Reading a function from left to right — Flash-check repair

PART I

Warm-up

Reconnect with a useful idea before starting reading a function from left to right. 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.

Recall note

A rough note is enough. You can revise it after the example.

PART II

Instruction & guided example

Find the first broken promise in a short helper

Read a suspicious helper against its purpose before looking for formatting differences. For a helper named remaining, addition can be well formed while implementing the wrong operation. Distinguish a plausible source expression from a correct feature rule.

The broken helper returns capacity + occupied. For capacity 8 and occupied 3, this predicts 11 free slots, more than the original capacity. The intended subtraction predicts 5. At occupied zero, both forms give 8, so the empty-container case alone conceals the defect.

Do not repair this by renaming the helper total while leaving callers expecting remaining space. Either the feature contract changes or the operator must change. A review should explain the violated invariant: for 0 ≤ occupied ≤ capacity, remaining cannot exceed capacity.

Worked reasoning and supplied artifact

// Broken for the stated remaining-space contract.
fnc remaining(capacity: i32, occupied: i32) -> i32 {
    return capacity + occupied;
}

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.

Walk through the example, one line at a time

// Broken for the stated remaining-space contract.
This comment explains intent for a reader. It is not an operation and should not be counted as an executed result.
fnc remaining(capacity: i32, occupied: i32) -> i32 {
Read the function name, its parameter names/types and the result type after ->. This is the contract the body must satisfy.
return capacity + occupied;
Evaluate the following expression using the current values, then send its result to the caller. Explain the value; do not confuse it with printed output.
}
Close the nested block or value begun earlier. Match it to its opening boundary to keep the structure readable.

Try the guided change

Trace the broken and repaired helper at (8,3) and (8,0), then state why one row is more revealing.

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.

Prediction or guided notes

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.

Your drafts remain here. Continue whenever you are ready.

PART IV

Independent practice

Project context: Snack-shop calculator. Build a small, understandable change around reading a function from left to right.

Repair a remaining-lives helper that adds used lives to the starting total. Include partially used and fully used cases and an invariant in words.

What to produce

Corrected subtraction, two counterexample traces and the invariant that valid use never increases remaining lives.

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.

Your .ws practice draft

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.

Need a hint?

Original learning-path task and reference

In a media review console, demonstrate reading a function from left to right. Explain the flash answer, locate a plausible mistake, and repair the relevant part of your task. Include .ws source and a host-resource contract; compare at least one normal case and one edge case.

fnc add(a: i32, b: i32) -> i32 {
    return a + b;
}
fnc main() -> i32 {
    return add(2, 3);
}

Where the original task needs a host API that is not supplied here, write the contract and predictions. Do not invent a runtime result.

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.

Why is returning 11 free slots suspicious when capacity is 8 and occupied is 3?It exceeds capacity despite some slots being occupied11 is not an integerThe helper name automatically prevents that result

Explain a normal or boundary case

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.

Find the first broken promise in a short helper
Read a suspicious helper against its purpose before looking for formatting differences. For a helper named remaining, addition can be well formed while implementing the wrong operation. Distinguish a plausible source expression from a correct feature rule.
Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Give one input where the broken addition happens to agree with subtraction.

Your recap

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