Functions as reusable contracts — Discover and trace

PART II

Instruction & guided example

Trace two calls through one function

A reusable function preserves one explicit promise. Read a function as inputs, result and allowed effects. Parameter names belong to a call’s local reasoning; callers supply values, not a new copy of the function definition. Keep pure calculations separate from host operations so a paper trace can substantiate the numeric rule without pretending to execute a host.

A shared pricing rule is fnc add(base:i32, fee:i32) -> i32 { return base + fee; }. Call A supplies (40,5); call B supplies (12,3). No printing or storage is specified.

For every call, substitute actual values for parameters, evaluate intermediate expressions, and return the result to the caller. Then inspect whether the caller uses that result. A function returning a value does not automatically print, store or display it. Worked case: A binds base=40 and fee=5, evaluates 40+5=45 and returns 45. B separately binds base=12 and fee=3, evaluates 15 and returns 15. A’s parameter values do not leak into B.

Compare the tempting alternative: Assuming the second call reuses A’s base gives 43, which violates B’s explicit arguments. Assuming either call prints a receipt invents an effect.

Worked reasoning and supplied artifact

// Paper trace / supplied exercise-host contract; no execution claimed.
// A shared pricing rule is fnc add(base:i32, fee:i32) -> i32 { return base + fee; }. Call A supplies (40,5); call B supplies (12,3). No printing or storage is specified.
// A binds base=40 and fee=5, evaluates 40+5=45 and returns 45. B separately binds base=12 and fee=3, evaluates 15 and returns 15. A’s parameter values do not leak into B.

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: Shared pricing rules. Build a small, understandable change around functions as reusable contracts.

Trace calls (7,0), (0,7) and (8,-2); label all results as paper predictions and state whether negative fees are valid under a separate business contract.

What to produce

A five-call substitution table and a separate input-domain question.

• 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.

• Trace two calls through one function
• Trace calls (7,0), (0,7) and (8,-2); label all results as paper predictions and state whether negative fees are valid under a separate business contract.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Name the two actual inputs for B.

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