forquantity0,-1 and3 atprice12; identify normal payload versus failure category.

• 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.

import wuix.widget;
import app;
domain Workspace {
    const application = Application({
        name: "Workspace",
        window: { title: "Dashboard", size: [1280, 800] },
        events: {
            "app.ready": fnc() -> void { console.log("Ready"); }
        }
    });
}

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.

• Specify invalid input without a sentinel collision
• The planner accepts zero quantity as a valid empty request producing subtotal0. A proposed design also returns0 for negative quantity.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Explain the decision in “Specify invalid input without a sentinel collision” using the supplied case, then state one input change that would invalidate your conclusion.

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