Keep event responsibilities small — Build the smallest useful slice

PART I

Warm-up

Reconnect with a useful idea before starting keep event responsibilities small. 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

Build an adapter with a bounded job

Give the event handler one observable responsibility. An event adapter translates a host event into a small application decision. Keeping unrelated work outside the adapter makes failures attributable: a request can be accepted even when an optional notification fails. A short body alone is not enough; its effects and ownership must also be narrow.

A refresh event should request one inventory snapshot and display its host-confirmed version. Optional CSV export is a different user action. Snapshot v12 contains 8 items.

Draw the effect chain with a boundary at each operation. Specify which effect is required, which is optional, and which results may change the visible state. Splitting code without splitting the contract merely moves the same ambiguity into a helper. Worked case: Refresh → request snapshot → receive v12 → display 8 items and version v12. No export occurs, because refresh has no export responsibility. Keeping the adapter bounded also makes its permission needs narrower.

Compare the tempting alternative: Automatically exporting on every refresh adds a storage effect and permission requirement that the user did not request.

Worked reasoning and supplied artifact

// Paper trace / supplied exercise-host contract; no execution claimed.
// A refresh event should request one inventory snapshot and display its host-confirmed version. Optional CSV export is a different user action. Snapshot v12 contains 8 items.
// Refresh → request snapshot → receive v12 → display 8 items and version v12. No export occurs, because refresh has no export responsibility. Keeping the adapter bounded also makes its permission needs narrower.

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: Support request workflow. Build a small, understandable change around keep event responsibilities small.

Specify the smallest refresh adapter, then write a separate export contract with its own trigger and permission.

What to produce

Two distinct trigger/effect contracts and the v12 refresh trace.

• 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.

• Build an adapter with a bounded job
• Specify the smallest refresh adapter, then write a separate export contract with its own trigger and permission.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Remove one effect your refresh event does not own.

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