PEGO
R070: Document Memo Edits
An edit should not walk and reposition every memo entry. A gap-buffer position index moves the nearby slot region, and lazy entry advancement defers unaffected-entry checks until lookup.
Mechanism and Invariants
memoTable.splice updates the edited positions and gap. Entries record the edit
generation they account for; advanceEntry replays later edits in order when
looked up, invalidating examined-overlap results or shifting eligible positions.
Positional results, recovered errors and unfinished seed dependencies retain
conservative invalidation. Unused entries need no immediate result-tree walk.
Scope and State
Default Document memo management in closure and both VMs. Generated Go/TypeScript have no editable memo API. Ordinary parse/stream lookups share core machinery but not Document edits.
Reference Control
No maintained same-source eager-walk reference control exists. Historical source comparisons are the available evidence.
Evidence and Implementation
Records 020/056 trace in-place splice and later lazy advancement. Record 056 reports Minilang edit-plus-reparse 0.73 to 0.17 ms in closure and smaller costs across VMs. Added entry-generation storage and lookup comparisons are part of the historical change; current chunked input and other improvements must not be attributed to that ratio.
Source owners: memoTable.splice,
advanceEntry, callBegin edit advancement.
The comparison policy distinguishes same-source controls, historical changes and full checkpoints.