Import only the public APIs you use — Boundary detective

PART I

Warm-up

Reconnect with a useful idea before starting import only the public apis you use. 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

Check a missing dependency separately from a denied resource

An import requests a named public API from the proposed library hierarchy. A narrow import is not evidence that sibling modules are visible, that native services are installed or that a capability is granted. Existing Willow module experience helps you ask precise questions, but it cannot fill missing WillowScript host contracts.

Consider two paper cases for a native screen: case A lacks the documented WUIX service export; case B has the API but denies the requested target. Sample diagnosis table calls A an availability/export problem and B an authorization problem. Both may prevent presentation, but they differ before any user-facing message is designed.

Retrying a wider import does not authorize a denied target. Likewise, adding a permission assumption cannot install a missing service. Keep the refusal contract category-specific and avoid inventing exact exception classes or return codes.

Worked reasoning and supplied artifact

// Worked contract artifact:
// Consider two paper cases for a native screen: case A lacks the documented WUIX service export; case B has the API but denies the requested target. Sample diagnosis table calls A an availability/export problem and B an authorization problem. Both may prevent presentation, but they differ before any user-facing message is designed.

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

Fill the two-case dependency/permission matrix and identify which prerequisite fails first.

• 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 import only the public apis you use.

Design separate diagnostics for an unavailable WDB service and an available service without permission to products. State a safe visible outcome and the missing host error-shape contract.

What to produce

Two distinct failure cards, no fabricated error syntax and no import-based authorization claim.

• 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.

• Check a missing dependency separately from a denied resource
• Fill the two-case dependency/permission matrix and identify which prerequisite fails first.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Fill the two-case dependency/permission matrix and identify which prerequisite fails first.

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