PEGO
R050: Bounded Variable Bindings
Repeated bindings should not retain every shadowed binding or make reads traverse binding history. A persistent environment keeps one current binding per name.
Mechanism and Invariants
Replacing a changed non-head value copies the prefix and shares the unchanged suffix. Saved environments therefore preserve rule-scope and backtracking state. Equal scalar binding can reuse the old environment; a monotonic name hint avoids searches for first bindings. Live snapshots and memo keys still retain values required by their contracts. This bounds binding history, not arbitrary user values.
Scope and State
Applied by default in closure, both VMs, generated Go Node/typed Go and TypeScript.
Reference Control
No maintained same-source append-history reference control exists. The documented comparison is historical.
Evidence and Implementation
Record 069 measures a three-name stream environment staying at three bindings instead of growing to 180,001. It records near-flat retained growth and faster outer-variable reads, but changed non-head counters increase allocation volume. Do not infer a universal allocation or speed reduction.
Evidence records: 069.
Source owners: environment lookup and replacement, generated environment binding, TypeScript persistent environment.
The comparison policy distinguishes same-source controls, historical changes and full checkpoints.