Evaluate a bound expression — Build the smallest useful slice

PART I

Warm-up

Reconnect with a useful idea before starting evaluate a bound expression. 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

Keep units attached to a balance estimate

A crafting estimator uses base cost 20 coins plus 5 coins per item. The selected quantity is 6 items.

The variable x carries items; 5 carries coins/item. Multiplying gives 30 coins; adding 20 coins yields 50 coins. Adding 6 directly to 20 would mix items with coins. A mathematically valid expression can still model the wrong quantity, so write the units before translating it into proposed syntax.

Use the supplied case as a paper design exercise. WillowScript and these library integrations are proposed and unimplemented here; no interpreter or native host has checked the example. Preserve the source API spellings, label new policies as exercise-host contracts, and distinguish a predicted result from measured execution.

Worked reasoning and supplied artifact

// PAPER FIXTURE — Keep units attached to a balance estimate
// Manual worked artifact; comments below are not executable source.
// INPUT / CONTRACT: A crafting estimator uses base cost 20 coins plus 5 coins per item. The selected
// quantity is 6 items.
// DERIVATION / EXPECTED ARTIFACT: The variable x carries items; 5 carries coins/item. Multiplying gives 30
// coins; adding 20 coins yields 50 coins. Adding 6 directly to 20 would mix items with coins. A
// mathematically valid expression can still model the wrong quantity, so write the units before translating
// it into proposed syntax.

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: Estimator specification. Build a small, understandable change around evaluate a bound expression.

Design a quantity-to-price table for 1, 4 and 8 items. Add the host policy for negative quantities before proposing a UI input.

What to produce

Design a quantity-to-price table for 1, 4 and 8 items. Add the host policy for negative quantities before proposing a UI input.

• 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 math;
domain Calculation {
    fnc sample() -> void {
        vary x: i32 = 2;
        vary value = [[ (x * 5) + 20 ]];
    }
}

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.

• Keep units attached to a balance estimate
• A crafting estimator uses base cost 20 coins plus 5 coins per item. The selected quantity is 6 items.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Explain why “Items per coin” fails for the supplied case, then give one changed input that would require revisiting your conclusion.

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