Plan try, recover, and raise boundaries — Discover and trace

PART I

Warm-up

Reconnect with a useful idea before starting plan try, recover, and raise boundaries. 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

Trace the failure boundary before choosing recovery code

WillowScript shares try/recover/raise vocabulary with the source grammar, but vocabulary alone does not define a native service’s failure type, recovery signature or retry safety. Design failure boundaries from protected state and observable outcomes, then implement only with a supplied API contract. Do not substitute JavaScript catch or claim the public site executed an error path.

A click requests opening workshop. Sample outcome trace has request accepted → destination available, or request refused → current screen retained and a host-supported explanation needed. The protected state is the current usable screen; no source contract says navigation destroys it before success. The artifact records that preservation requirement as desired behavior, not an observed guarantee.

Do not write a guessed recover parameter or error class for navigator.open. The source example gives the request but leaves its exact failure contract open. A boundary diagram can be complete about intent while explicit about missing signatures.

Worked reasoning and supplied artifact

// Worked contract artifact:
// A click requests opening workshop. Sample outcome trace has request accepted → destination available, or request refused → current screen retained and a host-supported explanation needed. The protected state is the current usable screen; no source contract says navigation destroys it before success. The artifact records that preservation requirement as desired behavior, not an observed guarantee.

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

Draw success/refusal branches and name the current state that must remain usable on refusal.

• 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: Safe extension design. Build a small, understandable change around plan try, recover, and raise boundaries.

Plan failure handling for an asset preview request. Name the protected current preview, success condition, unavailable-resource outcome and the exact host error-contract questions.

What to produce

A two-branch failure contract with protected state and unresolved API details.

• 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;
const button = widget.Button({
    text: "Continue",
    events: {
        click: fnc() -> void {
            navigator.open("dashboard");
        }
    }
});

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.

• Trace the failure boundary before choosing recovery code
• Draw success/refusal branches and name the current state that must remain usable on refusal.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Draw success/refusal branches and name the current state that must remain usable on refusal.

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