Unify rules-editor type variables with an occurs check
A recursive synthetic constraint produces an infinite inferred type. Reject self-containing substitutions.
- Focused work estimate
- 4h + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Unification · Algorithms
Estimated field mix
- Compiler and language tooling100%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
Review it, then add it to your workspace.
The board opens an editable draft; nothing is saved until you confirm it. Sign-in and workspace permissions apply, and Demo boards remain ephemeral.
Project context
Fictional rules editor Willow supports numbers, strings, booleans, records and functions in a deliberately small language. Define syntax and type rules locally; no arbitrary code execution is needed.
Setup prerequisites
- Create synthetic AST fixtures and a written type-rule table.
- Define source spans and structured diagnostic output.
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Acyclic constraints unify
- Recursive substitution fails with reason
- Failure does not corrupt remaining environment
Implementation constraints
- Bound this ticket to monomorphic variable unification.
Verification to include
- Unify variable with number
- Attempt variable equal to function containing itself
Deliverables
- Unifier and occurs-check cases
Rollout and recovery
Disable variable inference if substitution integrity fails.
Value of the work
For the engineer: Practice type environments, unification and explainable rejection.
For the team: Inspect whether developer tooling catches mistakes without hiding uncertainty.
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.