PEGO
G080: Equal Capture Type Reuse
Repeated capture labels can repeatedly normalize and format the same inferred record type. Structural equality lets the merger reuse an already equal immutable type.
Mechanism and Invariants
Equal basic, named, list and record shapes reuse the prior type. Ordered nested joins and named-node kinds compare conservatively; top-level optional/join forms retain the general normalizer. Capture availability remains the logical OR of occurrences, so equality of value type cannot erase conditional availability.
Scope and State
Default shared type checking before compilation/generation. No parser backend performs this analysis in its matching loop.
Reference Control
No maintained same-source general-join-only control exists.
Evidence and Implementation
Historical record 072 measures complete type checking on 1,024 recursive duplicate captures from 423.966 to 61.126 ms and 1.188 GB to 32.16 MB. Mixed optional/heterogeneous and unique-label controls remain near parity. Large single-iteration diagnostics are reported separately. The benefit concerns repeated equivalent capture types, not parser runtime or a promise of cheap arbitrary joins.
Evidence records: 072.
Source owners: equal captured type merge, immutable inferred type structures.
The comparison policy distinguishes same-source controls, historical changes and full checkpoints.