Names, parameters, and return types — Boundary detective

PART I

Warm-up

Reconnect with a useful idea before starting names, parameters, and return types. 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

Distinguish argument type errors from range errors

A type describes a kind of value; a range rule constrains values of that kind. A helper accepting i32 quantities may still need a requirement that quantities be nonnegative. These are different reasons a proposed call may be unsuitable.

For cost(quantity: i32,unitPrice: i32), cost(2,80) fits the shown type contract and predicts 160. cost(-2,80) still supplies integers and predicts -160 under arithmetic, but may violate a shop policy. cost(true,80) supplies a bool in an integer position and does not match the declared parameter type.

Do not claim that every invalid shop order is a type error. Conversely, do not repair a Boolean argument by silently treating true as 1; no coercion rule has been supplied for this exercise. Explain the mismatch before proposing an explicit corrected input.

Worked reasoning and supplied artifact

fnc cost(quantity: i32, unitPrice: i32) -> i32 {
    return quantity * unitPrice;
}
// Compare calls on paper: cost(2,80), cost(-2,80), cost(true,80).

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

Sort the three calls into type-compatible arithmetic and parameter-type mismatch; then annotate the negative quantity with its separate policy concern.

• 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: Snack-shop calculator. Build a small, understandable change around names, parameters, and return types.

For remaining(total: i32,used: i32), classify calls (10,4), (10,12) and (10,false). Give a mathematical prediction only where the supplied argument kinds match.

What to produce

A classification table: 6, -2 with a policy question, and bool/i32 mismatch with no fabricated runtime result.

• 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.

• Distinguish argument type errors from range errors
• A type describes a kind of value; a range rule constrains values of that kind. A helper accepting i32 quantities may still need a requirement that quantities be nonnegative. These are different reasons a proposed call may be unsuitable.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Give one example of a value that is type-compatible but violates a feature rule.

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