Expression IR

Expr has Constant, Symbol, Unary, and Binary variants. A symbol uses a validated core Identifier; its numerical value comes from the evaluation environment. The evaluator returns an error for a missing symbol or a non-finite result.

symbols() returns the referenced identifiers, and fingerprint() derives a stable structural hash from the canonical tree representation. A fingerprint supports ordering and cache keys; it is not a cryptographic digest.

The IR has no vectors, matrices, conditionals, comparisons, user functions, random draws, or side effects.