Module expr 

expr — reference evaluator for expression-ir.md (normative).

Value model: int = checked i64 (overflow → Failure, never wrap/panic), float = f64 (NaN/±Inf → Failure), string / bool / null / arr / obj.

Normative points (§6/§8 traps):

• int arithmetic is checked i64 (overflow = INT_OVERFLOW).
• a result that becomes NaN/±Inf is a Failure.
• mod is truncated division (sign follows dividend; Rust % already does this).
• string comparison is code-point order (Rust str Ord = UTF-8 byte order = code point).
• and/or/coalesce/cond short-circuit.
• unknown operators fail closed.

Structs

ExprFailure

Enums

ExprFailureCode

Expression failure codes (PROTOCOL §3.1).

Constants

FORBIDDEN_OBJECT_KEY

Forbidden object key (expression-ir.md §2.3/§8). Any path that builds an object from IR/JSON-derived arbitrary string keys must reject an own key equal to "__proto__" fail-closed: JS drops it (prototype setter), while Python/Rust/Go keep it, so the same IR diverges across languages (prototype-pollution footgun).

Functions

cmp_code_points

Compare two strings by code point. Rust str Ord IS UTF-8 byte order which equals Unicode code-point order, so we can delegate to the native comparison. Kept as a named function to make the normative choice explicit.

evaluate

Evaluate an IR expression node against a scope, producing a runtime Value.