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.
A rough note is enough. You can revise it after the example.
PART II
Instruction & guided example
Separate the arithmetic domain from feature validity
A helper accepting two integers can perform arithmetic on values that a feature should reject. For remaining capacity, occupied = 10 and capacity = 8 yields -2 mathematically, but the feature may define that state as invalid. A type promise does not state every business constraint.
Trace remaining(8,3) → 5, remaining(8,8) → 0, and remaining(8,10) → -2. The third result follows correctly from subtraction. It does not tell you whether negative capacity should be displayed, rejected or handled as debt. That decision needs a requirement.
Calling -2 a compiler failure would confuse arithmetic with validation. Silently returning 0 instead would introduce clamping without authorization. Record the exact current result and the policy question; later conditional lessons can implement an explicitly chosen rule.
Worked reasoning and supplied artifact
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
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
Complete the three-case table and label each row normal, full or over-capacity.
- 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 reading a function from left to right.
An inventory container has 12 slots. Trace occupied counts 0, 12 and 15. Write two possible over-capacity policies and explain which additional requirement would choose between them.
What to produce
Three arithmetic predictions 12/0/-3 and a policy comparison without fabricated runtime errors.
- 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.
Need a hint?
Trace remaining(8,3) → 5, remaining(8,8) → 0, and remaining(8,10) → -2. The third result follows correctly from subtraction. It does not tell you whether negative capacity should be displayed, rejected or handled as debt. That decision needs a requirement.
Calling -2 a compiler failure would confuse arithmetic with validation. Silently returning 0 instead would introduce clamping without authorization. Record the exact current result and the policy question; later conditional lessons can implement an explicitly chosen rule.
Original learning-path task and reference
In a classroom scheduling assistant, demonstrate reading a function from left to right. Add normal, boundary, and invalid-input cases and explain expected behavior. 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.
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.
- Separate the arithmetic domain from feature validity
- A helper accepting two integers can perform arithmetic on values that a feature should reject. For remaining capacity, occupied = 10 and capacity = 8 yields -2 mathematically, but the feature may define that state as invalid. A type promise does not state every business constraint.
- Separate source-backed behavior, host requirements and untested predictions.
One small recap task
Write an assumption that would make negative remaining capacity meaningful.
This marks your personal practice record only. It is not a certification or an official workspace assessment.