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
Follow nested helpers with different jobs
When helpers implement different operations, call order matters. Calculate a subtotal first, then apply the next transformation to that returned value. Keep a separate note for each contract so a result is not mistaken for its original inputs.
add(12,8) returns 20. main passes that 20 as capacity to remaining(20,5), giving 15. The route is two deliveries → combined capacity → remove occupied slots. Reversing the subtraction arguments would give -15, so parameter roles remain important even after the inner addition is correct.
Addition’s symmetry can tempt you to treat all calls as order-insensitive. remaining(capacity,occupied) is not symmetric. A good trace labels the destination parameter when moving the inner result into the outer call.
Worked reasoning and supplied artifact
fnc add(a: i32, b: i32) -> i32 {
return a + b;
}
fnc remaining(capacity: i32, occupied: i32) -> i32 {
return capacity - occupied;
}
fnc main() -> i32 {
return remaining(add(12, 8), 5);
}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 add(a: i32, b: i32) -> i32 {Read the function name, its parameter names/types and the result type after ->. This is the contract the body must satisfy.
return a + b;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.
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.
fnc main() -> i32 {Read the function name, its parameter names/types and the result type after ->. This is the contract the body must satisfy.
return remaining(add(12, 8), 5);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
Draw arrows from inner return 20 to capacity and from literal 5 to occupied, then finish the subtraction.
- 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.
Combine stock deliveries of 9 and 6, then remove 4 consumed units with the two helpers. Write a countertrace for reversing the remaining arguments and explain the difference.
What to produce
Nested-call source, correct result 11, reversed result -11, and parameter-role arrows.
- 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?
add(12,8) returns 20. main passes that 20 as capacity to remaining(20,5), giving 15. The route is two deliveries → combined capacity → remove occupied slots. Reversing the subtraction arguments would give -15, so parameter roles remain important even after the inner addition is correct.
Addition’s symmetry can tempt you to treat all calls as order-insensitive. remaining(capacity,occupied) is not symmetric. A good trace labels the destination parameter when moving the inner result into the outer call.
Original learning-path task and reference
In a community library utility, demonstrate reading a function from left to right. Integrate this section with the preceding section’s artifact; identify inputs, outputs, and host capabilities. 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.
- Follow nested helpers with different jobs
- When helpers implement different operations, call order matters. Calculate a subtotal first, then apply the next transformation to that returned value. Keep a separate note for each contract so a result is not mistaken for its original inputs.
- Separate source-backed behavior, host requirements and untested predictions.
One small recap task
Explain why swapping add arguments is less revealing than swapping remaining arguments.
This marks your personal practice record only. It is not a certification or an official workspace assessment.