Compose playback controls, device recovery contracts, and event cleanup — Flash-check repair

PART I

Warm-up

Reconnect with a useful idea before starting compose playback controls, device recovery contracts, and event cleanup. 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 playback button that double-starts

Proposed WAUDIO describes native audio integration, including MP3 and WAV rather than MP4 support. Loading, configuration, permission and playback are separate outcomes. Every device or control behavior in these exercises is a supplied host contract; no guessed audio methods or real playback are used.

Host contract permits one active voice per preview owner. Play at t0 starts V1. A second Play arrives at t1 while V1 is active. Policy: ignore duplicate Play until V1 completes at t4.

Worked reasoning: The owner transitions idle toplaying at t0. At t1 it staysplaying with V1 only. Completion returns it toidle. Counting clicks as voices violates the supplied one-active-preview rule.

Failed alternative: Assuming the device deduplicates automatically starts V2 under a host that honors every accepted request.

Worked reasoning and supplied artifact

t0:idle +Play ->V1,playing
t1:playing +Play ->ignored,no V2
t4:V1 complete ->idle
Started voices:1

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: Media operations console. Build a small, understandable change around compose playback controls, device recovery contracts, and event cleanup.

Trace Play at0,2,6 with V1 completing5 and V2 completing9. Identify exactly which requests start.

What to produce

A state/event/voice ledger and a one-active-preview policy.

• 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 wdb;
domain Inventory {
    const lowStock = wdb.query({
        from: products,
        select: [id, name, stock],
        where: [[ stock < 10 ]],
        order: { by: stock, direction: ascending }
    });
}

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 playback button that double-starts
• Trace Play at0,2,6 with V1 completing5 and V2 completing9. Identify exactly which requests start.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Track owner playback state before accepting another event.

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