PEGO
A050: Bounded Stream Storage
Streaming should discard committed prefixes and obsolete memo slots instead of growing input storage with every emitted element.
Mechanism and Invariants
Loaded input has a retained window relative to committed positions. Discard/prune drops prefixes while preserving bytes or code points still needed by active matching, memo and diagnostics. Published token strings/Nodes retain independent ownership. Reader chunks and decoded storage compact according to the stream policy; result callbacks can still retain arbitrary output.
Scope and State
Default engine streaming in closure and both VMs, and generated Go -stream
parsers, whose typed ParseStreamAST converts the elements the Node stream
commits. TypeScript exposes no streaming API. This bounds particular input/memo owners,
not total process heap.
Reference Control
No single same-source old-stream-storage reference is maintained. Frame/text/prefix/undo/stack controls are narrower independent mechanisms.
Evidence and Implementation
Historical record 022 combines result-chunk splitting and in-place read-ahead compaction. Streaming 50,000 CSV records changes 168.9 to 117.7 ms in closure, with allocated volume 686 to 351 MB. A retention fixture changes 233 to 0.5 MB after 300,000 records. These are different timing, cumulative-allocation and reachable-heap observations; later cleanup controls cannot be attributed to this historical ratio.
Evidence records: 022.
Source owners: input.discard and parser.commit,
memoTable.prune.
The comparison policy distinguishes same-source controls, historical changes and full checkpoints.