ZeroParse
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
Variables are numbered at compile time and held in a persistent vector: a flat copy-on-write array up to 16 variables, a 16-way trie above. Replacing a value copies one path and shares the rest, so saved environments preserve rule-scope and backtracking state. Equal scalar binding reuses the old environment. 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. Record 128 removes the name walk and the prefix copy. Do not infer a universal allocation or speed reduction.
Source owners: environment lookup and replacement, generated environment binding, TypeScript persistent environment.
The comparison policy distinguishes same-source controls, historical changes and full checkpoints.