nb-03 solutions: Exceptions and conflicting rules

← Back to lessonChapter 03 / 25 · Beginner · Worked solution

Exercise

Exercise

Bob holds a disability badge and has outstanding fines recorded.

1. What is the status of truth(permit_eligible(bob)), and which test name and expect line say so?
2. Which single package element explains why Ann’s fines case on the resident route answers FALSE_ONLY instead, and what would Ann’s answer become if that element were deleted?

Solution

1. BOTH. The test is without priority the conflict persists in packs/examples/language-demo/permits/tests/permits.lawtest, whose expectation is expect truth_status == BOTH;. Both BadgeEligibility (from disability_badge(bob)) and FinesRefusal (from outstanding_fines(bob)) fire, and no priority ranks that pair, so both supports stand.
2. The priority RefusalOverEligibility block in packs/examples/language-demo/permits/package.law (prefer FinesRefusal over PermitEligibility; reason lex_specialis;), which the badge pair lacks. If it were deleted, Ann’s fines case would become the same shape as Bob’s — PermitEligibility for, FinesRefusal against, no ranking — and the answer would be BOTH, as the badge test demonstrates.

Checked against: law test packs/examples/language-demo/permits (28 checked, 28 passed), which runs both tests.