Represent nested all-of and any-of rules without special-case depth handling
The current rule model has separate fields for one AND group and one OR group. A warehouse needs (north OR west) AND (express OR under-500g), which cannot be represented without duplicated conditions.
- Focused work estimate
- 2h 30m + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Tree modeling · Immutability · Serialization
Estimated field mix
- Compiler and language tooling75%
- System design25%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
Pattern topics
- CompositeCompare
Compare uniform leaf/group composition with the existing fixed-depth structure, retaining type safety without requiring a class per node.
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Project context
A fictional fulfillment product routes parcels using destination zone, weight in grams, and service level. Its next release needs nested eligibility rules, but arbitrary customer scripts are out of scope. Create a local TypeScript baseline and synthetic parcel/rule fixtures; no starter repository or fixtures are supplied. Keep parsing and evaluation in a local practice application with no network, filesystem, or host-code expressions in the language.
Setup prerequisites
- Recursive data structures
- Parser error handling
- Discriminated unions
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Model comparisons and nested all-of/any-of groups through one expression contract while preserving child order.
- Reject empty groups and enforce a documented maximum of 16 levels and 1,000 nodes at construction.
- Serialize and parse a valid tree without changing its grouping, field types, or language version.
Implementation constraints
- Compare a discriminated-union tree with a class hierarchy; choose the smaller representation that supports the required operations.
Verification to include
- Round-trip a four-level mixed rule and compare every node and child position.
- Reject a seventeenth level and a reused mutable child that would change an already constructed rule.
Deliverables
- Expression model, boundary tests, and a short representation decision
Rollout and recovery
Convert only synthetic flat rules first and compare their trees; retain flat input conversion until nested-rule behavior is checked.
Value of the work
For the engineer: Practice expression modeling, language compatibility, bounded evaluation, and deciding whether object-oriented patterns improve a small interpreter.
For the team: Review concrete tradeoffs around rule changes, diagnostic quality, resource limits, and the cost of adding an operator without breaking saved rules.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.