numeric_expr Design

Responsibility And Algorithm

numeric_expr is a syntax-only expression IR containing literals, named operations, source spans, and invocation trees. evaluate performs a strict depth-first post-order traversal: literal and operation semantics are supplied as callbacks, child failures are wrapped with the originating syntax node, and unsupported internal forms produce UnsupportedExpression.

Boundary

The representation of Expr is private so frontends cannot depend on tree layout. The package does not tokenize text, choose numeric types, define operation arity, round values, perform IO, or schedule parallel work. It is a pure orchestration layer; each frontend owns source policy and each backend owns numerical semantics.